Got mass? Princeton scientists observe electrons become both heavy and speedy
Posted June 13, 2012; 02:00 p.m.
A Princeton University-led team of scientists has shown how electrons moving in certain solids can behave as though they are a thousand times more massive than free electrons, yet at the same time act as speedy superconductors.
The observation of these seemingly contradictory electron properties is critical to the understanding of how certain materials become superconducting, in which electrons can flow without resistance. Such materials could dramatically increase the efficiency of electrical power networks and speed up computers.
This video displays heavy electrons at different energies and shows their standing wave patterns (like water in a pond) around individual atomic defects placed intentionally in a compound. The patterns in these images allowed the Princeton scientists to understand the formation of heavy electron waves and to identify a hard-to-measure quantum entanglement process that controls their mass. (Video by the Yazdani Group)
The concept of "heavy" electrons seems counterintuitive. The tiny particles flit through silicon chips to process information rapidly in digital electronics, and they flow with ease through copper wires carrying electricity to your desk lamp. But the Princeton research has revealed that a hard-to-measure process known as quantum entanglement determines the mass of electrons moving in a crystal and the delicate tuning of this entanglement can strongly alter the properties of a material.
Cool the electrons to far below room temperature in certain types of solid materials, and these flighty particles gain mass, acting like much heavier particles. Surprisingly, further cooling close to absolute zero makes these solids become superconducting, where the electrons, despite their heaviness, make a kind of perfect fluid that can flow without wasting any electrical power.
Electrons moving in certain solids can behave as if they are a thousand times more massive than free electrons, but at the same time act as superconductors. A new study led by Princeton scientists shows that this happens because of a process known as quantum entanglement that determines the mass of electrons moving in a crystal. The discovery can help improve understanding of how certain materials become superconducting, which may have applications in areas such as power network efficiency and computing speed. (Image by the Yazdani Group)
In a study to appear in the June 14 issue of the journal Nature, the Princeton-led team, which included scientists from Los Alamos National Laboratory (LANL) and the University of California-Irvine, used direct imaging of electron waves in a crystal. The researchers did so not only to watch the electrons gain mass but also to show that the heavy electrons are actually composite objects made of two entangled forms of the electron. This entanglement arises from the rules of quantum mechanics, which govern how very small particles behave and allow entangled particles to behave differently than untangled ones. Combining experiments and theoretical modeling, the study is the first to show how the heavy electrons emerge from such entanglement.
Observations made over the last 30 years indicate that electrons in certain solids behave as particles with masses hundreds to thousands of times larger than that of electrons moving freely in a vacuum. Until now, however, researchers had been unable to understand how this happens and lacked the tools to explore the connection between this process and the superconductivity of heavy electrons.
The published study comes after several years of setting up the precise experimental conditions needed to visualize these heavy electrons. The team employed a custom-designed cryogenic scanning tunneling microscope (STM), which allows visualization of electron waves in a crystal. The researchers used the STM to look at crystals prepared in such a way that their surfaces contained a few atomic imperfections. As they lowered the temperature in the experiment, the researchers saw the emergence of patterns of electron waves spread around the defects in a way similar to how ripples of water form around rocks in a pond. (See video.)
"It is remarkable to watch electrons moving in a crystal evolve into more massive particles as we cool them down," said Ali Yazdani, a professor of physics at Princeton and head of the team that conducted the study.
Making this groundbreaking observation of electrons as they transition from light to heavy particles is only part of the story. The researchers also showed how the process can be understood based on quantum theories of electron behavior. Subatomic particles such as electrons can exhibit strange behavior because of quantum entanglement, which can mix diametrically opposite behaviors together. By comparing the data with theoretical calculations, the study shows that heavy electrons emerge from entanglement of two opposite behaviors of electrons, one in which they are localized around individual atoms and the other in which they are hopping freely from atom to atom in the crystal.
"This is the first time we have a precise picture of formation of heavy electrons, thanks to our ability to probe them with high resolution," Yazdani said.
The degree of such entanglement appears to be the key to understanding what the heavy electrons do once they are formed and cooled even further. Adjusting the crystal composition or structure can tune the degree of entanglement and the heaviness of electrons. Make the electrons too heavy and they freeze into a magnetized state, stuck at each atom in the crystal while spinning in unison. But tweaking the crystal composition so that the electrons have just the right amount of entanglement turns these heavy electrons into superconductors when they are cooled.
"What is neat, and our studies confirm this, is that you really need to be on the verge of these two kinds of behaviors — sluggish and speedy — to get superconductivity," Yazdani said. "That is the circumstance most favorable to occurrence of heavy electron superconductivity."
Understanding superconducting behavior of exotic electrons is at the forefront of research in physics, where there are many examples of magnetic materials that turn superconducting with subtle changes in their composition or crystal structure.
The experiments may help physicists unravel the mysteries of high-temperature superconductivity, said Subir Sachdev, a theoretical physicist at Harvard University who was not involved with the work. Many physicists have argued that understanding this transition between magnetism and superconductivity, known as a quantum critical point, could help explain why the materials are superconducting. But physicists have lacked experimental evidence to prove their ideas.
"We have been waiting for observations like this for many years, so it is very exciting that such a beautiful experimental system has been found and characterized so well," Sachdev said.
The research was primarily supported by the U.S. Department of Energy's Basic Energy Sciences program. Additional support came from the National Science Foundation's Materials Research Science and Engineering Center program through the Princeton Center for Complex Materials; the W.M. Keck Foundation; and the Eric and Wendy Schmidt Transformative Technology Fund at Princeton.
In addition to Yazdani, Princeton scientists on the team included postdoctoral scientist Pegor Aynajian and graduate students Eduardo da Silva Neto and András Gyenis. The team also included Ryan Baumbach, Joseph Thompson and Eric Bauer from LANL and Zachary Fisk from UC Irvine.


Bose-Einstein condensation in the solid state
New experimental research shows that half-matter, half-light quasi-particles called polaritons show compelling evidence of Bose-Einstein condensation at the relatively high temperature of 19 degrees Kelvin. The creation of a polariton Bose-Einstein condensate in the solid state provides scientists with a unique opportunity to better understand and possibly exploit the quantum effects that occur in these very special conditions.
Researchers at EPFL (Ecole Polytechnique Federale de Lausanne), collaborating with colleagues at University of Grenoble, Cambridge, Oxford and MIT, have reported the observation of polaritons displaying the defining features of Bose Einstein condensation --a macroscopically ordered state, long-range spatial coherence and polarization – for the first time in solid state. Their results appear in an article in the September 28 issue of the journal Nature.
Bose-Einstein condensates are sometimes referred to as a "fifth state of matter", a special phase in which all the particles share the same quantum state. This phase was predicted by Satyendranath Bose and Albert Einstein in 1924. Getting atoms cold enough to provide experimental proof of its existence took seventy more years, and the first successful experiments using Rubidium atoms won Eric Cornell, Wolfgang Ketterle and Carl Wieman the 2001 Nobel prize in physics. Cooled to within a hair of absolute zero, the atoms in dilute clouds of bosonic gases stop moving and condense, not into a liquid, but into a new phase called a condensate, in which the atoms all share the same quantum state. Like photons in a laser, the particles are coherent, behaving en masse like a "super-particle."
The possibility of a phase change into a Bose-Einstein-like condensate theoretically applies for all bosonic particles, including electron-hole pairs called excitons and half exciton, half photon quasi-particles called polaritons. Exploring Bose-Einstein condensation and its intriguing quantum effects using these quasi-particles is particularly interesting because their light mass makes things much easier. A polariton is a billion times lighter than a Rubidium atom, and 10,000 times lighter than an electron. This means that polaritons can transform into a Bose-Einstein condensate at a much higher temperature than alkali gases. Some of the possibilities that have been suggested for applications of the quantum effects of the Bose-Einstein phase -- quantum computing, quantum clocks or atomic or lasers that use matter instead of light – are only realistically conceivable if these condensates can be achieved at room temperature, or at least temperatures that can be reached using standard cryogenic techniques.
Signatures of exciton and polariton coherence have been previously observed in semiconductor microcavities, but conclusive proof, such as evidence of polarization and long range particle coherence, has remained elusive because the particles only live a trillionth of a second.
The experiments of the EPFL-led team provide the first convincing evidence of a Bose-Einstein like condensate in the solid state. The researchers confined photons in a semiconductor microcavity containing a large number of quantum wells, and then used a laser to excite the semiconductor, generating polaritons. At a critical density, at the easily attainable temperature of 19 degrees Kelvin (about -254 Celsius), the polaritons showed evidence of spontaneous coalescence into a single coherent ground state. The classic phase transition characteristics -- macroscopic polarization and spatial coherence across the entire condensate -- are clearly seen here, and for the first time in solid state.
According to Professor Benoit Deveaud, leader of the research team, condensates at even higher temperatures could perhaps be achieved using other semiconductor materials.
"The magical properties of superfluidity, where matter flows with zero friction, and superconductivity, where a current flows with zero resistance, are quantum effects, and in the Bose-Einstein condensate they are directly brought to our perception," notes Deveaud. "It is exciting to envision exploring this magic without having to use an incredibly complex machine to get to temperatures just above absolute zero."
What practical applications will this lead to? "We are still exploring the basic physics of this phenomenon," says Deveaud. "But just achieving this phase in the solid state is exciting. In the mid 1900s, transistors replaced vacuum lamps, and now most useful devices are made in the solid state," he explains. "Polaritons, although made with a photon, are really quasi-particles in the solid. It is likely that they can be manipulated much as electrons are – an advance that has led to incredible new technologies such as the CCD chips in digital cameras."
