arXiv subjects

Atsushi Noguchi

Publications and source records attributed to Atsushi Noguchi.

At least 19 recordsLinked to original sources

arXiv2026

Approaching Carnot Efficiency at Finite Power in an Experimentally Feasible Quantum Heat Engine

Whether a heat engine can approach Carnot efficiency while maintaining finite power is a fundamental question in finite-time thermodynamics. For classical Markovian heat engines with local interactions, the power-efficiency trade-off forbids an asymptotic approach to Carnot efficiency at finite power. In quantum systems, by contrast, degeneracy, symmetry, and collective jumps have been theoretically predicted to enable such an asymptotic attainment by enhancing activity. It has remained open, however, whether this mechanism can be realized in an experimentally implementable heat engine. In this Letter, we propose a superconducting-circuit heat engine that emulates the collective enhancement, thereby enabling an asymptotic approach to Carnot efficiency at finite power. This result demonstrates that, in an implementable model, such an enhanced dissipative mechanism circumvents the power-efficiency trade-off of classical Markovian engines. Our work connects abstract bounds in finite-time thermodynamics to a concrete circuit-QED platform and suggests a route toward quantum-device design based on collectively enhanced dissipative processes.

quant-ph↗

arXiv2026

Cryogenic Time-Division-Multiplexed Voltage Control for Scalable Trapped-Ion Quantum Processors

Trapped-ion quantum computers based on the quantum charge-coupled device architecture require on the order of ten trap electrodes per qubit, making the number of vacuum feedthroughs a bottleneck at the system scale. Time-division multiplexed (TDM)-based voltage control for trap electrodes provides a natural route to alleviate this constraint. However, previous studies have been limited to architectural proposals for static trap-potential compensation and room-temperature demonstrations of dynamic-electrode control, leaving cryogenic operation of TDM-based voltage control for static and dynamic electrodes experimentally unexplored. In this study, we develop and cryogenically validate TDM-based voltage control schemes for two distinct electrode classes. For static electrodes used in trap-potential compensation, we implement a 32-channel demultiplexed system operating at approximately 27~K, achieving an effective voltage update rate of 37.5~kHz with an output range of $\pm10~\mathrm{V}$ per channel. For dynamic electrodes used in ion operations, such as shuttling, we implement a four-channel demultiplexed system operating at approximately 14~K, achieving an effective voltage update rate of 1~MHz with a comparable output range. These results establish TDM-based voltage control as a practical approach for both electrode classes, providing a path for mitigating the vacuum feedthrough bottleneck in scalable trapped-ion quantum processors.

quant-ph↗

arXiv2026

Focusing Surface-Acoustic-Wave Resonators on Thin-Film Lithium Niobate with Transverse-Mode Suppression

Surface-acoustic-wave (SAW) resonators are a promising platform for constructing hybrid quantum systems, where confined acoustic waves enable strong interaction with various physical systems. Focusing SAW resonators, reducing mode volume while suppressing diffraction losses, have recently been investigated for application in such hybrid systems. However, the resonator leads to additional transverse-mode resonances, which cause undesired responses. In this work, we develop focusing SAW resonators on a thin-film lithium niobate on sapphire. A film thinner than the SAW wavelength allows a highly confined acoustic-wave mode to be localized on the substrate surface. By using contoured electrodes following a two-dimensional Gaussian beam shape, we make the SAW mode focused to nearly a diffraction-limited and confirm it via optical imaging. Furthermore, by engineering the spatial mode overlap of the interdigital transducer electrodes, we suppress the excitation of higher-order transverse modes.

quant-ph↗

arXiv2026

Search for Dark Photon Dark Matter with a Mass around 36.1 μeV Using a Frequency-tunable Cavity Controlled through a Coupled Superconducting Qubit

We report the results of a search for dark photon dark matter using a cavity that employs a transmon qubit as a frequency tuner. The tuning mechanism utilizes the energy level shift arising from the mode mixing between the qubit and the cavity mode. This method is advantageous as it avoids the frictional heating and electromagnetic leakage associated with mechanical tuning. We searched for a dark matter signal in the mass range $36.132 - 36.179$ $μ$eV and found no significant evidence. As a result, we set the exclusion limit on the kinetic mixing parameter down to approximately $5 \times 10^{-13}$, surpassing the existing limit set by cosmology.

hep-ex↗

arXiv2025

High-fidelity all-microwave CZ gate with partial erasure-error detection via a transmon coupler

