Quantum

U of T researcher leads effort to protect power utilities from quantum attacks

Christopher.Sorensen — Thu, 23 May 2024 20:12:49 +0000

U of T researcher leads effort to protect power utilities from quantum attacks

Christopher.Sorensen Thu, 05/23/2024 - 16:12

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Faculty of Applied Science & Engineering researcher Deepa Kundur, second from right, is leading a collaboration between academia and industry that’s focused on developing solutions to protect power utilities from cyberattacks using quantum technologies (photo by Neil Ta)

Matthew Tierney

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“Technology is always changing the threat landscape. And quantum computing, which is becoming more feasible and practical, is a powerful tool that will make our classical defences obsolete”

A researcher from the University of Toronto is leading a multidisciplinary research group that aims develop quantum-based technology solutions to defend power utilities against future cyberattacks.

With the support of a first-of-its-kind NSERC Alliance-Mitacs Accelerate grant worth $1.45 million, the group is working at the intersection of quantum, cybersecurity and critical infrastructure.

“We have to stay ahead of the game,” says group lead Deepa Kundur, professor and chair of U of T’s Edward S. Rogers Sr. department of electrical and computer engineering in the Faculty of Applied Science & Engineering.

“Technology is always changing the threat landscape. And quantum computing, which is becoming more feasible and practical, is a powerful tool that will make our classical defences obsolete.”

Kundur’s project is a collaboration between academia, Hydro-Québec and Xanadu, one of Canada’s most successful quantum computer startups. A second team – headed by Associate Professor Atefeh Mashatan of Toronto Metropolitan University and involving quantum solution leaders Crypto4A and evolutionQ – will build a road map for the classical-to-quantum migration for power grids in preparation for a future transition.

Quantum enhancement is the next stage in the evolution of today’s smart grids, so-named because they incorporate information-communication technology (ICT) into their operations. ICT has allowed smart grids to adapt to changing conditions and electricity load, as well respond more efficiently to natural disasters in order to meet society’s increasing power needs in an intelligent, sustainable way.

“ICT and its advanced sensors generate more data than before,” says Kundur. “We transport this data to different parts of the grid to start co-ordinating information to make decisions based on synchronized information and enhanced situational awareness.”

One potential downside of a data-driven smart grid, however, is the introduction of new vulnerabilities since attackers can now target not just the physical infrastructure, but the information that flows through it.

That’s because a smart grid’s connectivity increases opportunities for access. Also, ICT adds a level of complexity that results in emergent properties that are difficult to predict and can be challenging to safeguard. And the standards and policies put in place to mitigate operational variations mean there’s a level of interoperability between working grids that hackers can use to their advantage.

While cybersecurity experts have so far incorporated layers of defences into our smart grids, Kundur warns that those safeguards are not ready for quantum technologies.

“Algorithms and cryptography that are incredibly difficult for classical computers to crack become solvable with a quantum computer,” she says. “And then other questions arise. For example, when the power utilities themselves start to use quantum sensors, is this quantum-enhanced information better for attack detection or does it give attackers an ability to hide themselves?”

The question is tough to answer when you consider that quantum sensors of this nature – and the quantum data they would generate – don’t exist yet.

“We’ll take classical data, use models to predict what quantum versions of the information would appear to be, and then perform anomaly and attack detection on it,” says Kundur.

“We’ll be experimenting with quantum machine learning for better pattern recognition to detect a cyberattack. This is a highly exploratory project.”

Even if it’s decades before manufacturers integrate quantum attack-detection algorithms in their devices, Kundur says foundational research that she and her team will carry out in the next few years is a valuable endeavour.

“Security is a process. It’s very much a dynamic interaction,” she says. “And though we can never get to 100-per-cent protection, it’s something we have to continually try to achieve.”

U of T researcher joins effort to establish transatlantic quantum communications link

Christopher.Sorensen — Tue, 02 May 2023 13:18:56 +0000

U of T researcher joins effort to establish transatlantic quantum communications link

Christopher.Sorensen Tue, 05/02/2023 - 09:18

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Li Qian is part of an international team of researchers in Canada and Europe developing a blueprint for future satellite-based quantum link technology (photo by Matthew Tierney)

Matthew Tierney

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Faculty of Applied Science & Engineering

Faculty of Arts & Science

Global

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Quantum

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Quantum communication links require a delicate touch even over relatively short distances – nevermind across continents. Yet, that’s precisely the challenge taken up by the University of Toronto’s Li Qian and her collaborators.

