Astronomers affiliated with the Supernova Legacy Survey (SNLS) have discovered two of the brightest and most distant supernovae ever recorded, 10 billion light-years away and a hundred times more luminous than a normal supernova. These newly discovered supernovae are especially puzzling because the mechanism that powers most of them cannot explain their extreme luminosity.
Noble gas molecules have been detected in space for the first time in the Crab Nebula, a supernova remnant, by astronomers at Univ. College London. Led by Prof. Mike Barlow, the team used ESA's Herschel Space Observatory to observe the Crab Nebula in far infrared light. Their measurements of regions of cold gas and dust led them to the serendipitous discovery of the chemical fingerprint of argon hydride ions.
An atmospheric peculiarity the Earth shares with Jupiter, Saturn, Uranus and Neptune is likely common to billions of planets, Univ. of Washington astronomers have found, and knowing that may help in the search for potentially habitable worlds. The paper uses basic physics to show why this happens, and suggests that tropopauses are probably common to billions of thick-atmosphere planets and moons throughout the galaxy.
Jupiter’s moon Europa features an intricate network of cracks in its icy surface. This unusual pattern is particularly pronounced around the equator. Scientists performing modeling studies on the potential marine currents below this ice layer have discovered that, near Europa’s equator, warmer water rises from deep within the moon.
A massive impact on the moon about 4 billion years ago left a 2,500-mile crater, among the largest known craters in the solar system. Smaller subsequent impacts left craters within that crater. Comparing the spectra of light reflected from the peaks of those craters may yield clues to the composition of the moon’s lower crust and mantle—and would have implications for models of how the moon formed.
NASA's Curiosity rover has uncovered signs of an ancient freshwater lake on Mars that may have teemed with tiny organisms for tens of millions of years, far longer than scientists had imagined, new research suggests. The watering hole near the Martian equator existed about 3.5 billion years ago. Scientists say it was neither salty nor acidic, and contained nutrients—a perfect spot to support microbes.
A research team has discovered a natural particle accelerator of interstellar scale. By analyzing data from NASA’s Van Allen probes, physicists have been able to measure and identify the “smoking gun” of a planetary scale process that accelerates particles to speeds close to the speed of light within the Van Allen radiation belt.
Using the powerful eye of NASA's Hubble Space Telescope, two teams of scientists have found faint signatures of water in the atmospheres of five distant planets. The presence of atmospheric water was reported previously on a few exoplanets orbiting stars beyond our solar system, but this is the first study to conclusively measure and compare the profiles and intensities of these signatures on multiple worlds.
Quantum entanglement, a perplexing phenomenon of quantum mechanics that Albert Einstein once referred to as “spooky action at a distance,” could be even spookier than Einstein perceived. A team of physicists believe the phenomenon might be intrinsically linked with wormholes, hypothetical features of space-time that in popular science fiction can provide a much-faster-than-light shortcut from one part of the universe to another.
NASA said Monday that the Hubble Space Telescope is the best bet for figuring out whether Comet ISON disintegrated during its brush with the sun last week. A pair of solar observatories saw something emerge from around the sun following ISON's close approach on Thanksgiving Day. But scientists don't yet know whether the spot of light was merely the comet's shattered remains or what's left of its icy nucleus.
Research has shed new light on the properties of neutron stars, super dense stars that form when a large star explodes and collapses into itself. Writing in Nature, the team describes a newly discovered process that happens within the star's crust, located just below the surface. Until now, scientists thought that nuclear reactions within the crust contributed to the heating of the star's surface.
Comet ISON will be only about 1 million miles away from the sun's super-hot surface during its close encounter on Thanksgiving. On Monday, it looked like it was about to die even before it got there. On Tuesday, it appeared healthy again. Will it meet a fiery death (or survive) when it whips around the sun on Thursday? Scientists haven’t seen a comet behave this way before.
In April, a bright flash of light burst from near the constellation Leo. Originating billions of light years away, this explosion of light, called a gamma ray burst, has now been confirmed as the brightest gamma ray burst ever observed. Astronomers around the world were able to view the blast in unprecedented detail and observe several aspects of the event. The data could lead to a rewrite of standard theories on how gamma ray bursts work.
For months, all eyes in the sky have pointed at the comet that's zooming toward a blisteringly close encounter with the sun. The moment of truth comes Thursday, Thanksgiving Day. The sun-grazing Comet ISON, now thought to be less than a mile wide, will either fry and shatter, victim of the sun's incredible power, or endure and quite possibly put on one fabulous celestial show. Talk about an astronomical cliffhanger.
In our universe there are particle accelerators 40 million times more powerful than the Large Hadron Collider at CERN. Scientists don’t know what these cosmic accelerators are or where they are located, but new results being reported from IceCube, the neutrino observatory buried at the South Pole, may show the way. These new results should also erase any doubts as to IceCube’s ability to deliver on its promise.
Orbiting telescopes got the fireworks show of a lifetime last spring when they spotted what is known as a gamma ray burst in a far-off galaxy. It’s not an unusual occurrence, but this one set records. Had it been closer, Earth would have been toast. But because this blast was 3.7 billion light-years away, mankind was spared.
For nearly as long as astronomers have been able to observe asteroids, a question has gone unanswered: Why do the surfaces of most asteroids appear redder than meteorites—the remnants of asteroids that have crashed to Earth? Scientists have now found that Mars, not Earth, shakes up some near-Earth asteroids.
The first solids to form in the solar system contain unusual isotopic signatures that show a nearby supernova injected material within ~100,000 years of their formation. That supernova, caused from the cataclysmic death of a star, could have even triggered the birth of the sun.
The Hubble Space Telescope has discovered a six-tailed asteroid in the asteroid belt between the orbits of Mars and Jupiter. Scientists say they've never seen anything like it. Incredibly, the comet-like tails change shape as the asteroid sheds dust. The streams have occurred over several months.
A pioneering technology called an atom interferometer promises to detect tiny perturbations in the curvature of space-time. With its potential picometer-level sensitivity, the instrument may one day detect what so far has remained imperceptible: gravitational waves or ripples in spacetime caused when massive celestial objects move and disrupt the space around them.
A Russian rocket soared into the cosmos Thursday carrying the Sochi Olympic torch and three astronauts to the International Space Station ahead of the first-ever spacewalk for the symbol of peace. The unlit torch for the 2014 Winter Olympics in the Russian city of Sochi is to be taken on a spacewalk Saturday, then return to Earth on Monday (late Sunday EST) with three departing space station astronauts.
A rare, recently discovered microbe that survives on very little to eat has been found in two places on Earth: spacecraft clean rooms in Florida and South America. Some other microbes have been discovered in a spacecraft clean room and found nowhere else, but none previously had been found in two different clean rooms and nowhere else.
Leslie Rosenberg and his colleagues are about to go hunting. Their quarry: A theorized-but-never-seen elementary particle called an axion. The search will be conducted with a recently retooled, extremely sensitive detector that is currently in a testing and shakeout phase at the University of Washington’s Center for Experimental Nuclear Physics and Astrophysics.
Over billions of years, small black holes can slowly grow into the supermassive variety by taking on mass from their surroundings and by merging with other black holes. But this slow process can't explain the problem of supermassive black holes existing in the early universe. New findings may help to test a model that solves this problem.
Space is vast, but it may not be so lonely after all: A study finds the Milky Way is teeming with billions of planets that are about the size of Earth, orbit stars just like our sun, and are not too hot or cold for life. For the first time, NASA scientists have calculated, not estimated, what percent of stars that are just like our sun have planets similar to Earth: 22%, with a margin of error of plus or minus 8 percentage points.


Ultimate slow motion
Media Lab postdoc Andreas Velten, left, and Associate Professor Ramesh Raskar with the experimental setup they used to produce slow-motion video of light scattering through a plastic bottle. Photo: M. Scott Brauer
Massachusetts Institute of Technology (MIT) researchers have created a new imaging system that can acquire visual data at a rate of one trillion exposures per second. That's fast enough to produce a slow-motion video of a burst of light traveling the length of a 1-L bottle, bouncing off the cap and reflecting back to the bottle’s bottom.
Media Lab postdoc Andreas Velten, one of the system's developers, calls it the "ultimate" in slow motion: "There's nothing in the universe that looks fast to this camera," he says.
The system relies on a recent technology called a streak camera, deployed in a totally unexpected way. The aperture of the streak camera is a narrow slit. Particles of light—photons—enter the camera through the slit and pass through an electric field that deflects them in a direction perpendicular to the slit. Because the electric field is changing very rapidly, it deflects late-arriving photons more than it does early-arriving ones.
The image produced by the camera is thus two-dimensional, but only one of the dimensions—the one corresponding to the direction of the slit—is spatial. The other dimension, corresponding to the degree of deflection, is time. The image thus represents the time of arrival of photons passing through a 1D slice of space.
The camera was intended for use in experiments where light passes through or is emitted by a chemical sample. Since chemists are chiefly interested in the wavelengths of light that a sample absorbs, or in how the intensity of the emitted light changes over time, the fact that the camera registers only one spatial dimension is irrelevant.
