Software-based phase locking of squeezed light with balanced photodetection

The detection of squeezed light has numerous applications in quantum optical communications, metrology, and photonic quantum computing. Balanced detection with coherent receivers provides a straightforward way to measure the quadrature statistics of these states for quantum state tomography. In this work, we develop a software-based phase-locking scheme compatible with any balanced detection setup using the coherent receiver output as the error signal. Due to its ease of use and software-based implementation, the developed scheme allows phase locking of squeezed light to an arbitrary quadrature without adding optical taps or lossy optical components. We implement our phase locking scheme with an off-the-shelf coherent receiver and an on-chip coherent receiver integrated on a silicon photonics platform. We develop a phase noise model to characterize the effectiveness of the locking scheme and quantify the errors in both phase-locked experimental setups.