QT/ First hybrid quantum bit based on topological insulators
Quantum news biweekly vol.25, 8th April — 25th April
TL;DR
- With their superior properties, topological qubits could help achieve a breakthrough in the development of a quantum computer designed for universal applications. So far, no one has yet succeeded in unambiguously demonstrating a quantum bit, or qubit for short, of this kind in a lab. Scientists have now succeeded in integrating a topological insulator into a conventional superconducting qubit.
- Researchers have successfully generated strongly nonclassical light using a modular waveguide-based light source. By combining a waveguide optical parametric amplifier (OPA) module created for quantum experiments and a specially designed photon detector, researchers were able to produce light in a superposition of coherent states. The achievement represents a crucial step toward creating faster and more practical optical quantum computers.
- Milling rice to separate the grain from the husks, produces about 100 million tons of rice husk waste globally each year. Scientists searching for a scalable method to fabricate quantum dots have developed a way to recycle rice husks to create the first silicon quantum dot LED light. Their new method transforms agricultural waste into state-of-the-art light-emitting diodes in a low-cost, environmentally friendly way.
- In a discovery that could speed research into next-generation electronics and LED devices, a research team has developed a reliable, scalable method for growing single layers of hexagonal boron nitride on graphene.
- A special form of light made using an ancient Namibian gemstone could be the key to new light-based quantum computers, which could solve long-held scientific mysteries, according to new research led by the University of St Andrews. The research used a naturally mined cuprous oxide (Cu2O) gemstone from Namibia to produce Rydberg polaritons, the largest hybrid particles of light and matter ever created.
- Lawrence Berkeley National Laboratory physicists have leveraged an IBM Q quantum computer through the Oak Ridge Leadership Computing Facility’s Quantum Computing User Program to capture part of a calculation of two protons colliding. The calculation can show the probability that an outgoing particle will emit additional particles.
- Teleportation may be a concept usually reserved for science fiction, but researchers have demonstrated that it can be used to avoid loss in communication channels on the quantum level. The team have highlighted the issues around inherent loss that occurs across every form of communication channel (for example, internet or phone) and discovered a mechanism that can reduce that loss.
- Magnetism, one of the oldest technologies known to humans, is at the forefront of new-age materials that could enable next-generation lossless electronics and quantum computers. Researchers have discovered a new ‘knob’ to control the magnetic behavior of one promising quantum material, and the findings could pave the way toward novel, efficient and ultra-fast devices.
- Researchers at the Weizmann Institute of Science have been trying to devise new and more advanced tools to study the basic interactions between a single pair of atoms. In a paper recently published in Nature Physics, they introduced a new technique based on quantum logic that can be used to study interactions between an ultracold neutral atom and a cold ion.
- Bank of Canada, Multiverse Computing complete preliminary quantum simulation of cryptocurrency market.
- And more!
Quantum Computing Market
According to the recent market research report ‘Quantum Computing Market with COVID-19 impact by Offering (Systems and Services), Deployment (On Premises and Cloud Based), Application, Technology, End-use Industry and Region — Global Forecast to 2026’, published by MarketsandMarkets, the Quantum Computing market is expected to grow from USD 472 million in 2021 to USD 1,765 million by 2026, at a CAGR of 30.2%. The early adoption of quantum computing in the banking and finance sector is expected to fuel the growth of the market globally. Other key factors contributing to the growth of the quantum computing market include rising investments by governments of different countries to carry out research and development activities related to quantum computing technology. Several companies are focusing on the adoption of QCaaS post-COVID-19. This, in turn, is expected to contribute to the growth of the quantum computing market. However, stability and error correction issues are expected to restrain the growth of the market.
According to ‘Quantum Computing Market Research Report: By Offering, Deployment Type, Application, Technology, Industry — Industry Share, Growth, Drivers, Trends and Demand Forecast to 2030’ report, the quantum computing market is projected to reach $64,988 million by 2030. Machine learning (ML) is expected to progress at the highest CAGR, during the forecast period, among all application categories, owing to the fact that quantum computing is being integrated in ML for improving the latter’s use case.