The three-year international endeavour HyperSpace is one of the largest collaborations yet for the Canadian quantum community.

It brings together researchers in five countries, including partners at U of T, the University of Waterloo, Quebec’s Institut national de la recherche scientifique and several European institutions.

“Establishing a quantum link over such large distances will involve satellites. We’d be sending a couple of photons from Earth’s orbit to ground. It’s quite a challenge and requires various areas of expertise,” says Qian, a professor of photonics in the Edward S. Rogers Sr. department of electrical and computer engineering in the Faculty of Applied Science & Engineering.

At U of T, Qian is working with John Sipe, a professor in the department of physics in the Faculty of Arts & Science whose research focuses on quantum optics and condensed matter physics.

“Our aim is to demonstrate the feasibility of the technology,” Sipe says. “By going through the ups and downs of a satellite mission that integrates the unique demands of quantum communication, we’ll have a solid blueprint in place. Ultimately, HyperSpace is about making quantum applications attractive and realistic in the near future.”

One such application is quantum cryptography that is virtually unbreakable during transmission and offers far better protection than its classical counterpart. While optical fibre can be used for short-reach quantum cryptography, the technology is currently limited to short distances because photons inevitably scatter in optical fibre after about 100 kilometres, degrading the transmission.

While simple amplifiers can boost the transmission signal in classical optical fibre communications, the quantum equivalent of these amplifiers – called quantum repeaters – is still in the early stages of development.

“That’s why grounded optical fibre is no longer feasible if you want to share quantum keys between Toronto and Berlin, for example,” Qian says.

“A quantum satellite is a way to overcome the challenges associated with this very large distance. Such a satellite would also be necessary someday for distributed quantum computing or a quantum internet.”

Qian’s role in HyperSpace’s mission architecture design project is to develop the photon source in space and on the ground. The transmitted photons must be bound with a partner photon, a quantum phenomenon called entanglement. When you measure an entangled photon – no matter how far it may have travelled – you instantly know that its partner shares the same measured property. This strange behaviour of particles in the quantum realm allows for the dramatic information-processing capacity promised by quantum computing.

Since nearly all the photons sent through the atmosphere will be scattered or absorbed – if they aren’t first diffracted by the aperture of the firing telescope – Qian needs to make the very few photons that will reach the destination count.

“Photons can be entangled in multiple ways, in multiple degrees of freedom, and thus carry more information,” she says.

“So we want to entangle not just in polarization, but also in frequency – in theory, that could be up to a hundred colours – or in the temporal domain. We call this hyperentanglement.”

Before transmitting the entangled photons, you need to align the telescopes on the ground and in the satellite – so the HyperSpace team is designing the necessary optical systems to do so with intense beacon lights. The satellite will be following the curvature of the Earth at orbital speed, which makes the angular tolerance very tight, with little room for error.

Once alignment is achieved, the beacon will be shut off and an entangled photon fired into the quantum channel towards the satellite. This procedure must be done at night to mitigate sunlight interference. Even so, cloud coverage, atmosphere, turbulence and distortions will all continue to have a detrimental effect.

“A benefit of projects like these, which I don’t think get talked about enough, is the simple fact that they provide a common goal,” Qian says. “The entire research process – getting top-flight minds working together and generating new ideas – is going to benefit society in some way. You may end up with some technology that can be used in other areas. Maybe the source I’m working on won’t be used for the satellite but something else, such as medical imaging.

“Ultimately, it’s exciting. You meet like-minded collaborators, get to know what they’re doing, learn from each other. That becomes part of the success story.”

U of T brings together researchers and policymakers to discuss how GTA can advance Canada's quantum sector

siddiq22 — Tue, 14 Feb 2023 18:46:52 +0000

U of T brings together researchers and policymakers to discuss how GTA can advance Canada's quantum sector

siddiq22 Tue, 02/14/2023 - 13:46

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(Photo courtesy of Xanadu Quantum Technologies)

Tabassum Siddiqui

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With quantum technologies rapidly becoming one of the fastest growing advanced sectors globally, experts and policymakers recently gathered at the University of Toronto to discuss Canada’s new National Quantum Strategy and the university’s role in supporting it.

Attended by federal and provincial government stakeholders, the discussion drew on the findings of a recent report commissioned from Deloitte Canada that compared Canada’s centres of quantum research. The GTA was the country’s strongest quantum hub, supported by U of T’s global research leadership, the report found.

