̽��ֱ�� of Cambridge - quantum physics

A peek inside the box that could help solve a quantum mystery

sc604 — Tue, 19 Nov 2024 15:22:24 +0000

Appearing as ‘bumps’ in the data from high-energy experiments, these signals came to be known as short-lived ‘XYZ states.’ They defy the standard picture of particle behaviour and are a problem in contemporary physics, sparking several attempts to understand their mysterious nature.

But theorists at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility in Virginia, with colleagues from the ̽��ֱ�� of Cambridge, suggest the experimental data could be explained with fewer XYZ states, also called resonances, than currently claimed.

̽��ֱ��team used a branch of quantum physics to compute the energy levels, or mass, of particles containing a specific ‘flavour’ of the subatomic building blocks known as quarks. Quarks, along with gluons, a force-carrying particle, make up the Strong Force, one of the four fundamental forces of nature.

̽��ֱ��researchers found that multiple particle states sharing the same degree of spin – or angular momentum – are coupled, meaning only a single resonance exists at each spin channel. This new interpretation is contrary to several other theoretical and experimental studies.

̽��ֱ��researchers have presented their results in a pair of companion papers published for the international Hadron Spectrum Collaboration (HadSpec) in Physical Review Letters and Physical Review D. ̽��ֱ��work could also provide clues about an enigmatic particle: X(3872).

̽��ֱ��charm quark, one of six quark ‘flavours’, was first observed experimentally in 1974. It was discovered alongside its antimatter counterpart, the anticharm, and particles paired this way are part of an energy region called ‘charmonium.’

In 2003, Japanese researchers discovered a new charmonium candidate dubbed X(3872): a short-lived particle state that appears to defy the present quark model.

“X(3872) is now more than 20 years old, and we still haven’t obtained a clear, simple explanation that everyone can get behind,” said lead author Dr David Wilson from Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP).

Thanks to the power of modern particle accelerators, scientists have detected a hodgepodge of exotic charmonium candidate states over the past two decades.

“High-energy experiments started seeing bumps, interpreted as new particles, almost everywhere they looked,” said co-author Professor Jozef Dudek from William & Mary. “And very few of these states agreed with the model that came before.”

But now, by creating a tiny virtual ‘box’ to simulate quark behaviour, the researchers discovered that several supposed XYZ particles might actually be just one particle seen in different ways. This could help simplify the confusing jumble of data scientists have collected over the years.

Despite the tiny volumes they were working with, the team required enormous computing power to simulate all the possible behaviours and masses of quarks.

̽��ֱ��researchers used supercomputers at Cambridge and the Jefferson Lab to infer all the possible ways in which mesons – made of a quark and its antimatter counterpart – could decay. To do this, they had to relate the results from their tiny virtual box to what would happen in a nearly infinite volume – that is, the size of the universe.

“In our calculations, unlike experiment, you can't just fire in two particles and measure two particles coming out,” said Wilson. “You have to simultaneously calculate all possible final states, because quantum mechanics will find those for you.”

̽��ֱ��results can be understood in terms of just a single short-lived particle whose appearance could differ depending upon which possible decay state it is observed in.

“We're trying to simplify the picture as much as possible, using fundamental theory with the best methods available,” said Wilson. “Our goal is to disentangle what has been seen in experiments.”

Now that the team has proved this type of calculation is feasible, they are ready to apply it to the mysterious particle X(3872).

“ ̽��ֱ��origin of X(3872) is an open question,” said Wilson. “It appears very close to a threshold, which could be accidental or a key part of the story. This is one thing we will look at very soon."

Professor Christopher Thomas, also from DAMTP, is a member of the Hadron Spectrum Collaboration, and is a co-author on the current studies. Wilson’s contribution was made possible in part by an eight-year fellowship with the Royal Society. ̽��ֱ��research was also supported in part by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). Many of the calculations for this study were carried out with the support of the Cambridge Centre for Data Driven Discovery (CSD3) and DiRAC high-performance computing facilities in Cambridge, managed by Cambridge’s Research Computing Services division.

Reference:
David J. Wilson et al. ‘Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD.’ Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.241901

David J. Wilson et al. ‘Charmonium xc0 and xc2 resonances in coupled-channel scattering from lattice QCD.’ Physical Review D (2024). DOI: 10.1103/PhysRevD.109.114503

Adapted from a Jefferson Lab story.

An elusive particle that first formed in the hot, dense early universe has puzzled physicists for decades. Following its discovery in 2003, scientists began observing a slew of other strange objects tied to the millionths of a second after the Big Bang.

gremlin via Getty Images

Abstract colourful lines

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Five hubs launched to ensure UK benefits from quantum future

sc604 — Fri, 26 Jul 2024 06:30:07 +0000

̽��ֱ��hub, called Q-BIOMED, is one of 5 quantum research hubs announced on 26 July by Peter Kyle MP, the Secretary of State for Science, Innovation and Technology, supported by £160 million in funding.

