Over-8-dB squeezed light generation by a broadband waveguide optical parametric amplifier toward fault-tolerant ultra-fast quantum computers

TL;DR

This paper reports the generation of over 8 dB of broadband squeezed light using a waveguide optical parametric amplifier, advancing quantum computing capabilities by improving detection efficiency and phase stability.

Contribution

The work demonstrates the first over-8-dB squeezing with waveguide OPAs without loss or circuit-noise correction, highlighting optimized experimental parameters for enhanced squeezing levels.

Findings

Achieved 8.3 dB squeezing in continuous-wave broadband light.

Optimized phase-locking and detection methods to improve squeezing.

Estimated potential of over 10 dB squeezing immediately after the waveguide.

Abstract

We achieved continuous-wave 8.3-dB squeezed light generation using a terahertz-order-broadband waveguide optical parametric amplifier (OPA) by improving a measurement setup from our previous work [T. Kashiwazaki, et al., Appl. Phys. Lett. 119, 251104 (2021)], where a low-loss periodically poled lithium niobate (PPLN) waveguide had shown 6.3-dB squeezing at a 6-THz frequency. First, to improve efficiency of the squeezed light detection, we reduced effective optical loss to about 12% by removing extra optics and changing the detection method into a low-loss balanced homodyne measurement. Second, to minimize phase-locking fluctuation, we constructed a frequency-optimized phase-locking system by comprehending its frequency responses. Lastly, we found optimal experimental parameters of a measurement frequency and a pump power from their dependences for the squeezing levels. The measurement frequency was decided as 11 MHz to maximize a clearance between shot and circuit noises. Furthermore, pump power was optimized as 660 mW to get higher squeezing level while suppressing anti-squeezed-noise contamination due to an imperfection of phase locking. To our knowledge, this is the first achievement of over-8-dB squeezing by waveguide OPAs without any loss-correction and circuit-noise correction. Moreover, it is shown that the squeezing level soon after our PPLN waveguide is estimated at over 10 dB, which is thought to be mainly restricted by the waveguide loss. This broadband highly-squeezed light opens the possibility to realize fault-tolerant ultra-fast optical quantum computers.