Hue-ing to quantum computingBy Eric Smalley, Technology Research News
The starting gun has sounded in the marathon of developing solid-state quantum computers, and one lead team jockeying for position is betting that shining different color lasers on impure diamonds will get them across the finish line.
The researchers are building their quantum computer using spectral hole burning, which tunes atoms or molecules trapped in a transparent solid to specific light wavelengths, or colors.
The researchers have tuned nitrogen atoms embedded in diamond to a range of slightly different wavelengths, said Selim M. Shahriar, a research scientist in the Research Laboratory of Electronics at the Massachusetts Institute of Technology. The differences in color are imperceptible to humans, he added.
Each atom is tuned to two wavelengths. If a laser beam of one of the wavelengths hits it, the atom will emit light of the other wavelength, Shahriar said. In addition, a pair of atoms each tuned to two wavelengths can be linked to each other. For example, if atom A is tuned to wavelengths 1 and 2 and atom B is tuned to wavelengths 2 and 3 and the atoms are hit with lasers tuned to wavelengths 1 and 3, both atoms emit light of wavelength 2, he
This allows the atoms to be coupled by quantum entanglement. When two atoms are entangled, a change in the state of one is immediately reflected by a corresponding change in the other regardless of the physical distances between the atoms.
An atom can serve as a quantum bit, or qubit, because it spins in one of two directions, and its spins can represent the ones and zeros of binary computing. Because isolated bits are of little use, linking atoms is a prerequisite for quantum computing.
The researchers expect their spectral hole burning technique to yield 300 or more qubits, Shahriar said. That number is significant because a 300-qubit quantum computer would be able to factor numbers larger than any conventional computer will likely ever be able to handle.
"The experiment is already in progress. We have already demonstrated that each atom has the two-color response that we need. We have already demonstrated how we can line [the atoms] all up to be spinning in the same direction. That's the starting point of the quantum computer," Shahriar said.
How long the qubits last is as important as the number of qubits. Qubits are fragile because the slightest influence from the outside environment can knock the atoms out of their quantum state. The nitrogen-infused diamond spectral hole burning technique would probably last long enough to yield 40,000 quantum operations, Shahriar said.
"You need to be able to do more operations, but there are ways to increase that number," he said.
The other early favorites in the race for solid-state quantum computing are techniques based on superconductors, electron spins in quantum dots and nuclear spins in semiconductors.
"It's very important to pursue a lot of different things at this stage because it's very unclear exactly what type of hardware is going to be useful in the long run," said John Preskill, professor of theoretical physics and director of the Institute for Quantum Information at the California Institute of Technology. "So it's a healthy thing that there are a lot of different ideas floating around, spectral hole burning being one of them."
The first step toward solid-state quantum computers is demonstrating good control over a qubit in a system "which has at least the potential to be scaled up," Preskill said.
Other researchers have demonstrated seven-qubit systems using nuclear magnetic resonance (NMR). However, NMR techniques are not expected to scale up significantly, hence the race to develop solid-state quantum computing. Solid-state devices are based on semiconductors or other crystalline solids.
Schemes that are good candidates for quantum computing should support reliably readable results, reliable preparation of the initial states of their qubits, and logic gates with good fidelity, Preskill said. NEC researchers in Japan have gone the furthest in solid-state quantum computing with a superconducting implementation in which they have established a qubit, he said.
The nitrogen-diamond spectral hole team is in the last year of a three-year project to establish the viability of the technique, Shahriar said.
"We expect to demonstrate quantum entanglement within nine months," he said. "At the end of the next three-year [period] we expect to have at least 10 of these atoms coupled to one another. And that'll be a pretty significant step."
Though useful quantum computers are at least 20 years away, quantum information processing could be used for secure communications in five to ten years, Shahriar said.
Shahriar's colleagues are Philip R. Hemmer of the U.S. Air Force, Seth Lloyd and Jeffery A. Bowers of MIT, and Alan E. Craig of Montana State University. The research is funded by the Air Force Office of Scientific Research, the Army Research Office and the National Security Agency.
Timeline: 5-10 years; >20 years
TRN Categories: Quantum Computing
Story Type: News
Related Elements: Technical paper "Solid State Quantum Computing Using Spectral Holes" posted on CoRR
September 20, 2000
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Quantum computer keeps it simple
Technology Research News
Quantum computers promise to be fantastically
fast at solving certain problems like cracking codes and searching large
databases, which provides plenty of incentive for overcoming the tremendous
obstacles involved in building them.
The basic component of quantum computers, the qubit, is made from
an atom or subatomic particle, and quantum computers require that qubits
exchange information, which means the interactions between these absurdly
tiny objects must be precisely controlled.
Researchers from the University of Oxford and University College
London in England have proposed a type of quantum computer that could
greatly simplify the way qubits interact.
The scheme allows qubits to be constantly connected to each other
instead of repeatedly connected and disconnected, and it allows a computer's
qubits to be controlled all at once, said Simon Benjamin, a senior research
fellow at the University of Oxford in England. Global control is a fairly
unconventional idea that "allows you to send control signals to all the
elements of the device at once instead of having to separately wire up
each element," he said.
The scheme can be implemented with different types of qubits.
A common type uses the spin of an electron. Electrons can be oriented
in one of two directions, spin up and spin down. These are analogous to
the poles of a kitchen magnet and can represent the 1s and 0s of computer
Key to the potential power of quantum computers is a weird trait
of quantum particles like electrons. When an electron is isolated from
its environment, it enters into superposition, meaning it is in some mix
of both spin up and spin down.
Linking two qubits that are in superposition makes it possible
for a quantum computer to examine all of the possible solutions to a problem
at once. But controlling how two qubits interact is extremely challenging,
said Benjamin. Qubits "must be made to talk to each other, and when the
operation is over they must be made to stop talking," he said.
In traditional quantum computing schemes that use electron spins,
pairs of qubits have a metal electrode between them. When the electrode
is negatively charged, it repels the negatively charged electrons that
make up the qubits, keeping them separated. But giving the electrode a
positive charge draws the electrons toward each other, allowing them to
interact by exchanging energy. Allowing the qubits to interact for half
the time it takes to completely swap energy is the basis of two-qubit
The energy of the two qubits has to be resonant or errors can
arise, but off-resonant energy can also be harnessed, said Benjamin. Particles
resonate at specific energies in the same way that larger objects vibrate
more readily at certain frequencies. Different energies can be more or
less resonant with each other much like certain musical notes sounding
better together than others. "Something that we were used to thinking
of as a source of error could in fact be a means of controlling the computer,"
The researchers' proposal replaces the electrode with a third
electron. These three electrons are constantly interacting, but they don't
always exchange energy. When the middle electron is off resonant, the
qubits are blocked from exchanging energy. This way, the interaction "is
always on, but we can effectively negate it by ensuring that the energies
of neighboring spins are completely incompatible," said Benjamin.
Avoiding electrodes is useful for several reasons. Fabricating
qubits with electrodes between them "will require a fantastic degree of
control," said Benjamin. "If a particular pair of electrons are too close,
then the interaction will be jammed on, and if they are too far away then
the interaction will be jammed off," he said.
Electrodes can also knock qubits out of superposition. "Each electrode
can act as an [antenna], channeling electromagnetic noise from the room-temperature
world right down to the qubits," said Benjamin.
The researchers took their proposal a step further by removing
the need to control electrons individually. Every change to the energy
of the electrons is applied to the whole device. The researchers divide
a string of qubits into two groups, odd and even, with every other qubit
in one group. A set of six specific changes to the energies of the electrons
covers all of the logic gates required for quantum computing, according
to the researchers. Quantum programs would consist of timed sequences
of the changes.
The main disadvantage of the researchers' proposal is that it
could require as many as two spins per qubit rather than the usual single
spin, which would make for a larger device, said Benjamin. "Right now
experimentalists are struggling to make even two qubits in solid-state
systems," he said.
The researchers' work is valuable because it extends the range
of candidates for quantum computing, said Barry Sanders, a professor of
quantum information science at the University of Calgary in Canada. The
work is "stoking the fires of creativity so that we physicists can dream
up other quantum computing realizations that lead to easier control and
less experimental complexity," he said.
There is a growing realization that there are many ways to perform
qubit operations, said Robert Joynt, a physics professor at the University
of Wisconsin at Madison. The Oxford and University College London work
is significant for people trying to make a real machine, because it means
that the constraints on the hardware are a lot looser than people thought
at first, he said. This research "is particularly nice since it gets rid
of the usual need to precisely tune two-qubit operations."
The researchers are currently exploring how the method would work
in a two- or three-dimensional array of qubits, said Benjamin. "We'd also
like to build up a more detailed description of how to implement our scheme
with specific technologies like... electron spin," he said.
Researchers generally agree that practical quantum computers are
two decades away. It is possible that quantum computers capable of computations
that are impossible on conventional computers could be built within ten
years, said Benjamin.
