Jun 24 2024Reviewed by Lexie Corner

In a studypublished in PeerJ Computer Science, Professor Kazuhiro Ogataand Assistant Professor Canh Minh Do of the Japan Advanced Institute of Science and Technology (JAIST) suggested using symbolic model checking to validate quantum circuits.

Quantum computing is a fast-developing technology that utilizes the principles of quantum physics to tackle complicated computational problems that are extremely difficult for classical computing.

To take advantage of quantum computing, researchers worldwide have created a large number of quantum algorithms that show notable gains over classical algorithms.

Creating these algorithms requires the use of quantum circuits, which are models of quantum processing. Before they are actually deployed on quantum hardware, they are utilized to design and implement quantum algorithms.

Quantum circuits consist of a series of quantum gates, measurements, and qubit initializations, among other events. Quantum gates execute quantum computations by working on qubits, the quantum equivalents of conventional bits (0s and 1s), and manipulating the system's quantum states.

Quantum states are the output of quantum circuits that can be monitored to provide classical outcomes with probabilities from which additional actions can be taken. Since quantum computing is frequently counterintuitive and substantially distinct from classical computing, the likelihood of mistakes is significantly larger. As a result, it is critical to ensure that quantum circuits have the correct features and perform as planned.

This can be accomplished using model checking, a formal verification approach used to ensure that systems meet desirable attributes. Although certain model checkers are specialized to quantum programs, there is a distinction between model-checking quantum programs and quantum circuits due to differences in representation and the absence of iterations in quantum circuits.

Considering the success of model-checking methods for verification of classical circuits, model-checking of quantum circuits is a promising approach. We developed a symbolic approach for model checking of quantum circuits using laws of quantum mechanics and basic matrix operations using the Maude programming language.

Canh Minh Do, Assistant Professor, Japan Advanced Institute of Science and Technology

Maude is a high-level specification/programming language based on rewriting logic that enables the formal definition and verification of complicated systems. It comes with a Linear Temporal Logic (LTL) model checker that determines if systems meet the necessary features. Maude also enables the development of exact mathematical models of systems.

Using the Dirac notation and the rules of quantum physics, the researchers formally defined quantum circuits in Maude as a set of quantum gates and measurement applications. They provided the systems intended attributes and its initial state in LTL.

By using a set of quantum physics laws and basic matrix operations formalized in our specifications, quantum computation can be reasoned in Maude.The researchers then automatically checked whether quantum circuits satisfied the required characteristics using the integrated Maude LTL model checker.

Using this method, several early quantum communication protocols, each with increasing complexity, were checked: Superdense Coding, Quantum Teleportation, Quantum Secret Sharing, Entanglement Swapping, Quantum Gate Teleportation, Two Mirror-image Teleportation, and Quantum Network Coding.

They discovered that the initial iteration did not meet the desired property of Quantum Gate Teleportation. By employing this method, the researchers suggested an updated version and verified that it was accurate.

These findings highlight the significance of the suggested novel technique for the verification of quantum circuits. However, the researchers highlight certain drawbacks of their strategy that need more investigation.

Dr. Do added, In the future, we aim to extend our symbolic reasoning to handle more quantum gates and more complicated reasoning on complex number operations. We also would like to apply our symbolic approach to model-checking quantum programs and quantum cryptography protocols.

Verifying the expected functionality of quantum circuits will be extremely useful in the approaching era of quantum computing. In this context, the current technique is the first step toward a broader framework for verifying and specifying quantum circuits, opening the way for error-free quantum computing.

The study was supported by JST SICORP Grant Number JPMJSC20C2, Japan, and JSPS KAKENHI Grant Numbers JP23H03370, JP23K19959, and JP24K20757.

Do, C. M., etal. (2024) Symbolic model checking quantum circuits in Maude. PeerJ Computer Science. doi:10.7717/peerj-cs.2098

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The Road to Error-Free Quantum Computing - AZoQuantum

image:

Schematic of a hybrid cavity architecture to achieve efficient light-matter coupling. This design consists in a metasurface, formed of metallic cross-shaped array, onto which a thin film of organic material (glucose) is deposited. A mirror located above the metasurface ensures that light is trapped to form a photonic mode (rainbow colored beam) strongly interacting with glucose.