But it's a serious drawback in a video camera. To produce their super-slow-mo videos, Velten, Media Lab Associate Professor Ramesh Raskar and Moungi Bawendi, the Lester Wolfe Professor of Chemistry, must perform the same experiment—such as passing a light pulse through a bottle—over and over, continually repositioning the streak camera to gradually build up a two-dimensional image. Synchronizing the camera and the laser that generates the pulse, so that the timing of every exposure is the same, requires a battery of sophisticated optical equipment and exquisite mechanical control. It takes only a nanosecond for light to scatter through a bottle, but it takes about an hour to collect all the data necessary for the final video. For that reason, Raskar calls the new system “the world’s slowest fastest camera.”
Doing the math
After an hour, the researchers accumulate hundreds of thousands of data sets, each of which plots the 1D positions of photons against their times of arrival. Raskar, Velten, and other members of Raskar’s Camera Culture group at the Media Lab developed algorithms that can stitch that raw data into a set of sequential 2D images.
The streak camera and the laser that generates the light pulses—both cutting-edge devices with a cumulative price tag of $250,000—were provided by Bawendi, a pioneer in research on quantum dots: tiny, light-emitting clusters of semiconductor particles that have potential applications in quantum computing, video-display technology, biological imaging, solar cells, and a host of other areas.
The trillion-frame-per-second imaging system, which the researchers have presented both at the Optical Society's Computational Optical Sensing and Imaging conference and at Siggraph, is a spinoff of another Camera Culture project, a camera that can see around corners. That camera works by bouncing light off a reflective surface—say, the wall opposite a doorway—and measuring the time it takes different photons to return. But while both systems use ultrashort bursts of laser light and streak cameras, the arrangement of their other optical components and their reconstruction algorithms are tailored to their disparate tasks.
Because the ultrafast-imaging system requires multiple passes to produce its videos, it can't record events that aren't exactly repeatable. Any practical applications will probably involve cases where the way in which light scatters—or bounces around as it strikes different surfaces—is itself a source of useful information. Those cases may, however, include analyses of the physical structure of both manufactured materials and biological tissues—"like ultrasound with light," as Raskar puts it.
As a longtime camera researcher, Raskar also sees a potential application in the development of better camera flashes. "An ultimate dream is, how do you create studio-like lighting from a compact flash? How can I take a portable camera that has a tiny flash and create the illusion that I have all these umbrellas, and sport lights, and so on?" asks Raskar, the NEC Career Development Associate Professor of Media Arts and Sciences. "With our ultrafast imaging, we can actually analyze how the photons are traveling through the world. And then we can recreate a new photo by creating the illusion that the photons started somewhere else."
"It's very interesting work. I am very impressed," says Nils Abramson, a professor of applied holography at Sweden's Royal Institute of Technology. In the late 1970s, Abramson pioneered a technique called light-in-flight holography, which ultimately proved able to capture images of light waves at a rate of 100 billion frames per second.
But as Abramson points out, his technique requires so-called coherent light, meaning that the troughs and crests of the light waves that produce the image have to line up with each other. "If you happen to destroy the coherence when the light is passing through different objects, then it doesn’t work," Abramson says. "So I think it's much better if you can use ordinary light, which Ramesh does."
Indeed, Velten says, "As photons bounce around in the scene or inside objects, they lose coherence. Only an incoherent detection method like ours can see those photons." And those photons, Velten says, could let researchers "learn more about the material properties of the objects, about what is under their surface and about the layout of the scene. Because we can see those photons, we could use them to look inside objects—for example, for medical imaging, or to identify materials."
"I'm surprised that the method I've been using has not been more popular," Abramson adds. "I've felt rather alone. I'm very glad that someone else is doing something similar. Because I think there are many interesting things to find when you can do this sort of study of the light itself."SOURCE


Quantum dice debut
Technology Research News
Researchers have overcome a major obstacle
to generating random numbers on quantum computers by limiting the possibilities
in the otherwise unlimited randomness of a set of quantum particles.
Random numbers play a key role in classical computing by providing
an element of chance in games and simulations, a reliable method for encrypting
messages, and a means of accurately sampling huge amounts of data.
Researchers from the Massachusetts Institute of Technology and
the National Atomic Energy Commission in Argentina have shown that short
sequences of random operations -- randomly shifting laser pulses or magnetic
fields -- acting on a string of quantum bits can, in effect, generate
random configurations of qubits.
Being able to generate random numbers in quantum computing could
make quantum computers easier to build by countering the noise that eventually
destroys qubits, which represent the 1s and 0s of computer information.
Quantum computers promise to be fantastically fast at solving certain
types of large problems, including the mathematics that underpins today's
Quantum random numbers could also be useful for increasing the
efficiency of quantum secret-sharing schemes, quantum encryption and various
forms of quantum communications.
Qubits can represent not only 1 and 0 but any number in between;
a string of 100 qubits can represent every possible 100-digit binary number,
and a single set of operations can search every possible answer to a problem
at once. This gives quantum computers their power, but also poses a problem
for generating random numbers. The nearly infinite number of possible
qubit configurations theoretically requires an impossibly large number
In the quantum world, no outcome is certain, and in most aspects
of quantum computing, the goal is to reduce the uncertainty in order to
get a definite answer to a problem. The researchers' scheme, however,
aims for uncertainty. It limits the possible outcomes without making them
The scheme generates quantum states in such a way that the probabilities
of the limited set of outcomes are as evenly distributed over the nearly
infinite range of possible outcomes as quantum theory allows, said Joseph
Emerson, one of the MIT researchers who is now a fellow at the Perimeter
Institute for Theoretical Physics in Canada. "These pseudo-random transformations
are a practical substitute for truly... random transformations," he said.
The number of operations required to represent a truly random
configuration increases exponentially with the number of qubits in the
configuration. For example, if the quantum equivalent of generating random
numbers takes 22, or four, operations for two qubits, 15 qubits would
require 215, or 32,768, operations.
The researchers' pseudo-random number method could be used to
help build quantum computers by providing a practical way to estimate
imperfections or errors in quantum processors, said Emerson. "This is
addressing a very big problem -- imperfections such as decoherence and
inadequate control of the coherence between the qubits are the main limiting
factors in the creation of large-scale quantum computers," he said.
A quantum particle decoheres, or is knocked out of its quantum
state, when it interacts with energy from the environment in the form
of light, heat, electricity or magnetism. Researchers are looking for
ways to fend off decoherence for as long as possible in order to make
qubits last long enough to be useful.
A way to estimate decoherence would allow researchers to assess
the strength and type of environmental noise limiting the precision of
a given quantum device, said Emerson. Random quantum operations can be
used as control operations that, when subjected to the noise affecting
a prototype quantum computer, will generate a response that depends only
on the noise, he said. This way the noise can be characterized with many
fewer measurements than existing methods, which are dependent on the interactions
of the qubits and so require a number of measurements that increases exponentially
with the number of qubits, he said.
In addition to helping build quantum computers, random operators
would be useful for quantum communications tasks like encryption, said
Emerson. "The idea is to randomize a specific configuration of qubits
containing the message, and then transmit this randomized state," he said.
In this case, if each bit that makes up the message is encrypted,
or changed randomly, it is not possible for an eavesdropper to find any
type of pattern that may lead to cracking the message.
The researchers tested the method on a three-qubit prototype liquid
nuclear magnetic resonance (NMR) quantum computer. The computer consists
of a liquid sample containing the amino acid alanine, which is a molecule
made of three carbon-13 atoms. The qubits are the atoms' spins, which
are analogous to a top spinning clockwise or counterclockwise. The two
directions, spin up and spin down, can be used to represent 1 and 0. The
qubits are controlled by magnetic fields generated by the nuclear magnetic
Being able to diagnose faulty quantum computer components in a
way that is independent of the number of qubits is very important, said
Daniel Lidar, an assistant professor of theoretical chemical physics at
the University of Toronto. "For this reason alone I suspect random [operators]
will find widespread applications as quantum computer benchmarking becomes
an experimental reality," he said.
It is also likely that future quantum algorithms will make increasing
use of pseudo-random operators, said Lidar.
The researchers are working on making the random-number-generation
system more precise, said Emerson. "Right now one can only estimate very
coarse properties of the noise, such as [its] overall strength," he said.
"I would like to devise methods to get a much more detailed analysis of
the noise operators."
Complete noise-estimation experiments could be implemented in
rudimentary quantum computers within the next few years, said Emerson.
Researchers generally agree that practical quantum computers are a decade
or two away.
Emerson's research colleagues were Yaakov S. Weinstein, Marcos
Saraceno, Seth Lloyd, and David G. Corey. The work appeared in the December
19, 2003 issue of Science. The research was funded by the National
Science Foundation (NSF), the Defense Advanced Research Projects Agency
(DARPA) and the Cambridge-MIT Institute.
