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Showing posts with label Computing. Show all posts
Showing posts with label Computing. Show all posts

Saturday, 23 May 2020

How a Quantum Physicist Invented New Code to Achieve What Many Thought Was Impossible

A scientist at the University of Sydney has achieved what one quantum industry insider has described as "something that many researchers thought was impossible."

Dr Benjamin Brown from the School of Physics has developed a type of error-correcting code for quantum computers that will free up more hardware to do useful calculations. It also provides an approach that will allow companies like Google and IBM to design better quantum microchips.

He did this by applying already known code that operates in three-dimensions to a two-dimensional framework.

"The trick is to use time as the third dimension. I'm using two physical dimensions and adding in time as the third dimension," Dr Brown said. "This opens up possibilities we didn't have before."

His research is published today in Science Advances.

"It's a bit like knitting," he said. "Each row is like a one-dimensional line. You knit row after row of wool and, over time, this produces a two-dimensional panel of material."

Fault-tolerant quantum computers

Reducing errors in quantum computing is one of the biggest challenges facing scientists before they can build machines large enough to solve useful problems.

"Because quantum information is so fragile, it produces a lot of errors," said Dr Brown, a research fellow at the University of Sydney Nano Institute.

Completely eradicating these errors is impossible, so the goal is to develop a "fault-tolerant" architecture where useful processing operations far outweigh error-correcting operations.

"Your mobile phone or laptop will perform billions of operations over many years before a single error triggers a blank screen or some other malfunction. Current quantum operations are lucky to have fewer than one error for every 20 operations -- and that means millions of errors an hour," said Dr Brown who also holds a position with the ARC Centre of Excellence for Engineered Quantum Systems.

"That's a lot of dropped stitches."

Most of the building blocks in today's experimental quantum computers -- quantum bits or qubits -- are taken up by the "overhead" of error correction.

"My approach to suppressing errors is to use a code that operates across the surface of the architecture in two dimensions. The effect of this is to free up a lot of the hardware from error correction and allow it to get on with the useful stuff," Dr Brown said.

Dr Naomi Nickerson is Director of Quantum Architecture at PsiQuantum in Palo Alto, California, and unconnected to the research. She said: "This result establishes a new option for performing fault-tolerant gates, which has the potential to greatly reduce overhead and bring practical quantum computing closer."

Path to universal computation

Start-ups like PsiQuantum, as well as the big technology firms Google, IBM and Microsoft, are leading the charge to develop large-scale quantum technology. Finding error-correcting codes that will allow their machines to scale up is urgently needed.

Dr Michael Beverland, a senior researcher at Microsoft Quantum and also unconnected with the research, said: "This paper explores an exciting, exotic approach to perform fault-tolerant quantum computation, pointing the way towards potentially achieving universal quantum computation in two spatial dimensions without the need for distillation, something that many researchers thought was impossible."

Two-dimensional codes that currently exist require what Dr Beverland refers to as distillation, more precisely known as 'magic-state distillation'. This is where the quantum processor sorts through the multiple computations and extracts the useful ones.

This chews up a lot of computing hardware just suppressing the errors.

"I've applied the power of the three-dimensional code and adapted it to the two-dimensional framework," Dr Brown said.

Dr Brown has been busy this year. In March he published a paper in top physics journal Physical Review Letters with colleagues from EQUS and the University of Sydney. In that research he and colleagues developed a decoder that identifies and corrects more errors than ever before, achieving a world record in error correction.

"Identifying the more common errors is another way we can free up more processing power for useful computations," Dr Brown said.

Professor Stephen Bartlett is a co-author of that paper and leads the quantum information theory research group at the University of Sydney.

"Our group at Sydney is very focused on discovering how we can scale-up quantum effects so that they can power large-scale devices," said Professor Bartlett, who is also Associate Dean for Research in the Faculty of Science.

"Dr Brown's work has shown how to do this for a quantum chip. This type of progress will enable us to go from small numbers of qubits to very large numbers and build ultra-powerful quantum computers that will solve the big problems of tomorrow."