Latest Research
Integration of Topological Insulator Josephson Junctions in Superconducting Qubit Circuits
by Tobias W. Schmitt, Malcolm R. Connolly, Michael Schleenvoigt, Chenlu Liu, Oscar Kennedy, José M. Chávez-Garcia, Abdur R. Jalil, Benjamin Bennemann, Stefan Trellenkamp, Florian Lentz, Elmar Neumann, Tobias Lindström, Sebastian E. de Graaf, Erwin Berenschot, Niels Tas, Gregor Mussler, Karl D. Petersson, Detlev Grützmacher, Peter Schüffelgen in Nano Letters
With their superior properties, topological qubits could help achieve a breakthrough in the development of a quantum computer designed for universal applications. So far, no one has yet succeeded in unambiguously demonstrating a quantum bit, or qubit for short, of this kind in a lab. However, scientists from Forschungszentrum Jülich have now gone some way to making this a reality. For the first time, they succeeded in integrating a topological insulator into a conventional superconducting qubit.
Quantum computers are regarded as the computers of the future. Using quantum effects, they promise to deliver solutions for highly complex problems that cannot be processed by conventional computers in a realistic time frame. However, the widespread use of such computers is still a long way off. Current quantum computers generally contain only a small number of qubits. The main problem is that they are highly prone to error. The bigger the system, the more difficult it is to fully isolate it from its environment.
Many hopes are therefore pinned on a new type of quantum bit — the topological qubit. This approach is being pursued by several research groups as well as companies such as Microsoft. This type of qubit exhibits the special feature that it is topologically protected; the particular geometric structure of the superconductors as well as their special electronic material properties ensure that quantum information is retained. Topological qubits are therefore considered to be particularly robust and largely immune to external sources of decoherence. They also appear to enable fast switching times comparable to those achieved by the conventional superconducting qubits used by Google and IBM in current quantum processors.
However, it is not yet clear whether we will ever succeed in actually producing topological qubits. This is because a suitable material basis is still lacking to experimentally generate the special quasiparticles required for this without any doubt. These quasiparticles are also known as Majorana states. Until now, they could only be unambiguously demonstrated in theory, but not in experiments. Hybrid qubits, as they have now been constructed for the first time by the research group led by Dr. Peter Schüffelgen at the Peter Grünberg Institute (PGI-9) of Forschungszentrum Jülich, are now opening up new possibilities in this area. They already contain topological materials at crucial points. Therefore, this novel type of hybrid qubit provides researchers with a new experimental platform to test the behaviour of topological materials in highly sensitive quantum circuits.
Generation of Schrödinger cat states with Wigner negativity using a continuous-wave low-loss waveguide optical parametric amplifier
by Kan Takase, Akito Kawasaki, Byung Kyu Jeong, Mamoru Endo, Takahiro Kashiwazaki, Takushi Kazama, Koji Enbutsu, Kei Watanabe, Takeshi Umeki, Shigehito Miki, Hirotaka Terai, Masahiro Yabuno, Fumihiro China, Warit Asavanant, Jun-ichi Yoshikawa, Akira Furusawa in Optics Express
For the first time, researchers have successfully generated strongly nonclassical light using a modular waveguide-based light source. The achievement represents a crucial step toward creating faster and more practical optical quantum computers.
“Our goal is to dramatically improve information processing by developing faster quantum computers that can perform any type of computation without errors,” said research team member Kan Takase from the University of Tokyo. “Although there are several ways to create a quantum computer, light-based approaches are promising because the information processor can operate at room temperature and the computing scale can be easily expanded.”
In the Optica Publishing Group journal Optics Express, a multi-institutional team of researchers from Japan describe the waveguide optical parametric amplifier (OPA) module they created for quantum experiments. Combining this device with a specially designed photon detector allowed them to generate a state of light known as Schrödinger cat, which is a superposition of coherent states.