Such systems "will be mainly of interest to the scientific community
because they will involve using quantum computers to simulate other quantum
systems, such as fundamental biological processes," said Benjamin. "These
first quantum computers may require an entire lab built around them, and
may be treated as a national or international resource for research --
a bit like today's supercomputers or... particle accelerators."
However, it is also possible that quantum computing research could
stall if there's not enough experimental progress in the next few years,
said Benjamin. "It's possible that quantum computing is an idea born before
it's time. Our technology may simply be to crude to achieve it," he said.
Benjamin's research colleague was Sougato Bose. The work appeared
in the June 20, 2003 issue of Physical Review Letters. The research
was funded by the Royal Society, the Oxford-Cambridge-Hitachi Nanoelectronics
at the Quantum Edge project in England, and the National Science Foundation
Timeline: 10-20 years
Funding: Corporate, Government, University
TRN Categories: Quantum Computing and Communications
Story Type: News
Related Elements: Technical paper, "Quantum Computing with
an Always-On Heisenberg Interaction," Physical Review Letters, June 20,
August 13/20, 2003
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Science tells us that it is impossible for an object to travel at light speed, let alone faster than that. But so many of our favorite science-fiction movies, games, and TV shows rely on faster-than-light travel to craft their interplanetary adventures.
Let’s take a look at five means of FTL found in sci-fi that don’t break the rules of relativity and examine how plausible they are based on the science behind them.
Popularized by Star Wars and used extensively in fiction, a hyperdrive enables a spaceship to travel at FTL speeds by entering another dimension known as “hyperspace.” The spaceship isn’t actually traveling faster than the speed of light, but rather is making use of hyperspace as a shortcut, and the hyperdrive is the mechanism that shunts the spaceship into and out of this parallel dimension.
Specific coordinates within hyperspace have corresponding coordinates in normal space, but the distance between those two points will be shorter in hyperspace, allowing for a faster journey. Before making a “hyperspace jump,” calculations must be made to find the matching coordinates between hyperspace and normal space in order to know when and where to exit hyperspace at the desired normal space destination.
Is it plausible?
Physicist Bukrhard Heim proposed a theory in 1977 that FTL travel may be possible by using magnetic fields to enter higher-dimensional space. The theory uses a mathematical model that calls upon six or more dimensions in an attempt to resolve incompatibilities between quantum mechanics and general relativity, but Heim’s ideas have not been accepted in mainstream science. Still, the fact that a theoretical physicist devoted a large portion of his life in pursuit of a theory that could lead to a means of space travel lends the concept of hyperspace a little more credibility than if it were simply the fancy of a sci-fi writer.
2. Jump Drive
Seen in such works as Battlestar Galactica, a jump drive allows for instantaneous teleportation between two points. Similar to a hyperdrive, coordinates must be calculated to ensure a safe jump; the longer the desired travel distance, the more complex the calculation. In theory, there is no limit to how far a jump can take a ship, but an incorrect calculation may result in a catastrophic collision with a planet or space debris.
The Dune universe’s FTL, based on the fictional “Holtzman effect,” can also be considered a jump drive.
Is it plausible?
Master of hard sci-fi Isaac Asimov was the first to suggest the idea of a jump drive in the Foundation series, which lends some credibility to the idea. However, most fiction doesn’t clearly explain the principles of physics that allow for this teleportation, making it impossible to claim a jump drive as plausible. However, if it functions by opening a wormhole…
A wormhole, as seen in the Stargate franchise, allows for near-instantaneous travel across vast distances. Wormholes may be naturally-occurring or man-made, but are almost always temporary and serve as tunnels through spacetime.
Imagine our universe as a piece of paper, and an ant walking on that piece of paper as a spaceship. If the ant wants to walk from one end of that piece of paper to the other, the fastest way to do so would be to travel in a straight line. But paper, like space, bends. If you bend the paper into a U shape, the ant’s journey goes largely undisturbed – it still has to traverse the same distance along that line. However, in 3D space, the two ends of the paper are very close to each other now. Cut off a piece of a drinking straw and let the ant use it as a bridge or tunnel between the two ends of the paper, and the journey is suddenly much shorter.
Is it plausible?
While we have never directly observed any evidence for one, wormholes are theoretically possible. Albert Einstein and his colleague Nathan Rosen first discovered wormholes in 1935 as solutions to equations within Einstein’s general theory of relativity – the math says they can exist.
Since then, other scientists, including Stephen Hawking, have argued that it may be possible to traverse a wormhole, under the right circumstances. The debate surrounding wormholes isn’t about their plausibility, but rather how they may be created and sustained.
The concept of slipstream can be found in such works as Star Trek, Doctor Who, and the Halo video game franchise, but there is no widely-agreed upon definition of what slipstream is or how it works beyond it being a means of FTL. We’ll consider the slipstream seen in Gene Roddenberry’s Andromeda, where it is “not the best way to travel faster than light, it’s just the only way,” as per the show’s protagonist.
Slipstream is a form of interdimensional highway in which ships ride a series of slipstream “strings” – the unseen connections between all objects in the universe. These strings are in constant flux and form a tangled mess of intersections and divergent paths. Any time a pilot reaches a fork in the road, he has to guess which is the correct path to take to continue along toward his desired destination. Before the pilot makes that decision, both paths are simultaneously the correct and incorrect route, and it is the act of choosing a path that forces one to be correct and the other to be incorrect – if this made you think of Shrödinger’s cat, that does seem to be the basis for this concept. A computer selects the “correct” path 50% of the time, but due to intuition, a human picks the correct path 99.9% of the time.
Is it plausible?
There are no mainstream scientific theories that support this idea of slipstream. Reading the “lore” of this means of FTL evokes fantastical interpretations of string theory, quantum entanglement, and other concepts in modern physics, but the ideas are supported only through their internal consistency rather than actual fact, much like a well-explained magic system that allows fictional wizards to cast spells.
5. Warp Drive
Popularized by Star Trek, a warp drive distorts space around a ship while leaving the ship itself inside a “bubble” of normal space. The space in front of the ship is contracted, while the space behind it is expanded, and the ship “rides” the distortion wave at FTL speeds. Technically, it is not the ship that is moving, but rather space itself, which is how we avoid breaking any laws of physics.
Imagine a surfer slowly paddling back to shore. When a wave comes, it will lower the water level in front of him and raise the water level behind him, and he can ride the downward slope all the way to shore. Relative to the wave, the surfer isn’t moving – he’s staying between the crest and the trough, and it is instead the wave that is moving.
Surfing doesn’t quite work like that, but it’s a simplification that we can all visualize. In a similar manner to how a wave will distort water to propel a surfer, a warp drive will distort space to propel a ship.
Is it plausible?
In 1994, the Alcubierre drive was proposed as a theoretical means of FTL travel and is based on a mathematical solution to equations within Einstein’s general theory of relativity. Just like a warp drive, the Alcubierre drive would contract space in front of a spaceship and expand space behind it.
NASA has been actively researching this technology since 2012, and the lead researcher even worked with a 3D artist to develop a model of what a warp-capable ship might look like. As far as real-life FTL goes, warp is the current front-runner to becoming reality.
As far as real-life FTL travel goes, the fictional favorites can be found in Star Trek and Stargate: the warp drive, and wormholes. Both are theoretically possible; however, both require further scientific breakthroughs before practical testing can begin. In either case, we need to discover “exotic matter” – hypothetical particles with negative mass – to get these mechanisms to work. “Element zero” from the Mass Effect series, the rare material that is essential to FTL travel in that universe, doesn’t quite fit the description, but the lore is at least scientifically sound in suggesting that some new, rare form of matter is required to make this technological leap.
The good news is that scientists don’t believe this is a matter of if, but rather when. There will be a time in the future when a stately, bald man in uniform will sit back in a command chair and relay the order, “Engage.”


Quantum Hoverboards on Superconducting Circuits
Building a quantum computer or quantum simulation device is a multidisciplinary undertaking that has driven a lot of cutting-edge research. But there is still a long way to go before a fully operational quantum machine becomes a reality. The basic recipe for achieving this goal may sound quite simple. First, identify a set of suitable quantum systems that can be well isolated from the environment to protect their “quantumness.” Second, assemble them together in a controlled and scalable way. The problem is, however, that in nature, isolation does not come along easily with control and scalability. Ge Yang from the University of Chicago, Illinois, and his colleagues have demonstrated a device  that could potentially lead to robust yet controllable qubit architectures. In the new scheme, electrons floating on top of a superfluid-helium film (which could encode quantum bits) are combined with a high-quality superconducting circuit (which could enable the readout and control of the qubits).
Since atoms and molecules tend to either stick to solid surfaces or sink into a liquid, it might at first seem surprising that electrons could stably float on top of a liquid-helium film. This long-studied phenomenon arises from two competing phenomena . On the one hand, an effect known as Pauli blocking prevents two electrons from occupying the same quantum state. This makes the densely packed fluid of closed-shell helium atoms impenetrable for an additional incoming electron. On the other hand, the electrons are still attracted towards the helium by the “image charge” they induce, similarly to a charge attracted towards a metallic surface. The combination of the two effects results in a potential that traps the electrons and localizes them within a 2D sheet floating at a distance of a few nanometers above the helium film.
The key word here is “above,” meaning that the electrons are well separated from all the “dirt” (crystal impurities, phonons, nuclear spins, and the like) that usually quickly destroys electronic quantum coherence inside a solid. The record-high electron mobilities  that have been measured for such electron “hoverboards” are direct evidence of their exceptional degree of isolation. One of the few remaining, yet small, sources of decoherence for the electron motion is the coupling of the electrons to tiny ripples on the helium surface (so-called ripplons) . Theoretical studies suggest that such isolation from the environment would lead to quantum-coherence times of spin-superposition states exceeding hundreds of seconds . Using electrodes, the floating electrons can also be confined horizontally, and at sufficiently high densities they are predicted to self-organize and form a triangular Wigner crystal —a neat way to obtain a whole lattice of single-electron quantum systems.
Such a crystal of electrons on top of superfluid helium might sound like an ideal starting point for building quantum devices. However, a major obstacle is the lack of reliable techniques to detect the quantum state or even the presence of individual electrons. The floating electron gas cannot be easily accessed by direct electrical contacts or by optical means. Over 15 years have passed since the first ideas for exploiting liquid helium electrons in quantum computing were put forward [4, 5], but the experimental progress in this direction has been modest. Now, Yang and his colleagues have successfully demonstrated a new readout technique that allows fast and nondestructive detection of electrons on liquid helium thanks to their effect on a nearby high-quality-factor superconducting circuit. This could be just the missing ingredient needed to drive this field forward.
The authors confined the helium film and the surface electrons within a narrow gap between the ground and the center electrodes of a planar superconducting microwave resonator (see Fig. 1). Being superconducting, the resonator (which can be thought of as a centimeter-long planar version of a coaxial cable) can exhibit sharp electromagnetic resonances at GHz frequencies. These resonances depend very sensitively on the dielectric properties of the surrounding environment. Therefore, tiny changes in the electron configuration—in principle, as small as the addition or loss of a single electron—can be monitored in situ and nondestructively by looking at the drift of the resonance frequency. Over the past years, similar readout schemes have found widespread use for quantum state detection in superconducting quantum computation architectures .
Yang et al. have successfully applied such ideas to electrons on liquid helium by trapping the floating electrons in the vicinity of such a circuit, where their coupling to the electric field around the resonator is strongest. First, they used the readout technique to measure and adjust the thickness of the helium film with subnanometer resolution—an important parameter defining the trapping conditions. They then sprayed a bunch of electrons emitted from a tungsten filament onto the helium surface, generating a big jump in the circuit’s resonance frequency as these electrons got trapped. Finally, by expelling the electrons a fraction at a time with a negative voltage, they were able to determine the relationship between the number of trapped electrons and the shift of the resonance. A key figure of merit extracted from those measurements (performed with thousands of electrons) is the coupling strength per electron, which quantifies the maximal resonance shift that can be induced by the addition of one electron. Such coupling strength was found to exceed the linewidth of the resonance. This means that in a setup with smaller traps containing only a few electrons , the measurement resolution would be sufficient not only to count individual electrons but also to detect in which quantized vibrational state they are in.
What’s next? To realize the full potential of the new scheme, researchers will now need to bring the hybrid systems into a regime in which the electron trapping frequency matches the circuit’s resonance . Under such conditions, a quantum superposition of two microwave photons can be converted into a quantum superposition of two vibrational states, and vice versa. The microwave resonator could then serve as a quantum “bus” that mediates interactions between distant electrons or interfaces the electrons with other quantum systems, like superconducting qubits. Beyond quantum computing applications, such control possibilities may help realize new quantum states of matter in an electron lattice whose constituents can be individually observed and controlled by quantum circuits.
This research is published in Physical Review X.
- G. Yang, A. Fragner, G. Koolstra, L. Ocola, D. A. Czaplewski, R. J. Schoelkopf, and D. I. Schuster, “Coupling an Ensemble of Electrons on Superfluid Helium to a Superconducting Circuit,” Phys. Rev. X 6, 011031 (2016).
- M. W. Cole and M. H. Cohen, “Image-Potential-Induced Surface Bands in Insulators,” Phys. Rev. Lett. 23, 1238 (1969).
- K. Shirahama, S. Ito, H. Suto, and K. Kono, “Surface Study of Liquid Using Surface State Electrons,” J. of Low Temp. Phys. 101, 439 (1995).
- P. M. Platzman and M. I. Dykman, “Quantum Computing with Electrons Floating on Liquid Helium,” Science 284, 1967 (1999).
- S. A. Lyon, “Spin-Based Quantum Computing Using Electrons on Liquid Helium,” Phys. Rev. A 74, 052338 (2006).
- C. C. Grimes and G. Adams, “Evidence for a Liquid-to-Crystal Phase Transition in a Classical, Two-Dimensional Sheet of Electrons,” Phys. Rev. Lett. 42, 795 (1979).
- R. J. Schoelkopf and S. M. Girvin, “Wiring up Quantum Systems,” Nature 451, 664 (2008).
- G. Papageorgiou, P. Glasson, K. Harrabi, V. Antonov, E. Collin, P. Fozooni, P. G. Frayne, M. J. Lea, D. G. Rees, and Y. Mukharsky, “Counting Individual Trapped Electrons on Liquid Helium,” Appl. Phys. Lett. 86, 153106 (2005).
- D. I. Schuster, A. Fragner, M. I. Dykman, S. A. Lyon, and R. J. Schoelkopf, “Proposal for Manipulating and Detecting Spin and Orbital States of Trapped Electrons on Helium Using Cavity Quantum Electrodynamics,” Phys. Rev. Lett. 105, 040503 (2010).


New Superconducting Current Found Traveling Along the Outer Edges of a Superconductor
For the first time, scientists at Princeton University believe that they have spotted a superconducting current travelling along the edge of a material without straying into the middle.
A discovery that has eluded physicists for decades has reportedly been detected for the first time in a laboratory at Princeton University.
A team of physicists at the university found that superconducting currents were flowing along the exterior edge of a superconducting material.
Superconducting Currents Detected Along the Exterior Edge of a Material
Nai Phuan Ong, the senior author of the team’s study, published in the journal Science on May 1, said, “Our motivating question was, what happens when the interior of the material is not an insulator but a superconductor? What novel features arise when superconductivity occurs in a topological material?”
To investigate superconductivity in topological materials, the team used a crystalline material, which features topological properties and is a superconductor under 100 milliKelvin (- 459 degrees Fahrenheit), called molybdenum ditelluride.
Normally, superconducting currents, where electricity flows without losing energy, would permeate an entire material. However, in a thin sheet of molybdenum ditelluride which was chilled to near absolute zero, the interior and edge make up two superconductors that are distinct from one another. In the material, the tow superconductors are “basically ignoring each other,” added Ong.
The distinction between exterior and interior makes molybdenum ditelluride an example of a topological material. These materials exhibit behaviour that is closely tied to topology, a mathematical field, and can be used as topological insulators where electric currents can flow on the surface of a material but not the interior.
Topological insulators are crystals with an insulating interior and a conducting surface. In contrast to conducting materials where electrons can hop from one atom to another, the electrons in insulators cannot move, however, topological insulators allow the movement of electrons on their conducting surface.
Graphic illustrating superconductivity and its resistance to current flow. The jagged pattern in the diagram represents oscillation of the superconductivity which varies with the strength of an applied magnetic field. Image credited to Stephan Kim, Princeton University
Pushing the Superconducting State to Its Limit
Stephan Kim, a graduate student in electrical engineering, who conducted many of the project’s experiments, said, “Most of the experiments done so far have involved trying to ‘inject’ superconductivity into topological materials by putting the one material close to the other. What is different about our measurement is we did not inject superconductivity, and yet we were able to show the signatures of edge states.”
Initially, the team grew crystals in the lab and then cooled them down to a temperature where superconductivity occurs. Then, by applying a weak magnetic field to the crystal, the current displays oscillations as the magnetic field is increased. In their experiment, Kim and colleagues gradually increased the magnetic field on the material and measured how much they could increase it by before the superconducting state was lost, a value known as the ‘critical current.’
As the magnetic field grew, the critical current oscillated in a repeating pattern—a tell-tale sign of an edge superconductor. This oscillation is caused by the physics of superconductors in which electrons form Cooper pairs. The pairs act as a unified whole, all taking on the same quantum state or wave function.
What Could This Mean for Quantum Computing?
Molybdenum Ditelluride is a metal-like compound known as a Weyl semimetal. Due to its unusual properties, scientists believe that it could keep Majorana fermions, disturbances within a material that holds promise for better quantum computers. Computers based on quantum topology are expected to resist the jitter that can impair quantum calculations.