Last reviewed: By John M. Grohol, Psy.D. on 30 Apr 2016
Published on PsychCentral.com. All rights reserved.


Another two mind-bending, paradigm-shattering findings in the new physics are known as “Non-Locality” and “Quantum Entanglement.” In classical physics, objects were seen as localized and isolated from one another within space; through dozens of replicated and verified experiments we now know, however, that the universe at the quantum level is entangled, non-local, One integrated whole.
“Quantum physicists discovered a strange property in the subatomic world called ‘nonlocality’. This refers to the ability of a quantum entity such as an individual electron to influence another quantum particle instantaneously over any distance despite there being no exchange of force or energy. It suggests that quantum particles once in contact retain a connection even when separated, so that the actions of one will always influence the other, no matter how far they get separated.” -Lynne McTaggart, “The Field: The Quest for the Secret Force of the Universe,” (11)
Before the advent of quantum physics, Albert Einstein, still thinking in the classical paradigm, thought that nothing in the universe could travel faster than light. In the past two decades, however, it has been experimentally proven that one thing can indeed move faster than the speed of light: information. Information can be sent between two objects at any distance instantaneously.
“In 1997, scientific journals throughout the world published the results of something that traditional physicists say shouldn’t have happened. Reported to over 3,400 journalists, educators, scientists, and engineers in more than 40 countries, an experiment had been performed by the University of Geneva in Switzerland on the stuff that our world is made of – particles of light called photons – with results that continue to shake the foundation of conventional wisdom.” -Gregg Braden, “The Divine Matrix” (30)
This ground-breaking experiment conclusively proved the existence of “Quantum Entanglement” which is basically a fancy name for “instantaneous information travel.” First scientists took single photons and split them into separate “twin” particles with identical properties. Then they fired both particles away from each other in opposite directions through specially designed fiber-optic chambers. At the end of these long pathways, the twin particles were forced to choose between two random but exactly identical routes. Curiously, without fail, in every trial the particles made precisely the same choices and traveled the same paths. Classical physics has always assumed that separate particles have no communication with one another, but quantum physics has now proven that assumption erroneous.
The first entanglement experiments were designed and tested in 1982 by French physicist Alain Aspect at Orsay’s Institut d’Optique. These crude but conclusive studies later inspired Nicholas Gisin’s University of Geneva group of physicists to replicate them at greater distances. In 1997 Gisin built a 14 mile fiber-optic chamber and repeated Aspect’s experiment with exactly the same results. Later in 2004 Gisin extended the chamber to 25 miles and once again, as usual, no matter how far apart, the particles always chose and traveled the same random pathways.
“Quantum mechanics has shown through experimentation that particles, being after all but moving points on some infinite wave, are in communication with one another at all times. That is to say, if our quantum mechanic does something to particle A over in Cincinnati, Ohio, planet Earth, the experience of this event will be instantly communicated to particle Z, at speeds faster than light, over in Zeta Reticuli. What this suggests is that anything one given particle experiences can be experienced by another particle simultaneously, and perhaps even by all particles everywhere. The reason for this is that they are all part of the same wave, the same energy flow.” –Jake Horsley, “Matrix Warrior” (90-91)
“For a message to travel between them, it would have to be moving faster than the speed of light. But according the Einstein’s theory of relativity, nothing can travel that quickly. So is it possible that these particles are violating the laws of physics … or are they demonstrating something else to us? Could they be showing us something so foreign to the way we think about our world that we’re still trying to force the mystery of what we see into the comfortable familiarity of how we believe energy gets from one place to another? What if the signal from one photon never traveled to reach the other? Is it possible that we live in a universe where the information between photons, the prayer for our loved ones, or the desire for peace in a place halfway around the world never needs to be transported anywhere to be received? The answer is yes! This appears to be precisely the kind of universe we live in.” -Gregg Braden, “The Divine Matrix” (105-6)
In it they state, “All particles in the history of the cosmos have interacted with other particles in the manner revealed by the Aspect experiments … Also consider … that quantum entanglement grows exponentially with the number of particles involved in the original quantum state and that there is no theoretical limit on the number of these entangled particles. If this is the case, the universe on a very basic level could be a vast web of particles, which remain in contact with one another over any distance in ‘no time’ in the absence of the transfer of energy or information. This suggests, however strange or bizarre it might seem, that all of physical reality is a single quantum system that responds together to further interactions.”
The fact is quanta can exchange information over any distance in the universe instantaneously. These entanglement experiments prove that Eintstein was incorrect in stating that nothing travels faster than light (186,000 miles per second). Quantum information “travels” at infinite speed “arriving” at its destination without any time elapsing. Here we see how the Newtonian/Einsteinian language of a local universe fails to describe our actual reality. It’s not that information is “traveling” at infinite “speed” to “arrive” at another location, but rather that the universe with all its so-called parts and particles is actually One non-local quantum system. Information from one particle to another doesn’t need to “travel” there because the space between them is illusory, as is the language of calling them “separate” particles. As we have seen, before observation quanta are not particles with definite attributes and location; they are merely waves in the One universal quantum ocean until our conscious observation individualizes the wave into droplets of experience.
“Nonlocality shatters the very foundations of physics. Matter can no longer be considered separate. Actions do not have to have an observable cause over an observable space. Einstein’s most fundamental axiom isn’t correct: at a certain level of matter, things can travel faster than the speed of light. Subatomic particles have no meaning in isolation but can only be understood in their relationships. The world, at its most basic, exists as a complex web of interdependent relationships, forever indivisible.” -Lynne McTaggart, “The Field: The Quest for the Secret Force of the Universe,” (11)
“As an aside, it’s interesting to note that Nadeau and Kafatos mention early in their book that readers accidentally encountering their book in the ‘new age’ section of a bookstore would likely be disappointed. That’s because the book is about physics and not new age ideas. But the fact that Nadeau and Kafatos felt it important to mention this at all illustrates the rising tension between the leading edge of interpretations in physics and the tail end of metaphysics. Physicists interested in quantum ontology are painfully aware that some interpretations of quantum reality are uncomfortably close to mystical concepts. In the eyes of mainstream science, to express sympathy for mysticism destroys one’s credibility as a scientist. Thus the taboo persists.” -Dean Radin, “Entangled Minds” (262)
Download the Spiritual Science 284-page E-book


Optogenetics: Helping Blind Mice See The Light
Last week, researchers formally announced in Molecular Therapy that they had at last found a way to make blind mice see — a true glimmer of hope for the 15+ million worldwide who lose their site to genetic or age-related macular degeneration and retinitis pigmentation. The work comes from a collaboration of labs out of California, Florida and MIT — and it all starts with, yes, algae.
Now here’s how it works:
1) Certain types of algae possess proteins called channelrhodopsins that respond to light by firing up activity in the cells that host them. The genes for these proteins can be pulled out, cleaned up and inserted into completely different types of cells like neurons and retinas where they’ll act in exactly the same way: light goes on, cell goes on.
2) In this study, the researchers isolated a gene for channelrhodopsin-2 (ChR2) and piggybacked it — by way of viral vehicle — into the degenerated retinas of mice bred for adult blindness.
3) Once in, the genes slipped into the remaining layer of retinal cells and transformed them into working, light-sensitive substitutes for photoreceptors, which is the type of cell typically lost in adult onset blindness.
10 weeks later, treated mice were successfully swimming through illuminated water mazes almost as well as their naturally sighted cousins and far, far better than their untreated, blind counterparts. To be sure, it’s doubtful they’re seeing 20/20 color vision — a substitute photoreceptor still isn’t the real thing — and in fact, this early on, researchers can’t know exactly how well the mice see, only that they do.
But the fact remains: they can see.
This alone is mind-boggling, but in fact, it’s only the latest breakthrough in the field of optogenetics, a study in which cells and neurons can be quite literally flipped on or off with a flash of light thanks to the embedded genes within. The field was co-invented in 2004 by the MIT Media Lab’s Ed Boyden, then a Ph.D. candidate at Stanford University, in collaboration with Georg Nagel at the University of Wurzburg and Karl Deisseroth, then also of Stanford. Since then, it has leapt from a single lab bench to over 1,000 research groups across the world; potential applications extend far beyond blindness to encompass Parkinson’s, PTSD, addiction, mood disorders, and neuron-by-neuron mapping of the entire brain from the inside out. Late last year, Nature Methods awarded it the Method of the Year.
These days, though, blindness research comprises only a small portion of Boyden’s projects. A methods man at heart, his primary focus is on perfecting his technology and finding better ways to understand exactly how the brain itself actually works.
On the eve of this latest report, I stopped by the Media Lab to speak with this man who, late one August night in 2004, all but revolutionized the field of neuroscience. Here’s what he had to say:
So this field has absolutely exploded since you kicked it off in 2005. What’s next on the horizon?
Well, so there are three main things that are important right now. One, of course, is to make more powerful tools — though eventually, those will get as far as they can. Another one of the big things that we’re still working on is mining genomes throughout the tree of life to find new genes that are higher performance, faster, with better light sensitivity, with higher magnitudes of currents, respond to different colors, and so on. For example, last year we had the first paper to report multi-color silencing [Editor’s Note: By implanting a different gene in a cell, yellow light will cause it to turn off]. There are definitely still new things to come up with, but that said, we’re also always looking for more technologies to come up with as well. In my lab, only about a third of the group works on the molecular perturbation sort of stuff.
