News Archive
Joshua Nunn
A third breakthrough concerns the transfer of coherence between optical and material systems, one of the major goals of QIP IRC. Quantum memories for light are required to store photons within quantum optical networks, allowing probabilistic operations to be synchronized.
Sougato Bose
Entanglement or "quantum correlations" between distant systems is a pivotal resource in quantum information processing. For example, if entanglement could be established between qubits belonging to two separate quantum processors, they could effectively act as a single, more powerful, quantum processor. Thus emerges the idea of having substantial entanglement between opposite ends of a spin chain, so that this chain could be used as a quantum bus connecting spins (qubits) in two separate processors.
A full booklet of abstracts can be requested by emailing qucocoworkshop@gmail.com. Here I will summarize a selection of the results presented:
Dr. Jeremy L. O'Brien
Congratulations to Dr Jeremy O'Brien for being awarded the 2009 European Quantum Information Young Investigator Award ......
Janus Wesenberg
While the building blocks for few-bit quantum computers have already been demonstrated, scaling these systems up to large quantum computers remains a challenge. One problem is to develop physical systems that can reliably store thousands of qubits, while allowing individual addressing of each bit. With this issue in mind researchers, from the University of Oxford, Yale University, and the University of Aarhus in Denmark, have proposed to store hundreds of qubits as spinwaves in an ensemble of billions of electron spins.
Dan Browne
John Morton
Quantum entangled, or "Schrödinger cat", states can be very delicate and easily perturbed by their external environment. This sensitivity can be harnessed in measurement technology to create a quantum sensor with a capability of outperforming conventional devices at a fundamental level. In a paper recently published in Science, Jonathan Jones and his colleagues compared the magnetic field sensitivity of a classical (unentangled) system with that of a 10-qubit entangled state, realised by nuclear spins in a highly symmetric molecule (comprising nine 1H nuclei around a central 31P). They observed a 9.4-fold quantum enhancement in the sensitivity to an applied field for the entangled system and showed that this spin-based approach can scale favorably compared to approaches where qubit loss is prevalent. This result demonstrates a method for magnetic field sensing technology, based on quantum entanglement.
Professor Sir Peter Knight
Imperial College London
For his outstanding contributions to Physics in the UK and globally through both his scholarship as a pre-eminent Atomic and Molecular Optics theoretician and as a charismatic and effective leader of research and research organisations.
John Morton
Dr John Morton is the 2009 recipient of the Nicholas Kurti European Science Prize. John is a Royal Society University Research Fellow at St. John's College, Oxford. He has pioneered the application of techniques of magnetic resonance spectroscopy to combinations of electron and nuclear spins to store quantum information for extended times and to manipulate it with exquisite precision. He was able to establish that such systems, including those based on molecular materials, are viable for a quantum nanotechnology.
Andrew Ramsay
Coherent light-matter interactions are often understood in terms of dressed states: states that are a composite of light and matter. Recently, we have made a number of experiments to time-resolve the excitonic dressed states of a single self-assembled InAs quantum dot. We demonstrate the possibility of controlling the composition, and energies of the excitonic dressed states on a picosecond timescale. Furthermore, an experiment illustrating that a Rabi oscillation may be interpreted as a beat between two dressed states was performed.
Professor Maurice Skolnick FRS
Congratulations to Professor Skolnick for being elected as Fellow of The Royal Society!
David Ritchie
We have fabricated and optimized triggered sources of entangled photon pairs using self-assembled InAs quantum dots. After optimization, a fidelity to the ideal entangled state of over 90% has been achieved.
Martin Plenio
Martin Plenio
Entangled quantum systems can be harnessed to transmit, store, and manipulate information in a more efficient and secure way than possible in the realm of classical physics. Given this resource character of entanglement, it is an important problem to characterize ways to manipulate it and meaningful approaches to its quantification. This is the objective of entanglement theory.
Ed Hinds
For efficient scalable QIP networks, we require suitable qubits both for long-lived storage, and for point-to-point communications. Atomic systems offer extremely long coherence times (on the order of 1 second), but are not easily transported over long distances; photons are ideal for long-distance communication, but are not easily stored. Fortunately the essential gate operations have been performed with some success on both atomic and photonic systems. The outstanding challenge therefore is to develop robust and efficient means for transferring quantum information between light and matter.
Martin Plenio
We demonstrate that Nature may be utilizing noise in order to harness fundamental quantum mechanical properties and optimize the energy transport in natural processes such as photosynthesis. We identify the basic mechanisms underlying this phenomenon, apply it to the Fenna-Matthew-Olson complex and argue for the possibility of designing artificial nano-structures for optimized noise-assisted transport.
