Computers based on physical systems are increasingly anticipated to overcome the impending limitations on digital computer performance. One such computer is a coherent Ising machine (CIM) for solving combinatorial optimization problems. Here, we report a CIM with 100,512 degenerate optical parametric oscillator pulses working as the Ising spins. We show that the CIM delivers fine solutions to maximum cut problems of 100,000-node graphs drastically faster than standard simulated annealing. Moreover, the CIM, when operated near the phase transition point, provides some extremely good solutions and a very broad distribution. This characteristic will be useful for applications that require fast random sampling such as machine learning.
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 to avoid degradation of squeezing. In addition, the directly bonded ZnO-doped waveguide has durability for highpower 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.
We experimentally demonstrated the simultaneous nonlinearity mitigation of PDM-16QAM WDM signals using complementary-spectrally-inverted optical phase conjugation (CSI-OPC). We achieved reserved-band-less, guard-band-less, and polarization independent OPC based on periodically poled LiNbO3 waveguides. By employing the CSI-OPC, 2.325-THz-band (93 × 25 GHz) complementary spectral inversion was achieved while retaining the original WDM bandwidth. A Q2-factor improvement of over 0.4 dB and a 5120 km transmission with a Q2-factor above the FEC limit were confirmed using a 10-channel WDM transmission at the signal band center and signal band edge. We then demonstrated the mitigation of the nonlinear impairments in a 3840 km long-haul WDM signal transmission for all 92-channel 180-Gbit/s PDM-16QAM quasi-Nyquist-WDM signals.
This paper proposes an optical parametric amplifier (OPA), as an inline-repeater, using a periodically-poled-LiNbO3 (PPLN) waveguide with over-10-THz amplification bandwidth, and also presents wide-band wavelength-division-multiplexing (WDM) inline-amplified transmission with the OPA. Our PPLNbased OPA is polarization-independent and has a spectrally efficient configuration by filtering phase-conjugated signals (idlers). We implemented our PPLN-based OPA with half its ideal configuration with an over-10-THz amplification bandwidth because of the limited number of PPLN waveguides. The implemented OPA had 5.125-THz amplification bandwidth, gain of beyond 15 dB, and noise figure of less than 5.1-dB. The gain excludes the 5.6-dB loss of an idler rejection filter employed in the transmission experiment so that the implemented OPA can compensate 9.5-dB link loss of transmission fibers and optical components. A 3 × 30.8-km inline-amplified transmission with 41channel 800-Gbps WDM signal in 125-GHz spacing was successfully demonstrated using our PPLN-based OPA as an inline-repeater. The results also indicate that the OPA's amplification bandwidth can potentially be extended to 10.25 THz.
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