“Our method for generating quantum light can be used to increase the computing power of quantum computers and to make the information processer more compact,” said Takase. “Our approach outperforms conventional methods, and the modular waveguide OPA is easy to operate and integrate into quantum computers.”
Continuous wave squeezed light is used to generate the various quantum states necessary to perform quantum computing. For the best computing performance, the squeezed light source must exhibit very low levels of light loss and be broadband, meaning it includes a wide range of frequencies.
“We want to increase the clock frequency of optical quantum computers, which can, in principle, achieve Terahertz frequencies,” said Takase. “Higher clock frequencies enable faster execution of computational tasks and allow the delay lines in the optical circuits to be shortened. This makes optical quantum computers more compact while also making it easier to develop and stabilize the overall system.”
OPAs use nonlinear optical crystals to generate squeezed light, but conventional OPAs don’t generate the quantum light with the properties necessary for faster quantum computing. To overcome this challenge, researchers from the University of Tokyo and NTT Corporation developed an OPA based on a waveguide-type device that achieves high efficiency by confining light to a narrow crystal.
By carefully designing the waveguide and manufacturing it with precision processing, they were able to create an OPA device with much smaller propagation loss than conventional devices. It can also be modularized for use in various experiments with quantum technologies.
The OPA device was designed to create squeezed light at telecommunications wavelengths, a wavelength region that tends to exhibit low losses. To complete the system, researchers needed a high-performance photon detector that worked at telecom wavelengths. However, standard photon detectors based on semiconductors don’t meet the performance requirements for this application.
Thus, researchers from University of Tokyo and National Institute of Information and Communications Technology (NICT) developed a detector designed specifically for quantum optics. The new superconducting nanostrip photon detector (SNSPD) uses superconductivity technology to detect photons.
“We combined our new waveguide OPA with this photon detector to generate a highly non-classical — or quantum — state of light called Schrödinger cat,” said Takase. “Generating this state, which is difficult with conventional, low-efficiency waveguide OPAs, confirms the high performance of our waveguide OPA and opens the possibility of using this device for a wide range of quantum experiments.”
The researchers are now looking at how to combine high-speed measurement techniques with the new waveguide OPA to get closer to their goal of ultrafast optical quantum computing.
Scalable Synthesis of Monolayer Hexagonal Boron Nitride on Graphene with Giant Bandgap Renormalization
by Ping Wang, Woncheol Lee, Joseph P. Corbett, William H. Koll, Nguyen M. Vu, David Arto Laleyan, Qiannan Wen, Yuanpeng Wu, Ayush Pandey, Jiseok Gim, Ding Wang, Diana Y. Qiu, Robert Hovden, Mackillo Kira, John T. Heron, Jay A. Gupta, Emmanouil Kioupakis, Zetian Mi in Advanced Materials
In a discovery that could speed research into next-generation electronics and LED devices, a University of Michigan research team has developed the first reliable, scalable method for growing single layers of hexagonal boron nitride on graphene.
The process, which can produce large sheets of high-quality hBN with the widely used molecular-beam epitaxy process, is detailed in a study in Advanced Materials.
Graphene-hBN structures can power LEDs that generate deep-UV light, which is impossible in today’s LEDs, said Zetian Mi, U-M professor of electrical engineering and computer science and a corresponding author of the study. Deep-UV LEDs could drive smaller size and greater efficiency in a variety of devices including lasers and air purifiers.
“The technology used to generate deep-UV light today is mercury-xenon lamps, which are hot, bulky, inefficient and contain toxic materials,” Mi said. “If we can generate that light with LEDs, we could see an efficiency revolution in UV devices similar to what we saw when LED light bulbs replaced incandescents.”
Hexagonal boron nitride is the world’s thinnest insulator while graphene is the thinnest of a class of materials called semimetals, which have highly malleable electrical properties and are important for their role in computers and other electronics.
Bonding hBN and graphene together in smooth, single-atom-thick layers unleashes a treasure trove of exotic properties. In addition to deep-UV LEDs, graphene-hBN structures could enable quantum computing devices, smaller and more efficient electronics and optoelectronics and a variety of other applications.