Timothy Chan

“Quantum research at the University of Toronto places the university among the world’s leading producers of impactful knowledge in this domain,” said Timothy Chan, associate vice-president and vice-provost, strategic initiatives and a professor of mechanical and industrial engineering in the Faculty of Applied Science & Engineering.

“The quantum ecosystem is strong here – not just because of our world-leading quantum expertise, but because we have the best scientists in other fields that will integrate quantum technologies and their applications.”

In January, the federal government launched the $360-million National Quantum Strategy to support the sector in an increasingly competitive global market. It aims to boost research, talent and commercialization in quantum and solidify Canada’s position in the field.

A rapidly emerging and economically promising field, quantum science and its applications draw on the unintuitive principles of quantum mechanics to solve problems too complex for everyday computers.

By 2045, quantum applications – including artificial intelligence, cybersecurity, medical imaging and many more – are projected to be a $138-billion market, leading to more than 200,000 jobs in Canada, according to a study commissioned by the National Research Council of Canada.

The findings from the Deloitte report were presented during the U of T event, which was hosted by the Munk School of Global Affairs & Public Policy as part of its New Frontiers series, which promotes dialogue between decision-makers and U of T researchers on how to advance public policy priorities. The report’s analysis of Canada’s centres of quantum research ranked the country fourth in the world in the strength of its research in quantum science and technology.

Canada is ranked No. 4 in the world in the impact of its research on quantum science. Thanks to the policymakers, researchers & startups who came together today to think about how to turn that advantage into economic growth. pic.twitter.com/PHHlVWaALA
— U of T Government Relations Office (@uoftgro) February 1, 2023

U of T is a key contributor to Canada’s performance, with the university’s research impact in quantum-related sciences ranked fifth globally.

The breadth of expertise across quantum fields is one of the university’s strengths, said Anna Dyring, quantum strategic initiative lead at U of T’s Centre for Quantum Information and Quantum Control (CQIQC).

CQIQC’s activities, which promote research collaborations in the sector, encompass U of T’s departments of chemistry, physics, mathematics and computer science in the Faculty of Arts & Science, as well as the departments of electrical engineering and materials science in the Faculty of Applied Science & Engineering.

“Quantum computing is a field where you need many different types of thinkers and knowledge in order to innovate and lead,” Dyring said.

U of T and partners such as the Vector Institute are leading in AI, data sciences, regenerative and precision medicine, climate change, pandemic preparedness and advanced materials – just some of the fields the university is supporting through its Institutional Strategic Initiatives, Chan told attendees. U of T's Schwartz Reisman Institute for Technology and Society also convenes and facilitates research on how these technologies improve human lives.

“Our approach is interdisciplinary because the challenges Canada and the world face cannot be solved by remaining within our disciplinary boundaries. We aim to transform how we solve problems, and to work at the frontiers of knowledge – that is where quantum research currently resides.”

(Photo by Geoffrey Vendeville)

Other countries are making major investments in the quantum sector as the field becomes increasingly competitive globally, the discussion heard. Large companies in Europe, Asia and the United States are interested in research and development and in being early adopters, while there has been more caution about quantum tech adoption in Canada.

However, Canada remains a strong location for startups – and the GTA boasts the largest number of quantum companies in the country. U of T is behind many of these successful startups, thanks to initiatives such as the Rotman School of Management’s Creative Destruction Lab (CDL) – the only dedicated early-stage quantum incubator in the country.

"CDL’s mission is to enhance the commercialization of science for the betterment of humankind. Our objectives-based mentorship process has the potential to positively impact a startup's trajectory at the very early stages of their journey,” said Sonia Sennik, CDL’s executive director.

CDL’s graduates include Xanadu Quantum Technologies – founded by former U of T post-doctoral physics researcher Christian Weedbrook – which recently received $40 million in federal funding to support its cutting-edge quantum computing technology. Xanadu is one of Canada’s unicorn companies, valued at over $1 billion.

Christian Weedbrook, founder and CEO of Xanadu, at the Collision tech conference in 2022 (photo by Lukas Schulze/Sportsfile for Collision/Getty Images)

“The GTA is a great place for innovative companies to start and grow because all the ingredients are here: talent, investors, public and private partners, customers and support networks,” said David Asgeirsson, manager of research partnerships and intellectual property at Xanadu.