̽��ֱ��hub will exploit advances in quantum sensors capable of detecting cells and molecules, potentially orders of magnitude more sensitively than traditional diagnostic tests.

This includes developing quantum-enhanced blood tests to diagnose infectious diseases and cancer quickly and cheaply using portable instruments, and sensors measuring tiny changes to the magnetic fields in the brain that have the potential to detect early markers of Alzheimer’s disease before symptoms occur.

Other research will include quantum-enhanced MRI scans, heart scanners and surgical and treatment interventions for early-stage and hard-to-treat cancers.

“Quantum technologies harness quantum physics to achieve a functionality or a performance which is otherwise unattainable, deriving from science which cannot be explained by classical physics,” said Hub Co-Director Professor Mete Atatüre, Head of Cambridge’s Cavendish Laboratory. “Q-BIOMED will be delivered by an outstanding team of researchers from academia, the NHS, charities, government and industry to exploit quantum-enhanced advances for human health and societal good.”

“Our hub aims to grow a new quantum for health innovation ecosystem in the UK, and has already shaped the UK's new Quantum Mission for Health,” said Hub Co-Director Professor Rachel McKendry, from the London Centre for Nanotechnology and Division of Medicine at UCL. “Our long-term vision is to accelerate the entire innovation pipeline from discovery research, to translation, adoption and implementation within the NHS and global health systems, for the benefit of patients and societal good.”

“Quantum sensing allows us to gather information at cellular and molecular levels with unprecedented sensitivity to electric and magnetic fields," said Dr Ljiljana Fruk from the Department of Chemical Engineering and Biotechnology, a member of the Q-BIOMED team. "I look forward to learning from colleagues and engaging in challenging discussions to develop more sensitive, affordable tools for doctors and patients, advancing the future of healthcare.”

Cambridge researchers are also involved in three of the other newly-announced hubs:

̽��ֱ��UK Hub for Quantum Enabled Position, Navigation and Timing (QEPNT), led by the ̽��ֱ�� of Glasgow, will develop quantum technologies which will be key for national security and critical infrastructure and sectors such as aerospace, connected and autonomous vehicles (CAVs), finance, maritime and agriculture. Luca Sapienza (Engineering), Louise Hirst (Materials Science and Metallurgy/Cavendish Laboratory) and Dave Ellis (Cavendish Laboratory) are part of the QEPNT team.
QCI3: Hub for Quantum Computing via Integrated and Interconnected Implementations, led by the ̽��ֱ�� of Oxford, aims to develop the technologies needed for the UK to play a key role in the development of quantum computers, a market estimated to be worth $1.3 trillion by 2030. Ulrich Schneider (Cavendish Laboratory), Helena Knowles (Cavendish Laboratory), and Chander Velu (Institute for Manufacturing) are part of the QCI3 team.
̽��ֱ��Integrated Quantum Networks (IQN) Quantum Technology Research Hub, led by Heriot-Watt ̽��ֱ��, will undertake research towards the ultimate goal of a ‘quantum internet’, globally interlinked quantum networks connecting multiple quantum computers to produce enormous computational power. Richard Penty, Adrian Wonfor and Qixiang Cheng (Engineering), Atatüre and Dorian Gangloff (Cavendish Laboratory) are part of the IQN team.

̽��ֱ��fifth hub, UK Quantum Technology Hub in Sensing, Imaging and Timing (QuSIT), is led by the ̽��ֱ�� of Birmingham.

̽��ֱ��five hubs are delivered by the UKRI Engineering and Physical Sciences Research Council (EPSRC), with a £106 million investment from EPSRC, the UKRI Biotechnology and Biological Research Council, UKRI Medical Research Council, and the National Institute for Health and Care Research. Added to this are contributions from industry and other partners worth more than £54 million.

Peter Kyle, Secretary of State for Science, Innovation and Technology, said: “We want to see a future where cutting-edge science improves everyday lives. That is the vision behind our investment in these new quantum technology hubs, by supporting the deployment of technology that will mean faster diagnoses for diseases, critical infrastructure safe from hostile threats and cleaner energy for us all.

“This isn’t just about research; it’s about putting that research to work. These hubs will bridge the gap between brilliant ideas and practical solutions. They will not only transform sectors like healthcare and security, but also create a culture of accelerated innovation that helps to grow our economy.”

EPSRC Executive Chair Professor Charlotte Deane said: “Technologies harnessing quantum properties will provide unparalleled power and capacity for analysis at a molecular level, with truly revolutionary possibilities across everything from healthcare to infrastructure and computing.

“ ̽��ֱ��5 Quantum Technology Hubs announced today will harness the UK’s expertise to foster innovation, support growth and ensure that we capitalise on the profound opportunities of this transformative technology.”

