As mysterious as the Italian scientist for which it is named, the Majorana particle is one of the most compelling quests in physics.
Its fame stems from its strange properties – it is the only particle that is its own antiparticle – and from its potential to be harnessed for future quantum computing.
By Catherine Zandonella, Office of the Dean for Research
First Posted on June 13, 2019 to the Discovery blog of the Office of the Dean for Research
In recent years, a handful of groups including a team at Princeton University have reported finding the Majorana in various materials, but the challenge is how to manipulate it for quantum computation.
In a new study published this week, the Princeton team reports a way to control Majorana quasiparticles in a setting that also makes them more robust. The setting – which combines a superconductor and an exotic material called a topological insulator – makes Majoranas especially resilient against destruction by heat or vibrations from the outside environment. What is more, the team demonstrated a way to turn on or off the Majorana using small magnets integrated into the device. The report appeared online in the journal Science.
“With this new study we now have a new way to engineer Majorana quasiparticles in materials,” said Ali Yazdani, Class of 1909 Professor of Physics and senior author on the study. “We can verify their existence by imaging them and we can characterize their predicted properties.”
“The new platform combines the edge states of a newly discovered type of topology, the higher order topological insulator with magnetism, to give the largest gap one-dimensional topological superconductor with Majorana modes,” said B. Andrei Bernevig, a study co-author and professor of physics at Princeton. “We are entering a new age of material design, where three-dimensional bulk topological materials can be combined with magnetic islands, domain walls and step edges to engineer structures whose properties can fulfill the most exotic requirements of quantum mechanics.”
The Majorana is named for physicist Ettore Majorana, who predicted the existence of the particle in 1937 just a year before mysteriously disappearing during a ferry trip off the Italian coast. Building on the same logic with which physicist Paul Dirac predicted in 1928 that the electron must have an antiparticle, later identified as the positron, Majorana theorized the existence of a particle that is its own antiparticle.
Typically when matter and antimatter come together, they annihilate each other in a violent release of energy, but the Majoranas, when they appear as pairs each at either end of specially designed wires, can be relatively stable and interact weakly with their environment. The pairs enable the storing of quantum information at two distinct locations, making them relatively robust against disturbance because to change the quantum state requires operations at both ends of the wire at the same time.
This capability has captivated technologists who envision a way to make quantum bits – the units of quantum computing – that are more robust than current approaches. Quantum systems are prized for their potential to tackle problems impossible to solve with today’s computers, but they require maintaining a fragile state called superposition, which if disrupted, can result in system failures.
A Majorana-based quantum computer would store information in pairs of particles and perform computation by braiding them around each other. The results of computation would be determined by annihilation of Majoranas with each other, which can result in either the appearance of an electron (detected by its charge) or nothing, depending on how the pair of Majoranas have been braided. The probabilistic outcome of the Majorana pair annihilation underlies its use for quantum computation.
The challenge is how to create and easily control Majoranas. One of the places they can exist is at the ends of a single-atom-thick chain of magnetic atoms on a superconducting bed. In 2014, reporting in Science, Yazdani and collaborators used a scanning tunneling microscope (STM), in which a tip is dragged over atoms to reveal the presence of quasiparticles, to find Majoranas at both ends of a chain of iron atoms resting on the surface of a superconductor.
The team went on to detect the Majorana’s quantum “spin,” a property shared by electrons and other subatomic particles. In a report published in Science in 2017, the team stated that the Majorana’s spin property is a unique signal with which to determine that a detected quasiparticle is indeed a Majorana.
In this latest study, the team explored another predicted place for finding Majoranas: in the channel that forms at the edge of a topological insulator when it is placed in contact with a superconductor. Superconductors are materials in which electrons can travel without resistance, and topological insulators are materials in which electrons flow only along the edges.
The theory predicts that Majorana quasiparticles can form at the edge of a thin sheet of topological insulator that comes in contact with a block of superconducting material. The proximity of the superconductor coaxes electrons to flow without resistance along the topological insulator edge, which is so thin that it can be thought of as a wire. Since Majoranas form at the end of wires, it should be possible to make them appear by cutting the wire.
“It was a prediction, and it was just sitting there all these years,” said Yazdani. “We decided to explore how one could actually make this structure because of its potential to make Majoranas that would be more robust to material imperfections and temperature.”
The team built the structure by evaporating a thin sheet of bismuth topological insulator atop a block of niobium superconductor. They placed nanometer-sized magnetic memory bits on the structure to provide a magnetic field, which derails the flow of electrons, producing the same effect as cutting the wire. They used STM to visualize the structure.
When using their microscope to hunt for the Majorana, however, the researchers were at first perplexed by what they saw. Some of the time they saw the Majorana appear, and other times they could not find it. After further exploration they realized that the Majorana only appears when the small magnets are magnetized in the direction parallel to the direction of electron flow along the channel.
“When we began to characterize the small magnets, we realized they are the control parameter,” said Yazdani. “The way the magnetization of the bit is oriented determines whether the Majorana appears or not. It is an on-off switch.”
The team reported that the Majorana quasiparticle that forms in this system is quite robust because it occurs at energies that are distinct from the other quasiparticles that can exist in the system. The robustness also stems from its formation in a topological-edge mode, which is inherently resistant to disruption. Topological materials derive their name from the branch of mathematics that describes how objects can be deformed by stretching or bending. Electrons flowing in a topological material thus will continue moving around any dents or imperfections.
The study, “Observation of a Majorana zero mode in a topologically protected edge channel,” by Berthold Jäck, Yonglong Xie, Jian Li, Sangjun Jeon, B. Andrei Bernevig and Ali Yazdani, was published online in the journal Science on June 13, 2019. DOI http://dx.doi.org/10.1126/science.aax1444
Funding was provided by the Gordon and Betty Moore Foundation as part of EPiQS initiative (GBMF4530), the U.S. Office of Naval Research (ONR-N00014-17-1-2784, ONR-N00014-14-1-0330), the National Science Foundation’s NSF-MRSEC programs through the Princeton Center for Complex Materials (DMR-142054, DMR-1608848), the Alexander-von-Humboldt Foundation through a Feodor-Lynen postdoctoral fellowship (BJ). Support was also provided by the U.S. Department of Energy (DE-SC016239, NSF EAGER 1004957, Simons Investigator Grants, U.S. Army Research Office MURI W911NF- 12-1-0461, the David and Lucile Packard Foundation, and Princeton’s Eric and Wendy Schmidt Transformative Technology Fund. The theory effort was also supported by the National Natural Science Foundation of China under Project 11774317 (JL).


The main difference between a quantum computer and a classical one is the qubit. Qubits are like classical bits, in that they hold binary values of either 1 or 0, on or off, true or false, etc. However, qubits, being quantum objects, can be in a superposition of both states at once. The physical manifestation is often something like a particle in either a spin up or spin down state.
(This is true for digital quantum computing, where a discrete state is necessary. There is also analog quantum computing, which presumably works with other properties that are more continuous.)
We might write the superposition of a qubit as:
meaning it can be in a superposition of both 1 and 0 at the same time. So far so boring. But if we add a second qubit and have the two interact, we now have two entangled quantum objects which, together, can be in a superposition of four different states, which we might write as:
In other words, adding a second qubit doubled the number of parallel states they can collectively be in. If we add a third qubit into the mix, which also, through interaction, joins the entanglement, we get this list of states in the superposition:
It’s important to understand that these are superpositions, not alternatives. The three qubits, until a measurement is done, can be in all these states at the same time. If we increase the number to ten qubits, then the overall system can be in 210, or 1024 states at the same time. (Which I won’t attempt to lay out.)
The Google quantum computer that demonstrated quantum supremacy (over classical computers) was reported to have 53 qubits, which in principle meant it should have been capable of being in 253 or 9 x 1015 states concurrently. This is the power of quantum computing. It allows a level of parallel processing not possible with classical systems.
A 300 qubit system would be able to be in a superposition of more states than there are particles in the observable universe. Consider this. Where are all those states? According to quantum mechanics, they’re all right there, in those 300 particles.
Well, at least under interpretations that consider the wave function to model something real. The question is, under the interpretations that don’t, how do they account for these kinds of systems? One thing I’ve read indicates that maybe the systems aren’t really running in parallel. Maybe they’re just executing a far more clever algorithm, and the wave function mathematics are just a convenient mechanism to keep track of it. This move seems, to me, increasingly dubious as the number of qubits increase.
The interesting question is, what happens when the overall system is measured? In all interpretations, that act only provides access to one of the states, with no control over which one. A successful quantum circuit has to promote the desired answer so that all its states have it as the end result.
But it’s interesting to think about what happens under each interpretation. Before doing so, it’s worth noting the raw physics of the situation. When a measurement begins, the quantum particles / waves / objects in the measuring device interact with the quantum objects, the qubits, in the quantum circuit. There’s no real distinction between the atoms in the quantum circuitry and the ones in the measuring system. In most interpretations, what changes are the sheer number of interactions involved.
Under the Copenhagen interpretation, the involvement of macroscopic classical mechanisms cause the massive superposition of states to collapse to one classical state, although Copenhagen seems agnostic on the exact mechanisms. Various physical collapse interpretations see the wave physically reducing to a single state. Under the pilot-wave interpretation, there were always waves and particles, with the waves guiding the particles, and interaction with the environment causes the wave to lose coherence so that the actual particle states are now accessible. (At least I think that’s the way it would work under pilot-wave.)
