UK Scientists make major breakthrough in developing practical quantum computers that can solve big challenges of our time

Universal of Sussex and Universal Quantum scientists have, for the first time, connected quantum microchips together, like a jigsaw puzzle, to make powerful quantum computers and with record breaking connection speed and accuracy

Peer-Reviewed Publication

UNIVERSITY OF SUSSEX

 

IMAGE: GRAPHIC SHOWING TWO QUANTUM COMPUTER MODULES BEING ALIGNED SO THAT ATOMS CAN TRANSFER FROM ONE QUANTUM COMPUTER MICROCHIP TO ANOTHER view more 

CREDIT: UNIVERSITY OF SUSSEX

Researchers from the University of Sussex and Universal Quantum have demonstrated for the first time that quantum bits (qubits) can directly transfer between quantum computer microchips and demonstrated this with record-breaking speed and accuracy.  This breakthrough resolves a major challenge in building quantum computers large and powerful enough to tackle complex problems that are of critical importance to society.

Today, quantum computers operate on the 100-qubit scale. Experts anticipate millions of qubits are required to solve important problems that are out of reach of today’s most powerful supercomputers [1, 2]. There is a global quantum race to develop quantum computers that can help in many important societal challenges from drug discovery to making fertilizer production more energy efficient and solving important problems in nearly every industry, ranging from aeronautics to the financial sector.

In the research paper, published today (from 10:00 GMT, Wednesday 8 February 2023) in Nature Communications, the scientists demonstrate how they have used a new and powerful technique, which they dub ‘UQ Connect’, to use electric field links to enable qubits to move from one quantum computing microchip module to another with unprecedented speed and precision. This allows chips to slot together like a jigsaw puzzle to make a more powerful quantum computer.

The University of Sussex and Universal Quantum team were successful in transporting the qubits with a 99.999993% success rate and a connection rate of 2424/s, both numbers are world records and orders of magnitude better than previous solutions.

Professor Winfried Hensinger, Professor of Quantum Technologies at the University of Sussex and Chief Scientist and Co-founder at Universal Quantum said: “As quantum computers grow, we will eventually be constrained by the size of the microchip, which limits the number of quantum bits such a chip can accommodate. As such, we knew a modular approach was key to make quantum computers powerful enough to solve step-changing industry problems. In demonstrating that we can connect two quantum computing chips – a bit like a jigsaw puzzle – and, crucially, that it works so well, we unlock the potential to scale-up by connecting hundreds or even thousands of quantum computing microchips.”

While linking the modules at world-record speed, the scientists also verified that the ‘strange’ quantum nature of the qubit remains untouched during transport, for example, that the qubit can be both 0 and 1 at the same time.

Dr Sebastian Weidt, CEO and Co-founder of Universal Quantum, and Senior Lecturer in Quantum Technologies at the University of Sussex said: “Our relentless focus is on providing people with a tool that will enable them to revolutionise their field of work. The Universal Quantum and University of Sussex teams have done something truly incredible here that will help make our vision a reality. These exciting results show the remarkable potential of Universal Quantum’s quantum computers to become powerful enough to unlock the many lifechanging applications of quantum computing.”

Universal Quantum has just been awarded €67 million from the German Aerospace Center (DLR) to build two quantum computers where they will deploy this technology as part of the contract. The University of Sussex spin-out was also recently named as one of the 2022 Institute of Physics award winners in the Business Start-up category.

Weidt added: “The DLR contract was likely one of the largest government quantum computing contracts ever handed out to a single company. This is a huge validation of our technology. Universal Quantum is now working hard to deploy this technology in our upcoming commercial machines.”

Dr Mariam Akhtar led the research during her time as Research Fellow at the University of Sussex and Quantum Advisor at Universal Quantum. She said: “The team has demonstrated fast and coherent ion transfer using quantum matter links. This experiment validates the unique architecture that Universal Quantum has been developing – providing an exciting route towards truly large-scale quantum computing.”

Professor Sasha Roseneil, Vice-Chancellor of the University of Sussex, said: “It’s fantastic to see that the inspired work of the University of Sussex and Universal Quantum physicists has resulted in this phenomenal breakthrough, taking us a significant step closer to a quantum computer that will be of real societal use. These computers are set to have boundless applications – from improving the development of medicines, creating new materials, to maybe even unlocking solutions to the climate crisis. The University of Sussex is investing significantly in quantum computing to support our bold ambition to host the world’s most powerful quantum computers and create change that has the potential to positively impact so many people across the world. And with teams spanning the spectrum of quantum computing and technology research, the University of Sussex has both a breadth and a depth of expertise in this. We are still growing our research and teaching in this area, with plans for new teaching programmes, and new appointments.”