A major new research hub led by the ̽��ֱ�� of Cambridge and UCL aims to harness quantum technology to improve early diagnosis and treatment of disease.

James Tye/UCL

L-R: Professor John Morton (UCL), Professor Rachel McKendry (UCL), Professor Mete Atatüre (Cambridge), Professor Eleni Nastouli (UCL)

Yes

Diamonds and rust help unveil ‘impossible’ quasi-particles

sc604 — Tue, 05 Dec 2023 10:02:43 +0000

Researchers led by the ̽��ֱ�� of Cambridge used a technique known as diamond quantum sensing to observe swirling textures and faint magnetic signals on the surface of hematite, a type of iron oxide.

̽��ֱ��researchers observed that magnetic monopoles in hematite emerge through the collective behaviour of many spins (the angular momentum of a particle). These monopoles glide across the swirling textures on the surface of the hematite, like tiny hockey pucks of magnetic charge. This is the first time that naturally occurring emergent monopoles have been observed experimentally.

̽��ֱ��research has also shown the direct connection between the previously hidden swirling textures and the magnetic charges of materials like hematite, as if there is a secret code linking them together. ̽��ֱ��results, which could be useful in enabling next-generation logic and memory applications, are reported in the journal Nature Materials.

According to the equations of James Clerk Maxwell, a giant of Cambridge physics, magnetic objects, whether a fridge magnet or the Earth itself, must always exist as a pair of magnetic poles that cannot be isolated.

“ ̽��ֱ��magnets we use every day have two poles: north and south,” said Professor Mete Atatüre, who led the research. “In the 19th century, it was hypothesised that monopoles could exist. But in one of his foundational equations for the study of electromagnetism, James Clerk Maxwell disagreed.”

Atatüre is Head of Cambridge’s Cavendish Laboratory, a position once held by Maxwell himself. “If monopoles did exist, and we were able to isolate them, it would be like finding a missing puzzle piece that was assumed to be lost,” he said.

About 15 years ago, scientists suggested how monopoles could exist in a magnetic material. This theoretical result relied on the extreme separation of north and south poles so that locally each pole appeared isolated in an exotic material called spin ice.

However, there is an alternative strategy to find monopoles, involving the concept of emergence. ̽��ֱ��idea of emergence is the combination of many physical entities can give rise to properties that are either more than or different to the sum of their parts.

Working with colleagues from the ̽��ֱ�� of Oxford and the National ̽��ֱ�� of Singapore, the Cambridge researchers used emergence to uncover monopoles spread over two-dimensional space, gliding across the swirling textures on the surface of a magnetic material.

̽��ֱ��swirling topological textures are found in two main types of materials: ferromagnets and antiferromagnets. Of the two, antiferromagnets are more stable than ferromagnets, but they are more difficult to study, as they don’t have a strong magnetic signature.

To study the behaviour of antiferromagnets, Atatüre and his colleagues use an imaging technique known as diamond quantum magnetometry. This technique uses a single spin – the inherent angular momentum of an electron – in a diamond needle to precisely measure the magnetic field on the surface of a material, without affecting its behaviour.

For the current study, the researchers used the technique to look at hematite, an antiferromagnetic iron oxide material. To their surprise, they found hidden patterns of magnetic charges within hematite, including monopoles, dipoles and quadrupoles.

“Monopoles had been predicted theoretically, but this is the first time we’ve actually seen a two-dimensional monopole in a naturally occurring magnet,” said co-author Professor Paolo Radaelli, from the ̽��ֱ�� of Oxford.

“These monopoles are a collective state of many spins that twirl around a singularity rather than a single fixed particle, so they emerge through many-body interactions. ̽��ֱ��result is a tiny, localised stable particle with diverging magnetic field coming out of it,” said co-first author Dr Hariom Jani, from the ̽��ֱ�� of Oxford.

“We’ve shown how diamond quantum magnetometry could be used to unravel the mysterious behaviour of magnetism in two-dimensional quantum materials, which could open up new fields of study in this area,” said co-first author Dr Anthony Tan, from the Cavendish Laboratory. “ ̽��ֱ��challenge has always been direct imaging of these textures in antiferromagnets due to their weaker magnetic pull, but now we’re able to do so, with a nice combination of diamonds and rust.”

̽��ֱ��study not only highlights the potential of diamond quantum magnetometry but also underscores its capacity to uncover and investigate hidden magnetic phenomena in quantum materials. If controlled, these swirling textures dressed in magnetic charges could power super-fast and energy-efficient computer memory logic.

̽��ֱ��research was supported in part by the Royal Society, the Sir Henry Royce Institute, the European Union, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
K C Tan, Hariom Jani, Michael Högen et al. ‘Revealing Emergent Magnetic Charge in an Antiferromagnet with Diamond Quantum Magnetometry.’ Nature Materials (2023). DOI: 10.1038/s41563-023-01737-4.