The sequence under relational quantum mechanics (RQM) seems particularly interesting. If I’m understanding it correctly, each interaction results in a collapse, but only relative to a particular system. So from the second qubit’s perspective, its interaction with the first qubit causes it to collapse. But from the third qubit’s perspective, the first two qubits are in superposition until the interactions reach it. This sequence of disagreements continue all the way through the sequence. Of course, from the measuring device’s perspective, nothing has collapsed until it interacts with the system.
This seems similar to the sequence under the relative state formulation, also known as the many-worlds interpretation (MWI). The difference is under this interpretation, the disagreements are resolved into an objective reality. Of course, the only way to resolve them is to have a copy of qubit 2 seeing qubit 1 in its 0 state, and another copy seeing it in its 1 state. All of these copies exist in their own branch of the superposition.
Under both RQM and MWI, nothing fundamental changes on the event we label as “measurement.” The physical processes just cascade into a larger environment. Under RQM, this is handled by the stipulation that all states are only meaningful relative to a particular system, and that no universal description is possible.
MWI instead simply sees the superpositions continue to cascade out in an unending process. As the number of quantum objects involved skyrocket, the phase relation between the branches of the superposition that allowed for interference between them, begins to alter. As the number of constituents increase, each branch’s phase increasingly becomes more unique, isolated from the others, until they no longer interfere with each other. Each becomes causally isolated, their own separate world.
Some quantum computational theorists see the success of quantum computing as evidence for the MWI. Others point out that each of the other interpretations can provide an accounting. What that success does seem to do is put pressure on the interpretations that have an anti-real stance toward the wave function. As noted above, the idea that those computations aren’t physically happening in parallel somewhere seems dubious.
Unless of course, in my admittedly very amateurish musings here, I’ve missed something. In particular, is there a stronger anti-real account that I’m overlooking? Are there problems with the other interpretations that do take a realist stance?


The technology behind the quantum computers of the future is fast developing, with several different approaches in progress. Many of the strategies, or “blueprints,” for quantum computers rely on atoms or artificial atom-like electrical circuits. In a new theoretical study in the journal Physical Review X, a group of physicists at Caltech demonstrates the benefits of a lesser-studied approach that relies not on atoms but molecules.
“In the quantum world, we have several blueprints on the table and we are simultaneously improving all of them,” says lead author Victor Albert, the Lee A. DuBridge Postdoctoral Scholar in Theoretical Physics. “People have been thinking about using molecules to encode information since 2001, but now we are showing how molecules, which are more complex than atoms, could lead to fewer errors in quantum computing.”
At the heart of quantum computers are what are known as qubits. These are similar to the bits in classical computers, but unlike classical bits they can experience a bizarre phenomenon known as superposition in which they exist in two states or more at once. Like the famous Schrödinger’s cat thought experiment, which describes a cat that is both dead and alive at the same time, particles can exist in multiple states at once. The phenomenon of superposition is at the heart of quantum computing: the fact that qubits can take on many forms simultaneously means that they have exponentially more computing power than classical bits.
But the state of superposition is a delicate one, as qubits are prone to collapsing out of their desired states, and this leads to computing errors.
“In classical computing, you have to worry about the bits flipping, in which a ‘1’ bit goes to a ‘0’ or vice versa, which causes errors,” says Albert. “This is like flipping a coin, and it is hard to do. But in quantum computing, the information is stored in fragile superpositions, and even the quantum equivalent of a gust of wind can lead to errors.”
However, if a quantum computer platform uses qubits made of molecules, the researchers say, these types of errors are more likely to be prevented than in other quantum platforms. One concept behind the new research comes from work performed nearly 20 years ago by Caltech researchers John Preskill, Richard P. Feynman Professor of Theoretical Physics and director of the Institute of Quantum Information and Matter (IQIM), and Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics at Caltech, along with their colleague Daniel Gottesman (Ph.D. ’97) of the Perimeter Institute in Ontario, Canada. Back then, the scientists proposed a loophole that would provide a way around a phenomenon called Heisenberg’s uncertainty principle, which was introduced in 1927 by German physicist Werner Heisenberg. The principle states that one cannot simultaneously know with very high precision both where a particle is and where it is going.
“There is a joke where Heisenberg gets pulled over by a police officer who says he knows Heisenberg’s speed was 90 miles per hour, and Heisenberg replies, ‘Now I have no idea where I am,'” says Albert.
The uncertainty principle is a challenge for quantum computers because it implies that the quantum states of the qubits cannot be known well enough to determine whether or not errors have occurred. However, Gottesman, Kitaev, and Preskill figured out that while the exact position and momentum of a particle could not be measured, it was possible to detect very tiny shifts to its position and momentum. These shifts could reveal that an error has occurred, making it possible to push the system back to the correct state. This error-correcting scheme, known as GKP after its discoverers, has recently been implemented in superconducting circuit devices.
“Errors are okay but only if we know they happen,” says Preskill, a co-author on the Physical Review X paper and also the scientific coordinator for a new Department of Energy-funded science center called the Quantum Systems Accelerator. “The whole point of error correction is to maximize the amount of knowledge we have about potential errors.”
In the new paper, this concept is applied to rotating molecules in superposition. If the orientation or angular momentum of the molecule shifts by a small amount, those shifts can be simultaneously corrected.
“We want to track the quantum information as it’s evolving under the noise,” says Albert. “The noise is kicking us around a little bit. But if we have a carefully chosen superposition of the molecules’ states, we can measure both orientation and angular momentum as long as they are small enough. And then we can kick the system back to compensate.”
Jacob Covey, a co-author on the paper and former Caltech postdoctoral scholar who recently joined the faculty at the University of Illinois, says that it might be possible to eventually individually control molecules for use in quantum information systems such as these. He and his team have made strides in using optical laser beams, or “tweezers,” to control single neutral atoms (neutral atoms are another promising platform for quantum-information systems).
“The appeal of molecules is that they are very complex structures that can be very densely packed,” says Covey. “If we can figure out how to utilize molecules in quantum computing, we can robustly encode information and improve the efficiency in which qubits are packed.”
Albert says that the trio of himself, Preskill, and Covey provided the perfect combination of theoretical and experimental expertise to achieve the latest results. He and Preskill are both theorists while Covey is an experimentalist. “It was really nice to have somebody like John to help me with the framework for all this theory of error-correcting codes, and Jake gave us crucial guidance on what is happening in labs.”
Says Preskill, “This is a paper that no one of the three of us could have written on our own. What’s really fun about the field of quantum information is that it’s encouraging us to interact across some of these divides, and Caltech, with its small size, is the perfect place to get this done.”
The Physical Review X study is titled “Robust encoding of a qubit in a molecule.”
More information: Victor V. Albert et al. Robust Encoding of a Qubit in a Molecule. Physical Review X (2020). DOI: 10.1103/PhysRevX.10.031050
Image: In a new theoretical study, Caltech physicists have shown how molecules can, in theory, be used to reduce errors in quantum computing. This strategy would involve placing a rotating molecule in “superposition,” which means that it would exist in multiple orientations at once. In this illustration, three different molecular orientations are shown at left; the drawing at far right signifies a superposition of these molecular states.


A new method of implementing an ‘unbreakable’ quantum cryptographic system is able to transmit information at rates more than ten times faster than previous attempts.
Researchers have developed a new method to overcome one of the main issues in implementing a quantum cryptography system, raising the prospect of a useable ‘unbreakable’ method for sending sensitive information hidden inside particles of light.
By ‘seeding’ one laser beam inside another, the researchers, from the University of Cambridge and Toshiba Research Europe, have demonstrated that it is possible to distribute encryption keys at rates between two and six orders of magnitude higher than earlier attempts at a real-world quantum cryptography system. The results are reported in the journal Nature Photonics.
Encryption is a vital part of modern life, enabling sensitive information to be shared securely. In conventional cryptography, the sender and receiver of a particular piece of information decide the encryption code, or key, up front, so that only those with the key can decrypt the information. But as computers get faster and more powerful, encryption codes get easier to break.
Quantum cryptography promises ‘unbreakable’ security by hiding information in particles of light, or photons, emitted from lasers. In this form of cryptography, quantum mechanics are used to randomly generate a key. The sender, who is normally designated as Alice, sends the key via polarised photons, which are sent in different directions. The receiver, normally designated as Bob, uses photon detectors to measure which direction the photons are polarised, and the detectors translate the photons into bits, which, assuming Bob has used the correct photon detectors in the correct order, will give him the key.
The strength of quantum cryptography is that if an attacker tries to intercept Alice and Bob’s message, the key itself changes, due to the properties of quantum mechanics. Since it was first proposed in the 1980s, quantum cryptography has promised the possibility of unbreakable security. “In theory, the attacker could have all of the power possible under the laws of physics, but they still wouldn’t be able to crack the code,” said the paper’s first author Lucian Comandar, a PhD student at Cambridge’s Department of Engineering and Toshiba’s Cambridge Research Laboratory.