Professor Keith Jones, Interim Provost and Pro-Vice Chancellor for Research and Enterprise at the University of Sussex, said of the development: “This is a very exciting finding from our University of Sussex physicists and Universal Quantum. It proves the value and dynamism of this University of Sussex spin-out company, whose work is grounded in rigorous and world-leading academic research. Quantum computers will be pivotal in helping to solve some of the most pressing global issues. We're delighted that Sussex academics are delivering research that offers hope in realising the positive potential of next-generation quantum technology in crucial areas such as sustainability, drug development, and cybersecurity.”  

-ENDS-

NOTES TO EDITOR

[1] Webber, M., et. al. AVS Quantum Sci. 4, 013801 (2022)

[2] Lekitsch, B., et al., Science Advances, 3(2), 1–12 (2017)

MEDIA CONTACTS

University of Sussex

Alice Ingall: a.r.ingall@sussex.ac.uk / 07899096299
Anna Ford: a.ford@sussex.ac.uk / press@sussex.ac.uk

Universal Quantum

Gemma Church: gemma@universalquantum.com / media@universalquantum.com /+44 7967 565 080

ABOUT THE UNIVERSITY OF SUSSEX

For over 60 years the aim of our courses, research, culture and campus has been to stimulate, excite and challenge. So, from scientific discovery to global policy, from student welfare to career development, the University of Sussex innovates and takes a lead. And today, in every part of society and across the world, you will find someone from the University of Sussex making an original and valuable contribution. Visit www.sussex.ac.uk     

ABOUT UNIVERSAL QUANTUM

Universal Quantum builds quantum computers that will one day help humanity solve some of its most pressing problems in areas such as drug discovery and climate change as well as shed light on its biggest scientific mysteries. To achieve this, quantum computers with millions of qubits are required, which is often described as one of the biggest technology challenges of our time.

Universal Quantum has developed a unique modular architecture to solve exactly that challenge. Its trapped ion-based electronic quantum computing modules are manufactured using available silicon technology. Individual modules are connected using its record-breaking UQ Connect technology to form an architecture that can scale to millions of qubits.

With 15+ years of quantum computing experience, Universal Quantum is a spin-out from the University of Sussex, founded by Dr Sebastian Weidt and Professor Winfried Hensinger in 2018 and supported by leading investors. Visit www.universalquantum.com
 

University of Sussex and Universal Quantum scientists, Professor Winfried Hensinger and Dr Sebastian Weidt in University of Sussex quantum computing labs.

Quantum computer setup at the University of Sussex with two quantum computer microchips where quantum bits are transferred from one microchip to another with record speed.

CREDIT

University of Sussex

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JOURNAL

Nature Communications

DOI

10.1038/s41467-022-35285-3 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

A high-fidelity quantum matter-link between ion-trap microchip modules

ARTICLE PUBLICATION DATE

8-Feb-2023

COI STATEMENT

The authors declare the following competing interests: M.A., F.B., F.R.L.-G., S.W. and W.K.H. are associated and/or hold shares with quantum computing company Universal Quantum Ltd. that will make use of some of the findings of this article in the quantum computers they develop. The remaining authors declare no other competing interests.

Quantum literacy is Canada’s next tech gap. NAIT and Qubo want to fix it


ByJennifer Friesen
February 21, 2025


Photo by Planet Volumes on Unsplash

If the term “quantum computing” makes you think of sci-fi movies or expensive lab experiments, you’re not alone. But in reality, quantum technology is moving fast — and most industries aren’t ready.

That’s a problem, say Katanya Kuntz and A.J. Sikora, co-founders of Qubo Consulting Corp. Since their launch in 2023, the duo has been working to close the gap between quantum scientists and the business world, making the case that quantum literacy is no longer optional.

“The first movers are going to gain the majority of the opportunity,” says Sikora. “The people who sit on their hands and wait until a quantum computer breaks RSA encryption before they start investigating are going to struggle to get access to talent and technology.”

To get ahead of the curve, Qubo has partnered with the Northern Alberta Institute of Technology (NAIT) to launch two new certificate programs to make quantum more accessible to professionals across Canada.

What is quantum computing, and why does it matter?

Before diving into why quantum literacy is so urgent, let’s clear up one thing: what exactly is quantum computing?

