Toward a multi-core ultra-fast optical quantum processor: 43-GHz bandwidth real-time amplitude measurement of 5-dB squeezed light using modularized optical parametric amplifier with 5G technology



Asuka Inoue, Takahiro Kashiwazaki, Taichi Yamashima, Naoto Takanashi, Takushi Kazama, Koji Enbutsu, Kei Watanabe, Takeshi Umeki, Mamoru Endo, and Akira Furusawa


Continuous-variable optical quantum information processing, where quantum information is encoded in a traveling wave of light called a f lying qubit, is a candidate for a practical quantum computer with high clock frequencies. Homodyne detectors for quadrature-phase amplitude measurements have been the major factor limiting the clock frequency. Here, we developed a real-time amplitude measurement method using a modular optical parametric amplifier (OPA) and a broadband balanced photodiode that is commercially used for coherent wavelength-division multiplexing telecommunication of the fifth-generation mobile communication systems (5G). The OPA amplifies one quadrature-phase component of the quantum-level signal to a loss-tolerant macroscopic level and suppresses the loss after the OPA from 92.4% to only 0.4%. This method was applied to a broadband squeezed vacuum measurement with a center wavelength of 1545.32nm. In the time-domain measurement, the squeezing level of 5.160.1dB without loss correction was obtained by a real-time oscilloscope with a sampling rate of 160GHz and an analog bandwidth of 63GHz. The frequency-domain analysis also shows that a squeezing level of 5.260.5dB is obtained from DC to 43GHz, which is limited by the balanced detector. This indicates that the proposed method can be easily broadened by using a broader bandwidth measurement instrument. By applying this method, not only can optical quantum computers with high clock frequencies be realized but also multi-core systems can be realized.



Applied Physics Letters: