Coherence of quantum non-Gaussian states via nonlinear absorption of quanta

TL;DR

This paper demonstrates how combining linear and nonlinear absorption processes can generate and enhance quantum coherence in non-Gaussian states of oscillators without external drives, advancing quantum state engineering.

Contribution

It introduces a minimal nonlinear phase-insensitive absorption process that, combined with linear absorption, enables coherence in quantum non-Gaussian states, overcoming previous limitations.

Findings

Coherent addition of linear and nonlinear absorption creates complex asymmetric Wigner functions.

The method allows coherence to emerge without external drives.

Switching between absorption types is feasible for various experimental setups.

Abstract

The linear and phase insensitive absorption of a single quanta via coherent interactions with a saturable system, even a single ground state qubit, is sufficient to deterministically generate quantum non-Gaussian states in an oscillator, even stimulated merely by increasing thermal oscillator energy. However, the resultant states only approach Fock states and therefore do not exhibit quantum coherence. Here we overcome this limitation using a minimal step: a nonlinear phase-insensitive absorption process added to the linear one. The coherent addition of such individually passive processes allows coherence to emerge and increase in phase space without an external drive and with minimal interaction requirements. The coherence of quantum non-Gaussian states emerges because the linear and nonlinear absorption processes are not mutually passive. In the simplest case rotationally symmetric Wigner functions of the oscillator Fock states convert their many negative regions to an extremely complex asymmetric structure in sharp contrast to the rotational symmetry of those obtained by the individual interactions. We extend this case to include an unsaturable absorber (oscillator) and analyse switching between linear and nonlinear absorptions, suitable for broad classes of experiments.