For decades, computers have run on classical bits, which can be either zero or one — like flipping a light switch on or off. Quantum computers, on the other hand, use qubits, which can exist in both zero and one at the same time thanks to a principle called superposition. This allows quantum computers to process multiple possibilities simultaneously, instead of one at a time.

Then there’s entanglement, another uniquely quantum phenomenon that allows qubits to become linked, meaning a change to one qubit instantly affects another, no matter how far apart they are.

The result? Quantum computers have the potential to solve complex problems that would take today’s supercomputers millions of years to crack. This could revolutionize industries like drug discovery, finance, logistics, and cybersecurity.

“When I understood the magnitude of the paradigm shift that we’re going to see when quantum computers come online, I knew that everybody needed to know about this,” says Sikora. “I’m a pretty tech savvy guy — I have the latest iPhone — but I had never heard of this … and I don’t think your average businessman knows about this either. But I understood the potential impact on security and national sovereignty, so Katanya and I decided, ‘Let’s make an impact in this space.’”

Meet the experts making quantum accessible

Qubo’s mission is to make quantum computing, and other quantum technologies, understandable and actionable for business leaders, engineers, and policymakers.

Kuntz, a quantum physicist, has spent years explaining complex concepts to everyone from CEOs to grade-school students.

“Being a quantum scientist, I’ve had to go to a dinner party, and everyone’s going around the room saying what their career is — I drop ‘quantum physicist’ and half the people leave the room,” she jokes. “So I’ve had to be able to communicate what I do to a broad range of audiences, just in my own everyday life.”

Katanya Kuntz. Photo courtesy of the Wave Tech Centre

She also works on Canada’s first quantum communication satellite mission (QEYSSat) and has given outreach talks explaining quantum principles to fourth graders. And if she can make a bunch of kids excited about photons in space, why not help an executive understand how quantum computing affects their business?

Sikora, meanwhile, comes from an education and business background. His experience in training and curriculum design means Qubo’s programs are structured to actually teach people what they need to know.

“Katanya and I really have complementary skills, and it shows in some of these projects,” says Sikora. “There are a ton of quantum experts that can talk about quantum, but it’s how they explain quantum. It’s like, A) Is it applicable to me? And B) Can I understand it, even if it is?”
NAIT steps in with executive and engineering training

NAIT, a polytechnic focused on applied learning, is offering one of Canada’s first continuing education programs in quantum training for professionals.

The courses are offered through Continuing Education and Corporate Training, which allows NAIT to respond quickly to industry needs with non-credit programs designed for upskilling and reskilling.

“We want to stay in the forefront,” says Surinder Padem, program manager for digital literacy and IT training at NAIT. “And in continuing education, we can move quickly to bring programs in front of students as industry needs change.”

The two certificate programs — Quantum for Executives and Quantum for Engineers — are designed for different levels of technical experience.Quantum for Executives is a four-part series of one-hour “lunch and learn” sessions designed for business leaders who need a clear, non-technical introduction to quantum. It covers industry applications, cybersecurity risks, and why quantum is a game-changer across sectors.
Quantum for Engineers is a deeper dive, offering four two-hour sessions for technical professionals looking to understand quantum computing, sensing, secure communication, and data security. No prior quantum experience required.

Both programs are delivered live online, making them accessible across Canada. The first round kicks off on February 27, with additional sessions scheduled through the spring.

According to Sikora, the programs are ideal for tech professionals looking to specialize, such as software engineers, data scientists or analysts and hardware engineers. They’re also a fit for entrepreneurs, startup founders, and tech leaders looking for insights into how quantum will shape the industry. The courses also cater to government and policymakers making decisions around cybersecurity and national security.

But ultimately, Sikora notes, “anybody with a strong interest in emerging technologies” can benefit — whether they’re in the field or simply fascinated by what’s coming next.A.J. Sikora. Photo courtesy of the Wave Tech Centre
Don’t wait for quantum to disrupt your industry

Kuntz and Sikora say they designed the courses to be practical, engaging, and directly relevant to Canadian industries.

“Every time we have a conversation with someone, nine times out of 10, unless they’re a quantum physicist, I have to explain: what is quantum?” says Kuntz. “So that’s what these NAIT courses are doing. They’re starting that conversation.”

The urgency isn’t just theoretical. Earlier this year, Canadian quantum computing company Xanadu introduced Aurora, a modular photonic quantum computer designed for large-scale scalability. The company has long-term ambitions to develop fault-tolerant quantum computing, with earlier reports indicating a goal of reaching one million qubits by the end of the decade. While no updated qubit target has been confirmed, if that timeline holds, the shift to quantum could be closer than many expect.