For more information on energy-related research in Cambridge, please visit the Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come.

Researchers have discovered magnetic monopoles – isolated magnetic charges – in a material closely related to rust, a result that could be used to power greener and faster computing technologies.

If monopoles did exist, and we were able to isolate them, it would be like finding a missing puzzle piece that was assumed to be lost

Mete Atatüre

Anthony Tan and Michael Hoegen

Magnetic monopoles in hematite

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Simulations of ‘backwards time travel’ can improve scientific experiments

vb425 — Thu, 12 Oct 2023 15:00:00 +0000

If gamblers, investors and quantum experimentalists could bend the arrow of time, their advantage would be significantly higher, leading to significantly better outcomes.

Researchers at the ̽��ֱ�� of Cambridge have shown that by manipulating entanglement – a feature of quantum theory that causes particles to be intrinsically linked – they can simulate what could happen if one could travel backwards in time. So that gamblers, investors and quantum experimentalists could, in some cases, retroactively change their past actions and improve their outcomes in the present.

Whether particles can travel backwards in time is a controversial topic among physicists, even though scientists have previously simulated models of how such spacetime loops could behave if they did exist. By connecting their new theory to quantum metrology, which uses quantum theory to make highly sensitive measurements, the Cambridge team has shown that entanglement can solve problems that otherwise seem impossible. The study appears in the journal Physical Review Letters.

“Imagine that you want to send a gift to someone: you need to send it on day one to make sure it arrives on day three,” said lead author David Arvidsson-Shukur, from the Hitachi Cambridge Laboratory. “However, you only receive that person’s wish list on day two. So, in this chronology-respecting scenario, it’s impossible for you to know in advance what they will want as a gift and to make sure you send the right one.

“Now imagine you can change what you send on day one with the information from the wish list received on day two. Our simulation uses quantum entanglement manipulation to show how you could retroactively change your previous actions to ensure the final outcome is the one you want.”

̽��ֱ��simulation is based on quantum entanglement, which consists of strong correlations that quantum particles can share and classical particles—those governed by everyday physics—cannot.

̽��ֱ��particularity of quantum physics is that if two particles are close enough to each other to interact, they can stay connected even when separated. This is the basis of quantum computing – the harnessing of connected particles to perform computations too complex for classical computers.

“In our proposal, an experimentalist entangles two particles,” said co-author Nicole Yunger Halpern, researcher at the National Institute of Standards and Technology (NIST) and the ̽��ֱ�� of Maryland. “ ̽��ֱ��first particle is then sent to be used in an experiment. Upon gaining new information, the experimentalist manipulates the second particle to effectively alter the first particle’s past state, changing the outcome of the experiment.”

“ ̽��ֱ��effect is remarkable, but it happens only one time out of four!” said Arvidsson-Shukur. “In other words, the simulation has a 75% chance of failure. But the good news is that you know if you have failed. If we stay with our gift analogy, one out of four times, the gift will be the desired one (for example a pair of trousers), another time it will be a pair of trousers but in the wrong size, or the wrong colour, or it will be a jacket.”

To give their model relevance to technologies, the theorists connected it to quantum metrology. In a common quantum metrology experiment, photons—small particles of light—are shone onto a sample of interest and then registered with a special type of camera. If this experiment is to be efficient, the photons must be prepared in a certain way before they reach the sample. ̽��ֱ��researchers have shown that even if they learn how to best prepare the photons only after the photons have reached the sample, they can use simulations of time travel to retroactively change the original photons.

To counteract the high chance of failure, the theorists propose to send a huge number of entangled photons, knowing that some will eventually carry the correct, updated information. Then they would use a filter to ensure that the right photons pass to the camera, while the filter rejects the rest of the ‘bad’ photons.

“Consider our earlier analogy about gifts,” said co-author Aidan McConnell, who carried out this research during his master’s degree at the Cavendish Laboratory in Cambridge, and is now a PhD student at ETH, Zürich. “Let’s say sending gifts is inexpensive and we can send numerous parcels on day one. On day two we know which gift we should have sent. By the time the parcels arrive on day three, one out of every four gifts will be correct, and we select these by telling the recipient which deliveries to throw away.”

“That we need to use a filter to make our experiment work is actually pretty reassuring,” said Arvidsson-Shukur. “ ̽��ֱ��world would be very strange if our time-travel simulation worked every time. Relativity and all the theories that we are building our understanding of our universe on would be out of the window.

“We are not proposing a time travel machine, but rather a deep dive into the fundamentals of quantum mechanics. These simulations do not allow you to go back and alter your past, but they do allow you to create a better tomorrow by fixing yesterday’s problems today.”

This work was supported by the Sweden-America Foundation, the Lars Hierta Memorial Foundation, Girton College, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
David R M Arvidsson-Shukur, Aidan G McConnell, and Nicole Yunger Halpern, ‘Nonclassical advantage in metrology established via quantum simulations of hypothetical closed timelike curves’, Phys. Rev. Lett. 2023. DOI: 10.1103/PhysRevLett.131.150202

Physicists have shown that simulating models of hypothetical time travel can solve experimental problems that appear impossible to solve using standard physics.

We are not proposing a time travel machine, but rather a deep dive into the fundamentals of quantum mechanics

David Arvidsson-Shukur

Yaroslav Kushta via Getty Images

Digital generated image of abstract glowing tech data tunnel

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Switching ‘spin’ on and off (and up and down) in quantum materials at room temperature

sc604 — Wed, 16 Aug 2023 15:00:00 +0000

Spin is the term for the intrinsic angular momentum of electrons, which is referred to as up or down. Using the up/down spin states of electrons instead of the 0 and 1 in conventional computer logic could transform the way in which computers process information. And sensors based on quantum principles could vastly improve our abilities to measure and study the world around us.

An international team of researchers, led by the ̽��ֱ�� of Cambridge, has found a way to use particles of light as a ‘switch’ that can connect and control the spin of electrons, making them behave like tiny magnets that could be used for quantum applications.

̽��ֱ��researchers designed modular molecular units connected by tiny ‘bridges’. Shining a light on these bridges allowed electrons on opposite ends of the structure to connect to each other by aligning their spin states. Even after the bridge was removed, the electrons stayed connected through their aligned spins.

This level of control over quantum properties can normally only be achieved at ultra-low temperatures. However, the Cambridge-led team has been able to control the quantum behaviour of these materials at room temperature, which opens up a new world of potential quantum applications by reliably coupling spins to photons. ̽��ֱ��results are reported in the journal Nature.

Almost all types of quantum technology – based on the strange behaviour of particles at the subatomic level – involve spin. As they move, electrons usually form stable pairs, with one electron spin up and one spin down. However, it is possible to make molecules with unpaired electrons, called radicals. Most radicals are very reactive, but with careful design of the molecule, they can be made chemically stable.

“These unpaired spins change the rules for what happens when a photon is absorbed and electrons are moved up to a higher energy level,” said first author Sebastian Gorgon, from Cambridge’s Cavendish Laboratory. “We’ve been working with systems where there is one net spin, which makes them good for light emission and making LEDs.”

Gorgon is a member of Professor Sir Richard Friend’s research group, where they have been studying radicals in organic semiconductors for light generation, and identified a stable and bright family of materials a few years ago. These materials can beat the best conventional OLEDs for red light generation.

“Using tricks developed by different fields was important,” said Dr Emrys Evans from Swansea ̽��ֱ��, who co-led the research. “ ̽��ֱ��team has significant expertise from a number of areas in physics and chemistry, such as the spin properties of electrons and how to make organic semiconductors work in LEDs. This was critical for knowing how to prepare and study these molecules in the solid state, enabling our demonstration of quantum effects at room temperature.”

Organic semiconductors are the current state-of-the-art for lighting and commercial displays, and they could be a more sustainable alternative to silicon for solar cells. However, they have not yet been widely studied for quantum applications, such as quantum computing or quantum sensing.

“We’ve now taken the next big step and linked the optical and magnetic properties of radicals in an organic semiconductor,” said Gorgon. “These new materials hold great promise for completely new applications, since we’ve been able to remove the need for ultra-cold temperatures.”

“Knowing what electron spins are doing, let alone controlling them, is not straightforward, especially at room temperature,” said Friend, who co-led the research. “But if we can control the spins, we can build some interesting and useful quantum objects.”

̽��ֱ��researchers designed a new family of materials by first determining how they wanted the electron spins to behave. Using this bottom-up approach, they were able to control the properties of the end material by using a building block method and changing the ‘bridges’ between different modules of the molecule. These bridges were made of anthracene, a type of hydrocarbon.

For their ‘mix-and-match’ molecules, the researchers attached a bright light-emitting radical to an anthracene molecule. After a photon of light is absorbed by the radical, the excitation spreads out onto the neighbouring anthracene, causing three electrons to start spinning in the same way. When a further radical group is attached to the other side of the anthracene molecules, its electron is also coupled, bringing four electrons to spin in the same direction.

“In this example, we can switch on the interaction between two electrons on opposite ends of the molecule by aligning electron spins on the bridge absorbing a photon of light,” said Gorgon. “After relaxing back, the distant electrons remember they were together even after the bridge is gone.

“In these materials we’ve designed, absorbing a photon is like turning a switch on. ̽��ֱ��fact that we can start to control these quantum objects by reliably coupling spins at room temperature could open up far more flexibility in the world of quantum technologies. There’s a huge potential here to go in lots of new directions.”