However, issues with quantum cryptography arise when trying to construct a useable system. In reality, it is a back and forth game: inventive attacks targeting different components of the system are constantly being developed, and countermeasures to foil attacks are constantly being developed in response.
The components that are most frequently attacked by hackers are the photon detectors, due to their high sensitivity and complex design – it is usually the most complex components that are the most vulnerable. As a response to attacks on the detectors, researchers developed a new quantum cryptography protocol known as measurement-device-independent quantum key distribution (MDI-QKD).
In this method, instead of each having a detector, Alice and Bob send their photons to a central node, referred to as Charlie. Charlie lets the photons pass through a beam splitter and measures them. The results can disclose the correlation between the bits, but not disclose their values, which remain secret. In this set-up, even if Charlie tries to cheat, the information will remain secure.
MDI-QKD has been experimentally demonstrated, but the rates at which information can be sent are too slow for real-world application, mostly due to the difficulty in creating indistinguishable particles from different lasers. To make it work, the laser pulses sent through Charlie’s beam splitter need to be (relatively) long, restricting rates to a few hundred bits per second (bps) or less.
The method developed by the Cambridge researchers overcomes the problem by using a technique known as pulsed laser seeding, in which one laser beam injects photons into another. This makes the laser pulses more visible to Charlie by reducing the amount of ‘time jitter’ in the pulses, so that much shorter pulses can be used. Pulsed laser seeding is also able to randomly change the phase of the laser beam at very high rates.
The result of using this technique in a MDI-QKD setup would enable rates as high as 1 megabit per second, representing an improvement of two to six orders of magnitude over previous efforts.
“This protocol gives us the highest possible degree of security at very high clock rates,” said Comandar. “It could point the way to a practical implementation of quantum cryptography.”
The Latest on: Quantum cryptography
via Google News
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Quantum Computing Is a Bigger Deal Than the Internet
A Paper published in the journal Nature on October 23, researchers reported that the group supporting Google’s quantum computer”Sycamore” were able to use their machine to address a problem in only 200 minutes. This was not just any difficulty — it had been one so tough it could have taken the world’s strongest traditional supercomputer within 10,000 years to finish.
This Is only a very small fraction of what quantum computing might accomplish.
For Hundreds of thousands of years, the only real tools humans had were stones, our brains, and fire. But the best tool we have ever invented is the computer. In the very small span of time extending from the mid-20th century to the present, we have entered a realm of exponential progress as processing power approximately doubles every few years.
Computers Are essentially a collection of simple elements that each have defined responsibilities: memory card storage, processing information via logic and math, and a means to control all of it through directions. A computer processor is one of the most fundamental components. Every chip has different modules that each do something special. Each module has logic gates that are made of transistors. Transistors are the 1 or 0″pieces,” off or on. A lot of transistors make up the logic gates, which allow for combinations that can do more advanced operations like multiplication and division. With a lot of these, you can calculate a lot of information, which now lets us do important work like mathematics fiction and… video games!
Right Today, a transistor can be about 40 nanometers or smaller, nearly 500 times smaller than an average cell in your system.
Transistors Are switches which turn off the stream of electrons. Right now, a transistor may be about 40 nanometers or smaller, nearly 500 times bigger than an ordinary cell within your body.
Basically, At this level, the electrons do not have to stream — they can simply proceed using”quantum tunneling.”
So To take advantage of physics in a quantum level, we’re producing quantum computers. Rather than using bits as our tiniest unit of information, we finally have qubits. Beyond this, in quantum physics that the countries don’t have to be just on or off / yes or no — they can also reap the benefits of”superposition,” a quantum property which allows a particle to be in any combination or proportion of these countries. Like Schrodinger’s Cat, the particle could be anything, but if you really test or observe it, it will only be one condition. So once you’re not celebrating it, the particle can be both partially vertically and horizontally polarized. But while you check on it, the particle is only going to show you one of those countries.
What Superposition truly means is that we now have a radically increased number of possible combinations. In regular computing, 4 pieces yields 16 total possible combinations, but you can just use one of them. But, 4 qubits can actually store all 16 of those values at the same time.
Another Awesome property that qubits can display is quantum entanglement, in which two qubits are strangely connected and react to another’s conditions, however far apart they could be from the physical universe. With this property, we can quantify one qubit and be able to know the properties of its entangled qubit in the exact same time.
A Quantum internet will greatly increase information access and allow dispersed computational attempts to achieve even greater heights.
If You will allow me a tangent, quantum entanglement has also enabled research into quantum teleportation. By taking formerly entangled particles and putting them in various locations, we could use traditional communication methods to send the conditions of particle into the entangled partner no matter how far apart they could be.
And Yet another property we can make the most of is called qubit manipulation. Our routine calculating logic gates get a pair of inputs and provide us a single output. A”quantum gate” takes an input signal of superpositioned qubits, rotates probabilities, and sparks a new superposition. Now the qubits can be measured and also we get the 0s and 1s which represent the data we need. The important thing here is that each one of the possible replies are generated at precisely the same time, not just the single output in a conventional logic gate. The answer we get is likely correct, but there’s a very slight chance it may not be. But since all of the possibilities have been created, it’s quick work to experience the rest until we receive the exact right one.
Though Not perfect, what actually makes quantum computing particular beyond storage capacity is how efficient and fast it is. One great application of this can be databases. We can now save a stunningly massive number of information and also search through it much quicker than with traditional computing.
“It’s My private belief that quantum computing can help us make sense of this deluge of data we find ourselves creating to fix some rather interesting problems. You will find systems generating countless information sets daily, and those might be the answer to a Essential problems affecting society…”
William Hurley, seat of the Quantum Computing Standards Workgroup at the Institute of Electrical and Electronics Engineers (IEEE)
Quantum Computing can also generate huge quantities of calculations and probabilities at amazing rates, which also rewards simulations. These quantum simulations will help us in research on climate, genetics and disease, quantum physics, and generally anything that requires massive amounts of number crunching.
Since a Quantum internet will improve data access and allow dispersed computational efforts to reach even higher heights.
One Negative impact of quantum computing is that it vastly increases the rate at which someone can decode passwords or other security measures, compared to brute force attempts utilizing a traditional computer.
We Want a new paradigm for our advancement to continue, and quantum computing can it be. We likely won’t see quantum computers households everywhere soon, but scientists and researchers are already using them for large-scale projects.
The Information Age has been a hugely profitable time for our planet: The power of computing has led to amazing advances in most fields of human effort, while also greatly contributing to raising the standard of living for most people. We now generate more new information and knowledge annually than we’ve recorded in most of human history. However, as we progress ever further in the ability of those artificial minds, we are playing with a tool that’s more powerful and dangerous in some ways than atomic power.
Quantum Computing may get rid of any conceivable space that A.I. may face between its current condition and the”singularity” — the stage in the future when A.I. will become self-aware. But in the incorrect hands, quantum computing could lead to genetic tampering that may produce super-soldiers or super-diseases. We Have to continue to push whole steam ahead on research in order that we can comprehend These risks, while also benefiting from the unique advantages of quantum computing.
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- Quantum computing
- Quantum teleportation
- Quantum cryptography
- Sources for single or entangled photons
It was only short time after the formulation and acceptance of quantum theory when scientists started to discuss possible benefits of this theory for mankind. The quantum computer, probably the most famous application of quantum theory, is expected to reach incredible computing speeds that enable calculations which were not possible before. Any coupled quantum mechanical system can be used for quantum computing. Solid state systems, trapped ions, atoms in optical lattices, and photons with linear optical elements are at the heart of quantum computer research. First quantum operations have been demonstrated with solid state systems and trapped ions but the race is still open.
Basis for quantum technologies
The basis for quantum computing is “entanglement”, a quantum mechanical property of a system in which the state of one part of the system is fully linked to the state of another part. The famous “Schrödinger cat” example tries to visualize how strange entanglement is compared to experiences in daily life. Even Einstein doubted this property so much that he and his colleagues Podolski and Rosen published an article in 1935 in which they thought to proof that quantum theory cannot be complete and would have to be substituted by another theory including variables that in quantum theory are still “hidden”. Their “EPR paradox” argument was first theoretically falsified by Bell (“Bell’s theorem”) who showed that quantum mechanics is indeed complete. Until today, Bells theorem was experimentally supported many times. No hidden variables are needed to describe the quantum nature completely.
The strange property entanglement is also the basis for quantum teleportation – where one transfers a quantum mechanical state from one system at one place to another system at another place - and quantum cryptography. The goal of the latter is to send information from one place to another in a completely secure way. Obviously, a quantum cryptography apparatus would be a very powerful and important instrument. Quantum cryptography relies mostly on single on entangled photons and is already commercialized.
High speed with Quantum computing
Quantum computing is expected to allow for calculations, simulations or operations at a speed that classical computing can never reach. For example, it was theoretically shown that a quantum computer would be able to perform database searches or factorization of large numbers much faster than classical computers. The enormous calculation power of a quantum computer is a consequence of two main ingredients. First of all, the fundamental piece of information is a quantum mechanical two state system (|0> and |1>) called QuBit that – unlike a classical bit which is either 0 or 1 – can be in any superposition (a|0> + b|1>) of the two states. Second, the basic calculations are coherent operations that act on such a superposition state. This way, all possible realizations of anything between |0> and |1> can be computed simultaneously and highly parallel computation is realized. Gate operations, the fundamental operations of computing, were shown with trapped ions and with photon based quantum computers. Using solid state systems (NMR), a proof of principle for quantum computed factorization of the number 15 was demonstrated.
