Quantum Information and Control
Systems of many particles evolving through the well-established theories of electromagnetism and quantum mechanics often collectively organise themselves in elegant ways. As a condensed matter theorist, my research aims to predict and understand such behaviour from a microscopic basis. I am particularly interested in systems where quantum mechanics and interactions play a crucial role. My group's research has a particular focus on collective effects in ultracold atomic gases. It is often straightforward to write down a simple and intuitive effective Hamiltonian which captures the relevant physics of these systems, but these Hamiltonians can be difficult to solve and can exhibit rich behaviour. Topics ('keywords') of current research include: interacting topological band models, non-equilibrium quantum dynamics, spinor condensates, Majorana fermions, and quantum vortices.
My research is in quantum information science, with a focus on quantum Shannon theory and quantum cryptography. The former is about the general theory of information processing in the quantum setting, whereas the latter is more specifically about techniques for secure communication in the presence of malicious parties. I am interested in the mathematical aspects of quantum information theory and connections to mathematical physics, most importantly through the fields of matrix analysis and non-commutative optimization theory.
We are working on the theory of quantum optics and quantum technology. In particular our research includes the characterisation and control of nonclassicalities in various physical systems including multi-photon interferences, cavity QED and mechanical oscillators. Quantum mechanics has been very successful to predict and explain nature at a very small scale. However, as the system becomes complex, the simple picture suggested by quantum mechanics might become less obvious. We are interested in pushing the boundary of quantum mechanics to understand a broader class of phenomena from first principles. Recently we are interested in the tabletop tests of gravitational effects in quantum mechanics as well as the effects of quantum mechanics in new parameter regimes.
Coordination of the National Quantum Technology Programme and Chair of the NPL Quantum Metrology Institute. In addition my personal interests: Quantum states of many particles offer the opportunity to study the rich physics of large-scale quantum correlations. Such multi-partite correlations are believed to underlie a range of physical phenomena such as structure and transport in many-body quantum systems and promises extraordinary new power, characterized by performance that dramatically exceeds any classical processor. Building machines able to achieve this so-called Quantum Supremacy has obvious motivation from a purely technological standpoint. Systems in which all the particles and their interactions can be controlled to some degree can deliver functionality for sensing, imaging, communications, simulation and computation that goes well beyond what is possible with classical systems possessing a similar set of resources (e.g. number of particles). Thus new technologies can emerge which hold the potential to revolutionize information processing, when the size of the system becomes large enough. One approach to these challenges is to try to build large quantum states out of light, constructing quantum correlated light beams across multiple modes, and setting up a system comprising many photons in which each elementary input and their interactions are controllable.This is supported by the EPSRC Programme BLOQS (Building Large Quantum States out of Light), a collaboration between Oxford and Southampton Universities and Imperial College London.
Our group works on post-quantum cryptography, the interaction between quantum computing and lattice-based cryptography, and quantum information theory.
We are using optimal control techniques to design control for quantum systems that makes these systems perform desired tasks with high fidelity despite system imperfections. Our work is theoretical, but we collaborate intensively with experimentalist and goals of our work are towards quantum simulations and quantum computation.
Starting in December 2019, we have joined the UK Quantum Imaging Hub, QuantIC2. The consortium is funded by EPSRC to the tune of ~£26m, with the guiding aim of exploiting quantum-based techniques to enhance imaging capabilities across a range of disciplines that offer the prospect of commercial exploitation.
Our own speciality is in the mid-Infrared, a part of the spectrum where different chemical groups absorb specific wavelengths as vibronic transitions. This allows spectral information to be used for chemical analysis. Already we are using this to trial and commercialise a new technology “Digistain” that has been proven to give more trustworthy cancer diagnosis, by measuring the presence of chemical changes in biopsy samples that are already known to accompany the disease.
With QuantIC, we will develop new sources of entangled photon pairs in this part of the spectrum for the first time. We will do it with nano-optical arrays, tiny artificial metallic structures that can be designed to split visible photons into entangled pairs with wavelengths that are much more widely separated that was possible previously. Very recently it has been shown that these types of light source can be used to image an object by detecting photons that have themselves never actually interacted with it. This happens because of the eerie property of entangled photons, that if you do something to one of the pair, its partner instantaneously reacts to whatever it is that you have done, no matter how far away it might be at the time.
Einstein famously refused to accept this “Spooky Action at a distance”, but nowadays it is a very well-tested, if still rather unsettling quantum phenomenon. For us, the exciting practical aspect is that the photon you detect can have a wavelength where e.g. detector technology is extremely fast, and sensitive, whilst the imaging wavelength is one where the currently available detectors are not up to much.
We cool molecules to ultracold temperatures. We plan to trap individual molecules in optical tweezer traps in order to build up small, reconfigurable arrays of molecules. The molecules in the array will interact through long-range dipole-dipole interactions, making a simulator for strongly-interacting many-body quantum systems. We also plan to place our ultracold molecules in chip-based electric traps where they can be coupled to microwave photons, making a building block for a hybrid quantum information processor.
We use the Penning trap for studies of the laser cooling process and for the preparation of single laser-cooled ions and small ion Coulomb crystals. Our experiments aim to use ions in a Penning trap for applications in quantum optics and quantum information processing. We have demonstrated the first laser cooling to the motional ground state in a Penning trap. Our current goal is to study the decoherence processes taking place when single ions are prepared in quantum superposition states in the trap. We are also studying coherent states of motion of the ion. In future work we will study the cooling of the radial motion of the ion. With small ion Coulomb crystals we are investigating ground state cooling of all the axial vibrational modes of the crystal with a view to demonstrating elementary quantum gates in this system.