“Do you see how the computer changed everything back in the 60s and the 70s?” asks Kuntz. “That’s the type of technology change that we’re talking about.”

Sikora warns that businesses slow to adopt quantum literacy could find themselves playing catch-up — especially when it comes to security.

“With computing power comes the risk that a quantum computer could come online that could break current encryption standards that we use,” he says. “So there are a couple of solutions available, and it’s important for businesses to understand what those threats and solutions are.”

With the United Nations declaring 2025 the International Year of Quantum Science and Technology, the momentum behind quantum is only growing.

And with the launch of NAIT’s new programs, Canadian professionals have a chance to get ahead of the curve before it’s too late.

For more information, visit here.

Written ByJennifer Friesen
Jennifer Friesen is Digital Journal's associate editor and content manager based in Calgary.

 

Physicists ‘entangle’ individual molecules for the first time, hastening possibilities for quantum information processing

In work that could lead to more robust quantum computing, Princeton researchers have succeeded in forcing molecules into quantum entanglement.

Peer-Reviewed Publication

PRINCETON UNIVERSITY

 

IMAGE: 

LASER SETUP FOR COOLING, CONTROLLING, AND ENTANGLING INDIVIDUAL MOLECULES.

view more 

CREDIT: PHOTO BY RICHARD SODEN, DEPARTMENT OF PHYSICS, PRINCETON UNIVERSITY

For the first time, a team of Princeton physicists have been able to link together individual molecules into special states that are quantum mechanically “entangled.” In these bizarre states, the molecules remain correlated with each other—and can interact simultaneously—even if they are miles apart, or indeed, even if they occupy opposite ends of the universe. This research was recently published in the journal Science.

“This is a breakthrough in the world of molecules because of the fundamental importance of quantum entanglement,” said Lawrence Cheuk, assistant professor of physics at Princeton University and the senior author of the paper. “But it is also a breakthrough for practical applications because entangled molecules can be the building blocks for many future applications.”

These include, for example, quantum computers that can solve certain problems much faster than conventional computers, quantum simulators that can model complex materials whose behaviors are difficult to model, and quantum sensors that can measure faster than their traditional counterparts.

“One of the motivations in doing quantum science is that in the practical world it turns out that if you harness the laws of quantum mechanics, you can do a lot better in many areas,” said Connor Holland, a graduate student in the physics department and a co-author on the work.

The ability of quantum devices to outperform classical ones is known as “quantum advantage.” And at the core of quantum advantage are the principles of superposition and quantum entanglement. While a classical computer bit can assume the value of either 0 or 1, quantum bits, called qubits, can simultaneously be in a superposition of 0 and 1. The latter concept, entanglement, is a major cornerstone of quantum mechanics, and occurs when two particles become inextricably linked with each other so that this link persists, even if one particle is light years away from the other particle. It is the phenomenon that Albert Einstein, who at first questioned its validity, described as “spooky action at a distance.” Since then, physicists have demonstrated that entanglement is, in fact, an accurate description of the physical world and how reality is structured. 

“Quantum entanglement is a fundamental concept,” said Cheuk, “but it is also the key ingredient that bestows quantum advantage.”

But building quantum advantage and achieving controllable quantum entanglement remains a challenge, not least because engineers and scientists are still unclear about which physical platform is best for creating qubits. In the past decades, many different technologies—such as trapped ions, photons, superconducting circuits, to name only a few—have been explored as candidates for quantum computers and devices. The optimal quantum system or qubit platform could very well depend on the specific application.

Until this experiment, however, molecules had long defied controllable quantum entanglement. But Cheuk and his colleagues found a way, through careful manipulation in the laboratory, to control individual molecules and coax them into these interlocking quantum states. They also believed that molecules have certain advantages—over atoms, for example—that made them especially well-suited for certain applications in quantum information processing and quantum simulation of complex materials. Compared to atoms, for example, molecules have more quantum degrees of freedom and can interact in new ways.

“What this means, in practical terms, is that there are new ways of storing and processing quantum information,” said Yukai Lu, a graduate student in electrical and computer engineering and a co-author of the paper. “For example, a molecule can vibrate and rotate in multiple modes. So, you can use two of these modes to encode a qubit. If the molecular species is polar, two molecules can interact even when spatially separated.”

