A A A

Archive for the 'News' Category

News update: UCL Quantum Science & Technology Institute launches

By Oli Usher, on 12 May 2014

UCL is today inaugurating a new Quantum Science & Technology Institute (UCLQ). The new institute will coordinate and support research into quantum science and technology across UCL, helping to develop this fast-advancing field of research.

The institute will link researchers across a range of departments and disciplines, including the London Centre for Nanotechnology, and the Departments of Physics & Astronomy, Electronic & Electrical Engineering, Computer Science, Science & Technology Studies, and Chemistry, as well as UCL’s new EPSRC Centre for Doctoral Training in Delivering Quantum Technologies.

Research in UCL Quantum labs. Photo credit: O. Usher (UCL MAPS)

Research in UCL Quantum labs. Photo credit: O. Usher (UCL MAPS)

Prof Michael Arthur, UCL President & Provost said: “The UCL Quantum Science & Technology Institute will push the boundaries of our understanding of quantum science and use these insights to deliver disruptive future technologies. Meeting these challenges requires a major interdisciplinary effort, such as that brought together in UCLQ.”

Quantum science and technology harnesses the special properties of matter on tiny scales, to go beyond the limits of classical physics and conventional technologies. It has potentially revolutionary applications in electronics, computer science, communications and many other important fields.

Key areas of expertise at UCL include:

  • Quantum communication:
    Taking advantage of quantum properties of systems, research in quantum communications aims to develop means of communicating which are completely impervious to eavesdropping – something of crucial importance both to industry and private users.
  • Quantum computation:
    Exploiting the complexity of quantum systems, it is possible to achieve computing power far superior to what is achievable with existing technologies.
  • Quantum metrology and sensing:
    The sensitivity of quantum systems to tiny variations in their environment makes them excellent tools for measurement, with precision reaching single-molecule or single-electron levels. This has potential applications ranging from healthcare to space and defence technologies.

Prof David Price, UCL Vice-Provost (Research) said: “Leading UCL researchers have made pioneering contributions to quantum technologies over several decades, and helped to develop a thriving community of quantum researchers across the UK. UCLQ is our flagship commitment to the next phase of our quantum technologies, which will see these breakthroughs translated to applications in partnership with industry. This will require both large-scale investment in and expert coordination of cross-disciplinary research and development.”

The institute will promote engagement with quantum science and technology, both for the public and for end users, including a range of public events, a network of government and industry stakeholders, and research into the responsible innovation policies.

Related links

High-resolution image

This image is Creative Commons Attribution licensed, and so may be reproduced freely providing the credits are retained

Media contact

Oli Usher
UCL Faculty of Mathematical and Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk

Research news: “Like melting an entire iceberg with a hot poker” – spotting phase transitions triggered by impurities

By Oli Usher, on 7 May 2014

“What a curious feeling,” says Alice in Lewis Carroll’s tale, as she shrinks to a fraction of her size, and everything around her suddenly looks totally unfamiliar. Scientists too have to get used to these curious feelings when they examine matter on tiny scales and at low temperatures: all the behaviour we are used to seeing around us is turned on its head.

In research published today in the journal Nature Communications, UCL scientists have made a startling discovery about a familiar physical effect in this unfamiliar setting.

Phase transitions are a category of physical phenomena in which the properties of a sample and the relationships between the particles that make it up suddenly change. Phase transitions include familiar events such as water turning to ice when temperature drops, or a magnet losing its magnetisation when temperature rises.

On human scales, and at ambient temperatures, phase transitions are well understood. They are linked to the temperature (and hence the vibration, orientation and movement of particles) of an object. In quantum physics, however, phase transitions behave slightly differently, and can even occur close to absolute zero, when virtually no heat is present in a sample. These occur when a factor which affects the whole sample, such as a magnetic field, is changed. But in certain cases, quantum phase transitions can also happen when varying a highly localised factor, such as changing the coupling between a single pair of particles on the edge of such a system. These are called boundary phase transitions and would be like melting an entire iceberg by touching a corner of it with a hot poker.

Dr Abolfazl Bayat and Prof Sougato Bose (both UCL Physics & Astronomy), along with colleagues at other institutions, have probed the nature of boundary phase transitions in quantum systems. For the first time they have identified a measurable quantity that can label the distinct phases of such a system.