The next big challenge for scientists is to take these Majorana fermions and make them into qubits, or individual computational units, which would be a huge leap forward towards practical quantum computing.
Theoretically, a qubit would be made of combinations of pairs of Majorana fermions, each of which would be separated from its partner. If one member of the pair is disrupted by noise errors, the other should remain unaffected and thereby preserve the integrity of the qubit, enabling it to correctly carry out a computation.
The Difficulty with Developing Qubits
To date, semiconductor-based setups with Majorana fermions have been difficult to scale up. This is because a practical quantum computer requires thousands or millions of qubits, and these require growing very precise crystals of semiconducting material which are difficult to turn into high-quality superconductors. This is where topological insulators come in.


The first time a person hears of the Rutherford Model, it’s likely to cause a flurry of excited conversation.
For some, the name means something akin to the idea that you can build a computer with the power of atoms, a kind of super-computer that can do more than what the human mind can.
But for others, the model’s origins lie with a pair of scientists who are building the next-generation of supercomputers – a pair whose first major milestone is already well underway.
In a new paper published in the journal Nature Physics, the pair, Calvin Klein and Thomas Bohr, describe a way of modelling the human cortex using the atomic model.
As the name suggests, the researchers’ method is based on the work of Nobel laureate Calvin Klein, a physicist at MIT who first described the theory of quantum entanglement in 1959.
As part of his work, Klein showed how the atomic models could allow for much more detailed understanding of the structure of a human brain.
In the 1980s, a team led by Klein led by James Oakes at the University of New South Wales (UNSW) used the model to build an atomic computer, which was used to test the properties of a computer chip.
The team used a version of the model called the CERN-EPSY-Klein model to run simulations of the structures of the cortex.
They then built a computer that could perform the task of calculating the position of atoms in the cortex and of measuring the electric charge of individual atoms.
Using this computer, the team was able to map the structures and dynamics of the cells of the cerebral cortex.
The model has become so widely used because of its remarkable properties.
But its success is not limited to neuroscience.
It also works in other areas of physics, including particle physics, and could be used to design computers and other devices that perform calculations in a variety of fields.
A big challenge for researchers in the field of quantum computing is to get the models to perform the work they require.
For instance, it may be impossible to build computers that perform computations that can’t be done by humans, or that cannot be performed by computers at scale.
In this sense, the models are a powerful tool.
But if you want to build something that can perform calculations that are computationally feasible on a human scale, the challenge becomes scaling.
A better way of getting them to perform The scientists’ work on the Rutherford model is the result of decades of work by several groups around the world, including at the Universities of Washington, Princeton, and Oxford.
The groups’ initial effort involved using the Rutherford models to build quantum computers, which could perform calculations with a fraction of the power and accuracy of a conventional computer.
The first computer to perform calculations using the models was constructed by researchers at Princeton in 1989, and it was called the SDSS-A.
However, in the early 2000s, the two groups behind the Rutherford computers decided to move on to a new direction.
They began to build the model based on a different quantum field theory, which is known as the quantum field theories of relativity.
The work led to the design of the SDP-10 (for Spinozium-doped) model, which they also used to build their model of human brains.
But the researchers said they were also trying to make their work accessible to a wider audience.
“Our goal is to make the model accessible to the scientific community, so that the model can be built into any computing platform,” Klein said.
“The goal is also to use the model as a reference for building other models of the brain, for example, models of synaptic activity or of the dynamics of neurons.
And we hope that the models can be used as reference for the computation of the neural network models.”
The Rutherford models’ ability to simulate the structure and dynamics not only of neurons but also of synapses in the brain is important for understanding the brain’s underlying principles.
“What we are doing is going to build on what is known about synaptic connections, which are fundamental processes in the way that the brain works,” Klein explained.
“So the models of synapse structure can help us to understand how neurons and synapses work.”
The models have also been used to understand the evolution of the synapse, which Klein said was a key step towards understanding the structure-function relationship of the neocortex.
But it wasn’t until last year that they had a chance to build another model of synaptosomes, which serve as the core building blocks of neurons and are involved in the process of synapsis, the process by which new connections are established between neighbouring neurons.
“That was the first time we could build a model that has this level of detail,” Klein noted.
The SDP 10 model is one of a number of models currently being built using the theory.
The Rutherford model has been used by researchers in several


For most quantum computers, heat is the enemy. Heat creates error in the qubits that make a quantum computer tick, scuttling the operations the computer is carrying out. So quantum computers need to be kept very cold, just a tad above absolute zero.
“But to operate a computer, you need some interface with the non-quantum world,” says Jan Cranickx, a research scientist at imec. Today, that means a lot of bulky backend electronics that sit at room temperature. To make better quantum computers, scientists and engineers are looking to bring more of those electronics into the dilution refrigerator that houses the qubits themselves.
At December’s IEEE International Electron Devices Meeting (IEDM), researchers from than a half dozen companies and universities presented new ways to run circuits at cryogenic temperatures. Here are three such efforts:
Google’s cryogenic control circuit could start shrinking quantum computers
Google’s cryo-CMOS integrated circuit, ready to control a single qubit. Photo: Google
At Google, researchers have developed a cryogenic integrated circuit for controlling the qubits, connecting them with other electronics. The Google team actually first unveiled their work back in 2019, but they’re continuing to scale up the technology, with an eye for building larger quantum computers.
This cryo-CMOS circuit isn’t much different from its room-temperature counterparts, says Joseph Bardin, a research scientist with Google Quantum AI and a professor at the University of Massachusetts, Amherst. But designing it isn’t so straightforward. Existing simulations and models of components aren’t tailored for cryogenic operation. Much of the researchers’ challenge comes in adapting those models for cold temperatures.
Google’s device operates at 4 kelvins inside the refrigerator, just slightly warmer than the qubits that are about 50 centimeters away. That could drastically shrink what are now room-sized racks of electronics. Bardin claims that their cryo-IC approach “could also eventually bring the cost of the control electronics way down.” Efficiently controlling quantum computers, he says, is crucial as they reach 100 qubits or more.
Cryogenic low-noise amplifiers make reading qubits easier
A key part of a quantum computer are the electronics to read out the qubits. On their own, those qubits emit weak RF signals. Enter the low-noise amplifier (LNA), which can boost those signals and make the qubits far easier to read. It’s not just quantum computers that benefit from cryogenic LNAs; radio telescopes and deep-space communications networks use them, too.
Researchers at Chalmers University of Technology in Gothenburg, Sweden, are among those trying to make cryo-LNAs. Their circuit uses high-electron-mobility transistors (HEMTs), which are especially useful for rapidly switching and amplifying current. The Chalmers researchers use transistors made from indium phosphide (InP), a familiar material for LNAs, though gallium arsenide is more common commercially. Jan Grahn, a professor at Chalmers University of Technology, states that InP HEMTs are ideal for the deep freeze, because the material does an even better job of conducting electrons at low temperatures than at room temperature.
Researchers have tinkered with InP HEMTs in LNAs for some time, but the Chalmers group are pushing their circuits to run at lower temperatures and to use less power than ever. Their devices operate as low as 4 kelvins, a temperature which makes them at home in the upper reaches of a quantum computer’s dilution refrigerator.
imec researchers are pruning those cables
Any image of a quantum computer is dominated by the byzantine cabling. Those cables connect the qubits to their control electronics, reading out of the states of the qubits and feeding back inputs. Some of those cables can be weeded out by an RF multiplexer (RF MUX), a circuit which can control the signals to and from multiple qubits. And researchers at imec have developed an RF MUX that can join the qubits in the fridge.
Unlike many experimental cryogenic circuits, which work at 4 kelvins, imec’s RF MUX can operate down to millikelvins. Jan Cranickx says that getting an RF MUX to work that temperature meant entering a world where the researchers and device physicists had no models to work from. He describes fabricating the device as a process of “trial and error,” of cooling components down to millikelvins and seeing how well they still work. “It’s totally unknown territory,” he says. “Nobody’s ever done that.”
This circuit sits right next to the qubits, deep in the cold heart of the dilution refrigerator. Further up and away, researchers can connect other devices, such as LNAs, and other control circuits. This setup could make it less necessary for each individual qubit to have its own complex readout circuit, and make it much easier to build complex quantum computers with much larger numbers of qubits—perhaps even thousands.


Pyramid pixels promise sharp picturesBy Kimberly Patch, Technology Research News
Pyramids may be the key to sharper, cheaper electronic displays.
The color flatscreens used in electronic devices like laptops, cellphones and miniature television screens are made up of many tiny red, green and blue light emitting diodes (LED's) that produce the tiny dots, or pixels of light that make up the picture. One focus of flatscreen research has been cramming more pixels on the screen, because this makes for a higher resolution picture.