Benjamin J. Brown.

A fault-tolerant non-Clifford gate for the surface code in two dimensions.

Science Advances, 2020

DOI: 10.1126/sciadv.aay4929

Tuesday, 7 April 2020

One Step Closer to Quantum Spin Liquids

A recent discovery by University of Arkansas physicists could help researchers establish the existence of quantum spin liquids, a new state of matter. They’ve been a mystery since they were first proposed in the 1970s. If proven to exist, quantum spin liquids would be a step toward much faster, next-generation quantum computing.

Scientists have focused attention and research on the so-called Kitaev-type of spin liquid, named in honor of the Russian scientist, Alexei Kitaev, who first proposed it. In particular, they have looked extensively at two materials – RuCl3  and Na2IrO – as candidates for this type. Both have small quantum spin numbers.

“Traditional candidates are pretty limited to only these two,” said Changsong Xu, a researcher in the Department of Physics and first author of a paper published in the journal Physical Review Letters.

In their recent work, U of A physicists have greatly expanded the number of materials that might be candidates as Kitaev quantum spin liquids by looking at materials with higher quantum spin numbers, and by putting materials under physical strain to tune their magnetic states.

“Suddenly, we realize there are dozens of candidates we can propose,” said Xu.

Quantum spin liquids are defined by their unusual magnetic arrangement. Magnets have a north and south pole, which combined are called dipoles. These are typically produced by the quantum spin of electrons. Inside a magnetic material, dipoles tend to all be parallel to each other (ferromagnetism) or periodically alternate their up and down direction (antiferromagnetism).

In the case of hypothetical quantum spin liquids, dipoles aren’t as well ordered. Instead, they exhibit unusual ordering within a small distance of each other. Different ordering creates different types of spin liquids.

Quantum spin liquids (QSLs) form an extremely unusual magnetic state in which the spins are highly correlated and fluctuate coherently down to the lowest temperatures, but without symmetry breaking and without the formation of any static long-range-ordered magnetism. Such intriguing phenomena are not only of great fundamental relevance in themselves, but also hold promise for quantum computing and quantum information.

Xu, along with Distinguished Professor of Physics Laurent Bellaiche and colleagues in China and Japan, used computational models to predict a Kitaev quantum spin liquid state in materials such as chromium iodide and chromium germanium telluride. The work, which was supported by grants from the Arkansas Research Alliance and the Department of Energy, will give researchers many more materials to study in a search to prove the existence of quantum spin liquids, said Xu.


Changsong Xu, Junsheng Feng, Mitsuaki Kawamura, Youhei Yamaji, Yousra Nahas, Sergei Prokhorenko, Yang Qi, Hongjun Xiang, L. Bellaiche.

Possible Kitaev Quantum Spin Liquid State in 2D Materials with S=3/2.

Physical Review Letters, 2020; 124 (8)

DOI: 10.1103/PhysRevLett.124.087205

Sunday, 2 February 2020

The laws of physics that explain political polarization in elections

The study of political polarization, which has emerged around the world, may have much to gain from the use of some tools and formulas used by physics. [Image: MIT]

It may seem surprising, but theories and formulas derived from physics can be useful tools for understanding how democratic elections work, including how these systems fail to deliver on their promises and how they can be improved.

Alexander Siegenfeld (MIT) and Yaneer Bar-Yam (New England Institute of Complex Systems) took political-electoral data and analyzed it using various well-known laws of physics as tools. And they demonstrated how these laws can be used to describe the behavior of the data.

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The application of several of the physics formulas to the US electoral system revealed that the elections went through a transition in 1970, from a condition in which the election results reasonably captured the electorate's greatest political preferences, to a period of increasing instability, in which very small changes in voter preferences have led to significant changes towards more extreme political results in both directions.

The two physicists found that the Ising model , developed to explain the behavior of ferromagnets and other physical systems, is mathematically equivalent to certain election models and accurately describes the onset of instability in electoral systems.