To stay competitive in the sector, Canada will need further investments to create quantum-literate talent, including funding for graduate students and the scaling of successful partnerships with industry to integrate quantum-ready talent into existing companies.

“It’s critical that we have the funding to recruit top researchers to the quantum hubs in Canada,” Dyring said. “Having strong faculty to continue adding new courses in this emerging field – and to ensure students have opportunities to work on research at the graduate level – is important in growing the field, because we will need more people trained in this area going forward. And we’re seeing that there’s growing interest from students to explore studies and research in quantum.”

Quantum computing startup Xanadu receives $40 million in federal funding: Globe and Mail

bresgead — Thu, 26 Jan 2023 18:17:57 +0000

Quantum computing startup Xanadu receives $40 million in federal funding: Globe and Mail

bresgead Thu, 01/26/2023 - 13:17

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From left to right: Xanadu CEO and former U of T post-doctoral researcher Christian Weedbrook, Prime Minister Justin Trudeau and Innovation, Science and Industry Minister François-Philippe Champagne (photo by Alex Tetreault)

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Xanadu Quantum Technologies, founded by former University of Toronto post-doctoral physics researcher Christian Weedbrook, has received $40 million in federal funding to support its leading quantum computing technology, the Globe and Mail reports.

Prime Minister Justin Trudeau recently visited the Toronto startup’s headquarters to announce the investment through the federal Strategic Investment Fund, to allow Xanadu to build and commercialize the world’s first photonic-based, fault-tolerant quantum computer.

“What’s happening here is cutting edge not just in Canada, but around the world,” said Trudeau, whose government has pledged to spend $360 million in a national strategy to advance quantum technologies.

Xanadu, an alumnus of the Creative Destruction Lab seed-stage accelerator at U of T’s Rotman School of Management, revealed last year that its system, called Borealis, had achieved “quantum advantage” by solving in 36 millionths of a second a specific math problem that would take some 9,000 years for the world’s most powerful supercomputers to complete.

Experimental physicists take step toward understanding natural quantum systems

Christopher.Sorensen — Mon, 16 Jan 2023 16:54:59 +0000

Experimental physicists take step toward understanding natural quantum systems

Christopher.Sorensen Mon, 01/16/2023 - 11:54

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Physics graduate student Frank Corapi adjusts the alignment of a laser beam in the Ultracold Atoms Lab at U of T (photo by Jo-Anne McArthur)

Chris Sasaki

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“Suppose you knew everything there was to know about a water molecule – the chemical formula, the bond angle, etc.,” says experimental physicist Joseph Thywissen.

“You might know everything about the molecule, but still not know there are waves on the ocean – much less how to surf them,” he says. “That’s because when you put a bunch of molecules together, they behave in a way you probably cannot anticipate.”

Thywissen is a professor in the University of Toronto’s department of physics in the Faculty of Arts & Science and a member of the Centre for Quantum Information & Quantum Control. He is describing the concept in physics known as emergence: the relationship between the behaviour and characteristics of individual particles and large numbers of those particles.

Thywissen and his collaborators have taken a first step toward understanding the transition from “one-to-many" particles by studying not one, not many, but two isolated, interacting particles – in this case potassium atoms. The result is described in a paper published recently in the journal Nature.

A team that included experimental physicists from U of T and theoretical physicists from the University of Colorado (UC) measured the strength of a type of interaction – known as “p-wave interactions” – between two potassium atoms and found the result confirms a longstanding prediction.

P-wave interactions are weak in naturally occurring systems, but researchers predicted that they have a much higher maximum theoretical limit. The team is the first to confirm that the p-wave force between particles reached this maximum.

Graduate students Robyn Learn and Frank Corapi with Professor Joseph Thywissen in Thywissen’s lab (photo by Jo-Anne McArthur)

The paper’s co-authors from U of T include co-lead authors Vijin Venu and Peihang Xu, both of whom earned their doctorate last year, as well as a post-doctoral researcher, Cora Fujiwara and Frank Corapi, a current PhD candidate.

Their collaborators include researchers from UC Boulder, led by Professor Ana Maria Rey. The theory team includes PhD candidate Michael Mamaev; Thomas Bilitewski, a former post-doc in Rey’s group who is currently an assistant professor in the department of physics at Oklahoma State University; and Jose D’Incao, a UC associate research professor.