Timeline: 2 years, 10-20 years
Funding: Government; University
TRN Categories: Quantum Computing and Communications; Physics
Story Type: News
Related Elements: Technical paper, "Pseudo-Random Unitary
Operators for Quantum Information Processing," Science, December 19, 2003
January 14/21, 2004
Quantum dice debut
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itself on the go
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make nano channels
Wet biochip preserves
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Recent developments bring quantum computers closer to implementation
8 January 2011
Richard Feynman first seriously posed the question of designing computers based on quantum mechanics in a paper published in 1982. The most recent research into this field comes from a team from the Delft University of Technology and Eindhoven University of Technology, both in the Netherlands. In a paper recently published in the scientific journal Nature, a new technique to manipulate the fundamental building blocks of quantum computers was examined.
Inspired by basic questions about the nature of light, quantum mechanics is the study of the most fundamental particles of matter. The most advanced quantum computing application currently imagined involves utilizing the inherent link that two particles, such as electrons, can form on the most elementary level to perform specified calculations.
Current computers are based on a binary digit, called a bit. The information stored is held in two distinct states, generally referred to as 0 and 1. The basic unit of a quantum computer is called a qubit. The value of a qubit is generally based in the inherent rotation of an electron, which is either negative or positive. Unlike a classical bit, which is always one value or the other, a qubit initially has both of these values. Only when acted upon will the qubit take on a single value, and it will do so following the probabilistic laws governing quantum mechanics.
A bit has a distinct disadvantage compared to a qubit. While 1000 bits could deliver about 1000 pieces of information at a time, 1000 qubits could deliver approximately 2^1000 (or 10^300) pieces of information simultaneously. This number is so large, that it is incomprehensibly larger than the number of grains of rice it would take to fill up the Solar System.
While exponentially more powerful than classical computers, quantum computers have also proven to be exponentially more difficult to build. Quantum computers revolve around the manipulation of individual quantum particles. While dealing with 1000 bits is easy for modern-day technology, working with 1000 qubits it incredibly hard. The quantum mechanical nature of qubits can cause unwanted interaction with their physical surroundings, destabilizing the entire system. Imagine a line of dominoes falling one after the other. This issue has been the reason that quantum computers have yet to exceed their classical counterparts.
Physics simulations were the original goal for quantum computers, and the impetus for Richard Feynman to write his 1982 paper. Feynman wanted to look at the possibility of a computer being able to fully simulate physical events, not just approximate them. Quantum mechanical systems were the particular focus. Unlike the random-event generators found in classical computers, the probabilistic nature of qubit states lets a quantum system be truly represented. This lets large systems of quantum particles be studied, which is utterly beyond the capabilities of classical computing.
Success at building a quantum computer would also be the most stringent test of quantum mechanics ever devised. If quantum computers can be built to outstrip classical computers, it would be the most powerful vindication of quantum theory yet. On the flip side, a demonstration of a fundamental reason that quantum computers cannot be built would require a serious re-thinking of much of physics.
A consequence of this technology would be immediately felt in the field of electronic security. Most secure communications and information storage revolve around a technique called RSA encryption. The process involves multiplying two prime numbers, such as 5 and 3, and using the product, 15, to encode data. The power of this approach is based on multiplying prime numbers so large, that the product is hundreds of digits long. Classical computers simply cannot factor such a large number in any reasonable timescale. The original information, encrypted based on the two original numbers, is thus safeguarded.
In contrast, quantum computers would be able to take advantage of a procedure known as Shor's algorithm. The essence of the formula is that, using quantum computers, even extremely large numbers could be factored in a matter of moments. This would give the user of a quantum computer the ability to break into bank accounts, private email, and decipher computer passwords at a whim.
The specific advances of the new research involve the direct manipulation of electrons through electric fields. Previous experiments used magnetic fields, which do not have the precision necessary to form large numbers of qubits into a functioning system. The precision granted by using electric fields shows potential in keeping large amounts of qubits coherent long enough to perform calculations.
What should be noted is that quantum computers will not solve all problems posed in computer science. If they ever reach fruition, the highest use will be simulating quantum physics. They will not be adept at proving mathematical theorems nor will they discover new physics. Those would still be the province of human beings.
A major drawback of quantum computers is the issue of usage. Much of the research done on the subject is funded by private institutions and nation states. Any private institution with a quantum computer would be able to break down any barriers encountered in breaking into a competitor's system in seconds, giving an unparalleled edge in development. Even more disturbing, a government with a quantum computer could access secrets held by other nations with ease. Its apparatus for electronic spying, both foreign and domestic, would be without rival.
Quantum computing is an exercise in contradictions. The technical difficulties make it difficult to achieve, and the social and political consequences give pause over whether and how fast to move forward with this effort. On the other hand, humanity's knowledge of physics itself is in many ways bound up in showing whether such tools are possible. We owe it to ourselves to find out.
 R. P. Feynman. Simulating Physics with Computers.
 S. Nadj-Perge, S.M. Frolov, E.P.A.M. Bakkers, L.P. Kouwenhoven. “Spin-orbit qubit in a semiconductor nanowire.”


By Jason Palmer
Science and technology reporter, BBC News
The "quantum resonator" can be seen with the naked eye
Researchers have created a "quantum state" in the largest object yet.
Such states, in which an object is effectively in two places at once, have until now only been accomplished with single particles, atoms and molecules.
In this experiment, published in the journal Nature, scientists produced a quantum state in an object billions of times larger than previous tests.
The team says the result could have significant implications in quantum computing.
One of the pillars of quantum mechanics is the idea that objects absorb and emit energy in tiny discrete packets known as quanta.
This can be seen in a piece of coloured glass, which absorbs a certain colour of light.
That light is made up of photons - packets of light energy - and the glass atoms absorb only photons with the quanta (or amount) of energy that corresponds to that colour.
What we see through the glass is the light that has not been absorbed.
At the atomic level, quantum mechanics predicts - and experiments demonstrate - a number of surprising effects beyond that, however.
If all the energy that an atom gets from the jostling atoms in its environment is removed by cooling it to phenomenally low temperatures, it can reach its "quantum ground state" - no more energy can be removed.
If just one quantum of energy is then carefully put back in a certain way, the atom can be said to be in two states at the same time: a superposition of states.
Although only one quantum of energy is put in, any measurements will show either zero or one quanta; strictly, the atom has both.
Down to ground
These superpositions of states have long been predicted to be useful for a pursuit known as quantum computing; if used in place of the zeroes and ones of digital computing, a quantum computer would be vastly more powerful.
Similar approaches could lead to the quantum ground state of a virus
However, creating these states in anything bigger than single atoms and molecules has proven difficult, because the larger an object is, the more tricky it becomes to isolate it from its environment and put it in its ground state.
"There is this question of where the dividing line is between the quantum world and the classical world we know," said Andrew Cleland of the University of California, Santa Barbara.
"We know perfectly well that things are not in two places at the same time in our everyday experience, but this fundamental theory of physics says that they can be," he told BBC News.
Now, Professor Cleland and his team have moved that dividing line, using an object just big enough to be seen with the naked eye.
They used a tiny piece of what is known as a piezoelectric material, which expands and contracts when an electrical current is run through it.
A current applied at a certain frequency causes it to expand and contract regularly and, just like a violin string, the material has a frequency at which it is inclined to vibrate.
They connected this resonator to an electric circuit that the team has been developing for three years. This can be tuned to put in just one quantum of electrical energy.
They cooled the whole apparatus down to a thousandth of a degree above absolute zero and confirmed that their resonator was in its quantum ground state.
The researchers designed the system so that they could "pump in" just one quantum of electrical energy at a time and see the oscillator begin to vibrate as it converted that quantum into one quantum of vibrational energy.
As it vibrated, the team showed that the resonator was in one of the slippery superpositions of states, with both one and zero quanta of energy.
Sensors and sensibility
The result is a huge push toward answering the question of whether quantum mechanical effects simply disappear in objects beyond a certain size.
"As far as mechanical objects are concerned, the dividing line was at around 60 atoms," Professor Cleland said.
"With this experiment, we've shown that the dividing line can be pushed up all the way to about a trillion atoms."
The ability to create these superpositions of states and to read them out using the same circuit that created them would make for a quantum-based memory storage system - the heart of a potential quantum computer.
Previously, the largest quantum state was achieved in a buckyball
Markus Aspelmeyer of the University of Vienna believes that the mechanical oscillator approach will, in time, prove its worth in the business of quantum computing.
"What they've shown here is a mechanical oscillator as a completely new quantum system, and I personally think it's a really important one," he told BBC News.
"It means that you can now utilise mechanical resonators in quantum experiments and that opens a completely new perspective, in particular for quantum information science."
Although these tiny resonators could be made in huge arrays using techniques that are standard in the computer industry, Professor Cleland says that using different systems based on photons instead of vibrations would most likely perform better in any eventual computers.
But, he said, the devices might be used in reverse, to detect the tiniest of vibrations that are created when light interacts with matter or when chemical reactions take place.