Researchers from the University of California at Los Angeles have come up with a different angle on the problem. They have devised a way to coax light from three colored LED's through a single, tiny plastic pyramid. Effectively, the three types of pixels are stacked into one space, tripling resolution in one fell swoop.
"We built the red, green and blue [LED's] in a vertical structure" said Yang Yang, an associate professor at UCLA. "They mix the light to give you any color that you want, [and] they do not take the real estate" of separate LED's, he said.
Because the pyramids mix light at the pixel level, a screen made with this technology will continue to produce a range of colors close up. In contrast, taking a magnifying glass to a conventional screen will reveal the separate red, blue, and green dots that give the illusion of many colors.
The pyramid pixel method may also prove cheaper than traditional flatscreens because it does not require shadow masking. Today's LED displays are manufactured using sheets of metal containing many tiny holes to guide the separate dots of red, green and blue organic materials as they are deposited on the screen. "The holes are so small it requires [a] very thin metal sheet for the shadow mask. It's not easy to fabricate a large [shadow mask and] it's not easy to maintain," said Yang.
In practice, the pyramid shape acts like its own shadow mask, shielding the different color LED's from each other.
"Permanent shadow masks have been used ... but not in the way Yang has been using them here," said Mark Thompson, a chemistry professor at the University of Southern California. "I don't know that anybody else has looked at building structures and using those as sort of in situ shadow masks -- using the shadowing of the pyramid," Thompson said. "It's an interesting approach that could have a lot of interesting applications," he added.
Some of the pyramid pixel's potential advantages are also shared by a pixel stacking scheme under development by Universal Display Corp. Thompson contributed to the basic research behind that scheme, which literally stacks red, blue, and green elements like pancakes into one pixel using a standard manufacturing process that includes shadow masking. The stacked pixels emit mixed light that changes color as the the ratio of currents in the three pixels is varied.
Like the pyramids, the stacked approach produces true color pixels that are effectively higher resolution and can be looked at closely without breaking up. The tricky part of the pancake pixel scheme was working out how to connect all the pixel elements, something Yang has not yet reported on, said Thompson.
In theory, the pyramid pixel displays could cost 30 percent less to manufacture then screens that use sheets of metal for shadow masking, Yang said. The manufacturing process for depositing the pyramid pixels has yet to be worked out, but it will be similar to a process used by a type of 3M film, Yang said.
Yang has implemented his scheme in a prototype pyramid about ten times the size needed. The next step is to shrink the prototype down to about 100 microns, he said.
According to Yang, the technology could be ready for practical use in about two years.
The pyramid pixel research was funded by UCLA and by a corporate partner who did not want to be named. Yang Yang's research partner was Shun-Chi Chang, also from UCLA. They published a technical paper on their research in the August 14, 2000 issue of Applied Physics Letters.
The research behind Universal Display's stacked pixel scheme was published in Science June 27, 1997 and Applied Physics Letters, November 11, 1996.
Timeline: 2 years
Funding: Corporate, University
TRN Categories: Semiconductors and Materials
Story Type: News
Related Elements: Photo 1, Photo 2; Technical paper, "Pyramid-Shaped Pixels for Full-Color Organic Emissive Displays," Applied Physics Letters, August 14, 2000; Technical paper "Three Color Tunable Organic Light Emitting Devices," Science, June 27, 1997; Technical paper "Color-tunable organic light-emitting devices," Applied Physics Letters November 11, 1996.
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The applications running on the Internet today rely on a combination of symmetric and asymmetric encryption for security.
The asymmetric protocols are typically used for authentication and key establishment. Examples of such protocols include RSA, RSA-EC, DSA, DH, and DHEC.
The security of these protocols relies on the assumption that it would take even the most powerful classical computers thousands of years to solve certain mathematical problems (e.g. factoring large numbers or computing a discrete logarithm).
Shor’s Algorithm: Challenging classical assumptions
The assumption that these protocols were difficult to crack was held with confidence until 1994, when MIT professor, Peter Shor, showed that a quantum computer could break the encryption with ease. Using Shor’s algorithm, a large-scale quantum computer can solve the mathematical problems underlying existing encryption protocols in minutes.
Once a sufficiently large and reliable (fault-tolerant) quantum computer exists that can run Shor's algorithm, security as it is deployed on the internet today will be broken. The quantum computer will be able to decrypt all traffic without needing the keys.
How QKD works
Quantum key distribution (QKD) offers a solution to this problem by relying only on the laws of quantum physics to distribute keys instead of the complexity of mathematical problems for encryption.
Two communicating parties can use QKD to agree on a secret key, which can then be used for standard encryption algorithms like AES. The secret key bits are encoded as quantum states into individual photons that are sent over optical fibers or across free space (e.g. satellites).
There are many different QKD protocols, each with their own pros and cons. But they all rely on a quantum phenomenon that is called the collapse of the wave function. If an attacker tries to steal the key by observing photons as they fly across the fiber, the laws of quantum physics dictate that this will inevitably cause the photons to change. These changes, and hence the presence of an attacker, can be detected. Once the presence of an attacker is detected, the key is not used since it is deemed unsafe.
QKD systems have been commercially available for several years now.
It can be mathematically proven that the QKD protocols are unbreakable by both classical and quantum computers.
Nevertheless, critics of QKD (which includes, notably, the NSA) point to the following challenges:
- Side-channel attacks: While QKD is provably secure from a theoretical point of view, several attack vectors have been discovered for actual QKD products. There are side-channel attacks, not because the theory is incorrect, but because the actual product implementations are sometimes flawed. As one concrete example, actual products often use weak coherent pulse lasers, which are cheaper, but which sometimes send multiple photons instead of a single photon as assumed by the security proof. This gives rise to the so-called photon number splitting (PNS) attack where the attacker can observe the secret qubits without being detected. The European Telecommunication Standards Institute (ETSI) has published a list of known attacks.
- Complexity: The complexity of QKD protocols further increases vulnerabilities. In addition to processing qubits, the protocols require classical post-processing algorithms to analyze the statistics of the noise and detect the presence of an attacker. Each of these steps is highly complex, introducing additional security risks.
- Deployment: QKD requires new equipment to be deployed. The existing telco fibers can often be reused, but new quantum-enabled endpoints and relay stations need to be deployed.
- Authentication: QKD requires two parties to authenticate each other. There are several approaches, each with its own set of challenges. Pre-shared keys, refreshed with QKD-produced keys, can be used, but this is fragile. Existing protocols or post-quantum cryptography (PQC) can be used, but this of course loses some of the advantage of QKD. Luckily, authentication risk is not retro-active.
- Special purpose: Today’s implementations of QKD have generally used networks purpose-built to run QKD. As a classical analogy, the plain old telephone service (POTS) network at the end of the 20th century was a special-purpose network that only provided voice service. It has now been replaced by voice-over-IP (VOIP) which is just one of many services running over the general-purpose Internet.
QKD promises to protect internet communication by offering protection with the laws of physics. Early QKD hardware is already commercially available. While current technology faces several challenges, methods have been proposed to bring practical quantum secure communication into reality. For instance, Entanglement as a Service (EaaS) networks overcome a number of these challenges by distributing entanglement directly. In addition, EaaS networks support the broad range of quantum network applications, such as clustered quantum computing and quantum sensing.
To stay up to date about the latest developments in each of these network technologies, please sign up for the Aliro newsletter in the footer of this page. Please reach out to firstname.lastname@example.org if you have any questions or comments about this post.


Quantum engineers from UNSW Sydney have created artificial atoms in silicon chips that offer improved stability for quantum computing.
In a paper published today in Nature Communications, UNSW quantum computing researchers describe how they created artificial atoms in a silicon ‘quantum dot’, a tiny space in a quantum circuit where electrons are used as qubits (or quantum bits), the basic units of quantum information.
Scientia Professor Andrew Dzurak explains that unlike a real atom, an artificial atom has no nucleus, but it still has shells of electrons whizzing around the centre of the device, rather than around the atom’s nucleus.
“The idea of creating artificial atoms using electrons is not new, in fact it was first proposed theoretically in the 1930s and then experimentally demonstrated in the 1990s—although not in silicon. We first made a rudimentary version of it in silicon back in 2013,” says Professor Dzurak, who is an ARC Laureate Fellow and is also director of the Australian National Fabrication Facility at UNSW, where the quantum dot device was manufactured.
“But what really excites us about our latest research is that artificial atoms with a higher number of electrons turn out to be much more robust qubits than previously thought possible, meaning they can be reliably used for calculations in quantum computers. This is significant because qubits based on just one electron can be very unreliable.”
Professor Dzurak likens the different types of artificial atoms his team has created to a kind of periodic table for quantum bits, which he says is apt given that 2019—when this ground-breaking work was carried out—was the International Year of the Periodic Table.
“If you think back to your high school science class, you may remember a dusty chart hanging on the wall that listed all the known elements in the order of how many electrons they had, starting with Hydrogen with one electron, Helium with two, Lithium with three and so on.