Entangling gates between neighboring physical qubits are essential for quantum error correction. Implementing them in an all-microwave manner simplifies signal routing and control apparatus of superconducting quantum processors. We propose and experimentally demonstrate an all-microwave controlled-Z (CZ) gate that achieves high fidelity while suppressing residual ZZ interactions. Our approach utilizes a fixed-frequency transmon coupler and multi-path coupling, thereby sufficiently reducing the net transverse interaction between data transmons to suppress residual ZZ interactions. The controlled phase arises from the dispersive frequency shift of the $|gf\rangle$$\unicode{x2013}$$|eg\rangle$ transition between the coupler and one of the data transmons conditioned on the state of the other data transmon. Driving the transitions at the midpoint of two dispersively shifted resonance frequencies induces state-dependent geometric phases to achieve the CZ gate. Crucially, with this scheme, we can maintain a small net transverse interaction between two data transmons while increasing the coupling between the data and coupler transmons to accelerate the CZ-gate speed. Additionally, we measure the coupler state after the gate to detect a subset of decoherence-induced failures that occur during the gate operation. These events constitute erasure errors with known locations, enabling erasure-aware quantum error-correcting codes to improve future logical qubit performance.

quant-ph↗

arXiv2025

Trapping an Atomic Ion using Time-Division Multiplexed Digital-to-Analog Converters

Independent control of numerous electrodes in quantum charge-coupled device architectures presents a significant challenge for wiring and hardware scalability. To address this issue, we demonstrate a voltage control method based on time-division multiplexing (TDM). This approach utilizes a single high-update-rate digital-to-analog converter (DAC) to sequentially generate control signals for multiple electrodes, thereby reducing both the number of required DACs and associated wiring. We experimentally validate this concept by developing a 10-channel system that operates with only two DACs. The developed TDM-based voltage control system is applied to a surface-electrode trap, where we successfully trap a single $^{40}\mathrm{Ca}^+$ ion and demonstrate a simple ion transport primitive. This approach offers a resource-efficient and scalable solution for advanced quantum computing systems based on trapped ions.

quant-ph↗

arXiv2025

High-$Q$ membrane resonators using ultra-high-stress crystalline TiN films

High-quality-factor ($Q$) mechanical resonators are essential components for precise sensing and control of mechanical motion at a quantum level. While amorphous materials such as SiN have been widely used in high-$Q$ mechanical resonators utilizing stress-induced dissipation dilution, crystalline materials have emerging potential to achieve higher quality factors by combining low intrinsic loss and high tensile stress. In this paper, we demonstrate high-Q membrane resonators using ultra-high-stress crystalline TiN. Our membrane resonator exhibits a tensile stress exceeding 2.3 GPa and a quality factor of $Q = 8.0 \times 10^6$ at 2.2 K. By estimating the dilution factor, we infer that our TiN resonator has a intrinsic quality factor comparable to that of SiN membrane resonators. With its ultra-high stress and crystalline properties, our TiN films can serve as a powerful tool for opto- and electromechanical systems, offering highly dissipation-diluted mechanical resonators.

cond-mat.mes-hall↗

arXiv2025

Multiplexed Control at Scale for Electrode Arrays in Trapped-Ion Quantum Processors

The scaling up of trapped-ion quantum processors based on the quantum charge-coupled device (QCCD) architecture is difficult owing to the extensive electronics and high-density wiring required to control numerous trap electrodes. In conventional QCCD architectures, each trap electrode is controlled via a dedicated digital-to-analog converter (DAC). The conventional approach places an overwhelming demand on electronic resources and wiring complexity. This is because the number of trap electrodes typically exceeds the number of trapped-ion qubits. This study proposes a method that leverages a high-speed DAC to generate time-division multiplexed signals to control a large-scale QCCD trapped-ion quantum processor. The proposed method replaces conventional DACs with a single high-speed DAC that generates the complete voltage waveforms required to control the trap electrodes, thereby significantly reducing the wiring complexity and overall resource requirements. Based on realistic parameters and commercially available electronics, our analysis demonstrates that a QCCD trapped-ion quantum computer with 10,000 trap electrodes can be controlled using only 13 field-programmable gate arrays and 104 high-speed DACs. This is in stark contrast to the 10,000 dedicated DACs required by conventional control methods. Consequently, employing this approach, we developed a proof-of-concept electronic system and evaluated its analog output performance.

quant-ph↗

arXiv2025

Quantum Logic Spectroscopy of an Electron and Positron for Precise Tests of the Standard Model