In either case, these devices have added to the debate about quantum mechanics and whether its surprising and, as Albert Einstein famously put it, "spooky" effects play a role in the everyday objects around us.
"I don't think there is a limit, that there will be a certain size where quantum mechanics starts to break down," Dr Aspelmeyer said.
"The larger we go, it becomes increasingly difficult and we will bump into more and more practical limitations. So the only reason that things could break down is that we run out of money."


How close are we to the quantum computational revolution? Quantum computers promise drastic speedups for tackling the most complex mathematical problems. Nonetheless, current precursors of quantum computers cannot be scaled efficiently to reasonably sized systems. Now, researchers have realized a new setup that can be scaled more easily than ever before.
The heart of the quantum computer. This is where the ions are physically stored and processed, surrounded by lasers, electronics and vacuum systems. Tiny trap segments located at the end of this bar confine and control the ions. Quantum information processing and cooling are done by shining laser beams onto the ions. Credit: J. Jost/NIST.
Imagine an engineer having to work with materials that are constantly changing: iron morphing into wax, wood draining off as water, or cement disintegrating into ashes. Luckily, in classical physics this is a not very common problem — making life relatively easy for classical engineers. In quantum physics, however, things are different: even the most slightly uncontrolled interaction can potentially turn quantum objects into classical ones. As a consequence, it is extremely difficult to build large setups that utilize the quantum nature of matter, such as scalable quantum computers. Now, researchers led by David Wineland at the National Institute of Standards and Technology (NIST) in Boulder (Colorado, USA) have been able to realize a scalable setup for quantum computation.
Classical computers have increased their computational power enormously over the last decades — so why are scientists interested in the possibility of quantum computers? On the one hand, advances in microelectronics have depended largely on continued miniaturization, and engineers are now starting to reach the fundamental quantum-physical limit that will make it impossible to further miniaturize classical technology. On the other hand, classical computers are intrinsically sequential: they execute a list of instructions one after the other. Their limits become evident with certain tasks that do not naturally conform to a sequential solution, such as factorizing prime numbers, sorting long lists, or simulating complex systems. Today's high-power computers, therefore, use multiple processors which share the workload like mechanics building different parts of an apparatus. Even this parallel approach, however, relies on a substantially sequential approach which can only cope with a few small subsystems at any one given time.
Quantum computation schematic. (1) Qubits are prepared or read-out individually, in spatially different zones. (2) Two qubits are brought together in order to perform a two-qubit operation. (3,4) Qubits can be transported to and from other trap segments, allowing for the experimental realization of complex quantum algorithms involving several interacting qubits. Credit: NIST.
Quantum computers would be able to perform intrinsically parallel, collective algorithms. All the parts of the quantum system can be directly connected and made to simultaneously respond, thereby potentially solving complex problems a lot faster. Being so deeply connected, however, is extremely delicate, since it also implies that any uncontrolled interactions may break the quantum parallelism needed for quantum computation. Of course, if a quantum particle loses its quantumness — a process called decoherence — it does not usually disappear, it simply turns itself — and possibly even part of the system it is connected to — into a classical object that can no longer be used for quantum computation.
Today, most setups for quantum computation use about 5-10 qubits (quantum bits). This is not yet enough to outperform classical computers. For ground-breaking results, far more qubits — between 50 to several 1000 — are expected to be necessary. Therefore, it is important to find ways to scale up a quantum computing device to a large number of qubits. Scalability here refers to how easily the setup can be implemented for a larger number of qubits. At present, miniaturization — scaling the size — is not yet a major concern since current error rates are still too high for performing large quantum computations reliably, anyway.
Quantum algorithms can be implemented by operations of at most two qubits at a time. Therefore, given enough qubits and small error rates, sequential treatment of one, or at most two qubits is enough to implement intrinsically parallel quantum algorithms — nature itself will take care of the rest.
The most complex physical, mathematical and engineering problems could thus be tackled in a completely new way, possibly revolutionizing science and technology. One consequence, for example, would be that we would no longer be able to trust current cryptographic protocols used for credit cards and internet security. At the same time, much safer technologies would be implemented exploiting related quantum information technologies, such as quantum key distribution.
There are currently many different approaches to quantum computation. Physically, qubits can be realized using, for example, neutral atoms, ions or even superconducting materials. The NIST setup, in particular, uses an array of radio-frequency traps, each able to cope with a small number of ions. The setup was divided into regions for storing qubits, regions for performing quantum operations and regions for transporting the qubits. The big problem with this approach is heating up of ions during transport because hot ions are likely to emit photons, thereby altering their internal state and thus the qubit.
NIST researchers have found a way to inhibit the adverse effects of heating during transport, thereby securing the scalability of their experiment. "Our trick was to use two types of ions in our experiments," Jonathan Home explains, "one for carrying the quantum information and one as a cooling agent." Home performed the NIST experiment and points out how important the controlled interplay between the ions is. "Beryllium ions have a favorable atomic level structure for storing our quantum information which renders them essentially insensitive to remaining external magnetic fields," Home continues, "and Magnesium can be cooled efficiently without disturbing the Beryllium ions." Beryllium-Magnesium couples were used for their experiments. During transport the ions heated up, once at the target location, however, they could be cooled down to the low temperatures necessary for performing quantum operations using dedicated lasers. Achieving this with single quantum bits, as well as with pairs, constitutes the proof that all the necessary operations for a quantum computer could be achieved using this same, scalable setup.
"Today, quantum computers are probably at the stage at which conventional computers were in the first half of the 20th century," says Renato Renner, head of the Quantum Information Theory group at the Swiss Federal Institute of Technology in Zurich (ETH). Ion trap technology, according to Renner, is a very promising way for studying quantum computers, even though he expects further technological and scientific breakthroughs — similar to a transistor replacing tubes for classical computation — to be necessary before real quantum computers will be built. "Nonetheless," Renner insists, "being able to perform all the relevant steps, including transport, in the same scalable experiment is a great achievement." "The usefulness of current setups, as both Home and Renner agree, is in exploring quantum," Renner adds, "even quantum simulators, the precursors of general purpose quantum computers, might soon be useful for studying open problems in quantum physics, for example." "Quantum information," Home concludes, "has been a very fast-paced topic over the last couple of years and it is simply extremely fascinating to see how we advance in our concepts in mathematics, our understanding of physics, and our possibilities in engineering. It is truly exciting to see how all of this evolves!"
AN is currently working on his PhD on disordered ultracold quantum systems at ICFO - The Institute of Photonic Sciences in Barcelona (Spain).
Jonathan P. Home, David Hanneke, John D. Jost, Jason M. Amini, Dietrich Leibfried & David J. Wineland, Complete Methods Set for Scalable Ion Trap Quantum Information Processing, Science (2009) 325, 1227-1230 (link).
How to compute with qubits. (Video)
Animation of the NIST experiment on sustained quantum information processing. Credit: Jonathan Home/NIST.


Physicists at the National Institute of Standards and Technology have designed and built a novel electromagnetic trap for ions that could be easily mass produced to potentially make quantum computers large enough for practical use. The new trap, described in the June 30 issue of Physical Review Letters, may help scientists surmount what is currently the most significant barrier to building a working quantum computer—scaling up components and processes that have been successfully demonstrated individually.
Quantum computers would exploit the unusual behavior of the smallest particles of matter and light. Their theoretical ability to perform vast numbers of operations simultaneously has the potential to solve certain problems, such as breaking data encryption codes or searching large databases, far faster than conventional computers.
Ions (electrically charged atoms) are promising candidates for use as quantum bits (qubits) in quantum computers. The NIST team, one of 18 research groups worldwide experimenting with ion qubits, previously has demonstrated at a rudimentary level all the basic building blocks for a quantum computer, including key processes such as error correction, and also has proposed a large-scale architecture.
The new NIST trap is the first functional ion trap in which all electrodes are arranged in one horizontal layer, a “chip-like” geometry that is much easier to manufacture than previous ion traps with two or three layers of electrodes. The new trap, which has gold electrodes that confine ions about 40 micrometers above the electrodes, was constructed using standard microfabrication techniques.
NIST scientists report that their single-layer device can trap a dozen magnesium ions without generating too much heat from electrode voltage fluctuations—also an important factor, because heating has limited the prospects for previous small traps. Microscale traps are desirable because the smaller the trap, the faster the future computer. Work is continuing at NIST and at collaborating industrial and federal labs to build single-layer traps with more complex structures in which perhaps 10 to 15 ions eventually could be manipulated with lasers to carry out logic operations.
Quantum Information Research at NIST: Goals and Vision
America’s future prosperity and security may rely in part on the exotic properties of some of the smallest articles in nature. Research on quantum information (QI) seeks to control and exploit these properties for scientific and societal benefits. This remarkable field combines physics, information science, and mathematics in an effort to design nanotechnologies that may accomplish feats considered impossible with today’s technology. QI researchers are already generating “unbreakable” codes for ultra-secure encryption. They may someday build quantum computers that can solve problems in seconds that today’s best supercomputers could not solve in years. QI has the potential to expand and strengthen the U.S. economy and security in the 21st century just as transistors and lasers did in the 20th century.