“In our lab, we were able to isolate two atoms at a time,” Venu says. “This approach avoids the complexity of many-atom systems and allows full control and study of interactions between atoms in a pair.”

The team isolated pairs of atoms within a 3D optical lattice – a “crystal of light,” as Fujiwara describes it – created at the intersection of three laser beams at 90 degrees to each other. The intersecting beams generated stationary nodes of high intensity which trapped pairs of particles. With pairs isolated in this way, the researchers were able to measure the strength of their mutual interaction.

The result has ramifications in different technologies, including the study of superfluids, superconductivity and quantum simulations.

Quantum simulations are models designed to understand quantum systems like atoms, molecules or chemical reactions – systems ruled by quantum mechanics. These simulations can help understand how properties of materials emerge from particle-particle interactions.

The challenge of solving quantum models with existing computers is daunting, with the task having been described as teaching quantum mechanics to a computer. A promising alternative is to use existing quantum systems – in other words, actual atoms and molecules.

“What's hard for us, is easy for nature,” Thywissen says. “And so, we can harness the computational power of nature just ‘doing its thing’ to solve problems that are otherwise intractable to us.”

The team’s insight into how two particles interact is a step toward understanding natural quantum systems and how they can lead to more powerful and effective quantum simulations.

“What we saw in our experiment was remarkable,” Fujiwara says. “It's a perfect little system. And now that we have this understanding of this two-particle system, we can start to create these sorts of exotic systems which involve many, many more particles.”

How quantum is it? U of T physicist Aaron Goldberg may have the answer

Christopher.Sorensen — Tue, 26 Jan 2021 15:19:16 +0000

How quantum is it? U of T physicist Aaron Goldberg may have the answer

Christopher.Sorensen Tue, 01/26/2021 - 10:19

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(photo courtesy of Aaron Goldberg)

Chris Sasaki

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Faculty of Arts & Science

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Quantum

Research & Innovation

A team of physicists have developed a way to mathematically describe the “quantumness” of different objects or systems – that is, the degree to which they behave in a quantum manner.

The research is laid out in a new paper that was recently published in the journal AVS Quantum Science.

“Previously, researchers had measured quantumness in systems that involved light,” says lead author Aaron Goldberg, a PhD candidate in the University of Toronto’s department of physics in the Faculty of Arts & Science.

“But we can apply our generalized approach to any quantum system – systems involving light, atoms, molecules or even combinations of those things.”

So what, exactly, are researchers measuring?

The subatomic world described by quantum physics is very different from the world described by Newton’s classical laws of physics. In the familiar world of classical physics, we know the position and momentum of objects with enough precision to, for example, make a difficult shot in a game of billiards. We also know the ball won’t magically transform into something other than a ball. It won’t inexplicably pass through the side of the table. And we know when we strike a ball on our table, it won’t affect a ball on another table on the other side of the planet.

But in the quantum world, a subatomic particle – unlike a billiard ball on a pool table – has only a probable position and speed. Light acts sometimes like particles and sometimes like waves. Subatomic particles can quantum tunnel through seemingly impenetrable barriers. And particles can mirror each other over vast distances – a phenomenon known as quantum entanglement.

Such characteristics define an object’s “quantumness.”

Goldberg says that many initially believed there was a clear distinction between the classical and quantum – that objects were one or the other. But as our understanding of the quantum realm grew, he says that idea changed.

“Over the years, scientists conducted more and more sophisticated experiments but failed to see a distinct boundary between the two,” says Goldberg. “And now, the prevailing theory is that quantum mechanics describes everything from photons to billiard balls to planets.

“In fact, there are probably an infinite number of degrees of quantumness.”

For example, a billiard ball is in fact a quantum object that could tunnel through the side of the table. But that would only happen if the quantum state of the atoms and molecules in the ball aligned – and the chances of that are as small as the number of atoms and molecules in the ball is large.

Goldberg and his collaborators looked at the quantum end of the classical-to-quantum spectrum and identified the two highest degrees of quantumness, which they labeled as “King” and “Queen.”

“And there are definitely more than just Kings and Queens,” says Goldberg.

While the research seems esoteric, there are important applications in our increasingly quantum world.

Knowledge about the degree of quantumness of a system may help in the development of quantum computers, sensing technologies and in the technologies used to measure physical constants and other properties with extreme precision. For example, the research could potentially help in detecting gravitational waves because the observations involve measurements that must be accurate to 1/10,000th the diameter of a proton.