The first experimental demonstration of detector tomography
Awarded to John Morton by SET for BRITAIN 2009
Presented to Professor E. A. Hinds FRS of Imperial College
*** CALL FOR PAPERS AND REGISTRATION ***
J. Wabnig, B.W. Lovett, G.A.D. Briggs, J.H. Jefferson
A new Nature Physics publication.
Registering the position of quantum dots optically allows photonic crystals to be written around them lithographically with high precision.
Available on iTunes U from Oxford.
The final QIP IRC Annual Conference.
Programme Grant award
A recent publication from the Department of Physics, Oxford.
From 1st April 2008 Dr Almut Beige will hold the position of Reader (Quantum Optics and Quantum Information) at the University of Leeds.
A Science publication from work partly supported by the QIP IRC.
A PRL from work partly supported by the QIP IRC.
By Jens Eisert
The Institute of Physics and Royal Society recognise outstanding researchers in the field
Bristol., 17-19 March 2008
Research posts available now.
A recent APL
A new technique lines up more nuclear spins than was previously possible.
Two postdocs in quantum information from 1st Oct, 2007
New awards.
PhD studentship in Quantum Information Science
An exciting result from Koenraad Audenaert and Frank Verstraete, with the group of Emili Bagan...
D. G. Angelakis(Univ. of Cambridge), M. Santos (Univ of Minas Gerias) and S. Bose(U.C.L) have recently proposed a system of individually addressable atom-cavity configurations, for simulations of quantum many body effects and applications in quantum information processing.
M.J. Hartmann, F.G.S.L. Brandao and M.B. Plenio (Imperial College) have now proposed a quantum simulator in a new system, which allows for experimental access to properties of individual particles.
by Martin Plenio and Shashank Virmani
Science Communication Workshop took place at St Anne’s College,
Entanglement is a key resource in quantum information tasks and much effort is being expended in its theoretical and experimental exploration. As a consequence, the quantitative exploration of entanglement as a resource is a central concern of quantum information science. Basic questions such as the characterization, the manipulation, and the quantification of entangled states are addressed in this endeavour. Their answers establish the theory of entanglement and are of interest to theorists and experimentalists alike.
Over the last years the theory of entanglement has grown enormously and many fundamental properties are now well established. Unfortunately, the forest of publications is becoming increasingly dense and frightening for novice and expert alike. QIP IRC partners Martin Plenio and Shashank Virmani from the Institute for Mathematical Sciences at Imperial College http://www.imperial.ac.uk/quantuminformation have recently finished a comprehensive tutorial overview on the subject, presenting the basics and offering many useful explicit formulae.
The article, soon to be published in Quantum Information and Computation, is also available at http://xxx.arxiv.org/abs/quant-ph/0504163
The annual report describes a selection of the activities in QIP IRC. It is hoped that it will convey some of the challenges that have been addressed and some of the results that have been achieved. The annual report serves to inform the QIP IRC Board and EPSRC about progress. The scientific summaries are edited from annual reports from investigators, which will be available on this website shortly. Investigators are asked to check that the list of publications is accurate and complete, and to send corrections to qipirc@materials.ox.ac.uk.
The Annual Report can be downloaded from the Forms and Documents section of the website.
This document, produced within the QIP IRC in Autumn 2005, brings out some common scientific themes which have emerged from the first year or so of the QIP IRC's work. It is not intended to be any kind of full progress report, a quality review of the projects, or a list of scientific highlights; rather, it is a subset of the results recently reported by the IRC (either in quarterly scientific progress reports to the management team, or in publications and preprints) that, while interesting in themselves, relate to more than one of the IRC projects or seem to have the potential to lead to further work in several different areas.
It was discussed at the QIP IRC Conference in September 2005; two of the areas highlighted for their developing connections were chosen for discussion symposia at that meeting. For each topic we mention one or two names as contact points for those who are interested in the work; this is not intended to be any kind of formal assignment of scientific credit, for which the author lists of the papers referenced provide a better indication.
The present document was written by Andrew Fisher and the selection corresponds to his own subjective choices. It has benefited from the input of others in the IRC, but the responsibility for the selection and any remaining errors is entirely his – comments are welcome (andrew.fisher@ucl.ac.uk), If it is found to be useful we will update it regularly and also produce versions for other audiences.
The document can be downloaded from the Forms and Documents section of this website.
The QIP IRC/QAP EC Summer School was held from 20th to 25th August in Gregynog, Wales.
The QIP IRC conference took place on the 26th and 27th of June 2006 at St Anne's College, Oxford.
Professor John Rarity has been awarded a Royal Society Wolfson Research Merit Award.