Nations around the world are investing heavily in QI research in recognition of the economic and security implications. A significant part of the U.S. effort is based at the National Institute of Standards and Technology (NIST), which has the largest internal QI research program of any federal agency.
NIST laboratories routinely develop the measurement and standards infrastructure needed to promote innovation in emerging fields that may transform the future. Few fields need this support as much as QI, which involves entirely new concepts of information processing as well as complex hardware for precision control of individual atoms, very small quantities of light, and electrical currents 1 billion times weaker than those in light bulbs. As the nation’s measurement experts, NIST researchers long have had world-class capabilities in precision measurement and control of atoms, light, and other quantum systems. NIST, therefore, has the world-class skills and facilities needed to advance QI through technology demonstrations, development of new methods and tests for evaluating QI system components, and related scientific discoveries.
NIST first became involved in quantum information science in the early 1990s when physicist David Wineland and colleagues realized that engineering of exotic quantum states could lead to a significantly more precise atomic clock. A few years later, Wineland demonstrated the first quantum logic operation, a pioneering step toward a future quantum computer using ions (electrically charged atoms) to process information. In 1999, the NIST Physics Laboratory launched a broader Quantum Information Program, joined shortly thereafter by NIST’s Information Technology Laboratory and Electronics and Electrical Engineering Laboratory.
This interdisciplinary program, featuring strong collaborations among physicists, electrical engineers, mathematicians, and computer scientists, has established NIST as one of the premier QI programs in the world. Participants include Wineland, a NIST Fellow and Presidential Rank Award winner; physicist William D. Phillips, a 1997 Nobel Prize winner in physics; mathematician Emanuel Knill, a leading QI theorist; and physicist Sae Woo Nam, winner of a Presidential Early Career Award for Scientists and Engineers. A total of nine technical divisions within three different laboratories at NIST’s Gaithersburg and Boulder campuses are involved.
NIST’s work in ion-trap quantum computing is widely recognized as one of the most advanced QI efforts in the world. Scientists building the NIST quantum communications testbed set a record in 2004 for the fastest system for distributing quantum cryptographic “keys,” codes for encrypting messages that, due to the peculiarities of quantum physics, cannot be intercepted without detection. Other NIST research with single photon sources and detectors, and computing with neutral atoms and “artificial atoms,” are also among the leading efforts worldwide. For instance, prospects for practical quantum communications have been improved by NIST’s recent demonstration of a device that detects single photons with 88 percent efficiency, a QI record.
There is strong synergy between NIST’s core mission work on measurement and standards and the QI research program. For instance, NIST scientists gained much of their expertise in quantum systems from decades of work developing atomic clocks. NIST’s ultra-precise atomic fountain clock—the world’s most accurate device for measuring time—is based on the precise manipulation and measurement of two quantum energy levels in the cesium atom. This clock would neither gain nor lose one second in 60 million years (as of March 2005), an accuracy level that is continually being improved. NIST quantum computing research is producing new techniques that may lead to even more accurate atomic clocks in the future.
Ultimately, NIST measurements, tests, and technologies for quantum information science are helping U.S. industry develop new information technologies in an effort to ensure U.S. technological leadership and strengthen national security. The United States may have the lead in this field for now—based in part on NIST’s contributions—but competition from Europe, Japan, Australia, and developing countries such as China is strong and growing.
Citation: S. Seidelin, J. Chiaverini, R. Reichle, J.J. Bollinger, D. Leibfried, J. Britton, J.H. Wesenberg, R.B. Blakestad, R.J. Epstein, D.B. Hume, W.M. Itano, J.D. Jost, C. Langer, R. Ozeri, N. Shiga, and D.J. Wineland. 2006. A microfabricated surface-electrode ion trap for scalable quantum information processing. Physical Review Letters. June 30
Explore further: How the physics of champagne bubbles may help address the world's future energy needs


scheme lightens load
Technology Research News
Two years ago, scientists proved it possible
to build a quantum computer from simple optical equipment commonly found
in university classrooms and laboratories. Now researchers at Johns Hopkins
University have refined the approach, reducing the amount of equipment
linear optical quantum computers would need by about two orders of magnitude.
Quantum computers use the weird nature of particles like atoms, electrons
and photons to perform many computations in parallel. If a big enough
quantum computer could be built, it would far outstrip classical computers
for solving certain problems like cracking secret codes. So far, however,
only the most rudimentary quantum prototypes have been constructed.
The Johns Hopkins plan shows that equipment like mirrors, half mirrors
and phase shifters could be used to make practical, photon-based quantum
computers, said James Franson, principal staff at the Johns Hopkins University
Applied Physics Laboratory and a research professor the university's electrical
and computer engineering department. "Our approach may make it more feasible
to develop a full-scale quantum computer," he said.
Controlling single photons using linear optics equipment is simpler than
manipulating individual or small numbers of atoms or electrons, which
are the basic units of most other quantum computing schemes.
Capturing and manipulating atoms and electrons involves precisely tuned
lasers or magnetic fields, or carefully constructed microscopic devices.
It's also much harder to transport isolated atoms and electrons than it
is to move photons. "An optical approach to quantum computing would have
a number of potential advantages, including the ability to connect different
devices using optical fibers in analogy with the wires of a conventional
computer," said Franson.
Linear optical quantum computers, like ordinary electronic computers,
would use circuits that link simple logic devices in intricate patterns
that make the output from one device the input to the next. The 1s and
0s of linear optical quantum computing would be represented by properties
of photons like horizontal versus vertical polarization rather than the
presence or absence of a current of electrons.
The potential power of any type of quantum computer comes from its ability
to examine all possible solutions to a problem at once rather than having
to check one at a time.
This is possible because when a particle like a photon is isolated from
its environment it is in the weird quantum state of superposition, meaning
it can be horizontally and vertically polarized at once, and so can represent
a mix of 1 and 0. This allows a string of photons in superposition to
represent every combination of 1s and 0s at the same time so that a quantum
computer could process all the numbers that represent possible solutions
to a problem using one set of operations on the single string of photons.
Linear optical devices perform quantum logic operations by altering photons
according to probabilities. Half mirrors, or beam splitters, for example,
can direct photons along one of two paths, with an even chance for each
The challenge of linear optical quantum computing is to pass the correct
result of a quantum logic operation from one device to the next without
directly observing the states of the photons that represent the results,
because this would change the states and therefore destroy the information
the photons contain.
The trick is to put additional photons through the logic operation at
the same time. These additional, ancilla photons trigger the optical circuitry
that passes along the output of the logic operation when the result of
the operation is correct. The ancilla photons are absorbed in photon detectors
in the circuitry, but the output photons are preserved and passed on.
The key advance in the Johns Hopkins researchers' approach is that it
uses fewer ancilla photons by entangling input and ancilla photons in
a way that minimizes the probability of errors, said Franson. When two
or more particles in superposition come into contact with each other,
they can become entangled, meaning one or more of their properties change
in lockstep even if the particles are separated.
Fewer ancilla photons means fewer pieces of equipment are needed. "Using
the current error correction techniques, our high-fidelity approach should
reduce the [equipment] required by roughly two orders of magnitude," said
Franson. The amount of equipment required to generate the entangled ancilla
state and the probability of an error "both increase rapidly with increasing
numbers of ancilla photons," he said.
The original linear optical quantum computing scheme had an average error
rate of 2/n, while the researchers' refined scheme has an average error
rate of 4/n2, according to Franson. N represents the number of ancilla
photons. This translates to error rates of 20 percent versus 4 percent
for 10 ancilla photons, and 2 percent versus 0.04 percent for 100 ancilla
This gives the Johns Hopkins scheme a practical error rate with far fewer
ancilla photons, said Franson. Quantum error correction will require error
rates on the order of 0.1 to 0.01 percent, he said. "That range of errors
could be achieved with 100 ancilla in our case, but that would require
5,000 ancilla in the original... method."
Because the scheme requires fewer mirrors and beam splitters to manipulate
the smaller number of ancilla photons, it makes it more likely that a
practical linear optical quantum computer could be built, said Jonathan
Dowling, supervisor of the quantum computing technologies group at NASA's
Jet Propulsion Laboratory. The researchers' method "seems to be a substantial
improvement over the original scheme," he said.
Devices enabled by this new approach will be used in quantum communications
systems before they are used in full-blown quantum computers, said Dowling.
With experience gained from making quantum communications devices, the
researchers' approach will eventually lead to "a practical, compact, all-optical
quantum computer," he said.
Dowling's group has developed a plan for a quantum repeater, a device
necessary to boost quantum communications over long distances, that is
based in part on the researchers' linear optical quantum logic, said Dowling.