In this regime of "unstable" elections, "a small change in voter opinion can dramatically alter the outcome of the election, just as the direction of a small push on a rock at the top of a hill can dramatically change its final location," said Siegenfeld .

"What happened in 1970 is a phase transition just like boiling water. The elections went from stable to unstable," added Bar-Yam.

Negative representation

The analysis shows that this instability can be associated with an unexpected situation in which the results oscillate in the opposite direction of how people's real preferences are changing. In other words, a small movement in the predominant opinions towards the left can result in a result more to the right and vice versa - a situation that the researchers call "negative representation".

"Our country seems more divided than ever, with the election results looking like a pendulum swinging with increasing strength," said Siegenfeld.

This long-term shift from a stable electoral situation to one marked by instability is similar to what happens with ferromagnetic metal exposed to a magnetic field, adds Siegenfeld, and can be described by the same mathematical formulas.

Predict the whole without knowing the parts

But why can the derived formulas for such different subjects be relevant to the political field?

Siegenfeld says that it is because in Physics it is not always necessary to know the details of the underlying objects or mechanisms in order to produce useful and significant results. He compares this to how physicists were able to describe the behavior of sound waves - which are essentially the aggregate movements of atoms - with great precision, long before they knew about the existence of atoms.

"When we apply physics to understand the fundamental particles of our Universe, we don't really know the underlying details of the theories," he said. "However, we can still make incredibly accurate predictions."

Likewise, researchers do not need to understand the reasons and opinions of each individual voter in order to conduct a meaningful analysis of their collective behavior.

As the pair's article states, "understanding the collective behavior of social systems can benefit from methods and concepts in physics, not because humans are similar to electrons, but because certain behaviors on a large scale can be understood without understanding small-scale details."


Article: Negative representation and instability in democratic elections

Authors: Alexander F. Siegenfeld, Yaneer Bar-Yam

Magazine: Nature Physics

DOI: 10.1038 / s41567-019-0739-6

Monday, 9 December 2019

The era of printed electronics is beginning

Large scale integrated circuit (LSI) prototypes straight out of the printer. [Image: Thor Balkhed]

Printed electronics

Swedish researchers say they have taken the missing step to bring electronic circuit printing from the laboratory to the factories, making it possible to apply organic electronics on a large scale.

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The decisive step was the integration between the new field of printed electronics and traditional silicon-based electronics manufactured by traditional mask and lithography techniques.

"This is a decisive step for a technology that was born at Linkoping University just over 17 years ago," said Professor Magnus Berggren.

"The advantage we have here is that we don't have to mix different manufacturing methods: Everything is done by screen printing and in relatively few processing steps. The key is to make sure the different layers finish in exactly the right place," added his colleague Peter Ersman.

Printing electronic circuits

Printing fully functional electronic circuits - they can be printed on flexible, transparent plastics or virtually any other material - has required a number of innovations over the past 17 years.

A first step was the creation of screen-printing screens that let you print extremely thin lines so that semiconductor inks can form components with precision and high density per area.

At least three additional challenges have since been faced: Reduce circuit size, increase quality so that the probability of all transistors in the circuit working is as close as possible to 100%, and - not least - integrating with the silicon-based circuits needed to process signals and communicate with the environment.

"One of the major advances is that we have been able to use printed circuits to interface with traditional silicon-based electronics. We have developed various types of printed circuits based on organic electrochemical transistors. One of them is the shift register, which can interface and handle contact between the silicon-based circuit and other electronic components such as sensors and displays. This means that we can now use a silicon chip with fewer contacts, which requires a smaller area and thus is much cheaper. , "said Berggren.

The internet of things will be the first major beneficiary of print electronics.

IoT and screens

The development of semiconductor inks was another decisive element for the miniaturization process and also for higher quality. "We can now place more than 1,000 organic electrochemical transistors on an A4 size plastic substrate and connect them in different ways to create different types of printed integrated circuits," said team member Professor Simone Fabiano.

These large-scale integrated circuits, or LSIs, can be used, for example, to power electrochromic screens themselves manufactured as printed electronics.

