Critical Schrdinger Cat Code: Quantum Computing Breakthrough for Better Qubits

Schrdinger's cat code

Schrdinger's cat code

An illustration of Schrdinger’s cat code. In a significant breakthrough in quantum computing, physicists at EPFL have proposed a critical Schrdinger cat code for advanced error resilience, a coding scheme inspired by Schrdinger’s thought experiment. This new system, operating in a hybrid regime, not only provides advanced error suppression capabilities, but also exhibits remarkable resistance to errors due to random frequency shifts, paving the way for devices with several interacting qubits, the minimum requirement for a quantum computer. Credit: Vincenzo Savona (EPFL)

EPFL scientists have proposed an innovative error resilience scheme for[{” attribute=””>quantum computing, known as a critical Schrdinger cat code. This novel system operates in a hybrid regime, exhibiting enhanced error suppression capabilities and impressive resistance to errors due to random frequency shifts, thus advancing the possibility of creating quantum computers with multiple interacting qubits.

Quantum computing uses the principles of quantum mechanics to encode and elaborate data, meaning that it could one day solve computational problems that are intractable with current computers. While the latter work with bits, which represent either a 0 or a 1, quantum computers use quantum bits, or qubits the fundamental units of quantum information.

With applications ranging from drug discovery to optimization and simulations of complex biological systems and materials, quantum computing has the potential to reshape vast areas of science, industry, and society, says Professor Vincenzo Savona, director of the Center for Quantum Science and Engineering at EPFL.

Unlike classical bits, qubits can exist in a superposition of both 0 and 1 states at the same time. This allows quantum computers to explore multiple solutions simultaneously, which could make them significantly faster in certain computational tasks. However, quantum systems are delicate and susceptible to errors caused by interactions with their environment.

Developing strategies to either protect qubits from this or to detect and correct errors once they have occurred is crucial for enabling the development of large-scale, fault-tolerant quantum computers, says Savona. Together with EPFL physicists Luca Gravina, and Fabrizio Minganti, they have made a significant breakthrough by proposing a critical Schrdinger cat code for advanced resilience to errors. The study introduces a novel encoding scheme that could revolutionize the reliability of quantum computers.

What is a critical Schrdinger cat code?

In 1935, physicist Erwin Schrdinger proposed a thought experiment as a critique of the prevailing understanding of quantum mechanics at the time the Copenhagen interpretation. In Schrdingers experiment, a cat is placed in a sealed box with a flask of poison and a radioactive source. If a single atom of the radioactive source decays, the radioactivity is detected by a Geiger counter, which then shatters the flask. The poison is released, killing the cat.

According to the Copenhagen view of quantum mechanics, if the atom is initially in superposition, the cat will inherit the same state and find itself in a superposition of alive and dead. This state represents exactly the notion of a quantum bit, realized at the macroscopic scale, says Savona.

In past years, scientists have drawn inspiration from Schrdingers cat to build an encoding technique called Schrdingers cat code. Here, the 0 and 1 states of the qubit are encoded onto two opposite phases of an oscillating electromagnetic field in a resonant cavity, similar to the dead or alive states of the cat.

Schrdinger cat codes have been realized in the past using two distinct approaches, explains Savona. One leverages anharmonic effects in the cavity, the other relying on carefully engineered cavity losses. In our work, we bridged the two by operating in an intermediate regime, combining the best of both worlds. Although previously believed to be unfruitful, this hybrid regime results in enhanced error suppression capabilities. The core idea is to operate close to the critical point of a phase transition, which is what the critical part of the critical cat code refers to.

The critical cat code has an additional advantage: it exhibits exceptional resistance to errors that result from random frequency shifts, which often pose significant challenges to operations involving multiple qubits. This solves a major problem and paves the way to the realization of devices with several mutually interacting qubits the minimal requirement for building a quantum computer.

We are taming the quantum cat, says Savona. By operating in a hybrid regime, we have developed a system that surpasses its predecessors, which represents a significant leap forward for cat qubits and quantum computing as a whole. The study is a milestone on the road toward building better quantum computers, and showcases EPFLs dedication to advancing the field of quantum science and unlocking the true potential of quantum technologies.

Reference: Critical Schrdinger Cat Qubit by Luca Gravina, Fabrizio Minganti and Vincenzo Savona, 7 June 2023, Physical Review X Quantum.
DOI: 10.1103/PRXQuantum.4.020337


#Critical #Schrdinger #Cat #Code #Quantum #Computing #Breakthrough #Qubits

Quantum materials: electron spin measured for the first time

Quantum materials: electron spin measured for the first time

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Three perspectives of the surface on which the electrons move. On the left the experimental result, in the center and on the right the theoretical modeling. The red and blue colors represent a measure of the speed of the electrons. Both theory and experiment reflect the symmetry of the crystal, very similar to the texture of traditional Japanese “kagome” baskets. Credits: University of Bologna

An international research group has succeeded for the first time in measuring the spin of the electron in matter, i.e. the curvature of the space in which electrons live and move within “kagome materials”, a new class of quantum materials.

