arXiv subjects

Yosuke Ito

Publications and source records attributed to Yosuke Ito.

5 recordsLinked to original sources

arXiv2026

QuBE/Qubex: an integrated hardware-software system for superconducting qubit experiments with broadband control

Achieving high-fidelity operation in large-scale superconducting qubit systems requires not only control hardware with broad frequency coverage, low crosstalk, and tight synchronization but also software that coordinates system configuration, experiment execution, and data analysis. Here we present an integrated qubit-control system that combines broadband microwave hardware with a pulse-level software stack for scalable superconducting qubit experiments. The hardware provides broadband microwave coverage, including an instantaneous span of up to 1.6 GHz from a control output, while the software reduces setup and calibration overhead through automated configuration and built-in experiment workflows. We validate the system on a 64-qubit fixed-frequency transmon chip through full-chip frequency identification and representative demonstrations, including multi-unit far-detuned cross-resonance calibration and benchmarking that yields a measured two-qubit gate fidelity of 98.34%, and multilevel readout beyond the computational subspace. By disclosing the hardware architecture and releasing the software stack as open source, this work provides an inspectable hardware-software foundation for scalable superconducting qubit control experiments.

quant-ph↗

arXiv2025

Microwave Output Stabilization of a Qubit Controller via Device-Level Temperature Control

We present the design and performance of QuEL-1 SE, which is a multichannel qubit controller developed for superconducting qubits. The system incorporates the active thermal stabilization of critical analog integrated circuits, such as phase-locked loops, amplifiers, and mixers, to suppress the long-term amplitude and phase drift. To evaluate the amplitude and phase stability, we simultaneously monitor 15 microwave output channels over 24 h using a common analog-to-digital converter. Across the channels, the normalized amplitude exhibits standard deviations of 0.09\%--0.22\% (mean: 0.15\%), and the phase deviations are 0.35$^\circ$--0.44$^\circ$ (mean: 0.39$^\circ$). We further assess the impact of these deviations on quantum gate operations by estimating the average fidelity of an $X_{\pi/2}$ gate under the coherent errors corresponding to the deviations. The resulting gate infidelities are $2\times 10^{-6}$ for amplitude errors and $2\times 10^{-5}$ for phase errors, which are significantly lower than typical fault-tolerance thresholds such as those of the surface code. These results demonstrate that the amplitude and phase stability of QuEL-1 SE enables reliable long-duration quantum operations, thus highlighting its utility as a scalable control platform for superconducting and other qubit modalities.

quant-ph↗

arXiv2025

Selective Excitation of Superconducting Qubits with a Shared Control Line through Pulse Shaping

In conventional architectures of superconducting quantum computers, each qubit is connected to its own control line, leading to a commensurate increase in the number of microwave lines as the system scales. Frequency-multiplexed qubit control addresses this problem by enabling multiple qubits to share a single microwave line. However, it can cause unwanted excitation of non-target qubits, especially when the detuning between qubits is smaller than the pulse bandwidth. Here, we propose a selective-excitation-pulse (SEP) technique that suppresses unwanted excitations by shaping a drive pulse to create null points at non-target qubit frequencies. In a proof-of-concept experiment with three fixed-frequency transmon qubits, we demonstrate that the SEP technique achieves single-qubit gate fidelities comparable to those obtained with conventional Gaussian pulses while effectively suppressing unwanted excitations in non-target qubits. These results highlight the SEP technique as a promising tool for enhancing frequency-multiplexed qubit control.

quant-ph↗

arXiv2024

Simplified Shielded MEG-MRI Multimodal System with Scalar-mode Optically Pumped Magnetometers as MEG Sensors

Magnetoencephalography (MEG) conventionally operates within high-performance magnetic shields due to the extremely weak magnetic field signals from the measured objects and the narrow dynamic range of the magnetic sensors employed for detection. This limitation results in elevated equipment costs and restricted usage. Additionally, the information obtained from MEG is functional images, and to analyze from which part of the brain the signals are coming, it is necessary to capture morphological images separately. When MEG and morphological imaging devices are separate, despite their individual high measurement accuracies, discrepancies in positional information may arise. In response, we have developed a low-field magnetic resonance imaging system that incorporates scalar-mode optically pumped magnetometers with a wide dynamic range and exceptionally high measurement sensitivity as sensors for MEG. Operating at low magnetic fields eliminates the need for superconducting coils in magnetic resonance imaging and the high-performance magnetic shields essential for MEG, promising a substantial cost reduction compared to traditional approaches. We achieved a noise level of about $16\,\rm{pT/Hz}^{1/2}$ with a single channel magnetometer, and reached a noise level of $367\,\rm{fT/cm/Hz}^{1/2}$ through differential measurements. The system successfully conducted MR imaging on a phantom, demonstrating the potential of MEG and MRI fusion.

physics.med-ph↗

arXiv2015

On the Existence of Generalized Parking Spaces for Complex Reflection Groups

Let $W$ be an irreducible finite complex reflection group acting on a complex vector space $V$. For a positive integer $k$, we consider a class function $φ_k$ given by $φ_k(w) = k^{\dim V^w}$ for $w \in W$, where $V^w$ is the fixed-point subspace of $w$. If $W$ is the symmetric group of $n$ letters and $k=n+1$, then $φ_{n+1}$ is the permutation character on (classical) parking functions. In this paper, we give a complete answer to the question when $φ_k$ (resp. its $q$-analogue) is the character of a representation (resp. the graded character of a graded representation) of $W$. As a key to the proof in the symmetric group case, we find the greatest common divisors of specialized Schur functions. And we propose a unimodality conjecture of the coefficients of certain quotients of principally specialized Schur functions.

math.CO↗