And what are the other two thirds working on?
Well, one of the big issues we’re working on is: how do we confront the complexity of the entire brain? So we’ve started to devise structures that allow us to perturb and record from sites throughout the brain. One of ideas we like to use to frame this whole endeavor is what we like to call brain coprocessors, basically using very fine probes to record data from throughout the brain, mine that data for information on the computations that are occurring in the brain, that can then be used to test theories of the brain. We also have an army grant to collaborate with Ki Goosens [at the MIT McGovern Institute], for which we’re going to try to figure out whether there are any sites in the brain where you can erase PTSD.
So you started out an electrical engineer and a physicist working on quantum computing. Now you’re in the middle of the brain and the co-founder of an entire field of neuroscience. What happened?
All through my undergrad work [at MIT] and when I started grad school [at Stanford], I was doing this quantum computer, and I really had two themes. One is, how do you control complex systems, and the second is how do we get at the essence of computation. For example, I wrote a control system for an autonomous submarine so that it could navigate underwater – actually, we won the Navy’s first international autonomous underwater vehicle competition with that – then I also wrote an animation for video games based on the laws of physics. So I’m very obsessed with controlling things, because that’s really what gives you a deep understanding of how things work — and it allows you to make stuff: you can make this submarine move underwater, or make this animation move realistically, and so on.
So I was really into control theory and controlling physical systems, and it all came to a head around the fall of 1998 when Motorola gave my undergraduate and masters lab $5 million. My then-PI said, okay, I’ll pay for anybody to go wherever you want for a month to learn something new. I went to Bell Labs, which at the time, was the place to go, and it was fantastic. I was only there for a matter of weeks literally, but I came out with three novel things and it was just like, wow. In contrast to physics where we often just felt like we were checking Einstein for the 800th time and he was still correct for the most part.
From there, I went to Stanford to study in Dick Tsein’s group – he was also an electrical engineer who switched into biology, and it was in his lab that I and Karl Deisseroth, the co-inventor who was also a student there, started doing the very first studies.
But why even head into the brain in the first place?
I’m interested in the brain for two reasons, one is a philosophical question: How do we think?
The second is pragmatic: The disease burden of the brain is huge, yet a lot of people have given up on figuring out how to treat them. The Wall Street Journal had an article a few weeks ago pointing out how the pharmaceutical companies — GlaxoSmithKline, AstraZeneca, and so on — have more or less given up on the vast majority of brain disorders, and that’s kind of worrisome. I mean, something like a billion people worldwide have some kind of brain disorder, and if you look at the disorder, most of them have very little treatment at all and for the ones that do have treatment, it’s not a cure if it usually has side effects. So how I think of it is: If the pharma industry is giving up on these, then that means that we have a duty to go after them and start working on them.
What was the transition like, from tidy engineering to messy biology?
I spent a full year just sort of getting used to that. There was a lot of floundering around.
Actually, I just came up with this analogy that I think finally captures it: I was listening to This American Life the other day, and poker was the theme for that week. In the opening spiel, they talked about this poker player who won a lot of money by breaking all the rules accidentally and at the end of it, he notes that the thing he hates about poker is that you can play all of your cards optimally, and you still might lose because of chance. I feel like neurotechnology is the same way. In some ways, it’s the highest form of gambling because you can have just an amazing technology, and then some weird thing about the brain will come back and bite you and it won’t work. There is a lot to wrestle with at this level.


When scientists develop a full quantum computer, the world of computing will undergo a revolution of sophistication, speed and energy efficiency that will make even our beefiest conventional machines seem like Stone Age clunkers by comparison.
But, before that happens, quantum physicists like the ones in UC Santa Barbara’s physics professor John Martinis’ lab will have to create circuitry that takes advantage of the marvelous computing prowess promised by the quantum bit (“qubit”), while compensating for its high vulnerability to environmentally-induced error.
In what they are calling a major milestone, the researchers in the Martinis Lab have developed quantum circuitry that self-checks for errors and suppresses them, preserving the qubits’ state(s) and imbuing the system with the highly sought-after reliability that will prove foundational for the building of large-scale superconducting quantum computers.
It turns out keeping qubits error-free, or stable enough to reproduce the same result time and time again, is one of the major hurdles scientists on the forefront of quantum computing face.
“One of the biggest challenges in quantum computing is that qubits are inherently faulty,” said Julian Kelly, graduate student researcher and co-lead author of a research paper that was published in the journal Nature. “So if you store some information in them, they’ll forget it.”
Unlike classical computing, in which the computer bits exist on one of two binary (“yes/no”, or “true/false”) positions, qubits can exist at any and all positions simultaneously, in various dimensions. It is this property, called “superpositioning,” that gives quantum computers their phenomenal computational power, but it is also this characteristic which makes qubits prone to “flipping,” especially when in unstable environments, and thus difficult to work with.
“It’s hard to process information if it disappears,” said Kelly.
However, that obstacle may just have been cleared by Kelly, postdoctoral researcher Rami Barends, staff scientist Austin Fowler and others in the Martinis Group.
The error detection process involves creating a scheme in which several qubits work together to preserve the information, said Kelly. To do this, information is stored across several qubits.
“And the idea is that we build this system of nine qubits, which can then look for errors,” he said. Qubits in the grid are responsible for safeguarding the information contained in their neighbors, he explained, in a repetitive error detection and correction system that can protect the appropriate information and store it longer than any individual qubit can.
“This is the first time a quantum device has been built that is capable of correcting its own errors,” said Fowler. For the kind of complex calculations the researchers envision for an actual quantum computer, something up to a hundred million qubits would be needed, but before that a robust self-check and error prevention system is necessary.
Key to this quantum error detection and correction system is a scheme developed by Fowler, called the surface code. It uses parity information — the measurement of change from the original data (if any) — as opposed to the duplication of the original information that is part of the process of error detection in classical computing. That way, the actual original information that is being preserved in the qubits remains unobserved.
Why? Because quantum physics.
“You can’t measure a quantum state, and expect it to still be quantum,” explained Barends. The very act of measurement locks the qubit into a single state and it then loses its superpositioning power, he said. Therefore, in something akin to a Sudoku puzzle, the parity values of data qubits in a qubit array are taken by adjacent measurement qubits, which essentially assess the information in the data qubits by measuring around them.
“So you pull out just enough information to detect errors, but not enough to peek under the hood and destroy the quantum-ness,” said Kelly.
This development represents a meeting of the best in the science behind the physical and the theoretical in quantum computing — the latest in qubit stabilization and advances in the algorithms behind the logic of quantum computing.
“It’s a major milestone,” said Barends. “Because it means that the ideas people have had for decades are actually doable in a real system.”
The Martinis Group continues to refine its research to develop this important new tool. This particular quantum error correction has been proved to protect against the “bit-flip” error, however the researchers have their eye on correcting the complimentary error called a “phase-flip,” as well as running the error correction cycles for longer periods to see what behaviors might emerge.
Martinis and the senior members of his research group have, since this research was performed, entered into a partnership with Google.


Less Wrong is a community blog devoted to refining the art of human rationality. Please visit our About page for more information.
Even babies think that objects have individual identities. If you show an infant a ball rolling behind a screen, and then a moment later, two balls roll out, the infant looks longer at the expectation-violating event. Long before we're old enough to talk, we have a parietal cortex that does spatial modeling: that models individual animals running or rocks flying through 3D space.
And this is just not the way the universe works. The difference is experimentally knowable, and known. Grasping this fact, being able to see it at a glance, is one of the fundamental bridges to cross in understanding quantum mechanics.
If you shouldn't start off by talking to your students about wave/particle duality, where should a quantum explanation start? I would suggest taking, as your first goal in teaching, explaining how quantum physics implies that a simple experimental test can show that two electrons are entirely indistinguishable —not just indistinguishable according to known measurements of mass and electrical charge.
To grasp on a gut level how this is possible, it is necessary to move from thinking in billiard balls to thinking in configuration spaces; and then you have truly entered into the true and quantum realm.
If the probability distribution over this 2D configuration space of two classical 1D particles, looks like a rectangular plaid pattern, then it will factorize into a distribution over A times a distribution over B.
In classical physics, the particles A and B are the fundamental things, and the configuration space is just an isomorphic way of looking at them.
In quantum physics, the configuration space is the fundamental thing, and you get the appearance of an individual particle when the amplitude distribution factorizes enough to let you look at a subspace of the configuration space, and see a factor of the amplitude distribution—a factor that might look something like this:
This isn't an amplitude distribution, mind you. It's a factor in an amplitude distribution, which you'd have to multiply by the subspace for all the other particles in the universe, to approximate the physically real amplitude distribution.
Most mathematically possible amplitude distributions won't factor this way. Quantum entanglement is not some extra, special, additional bond between two particles. "Quantum entanglement" is the general case. The special and unusual case is quantum independence.
Reluctant tourists in a quantum universe talk about the bizarre phenomenon of quantum entanglement. Natives of a quantum universe talk about the special case of quantum independence. Try to think like a native, because you are one.
I've previously described a configuration as a mathematical object whose identity is "A photon here, a photon there; an electron here, an electron there." But this is not quite correct. Whenever you see a real-world electron, caught in a little electron trap or whatever, you are looking at a blob of amplitude, not a point mass. In fact, what you're looking at is a blob of amplitude-factor in a subspace of a global distribution that happens to factorize.
