Quantum superposition of thermodynamic evolutions with opposing time's arrows

TL;DR

This paper explores quantum superpositions of thermodynamic processes with opposing arrows of time, showing how measurements can restore a definite thermodynamic direction and revealing quantum interference effects in entropy production.

Contribution

It demonstrates that quantum superpositions of forward and reverse thermodynamic processes can be projected onto a definite arrow of time through measurement, revealing interference effects.

Findings

Quantum superpositions of thermodynamic evolutions exist with opposing time arrows.

Measurements can project superpositions onto a definite thermodynamic direction.

Interference effects can lead to entropy distributions more reversible than classical expectations.

Abstract

Microscopic physical laws are time-symmetric, hence, a priori there exists no preferential temporal direction. However, the second law of thermodynamics allows one to associate the "forward" temporal direction to a positive variation of the total entropy produced in a thermodynamic process, and a negative variation with its "time-reversal" counterpart. This definition of a temporal axis is normally considered to apply in both classical and quantum contexts. Yet, quantum physics admits also superpositions between forward and time-reversal processes, whereby the thermodynamic arrow of time becomes quantum-mechanically undefined. In this work, we demonstrate that a definite thermodynamic time's arrow can be restored by a quantum measurement of entropy production, which effectively projects such superpositions onto the forward (time-reversal) time-direction when large positive (negative) values are measured. Remarkably, for small values (of the order of plus or minus one), the amplitudes of forward and time-reversal processes can interfere, giving rise to entropy-production distributions featuring a more or less reversible process than either of the two components individually, or any classical mixture thereof.