“When phase transitions happen, scientists often talk of an ‘order parameter’,” says Bayat. “This is the value which suddenly changes, such as the orientation of magnetisation in a metal, or the spacing of atoms in a sample which determines whether it is liquid or solid. Getting a handle on order parameters in quantum boundary phase transitions is much harder, but we have identified one in this research.”Understanding quantum phase transitions

Bayat and Bose studied a system in which a tiny change applied to a single pair of impurities causes a change in the entire system. The two impurities can either be entangled with each other, or can separately be entangled with the left and right hand parts of the system. Changing the pairing of the impurities acts like a switch on the whole system, triggering a phase transition in the form of a sudden change in the entire sample.

“We found that that a quantity called the Schmidt gap has all the features of an order parameter for this phase transition,” says Bose. “That means that mathematically it characterizes all the features of the phase transition in an analogous way to how magnetisation does for a magnet”.

However, unlike magnetisation, which can be easily measured, the Schmidt gap is a non-localised quantity which requires every particle in a system to be individually measured. Although, this a challenging task, it is becoming viable in recent experiments in ultra-cold atoms.

This research opens up new possibilities for exploring phase transitions in quantum physics. In particular, where conventional methods which use localised order parameters are not applicable, this gives a new means of studying phase transitions. It may help to determine new phases of matter and shed light into the structure of complex systems.

Notes

  • The research appears in a paper published in the journal Nature Communications, entitled “An order parameter for impurity systems at quantum criticality”

Related links

High-resolution image

This image is Creative Commons Attribution licensed, and so may be reproduced freely providing UCL Quantum is credited

Researcher profile

Science contact

Abolfazl Bayat
020 7679 3647
abolfazl.bayat@ucl.ac.uk

Sougato Bose
020 7679 3485
s.bose@ucl.ac.uk

Media contact

Oli Usher
UCL Faculty of Mathematical and Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk

In depth: Extending the life of the spin of single atoms

By news editor, on 27 January 2014

by Alexander Hellemans

A single quantum spin, found in single atoms and molecules, is the smallest magnet available.  The possibility to control the spin of single atoms is now intensively researched because they could serve as carriers of quantum information in future quantum computers.  Also within reach is their use for storing ordinary binary information, and this would allow the increase of the density of magnetic data storage by orders of magnitude. However, unlike the magnetization of materials currently used for data storage, the spin of single atoms is often too short-lived for data storage or quantum computing because of their interaction with other nearby physical systems.

Now a team lead by Cyrus Hirjibehedin in the London Centre for Nanotechnology at UCL has set out to investigate whether it would be possible to control the interactions between single magnetic atoms and their surrounding structure so that their spins can survive longer. Their research was published in the journal Nature Nanotechnology.

Cyrus Hirjibehedin in his lab at the London Centre for Nanotechnology

Cyrus Hirjibehedin in his lab at the London Centre for Nanotechnology. Photo: O. Usher (UCL MAPS)

In their work, the researchers focused primarily on the electrical interactions between single atom spins and nearby metallic electrodes, which can significantly decrease the lifetime of the spin in higher energy (or “excited”) states. One way to reduce these interactions is to separate the atoms from the conducting substrate by an insulating film.  To do this, the team grew large islands of an insulating copper nitride layer on a copper substrate, and on these islands they deposited cobalt atoms.

“As a test we put down a material we understood pretty well, cobalt, to see if there was a difference,” says Hirjibehedin.

First the team located a number of cobalt atoms on a copper nitride island with a scanning tunneling microscope (STM). Then they selected various atoms, starting at the edge of the island and then at increasing distances from the edge. They hovered the STM tip over each of the selected atoms, applied a bias voltage that ranged from – 15 mV to 15 mV, and measured the differential conductance (the ratio of the change in current passing through the atom to the change in bias voltage for very small changes in bias voltage)–a technique called scanning tunneling spectroscopy (STS).