We propose a scheme for quantum logic spectroscopy of an electron or positron in a Penning trap. An electron or positron in a spectroscopy trap is coupled to a remote logic electron or positron via a wire to achieve motional entanglement. By separating the two traps, one can significantly improve magnetic field homogeneity, microwave characteristics, and detection sensitivity. The proposed scheme will improve the measurement precision of the electron's and positron's magnetic moments and charge-to-mass ratios, enabling precise tests of the Standard Model of particle physics.

quant-ph↗

arXiv2025

Image Current Detection of Electrons in a Room-Temperature Paul Trap

We report the image current detection of electrons in a room-temperature Paul trap at microwave frequencies. By selectively leveraging distinct cavity modes for trapping and detection, our approach effectively extracts electron signals otherwise buried in the microwave drive used for pseudo-potential formation. When the trapped electrons resonate with the cavity mode, we observe a mode excitation and its exponential decay attributed to resistive cooling. Detuning electrons from the cavity resonance halts this decay, and sweeping electrons' secular frequency reveals their oscillatory spectrum. Implementing this experiment at cryogenic temperatures could enable the image current detection and ground-state cooling of a single electron in Paul traps.

quant-ph↗

arXiv2025

Semi-Analytical Engineering of Strongly Driven Nonlinear Systems Beyond Floquet and Perturbation Theory

Strongly driven nonlinear systems are frequently encountered in physics, yet their accurate control is generally challenging due to the intricate dynamics. In this work, we present a non-perturbative, semi-analytical framework for tailoring such systems. The key idea is heuristically extending the Floquet theory to nonlinear differential equations using the Harmonic Balance method. Additionally, we establish a novel constrained optimization technique inspired by the Lagrange multiplier method. This approach enables accurate engineering of effective potentials across a broader parameter space, surpassing the limitations of perturbative methods. Our method offers practical implementations in diverse experimental platforms, facilitating nonclassical state generation, versatile bosonic quantum simulations, and solving complex optimization problems across quantum and classical applications.

quant-ph↗

arXiv2025

Enhancing Intrinsic Quality Factors Approaching 10 Million in Superconducting Planar Resonators via Spiral Geometry

This study investigates the use of spiral geometry in superconducting resonators to achieve high intrinsic quality factors, crucial for applications in quantum computation and quantum sensing. We fabricated Archimedean Spiral Resonators (ASRs) using domain-matched epitaxially grown titanium nitride (TiN) on silicon wafers, achieving intrinsic quality factors of $Q_\mathrm{i} = (9.6 \pm 1.5) \times 10^6$ at the single-photon level and $Q_\mathrm{i} = (9.91 \pm 0.39) \times 10^7$ at high power, significantly outperforming traditional coplanar waveguide (CPW) resonators. We conducted a comprehensive numerical analysis using COMSOL to calculate surface participation ratios (PRs) at critical interfaces: metal-air, metal-substrate, and substrate-air. Our findings reveal that ASRs have lower PRs than CPWs, explaining their superior quality factors and reduced coupling to two-level systems (TLSs).

quant-ph↗

arXiv2025

Numerical Investigations of Electron Dynamics in a Linear Paul Trap

Trapped electrons have emerged as an interesting platform for quantum information processing due to their light mass, two-level spin states, and potential for fully electronic manipulation. Previous experiments have demonstrated electron trapping in Penning traps, Paul traps, on solid neon, and superfluid films. In this work, we consider electrons confined in Paul traps, with their spin states as the qubits. For this approach, if the two electrons are trapped in the same potential well, they must form Wigner crystals and remain stable under a static magnetic field to enable two-qubit gates, achievable only within certain trapping parameters. To identify feasible operating conditions, we performed numerical simulations of electron dynamics in linear Paul traps, finding the threshold temperatures required to form two-electron Wigner crystals and studying how the thresholds scale with trap frequencies. In addition, we numerically verified the cooling methods required to reach the crystallization thresholds. Lastly, we examined the stability of electrons under various magnetic field strengths and identified stable regions of trap operation.