The obtained results published in Physics of natureit could revolutionize the way quantum materials are studied in the future, opening the door to new developments in quantum technologies, with possible applications in a variety of technological fields, from renewable energy to biomedicine, from electronics to quantum computers.

The success was achieved by an international collaboration of scientists, in which Domenico Di Sante, professor at the “Augusto Righi” Department of Physics and Astronomy, participated for the University of Bologna as part of his Marie Curie research project BITMAP . He was joined by colleagues from the CNR-IOM of Trieste, the Ca’ Foscari University of Venice, the University of Milan, the University of Wrzburg (Germany), the University of St. Andrews (UK) , Boston College and the University of Santa Barbara (USA).

Through advanced experimental techniques, using the light generated by a particle accelerator, the synchrotron, and thanks to modern techniques for modeling the behavior of matter, scholars have been able to measure for the first time the spin of the electron, linked to the topology concept.

“If we take two objects like a soccer ball and a donut, we notice that their specific shapes determine different topological properties, for example because the donut has a hole, while the ball doesn’t,” explains Domenico Di Sante. “Similarly, the behavior of electrons in materials is influenced by some quantum properties that determine their rotation in the matter in which they are located, similarly to how the trajectory of light in the universe is modified by the presence of stars, black holes, matter and dark energy, which bend time and space.”

Although this characteristic of electrons has been known for many years, no one has been able to measure this “topological spin” directly until now. To achieve this, the researchers exploited a particular effect known as “circular dichroism”: a particular experimental technique that can only be used with a synchrotron source, which exploits the ability of materials to absorb light in different ways depending on their polarization.

Scholars have focused in particular on “kagome materials”, a class of quantum materials that owe their name to their resemblance to the weaving of woven bamboo threads that make up a traditional Japanese basket (called “kagome”). . These materials are revolutionizing quantum physics and the results obtained could help us better understand their special magnetic, topological and superconducting properties.

“These important results were possible thanks to a strong synergy between experimental practice and theoretical analysis”, adds Di Sante. ‘The theoretical researchers in the team employed sophisticated quantum simulations, which are only possible with the use of powerful supercomputers, and in doing so guided their experimental colleagues to the specific area of ​​the material where the effect of circular dichroism could be measured. “.

More information:
Domenico Di Sante et al, Flat Band Separation and Strong Spin Berry Curvature in Bilayer Kagome Metals, Physics of nature (2023). DOI: 10.1038/s41567-023-02053-z

About the magazine:
Physics of nature

Provided by the University of Bologna

#Quantum #materials #electron #spin #measured #time

The classical principle of least action now exists in the quantum realm

quantum entanglement, conceptual artwork

quantum entanglement, conceptual artwork

Quantum particles take the easy way outVICTOR de SCHWANBERG/PHOTO LIBRARY OF SCIENCE – Getty Images

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  • Researchers have demonstrated that a fundamental law of physics applies in the quantum realm.

  • The principle of least action dictates that objects (unless they are interfered with) always move along the path that requires the least amount of action.

  • Not all the rules of everyday physics apply to quantum particles, but measurements that are difficult to make certainly apply, according to a new study.

The shortest distance between two points is a straight line, but shorter distance doesn’t always mean less work. What if that distance is uphill or through difficult terrain? If you’re looking to do the least amount of work, a straight line may not always be your best bet.

Humans may not always be looking for the easiest path. But when it comes to natural motions in systems, one of the basic laws of physics states that objects will always travel along the path that requires the least action. In physics, action has to do with things like energy, momentum, distance, and time.

Essentially, without outside intervention, objects travel the path of least resistance and least change. This is called the principle of least action. We know it applies in our everyday world, and now, thanks to a new study, we know it applies in the quantum world as well.

A physicist’s ultimate dream is to write the secrets of the entire universe on a small piece of paper, and the principle of least action has to be on the list, said Shi-Liang, one of the project’s researchers, in an article for New scientist. Our ambition was to see [the principle] in a quantum experiment.

Easier said that done. The research team at South China Normal University had to come to terms with the fact that not only is everything in the quantum realm small and hard to see, but the motions of quantum particles are really complicated. For one thing, quantum states change when they’re measured. And for another, they can only be mapped using very complicated math.

To best describe their behavior, scientists use a combination of two things: a wave function and a propagator. Wavefunctions describe the state of the particle and propagators describe how that state changes during the motion of a particle in a system. The problem is that wavefunctions and propagators are purely mathematical, and while they are great at describing the behaviors of quantum particles, they often do so using imaginary numbers. Imaginary numbers are fine in mathematics, but are by definition impossible to measure.

To get around this, the team used a technique that had been established a few years earlier. In this technique, you basically bounce and filter individual particles of quantum light called photons through a maze of mirrors, crystals, and lenses. Eventually, the parts of photon behavior described by imaginary numbers will correspond to actual measurable properties. Parts originally described by ordinary real numbers will also be measurable, and researchers will be able to reconstruct waveforms and propagators from actual measured data.