The STM used by Hirjibehedin's team in the research

The STM used in the research

They found that the STS spectra for the atoms depended on their distance to the edge of the island. The researchers had expected that the surrounding atomic structure might play a small role, but the differences were much greater than expected. In particular, atoms at the edge of the island showed a prominent peak in the conductance centered on the bias voltage equalling zero, but this peak diminished the further the atom was from the edge of the island. At the same time, the energy needed to excite the atomic spin to a higher energy state, which appears as steps in the differential conductance at both positive and negative bias voltages, almost doubled as the atom’s distance from the edge increased. In the STS spectra, they found a clear correlation between the height of the conductance peak and the spin excitation energy.

“In principle,” says Hirjibehedin, “you can have various strain effects near the edges, so we thought there might be something small, but we were quite surprised that what we saw was very dramatic.”

“What we found is that the interaction between the cobalt atom and the copper is much stronger near the edges than it is at the center,” he says.

An obvious explanation is that the insulating copper nitride layer played an important role in reducing the effect of the copper substrate on the spin of the single atoms. This interaction is known as Kondo exchange. If the atom with spin is close enough to the metal, its spin couples to the spins of the conduction electrons in the metal, causing these electrons to hop on and off the atom. An electron with opposite spin to the spin on the atom will hop onto the atom, and the other electron with opposite spin will hop off the atom.  This process switches the spin of the atom up and down continuously, which makes data storage impossible.

Remarkably, the team also found that the same Kondo exchange that is responsible for this spin switching or “screening” also dramatically reduces the energy of the spin’s excitations, which also makes it less stable. This is significant because the excitation energy determines the spin’s stability, and normally this property is thought to be controlled by the surrounding physical structure rather than by electrical coupling.

It was clear to the team that near the edge of the island the Kondo exchange was strongly affecting the magnetic properties of the atom. What the team observed was that at the edges of the island, the Kondo effect was predominant, while more at the center the STS spectrum did not display this effect.  This allowed them to correlate the change in the Kondo effect with the changes in the spin excitation energies.  Two different calculations, performed by team members in Portugal and Germany, further support this explanation. “We use the Kondo effect as a sort of measurement for how strong this coupling is,” says Hirjibehedin, “and therefore how much it should affect the spin’s excitation energy.” He adds: “It still is an open question why the coupling is so much stronger at the edges of the island than in the middle.”

These new results suggest that tuning the electron density of a conducting material, as is often done in a field effect transistor, would enable the continuous tuning of the lifetime of the spins of nearby magnetic atoms. This could be done, for example, on a semiconductor substrate, which can be electrically gated to enhance or decrease the electron density. This would in turn affect the energies between the different spin states of nearby magnetic atoms, which would then modify the stability of the spins.  “The stability of the spin is very important, in particular if you want to store data with a single atom,” concludes Hirjibehedin.

Related links

High-resolution image

Cyrus Hirjibehedin

Scanning tunneling microscope

This text and the photos associated with it are Creative Commons Attribution licensed, and so may be reproduced freely providing the credits are retained.

Researcher profile

Cyrus Hirjibehedin

 

Research news: Quantum mechanics explains efficiency of photosynthesis

By news editor, on 9 January 2014

Light-gathering macromolecules in plant cells transfer energy by taking advantage of molecular vibrations whose physical descriptions have no equivalents in classical physics, according to the first unambiguous theoretical evidence of quantum effects in photosynthesis published today in the journal Nature Communications.

The majority of light-gathering macromolecules are composed of chromophores (responsible for the colour of molecules) attached to proteins, which carry out the first step of photosynthesis, capturing sunlight and transferring the associated energy highly efficiently. Previous experiments suggest that energy is transferred in a wave-like manner, exploiting quantum phenomena, but crucially, a non-classical explanation could not be conclusively proved as the phenomena identified could equally be described using classical physics.

When the difference in the excitation energy of two light-absorbing pigments within these light-gathering molecules is close to the frequency a collective vibrational motion, a resonance occurs. As the excitation is transferred from one pigment to the other, this collective vibration takes on a state with no classical analogue as indicated by negative regions of a (quasi)probability distribution illustrated here

When the difference in the excitation energy of two light-absorbing pigments within these light-gathering molecules is close to the frequency a collective vibrational motion, a resonance occurs. As the excitation is transferred from one pigment to the other, this collective vibration takes on a state with no classical analogue as indicated by negative regions of a (quasi)probability distribution illustrated here.

