Wednesday, August 20, 2014

Quantum entropy flows

Non-equilibrium quantum thermodynamics is a quite new fields in physics that surprisingly left  less explored in the last century. Recently this field is becoming active both experimentally and theoretically. 

When interaction occurs between two systems there is a flow of some conserved quantities, such as electric charge, energy etc. between the two.  Shannon entropy (as well as its generalized Renyi entropy) is a conserved quantity in a world made of subsystems A and B.  Owing to this conservation there are finite flows of entropy between A and B.

For the first time we present a consistent derivation of the flows of Shannon and Renyi entropies for a generic quantum heat engine to a probe environment kept in thermal equilibrium. The flows consist of heat flow and fictitious dissipation originating from quantum coherence. 

Rényi entropy flows from quantum heat engines
Mohammad H. Ansari, Yuli V. Nazarov

Tuesday, July 01, 2014

another contribution to quasiparticle poisoning

just appeared on arxiv:1406.7350 in a collaboration that connect people in Sanata Barabra, Waterloo, Kocaeli,  and Delft.

In a flux qubit, the energy spectrum versus magnetic flux must be single hyperbolic, but what is observed usually in practice is double lines.

Cooling down does not help to remove the second line but it helps only a little bit to reduce the gap between the two. Why is this so?

This paper explains that the reason is quasiparticle poisoning in the junction. These quasiparticles have nonequilibrium nature, which at higher temperature turns to the equilibrium one. We propose a detailed theory and exactly extracted the gap from a quasiparticle tunneling theory.

Previously I made 2 more contributions to the theory of qusiparticle tunneling, here arXiv:1211.4745 (published) and arxiv:1303.1453 (recently submitted for publication).

The new preprint is an experimental evidence to the problem.