Nonetheless, molecules have proven notoriously difficult to control in the laboratory because of their complexity. The very degrees of freedom that make them attractive also make them hard to control, or corral, in laboratory settings.

Cheuk and his team addressed many of these challenges through a carefully thought-out experiment. They first picked a molecular species that is both polar and can be cooled with lasers. They then laser-cooled the molecules to ultracold temperatures where quantum mechanics takes centerstage. Individual molecules were then picked up by a complex system of tightly focused laser beams, so-called “optical tweezers.” By engineering the positions of the tweezers, they were able to create large arrays of single molecules and individually position them into any desired one-dimensional configuration. For example, they created isolated pairs of molecules and also defect-free strings of molecules.

Next, they encoded a qubit into a non-rotating and rotating state of the molecule. They were able to show that this molecular qubit remained coherent, that is, it remembered its superposition. In short, the researchers demonstrated the ability to create well-controlled and coherent qubits out of individually controlled molecules.

To entangle the molecules, they had to make the molecule interact. By using a series of microwave pulses, they were able to make individual molecules interact with one another in a coherent fashion. By allowing the interaction to proceed for a precise amount of time, they were able to implement a two-qubit gate that entangled two molecules. This is significant because such an entangling two-qubit gate is a building block for both universal digital quantum computing and for simulation of complex materials.

The potential of this research for investigating different areas of quantum science is large, given the innovative features offered by this new platform of molecular tweezer arrays. In particular, the Princeton team is interested in exploring the physics of many interacting molecules, which can be used to simulate quantum many-body systems where interesting emergent behavior such as novel forms of magnetism can appear.

“Using molecules for quantum science is a new frontier and our demonstration of on-demand entanglement is a key step in demonstrating that molecules can be used as a viable platform for quantum science,” said Cheuk.

In a separate article published in the same issue of Science, an independent research group led by John Doyle and Kang-Kuen Ni at Harvard University and Wolfgang Ketterle at the Massachusetts Institute of Technology achieved similar results.

“The fact that they got the same results verify the reliability of our results,” Cheuk said. “They also show that molecular tweezer arrays are becoming an exciting new platform for quantum science.”

The study, “On-Demand Entanglement of Molecules in a Reconfigurable Optical Tweezer Array,” by Connor M. Holland, Yukai Lu, and Lawrence W. Cheuk was published in Science on December 8, 2023. DOI: 10.1126/science.adf4272

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JOURNAL

Science

DOI

10.1126/science.adf4272 

METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

On-Demand Entanglement of Molecules in a Reconfigurable Optical Tweezer Array

ARTICLE PUBLICATION DATE

8-Dec-2023

 

Two studies demonstrate on-demand quantum entanglement in ultracold molecules

Peer-Reviewed Publication

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE (AAAS)

The controlled creation of quantum entanglement with molecules has been a long-standing challenge in quantum science. Now, in two new studies, researchers report a method for tailoring the quantum states of individual molecules to achieve quantum entanglement on demand. Their strategy presents a promising new platform for the advancement of quantum technologies such as computation and sensing. Quantum entanglement is one of the key defining features of quantum mechanics. It is central to many quantum applications. Because of their rich internal structure and long-lived rotational states, ultracold molecules have been proposed as promising candidates for qubits in quantum computing and quantum simulations. However, while entanglement has been achieved in various atomic, photonic, and superconducting platforms, controlling and manipulating entanglement between molecules on demand experimentally has been difficult. Now, in two different studies, Yicheng Bao and colleagues and Conner Holland and colleagues report a method to achieve controlled quantum entanglement of calcium fluoride (CaF) molecules. Bao et al. and Holland et al. make use of the long-range dipolar interaction between pairs of laser-cooled CaF molecules trapped in a reconfigurable optical tweezer array and successfully demonstrate the creation of a Bell state – an important class of entangled quantum state characterized by maximal entanglement between two qubits. The Bell state is a foundational concept for many quantum technologies. Both studies show that two CaF molecules located in neighboring optical tweezers and placed close enough to sense their respective long-range electric dipolar interaction led to an interaction between tweezer pairs, which dynamically created a Bell state out of the two previously uncorrelated molecules. “The demonstrated manipulation and characterization of entanglement of individually tailored molecules by Bao et al. and Holland et al. paves the way for developing new versatile platforms for quantum technologies,” writes Augusto Smerzi in a related Perspective.