Often, to observe or exploit quantum mechanical phenomena systems need to be cooled to very low temperatures. This however does not seem to be the case in some biological systems, which display quantum properties even at ambient temperatures.

Now, a team at UCL have attempted to identify features in these biological systems which can only be predicted by quantum physics, and for which no classical analogues exist.

“Energy transfer in light-harvesting macromolecules is assisted by specific vibrational motions of the chromophores,” said Alexandra Olaya-Castro (UCL Physics & Astronomy), supervisor and co-author of the research. “We found that the properties of some of the chromophore vibrations that assist energy transfer during photosynthesis can never be described with classical laws, and moreover, this non-classical behaviour enhances the efficiency of the energy transfer.”

Molecular vibrations are periodic motions of the atoms in a molecule, like the motion of a mass attached to a spring.  When the energy of a collective vibration of two chromphores matches the energy difference between the electronic transitions of these chromophores a resonance occurs and efficient energy exchange between electronic and vibrational degrees of freedom takes place.

Providing that the energy associated to the vibration is higher than the temperature scale, only a discrete unit or quantum of energy is exchanged. Consequently, as energy is transferred from one chromophore to the other, the collective vibration displays properties that have no classical counterpart.

Photosynthesis in plants cannot be fully explained using classical physics. Photo credit: Scott Robinson (CC-BY). (flickr.com/photos/clearlyambiguous/19438696)

Photosynthesis in plants cannot be fully explained using classical physics. Photo credit: Scott Robinson

The UCL team found the unambiguous signature of non-classicality is given by a negative joint probability of finding the chromophores with certain relative positions and momenta. In classical physics, probability distributions are always positive.

“The negative values in these probability distributions are a manifestation of a truly quantum feature, that is, the coherent exchange of a single quantum of energy,” explained Edward O’Reilly (UCL Physics & Astronomy), first author of the study. “When this happens electronic and vibrational degrees of freedom are jointly and transiently in a superposition of quantum states, a feature that can never be predicted with classical physics.”

Other biomolecular processes such as the transfer of electrons within macromolecules (like in reaction centres in photosynthetic systems), the structural change of a chromophore upon absorption of photons (like in vision processes) or the recognition of a molecule by another (as in olfaction processes), are influenced by specific vibrational motions. The results of this research therefore suggest that a closer examination of the vibrational dynamics involved in these processes could provide other biological prototypes exploiting truly non-classical phenomena.

Notes

  • The research appears in a paper published in the journal Nature Communications, entitled “Non-classicality of the molecular vibrations assisting exciton energy transfer at room temperature”

Related links

High-resolution image

Negative probability distribution

Clover sphere

These images are Creative Commons Attribution licensed, and so may be reproduced freely providing the credits are retained

Researcher profile

Science contact

Alexandra Olaya-Castro
UCL Physics & Astronomy
a.olaya@ucl.ac.uk

Media contact

Oli Usher
UCL Faculty of Mathematical and Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk

News update: UCL launches quantum technologies PhD programme

By news editor, on 9 January 2014

Quantum

The Rt Hon David Willetts MP, Minister for Universities and Science, today announced government funding for a new Centre for Doctoral Training (CDT) in Delivering Quantum Technologies at UCL. The funding will be awarded through the Engineering & Physical Sciences Research Council (EPSRC).

Quantum technologies involve the control and manipulation of quantum states to achieve results not possible with classical matter; they promise a transformation of measurement, communication and computation.  The highly-skilled researchers who will be the future leaders in this field must be equipped to function in a complex research and engineering landscape where quantum physics meets cryptography, complexity and information theory, devices, materials, software and hardware engineering.

UCL’s CDT in Delivering Quantum Technologies brings together a team of almost forty academic experts with key players from commerce and government and a network of international partner institutes to train those research leaders.

The CDT will provide a new 4-year programme. The students will take a broadly based training year before undertaking a PhD research project in one of the centre’s research groups.  They will also be trained in entrepreneurship, outreach and scientific communication. As breakthroughs in quantum technologies begin to move out of the lab and into industrial applications, these students will be uniquely placed to benefit. Staff at UCL have strong links with enterprise and industry, giving students a short-cut directly into the heart of business.