Object transferation with quantum teleportation
Quantum teleportation is referring to a procedure in which the quantum mechanical state of one object is fully transferred to another object at a different place. It makes use of the non-locality of entanglement that confused not only Einstein. Using a clever sequence of measurements and entanglement operations on photons, the polarization state of one photon could be mapped to another photon completely. Just recently, quantum teleportation between distant matter QuBits was shown using two separate ion traps. Closely related to quantum teleportation and quantum computing is the so-called “quantum logic”. Here, depending on the quantum state of one object a specific state of another object is created. This controlled state preparation was used in metrology to realize one of the best atomic clocks in the world based on aluminum ions.
Secure communication with quantum crytography
Quantum cryptography uses quantum physics properties like entanglement and back action of the measurement process on a quantum state to achieve secure communication between a sender (Alice) and a receiver (Bob). The standard approach is that Alice and Bob perform measurements on entangled quantum systems, usually entangled photons, in order to create a key for Alice and Bob. Since they can then use this code to encrypt and decrypt the real message, the quantum cryptography method is called quantum key distribution. The real message is encrypted by Alice according to her measurement results and sent through an open channel (so anyone is allowed to “listen”) to Bob who decrypts the message according to his measurements. Any eavesdropping, so any attempt of a third party to detect the quantum key, can be detected because according to quantum physics laws each measurement influences the quantum mechanical state itself. Eavesdropping would be noticed always. Due to its obvious significance, quantum cryptography research is pushed a lot and many results have been achieved so far. Quantum key distribution over hundreds of km in fiber or over a whole city in free space was shown already while satellite-links of entangled photons between earth stations are currently explored. To proof the usability, a quantum encrypted bank transaction was undertaken.
Important tools for quantum computing & cryptography
Sources for single or entangled photons are important tools for quantum computing and quantum cryptography. Single photon sources emitting exactly one photon at a triggered time can be realized in many ways incorporating e.g. color centers or ions in solids, single atoms in traps or optical cavities, trapped ions or quantum dot systems. The most common source for entangled photons is based on spontaneous parametric down conversion. A “blue” photon is converted into two red photons within a non-linear optical crystal. Polarization, momentum and energy of the two photons are strongly correlated. A lot of research on this topic is under way. Main efforts are focused on the development of efficient – ideally full deterministic – sources and realizations with mass production potential.
TOPTICA’s added value
TOPTICA is a highly appreciated supplier for quantum information experiments that involve trapped ions or atoms. Our lasers are successfully applied to cool, trap, optically pump or coherently manipulate ions and atoms. They are fabricated or tuned to the required wavelength such that they can be used to excite single photon emitters. To create entangled photon pairs by parametric down conversion one needs a fundamental laser at half the wavelength of the photon pair in order to initiate the conversion process. Frequently, entangled photons in the near infrared around 800 nm are used and hence violet lasers around 400 nm are required. The development and fabrication of lasers in the UV is TOPTICA’s core competence. We were the first company to produce diode laser systems in the UV and offer a variety of systems with different linewidth/coherence characteristics and power levels for scientific research and industry. No other company has a similar product portfolio. Please contact us to find the best laser for your application.


17 Jun Sampling photons to simulate molecules
• Physics 13, 97
A quantum simulator uses microwave photons to tackle a useful chemistry problem—determining the vibronic spectra of molecules.
In 2019, researchers claimed they had achieved an important milestone in quantum computing—the demonstration that a programmable quantum computer can outperform the most powerful classical computer in a specific task . Using Google’s 53-qubit Sycamore quantum processor, they carried out, in just over three minutes, a “sampling” operation that could have taken, according to their estimates, thousands of years on a classical supercomputer. The task, which consisted of sampling the outputs of a random quantum circuit, had previously been identified as a promising testbed for demonstrating this quantum superiority . Alas, sampling isn’t generally linked to applications of any practical relevance. Now, experiments by Christopher Wang at Yale University and colleagues show that a superconducting quantum device manipulating microwave photons can tackle a useful sampling problem—determining the so-called vibronic spectra of small molecules . While the scheme doesn’t yet achieve a quantum advantage, it holds great potential for doing so if further scaled up.
In a vibronic transition, the absorption of a photon by a molecule results in the simultaneous change of both vibrational and electronic energy levels. These transitions are relevant to many important photoinduced molecular processes, including light absorption and emission, photoelectron emission, and Raman scattering. Theoretically, the intensities of these transitions depend on Franck-Condon factors, which quantify the transition probability based on the overlap between the wave functions of the initial and final vibrational states. While there is no definitive mathematical proof that a classical computer can’t reliably calculate these quantities, we know that classical algorithms are inefficient at this task. The difficulty stems from the fact that each vibrational mode of a molecule can’t be considered as an ideal, independent harmonic oscillator—one mode might be coupled to several other modes, for instance. As a consequence, computational complexity rises rapidly with the number of atoms, and even relatively small molecules can be hard to model.
In 2014, Harvard University researchers proposed that the computation of vibronic spectra can be viewed as a sampling problem, which could be simulated with a quantum setup . The result was based on an approach developed in 1977 by theorist Evgeny Doktorov and co-workers, who showed that three physical processes involved in the vibronic transition—molecular structural deformation, vibrational frequency changes, and mixing of vibrational modes—can be interpreted in terms of three quantum optical operators: displacement, squeezing, and rotation, respectively . Using this approach, the Harvard team showed that calculating the vibronic spectrum of a molecule is equivalent to solving a “boson sampling” task . Boson sampling consists in sampling the probability distribution of photons at the output of an optical network.
This idea inspired experimental implementations both with a quantum optical setup [6, 7] and with trapped ions . However, scaling up these quantum simulators to solve meaningful problems faces formidable challenges. Specifically, it requires the generation of hard-to-prepare squeezed states—in which quantum fluctuations in the photon number are reduced compared to conventional coherent light—as well as the simultaneous measurement of the quantum states of a large number of photons.
Following previous theoretical work , Wang and co-workers have now demonstrated experimentally another approach to vibronic-spectra computation based on superconducting microwave circuits. This solution overcomes most of the above-mentioned hurdles by exploiting the remarkable degree of control and tunability of superconducting microwave circuits. Their quantum simulator design consists of an array of superconducting microwave cavities, or resonators, each of which is coupled to the others through so-called transmon qubits (Fig. 1). These qubits allow the researchers to fine-tune the coupling between the resonators. Loosely speaking, each resonator represents one vibrational mode of a molecule, while the tunable coupling mimics the interaction between the modes.
In their proof-of-principle demonstration, the researchers used the photonic modes of two coupled superconducting resonators to simulate the photoelectron spectra of several simple triatomic molecules: water, ozone, nitrogen dioxide, and sulfur dioxide. By driving the transmon qubit at the appropriate frequencies, the researchers produced an interaction between resonators that implemented the rotation, displacement, and squeezing operations necessary to implement the Doktorov approach.
To reconstruct the Frank-Condon profiles of the molecules, the researchers needed to sample the photons in each of the resonators without perturbing them. To do so, they improved a previous quantum nondemolition (QND) scheme. In the scheme, a photon in a cavity can be measured nondestructively through the effect it has on the transition frequency of an “ancillary” qubit coupled to the cavity . This method has proven to work well with single photons but, so far, could not measure larger photon numbers. To address this issue, Wang and collaborators came up with a clever alternative: Using sequential QND measurements, they managed to resolve up to 15 photons in each of the resonators. This number is way beyond what was possible in previous photonic and trapped ion platforms, allowing the device to carry out a task that was challenging for previous simulators—simulating the vibronic spectra of molecules that are in vibrationally excited states.
The current capabilities of this quantum simulator are still far from surpassing those of classical computers for this particular chemistry problem, as the spectra for these triatomic molecules can be calculated more precisely and rapidly with conventional methods. But one can expect that further advances in superconducting circuit technology will soon allow for much more interesting simulations. If the number of anharmonically coupled resonators could be increased to more than ten, for instance, the scheme could already simulate molecules that are challenging for classical computations. More sophisticated circuits could also account for effects that are extremely hard to model classically. First, a tailored photon loss mechanism in the circuit could mimic dissipation in real molecules. Second, Kerr nonlinearity—the dependence of the refractive index on light intensity—could be introduced in the setup to simulate the anharmonic effects that lead to high-order correlations between vibrational modes. With these improvements, the setup could allow researchers to simulate a wealth of molecular processes and effects that are often beyond the reach of classical simulations, including non-Condon transitions, resonant Raman scattering, multiphoton processes, vibrational circular dichroism, conical intersections, open quantum dynamics, and many others.
This research is published in Physical Review X.
- F. Arute et al., “Quantum supremacy using a programmable superconducting processor,” Nature 574, 505 (2019).
- S. Aaronson and A. Arkhipov, “The computational complexity of linear optics,” Proc. ACM STOC 2011 (2011); S. Boixo et al., “Characterizing quantum supremacy in near-term devices,” Nat. Phys. 14, 595 (2018).