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JOURNAL

Science

DOI

10.1126/science.adf8999 

ARTICLE TITLE

Dipolar spin-exchange and entanglement between molecules in an optical tweezer array

ARTICLE PUBLICATION DATE

8-Dec-2023

Two qudits fully entangled

A new way to entangle high-dimensional quantum systems

Peer-Reviewed Publication

UNIVERSITY OF INNSBRUCK

 

IMAGE: VACUUM CHAMBER WITH A MICROFABRICATED SURFACE TRAP view more 

CREDIT: MARTIN VAN MOURIK

In the world of computing, we typically think of information as being stored as ones and zeros – also known as binary encoding. However, in our daily life we use ten digits to represent all possible numbers. In binary the number 9 is written as 1001 for example, requiring three additional digits to represent the same thing.

The quantum computers of today grew out of this binary paradigm, but in fact the physical systems that encode their quantum bits (qubit) often have the potential to also encode quantum digits (qudits), as recently demonstrated by a team led by Martin Ringbauer at the Department of Experimental Physics at the University of Innsbruck. According to experimental physicist Pavel Hrmo at ETH Zurich: “The challenge for qudit-based quantum computers has been to efficiently create entanglement between the high-dimensional information carriers.”

In a study published in the journal Nature Communications the team at the University of Innsbruck now reports, how two qudits can be fully entangled with each other with unprecedented performance, paving the way for more efficient and powerful quantum computers.

Thinking like a quantum computer

The example of the number 9 shows that, while humans are able calculate 9 x 9 = 81 in one single step, a classical computer (or calculator) has to take 1001 x 1001 and perform many steps of binary multiplication behind the scenes before it is able to display 81 on the screen. Classically, we can afford to do this, but in the quantum world where computations are inherently sensitive to noise and external disturbances, we need to reduce the number of operations required to make the most of available quantum computers.

Crucial to any calculation on a quantum computer is quantum entanglement. Entanglement is one of the unique quantum features that underpin the potential for quantum to greatly outperform classical computers in certain tasks. Yet, exploiting this potential requires the generation of robust and accurate higher-dimensional entanglement.

The natural language of quantum systems

The researchers at the University of Innsbruck were now able to fully entangle two qudits, each encoded in up to 5 states of individual Calcium ions. This gives both theoretical and experimental physicists a new tool to move beyond binary information processing, which could lead to faster and more robust quantum computers.

Martin Ringbauer explains: “Quantum systems have many available states waiting to be used for quantum computing, rather than limiting them to work with qubits.” Many of today's most challenging problems, in fields as diverse as chemistry, physics or optimisation, can benefit from this more natural language of quantum computing.

The research was financially supported by the Austrian Science Fund FWF, the Austrian Research Promotion Agency FFG, the European Research Council ERC, the European Union and the Federation of Austrian Industries Tyrol, among others.

Publication: Native qudit entanglement in a trapped ion quantum processor. Pavel Hrmo, Benjamin Wilhelm, Lukas Gerster, Martin W. van Mourik, Marcus Huber, Rainer Blatt, Philipp Schindler, Thomas Monz, Martin Ringbauer. Nature Communications 14, 2242 (2023) (Open Access) https://doi.org/10.1038/s41467-023-37375-2

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JOURNAL

Nature Communications

DOI

10.1038/s41467-023-37375-2 

METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

Native qudit entanglement in a trapped ion quantum processor

ARTICLE PUBLICATION DATE

19-Apr-2023

Sino-Brazilian study proves 

compatibility of two fundamental

principles of quantum theory

Non-locality and contextuality were born with quantum theory but followed independent paths for several decades

Peer-Reviewed Publication

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO

Quantum theory, which was formulated in the first three decades of the twentieth century, describes a wide array of phenomena at the molecular, atomic and subatomic scales. Among its many technological applications, three have become ubiquitous in daily life: laser barcode scanners, light-emitting diodes (LEDs) and the global positioning system (GPS).

Nevertheless, quantum physics is still not entirely understood, and some of the phenomena concerned appear to fly in the face of common sense or everyday empirical experience, surprising not only the average layperson but also physicists and philosophers of science. Some of the counterintuitive aspects of quantum theory are due to its probabilistic nature. It offers a set of rules for calculating the probabilities of the possible measurement outcomes of physical systems and in general cannot predict the actual result of a single measurement.

One of the challenging ideas presented by quantum physics is non-locality, an aspect of reality manifested when two or more systems are generated or interact in such a way that the quantum states of any system cannot be described independently of the quantum states of the others. Technically speaking, scientists call such systems entangled, since they are strongly correlated even at a distance and their quantum state is not defined by the quantum states of their component parts.