The researchers have shown that the overhead needed to achieve a given
fidelity for linear optical quantum logic gates can be significantly improved,
said Emanuel Knill, a mathematician at Los Alamos National Laboratory
and one of the scientists who developed the concept of linear optical
The Johns Hopkins researchers' approach does not address logical qubits,
however, said Knill. Logical qubits are encoded from two or more physical
qubits, and this makes them more resistant to errors. "My preference is
to use logical qubits," said Knill. "If one wishes to use physical, not
logical, qubits, then the authors' approach would help significantly,"
Quantum repeaters could be developed in five years, said Franson. "Full-scale
quantum computers would be much more difficult and would probably require
15 to 20 years in the most optimistic scenario," he said.
The researchers are working on making photon-based logic gates and memory
devices, and single-photon sources, said Franson. "These are the basic
building blocks of a linear optics approach to quantum computing," he
Franson's research colleagues were Michelle Donegan, Michael Fitch, Bryan
Jacobs, and Todd Pittman. They published the research in the September
23, 2002 issue of the journal Physical Review Letters. The research was
funded by the Office of Naval Research (ONR), the Army Research Office
(ARO), the National Security Agency (NSA) and the Department of Defense
(DOD) Independent Research and Development Program (IR&D).
Timeline: 5 years, 15-20 years
TRN Categories: Physics Quantum Computing and Communications
Story Type: News
Related Elements: Technical paper, "High-Fidelity Quantum
Logic Operations Using Linear Optical Elements," Physical Review Letters,
September 23, 2002
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Quantum cryptography is often touted as the ultimate in information security, but that doesn't make it immune to successful attack. A recent publication in IEEE Transactions on Information Theory details how the very process of ensuring security can be used by evildoers to send fake messages on a network. As with all good cryptography researchers, the publication also includes a method for defeating the attack.
The security provided by a quantum system relies on the fundamental laws of nature rather than the inability of computers to factor large numbers efficiently. The sender, traditionally called Alice, encodes information in the quantum states of, for instance, light. The recipient, imaginatively referred to as Bob, measures the quantum state. That measurement depends on what is called the basis and, if Bob and Alice don't have the same basis, Bob will not receive the same information that Alice sent. This feature is used to generate a secret key that can then be used to send information over more public channels.
Generating a key
The key generation process looks like this. Alice takes a random string of ones and zeros and encodes them in the quantum states of light. In doing so, she doesn't use the same basis, but rather flips randomly between two different basis sets. Bob also flips his basis sets and records the bit values that he receives. He then transmits his basis flips to Alice and she sends her basis flips to Bob. Those cases where, at random, the two agree on the value received, the bit values encoded by Alice are used as the key. An eavesdropper (who, amazingly enough, is always called Eve) can obtain all the publicly sent information and still not obtain the secret key. If she attempts to measure the quantum bits, they will be modified, meaning that Alice and Bob will see errors in the bits where their bases were not the same.
One vulnerability of this system is the man-in-the-middle attack, where Eve plays the role of Alice for Bob and Bob for Alice. Every security system fails at this point because sometimes you have to trust that Alice really is Alice. One way to try and ensure the security of the exchange is to begin communications using a small, shared key. This key is then expanded using the quantum cryptographic system. Part of the expanded key is set aside so it can act as the shared key that initiates the next session. The remainder is used to encode messages sent in the current session. Assuming Eve has no knowledge of the starting key, the system is secure.
But what if Eve knows some of the key already? Well, then problems can arise. Eve can grab the full key provided certain conditions are met: first, she has to be able to capture the quantum and classical information sent by Alice before Bob sees it. Second, she has to be able to modify the information in the quantum channel—a modification that may not necessarily be detectable, since it does not require measuring the quantum state—though I am not certain that this is truly practical. If these conditions are met, then Eve may be able to obtain the key for this session and, by extension, all future sessions.
Probabilities and coincidences
The explanation for how this works is a little technical but it involves probabilities. The key is generated from coincidences in two sets of random numbers, meaning that any number within a bit range is equally probable. However, if Eve has part of the key, it can be used to break up the distribution of possible numbers, making some of them much more probable while completely eliminating others.
Eve can then modify the information in the quantum channel to make just a few numbers within the distribution much more probable. Since Eve has not measured the information in the quantum channel, and the information in the classical channel is public, Alice and Bob remain unaware of Eve. At this point, Eve can simply try out the few remaining possible keys on various messages until she achieves success. Since sessions using the same key will last for a long time, Eve can be sure to get some of the good sauce from Alice and Bob.
So, what can Alice and Bob do about this? There are several solutions, which mainly involve making sure that Eve cannot delay transmissions in the quantum channel long enough to be able to modify it after receiving the classical information. What the authors propose is similar, but offers a guarantee that the message was not delayed. In their scheme, Alice sends a random string of ones and zeros on the quantum channel. Bob selects a bunch of bits from the message at random and sends them back to Alice using the quantum channel. Alice evaluates the bits and adds them to the bit string generated by the basis flips. This is then sent to Bob, who replies by sending his basis flips, and the key is generated. Now Eve cannot modify Alice's message before sending it on to Bob because she does not have the basis state string required to modify the message.
So what does this all mean? It means that a security protocol that is designed to counter a threat that does not yet exist (quantum computing) is slightly more secure than it was yesterday.
IEEE Transactions on Information Theory, 2008, DOI: 10.1109/TIT.2008.917697


Pairs of qubits
Pairs of qubits are much, much more than the sum of their parts.
Classical bits only become marginally more interesting when paired—it literally only makes the difference between counting to two and counting to four. Pairs of quantum bits, on the other hand, can be used to create entanglement, a phenomenon so... well, disturbing that one of the most controversial arguments in 20th century physics revolved around whether it could exist at all.
Before talking about the strange things that can be done using pairs of qubits, let's talk about the things that can't. Like copying qubits. The most basic operation one can perform using classical bits is to copy the value of one bit into another bit. Simple, right?
Not really. When we want to copy a single classical bit, we really perform two operations in sequence:
- Measure both bits.
- If they don't match, flip the second one.
Uh-oh. Not only can a single qubit take on a whole sphere full of values, it can only be measured along a single axis at a time. Not only that, but measuring it changes its state from whatever it was before the measurement to whatever state the measurement produced. That's a problem. In fact, it can be proven that even in principle it's not possible to copy an unknown qubit's state. You can move it—that's called quantum teleportation—but, just like in Star Trek, teleportation just moves the state from one place to another. It doesn't make a copy.
Why, then, is classical copying allowed? Classical bits act exactly like quantum bits that never leave a single axis on the sphere. If an unknown qubit is constrained to a single axis (as it is after a measurement along that axis), the classical recipe of measuring and flipping will work fine. But it only works for that one axis. This leads us to another broken classical assumption:
Classical Theory: All information can be perfectly copied.
Quantum Theory: Only the results of a measurement can be copied.
OK, no copying. Strange—definitely strange—but that doesn't sound worthy of a 75-year argument which had Nobel laureates on both teams. Let's get to the good stuff. Let's get to entanglement.
At the heart of entanglement is the concept of correlation, or how the results of measurements relate to each another. Specifically, it's about whether the results of two measurements are the same (correlation) or different (anti-correlation).
This sounds too easy. For states that are on the surface of the sphere, the two measurements will correlate if the states fall on the same axis as the measurement. Right? Time to eliminate another fundamental assumption about information.
Classical Theory: The state of multiple bits is defined by the states of all of the individual bits.
Quantum Theory: The whole is greater than the sum of its parts.
Many, many two-qubit states cannot be completely described by the state of the first qubit and the state of the second qubit. We call the states which are just a combination of the individual qubit states separable; we call all other states entangled, because they exhibit extra correlations that simple, single-qubit descriptions miss.
Consider the "singlet state," an example of an entangled two-qubit state. A singlet state has two defining characteristics:
- Any single-qubit measurement performed on one half of the
singlet state will give a totally random result.
- Any time the same single-qubit measurement is performed on
both qubits in a singlet state, the two measurements will give opposite
The first characteristic sounds like a pair of single qubit states plotted at the origin, the point that divides every measurement axis in half. The second characteristic, that of perfect anti-correlation, is an entirely new phenomenon. This second "rule of singlet states" means that, if horizontal/vertical measurements are made on the two qubits, one qubit will always be measured as H and one will always be measured as V. Which is which will be completely random.
If you've read the last paragraph carefully, this should seem very, very strange. Even impossible.
Imagine if someone showed you a pair of coins, claiming that when both were flipped at the same time, one would always come up heads and one would always come up tails, but that which was which would be totally random. What if they claimed that this trick would work instantly, even if the coins were on opposite sides of the Universe.
You would probably say that's impossible. Albert Einstein did.
In 1935, in one of the most famous scientific papers of all time, Einstein, Podolsky, and Rosen argued that because quantum mechanics allowed exactly this type of strange action at a distance, it must not be complete. Some part of the theory had to be missing.
In effect, they claimed that some extra information (called hidden variables) was programmed into the coins—although they seem random, they really only show correlation because of hidden instructions which tell the coins which way to flip. After all, dice seem random, but if you know precisely how a die is rolling, you can predict its outcome. This assumption—that, in principle, the outcome of any experiment is predictable—is called realism.