Goldberg and his colleagues are continuing to explore extreme quantum states with the help of teams in labs around the world, including the lab of Aephraim Steinberg in the department of physics.

“This result feels like a single step down a long road,” Goldberg says.

“I think research into extreme quantum states has just begun. I expect I’ll be revisiting this quest for a good while.”

The research received support from the Natural Sciences and Engineering Research Council of Canada, among others.

U of T physicists measure the duration of quantum tunneling for the first time

Christopher.Sorensen — Thu, 23 Jul 2020 14:41:08 +0000

U of T physicists measure the duration of quantum tunneling for the first time

Christopher.Sorensen Thu, 07/23/2020 - 10:41

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A team of quantum physicists at the University of Toronto have recorded the first measurement of the length of time it takes an atom to tunnel through a barrier, clocking it at a mere one millisecond (photo by Chris Thomaidis)

Arts & Science news staff

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The fact that quantum-scale objects like atoms or photons can appear to cross apparently insurmountable barriers would surprise most non-scientists – but not quantum physicists. This effect, known as quantum tunneling, was first reported in the 1920s. It’s so well-established that it is harnessed for advanced microscopes and quantum computers and is essential for photosynthesis and nuclear fusion.

The details of the phenomenon, however, remained mysterious. For 90 years, physicists have argued about how, exactly, the tunneling happens, what the atoms do as they tunnel, and how long they take to make the journey.

Now, a team of quantum physicists in the Faculty of Arts & Science at the University of Toronto have recorded the first measurement of the length of time it takes an atom to tunnel through a barrier, clocking it at a mere one millisecond – or 1/1000th of a second. The results are reported in a research study published in Nature.

“We wouldn't even be here if not for tunneling,” says Aephraim Steinberg, a professor in the department of physics and co-director of CIFAR’s quantum information science program and senior investigator of the study. “The first steps in fusion in the sun require one nucleus to tunnel into another nucleus. So, tunneling is a very fundamental process that actually happens in the universe, not just in quantum mechanics textbooks.”

Steinberg’s team, seeking to provide clarity on how long particles spend tunneling, timed how long ultra-cold rubidium atoms took to tunnel through a millionth of a metre-thick laser beam that should have reflected them. They set up a system where they would push atoms of rubidium, which they had cooled down to a billionth of a degree above absolute zero, into the laser barrier.

“We made one beam of light that acted like a guiding fibre for the atoms and held them in this line. Then we intersected that with a second beam that we set up so that it would repel the atoms,” says Steinberg. “That second beam acted like a barrier and we could very carefully adjust the height of that barrier. Our setup also allowed us to give the atoms a little push so we could adjust whether or not they had enough energy to classically surmount the barrier.”

They chose a particular set of states of the alkali atom Rubidium to build their clock because the transition between these states is very stable. Indeed, the oscillations of a related atom, cesium, define the length of a second. Mathematically, this oscillation can be treated like a clock hand that points in a certain direction and can move over time.

“Since we wanted [the atoms’ clock hands] to only tick in that one-micron region where the barrier is, we used the barrier light itself to also tickle the spin of the atoms and make it oscillate at a frequency that we knew,” explains Steinberg.

Once they had particles that could tunnel, the particles carried clocks and the clocks only ticked when they were in the barrier, they had to take photographs that showed where the clock hands were pointing once they reached the other side in order to calculate the amount of time the atoms must have spent in the barrier.

This breakthrough, built on nearly 20 years of refining experiments in Steinberg’s lab, is believed to be the world’s first such measurement and uncovers deep truths about the physical laws that govern quantum interactions.

“This whole idea of probing the history of a quantum particle is one that's been central to my research, and it's come up over and over again in discussions at CIFAR program meetings,” says Steinberg, who has been building, testing and improving on this delicate and complex experiment since 2001.

“This had been kind of a niche topic in quantum optics,” says Steinberg. “But I think as the technology evolves and as we're building these larger scale agglomerations of qubits – the basic unit of quantum information – and trying to learn how to characterize and control each of them, this has renewed practical importance.”

The result is not only proof that it is possible to time the tunneling process, but also that there is much more to learn to get the full picture of quantum systems.

The research was supported by the Natural Sciences and Engineering Research Council of Canada, CIFAR and the Fetzer Franklin Fund of the John E. Fetzer Memorial Trust.

