Projective filtering of a single spatial radiation eigenmode

TL;DR

This paper presents a method for lossless filtering of a single spatial mode from bright squeezed vacuum, enabling precise mode selection without degrading the quantum properties, which is vital for quantum optics applications.

Contribution

The authors demonstrate a technique to project and filter a single spatial Schmidt mode from bright squeezed vacuum without loss, preserving its quantum features for further use.

Findings

Lossless filtering of a single spatial mode achieved

First Schmidt mode captured by maximizing fiber-coupled intensity

Projection operation preserves the mode for subsequent applications

Abstract

Lossless filtering of a single coherent (Schmidt) mode from spatially multimode radiation is a problem crucial for optics in general and for quantum optics in particular. It becomes especially important in the case of nonclassical light that is fragile to optical losses. An example is bright squeezed vacuum generated via high-gain parametric down conversion or four-wave mixing. Its highly multiphoton and multimode structure offers a huge increase in the information capacity provided that each mode can be addressed separately. However, the nonclassical signature of bright squeezed vacuum, photon-number correlations, are highly susceptible to losses. Here we demonstrate lossless filtering of a single spatial Schmidt mode by projecting the spatial spectrum of bright squeezed vacuum on the eigenmode of a single-mode fiber. Moreover, we show that the first Schmidt mode can be captured by simply maximizing the fiber-coupled intensity. Importantly, the projection operation does not affect the targeted mode and leaves it usable for further applications.