Credit: University of Ottawa

A team of international scientists led by the University of Ottawa have gone back to the kitchen cupboard to create a recipe that combines organic material and light to create quantum states.

Professor Jean-Michel Mnard, leader of the Ultrafast Terahertz Spectroscopy group at the Faculty of Science, coordinated with Dr. Claudiu Genes at the Max Planck Institute for the Science of Light (Germany), and with Iridian Spectral Technologies (Ottawa) to design a device which can efficiently modify properties of materials using the quantum superposition with light.

The team designed a two-dimensional planar resonator known as a metasurface that captured light. Using a spray coating technique, they then deposited a thin glucose layer on that metasurface to induce a strong interaction between light and glucose molecules in sugar.

Their concept brings researchers closer to being technologically able to harvest some of the unique properties of quantum systems falling in a hybrid state of both light and matter.

Faculty of Science professors Ksenia Dolgaleva and Robert Boyd contributed to the work alongside Professor Menard, the lead author, who discusses the findings published in Nature Communications.

Question: What did you set out to do and what did you find? Jean-Michel Mnard: We present an innovative and efficient technique for synthesizing quantum organic materials by combining light and matter. When light in the far-infrared region at terahertz (THz) frequencies becomes trapped within an organic material, it can merge with molecules, resulting in a quantum state that exhibits unique properties which are of growing interest because of their potential application in modifying the physical and chemical properties of matter. These intriguing states only arise under specific conditions. Our team identified these critical conditions and created a photonic trap or device to effectively confine light within a small volume space during a substantial amount of time. This trap enables a strong coupling regime to be established between light and a molecular ensemble.

Unlike previous approaches that relied on optical cavities made of two facing mirrors, we instead designed and tested a two-dimensional planar resonator known as a metasurface. This metasurface effectively allows optical confinement within a planar geometry, opening new practical avenues to explore the quantum regime of strong light-matter interactions.

Finally, we combined metasurfaces with traditional cavity geometries to form hybrid cavity architectures and observe an enhancement of the coupling strength between light and matter. These results are demonstrated with glucose, an organic compound with properties useful to the fields of biology and medicine.

Q: Why use THz light and sugar? JM: Terahertz light is particularly interesting because it can induce vibrations in many molecules, including glucose molecules in sugar. The energy of vibration of molecules is intricately connected to their properties including their ability to engage in chemical reactions with other molecules. Therefore, by designing platforms enabling a strong coupling between terahertz light and the vibration of molecules, which are fundamental building blocks of organic substances, we have the potential to change their properties to potentially gain control over mechanisms at the foundation of life.

Q: What did you ultimately find through your research? JM: We discovered efficient approaches to couple terahertz light and matter. The most promising concept is based on a structured metallic surface, the metasurface, incorporated into the design of a photonic cavity. As a result, light becomes doubly trapped and remains tightly confined within the device.

Our robust plug-and-play platform allows potentially many organic materials to be inserted inside this device to create quantum systems with new properties. This is due to the fact that no precise alignment of the device is required to trap the light as this critical condition is mostly fulfilled by the geometry of the metasurfaces metallic pattern. Interestingly, since scalable fabrication techniques exist to fabricate metasurfaces interacting with terahertz light, we believe that these devices could be used relatively soon for real-life applications of quantum-enhanced chemical reactions.

Q: What kind of impact can this research have? JM: "These results bring us closer to being technologically able to harvest some of the unique properties of quantum systems consisting of a hybridized state of light and matter. By performing a systematic theoretical and experimental study of different types of photonic resonators, we discovered some novel photonic resonator designs that can create a quantum superposition between a molecular material, glucose, and light in a specific region of the far-infrared spectral window called the terahertz region. Previous work demonstrated that this hybridization process, when it involves terahertz light, modifies the original physical and chemical properties of the material. For example, the presence of a photonic resonator can change the rate of some chemical reactions involving that material.

In the future, we believe this approach could help regulate some molecular processes, leading to application in medicine for rapid diagnostics and potentially new therapeutic strategies.

Nature Communications

Experimental study

Not applicable

Hybrid architectures for terahertz molecular polaritonics

24-May-2024

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Sugar-coating quantum systems to harvest science - EurekAlert

By Leah Burrows, Harvard John A. Paulson School of Engineering and Applied Sciences June 23, 2024

The device uses a simple electric diode to manipulate qubits inside a commercial silicon wafer. Credit: Second Bay Studios/Harvard SEAS

By utilizing traditional semiconductor devices, researchers have unlocked new potentials in quantum communication, pushing us closer to realizing the vast potential of the quantum internet.