Once the maze was built, the researchers combined that technique with a new one they developed to primarily avoid the quantum state change when looking at the problem. Then, they sent single photons through the maze and compared their behavior with the behavior predicted by the principle of least action and found that reality agreed with the theory, proving that quantum particles do indeed follow the principle.

The measurements in this experiment are quite incredible and do not challenge our current understanding of quantum physics, said Jonathan Leach, a quantum science researcher who was not involved in the study. New scientist item. It’s nice to see this theory made real in an experiment.

There are a lot of places where the quantum world and the everyday world don’t intersect. It’s part of the reason why researchers are still trying to improve on the current standard model of physics. But in their desire to avoid action as much as possible, the quantum and the everyday are perfectly synchronized.

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#classical #principle #action #exists #quantum #realm

Scientists have just shown how to make a quantum computer using sound waves

Scientists have just shown how to make a quantum computer using sound waves

A strange and wonderful array of technologies are vying to become the standard bearer of quantum computing. The last contender wants to encode quantum information into sound waves.

One thing that all quantum computers have in common is that they manipulate information encoded in quantum states. But that’s where the similarities end, because those quantum states can be induced in everything from superconducting circuits to trapped ions to supercooled atoms, photons and even silicon chips.

While some of these approaches attracted more investment than others, they were still a long way from establishing the industry on a common platform. And in the world of academic research, experimentation still abounds.

Now, a team from the University of Chicago hasSt took the first crucial steps toward building a quantum computer that can encode information into phonons, the fundamental quantum units that make up sound waves in much the same way way that photons form beams of light.

The basic principles of how to create a phonon quantum computer are quite similar to those used in photonic quantum computers. Both involve the generation and detection of single particles, or quasiparticles, and their manipulation using beamsplitters and phase shifters. Phonons are quasiparticles, because although they behave like particles as far as quantum mechanics is concerned, they are actually made up of the collective behavior of large numbers of atoms.

The Chicago group had already proven that they could generate single phonons using surface acoustic waves, which travel along the surface of a material at frequencies about a million times higher than a human can hear, and use them to transfer quantum information between two superconducting qubits.

But in a new card inside Science, researchers demonstrate the first phonon beamsplitter, which, as the name suggests, is designed to split acoustic waves. This component is a key ingredient for a phonon quantum computer as it allows exploiting quantum phenomena such as superposition, entanglement and interference.

Their configuration involves two superconducting qubits fabricated on flat pieces of sapphire, joined together by a lithium niobate channel. Each qubit is connected via a tunable coupler to a device called a transducer, which converts electrical signals into mechanical signals.

This is used to generate vibrations that create individual phonons in the channel connecting the qubits, which has a beam splitter made up of 16 parallel metal fingers at its center. The entire setup is cooled to just above absolute zero.

To demonstrate the capabilities of their system, the researchers first excited one of the qubits to make it generate a single phonon. This traveled down the channel to the beamsplitter, but since quantum particles like phonons are basically indivisible, instead of splitting it went into a quantum superposition.

This refers to skill From a quantum system must be in several states at once, until they are measured and collapse into one of the possibilities. In this case the phonon was both reflected back to the original qubit and transmitted to the second qubit, which was able to capture the phonon and store the quantum superposition.

In a second experiment, the researchers managed to replicate a quantum phenomenon fundamental to how logic gates in photonic quantum computers are created called the Hong-Ou-Mandel effect. In optical setups, this results in two identical photons being input simultaneously into a beam splitter from opposite directions. Both then enter an overlap, but these outputs interfere with each such that both photons end up traveling together to only one of the detectors.

Researchers have shown that they can replicate this effect using phonons and, more importantly, that they can use qubits to alter the characteristics of the phonons so that they can control which direction the output travels. computer, says Andrew Cleland, who led the study.

The successful two-phonon interference experiment is the final piece showing that phonons are equivalent to photons, Cleland said in a Press release. The result confirms that we have the technology we need to build a linear mechanical quantum computer.

The researchers admit that the approach is unlikely to compete directly with optical approaches to quantum computing, because the components are much larger and slower. However, their ability to interface seamlessly with superconducting qubits could make them promising for hybrid computing schemes that combine the best of both worlds.

It is likely to be a long time before the underlying components reach the sophistication and industrial readiness of other quantum approaches. But it seems the race for quantum advantage has just begunten a little more crowded.

Image credit: BroneArtUlm / Pixabay

#Scientists #shown #quantum #computer #sound #waves

China’s fastest quantum computer still lags far behind the United States

China's fastest quantum computer still lags far behind the United States

China’s fastest quantum computer is set to roll out, but the machine will be nowhere near the fastest in the world, underlining China’s quantum lag behind the United States.

Known as Wukong, the Monkey King from Chinese mythology, the locally produced 72-qubit computer is now in its final testing phase and is scheduled to go online next month, said Zhang Hui, general manager of Origin Quantum Computing Technology based in Hefei.