“Researchers have known about the properties of hBN for years, but in the past, the only way to get the thin sheets needed for research was to physically exfoliate them from a larger boron nitride crystal, which is labor-intensive and only yields tiny flakes of the material,” Mi said. “Our process can grow atomic-scale-thin sheets of essentially any size, which opens a lot of exciting new research possibilities.”
Because graphene and hBN are so thin, they can be used to build electronic devices that are much smaller and more energy-efficient than those available today. Layered structures of hBN and graphene can also exhibit exotic properties that could store information in quantum computing devices, like the ability to switch from a conductor to an insulator or support unusual electron spins.
While researchers have tried in the past to synthesize thin layers of hBN using methods like sputtering and chemical vapor deposition, they struggled to get the even, precisely ordered layers of atoms that are needed to bond correctly with the graphene layer.
“To get a useful product, you need consistent, ordered rows of hBN atoms that align with the graphene underneath, and previous efforts weren’t able to achieve that,” said Ping Wang, a postdoctoral researcher in electrical engineering and computer science. “Some of the hBN went down neatly, but many areas were disordered and randomly aligned.”
The team, made up of electrical engineering and computer science, materials science and engineering, and physics researchers, discovered that neat rows of hBN atoms are more stable at high temperature than the undesirable jagged formations. Armed with that knowledge, Wang began experimenting with molecular-beam epitaxy, an industrial process that amounts to spraying individual atoms onto a substrate.
Wang used a terraced graphene substrate — essentially an atomic-scale staircase — and heated it to around 1600 degrees Celsius before spraying on individual boron and active nitrogen atoms.The result far exceeded the team’s expectations, forming neatly ordered seams of hBN on the graphene’s terraced edges, which expanded into wide ribbons of material.
“Experimenting with large amounts of pristine hBN was a distant dream for many years, but this discovery changes that,” Mi said. “This is a big step toward the commercialization of 2D quantum structures.”
This result would not have been possible without collaboration from a variety of disciplines. The mathematical theory that underpinned some of the work involved researchers in electrical engineering and computer science and materials science and engineering, from U-M and Yale University.
Orange–Red Si Quantum Dot LEDs from Recycled Rice Husks
by Shiho Terada, Honoka Ueda, Taisei Ono, Ken-ichi Saitow in ACS Sustainable Chemistry & Engineering
Milling rice to separate the grain from the husks produces about 100 million tons of rice husk waste globally each year. Scientists searching for a scalable method to fabricate quantum dots have developed a way to recycle rice husks to create the first silicon quantum dot (QD) LED light. Their new method transforms agricultural waste into state-of-the-art light-emitting diodes in a low-cost, environmentally friendly way.
“Since typical QDs often involve toxic material, such as cadmium, lead, or other heavy metals, environmental concerns have been frequently deliberated when using nanomaterials. Our proposed process and fabrication method for QDs minimizes these concerns,” said Ken-ichi Saitow, lead study author and a professor of chemistry at Hiroshima University.
Since porous silicon (Si) was discovered in the 1950s, scientists have explored its uses in applications in lithium-ion batteries, luminescent materials, biomedical sensors, and drug delivery systems. Non-toxic and found abundantly in nature, Si has photoluminescence properties, stemming from its microscopic (quantum-sized) dot structures that serve as semiconductors.
Aware of the environmental concerns surrounding the current quantum dots, the researchers set out to find a new method for fabricating quantum dots that has a positive environmental impact. Waste rice husks, it turns out, are an excellent source of high-purity silica (SiO2) and value-added Si powder.
The team used a combination of milling, heat treatments, and chemical etching to process the rice husk silica: First, they milled rice husks and extracted silica (SiO2) powders by burning off organic compounds of milled rice husks. Second, they heated the resulting silica powder in an electric furnace to obtain Si powders via a reduction reaction. Third, the product was a purified Si powder that was further reduced to 3 nanometer in size by chemical etching. Finally, its surface was chemically functionalized for high chemical stability and high dispersivity in solvent, with 3 nm crystalline particles to produce the SiQDs that luminesce in the orange-red range with high luminescence efficiency of over 20%.