- C. S. Wang et al., “Efficient multiphoton sampling of molecular vibronic spectra on a superconducting bosonic processor,” Phys. Rev. X 10, 021060 (2020).
- J. Huh et al., “Boson sampling for molecular vibronic spectra,” Nat. Photon. 9, 615 (2015).
- E. V. Doktorov et al., “Dynamical symmetry of vibronic transitions in polyatomic molecules and the Franck-Condon principle,” J. Molec. Spectrosc. 64, 302 (1977).
- W. R. Clements et al., “Approximating vibronic spectroscopy with imperfect quantum optics,” J. Phys. B 51, 245503 (2018).
- C. Sparrow et al., “Simulating the vibrational quantum dynamics of molecules using photonics,” Nature 557, 660 (2018).
- Y. Shen et al., “Quantum optical emulation of molecular vibronic spectroscopy using a trapped-ion device,” Chem. Sci. 9, 836 (2018).
- B. Peropadre et al., “Proposal for microwave boson sampling,” Phys. Rev. Lett. 117, 140505 (2016).
- B. R. Johnson et al., “Quantum non-demolition detection of single microwave photons in a circuit,” Nat. Phys. 6, 663 (2010).


Famed physicist Stephen Hawking proposed in 1974 that very small amounts of high-energy radiation, in the form of entangled particle pairs, known as Hawking radiation, could theoretically escape a black hole. This was controversial as it went against the conventional understanding that nothing, not energy or light, could escape a black hole. Since 1981, however, when physicist William Unruh discovered that fluid flows could mimic black holes, the hunt for this elusive process has driven researchers to create analogue black holes to test the possibilities of particles behaving unusually at a black hole’s event horizon.
Though so far it has not been possible to create a true black hole in a lab, researchers have used sound waves to make “dumb” or acoustic black holes since 2009. In 2015, Jeff Steinhauer, a physicist at the Israel Institute of Technology in Haifa, who has been working on these black holes for the past seven years, is the first researcher to claim to have seen Hawking radiation in his lab-made, analogue black hole.
Acoustic black hole use sound waves—phonons—not photons, by cooling rubidium atoms to barely above zero. The atoms then share a “quantum connection,” says Steinhauer, “so that even when they are far apart, they still have a connection to each other, known as quantum entanglement, where the pair of atoms mimic each other’s behavior, clumping up to form a Bose-Einstein condensate (BEC). He explains, “[The BEC] flows faster than the speed of sound, which means a sound wave trying to go against the flow falls back, which is analogous to a photon trying to escape a black hole.” He compares this to trying to swim against the direction of a river’s flow. “The river flows faster than you can swim, so you feel like you’re flowing forward, but you’re actually falling back.” This, he says, is like the sound waves, which are analogous to a light wave trying to escape a black hole.”
Hawking radiation makes the case that the universe is teeming with entangled particles. These particle pairs each contain an electron with a negative charge and a positron with a positive charge, which pop in and out of existence. If they come in contact, they will destroy each other, with one exception: if they should happen to appear at a black hole’s event horizon. There, he theorized, one particle falls into the hole, and the other dissipates into
space. This assumes that when the black hole eventually loses mass and evaporates, it also takes all the particles or “information” that fell into it with it, essentially destroying it. Steinhauer says the problem with this, which is known as the black hole information paradox, is that, “There’s a law of quantum mechanics that says information can’t be destroyed. So when information falls into a black hole, is it destroyed or does it exist in the hawking radiation coming out or somewhere else?”
Hawking published a theoretical solution to this problem earlier this year, suggesting that black holes may have a halo of soft hair around them capable of storing information, but no one knows for sure.
Others have theorized that the information is, in fact, contained in the Hawking radiation coming out of the black hole itself, which is what causes it to lose mass over time and dissipate. However Steinhauer argues that this conflicts with existing laws of physics, saying, “my work says there is a problem with that solution because outgoing particles are already entangled with in-falling particles, so they can’t be entangled with others,” he says.
Steinhauer and his research team ran their experiment 4600 times for six days straight, taking photos each time of the BEC to form a composite known as a “correlation function.” The composite image shows a very thin gray band, which, he says “means there are correlations between a point inside the black hole and outside the black hole. Waves are emitted from the horizon. The correlations between the waves falling in and coming out lets us see it.” Moreover, it’s the fact that the particles are in pairs that allow researchers to see that line. “My theoretical paper says if the gray band is narrow, the particles are entangled. They found that only high energy pairs were entangled, while low energy pairs were not. I knew immediately they were.” Thus, he is confident that he was seeing Hawking radiation for the first time.
In addition, the particles coming out of the acoustic black hole’s event horizon produced so much energy, their experiment may support “the firewall controversy”—yet another
hypothesis that suggests that the effort of breaking the entanglement between the Hawking particles and their partners creates actual flames at the edge of a black hole. “So I saw that the particles really were entangled in my black hole, which implied that there really is an issue to solve and one of the possible ways would be a firewall. It would naturally occur to preserve the laws of physics,” says Steinhauer.
While Steinhauer’s research team is understandably excited, the scientific community isn’t yet leaping up to confirm Hawking radiation yet, which will require further experiments to see if it can be replicated.
No one has ever created an actual black hole in a lab, says Harry E. Keller, PhD, President, Chief Science Officer and Founder of Smart Science Education. Nor has anyone been able to see Hawking radiation in space in a true black hole, which would make Hawking an instant candidate for a Nobel Prize. “Were such an artifact to be made, it would be so dangerous that it could swallow up our planet along with all of us.” Instead, this BEC, which he refers to as “a new state of matter beyond the usual gas, liquid, solid, and plasma” is in his estimation not a good enough analogue of a true black hole. He compares it to “playing with magnets to figure out how planetary systems work.” He continues, “The analogue experience might mimic the quantum mechanics of black holes and Hawking radiation, or it might not,” he says. “It’s still interesting in its own right.”
Steinhauer thinks it is more than a little bit interesting. “The point of seeing Hawking radiation is not to learn about black holes but to understand what the new laws of physics are.” Hawking was the first to combine gravity with quantum field theory to come up with the idea of Hawking radiation in the first place. “This combination is considered a first step on the road to a theory of quantum gravity,” Steinhauer says. “People have many ideas but nobody’s sure whose ideas are right.”


Diffie–Hellman key exchange (DH) is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman. DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography.
Traditionally, secure encrypted communication between two parties required that they first exchange keys by some secure physical means, such as paper key lists transported by a trusted courier. The Diffie–Hellman key exchange method allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure channel. This key can then be used to encrypt subsequent communications using a symmetric key cipher.
DH has been widely used on the Internet for improving the authentication encryption among parties. The only note is it useful if both the communication sides A and B are at your control, as what DH does is just strenghten the already established connection between client A and B and not protect from Man in the Middle Attacks. If some malicious user could connect to B pretending it is A the encryption will be established.
Alternatively, the Diffie-Hellman key exchange can be combined with an algorithm like the Digital Signature Standard (DSS) to provide authentication, key exchange, confidentiality and check the integrity of the data. In such a situation, RSA is not necessary for securing the connection.
TLS, which is a protocol that is used to secure much of the internet, can use the Diffie-Hellman exchange in three different ways: anonymous, static and ephemeral. In practice, only ephemeral Diffie-Hellman should be implemented, because the other options have security issues.
Anonymous Diffie-Hellman – This version of the Diffie-Hellman key exchange doesn’t use any authentication, leaving it vulnerable to man-in-the-middle attacks. It should not be used or implemented.
Static Diffie-Hellman – Static Diffie-Hellman uses certificates to authenticate the server. It does not authenticate the client by default, nor does it provide forward secrecy.
Ephemeral Diffie-Hellman – This is considered the most secure implementation because it provides perfect forward secrecy. It is generally combined with an algorithm such as DSA or RSA to authenticate one or both of the parties in the connection.
Ephemeral Diffie-Hellman uses different key pairs each time the protocol is run. This gives the connection perfect forward secrecy, because even if a key is compromised in the future, it can’t be used to decrypt all of the past messages.
DH encryption key could be generated with the openssl command and could be generated depending on your preference using a 1024 / 2048 or 4096 bit encryption.
Of course it is best to have the strongest encryption possible i.e 4096.
The Logjam attack
The Diffie-Hellman key exchange was designed on the basis of the discrete logarithm problem being difficult to solve. The most effective publicly known mechanism for finding the solution is the number field sieve algorithm.
The capabilities of this algorithm were taken into account when the Diffie-Hellman key exchange was designed. By 1992, it was known that for a given group, G, three of the four steps involved in the algorithm could potentially be computed beforehand. If this progress was saved, the final step could be calculated in a comparatively short time.
This wasn’t too concerning until it was realized that a significant portion of internet traffic uses the same groups that are 1024 bits or smaller. In 2015, an academic team ran the calculations for the most common 512-bit prime used by the Diffie-Hellman key exchange in TLS.
They were also able to downgrade 80% of TLS servers that supported DHE-EXPORT, so that they would accept a 512-bit export-grade Diffie-Hellman key exchange for the connection. This means that each of these servers is vulnerable to an attack from a well-resourced adversary.
