Extended analysis of distillation and purification of squeezed states of light

TL;DR

This paper provides an extended theoretical analysis of squeezing distillation and purification, introducing a flexible scheme combining photon subtraction with weak displacement, and proposing a Fock-state filter to improve squeezing from mixed states.

Contribution

It introduces a generalized scheme for squeezing enhancement, including a Fock-state filter, and explores connections to GKP state generation, advancing quantum optics resource distillation techniques.

Findings

Enhanced squeezing for arbitrary input levels using combined photon subtraction and displacement.

Arbitrary strong squeezing can be distilled with proper Gaussification.

Fock-state filter enables purification from mixed states despite losses.

Abstract

Squeezed states of light are one of the most important fundamental resources for quantum optics, optical quantum information processing and quantum sensing. Recently, it has been experimentally demonstrated that the squeezing of single-mode squeezed vacuum states can be enhanced by probabilistic two-photon subtraction. A further enhancement of the squeezing is subsequently possible by heralded Gaussification that distills a Gaussian state from the de-Gaussified two-photon subtracted state. Here we provide an extended theoretical analysis of squeezing distillation and purification. We consider a more general scheme in which photon subtraction is combined with a weak coherent displacement. This more flexible scheme allows to enhance squeezing for arbitrary input squeezing value. Moreover, if the modified two-photon subtraction operation is properly chosen, then arbitrary strong squeezing can be distilled by subsequent Gaussification. We go beyond pure states and show that the combination of photon subtraction and heralded Gaussification cannot suppress losses that have affected the input state. To overcome this limitation, we propose an alternative de-Gaussifying operation based on a Fock-state filter that removes the single-photon state. With this de-Gaussifying operation and subsequent re-Gaussification, pure single-mode squeezed states can be distilled from a large class of mixed input states. Interestingly, we have found that squeezing distillation by two-photon subtraction is closely related to certain methods for generating Gottesman-Kitaev-Preskill (GKP) states, which are crucial for optical quantum computing.