“People have spent years trying to get spins to reliably talk to each other, but by starting instead with what we want the spins to do and then the chemists can design a molecule around that, we’ve been able to get the spins to align,” said Friend. “It’s like we’ve hit the Goldilocks zone where we can tune the spin coupling between the building blocks of extended molecules.”

̽��ֱ��advance was made possible through a large international collaboration – the materials were made in China, experiments were done in Cambridge, Oxford and Germany, and theory work was done in Belgium and Spain.

̽��ֱ��research was supported in part by the European Research Council, the European Union, the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI), and the Royal Society. Richard Friend is a Fellow of St John’s College, Cambridge.

Reference:
Sebastian Gorgon et al. ‘Reversible spin-optical interface in luminescent organic radicals.’ Nature (2023). DOI: 10.1038/s41586-023-06222-1

Researchers have found a way to control the interaction of light and quantum ‘spin’ in organic semiconductors, that works even at room temperature.

These new materials hold great promise for completely new applications, since we’ve been able to remove the need for ultra-cold temperatures

Sebastian Gorgon

Artist's impression of aligned spins in an organic semiconductor

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Researchers devise a new path toward ‘quantum light’

sc604 — Thu, 02 Feb 2023 16:00:00 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, along with colleagues from the US, Israel and Austria, developed a theory describing a new state of light, which has controllable quantum properties over a broad range of frequencies, up as high as X-ray frequencies. Their results are reported in the journal Nature Physics.

̽��ֱ��world we observe around us can be described according to the laws of classical physics, but once we observe things at an atomic scale, the strange world of quantum physics takes over. Imagine a basketball: observing it with the naked eye, the basketball behaves according to the laws of classical physics. But the atoms that make up the basketball behave according to quantum physics instead.

“Light is no exception: from sunlight to radio waves, it can mostly be described using classical physics,” said lead author Dr Andrea Pizzi, who carried out the research while based at Cambridge’s Cavendish Laboratory. “But at the micro and nanoscale so-called quantum fluctuations start playing a role and classical physics cannot account for them.”

Pizzi, who is currently based at Harvard ̽��ֱ��, worked with Ido Kaminer’s group at the Technion-Israel Institute of Technology and colleagues at MIT and the ̽��ֱ�� of Vienna to develop a theory that predicts a new way of controlling the quantum nature of light.

“Quantum fluctuations make quantum light harder to study, but also more interesting: if correctly engineered, quantum fluctuations can be a resource,” said Pizzi. “Controlling the state of quantum light could enable new techniques in microscopy and quantum computation.”

One of the main techniques for generating light uses strong lasers. When a strong enough laser is pointed at a collection of emitters, it can rip some electrons away from the emitters and energise them. Eventually, some of these electrons recombine with the emitters they were extracted from, and the excess energy they absorbed is released as light. This process turns the low-frequency input light into high-frequency output radiation.

“ ̽��ֱ��assumption has been that all these emitters are independent from one another, resulting in output light in which quantum fluctuations are pretty featureless,” said Pizzi. “We wanted to study a system where the emitters are not independent, but correlated: the state of one particle tells you something about the state of another. In this case, the output light starts behaving very differently, and its quantum fluctuations become highly structured, and potentially more useful.”

To solve this type of problem, known as a many body problem, the researchers used a combination of theoretical analysis and computer simulations, where the output light from a group of correlated emitters could be described using quantum physics.

̽��ֱ��theory, whose development was led by Pizzi and Alexey Gorlach from the Technion, demonstrates that controllable quantum light can be generated by correlated emitters with a strong laser. ̽��ֱ��method generates high-energy output light, and could be used to engineer the quantum-optical structure of X-rays.

“We worked for months to get the equations cleaner and cleaner until we got to the point where we could describe the connection between the output light and the input correlations with just one compact equation. As a physicist, I find this beautiful,” said Pizzi. “Looking forward, we would like to collaborate with experimentalists to provide a validation of our predictions. On the theory side of things, our work suggests many-body systems as a resource for generating quantum light, a concept that we want to investigate more broadly, beyond the setup considered in this work.”

̽��ֱ��research was supported in part by the Royal Society. Andrea Pizzi is a Junior Research Fellow at Trinity College, Cambridge.

Reference:
Andrea Pizzi et al. ‘Light emission from strongly driven many-body systems.’ Nature Physics (2023). DOI: 10.1038/s41567-022-01910-7

Researchers have theorised a new mechanism to generate high-energy ‘quantum light’, which could be used to investigate new properties of matter at the atomic scale.

David Wall via Getty Images

Design of a glowing fractal pattern with stars floating on a black background

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Yes

Professor Suchitra Sebastian to receive the Schmidt Science Polymaths Award

sc604 — Thu, 30 Jun 2022 11:30:16 +0000

Professor Suchitra Sebastian from Cambridge’s Cavendish Laboratory has been awarded the Schmidt Science Polymaths award. Schmidt Futures, a philanthropic initiative founded by Eric and Wendy Schmidt, announced ten new recipients of the award, which provides $500,000 a year, paid through their institution, for up to five years to help support part of a research group.