The big expectation, however, is that printed electronics will give the final push to make the low cost, low power circuits required by the internet of things.


Article: All-Printed Large-Scale Integrated Circuits Based on Organic Electrochemical Transistors
Authors: Peter Andersson Ersman, Roman Lassnig, Jan Strandberg, Deyu You, Vahid Keshmiri, Robert Forchheimer, Simone Fabiano, Goran Gustafsson, Magnus Berggren
Journal: Nature Communications
Vol .: 10, Article number: 5053
DOI: 10.1038 / s41467-019-13079-4

Saturday, 7 December 2019

Quantum light processors are demonstrated in practice

Interlaced 3D light beams allow for quantum operations at room temperature and macro scale

Optical quantum processor

Two international teams, working separately, built prototypes of quantum processors made of light.

Qubits formed by intertwining laser beams are expected to make quantum computers less error prone and allow scalability, that is, scaling up processors to a large number of qubits.

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"While today's quantum processors are impressive, it's unclear whether today's designs can scale to extremely large sizes. Our approach starts with extreme scalability - built in from the start - because the processor, called a cluster state, is made of light. , "said Professor Nicolas Menicucci of RMIT University in Australia and leader of one of the teams.

A cluster state is a large collection of intertwined quantum components that perform quantum calculations when measured in a specific way - all operating at macroscopic scale using normal photonic components.

Both teams met the two fundamental requirements for cluster state operation, which comprise a minimum amount of qubits and quantum entanglement in the proper structure for their use in computational calculations.

To this end, specially designed crystals convert common laser light into a type of quantum light called compressed light , which is woven into a cluster state by a network of mirrors, light splitters, and optical fibers.

While the light compression levels achieved so far - which are a measure of photonic processor quality - are too low to solve practical problems, the design is compatible with approaches to achieving next-generation compression levels.

"Our experiment demonstrates that this design is workable - and scalable," said Professor Hidehiro Yonezawa of the University of New South Wales.

Animation showing the temporal evolution of the cluster state generation scheme

Quantum processor at room temperature

Mikkel Larsen and his colleagues at the Technical University of Denmark prefer to call his optical quantum processor prototype a "light carpet."

This is because, instead of the threads of an ordinary carpet, the processor is in fact a carefully crafted web of thousands of intertwined pulses of light.

"Unlike traditional cluster states, we use the temporal degree of freedom to achieve a two-dimensional interlaced network of 30,000 light pulses. The experimental setup is really surprisingly simple. Most of the effort has gone into developing the idea of ​​state generation. cluster, "said Larsen.

The Danish team has also been able to make its light carpet handle quantum entanglement at room temperature, noting that, in addition to error correction and simplification of technology, quantum optical processors can be cheaper and more powerful as they will allow the rapid increase in the number of qubits.

An optical quantum computer, therefore, does not require the expensive and complicated cooling technology used by superconducting qubits. At the same time, light-based qubits, which carry information in laser light, hold the information longer and can transmit it over long distances.

"By distributing the state of the cluster generated in space and time, an optical quantum computer can also scale more easily to contain hundreds of qubits. This makes it a potential candidate for the next generation of larger and more powerful quantum computers," reinforced Professor Ulrik Andersen.


Article: Generation of time-domain-multiplexed two-dimensional cluster state
Authors: Warit Asavanant, Yu Shiozawa, Shota Yokoyama, Baramee Charoensombutamon, Hiroki Emura, Rafael N. Alexander, Shuntaro Takeda, Jun-Ichi Yoshikawa, Nicolas C. Menicucci , Hidehiro Yonezawa, Akira Furusawa
Magazine: Science
Vol. 373-376
DOI: 10.1126 / science.aay2645

Article: Deterministic generation of a two-dimensional cluster state
Authors: Mikkel V. Larsen, Xueshi Guo, Casper R. Breum, Jonas S. Neergaard-Nielsen, Ulrik L. Andersen
Journal: Science
Vol. 366, Issue 6463, p. 369-372
DOI: 10.1126 / science.aay4354

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