Quantum correlations

Group leader : Rémy MOSSERI
Laboratoire de Physique Théorique de la Matière Condensée

Interacting quantum systems have a tendency to become entangled. The study of entanglement and its consequences is therefore of great interest. The team’s activity develops along two axes:
1- Quantum magnestism : For thirty years, two-dimensional systems of strongly correlated fermions are the subject of intense research in condensed matter ( high critical temperature superconductors , 3He films , quantum Hall effect, etc. . ) . Some of these systems , known as the spin liquids exhibit non-conventional magnetic properties . Our work focuses on the study of exotic orders characterizing these spin liquids , as well as neighboring models ( dimers and quantum partitions) , and are guided by both experiments on many compounds ( frustrated on the triangular lattice or grid systems kagome , nematic , spin ladders and tubes , etc. . ) and intimate links with quantum information ( entanglement, topological order , etc. . ) . In particular we study the structural changes of the ground states responsible for quantum phase transitions ( at zero temperature ) and the excitations which are often fractional . This phenomenon is the cause fractionalization of quantum statistics anyoniques quasiparticles ( present only two dimensions ) for the critical topological quantum computation . We also develop , more recently , interactions with experimentalists to elucidate the properties of liquid type spins new materials ( kapellasite , herbersmithite , etc. . ) . The tools used to carry out these various studies are not only numerical (exact diagonalizations , simulations, variational approaches) but also analytical and semi- analytical (perturbative continuous unitary transformations , effective theories of low energy, high temperature series).
2- Quantum Entanglement and decoherence
Interacting quantum systems have generically tend to entangle . The study of entanglement and its consequences is therefore of great interest . Our business is growing along two axes : (1) the entanglement of qubits , for which we are working on a detailed description of the Hilbert space , under an appropriate measure of the entanglement, in particular by using geometric tools , Hopf fibrations , Moebius transformations . We also plan , in the topological quantum computation , analysis by the intricacy of anyons interaction . (2 ) the consequences of entanglement with the environment. For small quantum systems , the environment can not be ignored. Under the influence of the latter, the system state does not remain pure ( decoherence ) and generally tends towards a steady state. We study (i ) the influence on the evolution of the characteristics of the environment ( thermodynamic phase … ), (ii ) steady-state non-equilibrium system when the environment is non-equilibrium , ( iii ) phenomena existing relaxation in an isolated system.