̽��ֱ��Polymath programme makes long-term bets on recently-tenured professors with remarkable track records, promising futures, and a desire to explore risky new research ideas across disciplines. ̽��ֱ��awardees are the second group to receive the Polymath award, joining just two other exceptionally talented interdisciplinary researchers named in 2021. ̽��ֱ��awards build upon Schmidt Futures’ commitment to identifying and supporting extraordinary talent, and growing networks empowered to solve hard problems in science and society.

Professor Sebastian’s research seeks to discover exotic quantum phases of matter in complex materials. Her group’s experiments involve tuning the co-operative behaviour of electrons within these materials by subjecting them to extreme conditions including low temperature, high applied pressure, and intense magnetic field.

Under these conditions, her group can take materials that are quite close to behaving like a superconductor – perfect, lossless conductors of electricity – and ‘nudge’ them, transforming their behaviour.

“I like to call it quantum alchemy – like turning soot into gold,” Sebastian said. “You can start with a material that doesn’t even conduct electricity, squeeze it under pressure, and discover that it transforms into a superconductor. Going forward, we may also discover new quantum phases of matter that we haven’t even imagined.”

Other awards she has received for her research include the World Economic Forum Young Scientist award, the L'Oreal-UNESCO Fellowship, the Lee Osheroff Richardson North American Science prize, the International Young Scientist Medal in Magnetism, the Moseley Medal, the Philip Leverhulme Prize, the Brian Pippard Prize. She is an ERC starting and consolidator grant awardee. Most recently, she was awarded the New Horizons in Physics Prize (2022) by the Breakthrough Foundation.

In addition to her physics research, Sebastian is also involved in theatre and the arts. She is Director of the Cavendish Arts-Science Project, which she founded in 2016. ̽��ֱ��programme has been conceived to question and explore material and immaterial universes through a dialogue between the arts and sciences.

“ ̽��ֱ��very idea of the Polymath Award is revolutionary,” said Sebastian. “It's so rare that an award selects people for being polymaths. Imagining new worlds and questioning traditional ways of knowing - whether by doing experimental theatre, or by bringing together art and science, is part of who I am.

“And this is why in our group, we love to research at the edge - to make risky boundary crossings and go on wild adventures into the quantum unknown. We do it because it's incredibly fun, you never know what each day will bring. To be recognised for this by Schmidt Futures is so unexpected and exciting, the possibilities this award opens up are endless. I look forward to embarking on new quantum explorations, it’s going to be a wild ride!”

̽��ֱ��awards build upon Schmidt Futures’ commitment to identifying and supporting extraordinary talent, and growing networks empowered to solve hard problems in science and society. Each Polymath will receive support at the moment in their careers when researchers have the most freedom to explore new ideas, use emerging technologies to test risky theories, and pursue novel scientific research that traverses fields and disciplines; which is otherwise unlikely to receive funding or support.

“ ̽��ֱ��interdisciplinary work that could herald the next great scientific breakthroughs are chronically under-funded,” said Eric Braverman, CEO of Schmidt Futures. “We are betting on the talent of the Schmidt Science Polymaths to explore new ideas across disciplines and accelerate discoveries to address the challenges facing our planet and society.”

Hopeful Polymaths from over 25 universities submitted applications outlining research ideas in STEM fields that represent a substantive shift from their current research portfolio and are unlikely to receive funding elsewhere for consideration to the Schmidt Science Polymaths program. Existing Polymaths’ ideas range from the artificial creation of complex soft matter like human tissue, to the development of synthetic biology platforms for engineering multicellular systems, to the discovery of exotic forms of quantum matter. ̽��ֱ��impact of this type of interdisciplinary research could result in innovations previously thought impossible like a 3D printer for human organs, climate change-resistant crops, or the unknown applications of quantum matter.

“Single-minded -specialisation coupled with rigid research and funding structures often hinder the ambition to unleash fresh perspectives in scientific inquiry,” said Stuart Feldman, Chief Scientist of Schmidt Futures. “From climate change to public health, the Schmidt Science Polymaths utilise the depth of their knowledge across a breadth of fields to find new ways to solve some of our hardest problems for public benefit.”

Cambridge physicist Professor Suchitra Sebastian to join group of ten recently tenured professors named to Polymath Program, awarded up to $2.5 million each for interdisciplinary research support.

To be recognised for this by Schmidt Futures is so unexpected and exciting, the possibilities this award opens up are endless. I look forward to embarking on new quantum explorations, it’s going to be a wild ride!

Suchitra Sebastian

Nick Saffell

Suchitra Sebastian

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‘Back to basics’ approach helps unravel new phase of matter

sc604 — Sun, 26 Sep 2021 23:48:57 +0000

Researchers from the ̽��ֱ�� of Cambridge used computer modelling to study potential new phases of matter known as prethermal discrete time crystals (DTCs). It was thought that the properties of prethermal DTCs were reliant on quantum physics: the strange laws ruling particles at the subatomic scale. However, the researchers found that a simpler approach, based on classical physics, can be used to understand these mysterious phenomena.

Understanding these new phases of matter is a step forward towards the control of complex many-body systems, a long-standing goal with various potential applications, such as simulations of complex quantum networks. ̽��ֱ��results are reported in two joint papers in Physical Review Letters and Physical Review B.

When we discover something new, whether it’s a planet, an animal, or a disease, we can learn more about it by looking at it more and more closely. Simpler theories are tried first, and if they don’t work, more complicated theories or methods are attempted.

“This was what we thought was the case with prethermal DTCs,” said Andrea Pizzi, a PhD candidate in Cambridge’s Cavendish Laboratory, first author on both papers. “We thought they were fundamentally quantum phenomena, but it turns out a simpler classical approach let us learn more about them.”

DTCs are highly complex physical systems, and there is still much to learn about their unusual properties. Like how a standard space crystal breaks space-translational symmetry because its structure isn’t the same everywhere in space, DTCs break a distinct time-translational symmetry because, when ‘shaken’ periodically, their structure changes at every ‘push’.

“You can think of it like a parent pushing a child on a swing on a playground,” said Pizzi. “Normally, the parent pushes the child, the child will swing back, and the parent then pushes them again. In physics, this is a rather simple system. But if multiple swings were on that same playground, and if children on them were holding hands with one another, then the system would become much more complex, and far more interesting and less obvious behaviours could emerge. A prethermal DTC is one such behaviour, in which the atoms, acting sort of like swings, only ‘come back’ every second or third push, for example.”

First predicted in 2012, DTCs have opened a new field of research, and have been studied in various types, including in experiments. Among these, prethermal DTCs are relatively simple-to-realise systems that don’t heat quickly as would normally be expected, but instead exhibit time-crystalline behaviour for a very long time: the quicker they are shaken, the longer they survive. However, it was thought that they rely on quantum phenomena.

“Developing quantum theories is complicated, and even when you manage it, your simulation capabilities are usually very limited, because the required computational power is incredibly large,” said Pizzi.

Now, Pizzi and his co-authors have found that for prethermal DTCs they can avoid using overly complicated quantum approaches and use much more affordable classical ones instead. This way, the researchers can simulate these phenomena in a much more comprehensive way. For instance, they can now simulate many more elementary constituents, getting access to the scenarios that are the most relevant to experiments, such as in two and three dimensions.

Using a computer simulation, the researchers studied many interacting spins – like the children on the swings – under the action of a periodic magnetic field – like the parent pushing the swing - using classical Hamiltonian dynamics. ̽��ֱ��resulting dynamics showed in a neat and clear way the properties of prethermal DTCs: for a long time, the magnetisation of the system oscillates with a period larger than that of the drive.

“It’s surprising how clean this method is,” said Pizzi. “Because it allows us to look at larger systems, it makes very clear what’s going on. Unlike when we’re using quantum methods, we don’t have to fight with this system to study it. We hope this research will establish classical Hamiltonian dynamics as a suitable approach to large-scale simulations of complex many-body systems and open new avenues in the study of nonequilibrium phenomena, of which prethermal DTCs are just one example.”

Pizzi’s co-authors on the two papers, who were both recently based at Cambridge, are Dr Andreas Nunnenkamp, now at the ̽��ֱ�� of Vienna in Austria, and Dr Johannes Knolle, now at the Technical ̽��ֱ�� of Munich in Germany.

Meanwhile, at UC Berkeley in the USA, Norman Yao’s group has also been using classical methods to study prethermal DTCs. Remarkably, the Berkeley and Cambridge teams have simultaneously addressed the same question. Yao’s group will be publishing their results shortly.

Reference:
Andrea Pizzi, Andreas Nunnenkamp, Johannes Knolle. ‘Classical Prethermal Phases of Matter.’ Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.127.140602
Andrea Pizzi, Andreas Nunnenkamp, Johannes Knolle. ‘Classical approaches to prethermal discrete time crystals in one, two, and three dimensions.’ Physical Review B (2021). DOI: 10.1103/PhysRevB.104.094308

A new phase of matter, thought to be understandable only using quantum physics, can be studied with far simpler classical methods.

We thought time crystals were fundamentally quantum phenomena, but it turns out a simpler classical approach let us learn more about them

Andrea Pizzi

Michael Dziedzic via Unsplash

Abstract, distorted view of computer motherboard

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