UCL’s location in central London means unparalleled access to partner institutions around the world, from multinational companies to top universities, as well as to UCL’s own world-class laboratory facilities.

The new CDT’s Director, Professor Andrew Fisher (also an LCN Principal Investigator), said: “UCL’s research base in quantum technologies is excellent and extremely broad.  We are delighted to have the chance to use those facilities and that expertise to give students the best possible research training across the range of disciplines they will need in their future careers.”

The CDT will take on its first students in September 2014.

More information:

 

News update: UCL Quantum research ‘among top 10 physics discoveries of 2013′

By Oli Usher, on 13 December 2013

The top 10 breakthroughs in physics in 2013, as judged by Physics World magazine, have been announced. Among them is a recent discovery by a team including UCL’s John Morton (London Centre for Nanotechnology & UCL Electronic & Electrical Engineering).

The research was into qubits (quantum bits) – a way of encoding information using quantum phenomena. Unlike normal bits, the fundamental unit of computer memory which can record only 0s and 1s, a qubit can encode 0 and 1 at the same time (much like Schrödinger’s Cat is both dead and alive at the same time).

An artistic rendition of a 'bound exciton' quantum state used to prepare and read out the state of the qubits. Credit: Stef Simmons (CC-BY)

An artistic rendition of a ‘bound exciton’ quantum state used to prepare and read out the state of the qubits. Credit: Stef Simmons (CC-BY)

Mastering qubits would open the door to quantum computing, which could revolutionise the way computers are designed and built, but until now, qubits have had to be kept close to absolute zero in order to reliably store information. This study showed how they can be maintained at room temperatures for up to 39 minutes without losing data.

The top 10 breakthroughs identified in the list were chosen by the Physics World editorial team, who reviewed over 350 news articles about advances in the physical sciences published on physicsworld.com in 2013.

The award was founded in 2009. Last year’s winner was the ATLAS and CMS collaborations at CERN for their joint discovery of a Higgs–like particle at the Large Hadron Collider.

Related links

High-resolution image

This image is Creative Commons Attribution licensed, and so may be reproduced freely providing the credits are retained

Researcher profile

Science contact

John Morton
London Centre for Nanotechnology
020 7679 2367
jjl.morton@ucl.ac.uk

Media contact

Oli Usher
UCL Faculty of Mathematical and Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk

News update: UCL Quantum is recruiting for new PhD students

By Oli Usher, on 12 December 2013

The Portico of UCL's main building

Starting in September 2014, UCL will be taking on PhD students as part of an ambitious new training programme in Quantum Technology. Students will work with world-class staff across the range of UCL departments that work on a broad range of projects related to quantum technologies and their applications.

The programme will build on the breadth of UCL’s research in this field (spanning computer science, quantum physics, and engineering), providing students with a foundation in both theory and experimental methods for quantum technologies, before they embark on their research project.

As breakthroughs in quantum technologies begin to move out of the lab and into industrial applications, students will be uniquely placed to benefit. Staff at UCL have strong links with enterprise and industry, giving students a short-cut directly into the heart of business. UCL’s location in central London means unparalleled access to partner institutions around the world, from multinational companies to top universities. Moreover, the university enjoys first-class laboratory facilities.

Information on funding and other course details will follow shortly, and there will be an open day for the programme in late January.

Partner organisations

Photo caption: The Portico of UCL’s main building. Credit: Mary Hinkley (UCL Creative Media Services)

Research news: Electrical control of single atom magnets

By news editor, on 9 December 2013

The energy needed to change the magnetic orientation of a single atom – which determines its magnetic stability and therefore its usefulness in a variety of future device applications – can be modified by varying the atom’s electrical coupling to nearby metals.

This striking result was published today in the journal Nature Nanotechnology by an international group of scientists working at the London Centre for Nanotechnology (LCN) at UCL, the Iberian Nanotechnology Laboratory (Portugal), the University of Zaragoza (Spain), and the Max Planck Institute of Microstructure Physics (Germany).

Anyone playing with two magnets can experience how they repel or attract each other depending on the relative orientation of their magnetic poles. The fact that in a given magnet these poles lie along a specific direction rather than being randomly oriented is known as magnetic anisotropy, and this property is exploited in a variety of applications ranging from compass needles to hard drives.