Clearly, then, an individual point in the configuration space does not have an identity of "blob of amplitude-factor here, blob of amplitude-factor there"; so it doesn't make sense to say that a configuration has the identity "A photon here, a photon there."
But what is an individual point in the configuration space, then?
Well, it's physics, and physics is math, and you've got to come to terms with thinking in pure mathematical objects. A single point in quantum configuration space, is the product of multiple point positions per quantum field; multiple point positions in the electron field, in the photon field, in the quark field, etc.
When you actually see an electron trapped in a little electron trap, what's really going on, is that the cloud of amplitude distribution that includes you and your observed universe, can at least roughly factorize into a subspace that corresponds to that little electron, and a subspace that corresponds to everything else in the universe. So that the physically real amplitude distribution is roughly the product of a little blob of amplitude-factor in the subspace for that electron, and the amplitude-factor for everything else in the universe. Got it?
'From the point of view of quantum field theory, particles are identical if and only if they are excitations of the same underlying quantum field. Thus, the question "why are all electrons identical?" arises from mistakenly regarding individual electrons as fundamental objects, when in fact it is only the electron field that is fundamental.'
Okay, but that doesn't make the basic jump into a quantum configuration space that is inherently over multiple particles. It just sounds like you're talking about individual disturbances in the aether, or something. As I understand it, an electron isn't an excitation of a quantum electron field, like a wave in the aether; the electron is a blob of amplitude-factor in a subspace of a configuration space whose points correspond to multiple point positions in quantum fields, etc.
The difficult jump from classical to quantum is not thinking of an electron as an excitation of a field. Then you could just think of a universe made up of "Excitation A in electron field over here" + "Excitation B in electron field over there" + etc. You could factorize the universe into individual excitations of a field. Your parietal cortex would have no trouble with that one—it doesn't care whether you call the little billiard balls "excitations of an electron field" so long as they still behave like little billiard balls.
The difficult jump is thinking of a configuration space that is the product of many positions in many fields, without individual identities for the positions. A configuration space whose points are "a position here in this field, a position there in this field, a position here in that field, and a position there in that field". Not, "A positioned here in this field, B positioned there in this field, C positioned here in that field" etc.
You have to reduce the appearance of individual particles to a regularity in something that is different from the appearance of particles, something that is not itself a little billiard ball.
Oh, sure, thinking of photons as individual objects will seem to work out, as long as the amplitude distribution happens t factorize. But what happens when you've got your "individual" photon A and your "individual" photon B, and you're in a situation where, a la Feynman paths, it's possible for photon A to end up in position 1 and photon B to end up in position 2, or for A to end up in 2 and B to end up in 1? Then the illusion of classicality breaks down, because the amplitude flows overlap:
In that triangular region where the distribution overlaps itself, no fact exists as to which particle is which, even in principle—and in the real world, we often get a lot more overlap than that.
I mean, imagine that I take a balloon full of photons, and shake it up.
Amplitude's gonna go all over the place. If you label all the original apparent-photons, there's gonna be Feynman paths for photons A, B, C ending up at positions 1, 2, 3 via a zillion different paths and permutations.
The amplitude-factor that corresponds to the "balloon full of photons" subspace, which contains bulges of amplitude-subfactor at various different locations in the photon field, will undergo a continuously branching evolution that involves each of the original bulges ending up in many different places by all sorts of paths, and the final configuration will have amplitude contributed from many different permutations.
It's not that you don't know which photon went where. It's that no fact of the matter exists. The illusion of individuality, the classical hallucination, has simply broken down.
And the same would hold true of a balloon full of quarks or a balloon full of electrons. Or even a balloon full of helium. Helium atoms can end up in the same places, via different permutations, and have their amplitudes add just like photons.
Don't be tempted to look at the balloon, and think, "Well, helium atom A could have gone to 1, or it could have gone to 2; and helium atom B could have gone to 1 or 2; quantum physics says the atoms both sort of split, and each went both ways; and now the final helium atoms at 1 and 2 are a mixture of the identities of A and B." Don't torture your poor parietal cortex so. It wasn't built for such usage.
Just stop thinking in terms of little billiard balls, with or without confused identities. Start thinking in terms of amplitude flows in configuration space. That's all there ever is.
And then it will seem completely intuitive that a simple experiment can tell you whether two blobs of amplitude-factor are over the same quantum field.
Just perform any experiment where the two blobs end up in the same positions, via different permutations, and see if the amplitudes add.
Part of The Quantum Physics Sequence
Next post: "Identity Isn't In Specific Atoms"
Previous post: "Feynman Paths"


(Click player button to hear story now.)
by Peter Fotis Kapnistos
Space-time is a mathematical coordinate system (3 dimensions of space and 1 of time) in which physical events are located in a single continuum.
According to Einstein’s Theory of Relativity, gravitation is the “curvature” of space-time. In other words, because an object’s mass makes the curve of space-time bend like a basin in its region, its gravitational force is amplified and attracts other nearby masses.
Things are going well up to this point. But imagine for a moment if you could undertake a sudden “reversal” of gravitation. Would you also experience a swift U-turn of space-time? If the force of the Earth’s gravitation is initially low under your feet, but abruptly gets reversed to a point high above your head, what kind of space-time turnaround might you undergo?
The reversal of space-time has far-reaching implications. It involves traveling into the past and relegating a great expanse to a tiny step. It’s the stuff of wormholes and Einstein-Rosen bridges. An Einstein-Rosen bridge is a geometrical property of a black hole that manifests itself as a “throat” attached to another set of dimensions or to another universe.
In two recent experiments at CERN (the Swiss site of the Large Hadron Collider) a neutrino beam was clocked traveling 60 nanoseconds faster than the velocity of light. The neutrinos seemingly traveled back in time (as if they could arrive at a destination before they even left). If the CERN experiments prove to be accurate, they may unlock the possibility of time travel into the past — or of convenient travel to other stars.
In the early stages of our solar system’s formation, fragments of matter were fiercely flung apart, but remained in “quantum entanglement” or superposition. Quantum entanglement is a phenomenon that connects two particles in such a way that changes to one of the particles are instantaneously reflected in the other, although they may seem physically separated by several light years. Einstein described superposition as “spooky action at a distance.”
Some clusters of ejected stellar mass eventually merged into planets and their moons. But numerous particles continued in quantum entanglement, because they shared the identical superposition, connected by Einstein-Rosen bridges (or stretched-out space-time wormholes). Since this bond took place at the beginning stages, matter in entanglement is more likely to be found in the interior or close to the core of a planet.
The Hollow Earth hypothesis, first put forward in 1692 by the English astronomer Edmund Halley, proposes that the planet Earth is either completely hollow or encloses an extensive interior space. The hollow Earth supposedly contains a small interior sun. There are said to be entrances at the north and south poles. During World War II Hitler sent an expedition to the Baltic Island of Rugen to search for proof of a hollow Earth.
Today, that theory has been extended to suggest that the hollow space that connects the north and south poles is really the throat of a space-time wormhole, and the interior sun is actually a rotating black hole, which is prevented by an event horizon from crunching the Earth.
* * *
Laura Magdalene Eisenhower is the great granddaughter of former US president Dwight Eisenhower. She claims that world leaders have made close contact with aliens. Laura said the US has established covert extraterrestrial bases. She revealed that in 2006 and 2007, she was invited to join a secret American “colony on Mars.”
Andrew D. Basiago and William Stillings just reported in the website “Exopolitics” that in the past they had stepped through time and space for the US Department of Defense. They referred to a covered up CIA program hosted at a California community college. Between 1981 and 1983, Barack Obama is said to have “visited Mars” with them by means of a teleportation chamber called a jump room. Regina Dugan, the director of Darpa, allegedly was another member.
* * *
In the autumn of 2009, a veteran intelligence operative, reactivated into defense agency programs, walked through the old-world streets of an eastern Mediterranean city. He gazed down and visualized structures deep under the pavement, to look into history.
In the past, he had performed groundbreaking experiments with remote exploration. Now, enormously behind him, a funicular tunnel of steel tracks drew railway carriages by cable through the base of a cliff and up to its peak. It offered a convincing display that the ancient city was hollow within. A series of complex bunkers deep inside the rock-face installation encircled a subterranean engine that powered a cabled hoisting machine.
Like the exotic Berghof elevator, the construction inspired by Bavarian masons and architects was suggestive of Nazi Germany’s suspected National Southern Redoubt, an inner stronghold from which Germany would retaliate. The Allies, who later said the Redoubt fortress existed only in the German imagination, searched for Nazi atomic weapons near the Mediterranean:
“Here, defended by nature and by the most efficient secret weapons yet invented, the powers that have hitherto guided Germany will survive to reorganize her resurrection; here armaments will be manufactured in bombproof factories, food and equipment will be stored in vast underground caverns and a specially selected corpus of young men will be trained in guerrilla warfare, so that a whole underground army can be fitted and directed to liberate Germany from occupying forces.” (Supreme Headquarters Allied Expeditionary Force, Weekly Intelligence Summary, March 11, 1945)
In his mind’s eye, the intelligence guardian pictured dugout walls, and the slab of a radiation shield with an air lock that opened like a submarine door. Several such doors were lined up along the dark passage where a tunnel of metal rails descended into the crater’s abyss.