“This is the first research to develop an LED from waste rice husks,” said Saitow, adding that the non-toxic quality of silicon makes them an attractive alternative to current semiconducting quantum dots available today.
“The present method becomes a noble method for developing environmentally friendly quantum dot LEDs from natural products,” he said.
The LEDs were assembled as a series of material layers. An indium-tin-oxide (ITO) glass substrate was the LED anode; it is a good conductor of electricity while sufficiently transparent for light emission. Additional layers were spin-coated onto the ITO glass, including the layer of SiQDs. The material was capped with an aluminum film cathode.
The chemical synthesis method the team developed has allowed them to evaluate the optical and optoelectrical properties of the SiQD light-emitting diode, including the structures, synthesis yields, and properties of the SiO2 and Si powders and SiQDs.
“By synthesizing high-yield SiQDs from rich husks and dispersing them in organic solvents, it is possible that one day these processes could be implemented on a large scale, like other high-yield chemical processes,” Saitow said.
The team’s next steps include developing higher efficiency luminescence in the SiQDs and the LEDs. They will also explore the possibility of producing SiQD LEDs other than the orange-red color they have just created. Looking ahead, the scientists suggest that the method they have developed could be applied to other plants, such as sugar cane bamboo, wheat, barley, or grasses, that contain SiO2. These natural products and their wastes might hold the potential for being transformed into non-toxic optoelectronic devices. Ultimately, the scientists would like to see commercialization of this eco-friendly approach to creating luminescent devices from rice husk waste.
Rydberg exciton–polaritons in a Cu2O microcavity
by Konstantinos Orfanakis et al in Nature Materials
A special form of light made using an ancient Namibian gemstone could be the key to new light-based quantum computers, which could solve long-held scientific mysteries, according to new research led by the University of St Andrews. The research, conducted in collaboration with scientists at Harvard University in the US, Macquarie University in Australia and Aarhus University in Denmark and published in Nature Materials, used a naturally mined cuprous oxide (Cu2O) gemstone from Namibia to produce Rydberg polaritons, the largest hybrid particles of light and matter ever created.
Rydberg polaritons switch continually from light to matter and back again. In Rydberg polaritons, light and matter are like two sides of a coin, and the matter side is what makes polaritons interact with each other.
This interaction is crucial because this is what allows the creation of quantum simulators, a special type of quantum computer, where information is stored in quantum bits. These quantum bits, unlike the binary bits in classical computers that can only be 0 or 1, can take any value between 0 and 1. They can therefore store much more information and perform several processes simultaneously.
This capability could allow quantum simulators to solve important mysteries of physics, chemistry and biology, for example, how to make high-temperature superconductors for highspeed trains, how cheaper fertilizers could be made potentially solving global hunger, or how proteins fold making it easier to produce more effective drugs.
Project lead Dr. Hamid Ohadi, of the School of Physics and Astronomy at the University of St Andrews, says that “making a quantum simulator with light is the holy grail of science. We have taken a huge leap towards this by creating Rydberg polaritons, the key ingredient of it.”
To create Rydberg polaritons, the researchers trapped light between two highly reflective mirrors. A cuprous oxide crystal from a stone mined in Namibia was then thinned and polished to a 30-micrometer thick slab (thinner than a strand of human hair) and sandwiched between the two mirrors to make Rydberg polaritons 100 times larger than ever demonstrated before.
One of the leading authors Dr. Sai Kiran Rajendran, of the School of Physics and Astronomy at the University of St Andrews, says that “purchasing the stone on eBay was easy. The challenge was to make Rydberg polaritons that exist in an extremely narrow color range.”
The team is currently further refining these methods in order to explore the possibility of making quantum circuits, which are the next ingredient for quantum simulators.
