Generation of Over-8-dB Squeezed Light by a Broadband Waveguide Optical Parametric Amplifier Toward Fault-Tolerant Quantum Computers

Measurement-based optical quantum computers (MBOQCs) using continuous-variables (CVs) of traveling wave of light have a potential for ultra-fast fault-tolerant quantum information processing [1]. In CV MBOQCs, broadband high-level squeezed light is the most essential quantum resource. Broad bandwidth not only enables high-clock frequency computation, but also contributes to the realization of large-scale quantum computers using time-domain-multiplexed quantum entanglement. This is because squeezed light with a broader bandwidth enables us to define many more quantum wave packets in a narrow time range. On the other hand, high-level squeezing contributes to high-fidelity quantum operation and suppression of quantum errors. For example, over-8.3-dB squeezing enables us to achieve a fault-tolerant CV MBOQC with Gottesman-Kitaev-Preskill (GKP) coding [2].