quant-ph↗

arXiv2024

Superconducting surface trap chips for microwave-driven trapped ions

Microwave-driven trapped ion logic gates offer a promising avenue for advancing beyond laser-based logic operations. In future microwave-based operations, however, the joule heat produced by large microwave currents flowing through narrow microwave electrodes would potentially hinder improvements in gate speed and fidelity. Moreover, scalability, particularly in cryogenic trapped ion systems, is impeded by the excessive joule heat. To address these challenges, we present a novel approach: superconducting surface trap chips that integrate high-$Q$ microwave resonators with large current capacities. Utilizing sub-ampere microwave currents in superconducting Nb resonators, we generate substantial magnetic field gradients with significantly reduced losses compared to conventional metal chips. By harnessing the high $Q$ factors of superconducting resonators, we propose a power-efficient two-qubit gate scheme capable of achieving a sub-milliwatt external microwave input power at a gate Rabi frequency of 1 kHz.

quant-ph↗

arXiv2023

All-microwave manipulation of superconducting qubits with a fixed-frequency transmon coupler

All-microwave control of fixed-frequency superconducting quantum computing circuits is advantageous for minimizing the noise channels and wiring costs. Here we introduce a swap interaction between two data transmons assisted by the third-order nonlinearity of a coupler transmon under a microwave drive. We model the interaction analytically and numerically and use it to implement an all-microwave controlled-Z gate. The gate based on the coupler-assisted swap transition maintains high drive efficiency and small residual interaction over a wide range of detuning between the data transmons.

quant-ph↗

arXiv2023

Compact atom source using fiber-based pulsed laser ablation

We designed, demonstrated, and characterized an atom source based on fiber-based pulsed laser ablation. By using commercially available miniature lens system for focusing nanosecond pulsed laser of up to 225~$μ$J delivered through a multimode fiber of 105~$μ$m core, we successfully ablate a SrTiO$_3$ target and generate a jet of neutral strontium atoms, though our method can be applied to other transparent ablation targets containing materials under concern. Our device endures 6\,000 cycles of pulse delivery and irradiation without noticeable damage on the fiber facets and lenses. The generated strontium beam is characterized with spectroscopic method and is revealed to exhibit the transverse temperature of 800~K and longitudinal velocity of 2\,300~m/s, which are typical of pulsed-laser-ablation-based atom source. The number of atoms generated by a single ablation pulse is estimated to be $2\times 10^5$. Our device provides a compact, cryo-compatible fiber-pigtailed atom source with minimized device footprints and reduced complexity of vacuum systems to further promote the developments of cold-atom experiments. It may also find interesting applications in atomic and molecular sciences.

physics.atom-ph↗

arXiv2023

Efficient low-energy single-electron detection using a large-area superconducting microstrip

Superconducting strip single-photon detectors (SSPDs) are excellent tools not only for single-photon detection but also for single-particle detection owing to their high detection efficiency, low dark counts, and low time jitter. Although the detection of various particles, including electrons with keV-scale energy, has been reported so far, there have been no studies for detecting low-energy electrons. It has yet to be clarified how low-energy electrons interact with electrons and/or phonons in a superconductor during electron detection. Here we report the detection property of a superconducting micro-strip single-electron detector (SSED) for electrons with energy below 200 eV. The detection efficiency is estimated as at least 37 % when electrons impinging on the stripline possess an energy of 200 eV. We also show that the minimum detectable energy of electrons is about 10 eV with our SSED, much lower than those of ions, which implies that the electron-electron interaction plays a significant role. SSEDs might open a wide range of applications, from condensed matter physics to quantum information science, because of their compatibility with the cryogenic environment.

quant-ph↗

arXiv2022

Feasibility study on ground-state cooling and single-phonon readout of trapped electrons using hybrid quantum systems

Qubits of long coherence time and fast quantum operations are long-sought objectives towards the realization of high-fidelity quantum operations and their applications to the quantum technologies. An electron levitated in a vacuum by a Paul trap is expected to be a good candidate, for its light mass and hence the high secular frequency which allows for the faster gate operations than those in trapped ions. Controlling the motional state of the trapped electron is a crucial issue, for it mediates an interaction between electron spins, intrinsic qubits embedded in electrons, and its decoherence results in degraded fidelity of two-qubit gates. In addition, an efficient readout of the motional state is important, regarding the possibility of detecting spin state by using it. Despite of such an importance, how to achieve the motional ground state and how to efficiently detect it are not reported so far. Here we propose methods addressing these issues by utilizing hybrid quantum systems involving electron-superconducting circuit and electron-ion coupled systems and analyze the feasibility of our schemes. In both systems, we show that the ground-state cooling and the single-phonon readout of the motional state of the trapped electron are possible. Our work shed light on the way to precisely control the motional states of the trapped electrons, that provides an interesting playground for the development of quantum technologies.

quant-ph↗