Simulating Collider Physics on Quantum Computers Using Effective Field Theories
by Christian W. Bauer et al in Physical Review Letters
Lawrence Berkeley National Laboratory physicists Christian Bauer, Marat Freytsis and Benjamin Nachman have leveraged an IBM Q quantum computer through the Oak Ridge Leadership Computing Facility’s Quantum Computing User Program to capture part of a calculation of two protons colliding. The calculation can show the probability that an outgoing particle will emit additional particles.
In the team’s recent paper, published in Physical Review Letters, the researchers describe how they used a method called effective field theory to break down their full theory into components. Ultimately, they developed a quantum algorithm to allow the computation of some of these components on a quantum computer while leaving other computations for classical computers.
“For a theory that’s close to nature, we showed how this would work in principle. Then we took a very simplified version of that theory and did an explicit calculation on a quantum computer,” Nachman said.
The Berkeley Lab team aims to uncover insights about the smallest building blocks of nature by observing high-energy particle collisions in laboratory environments, such as the Large Hadron Collider in Geneva, Switzerland. The team is exploring what happens in these collisions by using calculations to compare predictions with the actual collision debris.
“One of the difficulties of these kinds of calculations is that we want to describe a large range of energies,” Nachman said. “We want to describe the highest-energy processes down to the lowest-energy processes by analyzing the corresponding particles that fly into our detector.”
Using a quantum computer alone to solve these kinds of calculations requires a number of qubits that is well beyond the quantum compute resources available today. The team can calculate these problems on classical systems using approximations, but these ignore important quantum effects. Therefore, the team aimed to separate the calculation into different chunks that were either well-suited for classical systems or quantum computers.
The team ran experiments on the IBM Q through the OLCF’s QCUP program at the U.S. Department of Energy’s Oak Ridge National Laboratory to verify that the quantum algorithms they developed reproduced the expected results at a small scale that can still be computed and confirmed with classical computers.
“This is an absolutely critical demonstration problem,” Nachman said. “For us, it’s important that we describe these particles’ properties theoretically and then actually implement a version of them on a quantum computer. A lot of challenges that arise when you run on a quantum computer don’t happen theoretically. Our algorithm scales, so when we get more quantum resources, we will be able to make calculations that we couldn’t make classically.”
The team also aims to make quantum computers usable so that they can perform the kinds of science they hope to do. Quantum computers are noisy, and this noise introduces errors into the calculations. Therefore, the team also deployed error mitigation techniques that they had developed in previous work.
Next, the team hopes to add more dimensions to their problem, break their space up into a smaller number of points and scale up the size of their problem. Eventually, they hope to make calculations on a quantum computer that are not possible with classical computers.
“The quantum computers that are available through ORNL’s IBM Q agreement have around 100 qubits, so we should be able to scale up to bigger system sizes,” Nachman said.
The researchers also hope to relax their approximations and move to physics problems that are closer to nature so that they can perform calculations that are more than proof of concept.
Quantum channel correction outperforming direct transmission
by Sergei Slussarenko et al in Nature Communications
Teleportation may be a concept usually reserved for science fiction, but researchers have demonstrated that it can be used to avoid loss in communication channels on the quantum level. The team, including researchers from Griffith University’s Centre for Quantum Dynamics, have highlighted the issues around inherent loss that occurs across every form of communication channel (for example, internet or phone) and discovered a mechanism that can reduce that loss.
Professor Geoff Pryde, Dr. Sergei Slussarenko, Dr. Sacha Kocsis and Dr. Morgan Weston, along with researchers from The University of Queensland and the National Institute of Standards and Technology, say the finding is an important step towards implementing “quantum internet,” which will bring unprecedented capabilities not accessible with today’s web.
Dr. Slussarenko said this study was the first to demonstrate an error reduction method that improved the performance of a channel.
“First, we looked at the raw data transmitted via our channel and could see a better signal with our method, than without it,” he said.
“In our experiment, we first sent a photon through the loss — this photon is not carrying any useful information so losing it was not a big problem. We could then correct for the effects of loss via a device called noiseless linear amplifier developed at Griffith and the University of Queensland.