Last November, the American IBM launched the 433-qubit Osprey, the world’s fastest quantum computer to date. Intel unveiled its 49-qubit quantum chip, known as Tangle Lake, in January 2018, while Google debuted its 72-qubit Bristlecone in March of the same year.

Chinese scientists openly acknowledge the quantum gap with the West.

China is indeed in the top echelon of quantum scientific research in the world, Zhang said in a Guancha.cn article in December. “In quantum communication, China is among the first in the world for the number of documents and patents.” However, he said, “in quantum computing, we are relatively behind.

Zhang said this is because China’s overall industrial base is less advanced than the West. He noted that the development of quantum computers involves many advanced engineering issues, including the manufacturing of traditional superconductor and semiconductor chips, crucial high-tech realms where China lags behind the United States and the West.

Currently, China still needs foreign equipment such as electron beam lithography to make its superconducting chips. Japan, which is following America’s lead in limiting China’s access to high-end chip manufacturing equipment, is dominant in the e-beam lithography market.

Citing public data, Zhang estimated that China is about three to four years behind leading countries in terms of quantum hardware. He also added that there is a huge gap between China and the United States in industrial applications of quantum computing.

IBM’s Osprey is now the fastest quantum computer in the world. Photo: IBM

Players like IBM and Google started exploring industrial applications as early as the 1990s. But it’s only since the founding of Origin Quantum in 2017 that we’ve started exploring industrial applications,” he said.

He also said that Intel enjoys an edge in quantum chip manufacturing due to its experience and know-how in semiconductor manufacturing.

Banned by the United States from obtaining the most advanced chips and chip-making equipment, China is now investing heavily in quantum, artificial intelligence and aerospace technologies with the hope, as expressed by some Chinese media, of surpassing the West how to overtake others in cornering in car racing.

At this stage, Zhang said, “these strongest teams in the world are really far ahead of us in terms of funds, talent and equipment. I think the goal of overtaking the others in corners is still a long way off for us. What we are trying to do is follow them as closely as possible and make contributions.”

Power up supercomputers

So far, the 66-qubit Zuchongzhi 2, launched by Chinese scientist Pan Jianwei and his team at the Hefei University of Science and Technology in May 2021, is currently the fastest quantum computer in China.

While the Pan team focuses on academic results, Origin Quantum has its sights set on commercialization.

The company launched its 6-qubit superconducting chip, known as KF-C6-130, in 2020 and used it in its self-developed quantum computer called Benyuan Wuyuan. It unveiled Benyuan Wuyuan 2 with a 24-qubit quantum chip, KF-C24-100, in 2021.

In February this year, it shipped a 24-qubit quantum computer for the first time, making China the third country in the world to have built and delivered quantum computers after the United States and Canada.

Origin Quantum and the state-owned Shanghai Supercomputer Center said this month that they will establish an innovation technology center to connect their supercomputers and quantum computers.

“Quantum computers are much faster than traditional computers at solving specific problems, said Li Genguo, director of the Shanghai Supercomputing Center. They can be used as a supercomputer accelerator.

Li said a program will soon be launched to try to optimize the computing power of supercomputers and quantum computers.

Origin Quantum and Nexchip are investing funds in the production of superconducting chips. Photo: WeChat account: hefeigaoxinfabu]

Dou Meng, vice president of Origin Quantum, told the media that he met Li just two weeks ago for the first time, and both sides agreed to seek synergies.

Dou said that Origin Quantum plans to set up its second quantum center in Shanghai as there is huge growth potential in the Yangtze River Delta region, where 70% of China’s quantum experts and half of quantum companies are located.

Nexchip support

In April 2021, Origin Quantum and Nexchip Semiconductor Corp, which raised 9.96 billion yuan ($1.44 billion) in an initial public offering in Shanghai last month, set up a lab to make superconducting chips.

According to the listing prospectus, Nexchip is 52.99 percent owned by the Hefei government and 27.44 percent owned by Powerchip Technology, the parent company of Powerchip Semiconductor Manufacturing Corp (PSMC), Taiwan’s third-largest chip foundry. All five of Nexchip’s top executives are from Taiwan.

Nexchip mainly produces automotive chips between 55 and 150 nanometers, low-end products compared to 7nm to 22nm chips used in mobile electronic products. That means the company is unaffected by US sanctions, which target semiconductors smaller than 28n but not yet superconducting chips.

Origin Quantums Zhang said the company outsources chip manufacturing to Nexchip’s lab and follows IBM and Google’s superconductor chip standards and Intel’s semiconductor standards.

He said it’s not a problem to produce several thousand superconducting chips a year, but only those with the highest quality will be shipped to customers. The company said earlier this year that it is using its in-house developed MLLAS-100 laser annealing to improve the quality of its quantum chips.

