Quantum Computation and Information Seminar   RSS

11/09/2014, 14:00 — 15:00 — Room P8, Mathematics Building, IST
Stefano Iubini, CBM-CNRS Orléans

Discrete Breathers and Negative Temperature States

Since the pioneering work of Onsager and Ramsey in the 1940s and '50s, physical states at negative (absolute) temperatures have attracted the curiosity of researchers and shown how science can challenge common sense. In negative-temperature regimes, the temperature is above infinity and high-energy states are more populated than low-energy ones.

After many years elapsed since the first experimental evidences of negative temperatures in quantum nuclear-spin systems, recent experiments have realized a negative temperature state in a system of ultracold bosons trapped in optical lattice, modeled by a Bose-Hubbard Hamiltonian.

I will discuss the statistical behavior of a semi-classical limit of the Bose-Hubbard model, namely the Discrete Nonlinear Schroedinger Equation. By monitoring the microcanonical temperature, it is possible to show that there exists a parameter region where the system evolves towards a state characterized by a finite density of spatially localized nonlinear excitations (discrete breathers) and a negative temperature. Such a state persists over very long (astronomical) times since the convergence to equilibrium becomes increasingly slower as a consequence of a coarsening process.

I will also discuss possible mechanisms for the generation of negative-temperature states in experimental setups.

Please note exceptional day and place.

Supported by: Phys-Info (IT), SQIG (IT), CeFEMA and CAMGSD, with funding from FCT, FEDER and EU FP7, specifically through the Doctoral Programme in the Physics and Mathematics of Information (DP-PMI), FCT strategic projects PEst-OE/EEI/LA0008/2013 and UID/EEA/50008/2013, IT project QuSim, project CRUP-CPU CQVibes, the FP7 Coordination Action QUTE-EUROPE (600788), and the FP7 projects Landauer (GA 318287) and PAPETS (323901).

Instituto de TelecomunicaçõesCAMGSDFCT7th Framework Programme