Open Quantum Systems

Ideal superfulids offer insight into emergent many-body dynamics. But what of real superfluids encountered in the laboratory? Experiments are typically hot and noisy, even for ultracold quantum gases that operate at some of the coldest temperatures ever created. The regime of finite-temperature superfluids poses interesting challenges for theoretical description.

Quantum coherences, dissipation, and thermal noise all play a role in dynamics of phase transitions, and the dissipation of elementary excitations such as vortices and solitons.

Hot Matter Waves

Near the BEC phase transition the system contains many highly occupied modes driven by thermal noise. Open systems theory allows tracing over thermalized high-energy states that form a reservoir of particles and energy in contact with low-energy states that make up the condensate and other partially coherent modes.

C-Field theory adapts Wigner phase space methods of quantum optics to the description of ultracold atom systems. It allows the formalation of a generalized stochastic Gross-Pitaevskii equation to describe the phase transition and the lifetime and decay of BEC excitations.

Dissipative Dynamics

Decay can be driven by any mechanism that seeks to remove energy or angular momentum from the low-energy region of the c-field. Vortices and solitons are excellent test systems for c-field theory. Recent work has focused on the role of energy damping. We are exploring a number of quasi-eqiulibrium scenarios where energy damping is the dominant dissipative effect. For quantum vortex decay energy damping is in close agreement with existing experimental data.

Associated publications