Building the quantum internet could be significantly simplified by leveraging existing telecommunications technologies and infrastructure. In recent years, researchers have identified defects in silicona widely used semiconductor materialthat hold the potential for transmitting and storing quantum information across the prevalent telecommunications wavelengths. These silicon defects might just be the prime contenders to host qubits for efficient quantum communications.

Its still a Wild West out there, said Evelyn Hu, the Tarr-Coyne Professor of Applied Physics and of Electrical Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). Even though new candidate defects are a promising quantum memory platform, there is often almost nothing known about why certain recipes are used to create them, and how you can rapidly characterize them and their interactions, even in ensembles. And ultimately, how can we fine-tune their behavior so they exhibit identical characteristics? If we are ever to make a technology out of this wide world of possibilities, we must have ways to characterize them better, faster, and more efficiently.

Now, Hu and a team of researchers have developed a platform to probe, interact with and control these potentially powerful quantum systems. The device uses a simple electric diode, one of the most common components in semiconductor chips, to manipulate qubits inside a commercial silicon wafer. Using this device, the researchers were able to explore how the defect responds to changes in the electric field, tune its wavelength within the telecommunications band and even turn it on and off.

If we are ever to make a technology out of this wide world of possibilities, we must have ways to characterize them better, faster and more efficiently.

Evelyn Hu, Tarr-Coyne Professor of Applied Physics and of Electrical Engineering

One of the most exciting things about having these defects in silicon is that you can use well-understood devices like diodes in this familiar material to understand a whole new quantum system and do something new with it, said Aaron Day, a Ph.D. candidate at SEAS. Day co-led the work with Madison Sutula, a research fellow at Harvard.

While the research team used this approach to characterize defects in silicon, it could be used as a diagnostic and control tool for defects in other material systems.

The research is published in Nature Communications.

Quantum defects, also known as color centers or quantum emitters, are imperfections in otherwise perfect crystal lattices that can trap single electrons. When those electrons are hit with a laser, they emit photons in specific wavelengths. The defects in silicon that researchers are most interested in for quantum communications are known as G-centers and T-centers. When these defects trap electrons, the electrons emit photons in a wavelength called the O-band, which is widely used in telecommunications.

In this research, the team focused on G-center defects. The first thing they needed to figure out was how to make them. Unlike other types of defects, in which an atom is removed from a crystal lattice, G-center defects are made by adding atoms to the lattice, specifically carbon. But Hu, Day and the rest of the research team found that adding hydrogen atoms is also critical to consistently forming the defect.

Next, the researchers fabricated electrical diodes using a new approach that optimally sandwiches the defect at the center of every device without degrading the performance of either the defect or the diode. The fabrication method can create hundreds of devices with embedded defects across a commercial wafer. Hooking the whole device up to apply a voltage, or electric field, the team found that when a negative voltage was applied across the device, the defects turned off and went dark.

Understanding when a change in environment leads to a loss of signal is important for engineering stable systems in networking applications, said Day,

The scientists also found that by using a local electric field, they could tune the wavelengths being emitted by the defect, which is important for quantum networking when disparate quantum systems need to be aligned.

The team also developed a diagnostic tool to image how the millions of defects embedded in the device change in space as the electric field is applied.

We found that the way were modifying the electric environment for the defects has a spatial profile, and we can image it directly by seeing the changes in the intensity of light being emitted by the defects, said Day. By using so many emitters and getting statistics on their performance, we now have a good understanding of how defects respond to changes in their environment. We can use that information to inform how to build the best environments for these defects in future devices. We have a better understanding of what makes these defects happy and unhappy.

Next, the research team aims to use the same techniques to understand the T-center defects in silicon.

Reference: Electrical manipulation of telecom color centers in silicon by Aaron M. Day, Madison Sutula, Jonathan R. Dietz, Alexander Raun, Denis D. Sukachev, Mihir K. Bhaskar and Evelyn L. Hu, 3 June 2024, Nature Communications. DOI: 10.1038/s41467-024-48968-w

The research was co-authored by Sutula, Jonathan R. Dietz, Alexander Raun from SEAS, and AWS research scientists Denis D. Sukachev and Mihir K. Bhaskar.

This work was supported by AWS Center for Quantum Networking and the Harvard Quantum Initiative. Harvards Office of Technology Development has protected the intellectual property associated with this project and is pursuing commercialization opportunities.

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Silicon Magic: Powering the Quantum Internet of the Future - SciTechDaily

In 1948, Dutch physicist Hendrik Casimirwho worked with one of the fathers of quantum physics, Neils Bohrdeveloped an ingenious experiment to witness the invisible (at least, to us) wonders of quantum mechanics. Casimir placed two electrically neutral plates within one micrometer of each other in a vacuum. Without any forces acting upon them, you might expect the plates to remain perfectly still but they didnt. Instead, the plates were pulled together via the invisible quantum fluctuations that permeate spacetime.

This experiment was a stunning display of the invisible quantum world, and this phenomenon became known, quite rightly, as the Casimir effect. Itd be another 50 years before the Yale physicist Steve Lamoreaux finally measured this incredibly small effect, but with the rise of nanotechnology during that same period, understanding the Casimir effect and how it would impact these incredibly small machines became vitally important. Sort of how the designs of satellites need to take our understanding of relativity into account, so too must nanotechnologies be designed with the Casimir effect in mind.

Now, in the next step toward understanding this incredible phenomenon, scientists from the Chinese Academy of Sciences have found a method of tuning this effect. Using a ferrofluida fluid that can be manipulated using magnetic fieldsas an intermediate medium, the researchers used magnetic fields to create a reversible transition from Casimir attraction to repulsion. The results of the study were published in late May in the journal Nature Physics.

The quantum fluctuation-induced Casimir force can be either attractive or repulsive, depending on the dielectric permittivities [the ability of a substance to store electrical energy in an electric field] and magnetic permeabilities of the materials involved, the paper reads. Our theoretical calculations predict that, by varying the magnetic field, separation distance and ferrofluid volume fraction, the Casimir force can be tuned from attractive to repulsive over a wide range of parameters in this system.

As the paper notes, its challenging to alter the dielectric permittivities of a material, but you can manipulate the permeabilities of ferrofluids with magnetic fields. This is how the researchers designed an experiment examining this kind of manipulation between a gold sphere and a silicon dioxide substrate. As predicted, the experiment allowed the researchers to accurately manipulate the Casimir attraction or repulsion of the two materials.

Gaining some kind of control over this incredibly small effect could have big implications for the creation of future nano- and micro-electromechanical devices. Of course, there are other ideas surrounding the Casimir effectalso known as vacuum energy or zero-point energyespecially as it plays a role in studying the black hole-based Hawking radiation that features prominently in discussions about warp bubbles and warp drives. But for now, its very large technological impact mostly pertains to the world of very small machines.

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.

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Scientists Discovered How to Control the Casimir Effectand Supercharge Tiny Machines - Popular Mechanics

Quantum computing is like Forrest Gumps box of chocolates: You never know what youre gonna get. Quantum phenomena the behavior of matter and energy at the atomic and subatomic levels are not definite, one thing or another. They are opaque clouds of possibility or, more precisely, probabilities. When someone observes a quantum system, it loses its quantum-ness and collapses into a definite state.

Quantum phenomena are mysterious and often counterintuitive. This makes quantum computing difficult to understand. People naturally reach for the familiar to attempt to explain the unfamiliar, and for quantum computing this usually means using traditional binary computing as a metaphor. But explaining quantum computing this way leads to major conceptual confusion, because at a base level the two are entirely different animals.

This problem highlights the often mistaken belief that common metaphors are more useful than exotic ones when explaining new technologies. Sometimes the opposite approach is more useful. The freshness of the metaphor should match the novelty of the discovery.

The uniqueness of quantum computers calls for an unusual metaphor. As a communications researcher who studies technology, I believe that quantum computers can be better understood as kaleidoscopes.

The gap between understanding classical and quantum computers is a wide chasm. Classical computers store and process information via transistors, which are electronic devices that take binary, deterministic states: one or zero, yes or no. Quantum computers, in contrast, handle information probabilistically at the atomic and subatomic levels.