“It can recover the lost quantum state, but it cannot always succeed; sometimes it fails. However, once the recovery succeeds, we then use another purely quantum protocol — called quantum state teleportation — to teleport the information we wanted to transmit into the now corrected carrier, avoiding all the loss on the channel.”
Quantum technologies promise revolutionary changes in our information-based society, a quantum communication develops methods such as the one demonstrated in this study to transmit data in an extremely secure and safe way, so that it is impossible to access by a third party.
“Short-distance quantum encryption is already used commercially, however if we want to implement a global quantum network, photon loss becomes in issue because it is unavoidable,” Dr. Slussarenko said. “Our work implements a so-called quantum relay, a key ingredient of this long-distance communication network. The no cloning theorem forbids making copies of unknown quantum data, so if a photon that carries information is lost, the information it carried is gone forever. A working long-distance quantum communication channel needs a mechanism to reduce this information loss, which is exactly what we did in our experiment.”
Dr. Slussarenko said the next step in this study would be to reduce the errors to a level where the team could implement long-distance quantum cryptography, and test the method using real-life optical infrastructure, such as those used for fiber-based internet.
Interlayer magnetophononic coupling in MnBi2Te4
by Hari Padmanabhan, Maxwell Poore, Peter K. Kim, Nathan Z. Koocher, Vladimir A. Stoica, Danilo Puggioni, Huaiyu (Hugo) Wang, Xiaozhe Shen, Alexander H. Reid, Mingqiang Gu, Maxwell Wetherington, Seng Huat Lee, Richard D. Schaller, Zhiqiang Mao, Aaron M. Lindenberg, Xijie Wang, James M. Rondinelli, Richard D. Averitt, Venkatraman Gopalan in Nature Communications
Magnetism, one of the oldest technologies known to humans, is at the forefront of new-age materials that could enable next-generation lossless electronics and quantum computers. Researchers led by Penn State and the university of California, San Diego have discovered a new ‘knob’ to control the magnetic behavior of one promising quantum material, and the findings could pave the way toward novel, efficient and ultra-fast devices.
“The unique quantum mechanical make-up of this material — manganese bismuth telluride — allows it to carry lossless electrical currents, something of tremendous technological interest,” said Hari Padmanabhan, who led the research as a graduate student at Penn State. “What makes this material especially intriguing is that this behavior is deeply connected to its magnetic properties. So, a knob to control magnetism in this material could also efficiently control these lossless currents.”
Manganese bismuth telluride, a 2D material made of atomically thin stacked layers, is an example of a topological insulator, exotic materials that simultaneously can be insulators and conductors of electricity, the scientists said. Importantly, because this material is also magnetic, the currents conducted around its edges could be lossless, meaning they do not lose energy in the form of heat. Finding a way to tune the weak magnetic bonds between the layers of the material could unlock these functions.
“Phonons are tiny atomic wiggles — atoms dancing together in various patterns, present in all materials,” Padmanabhan said. “We show that these atomic wiggles can potentially function as a knob to tune the magnetic bonding between the atomic layers in manganese bismuth telluride.”
The scientists at Penn State studied the material using a technique called magneto-optical spectroscopy — shooting a laser onto a sample of the material and measuring the color and intensity of the reflected light, which carries information on the atomic vibrations. The team observed how the vibrations changed as they altered the temperature and magnetic field.
As they altered the magnetic field, the scientists observed changes in the intensity of the phonons. This effect is due to the phonons influencing the weak inter-layer magnetic bonding, the scientists said.
“Using temperature and magnetic field to vary the magnetic structure of the material — much like using a refrigerator magnet to magnetize a needle compass — we found that the phonon intensities were strongly correlated with the magnetic structure,” said Maxwell Poore, graduate student at UC San Diego, and co-author of the study. “Pairing these findings with theoretical calculations, we inferred that these atomic vibrations modify the magnetic bonding across layers of this material.”