Behind the doors were the jump rooms of quantum entanglement, connected by Einstein-Rosen bridges. One room shared the same superposition as a region within the interior of Mars. Behind another was a quantum-string conduit to the interior of Venus.
As the global elite played and exulted the top-secret enigma of their ancient city, its local residents were forced into a poverty and destitution that threatened to wipe out the Euro. Would the world at last awaken and comprehend that for millennia humans and celestial messengers traveled through the buried gates and jump rooms of quantum entanglement?


Over 400 million transistors are packed on dual-core chips manufactured using Intel's 45nm process. That'll double soon, per Moore's Law. And it'll still be like computing with pebbles compared to quantum computing.
Quantum computing is a pretty complicated subject—uh, hello, quantum mechanics plus computers. I'm gonna keep it kinda basic, but recent breakthroughs like this one prove that you should definitely start paying attention to it. Some day, in the future, quantum computing will be cracking codes, powering web searches, and maybe, just maybe, lighting up our Star Trek-style holodecks.
Before we get to the quantum part, let's start with just "computing." It's about bits. They're the basic building block of computing information. They've got two states—0 or 1, on or off, true or false, you get the idea. But two defined states is key. When you add a bunch of bits together, usually 8 of 'em, you get a byte. As in kilobytes, megabytes, gigabytes and so on. Your digital photos, music, documents, they're all just long strings of 1s and 0s, segmented into 8-digit strands. Because of that binary setup, a classical computer operates by a certain kind of logic that makes it good at some kinds of computing—the general stuff you do everyday—but not so great at others, like finding ginormous prime factors (those things from math class), which are a big part of cracking codes.
Quantum computing operates by a different kind of logic—it actually uses the rules of quantum mechanics to compute. Quantum bits, called qubits, are different from regular bits, because they don't just have two states. They can have multiple states, superpositions—they can be 0 or 1 or 0-1 or 0+1 or 0 and 1, all at the same time. It's a lot deeper than a regular old bit. A qubit's ability to exist in multiple states—the combo of all those being a superposition—opens up a big freakin' door of possibility for computational powah, because it can factor numbers at much more insanely fast speeds than standard computers.
Entanglement—a quantum state that's all about tight correlations between systems—is the key to that. It's a pretty hard thing to describe, so I asked for some help from Boris Blinov, a professor at the University of Washington's Trapped Ion Quantum Computing Group. He turned to a take on Schrödinger's cat to explain it: Basically, if you have a cat in a closed box, and poisonous gas is released. The cat is either dead, 0, or alive, 1. Until I open the box to find out, it exists in both states—a superposition. That superposition is destroyed when I measure it. But suppose I have two cats in two boxes that are correlated, and you go through the same thing. If I open one box and the cat's alive, it means the other cat is too, even if I never open the box. It's a quantum phenomenon that's a stronger correlation than you can get in classical physics, and because of that you can do something like this with quantum algorithms—change one part of the system, and the rest of it will respond accordingly, without changing the rest of the operation. That's part of the reason it's faster at certain kinds of calculations.
The other, explains Blinov, is that you can achieve true parallelism in computing—actually process a lot of information in parallel, "not like Windows" or even other types of classic computers that profess parallelism.
So what's that good for? For example, a password that might take years to crack via brute force using today's computers could take mere seconds with a quantum computer, so there's plenty of crazy stuff that Uncle Sam might want to put it to use for in cryptography. And it might be useful to search engineers at Google, Microsoft and other companies, since you can search and index databases much, much faster. And let's not forget scientific applications—no surprise, classic computers really suck at modeling quantum mechanics. The National Institute of Science and Technology's Jonathan Home suggests that given the way cloud computing is going, if you need an insane calculation performed, you might rent time and farm it out to a quantum mainframe in Google's backyard.
The reason we're not all blasting on quantum computers now is that this quantum mojo is, at the moment, extremely fragile. And it always will be, since quantum states aren't exactly robust. We're talking about working with ions here—rather than electrons—and if you think heat is a problem with processors today, you've got no idea. In the breakthrough by Home's team at NIST—completing a full set of quantum "transport" operations, moving information from one area of the "computer" to another—they worked with a single pair of atoms, using lasers to manipulate the states of beryllium ions, storing the data and performing an operation, before transferring that information to a different location in the processor. What allowed it to work, without busting up the party and losing all the data through heat, were magnesium ions cooling the beryllium ions as they were being manipulated. And those lasers can only do so much. If you want to manipulate more ions, you have to add more lasers.
Hell, quantum computing is so fragile and unwieldy that when we talked to Home, he said much of the effort goes into methods of correcting errors. In five years, he says, we'll likely be working with a mere tens of qubits. The stage it's at right now, says Blinov, is "the equivalent of building a reliable transistor" back in the day. But that's not to say those of tens of qubits won't be useful. While they won't be cracking stuff for the NSA—you'll need about 10,000 qubits for cracking high-level cryptography—that's still enough quantum computing power to calculate properties for new materials that are hard to model with a classic computer. In other words, materials scientists could be developing the case for the iPhone 10G or the building blocks for your next run-of-the-mill Intel processor using quantum computers in the next decade. Just don't expect a quantum computer on your desk in the next 10 years.
Special thanks to National Institute of Standards and Technology's Jonathan Home and the University of Washington Professor Boris Blinov!
Still something you wanna know? Send questions about quantum computing, quantum leaps or undead cats to email@example.com, with "Giz Explains" in the subject line.


Quantum entanglement is a state where two particles have correlated properties: when you make a measurement on one, it constrains the outcome of the measurement on the second, even if the two particles are widely separated. It's also possible to entangle more than two particles, and even to spread out the entanglements over time, so that a system that was only partly entangled at the start is made fully entangled later on.
This sequential process goes under the clunky name of "delayed-choice entanglement swapping." And, as described in a Nature Physics article by Xiao-song Ma et al., it has a rather counterintuitive consequence. You can take a measurement before the final entanglement takes place, but the measurement's results depend on whether or not you subsequently perform the entanglement.
Delayed-choice entanglement swapping consists of the following steps. (I use the same names for the fictional experimenters as in the paper for convenience, but note that they represent acts of measurement, not literal people.)
- Two independent sources (labeled I and II) produce pairs photons such that their polarization states are entangled. One photon from I goes to Alice, while one photon from II is sent to Bob. The second photon from each source goes to Victor. (I'm not sure why the third party is named "Victor".)
- Alice and Bob independently perform polarization measurements; no communication passes between them during the experiment—they set the orientation of their polarization filters without knowing what the other is doing.
- At some time after Alice and Bob perform their measurements, Victor makes a choice (the "delayed choice" in the name). He either allows his two photons from I and II to travel on without doing anything, or he combines them so that their polarization states are entangled. A final measurement determines the polarization state of those two photons.
The results of all four measurements are then compared. If Victor did not entangle his two photons, the photons received by Alice and Bob are uncorrelated with each other: the outcome of their measurements are consistent with random chance. (This is the "entanglement swapping" portion of the name.) If Victor entangled the photons, then Alice and Bob's photons have correlated polarizations—even though they were not part of the same system and never interacted.
The practicalities of delayed-choice entanglement swapping bears many similarities to other entanglement experiments. Ma et al. sent pulsed light from an ultraviolet laser through two separate beta-barium borate (BBO) crystals, which respond by emitting two photons with entangled polarizations, but equal wavelength. The BBO crystals acted as the sources labeled I and II above; the oppositely polarized photons they produced were sent down separate paths. One path for each BBO crystal led to a polarization detector ("Alice" and "Bob"), while the other passed through a fiber-optic cable 104 meters long before arriving at the "Victor" apparatus.
That little bit of cabling was enough to ensure that anything that happened at Victor occurred after Alice and Bob had done their measurements.
The choice about entangling the photons at the Victor apparatus was made by a random-number generator, and passed through a tunable bipartite state analyzer (BiSA). The BiSA contained two beam-splitters that select photons' paths depending on their polarization, along with a device that rotated the polarization of the photons. Depending on the "choice" to entangle or not, the polarization of the photons from I and II were made to correlate or left alone. Finally, the polarization of both photons at Victor were measured, and compared with the results from Alice and Bob.
Due to the 104-meter fiber-optic cable, Victor's measurements occurred at least 14 billionths of a second after those of Alice and Bob, precluding the idea that the setting of the BiSA caused the polarization results to change. While comparatively few photons made it all the way through every step of the experiment, this is due to the difficulty of measurements with so few photons, rather than a problem with the results.
Ma et al. found to a high degree of confidence that when Victor selected entanglement, Alice and Bob found correlated photon polarizations. This didn't happen when Victor left the photons alone.
Suffice it to say that facile explanations about information passing between Alice's and Bob's photons lead to violations of causality, since Alice and Bob perform their polarization measurement before Victor makes his choice about whether to entangle his photons or not. (Similarly, if you think that all the photons come from a single laser source, they must be correlated from the start, and you must answer how they "know" what Victor is going to do before he does it.)
The picture certainly looks like future events influence the past, a view any right-minded physicist would reject. The authors conclude with some strong statements about the nature of physical reality that I'm not willing to delve into (the nature of physical reality is a bit above my pay grade).
As always with entanglement, it's important to note that no information is passing between Alice, Bob, and Victor: the settings on the detectors and the BiSA are set independently, and there's no way to communicate faster than the speed of light. Nevertheless, this experiment provides a realization of one of the fundamental paradoxes of quantum mechanics: that measurements taken at different points in space and time appear to affect each other, even though there is no mechanism that allows information to travel between them.


