New techniques for nanokelvin condensed matter physics

The quest for colder and colder temperatures has led to many remarkable discoveries. The most difficult gas to liquify is helium but this was finally achieved at the beginning of the 20th century. That breakthrough led the observation of the intriguing phenomena of superfluidity (a liquid that flows without friction just like the current in a superconductor flows without resistance) and nowadays refrigeration with helium is of fundamental technological importance, e.g. for large international companies such as Oxford Instruments. At end of the the 20th century new techniques were developed that used laser light to cool atoms (although this may seem counterintuitive) and magnetic traps that confine the atoms in a region of very good vacuum. This new technology allowed dilute vapours of alkali metal atoms to be prepared a low temperatures. Amazingly this atoms of metal do no clump together (to form molecules) and evaporation cools the cloud further to extremely low temperatures of tens of nanokelvin. This allowed the first experimental observation of Bose-Einstein condensation (BEC) in a weakly interacting dilute gas, as predicted by the famous physicists Einstein and Bose. This extremely interesting quantum phenomenon has links with previous work on superfluid helium but the liquid is more complicated to understand than the ultra-cold atomic gases. Wonderfully detailed images of the cold atoms can be taken using state-of-the-art cameras developed for astronomy and microscopy and this ability to see directly what is going on in quantum fluids has allowed very rapid progress in understanding these systems and provided a wealth of new knowledge. This was evident in the very first experiment on BEC where the phase transition from an ordinary gas to the quantum regime was observed as a dramatic change in the density and shape.

We have built a novel apparatus in which in the the potential energy landscape that atoms experience as they move through the magnetic field is tailored in a precisely controllable way by the application of radio-frequency radiation. (The applied radiation changes the quantum state of the atoms at particular positions in space hence changing the potential they feel.) This has proven to be particularly useful for two-dimensional systems and for creating interesting geometries such as ring traps (with quantum coherence around the loop). A great advantage of this approach is that the potential is very smooth and free from defects, as compared to trapping atoms with laser light where interference fringes arise. We have combined this new approach with time-averaging to allow an even greater range of potentials and long lifetimes in the traps.

We shall continue to develop and test new schemes for trapping atoms, such as the create of double rings (atoms on two concentric circles) and trapping atoms at magnetic fields where there is resonant enhancement of the interactions (Fano-Feshbach resonance). We shall apply this technology to the direct quantum simulation of strongly correlated systems, and explore applications such a matter-wave interferometry for precision measuring devices.

This progress in cooling atomic gases to nanokelvin temperatures now allows us to fulfill the statement of Richard Feynman,``I therefore believe it's true that with a suitable class of quantum machines you could imitate any quantum system, including the physical world''. This is often quoted in the context of quantum information processing but it applies more directly to the creation of controllable quantum systems in which we engineer the quantum Hamiltonian so that it looks the same as that of the physical system of interest. This is the underlying principle of our work on Direct Quantum Simulation. In this context quantum mechanics is used to design a quantum machine, i.e. an apparatus to controllably create many-body quantum states, in the same way that automotive mechanics is used in the creation of vehicles.

In his Nobel speech, Onnes expressed the hope that his progress in cryogenics would "contribute towards lifting the veil which thermal motion at normal temperature spreads over the inner world of atoms and electrons".

Scientific Impact
Quantum effects inevitably become more and more important in technology as electronic and optical components get smaller and smaller, and some quantum technology has already been commercialised, e.g., quantum cryptography for secure communications. The quantum simulator that will be designed and built in this experimental programme is a machine that can be used to investigate the properties of many-body quantum systems over a wide range of conditions, leading to a deeper understanding of the physics in such systems that can be applied to future devices. Quantum simulators for the particular systems that we shall study can be viewed as a subset of quantum computers which could, in principle, be programmed to emulate any quantum system; however such universal quantum simulators are far from being realised with a useful number qubits. Quantum computing will not necessarily have an impact in the marketplace but has a niche application to deciphering and it is this that has attracted strong financial backing from the EPSRC as well as various security agencies in the USA. Also Oxford Quantum Associates has been established with private finance as a vehicle for developing quantum technologies in Oxford.

The importance of research on ultracold quantum matter is underlined by the two Science and Innovation grants jointly to the universities of i) Oxford, Cambridge and Imperial, ii) Birmingham and Nottingham, to strengthen the UK community in this area (not to replace the ongoing research). This area attracts extremely good graduate students and provides training in diverse skills that are highly valued by employers.

Dissemination work to a general audience

In addition to conference talks and seminars, Professor Foot has been invited to lecture to a more general audience, for example at the National University of Singapore, and at the European Open Science Forum (ESOF) in 2008. At ESOF he helped organize a session on cold atoms, under the auspices of European Science Foundation, and funded through the EuroQUAM programme in which he was one of the six Project Leaders. The session was well attended and chaired by Eduardo Punset, (professor, government adviser, former member of the European Parliament, and presenter of a Spanish language science TV show). This resulted in at least one article in a science magazine. In August 2010, Professor Foot had many discussions with the production team for a BBC Horizon program on 'What is temperature?', both on explaining the physics and logistics; they came to Oxford to film a demonstration of superfluidity in helium (set up by Profs. Taylor and Foot); the producer decided not to film in the BEC laboratory apparatus but we prepared a computer animation of the Bose-Einstein condensation as requested (final editing has not yet been completed, as far as we know). We will continue to carry out this type of presentation to general audiences as opportunities arise and this is strongly encouraged and financially supported by the Physics Department, e.g., talks and demonstrations for school students. The new single-atom imaging methods that we shall develop give extremely striking visual results that can readily be appreciated by non-specialists, as well as enabling the experiments to observe correlations.