Tunable passive squeezing of squeezed light through unbalanced double homodyne detection

TL;DR

This paper introduces a method using unbalanced double homodyne detection to passively perform tunable squeezing on quantum light states, enabling both state characterization and manipulation within a single setup.

Contribution

It demonstrates that unbalanced double homodyne detection can effectively implement tunable squeezing transformations during quantum state measurement.

Findings

Successfully realized tunable squeezing via unbalanced detection

Controlled deformation of the Q function confirmed

Technique enables simultaneous state characterization and manipulation

Abstract

The full characterization of quantum states of light is a central task in quantum optics and information science. Double homodyne detection provides a powerful method for the direct measurement of the Husimi Q quasi-probability distribution, offering a complete state representation in a simple experimental setting and a limited time frame. Here, we demonstrate that double homodyne detection can serve as more than a passive characterization tool. By intentionally unbalancing the input beamsplitter that splits the quantum signal, we show that the detection scheme itself performs an effective squeezing or anti-squeezing transformation on the state being measured. The resulting measurement directly samples the Q function of the input state as if it were acted upon by a squeezing operator whose strength is a tunable experimental parameter: the beamsplitter's reflectivity. We experimentally realize this technique using a robust polarization-encoded double homodyne detection to characterize a squeezed vacuum state. Our results demonstrate the controlled deformation of the measured Q function's phase-space distribution, confirming that unbalanced double homodyne detection is a versatile tool for simultaneous quantum state manipulation and characterization.