Classical computers use the flow of electricity to sequentially open and close gates to record or manipulate information. Information flows through circuits, triggering actions through a series of switches that record information as ones and zeros. Using binary math, bits are the foundation of all things digital, from the apps on your phone to the account records at your bank and the Wi-Fi signals bouncing around your home.

In contrast, quantum computers use changes in the quantum states of atoms, ions, electrons or photons. Quantum computers link, or entangle, multiple quantum particles so that changes to one affect all the others. They then introduce interference patterns, like multiple stones tossed into a pond at the same time. Some waves combine to create higher peaks, while some waves and troughs combine to cancel each other out. Carefully calibrated interference patterns guide the quantum computer toward the solution of a problem.

Physicist Katie Mack explains quantum probability.

The term bit is a metaphor. The word suggests that during calculations, a computer can break up large values into tiny ones bits of information which electronic devices such as transistors can more easily process.

Using metaphors like this has a cost, though. They are not perfect. Metaphors are incomplete comparisons that transfer knowledge from something people know well to something they are working to understand. The bit metaphor ignores that the binary method does not deal with many types of different bits at once, as common sense might suggest. Instead, all bits are the same.

The smallest unit of a quantum computer is called the quantum bit, or qubit. But transferring the bit metaphor to quantum computing is even less adequate than using it for classical computing. Transferring a metaphor from one use to another blunts its effect.

The prevalent explanation of quantum computing is that while classical computers can store or process only a zero or one in a transistor or other computational unit, quantum computers supposedly store and handle both zero and one and other values in between at the same time through the process of superposition.

Superposition, however, does not store one or zero or any other number simultaneously. There is only an expectation that the values might be zero or one at the end of the computation. This quantum probability is the polar opposite of the binary method of storing information.

Driven by quantum sciences uncertainty principle, the probability that a qubit stores a one or zero is like Schroedingers cat, which can be either dead or alive, depending on when you observe it. But the two different values do not exist simultaneously during superposition. They exist only as probabilities, and an observer cannot determine when or how frequently those values existed before the observation ended the superposition.

Leaving behind these challenges to using traditional binary computing metaphors means embracing new metaphors to explain quantum computing.

The kaleidoscope metaphor is particularly apt to explain quantum processes. Kaleidoscopes can create infinitely diverse yet orderly patterns using a limited number of colored glass beads, mirror-dividing walls and light. Rotating the kaleidoscope enhances the effect, generating an infinitely variable spectacle of fleeting colors and shapes.

The shapes not only change but cant be reversed. If you turn the kaleidoscope in the opposite direction, the imagery will generally remain the same, but the exact composition of each shape or even their structures will vary as the beads randomly mingle with each other. In other words, while the beads, light and mirrors could replicate some patterns shown before, these are never absolutely the same.

If you dont have a kaleidoscope handy, this video is a good substitute.

Using the kaleidoscope metaphor, the solution a quantum computer provides the final pattern depends on when you stop the computing process. Quantum computing isnt about guessing the state of any given particle but using mathematical models of how the interaction among many particles in various states creates patterns, called quantum correlations.

Each final pattern is the answer to a problem posed to the quantum computer, and what you get in a quantum computing operation is a probability that a certain configuration will result.

Metaphors make the unknown manageable, approachable and discoverable. Approximating the meaning of a surprising object or phenomenon by extending an existing metaphor is a method that is as old as calling the edge of an ax its bit and its flat end its butt. The two metaphors take something we understand from everyday life very well, applying it to a technology that needs a specialized explanation of what it does. Calling the cutting edge of an ax a bit suggestively indicates what it does, adding the nuance that it changes the object it is applied to. When an ax shapes or splits a piece of wood, it takes a bite from it.

Metaphors, however, do much more than provide convenient labels and explanations of new processes. The words people use to describe new concepts change over time, expanding and taking on a life of their own.

When encountering dramatically different ideas, technologies or scientific phenomena, its important to use fresh and striking terms as windows to open the mind and increase understanding. Scientists and engineers seeking to explain new concepts would do well to seek out originality and master metaphors in other words, to think about words the way poets do.

Sorin Adam Matei is an Associate Dean for Research at Purdue University. This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Quantum Computers Are Like Kaleidoscopes, Helping Illustrate Science and Technology - DISCOVER Magazine