Scientists at UC San Diego conducted experiments to track these atomic vibrations in real time. The phonons oscillate faster than a trillion times a second, many times faster than modern computer chips, the scientists said. A 3.5 gigahertz computer processor, for example, operates at a frequency of 3.5 billion times per second.
“What was beautiful about this result was that we studied the material using different complementary experimental methods at different institutions and they all remarkably converged to the same picture,” said Peter Kim, graduate student at UC San Diego, and co-author of the paper.
Further research is needed to directly use the magnetic knob, the scientists said. But if that can be achieved, it could lead to ultra-fast devices that can efficiently and reversibly control lossless currents.
“A major challenge in making faster, more powerful electronic processors is that they heat up,” said Venkatraman Gopalan, professor of materials science and engineering and physics at Penn State, Padmanabhan’s former adviser, and co-author of the paper. “Heating wastes energy. If we could find efficient ways to control materials that host lossless currents, that would potentially allow us to deploy them in future energy-efficient electronic devices.”
Quantum logic detection of collisions between single atom–ion pairs
Or Katz et al in Nature Physics
Researchers at the Weizmann Institute of Science have been trying to devise new and more advanced tools to study the basic interactions between a single pair of atoms. In a paper recently published in Nature Physics, they introduced a new technique based on quantum logic that can be used to study interactions between an ultracold neutral atom and a cold ion.
Quantum chemistry is the branch of chemistry that explores the applications of quantum mechanics to chemical systems. Studies in this field can help to better understand the behavior of pairs or groups of atoms in a quantum state as well as the chemical reactions resulting from their interactions.
Many quantum chemistry studies specifically explored the interactions between pairs of atoms in a quantum state. While some of these works gathered interesting insight, they were often limited by the lack of available techniques for observing and controlling the outcomes of individual atom collisions.
“When atoms are brought up at short distances, they can experience several processes such as energy release or a chemical reaction, which are governed by quantum mechanics,” Or Katz, one of the researchers who carried out the study, who is now at Duke University, told Phys.org. “Previously devised methods can be used to study these processes, but they require optical access and control of at least one of the atoms, which in turn severely limits the atomic species as well as the set of interactions that can be studied practice. Our work alleviates this requirement and allows us to study the interaction between many pairs of atoms using just a single additional atom, which acts as a probe.”
Essentially, the researchers laser cooled and then trapped a pair of ions and a cloud of neutral atoms. The ions were trapped in a Paul trap, using electromagnetic fields. The neutral atoms, on the other hand, were trapped in an optical lattice, which they could bring in and out of the Paul trap at will.
“We study the interaction of a single ‘chemistry ion’ with one neutral atom by measuring the imprint on the second ‘logic ion’ in the trap that acts as a probe,” Katz explained. “Specifically, when the chemistry ion gains energy by its interaction with an atom in an exothermic (energy releasing) process, it pushes the “logic ion,” which in our experimental configuration, consequent with fluorescence of light. Detection of this fluorescence light from the logic ion reveals information about the process the other ion and atom have experienced.”
The recent work by Katz and his colleagues opens new possibilities for the study of processes that were previously difficult or impossible to probe experimentally. For instance, the technique they introduced in their paper could be used to measure new effects in which the motion of atom and ion features is characterized by quantum interference. Using previously developed tools, these effects would be very difficult to observe and examine.
“One hint for such effect is already seen in this work, reflected in the difference of cross-sections that is measured for the interaction of different isotopes of Sr+ with 87Rb, but the technique is not limited to this example and can be applied to study quantum effects in many other pairs,” Katz added. “We plan to apply the same technique to study additional processes, such as exchange of spin as well as chemical reactions.”
In addition to using their technique to study other processes, Katz and his colleagues plan to gather more evidence of quantum interference effects. This will allow them to further assess the potential of quantum mechanics-based tools for the study of fundamental interactions between atoms.
MISC
- Bank of Canada, Multiverse Computing complete preliminary quantum simulation of cryptocurrency market:
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