Kenta Takata

Network of time-multiplexed optical parametric oscillators as a coherent Ising machine

A network of four degenerate optical parametric oscillators (OPOs) is employed to find the ground state of the Ising Hamiltonian. The good performance of the network reveals the potential of OPOs for many similar problems.

Mapping of Ising models onto injection-locked laser systems.

We propose a mapping protocol to implement Ising models in injection-locked laser systems. The proposed scheme is based on optical coherent feedback and can be potentially applied for large-scale Ising problems.

Quantum correlation in degenerate optical parametric oscillators with mutual injections

We theoretically and numerically study the quantum dynamics of two degenerate optical parametric oscillators with mutual injections. The cavity mode in the optical coupling path between the two oscillator facets is explicitly considered. Stochastic equations for the oscillators and mutual injection path based on the positive

Valence-band structure of ferromagnetic semiconductor (In,Ga,Mn)As

P

A 16-bit Coherent Ising Machine for One-Dimensional Ring and Cubic Graph Problems

representation are derived. The system of two gradually pumped oscillators with out-of-phase mutual injections is simulated, and its quantum state is investigated. When the incoherent loss of the oscillators other than the mutual injections is small, the squeezed quadratic amplitudes

Coherent control of high efficiency metasurface beam deflectors with a back partial reflector

\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}

Quantum Computing vs. Coherent Computing

in the oscillators are positively correlated near the oscillation threshold. It indicates finite quantum correlation, estimated via Gaussian quantum discord, and the entanglement between the intracavity subharmonic fields. When the loss in the injection path is low, each oscillator around the phase transition point forms macroscopic superposition even under a small pump noise. It suggests that the squeezed field stored in the low-loss injection path weakens the decoherence in the oscillators.

Binary phase oscillation of two mutually coupled semiconductor lasers.

To clarify the whole picture of the valence-band structures of prototype ferromagnetic semiconductors (III,Mn)As (III: In and Ga), we perform systematic experiments of the resonant tunneling spectroscopy on [(In_0.53Ga_0.47)_1-x Mn_x]As (x=0.06-0.15) and In_0.87Mn_0.13As grown on AlAs/ In_0.53Ga_0.47As:Be/ p+InP(001). We show that the valence band of InGaMnAs almost remains unchanged from that of the host semiconductor InGaAs, that the Fermi level exists in the band gap, and that the p-d exchange splitting in the valence band is negligibly small in (InGaMn)As. In the In0.87Mn0.13As sample, although the resonant peaks are very weak due to the large strain induced by the lattice mismatch between InP and InMnAs, our results also indicate that the Fermi level exists in the band gap and that the p-d exchange splitting in the valence band is negligibly small. These results are quite similar to those of GaMnAs obtained by the same method, meaning that there are no holes in the valence band, and that the impurity-band holes dominate the transport and magnetism both in the InGaMnAs and In_0.87Mn_0.13As films. This band picture of (III,Mn)As is remarkably different from that of II-VI-based diluted magnetic semiconductors.

A Degenerate Optical Parametric Oscillator Network for Coherent Computation

Many tasks in our modern life, such as planning an efficient travel, image processing and optimizing integrated circuit design, are modeled as complex combinatorial optimization problems with binary variables. Such problems can be mapped to finding a ground state of the Ising Hamiltonian, thus various physical systems have been studied to emulate and solve this Ising problem. Recently, networks of mutually injected optical oscillators, called coherent Ising machines, have been developed as promising solvers for the problem, benefiting from programmability, scalability and room temperature operation. Here, we report a 16-bit coherent Ising machine based on a network of time-division-multiplexed femtosecond degenerate optical parametric oscillators. The system experimentally gives more than 99.6% of success rates for one-dimensional Ising ring and nondeterministic polynomial-time (NP) hard instances. The experimental and numerical results indicate that gradual pumping of the network combined with multiple spectral and temporal modes of the femtosecond pulses can improve the computational performance of the Ising machine, offering a new path for tackling larger and more complex instances.

Coherent Computing with Injection-Locked Laser Network

Recently, coherent control of absorption in metallic metasurfaces has been demonstrated, and this phenomenon was applied to intriguing light-by-light switching operation. Here we experimentally demonstrate coherent control of beam deflection by high-efficiency metasurfaces for the first time. Although the beam deflection efficiency by a metasurface is generally small, high-efficiency metasurfaces, which consist of a single layer metasurface with a back reflector, are known to exhibit significantly high deflection efficiency. A key point of our study is to replace the back reflector with a partial reflector instead, which enables light-by-light control of a high-efficiency metasurface with a pair of counter-propagating coherent beam inputs. By adjusting the partial reflector thickness appropriately, the proposed device outperforms ones without a reflector, especially for the deflection efficiency. We finally experimentally demonstrate the expected operation of the fabricated device at a visible wavelength,...