Dr Simon Benjamin and Dr Arzhang Ardavan discuss the “bang-bang” technique to isolate quantum information in the April 2006 edition of Excellence in Science, the online newsletter from the Royal Society.
The QIP IRC report into the commercial prospects for Quantum Information Processing has now been published.
Sc@C82 is not isotropic, so its ESR response depends on its orientation. Understanding the orientation-dependence of this response is necessary if Sc@C82 is to be used in a QIP array.
Professor Martin Plenio (Imperial College, London) has been awarded a Royal Society Wolfson Research Merit Award.
QIP IRC members Dr Simon Benjamin and Dr Pieter Kok discuss quantum computing with graph states with Quentin Cooper on The Material World, BBC Radio 4. For more information and to listen to the programme (originally broadcast on 6th April 2006) go to http://www.bbc.co.uk/radio4/science/thematerialworld_20060406.shtml
There are many practical limitations to the implementation of quantum computing. One problem is dissipation, i.e. the loss of information due to unwanted interactions with the environment. Another limitation is the sensitivity to parameter fluctuations. For example, if the amplitude of an applied laser field fluctuates by a few percent, this should not result in a failure of the computation. One solution to these problems is to use measurements: They can be used to project a quantum system into any desired state and are commonly used for state preparation in quantum optics experiments.
However, measurements can also play a much more subtle role in quantum computing. They can provide the main ingredient for the implementation of entangling two-qubit gate operations. Together with single-qubit operations, entangling two-qubit gates are universal for quantum computing. To avoid the destruction of qubits, it is not allowed to measure the qubits directly. Measurements should be performed only on ancillas which have interacted and therefore share entanglement with the qubits [1]. In order to implement a quantum gate on the qubits, we measure the ancillas in a basis that is mutually unbiased with respect to the computational basis. This ensures that an observer does not learn anything about the state of the qubits and the information might remain stored inside the computer. The most famous example of such a measurement-based quantum computer is the linear optics scheme for photonic qubits by Knill, Laflamme and Milburn [2].
However, ancillas and qubits do not have to be of the same physical nature. For example, if the qubits are atoms in a cavity, the ancillas can be the quantised cavity field mode [3], a common vibrational mode [4], or newly generated photons [5,6]. Vice versa, one can use collective atomic states as ancillas for photonic qubits [7,8]. Quantum computing with hybrid systems should help to overcome some of the most pressing problems in existing non-hybrid proposals, including the difficulty of scaling conventional stationary qubit architectures and the lack of practical means for storing single photons in linear optics setups.
In a recent collaboration between Imperial College London and HP in Bristol, we analysed an architecture for robust and scalable quantum computation using both stationary qubits and flying qubits [9]. Our scheme combines elements of two previous proposals for distributed quantum computing, namely the efficient photon-loss tolerant build up of cluster states by Barrett and Kok [5] with the idea of Repeat-Until-Success (RUS) quantum computing by Lim, Beige and Kwek [6].
The considered setup consists of a network of single stationary qubits (like trapped atoms, molecules, ions, quantum dots or nitrogen-vacancy colour centres) inside optical cavities, which act as a source for the generation of single photons on demand. Read-out measurements and single qubit rotations can be performed on the stationary qubits using laser pulses and standard quantum optics techniques as employed in ion trap experiments.
The main building block for the realization of an eventually deterministic two-qubit gate is shown in the Figure. It requires the simultaneous generation of a photon in each source involved in the operation. Afterwards, the photons pass through a linear optics setup, and a two-photon measurement is performed in the output ports. This measurement results either in the completion of the two-qubit gate, or it will induce two correctable single-qubit gates on the qubits. In the latter event the gate can be repeated, as no quantum information is lost. Hence the name Repeat-Until-Success quantum computing [6].
When we use photon detectors with finite efficiencies and when the photon generation is not ideal, a failure of the two-qubit gate does not always leave the qubits undisturbed. Consequently, the Repeat-Until-Success procedure fails occasionally. However, the setup in the Figure can still be used for the efficient implementation of two-qubit gates with a very high fidelity. As shown recently by Barrett and Kok [5], it is possible to use entangling operations with arbitrarily high photon losses to efficiently generate graph states for one-way quantum computing [10]: A so-called "double-heralding" scheme employs two rounds of photo-detection which eliminate unwanted separable contributions to the density matrix. Combining the loss-tolerant mechanism behind double-heralding with the Repeat-Until-Success protocol leads to a quantum computer architecture that is robust against inevitable losses, and succeeds with reasonably high probability but, most importantly, does not require direct qubit-qubit interactions.