Read: Quantum computing clouds open to all in China

Read: China accelerates in quantum computing race

Follow Jeff Pao on Twitter at @jeffpao3


#Chinas #fastest #quantum #computer #lags #United #States

Quantum Speedup Quantum computers are better at guessing

Artistic rendering of the quantum computer

Artistic rendering of the quantum computer

Scientists have achieved quantum speedup by effectively suppressing errors in a bit string guessing game, handling strings up to 26 bits long. They showed that, with proper error control, quantum computers can execute complete algorithms with a better time scale than conventional computers, even in the current noisy era of quantum computing.

Researchers a[{” attribute=””>USC apply strategies to control the buildup of errors, showcasing the promise of quantum computing in the error-prone NISQ era.

Daniel Lidar, the Viterbi Professor of Engineering at USC and Director of the USC Center for Quantum Information Science & Technology, and first author Dr. Bibek Pokharel, a Research Scientist at IBM Quantum, achieved this quantum speedup advantage in the context of a bitstring guessing game.

By effectively mitigating the errors often encountered at this level, they have successfully managed bitstrings of up to 26 bits long, significantly larger than previously possible. (For context, a bit refers to a binary number that can either be a zero or a one).

Quantum computers promise to solve certain problems with an advantage that increases as the problems increase in complexity. However, they are also highly prone to errors, or noise. The challenge, says Lidar, is to obtain an advantage in the real world where todays quantum computers are still noisy.

This noise-prone condition of current quantum computing is termed the NISQ (Noisy Intermediate-Scale Quantum) era, a term adapted from the RISC architecture used to describe classical computing devices. Thus, any present demonstration of quantum speed advantage necessitates noise reduction.

The more unknown variables a problem has, the harder it usually is for a computer to solve. Scholars can evaluate a computers performance by playing a type of game with it to see how quickly an algorithm can guess hidden information. For instance, imagine a version of the TV game Jeopardy, where contestants take turns guessing a secret word of known length, one whole word at a time. The host reveals only one correct letter for each guessed word before changing the secret word randomly.

In their study, the researchers replaced words with bitstrings. A classical computer would, on average, require approximately 33 million guesses to correctly identify a 26-bit string. In contrast, a perfectly functioning quantum computer, presenting guesses in quantum superposition, could identify the correct answer in just one guess. This efficiency comes from running a quantum algorithm developed more than 25 years ago by computer scientists Ethan Bernstein and Umesh Vazirani. However, noise can significantly hamper this exponential quantum advantage.

Lidar and Pokharel achieved their quantum speedup by adapting a noise suppression technique called dynamical decoupling. They spent a year experimenting, with Pokharel working as a doctoral candidate under Lidar at USC. Initially, applying dynamical decoupling seemed to degrade performance. However, after numerous refinements, the quantum algorithm functioned as intended. The time to solve problems then grew more slowly than with any classical computer, with the quantum advantage becoming increasingly evident as the problems became more complex.

Lidar notes that currently, classical computers can still solve the problem faster in absolute terms. In other words, the reported advantage is measured in terms of the time-scaling it takes to find the solution, not the absolute time. This means that for sufficiently long bitstrings, the quantum solution will eventually be quicker.

The study conclusively demonstrates that with proper error control, quantum computers can execute complete algorithms with better scaling of the time it takes to find the solution than conventional computers, even in the NISQ era.

Reference: Demonstration of Algorithmic Quantum Speedup by Bibek Pokharel and Daniel A. Lidar, 26 May 2023, Physical Review Letters.
DOI: 10.1103/PhysRevLett.130.210602

The study was funded by the National Science Foundation and the U.S. Department of Defense.


#Quantum #Speedup #Quantum #computers #guessing

Researchers have ‘split’ phonons in the move towards a new kind of quantum computer

Researchers have 'split' phonons in the move towards a new kind of quantum computer

This article was reviewed based on Science X’s editorial process and policies. The editors have highlighted the following attributes ensuring the credibility of the content:

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Artist’s impression of a platform for linear quantum mechanical computing (LMQC). The central transparent element is a phonon beam splitter. The blue and red marbles represent individual phonons, which are the collective mechanical motions of quadrillions of atoms. These mechanical motions can be visualized as surface acoustic waves entering the beam splitter from opposite directions. Two-phonon interference at the beamsplitter is critical to LMQC. The output phonons emerging from the image are in a two-phonon state, with a “blue” and a “red” phonon clustered together. Credit: Peter Allen

When we listen to our favorite song, what sounds like a continuous wave of music is actually transmitted as tiny packets of quantum particles called phonons.

The laws of quantum mechanics hold that quantum particles are fundamentally indivisible and therefore cannot be split, but researchers at the University of Chicago’s Pritzker School of Molecular Engineering (PME) are exploring what happens when you try to split a phonon.

In two experiments, the first of their kind, a team led by Prof. Andrew Cleland used a device called an acoustic beamsplitter to ‘split’ phonons and thus demonstrate their quantum properties. By showing that the beamsplitter can be used both to induce a special quantum superposition state for a phonon and to create further interference between two phonons, the research team has taken the first critical steps towards creating a new type of quantum computer.

The results are published in the journal Science and built on years of groundbreaking work on phonons by the Pritzker Molecular Engineering team.