Another challenging idea, which seems to point in the opposite direction, is contextuality, according to which the outcome of measuring a quantum object depends on the context, meaning other compatible measurements performed at the same time.

Non-locality and contextuality were born with quantum theory but followed independent paths for several decades. In 2014, scientists conducted a study involving a particular case in which they showed that only one of them can be observed in a quantum system. This finding became known as monogamy. The authors conjectured that non-locality and contextuality were different facets of the same general behavior observed either in one way or the other.

Now, however, a study by Brazilian and Chinese researchers has shown both theoretically and experimentally that this is not so. An article on the study is published in Physical Review Letters and highlighted as an Editors’ Suggestion.

The research was led by Rafael Rabelo, last author of the article and a professor at the State University of Campinas’s Gleb Wataghin Institute of Physics (IFGW-UNICAMP) in Brazil. 

The first authors are Peng Xue and Lei Xiao of Beijing Computational Science Research Center in China.

The other co-authors, all affiliated with Brazilian institutions, are Gabriel Ruffolo and André Mazzari, also researchers at IFGW-UNICAMP; Marcelo Terra Cunha of the same university’s Institute of Mathematics, Statistics and Scientific Computing (IMECC-UNICAMP); and Tassius Temístocles of the Federal Institute of Alagoas.

“We proved that both phenomena can indeed be observed concurrently in quantum systems. The theoretical approach was developed here in Brazil and validated in a quantum optics experiment by our Chinese collaborators,” Rabelo told Agência FAPESP.

The new study shows definitively that two of the fundamental ways in which quantum physics differs from classical physics can be observed at the same time in the same system, contrary to the usual belief. “Non-locality and contextuality, therefore, are clearly not complementary manifestations of the same phenomenon,” Rabelo said.

In practical terms, non-locality is an important resource for quantum encryption, while contextuality is the basis for a specific quantum computing model, among other applications. “The possibility of having both at the same time in the same system could pave the way to the development of new quantum information processing and quantum communications protocols,” he said. 

Bell’s theorem

The idea of non-locality was a sort of answer to the objection raised by Albert Einstein (1879-1955) to the probabilistic nature of quantum physics. In a seminal article published in 1935, Einstein, Boris Podolsky (1896-1966) and Nathan Rosen (1909-1995), or EPR, questioned the completeness of quantum theory. They proposed a thought experiment known as the EPR paradox: to justify certain non-classical correlations deriving from entanglement, distant quantum systems would have to exchange information instantly, which is impossible according to the special theory of relativity. They concluded that this paradox was due to the incompleteness of quantum theory. The incompleteness, EPR argued, could be corrected by including local hidden variables that would make quantum physics as deterministic as classical physics.

“In 1964, British physicist J.S. Bell (1928-1990) revisited the EPR argument, introducing an elegant formalism that encompassed all theories of local hidden variables regardless of the particular properties each variable might have. Bell proved that none of these theories could reproduce the correlations between measurements performed on two systems predicted by quantum physics. In my view, this result, later known as Bell’s theorem, is one of the most important pillars of quantum physics. The property of having strong correlations that can’t be reproduced by any local theory is now known as Bell non-locality. Alain Aspect, John Clauser and Anton Zeilinger were awarded the 2022 Nobel Prize in Physics for observing Bell non-locality experimentally, among other achievements,” Rabelo said.

Another important result deriving from the discussion of hidden variables was presented in an article by Simon Kochen (1934-) and Ernst Specker (1920-2011), published in 1967. The authors demonstrated that, owing to the structure and mathematical properties of quantum measurements, any theory of hidden variables that reproduces the predictions of quantum physics must exhibit a contextuality aspect.

“Despite the common motivation, studies of Bell non-locality and Kochen-Specker contextuality followed independent paths for quite a long time. Only recently has there been growing interest in finding out whether both phenomena could be manifested concurrently in the same physical system. In an article published in 2014, Pawel Kurzynski, Adán Cabello and Dagomir Kaszlikowski said no. They showed why through a particular case but an interesting one, nonetheless. We’ve now refuted that ‘no’ in our study,” Rabelo said.

The study was supported by FAPESP via a Young Investigator Grant awarded to Rabelo; a doctoral scholarship awarded to Ruffolo; and a master’s scholarship awarded to Mazzari.

About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.