The researchers went on to extrapolate their results, estimating that a nation-state could break a 1024-bit prime. By breaking the single most-commonly used 1024-bit prime, the academic team estimated that an adversary could monitor 18% of the one million most popular HTTPS websites.
They went on to say that a second prime would enable the adversary to decrypt the connections of 66% of VPN servers, and 26% of SSH servers. Later in the report, the academics suggested that the NSA may already have these capabilities.
“A close reading of published NSA leaks shows that the agency’s attacks on VPNs are consistent with having achieved such a break.”
Despite this vulnerability, the Diffie-Hellman key exchange can still be secure if it is implemented correctly. As long as a 2048-bit key is used, the Logjam attack will not work. Updated browsers are also secure from this attack.
Is the Diffie-Hellman key exchange safe?
While the Diffie-Hellman key exchange may seem complex, it is a fundamental part of securely exchanging data online. As long as it is implemented alongside an appropriate authentication method and the numbers have been selected properly, it is not considered vulnerable to attack.
The Diffie-Hellman key exchange was an innovative method for helping two unknown parties communicate safely when it was developed in the 1970s. While we now implement newer versions with larger keys to protect against modern technology the protocol itself looks like it will continue to be secure until the arrival of quantum computing and the advanced attacks that will come with it.
Here is how easy it is to add this extra encryption to make the SSL tunnel between A and B stronger.
On a Linux / Mac / BSD OS machine install and use openssl client like so:
# openssl dhparam -out dhparams1.pem 2048
Generating DH parameters, 2048 bit long safe prime, generator 2
This is going to take a long time
Be aware that the Diffie-Hellman key exchange would be insecure if it used numbers as small as those in our example. We are only using such small numbers to demonstrate the concept in a simpler manner.
# cat dhparams1.pem
—–BEGIN DH PARAMETERS—–
—–END DH PARAMETERS—–
Copy the generated DH PARAMETERS headered key string to your combined .PEM certificate pair at the end of the file and save it
# vim /etc/haproxy/cert/ssl-cert.pem
—–BEGIN DH PARAMETERS—–
—–END DH PARAMETERS—–
Restart the WebServer or Proxy service wher Diffie-Hellman key was installed and Voila you should a bit more secure.


What is quantum physics? Put simply, it’s the physics that explains how everything works: the best description we have of the nature of the particles that make up matter and the forces with which they interact.
Quantum physics underlies how atoms work, and so why chemistry and biology work as they do. You, me and the gatepost – at some level at least, we’re all dancing to the quantum tune. If you want to explain how electrons move through a computer chip, how photons of light get turned to electrical current in a solar panel or amplify themselves in a laser, or even just how the sun keeps burning, you’ll need to use quantum physics.
The difficulty – and, for physicists, the fun – starts here. To begin with, there’s no single quantum theory. There’s quantum mechanics, the basic mathematical framework that underpins it all, which was first developed in the 1920s by Niels Bohr, Werner Heisenberg, Erwin Schrödinger and others. It characterises simple things such as how the position or momentum of a single particle or group of few particles changes over time.
But to understand how things work in the real world, quantum mechanics must be combined with other elements of physics – principally, Albert Einstein’s special theory of relativity, which explains what happens when things move very fast – to create what are known as quantum field theories.
Three different quantum field theories deal with three of the four fundamental forces by which matter interacts: electromagnetism, which explains how atoms hold together; the strong nuclear force, which explains the stability of the nucleus at the heart of the atom; and the weak nuclear force, which explains why some atoms undergo radioactive decay.
Over the past five decades or so these three theories have been brought together in a ramshackle coalition known as the “standard model” of particle physics. For all the impression that this model is slightly held together with sticky tape, it is the most accurately tested picture of matter’s basic working that’s ever been devised. Its crowning glory came in 2012 with the discovery of the Higgs boson, the particle that gives all other fundamental particles their mass, whose existence was predicted on the basis of quantum field theories as far back as 1964.
Conventional quantum field theories work well in describing the results of experiments at high-energy particle smashers such as CERN’s Large Hadron Collider, where the Higgs was discovered, which probe matter at its smallest scales. But if you want to understand how things work in many less esoteric situations – how electrons move or don’t move through a solid material and so make a material a metal, an insulator or a semiconductor, for example – things get even more complex.
The billions upon billions of interactions in these crowded environments require the development of “effective field theories” that gloss over some of the gory details. The difficulty in constructing such theories is why many important questions in solid-state physics remain unresolved – for instance why at low temperatures some materials are superconductors that allow current without electrical resistance, and why we can’t get this trick to work at room temperature.
But beneath all these practical problems lies a huge quantum mystery. At a basic level, quantum physics predicts very strange things about how matter works that are completely at odds with how things seem to work in the real world. Quantum particles can behave like particles, located in a single place; or they can act like waves, distributed all over space or in several places at once. How they appear seems to depend on how we choose to measure them, and before we measure they seem to have no definite properties at all – leading us to a fundamental conundrum about the nature of basic reality.
This fuzziness leads to apparent paradoxes such as Schrödinger’s cat, in which thanks to an uncertain quantum process a cat is left dead and alive at the same time. But that’s not all. Quantum particles also seem to be able to affect each other instantaneously even when they are far away from each other. This truly bamboozling phenomenon is known as entanglement, or, in a phrase coined by Einstein (a great critic of quantum theory), “spooky action at a distance”. Such quantum powers are completely foreign to us, yet are the basis of emerging technologies such as ultra-secure quantum cryptography and ultra-powerful quantum computing.
But as to what it all means, no one knows. Some people think we must just accept that quantum physics explains the material world in terms we find impossible to square with our experience in the larger, “classical” world. Others think there must be some better, more intuitive theory out there that we’ve yet to discover.
In all this, there are several elephants in the room. For a start, there’s a fourth fundamental force of nature that so far quantum theory has been unable to explain. Gravity remains the territory of Einstein’s general theory of relativity, a firmly non-quantum theory that doesn’t even involve particles. Intensive efforts over decades to bring gravity under the quantum umbrella and so explain all of fundamental physics within one “theory of everything” have come to nothing.
Meanwhile cosmological measurements indicate that over 95 per cent of the universe consists of dark matter and dark energy, stuffs for which we currently have no explanation within the standard model, and conundrums such as the extent of the role of quantum physics in the messy workings of life remain unexplained. The world is at some level quantum – but whether quantum physics is the last word about the world remains an open question. Richard Webb


The recent trends in information technology and communications have emerged as one of the main technological pillars of the modern age. The importance of cryptography has gained importance due to the requirement of security services (confidentiality, integrity, authenticity, and non-repudiation) in data storage/transmission.
Quantum computing, first introduced as a concept in 1982, has now become a nightmare for the currently deployed cryptographic mechanism. Extensive research has been done on quantum platforms to resolve complex mathematical problems, which are intractable for traditional computing platforms. The formalization of such quantum computing platforms poses serious threats to the cryptographic algorithms. This article informs the reader about the implications/repercussions of quantum computing on the present cryptography in detail.
Types of Cryptographic Algorithms
Three categories of cryptographic algorithms exist based on the number of cryptographic keys required as input for the algorithm.
- No Key - Hash Functions
- One Key - Symmetric Algorithms
- Two Keys - Asymmetric Algorithms
Hash algorithms transform a large random size input to a small fixed size output. The output calculated by the hash algorithm is referred to as a digest or hash value. Operation of the hash algorithms does not require any cryptographic key and securely operates in a one-way manner. The one-way process means that it is cryptographically and technically impossible to compute the input data from output data. There are two categories of hash algorithms based on their design:
- Hash algorithms based on Mathematical Problems: In the first category are those functions whose designs are based on a mathematical problem, and thus their security follows from rigorous mathematical proofs, complexity theory, and formal reduction. These functions are called Provably Secure Cryptographic Hash Functions. However, this does not mean that such a function could not be broken. Constructing them is very difficult, and only a few examples were introduced. Therefore, their practical use is limited.
- Hash Algorithms based on Confusion/Diffusion: In the second category are functions that are not based on mathematical problems, but on an ad hoc basis, where the bits of the message are mixed to produce the hash. They are then believed to be hard to break, but no such formal proof is given. Almost all widely spread hash functions fall in this category. Some of these functions are already broken and are no longer in use.
Symmetric algorithms are also known as secret key algorithms that employ one single cryptographic key for encryption/decryption mechanisms. Only the sender and receiver know the symmetric key. The further categorization of symmetric algorithms includes:
- Block Algorithms: A block algorithm breaks the input into fixed-size blocks and then process the crypto operations. Popular block algorithms are the Advanced Encryption Standard (AES) and the Data Encryption Standard (3DES).
- Stream Algorithms: Stream algorithms perform “bit-by-bit” crypto operations. The most commonly used stream algorithms are RC4, A5/1, A5/2, and Chameleon, etc.
Current Security of Symmetric & Hash Algorithms
The security of the symmetric and hash algorithms is based on the fact that the key range is extensive and a brute force attack (attempting all the possible/potential keys) is not possible because of limited computational power and time constraints.
The Advent of Quantum Computing
Quantum computers have threatened the cryptographic mechanisms behind the current secure communication standards and protocols because quantum computers can perform calculations/computations at a rate that cannot be achieved through conventional/traditional computing systems. Traditional computing systems are based on the vital blocks known as bits and can have only two states, 0 and 1. Quantum computing platforms are based on quantum bits, also known as qubits. Qubits can hold the state 0, 1, and both simultaneously. This property is known as superposition. The effect of quantum computing can be calculated in two directions:
- The solution of Complex/Hard problems: Due to the advantage of the superposition property, quantum computing platforms can solve hard and complex mathematical problems that are the security standpoints of various cryptographic algorithms.
- The exponential increase in Calculations: Some cryptographic algorithms, such as symmetric and hash are based on the fact that a brute-force attack is infeasible. Quantum computers can definitely affect these algorithms by exhaustively searching for all secret keys.
Quantum Platforms & Grover’s Algorithm
The main threat to the security of symmetric and hash algorithms is Grover’s algorithm. This algorithm utilizes the quantum computing platform to search through unsorted databases to find a particular entry in √N searches from an unsorted DB of N entries. Meanwhile, traditional computing platforms search for the same in N/2 searches.
Threats to Symmetric Algorithms from Quantum Computing
The Grover’s algorithm implementation on quantum platforms poses a serious threat to symmetric key algorithms by accelerating the speed of an exhaustive key search attack or brute force attack on symmetric algorithms so that the cryptographic key length is reduced by 50%. For an n-bit symmetric cryptographic algorithm, 2n possible keys exist. For the 128-bit AES algorithm, the key range is 2128, which is unbreakable using current computing platforms. After the formalization of a quantum platform and the implementation of Grover’s algorithm, the AES 128-bit key size will be reduced to an insecure 64-bit equivalent key length just like the 64-bit DES algorithm. Luckily, AES supports two other key lengths, and the applications would have to switch to the 192-bit and 256-bit versions of AES algorithms.
Threats to Hash Algorithms from Quantum Computing
Hash algorithms will also suffer from Grover’s Algorithm because they produce a fixed-size output of any random-sized input. The augmented speed of Grover’s algorithm can be used to expedite the collision-attack, which means finding two inputs with the same output. Similarly, the implementation of quantum-based platforms will be a problem for the Hash algorithms. However, because SHA-2 (256-bits) and SHA-3 (384-bits) have quite longer outputs, they appear to remain quantum-resistant.


Will Fusion Energy Power The Future?
Fusion Energy: The Next Power Revolution?
Fusion refers to a form of energy generation. It’s sometimes known as nuclear fusion, and it’s the opposite of nuclear fission (which powers nuclear reactors). Fusion energy holds a great deal of promise for humanity.
While nuclear fission produces energy by splitting an atom, fusion reactors fuse two light atoms into an heavier one. This release huge amounts of energy. Fusion energy is what powers the sun and other stars. Essentially, stars are actually huge fusion reactors.
Fusion Energy: How It Works
Despite what you learned in high school science classes, there are actually four fundamental types of matter. In addition to solids, liquids, and gases, there is also plasma. But, since plasma doesn’t occur naturally on Earth, we don’t often consider it. Plasma is a special electrically-charged, or ionized, gas. Plasma behaves differently than other types of matter, although the mechanics can be hard to understand.
For our purposes, it’s enough to know that plasma only occurs at low pressures and high temperatures. Usually, it’s created through the use of electromagnetic fields.
Fusion energy is created when special forms of hydrogen, know as deuterium and tritium, are heated to enormously hot temperatures. The only way to contain the plasma so far as we know is to use magnetic fields. Unfortunately, scientists are struggling to create a reactor that works. Current versions can’t hold the plasma for an extended period of time at sufficient temperature and size.
Which leads us to…
Fusion Energy: The Challenges
Fusion energy is the type of technology that is still faced with certain engineering barrier, much like the space elevator.
Currently, every type of fusion reactor design ends up having a negative energy balance. In short, this means that the reactor takes more energy to run then it produces.
This is because fusion plasma doesn’t like to be contained. We have to contain them at high pressures and temperatures over long enough period of time to actually generate energy. Otherwise the massive amount of energy spent making the plasma doesn’t get earned back.
Stars, like the sun, are able to contain plasma with their massive gravity. That’s why massive plasma flares on the surface of the sun end up being subsumed back into the sun. Germany recently brought online it’s Wendelstein X-7 Stellarator. This is expected to run for up to 30 minutes at a time, which would blow the current record of 102 seconds away. But the device in Germany was never intended to be net-positive on energy. Rather, it was meant to show proof of concept of fusion energy.
So faced with all these challenges, why do we still pursue fusion?
Fusion Energy: Applications
Because in many ways, fusion would be an almost perfect source of energy. The fuel itself, which is mostly deuterium, is found abundantly in Earth’s ocean. One out of every 6,500 hydrogen atoms in the ocean is deuterium. While that may not seem like a lot, there are literally trillions upon trillions of these atoms in the ocean. Furthermore, fusion produced so much more energy than other sources that not much would be needed to generate massive amounts of power.
And even though fusion energy isn’t technically renewable, it has many of its benefits. It emits no air pollution or greenhouse gas and much less radiation than fission. Unlike other renewable sources, it’s not dependent on weather or location either. Because of this it won’t suffer from either diseconomies of scale or power interruption.
And since solar energy isn’t available in interstellar space, fusion is a possible enabling technology for space-faring.
Building the Fusion Energy Reactor
The most promising solution to the problems facing fusion energy is the tokamak. Tokamak originally comes from a complicated Russian acronym, so sticking with tokamak is fine. The word is pretty awesome on its own. Essentially, the tokamak is a device that harnesses a powerful magnetic field to confine plasma in a torus. A torus is a fancy geometry term for a donut. You can see a torus in the picture above.
Tokamak technology is what is being used in ITER, discussed below.
However, recently a group of scientists say they think they’ve found a different solution. They designed a bizarre spherical reactor that could theoretically achieve net-positive nuclear fusion. This could be the key to commercially available fusion energy.
Their reactor would use hydrogen and boron instead. It also leverages lasers to “heat up the core to 200 times hotter than the center of the Sun.” The team that released the study believes it could be built sooner than any current design. In fact ,they think that pending any unexpected engineering issues, such a reactor could be built within a decade. It also pointed out that their process would produce no radioactive waste at all.
Is Fusion the Future?
That remains to be decided. Like the space elevator, we have some significant technological hurdles. But given the possibilities, it’s likely that scientists and governments will keep trying.
While the laser project discussed above is interesting, it’s still mostly conceptual.
ITER, or the International Thermonuclear Experimental Reactor, is the largest current nuclear fission project. It’s an international engineering megaproject. When it’s completed, it will be the world’s first fully functioning fusion reactor. It’s being supported by more than thirty-five nations including the USA, China, India, Japan and Russia. Construction began in earnest in 2008 in France.
Currently, the facility plans to complete construction by 2021. It will then aim to achieve plasma by 2025 and be operational by 2035.
Interestingly, scientists and governments are already planning the next generation project. DEMO, or DEMOnstratio Power Station, will build upon the ITER experimental fusion reactor. It will be the link between ITER and true commercially available fusion power. The hope is that the DEMO system will be operational before 2050.
Like other ambitious project – such as the Human Genome Project – the process will become cheaper and more efficient as time goes on. Because technology is designed, improved, and refined during the experimental stage, each subsequent experiment is easier.
Clean, cheap, plentiful energy could take human civilization to the next stage. It might even be one of the final steps before we can become a spacefaring species.
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For the first time, scientists have demonstrated laser communications between a microsatellite and a ground station while using the quantum nature of photons to secure the data being transmitted.
The work, carried out by researchers at the National Institute of Information and Communications Technology (NICT) in Japan and recently published in the journal Nature Photonics, demonstrates an "unhackable" quantum communications technology known as Quantum Key Distribution, or QKD.
As the world edges closer to quantum computing, current methods of securing transmitted data may be rendered obsolete so a new method to secure data will be required, the researchers argue. [Twisted Physics: 7 Mind-Blowing Findings]
"The main advantage [of QKD] is the unconditional security," team leader Alberto Carrasco-Casado told Space.com. "When quantum computers are developed, the security of conventional communications will be compromised, since current cryptography is based only on computational complexity.
"The development of practical quantum computers is only a matter of time, which has made quantum communication a hot topic in the last few years, and the tendency is foreseen to increase in the future," he added.
QKD is a very attractive method to totally secure communications. By recording data in the quantum states of individual photons, the process ensures that should the signal be intercepted, the quantum states will change — causing the recipient of the signal to be alerted of the breach.
This is a basic tenet of quantum mechanics, based on Heisenberg's uncertainty principle; one cannot simply observe a quantum particle (in this case a photon) without irrevocably changing that particle's quantum state. With QKD, a secret key is shared between the transmitter and receiver. If a hacker tries to decode the signal as it travels from one to the other, the signal itself changes on a quantum level. So the system detects the hacking event, the secret key is discarded and the signal is broken, preventing the hack from continuing.