Revision as of 10:30, 11 June 2010
Monads in Haskell can be thought of as composable computation descriptions. The essence of monad is thus separation of composition timeline from the composed computation's execution timeline, as well as the ability of computation to implicitly carry extra data as pertaining to the computation itself in addition to its one (hence the name) output. This lends monads to supplementing pure calculations with features like I/O, common environment or state, and to preprocessing of computations (simplification, optimization etc.).
Each monad, or computation type, provides a means of (a) creating a description of computation to produce a given value, (b) running a computation description (CD) and returning its output to Haskell, and (c) combining a CD with a Haskell function consuming of its output and returning another CD, to create a combined one. It might also define additional primitives to provide access and/or enable manipulation of data it implicitly carries, specific to its nature.
Thus in Haskell, though it is a purely-functional language, side effects that will be performed by a computation can be dealt with and combined purely at the monad's composition time. Monads thus resemble programs in a particular DSL. While programs may describe impure effects and actions outside Haskell, they can still be combined and processed ("compiled") purely inside Haskell, creating a pure Haskell value - a CD that describes an impure calculation. The combined computations don't have to be impure and can be pure themselves as well.
Because they are very useful in practice but rather mind-twisting for the beginners, numerous tutorials that deal exclusively with monads were created (see monad tutorials).
1 Common monads
Most common applications of monads include:
- Representing failure using monadMaybe
- Nondeterminism through backtracking using monadList
- State using monadState
- Read-only environment using monadReader
- I/O using monadIO
2 Monad classMonads can be viewed as a standard programming interface to various data or control structures, which is captured by the
class Monad m where (>>=) :: m a -> (a -> m b) -> m b (>>) :: m a -> m b -> m b return :: a -> m a fail :: String -> m a
In addition to implementing the class functions, all instances of Monad should obey the following equations:
return a >>= k = k a m >>= return = m m >>= (\x -> k x >>= h) = (m >>= k) >>= h
See this intuitive explanation of why they should obey the Monad laws.
Any Monad can be made a Functor by defining
fmap ab ma = ma >>= (return . ab)
However, the Functor class is not a superclass of the Monad class. See Functor hierarchy proposal.
3 Special notationIn order to improve the look of code that uses monads Haskell provides a special syntactic sugar called
thing1 >>= (\x -> func1 x >>= (\y -> thing2 >>= (\_ -> func2 y (\z -> return z))))
which can be written more clearly by breaking it into several lines and omitting parentheses:
thing1 >>= \x -> func1 x >>= \y -> thing2 >>= \_ -> func2 y >>= \z -> return z
do x <- thing1 y <- func1 x thing2 z <- func2 y return z
4 Commutative monads
Commutative monads are monads for which the order of actions makes no difference (they commute), that is when following code:
do a <- f x b <- g y m a b
is the same as:
do b <- g y a <- f x m a b
Examples of commutative include:
5 Monad tutorials
Monads are known for being deeply confusing to lots of people, so there are plenty of tutorials specifically related to monads. Each takes a different approach to Monads, and hopefully everyone will find something useful.
See Monad tutorials.
6 Monad reference guides
An explanation of the basic Monad functions, with examples, can be found in the reference guide A tour of the Haskell Monad functions, by Henk-Jan van Tuyl.
7 Monad research
A collection of research papers about monads.
8 Monads in other languages
Implementations of monads in other languages.
- C++, doc
- CML.event ?
- Clean State monad
- Java (tar.gz)
- LINQ, more, C#, VB
- Perl6 ?
- The Unix Shell
- More monads by Oleg
- CLL: a concurrent language based on a first-order intuitionistic linear logic where all right synchronous connectives are restricted to a monad.
And possibly there exist:
- Standard ML (via modules?)
Please add them if you know of other implementations.
9 Interesting monads
A list of monads for various evaluation strategies and games:
- Identity monad
- Optional results
- Random values
- Read only state
- Writable state
- Unique supply
- ST - memory-only effects
- Global state
- Undoable state effects
- Function application
- Functions which may error
- Atomic memory transactions
- IO - unrestricted side effects
- Non-deterministic evaluation
- List monad: computations with multiple choices
- Concurrent threads
- Backtracking computations
- Region allocation effects
- LogicT: backtracking monad transformer with fair operations and pruning
- Pi calculus as a monad
- Halfs, uses a read-only and write-only monad for filesystem work.
- House's H monad for safe hardware access
- Commutable monads for parallel programming
- The Quantum computing monad
- Simple, Fair and Terminating Backtracking Monad
- Typed exceptions with call traces as a monad
- Breadth first list monad
- Continuation-based queues as monads
- Typed network protocol monad
- Non-Determinism Monad for Level-Wise Search
- Transactional state monad
- A constraint programming monad
- A probability distribution monad
There are many more interesting instance of the monad abstraction out there. Please add them as you come across each species.
- If you are tired of monads, you can easily get rid of them.


The Next Big Scientific Breakthrough: Sun-Earth Interactions
Quantum computing, nanotechnology and genetic engineering are exciting fields. But understanding the interaction between the Sun and Earth is at least as important as a scientific frontier.
The Sun Affects Clouds and Ozone, Which In Turn Affect Climate
For example, one of the world’s most prestigious science labs has just demonstrated that cosmic rays affect cloud formation – which in turn affects climate – on Earth. Because the sun’s output directly determines the amount of cosmic rays which reach the Earth, the sun is an important driver of the Earth’s climate.
And as I noted last year:
Intense solar activity can destroy ozone in the Earth’s atmosphere, thus affecting climactic temperatures. See this, this, this and this. Indeed, the effects of solar energy on ozone may be one of the main ways in which the sun influences Earth’s climate.
The Sun’s Output Changes the Rate of Radioactive Decay On Earth
Believe it or not, Stanford University News reported Tuesday that solar flares change the rate of radioactive decay of elements on Earth:
When researchers found an unusual linkage between solar flares and the inner life of radioactive elements on Earth, it touched off a scientific detective investigation that could end up protecting the lives of space-walking astronauts and maybe rewriting some of the assumptions of physics.
The radioactive decay of some elements sitting quietly in laboratories on Earth seemed to be influenced by activities inside the sun, 93 million miles away.
Is this possible?
Researchers from Stanford and Purdue University believe it is. But their explanation of how it happens opens the door to yet another mystery.
There is even an outside chance that this unexpected effect is brought about by a previously unknown particle emitted by the sun. “That would be truly remarkable,” said Peter Sturrock, Stanford professor emeritus of applied physics and an expert on the inner workings of the sun.
The story begins, in a sense, in classrooms around the world, where students are taught that the rate of decay of a specific radioactive material is a constant. This concept is relied upon, for example, when anthropologists use carbon-14 to date ancient artifacts and when doctors determine the proper dose of radioactivity to treat a cancer patient.
As the researchers pored through published data on specific isotopes, they found disagreement in the measured decay rates – odd for supposed physical constants.
Checking data collected at Brookhaven National Laboratory on Long Island and the Federal Physical and Technical Institute in Germany, they came across something even more surprising: long-term observation of the decay rate of silicon-32 and radium-226 seemed to show a small seasonal variation. The decay rate was ever so slightly faster in winter than in summer.
On Dec 13, 2006, the sun itself provided a crucial clue, when a solar flare sent a stream of particles and radiation toward Earth. Purdue nuclear engineer Jere Jenkins, while measuring the decay rate of manganese-54, a short-lived isotope used in medical diagnostics, noticed that the rate dropped slightly during the flare, a decrease that started about a day and a half before the flare.
If this apparent relationship between flares and decay rates proves true, it could lead to a method of predicting solar flares prior to their occurrence, which could help prevent damage to satellites and electric grids, as well as save the lives of astronauts in space.
The decay-rate aberrations that Jenkins noticed occurred during the middle of the night in Indiana – meaning that something produced by the sun had traveled all the way through the Earth to reach Jenkins’ detectors. What could the flare send forth that could have such an effect?
Jenkins and Fischbach guessed that the culprits in this bit of decay-rate mischief were probably solar neutrinos, the almost weightless particles famous for flying at almost the speed of light through the physical world – humans, rocks, oceans or planets – with virtually no interaction with anything.
Going back to take another look at the decay data from the Brookhaven lab, the researchers found a recurring pattern of 33 days. It was a bit of a surprise, given that most solar observations show a pattern of about 28 days – the rotation rate of the surface of the sun.
The explanation? The core of the sun – where nuclear reactions produce neutrinos – apparently spins more slowly than the surface we see. “It may seem counter-intuitive, but it looks as if the core rotates more slowly than the rest of the sun,” Sturrock said.
All of the evidence points toward a conclusion that the sun is “communicating” with radioactive isotopes on Earth, said Fischbach.
“It doesn’t make sense according to conventional ideas,” Fischbach said. Jenkins whimsically added, “What we’re suggesting is that something that doesn’t really interact with anything is changing something that can’t be changed.”
“It’s an effect that no one yet understands,” agreed Sturrock. “Theorists are starting to say, ‘What’s going on?’ But that’s what the evidence points to. It’s a challenge for the physicists and a challenge for the solar people too.”
If the mystery particle is not a neutrino, “It would have to be something we don’t know about, an unknown particle that is also emitted by the sun and has this effect, and that would be even more remarkable,” Sturrock said.
