arXiv subjects

K. Toyoda

Publications and source records attributed to K. Toyoda.

7 recordsLinked to original sources

arXiv2023

A search for $\mu^+\to e^+\gamma$ with the first dataset of the MEG II experiment

The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay $\mu^+\to e^+\gamma$ from data taken in the first physics run in 2021. No excess of events over the expected background is observed, yielding an upper limit on the branching ratio of B($\mu^+\to e^+\gamma$) < $7.5 \times 10^{-13}$ (90% C.L.). The combination of this result and the limit obtained by MEG gives B($\mu^+\to e^+\gamma$) < $3.1 \times 10^{-13}$ (90% C.L.), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022-2023, and data-taking will continue in the coming years.

hep-ex↗

arXiv2023

Operation and performance of MEG II detector

The MEG II experiment, located at the Paul Scherrer Institut (PSI) in Switzerland, is the successor to the MEG experiment, which completed data taking in 2013. MEG II started fully operational data taking in 2021, with the goal of improving the sensitivity of the mu+ -> e+ gamma decay down to 6e-14 almost an order of magnitude better than the current limit. In this paper, we describe the operation and performance of the experiment and give a new estimate of its sensitivity versus data acquisition time.

physics.ins-det↗

arXiv2022

Study on degradation of VUV-sensitivity of MPPC for liquid xenon scintillation detector by radiation damage in MEG II experiment

In the MEG II experiment, the liquid xenon gamma-ray detector uses Multi-Pixel Photon Counters (MPPC) which are sensitive to vacuum ultraviolet (VUV) light under a high-intensity muon beam environment. In the commissioning phase of the detector with the beam, a significant degradation in the photon detection efficiency (PDE) for VUV light was found, while the degradation in the PDE for visible light was much less significant. This implies that the radiation damage is localized to the surface of the MPPC where incoming VUV photons create electron-hole pairs. It was also found that the PDE can recover to the original level by thermal annealing.

physics.ins-det↗

arXiv2020

Search for lepton flavour violating muon decay mediated by a new light particle in the MEG experiment

We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, $μ^+ \to \mathrm{e}^+\mathrm{X}, \mathrm{X} \to γγ$. This search uses a dataset resulting from $7.5\times 10^{14}$ stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013. No significant excess is found in the mass region 20--45 MeV/c$^2$ for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20--40 MeV/c$^2$, down to $\mathcal{O}(10^{-11})$ at 90\% confidence level.

hep-ex↗

arXiv2013

Realization of holonomic single-qubit operations

Universal single-qubit operations based on purely geometric phase factors in adiabatic processes are demonstrated by utilizing a four-level system in a trapped single $^{40}$Ca$^+$ ion connected by three oscillating fields. Robustness against parameter variations is studied. The scheme demonstrated here can be employed as a building block for large-scale holonomic quantum computations, which may be useful for large qubit systems with statistical variations in system parameters.

quant-ph↗

arXiv2011

Generation of Dicke states using adiabatic passage

Entangled states of two ions are realized by using an adiabatic process. Based on the proposal by Linington and Vitanov, we have generated Dicke states in optical qubits of two $^{40}$Ca$^+$ ions by applying frequency-chirped optical pulses with time-dependent envelopes to perform rapid adiabatic passage on sideband transitions. One of the biggest advantages of adiabatic approaches is their robustness against variations in experimental parameters, which is verified by performing experiments for different pulse widths or peak Rabi frequencies. Fidelities exceeding 0.5, which is the threshold for inseparable states, are obtained over wide ranges of parameter values.

quant-ph↗

arXiv2010

Quantum gate using qubit states separated by terahertz

A two-qubit quantum gate is realized using electronic excited states in a single ion with an energy separation on the order of a terahertz times the Planck constant as a qubit. Two phase locked lasers are used to excite a stimulated Raman transition between two metastable states $D_{3/2}$ and $D_{5/2}$ separated by 1.82 THz in a single trapped $^{40}$Ca$^+$ ion to construct a qubit, which is used as the target bit for the Cirac-Zoller two-qubit controlled NOT gate. Quantum dynamics conditioned on a motional qubit is clearly observed as a fringe reversal in Ramsey interferometry.

quant-ph↗