“Splitting” of a phonon in a superposition

In the experiments, the researchers used phonons that are about a million times higher in pitch than the human ear can hear. Earlier, Cleland and his team discovered how to create and detect single phonons and were the first to entangle two phonons.

To demonstrate the quantum capabilities of these phonons, the team, including Cleland’s graduate student Hong Qiao, created a beam splitter capable of splitting a beam of sound in half, transmitting half and reflecting the other half back to its source. (beam splitters already exist for light and have been used to demonstrate the quantum capabilities of photons). The entire system, including two qubits to generate and detect the phonons, operates at extremely low temperatures and uses single phonons of surface acoustic waves, which travel on the surface of a material, in this case lithium niobate.

However, quantum physics states that a single phonon is indivisible. So when the team sent a single phonon to the beamsplitter, instead of splitting, it entered a quantum superposition, a state in which the phonon is reflected and transmitted at the same time. Observing (measuring) the phonon collapses this quantum state into one of two outputs.

The team found a way to maintain that superposition state by capturing the phonon in two qubits. A qubit is the basic unit of information in quantum computing. Only one qubit actually captures the phonon, but researchers can’t tell which qubit until after the measurement. In other words, the quantum superposition is transferred from the phonon to the two qubits. The researchers measured this overlap of two qubits, providing “gold standard evidence that the beamsplitter is creating a quantum entangled state,” Cleland said.

Show that phonons behave like photons

In the second experiment, the team wanted to show another fundamental quantum effect that was first demonstrated with photons in the 1980s. Now known as the Hong-Ou-Mandel effect, when two identical photons are sent simultaneously from opposite directions into a beam splitter, the overlapping outputs interfere so that both photons are always found traveling together, in one direction or the other of exit.

Importantly, the same happened when the team conducted the phonon experiment: the overlapping output means that only one of the detector’s two qubits captures phonons, going in one direction but not the other. Although qubits only have the ability to capture a single phonon at a time, not two, the qubit positioned in the opposite direction never “feels” a phonon, demonstrating that both phonons are going in the same direction. This phenomenon is called two-phonon interference.

Getting phonons into these quantum entangled states is a much bigger leap than doing it with photons. The phonons used here, while indivisible, still require quadrillions of atoms working together quantum mechanically. And if quantum mechanics rules physics only in the smallest realm, it raises questions about where that realm ends and classical physics begins; this experiment further probes that transition.

“These atoms all have to behave consistently together to support what quantum mechanics says they should do,” Cleland said. “It’s quite amazing. The bizarre aspects of quantum mechanics aren’t limited by size.”

Creation of a new linear mechanical quantum computer

The power of quantum computers lies in the “strangeness” of the quantum realm. By harnessing the strange quantum powers of superposition and entanglement, researchers hope to solve previously unsolvable problems. One approach to doing this is to use photons, in what’s called a “linear optical quantum computer.”

A linear mechanical quantum computer that would use phonons instead of photons could have the ability to compute new types of calculations. “The successful two-phonon interference experiment is the final piece showing that phonons are equivalent to photons,” Cleland said. “The result confirms that we have the technology we need to build a linear mechanical quantum computer.”

Unlike photon-based linear optical quantum computing, the University of Chicago’s platform directly integrates phonons with qubits. This means that phonons could further be part of a hybrid quantum computer that combines the best of linear quantum computers with the power of qubit-based quantum computers.

The next step is to create a logic gate, an essential part of computer science, using phonons, which Cleland and his team are currently researching.

Other authors on the paper include . Dumur, G. Andersson, H. Yan, M.‑H. Chou, J. Grebel, CR Conner, YJ Joshi, JM Miller, RG Povey and X. Wu.

More information:
H. Qiao et al, Phonon Splitting: Building a Platform for Linear Quantum Mechanical Computing, Science (2023). DOI: 10.1126/science.adg8715. www.science.org/doi/10.1126/science.adg8715

About the magazine:
Science

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Next Generation Superconducting Diode: Improving AI performance and quantum computing scalability

High tech device illustration

High tech device illustration

Researchers have designed a new superconducting diode that promises to improve the performance of artificial intelligence systems and boost quantum computers for industrial applications. This device surpasses its counterparts with superior energy efficiency, the ability to process multiple electrical signals simultaneously, and a unique set of gates that control the flow of energy.

A team of researchers has developed a highly efficient superconducting diode with potential applications in augmentation[{” attribute=””>quantum computing and enhancing AI systems. This device can process multiple signals simultaneously, a feature beneficial for neuromorphic computing, and is designed with more industry-friendly materials, paving the way for broader industrial applications.

A University of Minnesota Twin Cities-led team has developed a new superconducting diode, a key component in electronic devices, that could help scale up quantum computers for industry use and improve the performance of artificial intelligence systems.

Compared to other superconducting diodes, the researchers device is more energy efficient; can process multiple electrical signals at a time; and contains a series of gates to control the flow of energy, a feature that has never before been integrated into a superconducting diode.