 

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JOURNAL

Physical Review Letters

DOI

10.1103/PhysRevLett.130.040201 

ARTICLE TITLE

Synchronous Observation of Bell Nonlocality and State-Dependent Contextuality

 

A new experimental system to bring quantum technologies closer to students

Study of phenomena unique to quantum mechanics

University of Barcelona

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The expert Raúl Lahoz and a group of students with the new equipment for studying quantum physics.

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Credit: Fundació Catalunya La Pedrera

The world of quantum physics is experiencing a second revolution, which will drive an exponential leap in the progress of computing, the internet, telecommunications, cybersecurity and biomedicine. Quantum technologies are attracting more and more students who want to learn about concepts from the subatomic world — such as quantum entanglement or quantum superposition — to explore the innovative potential of quantum science. In fact, understanding the non-intuitive nature of quantum technology concepts and recognizing their relevance to technological progress is one of the challenges of 2025, declared the International Year of Quantum Science and Technology by UNESCO.

 

Now, a team from the Faculty of Physics of the University of Barcelona has designed new experimental equipment that makes it possible for students to familiarize themselves with the more complex concepts of quantum physics. The configuration they present —versatile, cost-effective and with multiple ways of application in the classroom — is already operational in the Advanced Quantum Laboratory of the UB’s Faculty of Physics and could also be accessible in less specialized centres.

This innovation is presented in an article in the journal EPJ Quantum Technology, which results from a collaboration between professors Bruno Juliá, from the Department of Quantum Physics and Astrophysics and the UB Institute of Cosmos Sciences (ICCUB); Martí Duocastella, from the Department of Applied Physics and the UB Institute of Nanoscience and Nanotechnology (IN2UB), and José M. Gómez, from the Department of Electronic and Biomedical Engineering. It is based on the result of Raúl Lahoz’s master’s final project, with the participation of experts Lidia Lozano and Adrià Brú.

Study of phenomena unique to quantum mechanics
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Quantum mechanics makes it possible to create so-called entangled systems — for example, with two particles or two photons — that behave in a non-intuitive way. In 1964, the physicist John S. Bell experimentally proved that the predictions of quantum mechanics were totally incompatible with a classical description of physics — a hypothesis that had been advocated by Albert Einstein — and consolidated the probabilistic nature of quantum mechanics. In 2022, scientists Alain Aspect, John F. Clauser and Anton Zeilinger were awarded the Nobel Prize in Physics for pioneering experiments in quantum information on entangled photons and the experimental demonstration of the violation of Bell’s inequalities.

Quantum entanglement is today one of the fundamental resources to drive the development of quantum technologies (quantum computers, data encryption, etc.). “The study of Bell inequalities — in particular, observing violations of the inequalities — is fundamental to characterizing quantum entangled systems. It is important to be able to perform these experiments in a teaching laboratory to understand Bell’s inequalities, quantum entanglement and the probabilistic nature of quantum mechanics”, says Bruno Juliá.

Martí Duocastella explains in the article that they have designed “new experimental equipment capable of providing students with direct measurements of quantum entanglement”. “From our perspective, — says the researcher — we believe that allowing students to make these measurements will greatly facilitate their understanding of this unintuitive phenomenon”.

Introducing students to advanced tools
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The system designed by the UB team makes it possible to study Bell inequalities and also to perform full two-photon state tomography. With a simple operation, it can prepare different quantum entangled states. Compared to previous proposals, “the new equipment has improved the photon-capture process: it uses detectors assembled to optical fibres, one of the key innovations to simplify the experiment, which facilitates the alignment of the system and increases the efficiency of the detection. Thus, a complete measurement of the Bell inequalities can be performed during a practical laboratory session (between one and two hours)”, say Juliá and Duocastella.

 

The results reveal successful manipulation of the quantum state of photons and the achievement of high-fidelity entangled states and significant violations of Bell inequalities. Also, the elements of the system are widely used in current quantum technologies, facilitating students’ contact with advanced instrumentation.

This innovation, which has already been applied in bachelor’s and master’s degree courses, has received very positive feedback from all students. In the bachelor’s degree in Physics, it allows experimental demonstrations to be carried out to complement the subject of Classical and Quantum Information Theory and Quantum Mechanics. In the master’s degree course, it is one of the four experiments in the Advanced Quantum Laboratory of the Master’s degree in Quantum Science and Technologies.
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This study has received funding from both the Spanish Ministry of Science, Innovation and Universities and the European Union’s Next Generation EU funds.

 

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Journal

EPJ Quantum Technology

DOI

10.1140/epjqt/s40507-024-00298-y 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Undergraduate setup for measuring the Bell inequalities and performing quantum state tomography