The Sun Interacts With the Earth In Numerous Other Ways
I pointed out last year that the sun affects the Earth in many more ways than scientists knew:
The sun itself also affects the Earth more than previously understood. For example, according to the European Space Agency:
Scientists … have proven that sounds generated deep inside the Sun cause the Earth to shake and vibrate in sympathy. They have found that Earth’s magnetic field, atmosphere and terrestrial systems, all take part in this cosmic sing-along.
And NASA has just discovered that “space weather” causes “spacequakes” on Earth:
Researchers using NASA’s fleet of five THEMIS spacecraft have discovered a form of space weather that packs the punch of an earthquake and plays a key role in sparking bright Northern Lights. They call it “the spacequake.”
A spacequake is a temblor in Earth’s magnetic field. It is felt most strongly in Earth orbit, but is not exclusive to space. The effects can reach all the way down to the surface of Earth itself.
“Magnetic reverberations have been detected at ground stations all around the globe, much like seismic detectors measure a large earthquake,” says THEMIS principal investigator Vassilis Angelopoulos of UCLA.
It’s an apt analogy because “the total energy in a spacequake can rival that of a magnitude 5 or 6 earthquake,” according to Evgeny Panov of the Space Research Institute in Austria.
“Now we know,” says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. “Plasma jets trigger spacequakes.”
According to THEMIS, the jets crash into the geomagnetic field some 30,000 km above Earth’s equator. The impact sets off a rebounding process, in which the incoming plasma actually bounces up and down on the reverberating magnetic field. Researchers call it “repetitive flow rebuffing.” It’s akin to a tennis ball bouncing up and down on a carpeted floor. The first bounce is a big one, followed by bounces of decreasing amplitude as energy is dissipated in the carpet.
“When plasma jets hit the inner magnetosphere, vortices with opposite sense of rotation appear and reappear on either side of the plasma jet,” explains Rumi Nakamura of the Space Research Institute in Austria, a co-author of the study. “We believe the vortices can generate substantial electrical currents in the near-Earth environment.”
Acting together, vortices and spacequakes could have a noticeable effect on Earth. The tails of vortices may funnel particles into Earth’s atmosphere, sparking auroras and making waves of ionization that disturb radio communications and GPS. By tugging on surface magnetic fields, spacequakes generate currents in the very ground we walk on. Ground current surges can have profound consequences, in extreme cases bringing down power grids over a wide area.
What does this mean?
Some allege that spacequakes cause actual, physical earthquakes on Earth. I have no idea whether or not that is true.
The above-quoted NASA article concludes with a poem which implies such a connection:
a magnitude six
The poem may use artistic license rather than scientific rigor. However, some scientists do believe that the sun’s activity can even cause earthquakes, volcanic eruptions and extreme weather.
What is certain is that the science of the affect of space events on Earth is in its infancy, and that there are many fascinating discoveries in our future.
When scientists understand all of the ways that the Sun and Earth interact, we will know alot more about the Earth and our place in the universe than we do today.


by Paige Brown
Popular television shows such as “Doctor Who” have brought the idea of time travel into the vernacular of popular culture. But problem of time travel is even more complicated than one might think. LSU’s Mark Wilde has shown that it would theoretically be possible for time travelers to copy quantum data from the past.
It all started when David Deutsch, a pioneer of quantum computing and a physicist at Oxford, came up with a simplified model of time travel to deal with the paradoxes that would occur if one could travel back in time. For example, would it be possible to travel back in time to kill one’s grandfather? In the Grandfather paradox, a time traveler faces the problem that if he kills his grandfather back in time, then he himself is never born, and consequently is unable to travel through time to kill his grandfather, and so on. Some theorists have used this paradox to argue that it is actually impossible to change the past.
“The question is, how would you have existed in the first place to go back in time and kill your grandfather?” said Mark Wilde, an LSU assistant professor with a joint appointment in the Department of Physics and Astronomy and with the Center for Computation and Technology, or CCT.
Deutsch solved the Grandfather paradox originally using a slight change to quantum theory, proposing that you could change the past as long as you did so in a self-consistent manner.
“Meaning that, if you kill your grandfather, you do it with only probability one-half,” Wilde said. “Then, he’s dead with probability one-half, and you are not born with probability one-half, but the opposite is a fair chance. You could have existed with probability one-half to go back and kill your grandfather.”
But the Grandfather paradox is not the only complication with time travel. Another problem is the no-cloning theorem, or the no “subatomic Xerox-machine” theorem, known since 1982. This theorem, which is related to the fact that one cannot copy quantum data at will, is a consequence of Heisenberg’s famous Uncertainty Principle, by which one can measure either the position of a particle or its momentum, but not both with unlimited accuracy. According to the Uncertainty Principle, it is thus impossible to have a subatomic Xerox-machine that would take one particle and spit out two particles with the same position and momentum – because then you would know too much about both particles at once.
“We can always look at a paper, and then copy the words on it. That’s what we call copying classical data,” Wilde said. “But you can’t arbitrarily copy quantum data, unless it takes the special form of classical data. This no-cloning theorem is a fundamental part of quantum mechanics – it helps us reason how to process quantum data. If you can’t copy data, then you have to think of everything in a very different way.”
But what if a Deutschian closed timelike curve did allow for copying of quantum data to many different points in space? According to Wilde, Deutsch suggested in his late 20th century paper that it should be possible to violate the fundamental no-cloning theorem of quantum mechanics. Now, Wilde and collaborators at the University of Southern California and the Autonomous University of Barcelona have advanced Deutsch’s 1991 work with a recent paper in Physical Review Letters (DOI: 10.1103/PhysRevLett.111.190401). The new approach allows for a particle, or a time traveler, to make multiple loops back in time – something like Bruce Willis’ travels in the Hollywood film “Looper.”
“That is, at certain locations in spacetime, there are wormholes such that, if you jump in, you’ll emerge at some point in the past,” Wilde said. “To the best of our knowledge, these time loops are not ruled out by the laws of physics. But there are strange consequences for quantum information processing if their behavior is dictated by Deutsch’s model.”
A single looping path back in time, a time spiral of sorts, behaving according to Deutsch’s model, for example, would have to allow for a particle entering the loop to remain the same each time it passed through a particular point in time. In other words, the particle would need to maintain self-consistency as it looped back in time.
“In some sense, this already allows for copying of the particle’s data at many different points in space,” Wilde said, “because you are sending the particle back many times. It’s like you have multiple versions of the particle available at the same time. You can then attempt to read out more copies of the particle, but the thing is, if you try to do so as the particle loops back in time, then you change the past.”
To be consistent with Deutsch’s model, which holds that you can only change the past as long as you can do it in a self-consistent manner, Wilde and colleagues had to come up with a solution that would allow for a looping curve back in time, and copying of quantum data based on a time traveling particle, without disturbing the past.
“That was the major breakthrough, to figure out what could happen at the beginning of this time loop to enable us to effectively read out many copies of the data without disturbing the past,” Wilde said. “It just worked.”
However, there is still some controversy over interpretations of the new approach, Wilde said. In one instance, the new approach may actually point to problems in Deutsch’s original closed timelike curve model.
“If quantum mechanics gets modified in such a way that we’ve never observed should happen, it may be evidence that we should question Deutsch’s model,” Wilde said. “We really believe that quantum mechanics is true, at this point. And most people believe in a principle called Unitarity in quantum mechanics. But with our new model, we’ve shown that you can essentially violate something that is a direct consequence of Unitarity. To me, this is an indication that something weird is going on with Deutsch’s model. However, there might be some way of modifying the model in such a way that we don’t violate the no-cloning theorem.”
Other researchers argue that Wilde’s approach wouldn’t actually allow for copying quantum data from an unknown particle state entering the time loop because nature would already “know” what the particle looked like, as it had traveled back in time many times before.
But whether or not the no-cloning theorem can truly be violated as Wilde’s new approach suggests, the consequences of being able to copy quantum data from the past are significant. Systems for secure Internet communications, for example, will likely soon rely on quantum security protocols that could be broken or “hacked” if Wilde’s looping time travel methods were correct.
“If an adversary, if a malicious person, were to have access to these time loops, then they could break the security of quantum key distribution,” Wilde said. “That’s one way of interpreting it. But it’s a very strong practical implication because the big push of quantum communication is this secure way of communicating. We believe that this is the strongest form of encryption that is out there because it’s based on physical principles.”
Today, when you log into your Gmail or Facebook, your password and information encryption is not based on physical principles of quantum mechanical security, but rather on the computational assumption that it is very difficult for “hackers” to factor mathematical products of prime numbers, for example. But physicists and computer scientists are working on securing critical and sensitive communications using the principles of quantum mechanics. Such encryption is believed to be unbreakable – that is, as long as hackers don’t have access to Wilde’s looping closed timelike curves.
“This ability to copy quantum information freely would turn quantum theory into an effectively classical theory in which, for example, classical data thought to be secured by quantum cryptography would no longer be safe,” Wilde said. “It seems like there should be a revision to Deutsch’s model which would simultaneously resolve the various time travel paradoxes but not lead to such striking consequences for quantum information processing. However, no one yet has offered a model that meets these two requirements. This is the subject of open research.”


speed quantum crypto
Technology Research News
working to develop ultra powerful quantum computers and ultra secure quantum
cryptography systems generally use subtle aspects of particles like photons
and atoms to represent the 1s and 0s of computer information.
When these systems use photons, for example, they tend to tap polarization,
phase, or angular momentum -- aspects of light that have to do with the
orientation of a lightwave or its electric field.