The paper was published in Nature Communications, a peer-reviewed scientific journal that covers the natural sciences and engineering.

A diode allows current to flow one way but not the other in an electrical circuit. Its essentially half of a transistor, the main element in computer chips. Diodes are typically made with semiconductors, but researchers are interested in making them with superconductors, which have the ability to transfer energy without losing any power along the way.

Tunable Superconducting Diode

A University of Minnesota Twin Cities-led team has developed a more energy-efficient, tunable superconducting diodea promising component for future electronic devicesthat could help scale up quantum computers for industry and improve artificial intelligence systems. Credit: Olivia Hultgren / University of Minnesota Twin Cities

We want to make computers more powerful, but there are some hard limits we are going to hit soon with our current materials and fabrication methods, said Vlad Pribiag, senior author of the paper and an associate professor in the University of Minnesota School of Physics and Astronomy. We need new ways to develop computers, and one of the biggest challenges for increasing computing power right now is that they dissipate so much energy. So, were thinking of ways that superconducting technologies might help with that.

The University of Minnesota researchers created the device using three Josephson junctions, which are made by sandwiching pieces of non-superconducting material between superconductors. In this case, the researchers connected the superconductors with layers of semiconductors. The devices unique design allows the researchers to use voltage to control the behavior of the device.

Their device also has the ability to process multiple signal inputs, whereas typical diodes can only handle one input and one output. This feature could have applications in neuromorphic computing, a method of engineering electrical circuits to mimic the way neurons function in the brain to enhance the performance of artificial intelligence systems.

The device weve made has close to the highest energy efficiency that has ever been shown, and for the first time, weve shown that you can add gates and apply electric fields to tune this effect, explained Mohit Gupta, first author of the paper and a Ph.D. student in the University of Minnesota School of Physics and Astronomy. Other researchers have made superconducting devices before, but the materials theyve used have been very difficult to fabricate. Our design uses materials that are more industry-friendly and deliver new functionalities.

The method the researchers used can, in principle, be used with any type of superconductor, making it more versatile and easier to use than other techniques in the field. Because of these qualities, their device is more compatible for industry applications and could help scale up the development of quantum computers for wider use.

Right now, all the quantum computing machines out there are very basic relative to the needs of real-world applications, Pribiag said. Scaling up is necessary in order to have a computer thats powerful enough to tackle useful, complex problems. A lot of people are researching algorithms and usage cases for computers or AI machines that could potentially outperform classical computers. Here, were developing the hardware that could enable quantum computers to implement these algorithms. This shows the power of universities seeding these ideas that eventually make their way to industry and are integrated into practical machines.

Reference: Gate-tunable superconducting diode effect in a three-terminal Josephson device by Mohit Gupta, Gino V. Graziano, Mihir Pendharkar, Jason T. Dong, Connor P. Dempsey, Chris Palmstrm and Vlad S. Pribiag, 29 May 2023, Nature Communications.
DOI: 10.1038/s41467-023-38856-0

This research was funded primarily by the United States Department of Energy with partial support from Microsoft Research and the National Science Foundation.

In addition to Pribiag and Gupta, the research team included University of Minnesota School of Physics and Astronomy graduate student Gino Graziano and University of California, Santa Barbara researchers Mihir Pendharkar, Jason Dong, Connor Dempsey, and Chris Palmstrm.


#Generation #Superconducting #Diode #Improving #performance #quantum #computing #scalability

The quantum nothing could have given birth to the Universe

The quantum nothing could have given birth to the Universe

We can pragmatically define physical reality as everything that exists in the cosmos, and in it there is no complete vacuum. On the contrary, it seems that the more we learn about nature, the more crowded the space becomes. We can contemplate the idea of ​​a metaphysical void, a complete void where there is nothing. But these are concepts we create, not necessarily things that exist. Even calling nothing a “thing” turns it into something. Leucippus and Democritus, the Greek philosophers credited with inventing atomism – that everything is made of tiny fragments of matter that cannot be divided – suggested the joint existence of atoms and the void. Atoms make up all that exists, but they move in complete emptiness, the void.

As an exercise in the ever-changing way we understand things about the world, we can make a list of the things we know to fill in the blank. (The list changes. For example, 120 years ago, it would have included the aether, the medium in which light was supposed to travel.) Starting from classical physics, the key concept is that of a field. A field is a spatial manifestation of a source. If an object sensitive to the field is placed within its range, it will respond in some way, usually by being attracted to or repelled by the source creating the field.

In classical physics we know only two forces, gravitational and electromagnetic. Every object with mass attracts every other object. You attract and are attracted to everything that exists: butterflies and whales, the Sun and all the planets of this Solar System and throughout the Universe. The strength of an object’s gravitational field grows in proportion to its mass and decays with the square of the distance from it. In this sense, space is filled with interconnected fields that connect us to the rest of the Universe.