[1] G.G. Lapaire, P. Kok, J.P. Dowling, and J.E. Sipe, Phys. Rev. A 68, 042314 (2003).
[2] E. Knill, R. Laflamme, and G.J. Milburn, Nature 409, 46 (2001).
[3] A. Beige, D. Braun, B. Tregenna, and P. L. Knight, Phys. Rev. Lett. 85, 1762 (2000).
[4] A. Beige, Phys. Rev. A 69, 012303 (2004).
[5] S.D. Barrett and P. Kok, Phys. Rev. A 71, 060310(R) (2005).
[6] Y.L. Lim, A. Beige, and L.C. Kwek, Phys. Rev. Lett. 95, 030505 (2005).
[7] J.D. Franson, B.C. Jacobs, and T.B. Pittman, Phys. Rev. A 70, 062302 (2004).
[8] S.D. Barrett, P. Kok, K. Nemoto, R.G. Beausoleil, W.J. Munro, and T.P. Spiller, Phys. Rev. A 71, 060303(R) (2005).
[9] Y.L. Lim, S.D. Barrett, A. Beige, P. Kok, and L.C. Kwek, Phys. Rev. A (in press); quant-ph/0508218.
[10] R. Raussendorf and H.J. Briegel, Phys. Rev. Lett. 86, 5188 (2001).
(Almut Beige and Pieter Kok, November 2005)
Deciding whether some graphs are actually the same or not is a computationally difficult problem, with important practical applications ranging from communication theory and computer architecture design to the study of social networks.
..if this sounds paradoxical, it must be, since negative information can occur only in the strange world of quantum mechanics. In the classical world of our experience, information, i.e. the amount of communication required to 'inform', must always be positive or zero; and this is even true of partial information, which is the communication effort to inform a receiver who already has some (statistical) partial knowledge.
The Ion Trap Group at Oxford reports on three exciting news items:
Researchers at Toshiba Research Europe Ltd (TREL) in Cambridge, in collaboration with the University of Cambridge, have developed a light source that can be used to send single photons in a regular stream through optical fibre over long distances. The device is needed for future quantum networks exploiting the particle-like properties of light.
The following QIPIRC Coffee Talk seminar will be transmitted as an experimental Quicktime live streaming webcast at 11am (BST) on Thursday 6 October 2005.
The QIP IRC conference took place on the 15-16th September 2005 at St Anne's College, Oxford. Over 70 delegates enthusiastically participated in two days of lectures and discussions focussing on the theme of the QIP IRC and the exciting science that we are engaged in together. Read more about the event as seen through the eyes of Joshua Nunn, a DPhil student in the Clarendon Laboratory at the University of Oxford:
The School of Physics and Astronomy at the University of Leeds intends to create a new research group in Experimental Quantum Information consisting, in the first instance, of a Chair and one supporting lectureship. Applications are therefore invited for the post of Professor of Quantum Information Science (deadline 31 October 2005).
The QIP IRC conference will take place on the 15-16th September 2005 at St Anne's College, Oxford. Registration is now complete and we greatly look forward to welcoming you to Oxford and to two days focussing on the theme of the QIP IRC and the exciting science that we are engaged in together.
Physicists in Innsbruck and Oxford have invented a way to use a single atom as a transistor; one which would control the flow of atoms in a pipeline made from light.
The connection between entanglement and area has been found to be more general than first thought.
Photo of attendees at the QIP IRC Summer School was held at the Burlington Hotel, Sheringham, Norfolk from the 5th to the 10th June 2005.
The QIP-IRC is currently investigating the practical and commercial uses for QIP and quantum computing. Anyone with a view on this subject is invited to e-mail Ian Howlett at ian.howlett@sbs.ox.ac.uk
Salvador Elias Venegas-Andraca wins student award.
Many congratulations to Professor Peter Knight (Imperial College) who received a knighthood for services to optical physics and to Professor David Pettifor (Oxford) who received a CBE for services to science in the Queen's Birthday Honours List.
The QIP IRC Summer School, which will commence at 4pm on Sunday 5 June and conclude at 2pm on Friday 10 June 2005, is being held at Burlington Hotel, Sheringham, Norfolk.
"Two-Dimensional Exciton Behavior in GaN Nanocolumns Grown by Molecular-Beam Epitaxy,"
by Jong H. Na, Robert A. Taylor, James H. Rice, James W. Robinson, Kwan H. Lee, Young S. Park, Chang M. Park, & Tae W. Kang has been chosen as the cover of the 21/3/2005 edition of Applied Physics Letters
Professor Sandu Popescu (Bristol University and a member of the IRC) gave the 2004 Clifford Patterson lecture at the Royal Society.
Previous page: News
Next page: About QIP IRC