Quantum frequency conversion of vacuum squeezed light to bright tunable blue squeezed light and higher-order spatial modes

TL;DR

This paper demonstrates the experimental conversion of vacuum squeezed light at 1064 nm into bright tunable blue squeezed light at around 472 nm using sum-frequency generation, preserving quantum coherence and enabling higher-order spatial modes.

Contribution

It introduces a method for quantum frequency conversion that preserves quantum coherence and enables spatial mode conversion, expanding the capabilities of non-classical light sources.

Findings

Successfully converted vacuum squeezed light to bright blue squeezed light.

Preserved quantum squeezing during frequency conversion.

Achieved simultaneous frequency and spatial mode conversion.

Abstract

Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm $\pm$ 50 nm for the generation of bright squeezed light at 472~nm $\pm$ 4~nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2($\pm0.2$)~dB 1064 nm vacuum squeezed state is converted to a 1.6($\pm$0.2)~dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1($\pm$0.2)~dB and 0.4($\pm$0.2)~dB of squeezing in the TEM$_{01}$ and TEM$_{02}$ modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.