Gravitational fields extend their strings to all corners of space. Since fields carry energy, we can say that space is filled with the energy of these gravitational fields. Electromagnetic fields have energy too, of course. But because electric and magnetic forces can be attractive and repulsive, they are usually neutralized and rarely manifest over great distances.

Not a lot of anything is happening

At the quantum level, space becomes even more crowded. Indeed, quantum physics tells us that there is no such thing as zero energy. In the world of atoms and subatomic particles, motion is constant and there is an energy associated with the residual motion of a particle called zero point energyOR vacuum energy. If we now connect this fact to the famous E=mc2 formula, which states that energy and matter can be interconvertible, it is possible that particles of matter arise from the energy of the vacuum — the energy of empty space.

The Universe itself could emerge this way, as we have discussed. The fact that matter can come out of what we would call “nothing” shows that the “nothing” of quantum physics is far from a complete vacuum. Virtual particles they appear and disappear like bubbles in boiling soup. In the current view of quantum physics, the vacuum is constantly seething with the creation and destruction of particles of matter.

We encountered the concept of field in classical physics, but it affects quantum physics with even more dramatic effects. We no longer refer to particles, in fact, but to the fields that create them. An electron or proton is an excitation of the electron or proton field respectively, like small waves drifting on the surface of a lake. Particles are depicted as knots of energy moving in their fields, with physical properties such as mass.

The physical image that emerges is that of space filled with quantum fields bubbling with real and virtual particles. As the Fox said to the Little Prince in Antoine de Saint-Exupéry’s fairy tale, “The essential is invisible to the eye”. This is as true of love and friendship as it is of the “nothingness” of space.

#quantum #birth #Universe

A Quantum of Solace: Solving a mathematical puzzle in quarks and gluons in nuclear matter

Quark Gluon Plasma Illustration

From

Quark Gluon Plasma Illustration

A cartoon of the quark-gluon plasma (small red, green, and blue circles) produced in a relativistic collision of heavy ions between two heavy nuclei (white circles). The collision produces a heavy quark (red Q) and a heavy quark-antiquark pair (green QO). Credit: Image courtesy of Bruno Scheihing-Hitschfeld and Xiaojun Yao

Scientists have taken a significant step forward in studying the properties of quarks and gluons, the particles that make up atomic nuclei, by solving a long-standing problem with a theoretical calculation method known as axial gauge.[{” attribute=””>MIT and University of Washington researchers found that the method had mistakenly suggested two properties of quark-gluon plasma were identical. They also made a prediction on gluon distribution measurement, set to be tested in future experiments with the Electron-Ion Collider.

The Science

The building blocks of atomic nuclei are protons and neutrons, which are themselves made of even more fundamental particles: quarks and gluons. These particles interact via the strong force, one of the four fundamental forces of nature. They make up the nuclei at the heart of every atom. They also make up forms of hot or dense nuclear matter that exhibit exotic properties. Scientists study the properties of hot and cold nuclear matter in relativistic heavy ion collision experiments and will continue to do so using the future Electron-Ion Collider. The ultimate goal is to understand how complex forms of matter emerge from elementary particles affected by strong forces.

The Impact

Theoretical calculations involving the strong force are complex. One aspect of this complexity arises because there are many ways to perform these calculations. Scientists refer to some of these as gauge choices. All gauge choices should produce the same result for the calculation of any quantity that can be measured in an experiment. However, one particular choice, called axial gauge, has puzzled scientists for years because of difficulties in obtaining consistent results upon making this choice. This recent study resolves this puzzle and paves the way for reliable calculations of hot and cold nuclear matter properties that can be tested in current and future experiments.

Summary

The exotic form of nuclear matter that physicists study in relativistic heavy ion collisions is called the quark-gluon plasma (QGP). This form of matter existed in the early universe. Physicists explore its properties in heavy ion collision experiments by recreating the extremely high temperatures last seen microseconds after the Big Bang. By analyzing experimental data from the collisions and comparing them with theoretical calculations, physicists can ascertain various properties of the QGP. Using a calculation method called axial gauge had previously seemed to imply that two QGP properties that describe how heavy quarks move through the QGP were the same.

Researchers at the Massachusetts Institute of Technology and the University of Washington have now found this implication to be incorrect. The study also carefully analyzed the subtle conditions for when axial gauge can be employed and explained why the two properties are different. Finally, it showed that two distinct methods for measuring how gluons are distributed inside nuclei must yield different results. Gluons are the particles that carry the strong force, This prediction will be tested at the future Electron-Ion Collider.

Reference: Gauge Invariance of Non-Abelian Field Strength Correlators: The Axial Gauge Puzzle by Bruno Scheihing-Hitschfeld and Xiaojun Yao, 2 February 2023, Physical Review Letters.
DOI: 10.1103/PhysRevLett.130.052302

This work is supported by the Department of Energy Office of Science, Office of Nuclear Physics and by the Office of Science, Office of Nuclear Physics, InQubator for Quantum Simulation (IQuS).


#Quantum #Solace #Solving #mathematical #puzzle #quarks #gluons #nuclear #matter