Generation of Schrödinger cat states with Wigner negativity using a continuous-wave low-loss waveguide optical parametric amplifier

Abstract

Continuous-wave (CW) squeezed light is used in the generation of various optical quantum states, and thus is a fundamental resource of fault-tolerant universal quantum computation using optical continuous variables. To realize a practical quantum computer, a waveguide optical parametric amplifier (OPA) is an attractive CW squeezed light source in terms of its THz-order bandwidth and suitability for modularization. The usages of a waveguide OPA in quantum applications thus far, however, are limited due to the difficulty of the generation of the squeezed light with a high purity. In this paper, we report the first observation of Wigner negativity of the states generated by a heralding method using a waveguide OPA. We generate Schrödinger cat states at the wavelength of 1545 nm with Wigner negativity using a quasi-single-mode ZnO-doped periodically poled LiNbO3 waveguide module we developed. Wigner negativity is regarded as an important indicator of the usefulness of the quantum states as it is essential in the fault-tolerant universal quantum computation. Our result shows that our waveguide OPA can be used in wide range of quantum applications leading to a THz-clock optical quantum computer.

Generation of Highly Pure Single-Photon State at Telecommunication Wavelength

“…This result is achieved by constructing an unprecedentedly low-loss experimental system of the heralding scheme. In our previous experiments using a waveguide OPA and a SNSPD [23], the optical losses of the squeezed light source was about 10%, while in this experiment, we succeeded in reducing the optical losses of AOPO to 2% by a low-loss coatings of mirrors and a crystal.…”

“…The SNSPD used in the experiment is made of NbTiN [23]. The SNSPD is installed into an adiabatic demagnetization refrigerator and operated at the temperature of 3 K. Dark counts of the SNSPD is about 30 counts per a second (cps).…”

“…The issue on photon detection at telecommunication wavelengths is expected to be overcome by superconducting nano-strip photon detectors (SNSPDs) [21,22]. We have succeeded in generating quantum states with Wigner negativity in a system at only telecommunication wavelength (1545 nm) without wavelength conversion for the first time by using SNSPD [23]. The minimum value of Wiger negativity of the generated quantum state is recorded to be -0.12.…”

Quantum arbitrary waveform generator

“…Thanks to this, our method can be applied to recently developed efficient heralding methods [46,47] with a success probability around 10 −3 to 10 −2 . By incorporating these efficient heralding methods and Thz-bandwidth quantum light source [48,49] into our method, where the bandwidth is roughly corresponds to the trial rate of state generation, the Q-AWG in Fig. 2 (a) can operate semi-deterministically at a repetition rate over GHz.…”

“…By doing so, the temporal waveforms of the non-Gaussian states are directly decided by the impulse response of optical filters in the system. By incorporating timing control technique [24,[43][44][45], high-success-rate heralding methods [46,47], and THz-bandwidth quantum light source [48,49] into the basic idea, the Q-AWG can output states semideterministically with a repetition rate over GHz. As a demonstration, we generate non-Gaussian states with time-bin and balanced time-bin waveforms which have never been realized before.…”