“You may even remember that as each atom gets heavier, with more and more electrons, they organise into different levels of orbit, known as ‘shells’.
“It turns out that when we create artificial atoms in our quantum circuits, they also have well organised and predictable shells of electrons, just like natural atoms in the periodic table do.”
Connect the dots
Professor Dzurak and his team from UNSW’s School of Electrical Engineering—including Ph.D. student Ross Leon who is also lead author in the research, and Dr. Andre Saraiva—configured a quantum device in silicon to test the stability of electrons in artificial atoms.
They applied a voltage to the silicon via a metal surface ‘gate’ electrode to attract spare electrons from the silicon to form the quantum dot, an infinitesimally small space of only around 10 nanometres in diameter.
“As we slowly increased the voltage, we would draw in new electrons, one after another, to form an artificial atom in our quantum dot,” says Dr. Saraiva, who led the theoretical analysis of the results.
“In a real atom, you have a positive charge in the middle, being the nucleus, and then the negatively charged electrons are held around it in three dimensional orbits. In our case, rather than the positive nucleus, the positive charge comes from the gate electrode which is separated from the silicon by an insulating barrier of silicon oxide, and then the electrons are suspended underneath it, each orbiting around the centre of the quantum dot. But rather than forming a sphere, they are arranged flat, in a disc.”
Mr Leon, who ran the experiments, says the researchers were interested in what happened when an extra electron began to populate a new outer shell. In the periodic table, the elements with just one electron in their outer shells include Hydrogen and the metals Lithium, Sodium and Potassium.
“When we create the equivalent of Hydrogen, Lithium and Sodium in the quantum dot, we are basically able to use that lone electron on the outer shell as a qubit,” Ross says.
“Up until now, imperfections in silicon devices at the atomic level have disrupted the way qubits behave, leading to unreliable operation and errors. But it seems that the extra electrons in the inner shells act like a ‘primer’ on the imperfect surface of the quantum dot, smoothing things out and giving stability to the electron in the outer shell.”
Watch the spin
Achieving stability and control of electrons is a crucial step towards silicon-based quantum computers becoming a reality. Where a classical computer uses ‘bits’ of information represented by either a 0 or a 1, the qubits in a quantum computer can store values of 0 and 1 simultaneously. This enables a quantum computer to carry out calculations in parallel, rather than one after another as a conventional computer would. The data processing power of a quantum computer then increases exponentially with the number of qubits it has available.
It is the spin of an electron that we use to encode the value of the qubit, explains Professor Dzurak.
“Spin is a quantum mechanical property. An electron acts like a tiny magnet and depending on which way it spins its north pole can either point up or down, corresponding to a 1 or a 0.
“When the electrons in either a real atom, or our artificial atoms, form a complete shell, they align their poles in opposite directions so that the total spin of the system is zero, making them useless as a qubit. But when we add one more electron to start a new shell, this extra electron has a spin that we can now use as a qubit again.
“Our new work shows that we can control the spin of electrons in the outer shells of these artificial atoms to give us reliable and stable qubits.
“This is really important because it means we can now work with much less fragile qubits. One electron is a very fragile thing. However an artificial atom with 5 electrons, or 13 electrons, is much more robust.”
The silicon advantage
Professor Dzurak’s group was the first in the world to demonstrate quantum logic between two qubits in silicon devices in 2015, and has also published a design for a full-scale quantum computer chip architecture based on CMOS technology, which is the same technology used to manufacture all modern-day computer chips.
“By using silicon CMOS technology we can significantly reduce the development time of quantum computers with the millions of qubits that will be needed to solve problems of global significance, such as the design of new medicines, or new chemical catalysts to reduce energy consumption”, says Professor Dzurak.
In a continuation of this latest breakthrough, the group will explore how the rules of chemical bonding apply to these new artificial atoms, to create ‘artificial molecules’. These will be used to create improved multi-qubit logic gates needed for the realisation of a large-scale silicon quantum computer.
Nature Communications (2020). DOI: 10.1038/s41467-019-14053-w
Artificial atoms create stable qubits for quantum computing (2020, February 11)
retrieved 11 February 2020
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New research has demonstrated that a triple stack of graphene sheets twisted at a very specific angle could demonstrate superconductivity that survives exposure to intense magnetic fields. The study was published in the journal Nature.
Image Credit: ktsdesign/Shutterstock.com
Superconductors - substances capable of conducting electricity without resistance - are poised to form the foundation of future technological and electronic advances, particularly in quantum computing.
While traditional conductors gradually lose resistance as they get colder - allowing progressively more electrons to flow - superconductors have a ‘critical temperature’ at which resistance is lost completely, allowing the free flow of electrons.
The fact that most materials capable of becoming superconductors only do so at very low temperatures has made close-to-room temperature superconductors the ‘holy grail’ of the materials science field.
This near room-temperature superconducting behavior is something that can be seen in graphene — single layers of carbon atoms in a hexagonal arrangement. When these atom thin sheets of graphene are double stacked, and a little twist is applied, they begin to act as a superconductor — even at close to room temperatures.
High temperatures are not the only thing that ‘turn-off’ superconductivity in a material. Exposure to a high magnetic field can also knock a superconductor into a regular conductive state. This has posed a challenge to developers of magnetic resonance imaging (MRI) devices, machines that rely on both superconductivity and intense magnetic fields.
The Twist Between Superconductivity and Graphene Relationship
Physicists from the Massachusetts Institute of Technology have found that not only is bilayer graphene a superconductor with a higher critical temperature, adding a third layer and applying a very specific angle — 54.7356° also known as the ‘magic angle’ — seems to allow superconductivity to be retained even in strong magnetic fields¹.
The team, led by Pablo Jarillo-Herrero, a Physics professor at MIT, discovered that when a trilayer of graphene is twisted in this way it seems to exhibit superconductivity in magnetic fields with a magnetic flux density as high as 10 Tesla. This is three times greater than the material could endure if it were a standard superconductor.
What the researchers believe they are seeing is a rare form of superconductivity called spin-triplet superconductivity.
“The value of this experiment is what it teaches us about fundamental superconductivity, about how materials can behave,” says Jarillo-Herrero. “So with those lessons learned, we can try to design principles for other materials which would be easier to manufacture, that could perhaps give you better superconductivity.”
What Makes a Conductor ‘Super’?
One of the most striking demonstrations of how superconductors work can be seen by placing an ordinary magnet over the top of such a material while it is cooled with liquid nitrogen. The magnet ‘levitates’ in place above the superconductor during this experiment. Whereas a normal conductor produces currents in a magnet moving past it via electromagnetic induction, superconductors ‘push’ the magnetic fields out by inducing surface currents. Instead of allowing the magnetic field to pass through it — with this passage measured by magnetic flux — the superconductor acts as a faux-magnet with the opposite polarity, repelling the ‘real’ magnet — a phenomenon called the Meissner effect.
The key to explaining superconductivity lies in understanding how electrons behave in materials at extremely low temperatures. Thermal energy randomly vibrates atoms in a material, and the higher the temperature, the faster the atoms vibrate.
At high temperatures, electrons — which all have the same negative charge — repel each other and act as free particles. Yet, there is still a tiny attraction between electrons in solids and liquids, and at low temperatures, electrons group together into what is known as Cooper pairs.
In Cooper pairs — named after American physicist Leon Cooper who first described this pairing up phenomenon in the mid-1950s — the electrons have an opposite spin. This is a quantum mechanical quantity that describes how a particle will behave when exposed to a magnetic field. One electron possesses spin ‘up’ and the other has spin ‘down.’ This state is described as a spin-singlet.
Cooper pairs travel unimpeded through a superconductor until they are exposed to a strong magnetic field. The electrons are then pulled in opposite directions, ripping the Cooper pairing apart.
Magnetic fields, therefore, destroy superconductivity. This is at least the case for spin-singlet superconductors. For exotic superconductors such as spin-triplet superconductors, the situation can be quite different.
More ‘Super’ Superconductors
In some exotic superconductors, electrons pair up with the same spin rather than opposite spins — or so-called spin-triplet pairs.
Spin describes how a particle behaves in a magnetic field. Particles of opposite spin move in opposite directions. However, if these electrons have the same spin, the Cooper pairing is not destroyed. Superconductivity is then preserved, even in extremely strong magnetic fields.
What Jarillo-Herrero and his team — already known for their pioneering work with the electronic properties of twisted graphene — wanted to discover was whether magic-angle trilayer graphene may display signs of spin-triplet superconductivity.
The researchers previously observed signs of this phenomenon in magic-angle bilayer graphene, but their new study showed that the effect is much stronger when an extra layer is added, with superconductivity retained at higher temperatures.
Surprisingly, trilayer graphene retained superconductivity in strong magnetic fields that would have wiped it out in its bilayer counterpart. To test this, the researchers exposed the magic-angle trilayer graphene to magnetic fields of increasing strengths. They found that superconductivity disappeared at a specific strength, but the graphene regained superconductivity at high field strengths.
This behavior is not seen in conventional spin-singlet superconductors.
The reintroduced superconductivity lasted in the magic-angle trilayer graphene up to a magnetic flux of 10 Tesla, but this was the maximum flux the team’s magnet could achieve. This means that this resurrected superconductivity could actually persist in even stronger fields.
The conclusion reached by the team; magic-angle trilayer graphene is not a run-of-the-mill superconductor.
“In spin-singlet superconductors, if you kill superconductivity, it never comes back — it’s gone for good,” says MIT postdoctoral researcher Yuan Cao. “Here, it reappeared again. So this definitely says this material is not spin-singlet.”
The question is: what exactly is the spin-state demonstrated by the material? This is something the team will now attempt to further investigate. Even with this question yet unanswered, we can still predict the kinds of applications that would benefit from this boosted resistance to magnetic fields.
Applications of Magic-Angle Trilayer Graphene Superconductors
The fact that this type of superconductor can resist high magnetic fields makes it incredibly useful across a range of applications; in particular, magnetic resonance imaging (MRI), which uses superconducting wires under intense magnetic fields to image biological tissues.
The functioning MRI devices are currently limited to their ability to resist a magnetic flux of no more than 3 Tesla, so if magic-angle graphene trilayer does display spin-triplet superconductivity, it could be used in such machines to boost their resistance to magnetic flux. The net result of this should be MRIs that can produce sharper and deeper images of human tissues.
Magic-angle trilayer graphene could be used in quantum computers to provide more resistant superconductors and much more powerful machines.
“Regular quantum computing is super fragile. You look at it and, poof, it disappears,” says Jarillo-Herrero. “About 20 years ago, theorists proposed a type of topological superconductivity that, if realized in any material, could enable a quantum computer where states responsible for computation are very robust.”
This results in a quantum computer with computing power that far exceeds anything currently available. However, the team does not yet know if the exotic superconductivity they have found in the magic-angle trilayer graphene is the right type to facilitate this computing boost.
“The key ingredient to realizing that would be spin-triplet superconductors, of a certain type. We have no idea if our type is of that type,” concludes Jarillo-Herrero. “But even if it’s not, this could make it easier to put trilayer graphene with other materials to engineer that kind of superconductivity.
“That could be a major breakthrough. But it’s still super early.”
References and Further Reading
¹ Jarillo-Herrero. P., Cao. Y., Park. J. M., et al,  Pauli-limit violation and re-entrant superconductivity in moiré graphene. Nature. https://doi.org/10.1038/s41586-021-03685-y


While the scientific community holds its breath for a large-scale quantum computer that could carry out useful calculations, a team of IBM researchers has approached the problem with an entirely different vision: to achieve more and better results right now, even with the limited quantum resources that exist today.
By tweaking their method, the scientists successfully simulated some molecules with a higher degree of accuracy than before, with no need for more qubits. The researchers effectively managed to pack more information into the mathematical functions that were used to carry out the simulation, meaning that the outcome of the process was far more precise, and yet came at no extra computational cost.
"We demonstrate that the properties for paradigmatic molecules such as hydrogen fluoride (HF) can be calculated with a higher degree of accuracy on today's small quantum computers," said the researchers, at the same time priding themselves on helping quantum computers "punch above their weight".
SEE: Hiring Kit: Computer Hardware Engineer (TechRepublic Premium)
Car manufacturer Daimler, a long-term quantum research partner of IBM's, has shown a strong interest in the results, which could go a long way in developing higher-performing, longer-lasting and less expensive batteries.
Since 2015, Daimler has been working on upgrading lithium-ion batteries to lithium-sulfur ones – a non-toxic and easily available material that would increase the capacity and speed-of-charging of electric vehicles.
Designing a battery based on new materials requires an exact understanding of which compounds should come together and how. The process involves accurately describing all the characteristics of all the molecules that make up the compound, as well as the particles that make up these molecules, to simulate how the compound will react in many different environments. In other words, it is an incredibly data-heavy job, with infinite molecular combinations to test before the right one is found.
The classical methods that exist today fail to render these simulations with the precision that is required for a breakthrough such as the one Daimler is working towards. "This is a big problem to develop next-generation batteries," Heike Riel, IBM Research quantum lead, told ZDNet. "Classical computers, and the models we've developed in physics and chemistry for many years still cannot solve those problems."
But the task could be performed at speed by quantum computers. Qubits, and their ability to encode different information at the same time, enable quantum algorithms to run several calculations at once – and are expected, one day, to enable quantum computers to tackle problems that are seemingly impossible, in a matter of minutes.
To do that, physicists need quantum computers that support many qubits; but scaling qubits is no piece of cake. Most quantum computers, including IBM's, work with less than 100 qubits, which is nowhere near enough to simulate the complex molecules that are needed for breakthroughs, such as lithium-sulfur car batteries.
Some of the properties of these molecules are typically represented in computer experiments with a mathematical function called a Hamiltonian, which represents particles' spatial functions, also called orbitals. In other words, the larger the molecule, the larger the orbital, and the more qubits and quantum operations will be needed.
"We currently can't represent enough orbitals in our simulations on quantum hardware to correlate the electrons found in complex molecules in the real world," said IBM's team.
Instead of waiting for a larger quantum computer that could take in weighty calculations, the researchers decided to see what they could do with the technology as it stands. To compensate for resource limitations, the team created a so-called "transcorrelated" Hamiltonian – one that was transformed to contain additional information about the behavior of electrons in a particular molecule.
This information, which concerns the propensity of negatively charged electrons to repel each other, cannot usually fit on existing quantum computers, because it requires too much extra computation. By incorporating the behavior of electrons directly into a Hamiltonian, the researchers, therefore, increased the accuracy of the simulation, yet didn't create the need for more qubits.
The method is a new step towards calculating materials' properties with accuracy on a quantum computer, despite the limited resources available to date. "The more orbitals you can simulate, the closer you can get to reproducing the results of an actual experiment," said the scientists. "Better modelling and simulations will ultimately result in the prediction of new materials with specific properties of interest."
IBM's findings might accelerate the timeline of events for quantum applications, therefore, with new use cases emerging even while quantum computers work with few qubits. According to the researchers, companies like Daimler are already keen to find out more about the breakthrough.
This is unlikely to shift IBM's focus on expanding the scale of its quantum computer. The company recently unveiled a roadmap to a million-qubit system, and said that it expects a fault-tolerant quantum computer to be an achievable goal for the next ten years. According to Riel, quantum simulation is likely to be one of the first applications of the technology to witness real-world impacts.
"The car batteries are a good example of this," she said. "Soon, the number of qubits will be enough to generate valuable insights with which you can develop new materials. We'll see quantum advantage soon in the area of quantum simulation and new materials."
IBM's roadmap announces that the company will reach 1,000 qubits in 2023, which could mark the start of early value creation in pharmaceuticals and chemicals, thanks to the simulation of small molecules.


You’re a what?
Quantum computer research scientist
Imagine typing a very complex query into your computer and having to wait more than a lifetime for results. Thanks to scientists like Davide Venturelli, supercomputers of the future could return those results in a fraction of a second.
Davide is a quantum computer research scientist for the Universities Space Research Association. Quantum theory explains how matter acts at the tiniest levels; in applying it to computing, researchers study ways in which that behavior can advance processing power. “We explore how to control these quantum behaviors, to make them happen on demand, in order to crunch numbers and process information,” he says. “We’re pushing the boundaries of what is known in computer science.”
What they do
Quantum computer research scientists help to solve problems. In their research, they make scientific assumptions based on quantum theory and then conduct experiments to test whether their solutions work.
These scientists may be involved in a variety of projects but often focus on a specific goal. Davide focuses on finding new ways of applying quantum theory to improve how computers solve optimization problems—that is, problems for finding the best of all possible solutions. Digital computers, which are most common today, process information using variables with 1 value (either 0 or 1) at a time. Quantum computers can use both values simultaneously, which results in faster processing. “We know that quantum computers are more powerful than digital computers,” he says, “but we don’t know by how much yet.”
Research. In studying information technology, quantum computer research scientists think about possibilities. For example, Davide asks questions in his research such as, “What is the fastest possible way we can make computers process information?”
Davide and other research scientists use their understanding of quantum theory to come up with solutions. Their research may lead to problem-solving computer processes that calculate and sort information much faster. For example, research scientists might develop a theoretical solution that can be run only on quantum computers designed to produce better weather forecasts.
Experiments. To test whether their theories work, quantum computer research scientists may conduct experiments or work with experimental physicists. For example, they may create a quantum environment with computer hardware, then test how particles in that environment react to different levels of laser intensity. Experiments that verify a theory may lead to improvements, such as more efficient computer design and faster, more secure communication for computer networks.
But relying on theory means that scientists work with incomplete information—so they’re sometimes surprised at the outcomes. “Experiments may result in the opposite of what you expect,” says Davide, “and you analyze the data to try to figure out why.”
Other job duties. Research scientists may write articles about their findings for academic journals or devise ways to apply their research to advance their employer’s goals. Some research scientist have other responsibilities. For example, Davide also manages external research collaborations for NASA’s Quantum Artificial Intelligence Laboratory.
How to become one
To become a quantum computer research scientist, you usually need a doctoral degree (Ph.D.). But you need some qualities and skills in addition to the formal credential.
Qualities and skills. As researchers, quantum computer research scientists should enjoy being part of a team and sharing their findings with others, which may include engineers, mathematicians, physicists, and Ph.D. students. This collaboration helps bring varied perspectives to solving a problem. “There’s a cross-utilization of ideas when you work with different groups,” Davide says. “My colleagues are very smart and open-minded people.”
Like many scientists, quantum computer research scientists must have strong analytical, critical thinking, and reasoning skills to solve complex problems. Attention to detail is critical as scientists precisely record their theories and experiments, which must be reproducible and able to withstand peer review.
Communication skills are also important. To share their research with collaborators or the public, quantum research scientists must be able to write papers and present their findings at conferences. They may also need to write proposals for grants to fund research projects.
Education. Quantum computer research scientists usually need a Ph.D. to learn methods of discovery and to develop the tools needed for researching. Coursework in undergraduate and graduate degree programs typically includes computer science, mathematics, and physics.
You may decide to pursue a master’s degree with classes in quantum computing before entering a Ph.D. program. Davide studied physics at the bachelor’s and master’s levels, but he was passionate about computers, too. Not surprisingly, quantum computing piqued his interest. “It’s a wonderful interaction between the two disciplines,” he says. Davide earned his Ph.D. in nanophysics and numerical simulations of condensed matter.
What to expect
The U.S. Bureau of Labor Statistics (BLS) does not collect data specifically on quantum computer research scientists. Instead, BLS may count these workers among physicists, of which 15,650 were employed in May 2015. The median annual wage for physicists in colleges, universities, and professional schools—where most quantum computer research scientists are likely to work—was $63,840. That’s more than the median annual wage of $36,200 for all workers.
Quantum computer research scientists work primarily indoors, in academic settings, and may travel frequently to attend seminars or conferences. Area of focus or project type may dictate specific details of their work. For example, testing particularly intricate theories may take days or months, working either independently or with other scientists.
Whether alone or with colleagues, Davide enjoys his work for the independence his job offers. “You have lots of intellectual freedom. Nobody really tells you what to do,” he says. “It’s up to your skills and vision.”
About the Author
Domingo Angeles is an economist in the Office of Occupational Statistics and Employment Projections, BLS. He can be reached at (202) 691-5475 or email@example.com .
Domingo Angeles, "Quantum computer research scientist," Career Outlook, U.S. Bureau of Labor Statistics, July 2016.


In this new post on quantum computing, we are going to talk about quantum teleportation. Teleportation. OMG. Yes, I can see those stars sparking in your geeky eyes …
So … first, let’s clarify a few things, shall we ?
Quantum teleportation is a communications protocol that transfers the quantum state of a system to another spatially separated system. For this, it takes advantage of quantum entanglement. Contrary to what the name suggests, it is not a matter of transferring matter (or energy).
Quantum teleportation is defined as a process by which a quantum bit can be transmitted from one location to another, without the quantum bit actually being transmitted through space
So, although the name is inspired by the teleportation commonly used in fiction, quantum teleportation is not a form of transportation, but a form of communication.
Please stay. I won’t tell Captain Kirk. And Mr Spock would be so proud of you he could smile.
The seminal paper first expounding the idea of quantum teleportation was published by C. H. Bennett, G. Brassard, C. Crépeau, R. Jozsa, A. Peres and W. K. Wootters in 1993.
Quantum teleportation requirements are:
- Two locations A and B (Alice and Bob),
- The ability to create an entangled EPR pair
- A conventional communication channel, used to carry classical bits,
- A quantum channel, used to send qubits from the entangled pair to A and B
The protocol goes as follows:
- The teleportation protocol begins with a quantum state , in Alice’s possession. The purpose of the teleportation is to convey from Alice to Bob.
Generally speaking, this qubit can be written as: .
- Next, the protocol requires that Alice and Bob share a maximally entangled state. It can be any one of the four Bell states (it doesn’t matter which one).
Let’s say that Alice and Bob mutually agreed on: .
- Now, let’s assume that Alice and Bob are sharing the state .
- Through the quantum channel, Alice obtains one of the particles in the pair, with the other going to Bob. This can be implemented, for example, by preparing the particles together and shooting them to Alice and Bob from a common source.
- At this point:
- Alice has two particles : (the one that she wants to teleport), and one of the entangled pair (let’s call it A)
- Bob has one particle: the other part of the entangled pair (let’s call it B).
- A the global system level, the state is described by a three-particles quantum state:
- Alice makes a local measurement on the two particles in her possession. Alice’s two particles are now entangled to each other. The result of Alice’s (local) measurement is that the three-particle state would collapse to one of the four possible states. The entanglement originally shared between Alice’s and Bob’s particles is now broken.
Experimentally, this measurement may be achieved via a series of laser pulses directed at the two particles.
- Following the local measurement, Bob’s particle now takes on one of four possible superpositions. With a little math (expressing the quantum states in terms of the 4 Bell states basis), it is easy to show that these possible are unitary images of the qubits to be teleported.
- The result of Alice’s Bell measurement tells her which of the above four states the system is in. Alice then sends her result to Bob through a classical channel (using two classical bits to communicate which of the four results she obtained). This is the only potentially time-consuming step, due to speed-of-light considerations.
- After Bob receives the message from Alice, he knows then which of the four states his particle is in. Using this information, he can perform a unitary operation to transfer the state on its particle. Teleportation is thus achieved.
Please note that:
- After this operation, Bob’s qubit will take on the state and Alice’s qubit becomes an (undefined) part of an entangled state. Teleportation does not result in the copying of qubits, and hence is consistent with the no cloning theorem.
- There is no transfer of matter or energy involved. Alice’s particle has not been physically moved to Bob: only its state has been transferred.
- Every time a qubit is teleported, Alice needs to send Bob two bits of information thought the classical communication channel.These two classical bits do not carry complete information about the qubit being teleported.
If Eve (an eavesdropper) intercepts these two bits, she may know exactly what Bob needs to do in order to recover the desired state. However, this information is useless if she cannot interact with the entangled particle in Bob’s possession.
It is possible to express the previous quantum teleportation protocol in terms of quantum circuits. Typically, the unitary transformation that is the change of basis (from the standard product basis into the Bell basis) can be written using quantum gates:
This quantum circuit will be used in the next paragraph, as the basis of a little quantum algorithm experimentation with the Q# language and its Quantum Development Kit.
Experimenting with Q#
We introduced the basic concepts of Q# in our last post on Bell states. Basic quantum teleportation code is provided as a sample in the Quantum Development Kit. Let’s have fun and follow it !
Let’s start with the non-quantum part of the program, used to invoke the quantum simulator, feed it with input data and read outputs from it:
It is rather simple:
- it invokes the quantum simulator,
- it tries 8 quantum teleportations,
- for each round, it randomly chooses the boolean value (either “true” or “false”) to be sent, then checks if this value has been properly teleported.
Now comes the quantum part of the program. As we have seen earlier on, two communication channels are required:
- A classical channel (for classical data)
- A quantum channel (for the entangled EPR pair)
The implementations are following the circuit for quantum teleportation introduced in the previous paragraph.
The code for the classical channel is:
And the code for the quantum channel is:
… and the results (outputs from the classical part of the program) are:
Great ! We have successfully teleported 8 boolean values 🙂
Importance of quantum teleportation
Since 1993, many real life quantum teleportation experiments have been carried out. First verifications came as early as 1998, and subsequently, the record distance for quantum teleportation has been gradually increased.
On 26 February 2015, scientists at the University of Science and Technology of China in Hefei, led by Chao-yang Lu and Jian-Wei Pan carried out the first experiment teleporting multiple degrees of freedom of a quantum particle. Later on (2017), the team achieved the first quantum teleportation from Earth to a satellite, while their counterparts in Japan are the first to use a microsatellite for quantum communications.
Masahide Sasaki and colleagues at the National Institute of Information and Communications Technology in Japan demonstrated in late 2017 that they were able to receive and process the information at a ground station in Japan using a quantum key distribution (QKD) protocol. QKD uses principles of quantum mechanics to ensure that two parties can share an encryption key secure in the knowledge that it has not been intercepted by a third party.
Quantum teleportation is a very active subject of research, with concrete applications to telecommunications and encryption.
Note: to speedup the writing of this post, a few paragraphs and illustrations are based on wikipedia’s entries on quantum teleportation. Q# code is based on MS Quantum Development Kit documentations and samples.