ÃÛÌÒ´«Ã½

Research Interests

My research concerns quantum information theory and all things related to the complexity of quantum systems. Preprints to all my publications can be found on the quant-ph arXiv () or on Brunel's research archives.

Here are short summaries of my research work, loosely organised into various themes:

Entanglement theory and entanglement measures

I started out my scientific career as a graduate student at Imperial College under the supervision of  (now at Ulm) and , working on entanglement theory. Results include statements about the relative , , and computation of an (a paper for which most credit goes to coauthor for his quite heroic contribution). Since my PhD I have often revisited the topic of entanglement measures with the fortunate assistance of many insightful coauthors, e.g. and .

Quantum Computation with Triplet/Singlet measurements

In a collaboration with  that seems to become active with approximately the same period as a typical species of , I established the "STP=BQP" conjecture of , , and . We did this by building upon the insights of their  which proposed and evidenced the conjecture, and our own other on a related question from many years ago. The published proof of the conjecture is available at this . Loosely speaking, the work demonstrates that using only measurements of two qubit total angular momentum, one can perform quantum computation given almost any initial state that is not completely symmetric. This brings natural robustness to a certain form of error, and has interesting fundamental connections to the study of quantum reference frames. It is also perhaps surprising that quantum computation is possible with a single combined dynamical/measurement operation of such a simple and physically natural form, in a way that is almost completely agnostic about the initialisation of the qubits.

LOCC discrimination of quantum states

I had an early interest in the LOCC discrimination of quantum states (loosely speaking - how to distinguish quantum states of many quantum subsystems when you can only measure the subsystems in a distributed way). In collaboration with various colleagues I showed that even in the LOCC setting, and obtained , and obtained s with high symmetry.

Correlated error quantum information

I was introduced to this topic while I was a postdoc with at Pavia. We investigated the effect of . Motivated by some intriguing non-analyticity in that example, together with Martin Plenio I developed connections between correlated error quantum channel capacities and many-body physics, see and for details.

Classical simulation of quantum systems

Motivated by the ever increasing buzz concerning quantum computing, I became interested in how well classical computers can efficiently simulate quantum systems. Together with various coauthors I've developed bounds (e.g. and ) on the noise that quantum computers can tolerate before losing their advantage over classical computers. In more recent work have shown how ideas from the foundations of physics can be used to develop efficient simulations of some complex quantum systems, even without noise. Perhaps the most surprising example of this arises in certain pure entangled which we have shown can be efficiently simulated classically (see also for more explicit examples). Some of this work was supported by an and an EPSRC DTP.