With files from CIFAR

U of T researcher and global colleagues demonstrate key element of quantum internet

Christopher.Sorensen — Thu, 31 Jan 2019 15:04:32 +0000

U of T researcher and global colleagues demonstrate key element of quantum internet

Christopher.Sorensen Thu, 01/31/2019 - 10:04

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U of T Professor Hoi-Kwong Lo and his collaborators have performed a proof-of-principle experiment on a key aspect of all-photonic quantum repeaters (photo by Jessica MacInnis)

Jessica MacInnis

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A University of Toronto researcher is among a global group of experts who have demonstrated, in principle, a device that could serve as the backbone of a quantum internet.

Hoi-Kwong Lo, a professor in the department of electrical and computer engineering in the Faculty of Applied Science & Engineering, and his collaborators have developed a prototype for a key element of all-photonic quantum repeaters, a critical step in long-distance quantum communication.

“An all-optical network is a promising form of infrastructure for fast and energy-efficient communication that is required for a future quantum internet,” says Lo, who is cross-appointed to the department of physics in the Faculty of Arts & Science.

A quantum internet is considered the Holy Grail of quantum information processing, enabling many novel applications including information-theoretic secure communication. By contrast, today’s internet was not specifically designed for security, and it shows: breaches, break-ins and computer espionage are common challenges. Nefarious hackers are constantly poking holes in sophisticated layers of defence erected by individuals, corporations and governments.

In light of this, researchers have proposed other ways of transmitting data that would leverage key features of quantum physics to provide virtually unbreakable encryption. One of the most promising technologies involves a technique known as quantum key distribution, or QKD. QKD exploits the fact that the simple act of sensing or measuring the state of a quantum system disturbs that system. Because of this, eavesdropping by a third party would leave behind a detectable trace, and the communication could be aborted before sensitive information is lost.

Until now, this type of quantum security has been only demonstrated in small-scale systems. Lo and his team are among a group of global researchers who are laying the groundwork for a future quantum internet by addressing some of the challenges of transmitting quantum information over great distances using optical fibre communication.

Because light signals lose potency as they travel long distances through fibre-optic cables, devices called repeaters are inserted at regular intervals along the line. The repeaters boost and amplify the signals to help transmit the information.

But existing repeaters for quantum information are highly problematic. They require storage of the quantum state at the repeater sites, making the repeaters error prone, difficult to build, and very expensive because they often operate at cryogenic temperatures.

Lo and his team have proposed a different approach. They are working on the development of the next generation of repeaters, called all-photonic quantum repeaters, that would eliminate or reduce many of the shortcomings of standard quantum repeaters. With collaborators at Osaka University, Toyama University and NTT Corporation in Japan, Lo and his team have demonstrated proof-of-concept of their work in a paper recently published in Nature Communications.

“We have developed all-photonic repeaters that allow time-reversed adaptive Bell measurement,” says Lo.

“Because these repeaters are all-optical, they offer advantages that traditional – quantum-memory-based matter – repeaters do not. For example, this method could work at room temperature.”

A quantum Internet could offer applications that are impossible to implement in the conventional Internet, such as impenetrable security and quantum teleportation, which takes advantage of the phenomenon of quantum entanglement to transmit information between atoms separated by large distances.

“Our work helps pave the way toward this future,” Lo says.

The research was funded by the Natural Sciences and Engineering Research Council of Canada, among others.

‘Flying saucer’ quantum dots hold secret to brighter, better lasers, say U of T researchers

ullahnor — Mon, 20 Mar 2017 14:46:35 +0000

‘Flying saucer’ quantum dots hold secret to brighter, better lasers, say U of T researchers

ullahnor Mon, 03/20/2017 - 10:46

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Researcher Fengjia Fan shows off a vial of colloidal quantum dots that glow red when excited by UV light. Randy Sabatini, Alex Voznyy and Kris Bicanic are using the quantum dots to develop brighter lasers that use less energy (photo by Kevin Soobrian)

Tyler Irving

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Research team led by U of T's Faculty of Applied Science & Engineering ‘squashes’ the shape of nanoparticles, enabling inexpensive lasers that emit light in a customized rainbow of colours

More accurate medical tests, vivid video projectors and fresh insights into living cells are just three of the innovations that could result from new lasers that use nanoparticles to create brighter light in a rainbow of colours.