To demonstrate this secured, high-capacity transmission of data between an Earth-based station and a satellite in low-Earth orbit (LEO), Carrasco-Casado's team used the quantum-communication transmitter, called SOTA (Small Optical TrAnsponder), on board the microsatellite SOCRATES (Space Optical Communications Research Advanced Technology Satellite) that was launched by the Japan Aerospace Exploration Agency (JAXA) in 2014.
Weighing only 13 lbs. (6 kilograms), SOTA is the smallest quantum communications transmitter ever tested. Orbiting above Earth at 372 miles (600 kilometers), SOCRATES was traveling at over 15,000 mph (7 kilometers per second) when SOTA would establish contact with a 1-meter telescope located in Tokyo's Koganei city. The received signal was then guided to a quantum receiver to decode the information using a QKD protocol, the researchers wrote in their study.
SOTA encoded the individual photons with 1 bit of data — either a "1" or a "0" — achieved by switching the photons between two polarized states — a method known as a "single-photon regime." SOTA then beamed pulses of laser at a rate of 10 million bits per second. On reaching the ground station, the laser signal was extremely weak (the researchers say that, on average, only 0.1 laser photons were received per pulse), but the quantum receiver was still able to detect the signal and decode the information over a low level of noise.
Now that the technology has been demonstrated using a microsatellite, Carrasco-Casado said he is thinking about future applications.
"Maybe the most exciting application would be applying QKD to satellite constellations," he said. "Several constellations are now being considered with a huge number of satellites … SpaceX constellation plans to use over 4,000 satellites. If QKD can be miniaturized following the heritage of SOTA, this technology could be spread massively, enabling a truly-secure global communication network."
The SOCRATES/SOTA mission ended in September 2016 after the satellite failed, Carrasco-Casado added, but the experiment had more than doubled the originally designed mission duration of over a year. "We are working on other future missions that will leverage the expertise and knowledge acquired with the SOCRATES/SOTA mission," he said.
There is international interest in quantum communications, with research being carried out in Japan, China, Europe, Canada and the U.S.
A Chinese research team recently announced the successful quantum teleportation of individual photons from a ground station to the orbiting satellite Micius, which was launched by China last year. Like QKD, teleportation is a form of quantum communications. Teleportation involves the production of two quantum particles that form at the same time, in the same place — the two particles share the same quantum states, and measurements on one impact the other instantaneously. They are "entangled."
In the Chinese experiment, pairs of entangled photons were produced on the ground, and some of the photons were transmitted to the ultra-sensitive receiver on Micius orbiting overhead. When the photons were received by the satellite, the researchers were able to confirm entanglement with those on the ground by "teleporting" the quantum state of a photon between the two, over hundreds of miles.
"This work establishes the first ground-to-satellite up-link for faithful and ultra-long-distance quantum teleportation, an essential step toward global-scale quantum internet," the researchers wrote in their study, which was posted on the ArXiv preprint repository.
As low-Earth orbit becomes more crowded, competition for the shrinking availability of radio frequency (RF) bands will eventually create a communications bottleneck, Carrasco-Casado's team said in a statement, so quantum communications solutions using laser technology will be needed not only to transmit data secured against hacking attempts, but also to send much larger quantities of data in a smaller space, as laser transmission allows.


In the world of computers, silicon is king. The semiconducting element forms regular, near-perfect crystals into which chipmakers can carve the hundreds of millions of features that make the microchips that power the processors. Technological improvements let chipmakers cut the size of those features in half every 18 months-a feat known as Moore’s law, after Intel cofounder Gordon Moore. Today, that size hovers around 180 nanometers (180 billionths of a meter), and researchers expect to push below 50 nanometers within a decade. But that’s about as far as silicon can go: below that quantum physics makes electrons too unruly to stay inside the lines. If computers are to keep up with Moore’s law, they will have to move beyond silicon. After a couple of decades of theorizing, computer scientists, bioengineers and chemists in the mid-1990s began lab experiments seeking alternative materials for future CPUs and memory chips. Today, their research falls into three broad categories: quantum, molecular and biological computing.
In the field of quantum computing, researchers seek to harness the quantum effects that will be silicon’s undoing. Scientists succeeded in making rudimentary logic gates out of molecules, atoms and sub-atomic particles such as electrons. And incredibly, other teams have discovered ways to perform simple calculations using DNA strands or microorganisms that group and modify themselves.
Molecular Building Blocks
In one type of molecular computing (or nanocomputing), joint teams at Hewlett Packard Co. and UCLA sandwich complex organic molecules between metal electrodes coursing through a silicon substrate. The molecules orient themselves on the wires and act as switches. Another team at Rice and Yale universities has identified other molecules with similar properties.
Normally, the molecules won’t let electrons pass through to the electrodes, so a quantum property called tunneling, long used in electronics, is manipulated with an electric current to force the electrons through at the proper rate. If researchers can figure out how to lay down billions of these communicating molecules, they’ll be able to build programmable memory and CPU logic that is potentially millions of times more powerful than in today’s computers.
Molecular researchers like the HP/UCLA team, however, face a challenge in miniaturizing their current wiring technology-nanowires made from silicon strands-from several hundred to approximately 10 nanometers. Carbon nanotubes are promising substitutes. The rigid pipes make excellent conductors, but scientists must figure out how to wrangle them into the latticework needed for complex circuitry. “We’ve shown that the switching works,” says HP computer architect Philip Kuekes. “But there is still not as good an understanding of the basic mechanism so that an engineer can design with it.” Hewlett Packard and UCLA have jointly patented several techniques for manufacturing of molecular computers, most recently in January of 2002.
Although molecular circuits employ some quantum effects, a separate but related community of scientists is exploring the possibilities of quantum computing-computing with atoms and their component parts. It works from the notion that some aspect of a sub-atomic particle-say, the location of an electron’s orbit around a nucleus-can be used to represent the 1s and 0s of computers. As with molecules, these states can be manipulated-programmed, in effect.
One approach pursued by members of a national consortium involving Berkeley, Harvard, IBM, MIT and others, involves flipping the direction of a spinning electron to turn switches on or off. By applying electromagnetic radiation in a process called nuclear magnetic resonance (NMR) like that used in medical imaging, researchers can control the spin of the carbon and hydrogen nuclei in chloroform. Alternatively, filters and mirrors show promise for controlling photons’ light as a switching mechanism. Other researchers work with materials such as quantum “dots” (electrons in silicon crystal), and “ion traps” (ionized atoms suspended in an electrical field).
Quantum bits (qubits) have an unusual quality that makes them a double-edge sword for computing purposes, though. Due to the lack of determinism inherent in quantum mechanics, qubits can be on or off simultaneously, a phenomenon called superposition. This makes it harder to force qubits into digital lockstep, but it also multiplies exponentially the amount of information groups of qubits can store. It theoretically allows massively parallel computation to solve problems previously thought uncomputable, such as factoring large prime numbers. One implication: today’s encryption techniques depend on the unfeasibility of computing the two multipliers (factors) of certain numbers, so quantum computers may one day be able to crack most encrypted files that exist today. This possibility has given the research a boost from government agencies, including the National Security Agency.
To be manufacturable, quantum computers will require billions of such sub-atomic switches working together and interacting with their environments without falling into a disorganized state called decoherence. A quantum state called entanglement-where many atoms are made to behave exactly alike-provides one possible solution. Researchers also hope to fight decoherence by harnessing a phenomenon called interference, that is, the overlapping of quantum particles’ wavelike energy.
Getting Down to the Biology
In addition to molecular and quantum computing, a third approach, biological computing, relies on living mechanism to perform logic operations.
Bioengineers have long understood how to manipulate genes to function as switches that activate other genes. Now they’re using the technique to build rudimentary computer “clocks” and logic gates inside bacteria such as E. coli. Other researchers use genes to prod microorganisms into states that represent information. A team headed by Thomas Knight at the MIT Artificial Intelligence Laboratory genetically manipulates luciferase, an enzyme in luminescent creatures such as fireflies, to generate light that serves as a medium of cell-to-cell communication.
One of biological computing’s biggest challenges is calculating with elements that are flawed, unreliable and decentralized. To that end, Knight’s amorphous computing group studies ways to encourage bacteria to organize themselves into parallel-processing computers. “I don’t think of it as likely to be the path to making conventional computers,” Knight says. “It will be the way in which we build the molecular-scale computers.”
Molecular computers face similar reliability challenges. At HP, researchers used fault-tolerant algorithms to construct a silicon-based computer called Teramac that worked despite having 220,000 defects. Kuekes, Teramac’s project manager, says the company is now exploring ways to translate what they’ve learned to molecular computing.
Farther out on the biological curve is DNA computing, which attempts to exploit the way DNA strands recognize each other and combine into structures that could perform large, compute-intensive calculations in parallel.
Few in the biological community expect biocomputers to replace the general-purpose silicon computer. They hope instead to manufacture molecular computers cheaply and efficiently with organisms that can orient themselves into logic circuits or transform vats of chemicals to manufacture other chemicals.
Still more exciting possibilities come from the potential of special-purpose biological computers to interact with other biological systems. Miniature computers could be injected into living tissue to reprogram cancer-causing genes, for example, or administer insulin shots.
For now, all these applications loom distant on the horizon. But researchers agree that silicon’s days are numbered, and that radical new approaches will be needed to keep computers zooming through the 21st century.