Ultra-fast Continuous-wave Homodyne Measurement of Schrödlnger Cat States with 40-Ps Wavepackets

Light has a high carrier frequency of hundreds of THz and has the potential to realize ultrafast quantum information processing. Time-domain multiplexed continuous-variable optical quantum computation has recently attracted much attention [1]. In this method, it is important to encode optical quantum states in wavepackets with short temporal widths because the width of the quantum state determines the clock frequency of the computation. So far, in the continuous-wave (CW) light field, this wavepacket width has been limited by the bandwidth of homodyne measurements, which read out the quadratures of the quantum state. Recently, a technique using phase-sensitive amplifiers (PSAs) and broadband homodyne detectors with CW light has been developed [2]. Using that, the wavepacket width of quantum entangled states was successfully shortened to the picosecond scale [3]. However, the wavepacket width of the Schrödinger cat state, which is a phase-sensitive non-Gaussian state, was limited to the sub-nanosecond scale due to the timing jitter of the photon detector [4].