A new method, developed by an international research team from U of T's Faculty of Applied Science & Engineering, Vanderbilt University, the Los Alamos National Laboratory and others produces continuous laser light that is less expensive, brighter and more customized than current devices by using nanoparticles known as quantum dots.

“We’ve been working with quantum dots for more than a decade,” says Ted Sargent, a professor in the department of electrical and computer engineering at U of T. “They are more than five thousand times smaller than the width of a human hair, which enables them to straddle the worlds of quantum and classical physics and gives them useful optical properties.”

“Quantum dots are well-known bright light emitters,” says Alex Voznyy, a senior research associate in Sargent’s lab. “They can absorb a lot of energy and re-emit it at a particular frequency, which makes them a particularly suitable material for lasers.”

This solution of quantum dots glows bright red when in absorbs light from a UV lamp underneath. Researchers from U of T Engineering are optimizing these nanoparticles to create brighter lasers that use less energy than current models (photo by Kevin Soobrian)

By carefully controlling the size of the quantum dots, the researchers in Sargent’s lab can ‘tune’ the frequency or colour of the emitted light to any desired value. By contrast, most commercial lasers are limited to one specific frequency, or a very small range, defined by the materials they are made from.

The ability to produce a laser of any desired frequency from a single material would give a boost to scientists looking to study diseases at the level of tissues or individual cells by offering new tools to probe biochemical reactions. They could also enable laser display projectors that would be brighter and more energy efficient than current LCD technology.

But although the ability of colloidal quantum dots to produce laser light was first demonstrated by co-author Victor Klimov and his team at Los Alamos National Laboratory more than 15 years ago, commercial application has remained elusive. A key problem has been that until now, the amount of light needed to excite the quantum dots to produce laser light has been very high.

“You have to stimulate the laser using more and more power, but there are a lot of heating losses as well,” says Voznyy. “Eventually, it gets so hot that it just burns.”

Most quantum dot lasers are limited to pulses of light lasting just a few nanoseconds – billionths of a second.

The team, which included Voznyy, postdoctoral researchers Fengjia Fan and Randy Sabatini and master's student Kris Bicanic, overcame this problem by changing the shape of the quantum dots, rather than their size. They were able to create quantum dots with a spherical core and a shell shaped like a Skittle, an M&M or a flying saucer – a ‘squashed’ spherical shape known as an oblate spheroid.

The mismatch between the shape of the core and the shell introduces a tension that affects the electronic states of the quantum dot, lowering the amount of energy needed to trigger the laser. As reported in a paper published today in Nature, the innovation means that the quantum dots are no longer in danger of overheating, so the resulting laser can fire continuously.

This computer-generated model shows the spherical core of the quantum dot nanoparticle (in red) along with the ‘flying saucer’ shape of the outer shell (in yellow). The tension in the core induced by the shell affects the electronic states and lowers the energy threshold required to trigger the laser (image by Alex Voznyy)

While quantum dots are often built by depositing molecules one at a time in a vacuum, Sargent’s team mixes together liquid solutions that contain various quantum dot precursors. When the solutions react, they produce solid quantum dots that stay suspended in the liquid – these are known as colloidal quantum dots. The team’s key innovation was to add specific capping molecules into the mix, which allowed them to control the shape of the particles to obtain the desired properties, an approach Fan calls ‘smart chemistry.’

“Solution-based processing greatly reduces the cost of making quantum dots,” says Fan. “It will also make it easier to scale up production because we can use techniques already established in the printing industry.”

The project included a number of national and international partners. Computer simulations in collaboration with the University of Ottawa and the National Research Council guided the design of the quantum dots. Analytical tests from Vanderbilt’s Institute of Nanoscale Science and Engineering in Nashville, TN, as well as the University of New Mexico’s Center for High Technology Materials in Albuquerque, NM and Los Alamos confirmed that the final products had the desired shape, composition and behaviour by analyzing individual quantum dots at the atomic level.

“We were impressed not only by the engineered structure itself but also by the level of uniformity they have achieved,” says Sandra Rosenthal, director of the Vanderbilt Institute for Nanoscale Science and Engineering. “Sargent’s team has managed to create quantum dots with a unique and elegant structure. This is exciting research.”

The team has more work to do before they can look to commercialization.

“For this proof-of-concept device, we’re exciting the quantum dots with light,” says Sabatini. “Ultimately, we want to move to exciting them with electricity. We also want to scale up the power to milliwatts or even watts. If we can do that, then it becomes important for laser projection.”

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