Researchers from the University of Rochester are using photons to
represent data in a simpler way: a photon's position within an array of
pixels. The approach also packs more information per photon than standard
The researchers' pixel entanglement method could be used to increase
the speed of quantum cryptography systems. Quantum cryptography promises
potentially perfect security because the laws of quantum physics make it
theoretically impossible for someone eavesdropping on information transmitted
this way to go undetected. Today's systems are relatively slow, however.
The researchers method involves sending each photon of a quantum
mechanically linked, or entangled, pair of photons into identical arrays
of pixels and observing which pixels light up. Entangled photons have one
or more properties that are linked regardless of the distance between them.
Measuring one photon instantly causes the other to mirror it.
Standard ways of encoding data into photons use properties of a
photon that can be set one of two ways to represent a 1 or a 0. The researchers'
scheme packs more information per photon because the number of pixels is
the number of possible states. "[Pixel entanglement] allows us to impress
more information on the photon pairs, which... in communication schemes
can translate into higher bit rates," said Malcolm O'Sullivan-Hale, a researcher
at the University of Rochester.
The researchers scheme works by generating pairs of entangled photons
using the standard parametric downconversion method. When ultraviolet photons
are fired into a special crystal, some are split into a pair of entangled
infrared photons. The researchers then channel the entangled photons separately
through a series of lenses into identical arrays of pixels. The entangled
pairs occupy the same positions in the two arrays, which, in turn, causes
those positions, or pixels, to become entangled. The pixels that are entangled
are determined at random, and the random numbers resulting from a series
of entangled pixels makes up the secret key for encrypting information.
The researchers demonstrated their system using three-pixel arrays,
and they also showed that the method works for six-pixel arrays, said O'Sullivan-Hale.
A six-pixel array would allow a pair of entangled photons to represent three
bits of information.
Pixel entanglement could theoretically be used with much higher
numbers of pixels, and the researchers estimated that their system could
be used in 16-pixel arrays, meaning each photon pair could represent eight
bits of information. "With the possibility of using entangled states with
more [than two] levels, we foresee pixel entanglement being useful for distributing
quantum keys at high bit rates," said O'Sullivan-Hale.
Today's optical fiber does not preserve lightwaves well enough to
allow the method to work over optical networks, said O'Sullivan-Hale. "The
most readily imaginable application [of pixel entanglement] is free-space
quantum key distribution for the secure transmission of information," he
Another important advantage of pixel entanglement for quantum cryptography
is that the higher number of possible states for each photon pair makes
it harder for an eavesdropper to fool the system, said O'Sullivan-Hale.
Using the technique for practical quantum cryptography will require
preserving the entanglement over long distances, minimizing losses and detecting
photon positions with adequate resolution, said O'Sullivan-Hale.
Practical applications of pixel entanglement could be realized in
five to ten years, said O'Sullivan-Hale.
O'Sullivan-Hale's research colleagues were Irfan Ali Khan, Robert
W. Boyd and John C. Howell. They published the research in the June 7, 2005
issue of Physical Review Letters. The research was funded by the
National Science Foundation (NSF), the Army Research Office (ARO), the Office
of Naval Research (ONR), the Research Corporation, and the University of
Timeline: 5-10 years
Funding: Government; Private; University
TRN Categories: Quantum Computing and Communications; Optical
Computing, Optoelectronics and Photonics; Physics
Story Type: News
Related Elements: Technical paper, "Pixel Entanglement: Experimental
Realization of Optically Entangled d=3 and d=6 Qudits," Physical Review
Letters, June 7, 2005
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Focus: Nobel Prize—Tools for Quantum Tinkering
To understand the quantum world, researchers have developed lab-scale tools to manipulate microscopic objects without disturbing them. The 2012 Nobel Prize in Physics recognizes two of these quantum tinkerers: David Wineland, of the National Institute of Standards and Technology and the University of Colorado in Boulder, and Serge Haroche, of the Collège de France and the Ecole Normale Supérieure in Paris. Two of their papers, published in 1995 and ‘96 in Physical Review Letters, exemplify their contributions. The one by Wineland and collaborators showed how to use atomic states to make a quantum logic gate, the first step toward a superfast quantum computer. The other, by Haroche and his colleagues, demonstrated one of the strange predictions of quantum mechanics—that measuring a quantum system can pull the measuring device into a weird quantum state which then dissipates over time.
A quantum system can exist in two distinct states at the same time. The challenge in studying this so-called superposition of quantum states is that any nudge from the environment can quickly push the system into one state or the other. Wineland and Haroche both designed experiments that isolate particles—ions or photons—from the environment, so that they can be carefully controlled without losing their quantum character.
Since the 1980s, Haroche has been one of the pioneers in the field of cavity quantum electrodynamics, where researchers observe a single atom interacting with a few photons inside a reflective cavity. Haroche and his colleagues can keep a photon bouncing back and forth in a centimeter-sized cavity billions of times before it escapes. But only photons of specific wavelengths determined by the cavity size can survive. Haroche’s group was one of the first to show that this wavelength selectivity could amplify  or suppress  the emission from an atom inside the cavity. Haroche was later able to tune a cavity so that the allowed wavelengths were close to, but not equal to, those associated with transitions in an atom, so that the photons and atom did not exchange energy. Instead, they incurred a phase change that could carry information about, for example, the number of photons in the cavity .
In 1996, Haroche’s group used such a system to study the process by which a quantum superposition settles into a single state. The researchers placed a highly excited rubidium atom in a superposition of two energy states and then sent it through a cavity containing about ten photons. The matter-light interaction “entangled” the photons and atom together, so that the photons entered their own superposition of two states (a “Schrödinger cat” state, in the team’s language), which acted as a “measurement” of the atom’s superposition state. Measuring devices don’t ordinarily remain in two states; instead, they give up their quantum nature almost immediately through interactions with the environment. However, this so-called decoherence process was expected to take longer for a “small” device with only a few particles (photons in this case).
To see this effect, the team arranged for a second atom to enter the cavity shortly after the first. Separate observations of the atoms after each passed through the cavity showed that the superposition in the photons survived for several microseconds. This was the first experimental exploration of the quantum measurement process at the so-called “mesoscopic” boundary between the macroscopic and the microscopic world, says coauthor Jean-Michel Raimond of the Pierre and Marie Curie University in Paris. “The experiment is even now described in a few standard quantum mechanics textbooks,” he says.
Wineland performed similar sorts of quantum-probing experiments through his own pioneering work with trapped ions [4, 5]. The tight confinement of ions in these electric field traps causes ion motion to be restricted to distinct quantum states, each of which represents a different frequency of bouncing back-and-forth between the electric field “walls.” These motional, or “vibrational,” states are typically independent of the internal, electronic energy states of the ion, but Wineland and others showed that laser light could transfer energy from one set of states to the other. The researchers used this laser coupling to cool an ion to the state with the slowest motion  and to make the world’s most precise clocks .
In their 1995 paper, Wineland and his colleagues demonstrated the first quantum logic gate, the basic building block of a quantum computer. They trapped a single beryllium ion and prepared it with two quantum bits (quantum two-state systems, or “qubits”): one corresponding to the two lowest vibrational states and the other to a pair of electronic states. A series of laser pulses would either have no effect on the electronic qubit or would switch its value—say, from the lower- to the higher-energy state—depending on the vibrational qubit’s state. This “controlled NOT” operation did not measure either qubit, so the quantum nature of the states was preserved. “It was a simple gate, but it was interesting because it was clear how to scale the system up,” says coauthor Chris Monroe of the University of Maryland in College Park. Since then, researchers have succeeded in performing more complicated logic operations with as many as 14 ions.
“There is a beautiful duality between the two techniques,” Raimond says. Wineland traps matter particles (ions) and studies them with laser beams, while Haroche traps photons and studies them with a matter beam. “I think the match by the Nobel committee is quite perfect: Same generation, similar achievements, same global objectives,” says Raimond, “and two excellent friends.”
Michael Schirber is a freelance science writer in Lyon, France.
- P. Goy, J. M. Raimond, M. Gross, and S. Haroche, “Observation of Cavity-Enhanced Single-Atom Spontaneous Emission,” Phys. Rev. Lett. 50, 1903 (1983)
- W. Jhe, A. Anderson, E. A. Hinds, D. Meschede, L. Moi, and S. Haroche, “Suppression of Spontaneous Decay at Optical Frequencies: Test of Vacuum-Field Anisotropy in Confined Space,” Phys. Rev. Lett. 58, 666 (1987)
- S. Gleyzes, S. Kuhr, C. Guerlin, J. Bernu, S. Deléglise, U. Busk Hoff, M. Brune, J. M. Raimond, and S. Haroche, “Quantum Jumps of Light Recording the Birth and Death of a Photon in a Cavity,” Nature 446, 297 (2007)
- D. J. Wineland, R. E. Drullinger, and F. L. Walls, “Radiation-Pressure Cooling of Bound Resonant Absorbers,” Phys. Rev. Lett. 40, 1639 (1978)
- D.J. Wineland and Wayne M. Itano, “Spectroscopy of a Single Mg+ Ion,” Phys. Lett. A 82, 75 (1981)
- F. Diedrich, J. C. Bergquist, W. M. Itano, and D. J. Wineland, “Laser Cooling to the Zero-Point Energy of Motion,” Phys. Rev. Lett. 62, 403 (1989)
- Synopsis: Better timing with aluminum ions, http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.104.070802