Hayato Goto

Experimental determination of intracavity losses of monolithic Fabry-Perot cavities made of Pr 3+ :Y 2 SiO 5

We propose an experimental method with which all the following quantities can be determined separately: the intracavity loss and individual cavity-mirror transmittances of a monolithic Fabry-Perot cavity and furthermore the coupling efficiency between the cavity mode and the incident light. It is notable that the modified version of this method can also be applied to whispering-gallery-mode cavities. Using this method, we measured the intracavity losses of monolithic Fabry-Perot cavities made of Pr3+:Y2SiO5 at room temperature. The knowledge of the intracavity losses is very important for applications of such cavities, e.g., to quantum information technologies. It turns out that fairly high losses (about 0.1%) exist even for a sample with extremely low dopant concentration (2×10(-5) at. %). The experimental results also indicate that the loss may be mainly due to the bulk loss of Y2SiO5 crystal. The bulk loss is estimated to be 7×10(-4) cm(-1) (0.003 dB/cm) or lower.

Condition for fault-tolerant quantum computation with a cavity-QED scheme

A condition for fault-tolerant quantum computation (FTQC) with cavity schemes is discussed. It is shown that the condition is very hard if the standard error threshold of FTQC is simply applied. To relax the condition, we propose to combine the cavity-quantum-electrodynamics (QED) scheme proposed by Duan et al. [Phys. Rev. A 72, 032333 (2005)] and Xiao et al. [Phys. Rev. A 70, 042314 (2004)] with the recently proposed FTQC scheme with probabilistic two-qubit gates [Goto and Ichimura, Phys. Rev. A 80, 040303(R) (2009)]. It is shown that the condition for FTQC is dramatically relaxed compared to the case of the standard threshold. The optimization of the cavity-QED scheme is also discussed.

Cavity-enhanced spectroscopy of a rare-earth-ion-doped crystal: Observation of a power law for inhomogeneous broadening

We report an erratum regarding the polarization of the probe in the experiment reported in our paper [Opt. Express21, 24332-24343 (2013)]. Although we wrote in the paper that the polarization of the probe is set to be parallel to the D2 axis of YSO crystal, we found that the polarization was parallel to the D1 axis of YSO crystal. However, this fact does not affect the two main results of the work: observation of very small absorption and the power law for the inhomogeneous broadening.

Boltzmann sampling from the Ising model using quantum heating of coupled nonlinear oscillators

A network of driven nonlinear oscillators without dissipation has recently been proposed for solving combinatorial optimization problems via quantum adiabatic evolution through its bifurcation point. Here we investigate the behavior of the quantum bifurcation machine in the presence of dissipation. Our numerical study suggests that the output probability distribution of the dissipative quantum bifurcation machine is Boltzmann-like, where the energy in the Boltzmann distribution corresponds to the cost function of the optimization problem. We explain the Boltzmann distribution by generalizing the concept of quantum heating in a single oscillator to the case of multiple coupled oscillators. The present result also suggests that such driven dissipative nonlinear oscillator networks can be applied to Boltzmann sampling, which is used, e.g., for Boltzmann machine learning in the field of artificial intelligence.A network of Kerr-nonlinear parametric oscillators without dissipation has recently been proposed for solving combinatorial optimization problems via quantum adiabatic evolution through its bifurcation point. Here we investigate the behavior of the quantum bifurcation machine (QbM) in the presence of dissipation. Our numerical study suggests that the output probability distribution of the dissipative QbM is Boltzmann-like, where the energy in the Boltzmann distribution corresponds to the cost function of the optimization problem. We explain the Boltzmann distribution by generalizing the concept of quantum heating in a single nonlinear oscillator to the case of multiple coupled nonlinear oscillators. The present result also suggests that such driven dissipative nonlinear oscillator networks can be applied to Boltzmann sampling, which is used, e.g., for Boltzmann machine learning in the field of artificial intelligence.

Longitudinally excited CO2 laser with short laser pulse and high quality beam

We developed a longitudinally excited CO2 laser with a tail-free short pulse and a high quality beam. The laser system had a longitudinal discharge tube, a long optical cavity and a simple driver circuit. The discharge tube was made of an alumina ceramic pipe with an inner diameter of 16 mm and a length of 45 cm, two metallic electrodes and two windows. Gas medium was a 20:1 mixture of CO2/N2 at a pressure of 2.6 kPa. The optical cavity with the length of 180 cm was formed by an output coupler with a reflectivity of 70% and a high-reflection mirror. The optical cavity had an aperture or did not. The driver circuit consisted of −600 V pulse power supply and a primary capacitance of 9.6 μF, a step-up transformer, a storage capacitance of 700 pF, a spark gap and the discharge tube. The CO2 laser produced a tail-free short pulse with the width of 281 ns. The CO2 laser beam was a ununifomly distributed circular beam with the M2 factor of 22.8 in the laser system without an aperture, a top-hat shape of circular beam with the M2 factor of 9.61 in the laser system with a φ11-mm aperture, 5.40 in the laser system with a φ9-mm aperture, or a Gaussian shape of circular beam with the M2 factor of 3.01 in the laser system with a φ7-mm aperture.

Large-scale Ising-machines composed of magnetic neurons

We propose Ising-machines composed of magnetic neurons, that is, magnetic bits in a recording track. In large-scale machines, the sizes of both neurons and synapses need to be reduced, and neat and smart connections among neurons are also required to achieve all-to-all connectivity among them. These requirements can be fulfilled by adopting magnetic recording technologies such as race-track memories and skyrmion tracks because the area of a magnetic bit is almost two orders of magnitude smaller than that of static random access memory, which has normally been used as a semiconductor neuron, and the smart connections among neurons are realized by using the read and write methods of these technologies.We propose Ising-machines composed of magnetic neurons, that is, magnetic bits in a recording track. In large-scale machines, the sizes of both neurons and synapses need to be reduced, and neat and smart connections among neurons are also required to achieve all-to-all connectivity among them. These requirements can be fulfilled by adopting magnetic recording technologies such as race-track memories and skyrmion tracks because the area of a magnetic bit is almost two orders of magnitude smaller than that of static random access memory, which has normally been used as a semiconductor neuron, and the smart connections among neurons are realized by using the read and write methods of these technologies.