Artist's impression of magnetic anisotropy

When directly on a metal surface, the magnetism (black arrows) of a single cobalt atom (orange circles) is screened by strong interactions with the surrounding metallic sea (blue). By moving these atoms towards the centre of an island of thin insulator material (white), we can gradually decrease that strength of that interaction, which results in a remarkable enhancement of the magnetic anisotropy.
Illustration credit: Alfaro Cuevas (alfarocuevas.blogspot.com), CC-BY-ND

“For ‘large’ pieces of magnetic material,” emphasized Dr Joaquín Fernández-Rossier from the INL, “magnetic anisotropy is determined primarily by the shape of a magnet. The atoms that form the magnetic material are also magnetic themselves, and therefore have their own magnetic anisotropy. However, atoms are so small that it is hardly possible to ascribe a shape to them, and the magnetic anisotropy of an atom is typically controlled by the position and charge of the neighbouring atoms.”

Using a scanning tunnelling microscope, an instrument capable of observing and manipulating an individual atom on a surface, LCN researchers and their colleagues discovered a new mechanism that controls magnetic anisotropy at the atomic scale.

In their experiment, the research team observed dramatic variations in the magnetic anisotropy of individual cobalt atoms depending on their location on a copper surface capped with an atomically-thin insulating layer of copper nitride.

These variations were correlated with large changes in the intensity of another phenomenon – the Kondo effect – that arises from electrical coupling between a magnetic atom and a nearby metal. With the help of theoretical and computational modelling performed in Germany and Portugal, the researchers found that, in addition to the conventional structural mechanisms, the electronic interactions between the metal substrate and the magnetic atom can also play a major role in determining magnetic anisotropy.

“Electrical control of a property that formerly could only be tuned through structural changes will enable significant new possibilities when designing the smallest possible devices for information processing, data storage, and sensing,” said LCN researcher Dr Cyrus Hirjibehedin.

In contrast to the more conventional mechanisms, this contribution to the magnetic anisotropy can be tuned electrically using the same process that drives many transistors, the field effect. These results are particularly timely because they support efforts to find material systems with large magnetic anisotropy that are free of rare earth elements, scarce commodities whose mining has large environmental impact.

Notes

  • The research appears in a paper published in the journal Nature Nanotechnology, entitled “Control of single-spin magnetic anisotropy by exchange coupling”

Related links

High-resolution image

Artist’s impression of magnetic anisotropy

This image is Creative Commons Attribution-NoDerivatives licensed, and so may be reproduced freely providing the credits are retained and the artwork is not modified.

Researcher profile

Science contact

Cyrus Hirjibehedin
London Centre for Nanotechnology
c.hirjibehedin@ucl.ac.uk

Media contact

Oli Usher
UCL Faculty of Mathematical and Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk

News update: Quantum tech gets a boost in the Chancellor’s Autumn Statement

By Oli Usher, on 9 December 2013

The Chancellor George Osborne has announced £270m of new investment in quantum technologies. The new funding was announced at a meeting with top physicists, including UCL Quantum’s Prof Andrew Fisher.

This forms part of a package of public spending announcements in his Autumn Statement, and will cover five research centres at UK universities.

Prof Michael Arthur, President & Provost of UCL said:

This announcement is excellent news for the field of quantum technology, and will help put the UK at the forefront of the emerging quantum technology industry. UCL is one of the UK’s leading research centres in this field, and well placed to help realise this vision.”

 

News update: How to live longer…

By Oli Usher, on 22 November 2013

Cyrus Hirjibehedin, a member of UCL Quantum, writes in Nature Physics on the topic of how to increase spin lifetimes. In a News & Views article, he says:

The spin lifetime of a paramagnetic molecule on a superconducting surface is increased by orders of magnitude thanks to the effect of the superconducting gap, leading to improved control of molecular spin systems.

Decoupling an individual atom or molecule from its solid-state surroundings is often the key to allow it to clearly manifest its quantum spin properties, which can be exploited for new applications in information processing, data storage and sensing.

Hirjibehedin’s article is now available in the advance online publication section of the Nature Physics website (£). It will appear in a forthcoming issue of the journal.