Continuous-wave 6-dB-squeezed light with 2.5-THz-bandwidth from single-mode PPLN waveguide

• Published in: APL photonics Vol. 5; no. 3; pp. 036104 - 036104-7
• Main Authors: Kashiwazaki, Takahiro, Takanashi, Naoto, Yamashima, Taichi, Kazama, Takushi, Enbutsu, Koji, Kasahara, Ryoichi, Umeki, Takeshi, Furusawa, Akira
• Format: Journal Article
• Language: English
• Published: AIP Publishing LLC 01.03.2020
• ISSN: 2378-0967; 2378-0967
• DOI: 10.1063/1.5142437

Terahertz (THz)-bandwidth continuous-wave (CW) squeezed light is essential for integrating quantum processors with time-domain multiplexing (TDM) by using optical delay line interferometers. Here, we utilize a single-pass optical parametric amplifier (OPA) based on a single-spatial-mode periodically poled ZnO:LiNbO3 waveguide, which is directly bonded onto a LiTaO3 substrate. The single-pass OPA allows THz bandwidth, and the absence of higher-order spatial modes in the single-spatial-mode structure helps avoid degradation of squeezing. In addition, the directly bonded ZnO-doped waveguide has durability for high-power pump and shows small photorefractive damage. Using this waveguide, we observe CW 6.3-dB squeezing at 20-MHz sideband by balanced homodyne detection. This is the first realization of CW squeezing with a single-pass OPA at a level exceeding 4.5 dB, which is required for the generation of a two-dimensional cluster state. Furthermore, the squeezed light shows 2.5-THz spectral bandwidth. The squeezed light will lead to the development of a high-speed on-chip quantum processor using TDM with a centimeter-order optical delay line.