The EPR paper coupled this assumption with another basic assumption, locality, which states that events that are very far away can't affect nearby outcomes (unless there's enough time to for a signal to travel between the two events). They showed that as long as local realism is true, quantum mechanics can't be the whole story.
For 30 years, the EPR paradox went unresolved. Finally, in 1965, John Bell proposed an experiment which could directly measure the paradox and, if performed, disprove local realism. He proposed creating a stream of identical singlet states and, for each state, separating the first qubit from the second. In separate locations, each qubit would be randomly subjected to one of two measurements:
If they exhibited too much of the right types of correlation and anti-correlation—as defined by John Bell's equations—it would prove that a locally realistic universe could not exist. Over the past three decades, this experiment has been performed in many different settings using many different types of particles. The Bell experiment has most commonly been performed using polarized photons and the following procedure:
- Create many copies of a singlet state (i.e., many pairs of entangled
- Send the first photon in every pair through a polarizer. Randomly
choose, for every photon, whether to orient this polarizer at 90
degrees (V) or at 45 degrees (D). These two quantum measurements correspond to
the measurements (the red arrows) shown on the first sphere in Figure
- In the same way, send the second photon in every pair through a
polarizer. Randomly choose, for every photon, whether to orient this
polarizer at 22.5 degrees or at 67.5 degrees (corresponding to the red
arrows on the second sphere in Figure 8).
- Count the number of times the measurement results matched
(exhibited correlation) and the number of times they didn't
When this experiment is performed, the results are incredibly surprising. To illustrate why the results are so suprising, I will describe an equivalent implementation of the Bell experiment which, to the best of my knowledge, has never been performed: I call it "The Nemesis Experiment".
To perform this experiment, we're going to need 1000 pairs of people to play the part of singlet states. Remember that the singlet state is the permanently anti-correlated entangled state, and so we can't use just any pairs of people.
We need arch-enemies.


█ BRIAN HOYLE
A supercomputer is a powerful computer that possesses the capacity to store and process far more information than is possible using a conventional personal computer.
An illustrative comparison can be made between the hard drive capacity of a personal computer and a super-computer. Hard drive capacity is measured in terms of gigabytes. A gigabyte is one billion bytes. A byte is a unit of data that is eight binary digits (i.e., 0's and 1's) long; this is enough data to represent a number, letter, or a typographic symbol. Premium personal computers have a hard drive that is capable of storing on the order of 30 gigabytes of information. In contrast, a supercomputer has a capacity of 200 to 300 gigabytes or more.
Another useful comparison between supercomputers and personal computers is in the number of processors in each machine. A processor is the circuitry responsible for handling the instructions that drive a computer. Personal computers have a single processor. The largest supercomputers have thousands of processors.
This enormous computation power makes supercomputers capable of handling large amounts of data and processing information extremely quickly. For example, in April 2002, a Japanese supercomputer that contains 5,104 processors established a calculation speed record of 35,600 gigaflops (a gigaflop is one billion mathematical calculations per second). This exceeded the old record that was held by the ASCI White-Pacific supercomputer located at the Lawrence Livermore National Laboratory in Berkeley, California. The Livermore supercomputer, which is equipped with over 7,000 processors, achieves 7,226 gigaflops.
These speeds are a far cry from the first successful supercomputer, the Sage System CDC 6600, which was designed by Seymour Cray (founder of the Cray Corporation) in 1964. His computer had a speed of 9 megaflops, thousands of times slower than the present day versions. Still, at that time, the CDC 6600 was an impressive advance in computer technology.
Beginning around 1995, another approach to designing supercomputers appeared. In grid computing, thousands of individual computers are networked together, even via the Internet. The combined computational power can exceed that of the all-in-one supercomputer at far less cost. In the grid approach, a problem can be broken down into components, and the components can be parceled out to the various computers. As the component problems are solved, the solutions are pieced back together mathematically to generate the overall solution.
The phenomenally fast calculation speeds of the present day supercomputers essentially corresponds to "real time," meaning an event can be monitored or analyzed as it occurs. For example, a detailed weather map, which would take a personal computer several days to compile, can be complied on a supercomputer in just a few minutes.
Supercomputers like the Japanese version are built to model events such as climate change, global warming, and earthquake patterns. Increasingly, however, supercomputers are being used for security purposes such as the analysis of electronic transmissions (i.e., email, faxes, telephone calls) for codes. For example, a network of supercomputers and satellites that is called Echelon is used to monitor electronic communications in the United States, Canada, United Kingdom, Australia, and New Zealand. The stated purpose of Echelon is to combat terrorism and organized crime activities.
The next generation of supercomputers is under development. Three particularly promising technologies are being explored. The first of these is optical computing. Light is used instead of using electrons to carry information. Light moves much faster than an electron can, therefore the speed of transmission is greater.
The second technology is known as DNA computing. Here, recombining DNA in different sequences does calculations. The sequence(s) that are favored and persist represent the optimal solution. Solutions to problems can be deduced even before the problem has actually appeared.
The third technology is called quantum computing. Properties of atoms or nuclei, designated as quantum bits, or qubits, would be the computer's processor and memory. A quantum computer would be capable of doing a computation by working on many aspects of the problem at the same time, on many different numbers at once, then using these partial results to arrive at a single answer. For example, deciphering the correct code from a 400-digit number would take a supercomputer millions of years. However, a quantum computer that is about the size of a teacup could do the job in about a year.
█ FURTHER READING:
Stork, David G. (ed) and Arthur C. Clarke. HAL's Legacy: 2001's Computer Dream and Reality. Boston: MIT Press, 1998.
Cray Corporation. "What Is a Supercomputer?" Supercomputing. 2002. < http://www.cray.com/supercomputing >(15 December 2002).
The History of Computing Foundation. "Introduction to Supercomputers." Supercomputers. October 13, 2002. < http://www.thocp.net/hardware/supercomputers.htm >(15 December 2002).


Where would we be without singlet states? Almost all molecules in nature—and in our bodies—exist as singlet states, which arise when two particles with a spin of combine into an eigenstate with zero spin. Their most common occurrence is in stable atomic or molecular orbitals. Their combination into a spinless state frees the pair from angular/magnetic momenta, leading to a particularly stable diamagnetic combination. Because they don’t have a net magnetic moment, singlets are long-lived states. This is a property with important practical implications for nuclear magnetic resonance (NMR): although singlets are not directly measurable in NMR, their long lifetime can be exploited to enhance the sensitivity of NMR experiments and extend the range of dynamic phenomena that NMR can probe [in either its spectroscopic (NMR) or imaging (MRI) modes].
A sine qua non condition for creating such singlet states is that its constituents be identical—or at least so we believed. But now, a study in Physical Review Letters by Meike Emondts from RWTH Aachen University, Germany, and co-workers demonstrates a singletlike state made of two different spin- particles: a hydrogen () nucleus and a bonded carbon-13 () counterpart . Evidence for the singlet nature of the state they construct is given by the long lifetime of this state, which exceeds the lifetime of either atom by a factor of 3. The demonstration of heteronuclear singlets thus challenges theoretical preconceptions and dramatically extends the range of systems that can be potentially probed via enhanced forms of singlet-state-based NMR.
The creation of long-lived singlets has been previously reported for ions and electrons  but required complex manipulations. Nuclear spins, which interact more weakly with the environment, can offer a more sheltered “playground” for studying unusual spin states. Singlet nuclear states have, in fact, long been known and manipulated, starting with the discovery of the spin isomer of the molecule, known as parahydrogen. This isomer can be prepared by cooling below its characteristic rotational temperature (88 kelvin), and it is characterized by having its two protons in the antisymmetric combination. In this singlet state, the molecule has a total nuclear spin of zero. Although magnetically silent and thus invisible to NMR, parahydrogen can enhance the sensitivity of NMR and in vivo MRI. This is due to the fact that the singlet symmetry can be broken via a chemical reaction known as hydrogenation , whereby the two hydrogens bond to two inequivalent atoms, converting the pair’s perfect (but magnetically silent) antialignment into an effective spin polarization. This, in turn, leads to a pronounced difference in the spin populations of each hydrogen site—a so-called hyperpolarized state—enabling their resulting magnetic fields to be detected by NMR/MRI experiments with a dramatically enhanced sensitivity.
Unfortunately, there are few options for manipulating parahydrogen: other than chemical processes that break its symmetry, there are no ways of “talking” to it. Over the last decade, however, research has demonstrated that one could create an entangled singlet state out of a pair of homonuclear spins that are chemically slightly different . This can be done in a number of ways. The most intuitive option is to apply a series of so-called refocusing magnetic pulses that erase the spins’ chemical shifts (i.e., their different precession frequencies in an applied magnetic field). Such a pulse sequence can thus “turn off” the inequivalence of protons in the two different molecules. With proper magnetic manipulations, the pair of spins can be combined to create a singlet state. This long-lived state will be conserved while the pulse sequence is executed, but by stopping the refocusing pulses, it can be later transformed back into an observable that is detectable by NMR.
Now, Emondts et al. take this concept a step further and demonstrate that such toggling is also feasible when dealing with heteronuclear spins, i.e., pairs composed of nuclei as different as and . Key to generating a “heteronuclear singlet” is erasing the difference between the magnetic couplings that the spins will naturally present when inserted in a magnetic field. These differences will be stronger than in the homonuclear all- case. They will not be determined by chemical effects but rather by the different nuclei gyromagnetic ratios of and ; i.e., by the isotope-specific constants defining the species’ NMR precession frequencies in a magnetic field.
To cut the Gordian Knot presented by this intrinsic nuclear difference, Emondts et al.’s solution is as drastic as it is simple: make the magnetic field as close to zero as possible. The authors achieved this by exploiting tricks from zero-field NMR, a “shuttling” based technique first developed in the 1980s . To achieve the heteronuclear singlet state, this meant reducing the difference between the and Larmor frequencies from the usual 10 to 100 megahertz values, to only 3.2 hertz. This difference is much smaller than other interactions to which the spins may be subjected, including the mutual - coupling (a form of spin-spin coupling mediated by the electrons in the molecular bonds connecting the two spins). At zero magnetic field, this coupling becomes the dominant term in the spin Hamiltonian, and a suitable shuttling of the system will thus make the spin pair evolve into one of its allowed states, one of which is a singletlike state involving the two spins. Hence a paradoxical “heteronuclear singlet” state can be originated (see Fig. 1).
Emondts et al. confirmed that they reached this state by dividing their experiment into three phases: (i) a high-field stage that polarizes the spin system, (ii) a shuttling into zero-field where the original high-field eigenstates adiabatically transition into the triplet and singlet spin manifolds, and (iii) a final return to high-field conditions in order to probe the fate of the singlet and triplet populations. The group saw both expected and unexpected features upon performing the same experiment under a variety of conditions. Among the expected results was the generation of a long-lived state, which exceeded the polarized lifetimes of each constituent by about a factor of 3; this is the landmark characteristic of a spin singlet eigenstate. Among the experiment’s most unusual features was the possibility of creating spin coherence between the triplet and singlet manifolds, whose decay is slower than the actual lifetimes of each one of the states that it involves. In spectroscopic jargon one could describe this as the creation of a subspace where the effective spin’s is longer than its .
From a practical perspective, this new singlet-spin entity could find applications in hyperpolarized NMR and MRI and in the development of more sensitive NMR probes. The latter could be used to investigate slow biomolecular dynamics or the diffusive behavior of molecules in tissues. But at a more fundamental level, it is likely that the most remarkable impact will be the inspiration that this initial NMR observation may provide for the wider world of quantum coherent control in coupled two-level systems.
- M. Emondts, M. P. Ledbetter, S. Pustelny, T. Theis, B. Patton, J. W. Blanchard, M. C. Butler, D. Budker, and A. Pines, “Long-Lived Heteronuclear Spin-Singlet States in Liquids at a Zero Magnetic field,” Phys. Rev. Lett. 112, 077601 (2014).
- D. Kielpinski, V. Meyer, M. A. Rowe, C. A. Sackett, W. M. Itano, C. Monroe, and D. J. Wineland, “A Decoherence-Free Quantum Memory Using Trapped Ions,” Science 291, 1013 (2001); C. Langer et al., “Long-Lived Qubit Memory Using Atomic Ions,” Phys. Rev. Lett. 95, 060502 (2005); S. Kotler, N. Akerman, N. Navon, Y. Glickman, and R. Ozeri, “Measurement of the Magnetic Interaction between Two Electrons,” arXiv:1312.4881 (2013).
- C. R. Bowers and D. P. Weitekamp, “Transformation of Symmetrization Order to Nuclear-Spin Magnetization by Chemical Reaction and Nuclear Magnetic Resonance,” Phys. Rev. Lett. 57, 2645 (1986); R. W. Adams et al., “Reversible Interactions with para-Hydrogen Enhance NMR Sensitivity by Polarization Transfer,” Science 323, 1708 (2009).
- Malcolm H. Levitt, “Singlet Nuclear Magnetic Resonance,” Ann. Rev. Phys. Chem. 63, 89 (2012).
- D.B. Zax, A. Bielecki, K.W. Zilm, and A. Pines, “Heteronuclear zero-field NMR,” Chem. Phys. Lett. 106, 550 (1984).


How the Cell Exploits Genetic Code Degeneracy
In the context of making and analyzing codes, the term "degeneracy" refers to having excess codes that produce the same message. A non-degenerate code, like Morse code, is one for one: each code is unique, producing one and only one output. The genetic code, by contrast, is many-to-one in some cases. For instance, six different codons can produce the amino acid leucine. This would be like having six combinations of dots and dashes to produce the letter A in a "degenerate" version of Morse code. Other amino acids can be coded by 4, 3 or 2 codons, while two (methionine and tryptophan) each have only one unique code. Why is this?
One reason is that there are 20 standard amino acids used in living organisms, but 64 possible combinations of codons (4 letters in triplets, 43 = 64). This mismatch creates the degeneracy, but also allows for multiple codons to code for the same amino acid; these are called cognates. Is there a reason for this degeneracy other than happenstance?
In a recent paper in PNAS, a trio of researchers from Harvard and the University of Chicago experimented with E. coli bacteria to study the effects of multiple codons under environmental stress. Here is their explanation of the degeneracy in the genetic code:
The genetic code governing protein synthesis is a highly degenerate system because 18 of the 20 amino acids have multiple synonymous codons and 10 of the 20 amino acids are aminoacylated (charged) onto multiple tRNA [transfer RNA] isoacceptors. (Emphasis added.)To study the effects of the environment on the code, they first created a library of 29 versions of yellow fluorescent protein genes (yfp) using different cognate forms of the codons for leucine, arginine and serine (each with 6 cognates), proline (4 cognates), isoleucine (3), glutamine (2) and phenylalanine (2).
Under normal conditions, with amino acids plentiful, each of the cognate codes in their gene library produced the same amount of YFP protein. But then they created a supply-and-demand crisis by "starving" the cells of the amino acids, one at a time. What they found was a case of "degeneracy lifting."
Degenerate states that are indistinguishable under normal conditions can exhibit distinct properties under the action of external perturbations. This effect, called degeneracy lifting, allows degenerate systems to exhibit a wide range of behaviors, depending on the environmental context.This implies that degenerate systems provide a way to encode extra information; indeed, quantum computing and steganography exploit this capacity. It should be noted that the genetic code is not the only degenerate system in nature:
Degeneracy, the occurrence of distinct states that share a common function, is a ubiquitous property of physical and biological systems. Examples of degenerate systems include atomic spectra, condensed matter, the nervous system, and the genetic code. Degeneracy in physical systems is often associated with underlying symmetries and in biological systems with error minimization, evolvability, and robustness against perturbations.The question becomes: does E. coli "lift" the degeneracy of the genetic code under stress, and thereby encode environmental information in the extra space? Yes, they found:
Our study suggests that organisms can exploit degeneracy lifting as a general strategy to adapt protein synthesis to their environment.In a clever series of experiments, they found that the cells divide the cognates into a hierarchy: those that are robust with regard to perturbations, and those that are sensitive. The robust cognates have no effect on protein synthesis levels, whereas the sensitive ones show up to a 100-fold reduction in synthesis rate. These results are independent of tRNA supply and codon usage.
Rather, competition among tRNA isoacceptors for aminoacylation underlies the robustness of protein synthesis. Remarkably, the hierarchy established using the synthetic library also explains the measured robustness of synthesis for endogenous proteins in E. coli. We further found that the same hierarchy is reflected in the fitness cost of synonymous mutations in amino acid biosynthesis genes and in the transcriptional control of σ-factor genes.The team's results imply a "strategy" to exploit degeneracy to survive environmental stress. When tRNA isoacceptors are in short supply, the ribosome pauses, and sends feedback to the nucleus to reduce transcription. Other effects include messenger-RNA cleavage and translation recoding -- functions induced by the environmental stress to regulate protein supply.
The authors had nothing to say about how evolution produced these regulatory effects that promote robustness in a varying environment. Instead, in concluding, they concentrated on functional design:
Here, we have investigated the effect of a specific environmental perturbation associated with amino acid limitation in the bacterium E. coli. However, this type of perturbation plays a crucial role in the life cycle of other bacteria such as Myxococcus xanthus and Bacillus subtilis that undergo differentiation cued by amino acid limitation. Protein synthesis during such differentiation events might also be regulated by degeneracy lifting of the genetic code. Moreover, degeneracy lifting could be important during protein synthesis in eukaryotes, where clinically important conditions such as neoplastic transformation and drug treatment are often accompanied by a reduction in amino acid supply. Therefore, lifting the degeneracy of the genetic code might emerge as a general strategy for biological systems to expand their repertoire of responses to environmental perturbations.Feedback, regulation, robustness: When there turns out to be method in what appeared to be madness, it's reasonable to draw an inference to intelligent design.