arXiv subjects

Yasuo Oda

Publications and source records attributed to Yasuo Oda.

7 recordsLinked to original sources

arXiv2026

Noise-Robust Spin-Orbit Qubit in Germanium Holes via p-Orbital Encoding

Germanium hole spin qubits are a leading platform for semiconductor quantum computation due to their strong spin-orbit coupling, all-electrical operability, and absence of valley degeneracy. A central obstacle is charge noise, which couples to the qubit through the same spin-orbit interaction that enables fast electrical control. In this work, we propose a new operational mode of a three-hole quantum dot in a planar Ge/SiGe heterostructure, modeled within a four-band Luttinger-Kohn--Bir-Pikus framework: a spin-$p$-orbital (SpO) qubit encoded in the $p$-shell of the topmost hole. We characterize charge noise sweet spots in the parameter space of electrostatic confinement and magnetic field, and estimate that relaxation rates of the SpO qubit are comparable to those of spin qubits hosted in single holes. We then design and optimize an all-electrical Landau-Zener state-transfer protocol that induces logical qubit state transitions without microwave driving, and we show that the quadrupole-quadrupole Coulomb interaction between neighboring dots enables fast two-qubit entangling gates operated by adiabatic shuttling.

cond-mat.mes-hall↗

arXiv2025

Fast charge noise sensing using a spectator valley state in a singlet-triplet qubit

Semiconductor spin qubits are a promising platform for quantum computing but remain vulnerable to charge noise. Accurate, in situ measurement of charge noise could enable closed-loop control and improve qubit performance. Here, we propose a method for real-time detection of charge noise using a silicon singlet-triplet qubit with one electron initialized in an excited valley state. This valley excitation acts as a spectator degree of freedom, coupled to a high-quality resonator via the exchange interaction, which is sensitive to charge-noise-induced voltage fluctuations. Dispersive readout of the resonator enables a continuous, classical measurement of exchange fluctuations during qubit operation. Signal-to-noise analysis shows that, under realistic device parameters, sub-millisecond measurement times are possible using a quantum-limited amplifier. Even without such an amplifier, similar performance is achievable with appropriately engineered resonator parameters. This approach allows the probe to monitor slow drift in exchange in real time, opening the door to feedback and feedforward strategies for maintaining high-fidelity quantum operations. Importantly, the protocol preserves spin coherence and can be run concurrently with qubit logic gates.

cond-mat.mes-hall↗

arXiv2024

Sparse Non-Markovian Noise Modeling of Transmon-Based Multi-Qubit Operations

The influence of noise on quantum dynamics is one of the main factors preventing current quantum processors from performing accurate quantum computations. Sufficient noise characterization and modeling can provide key insights into the effect of noise on quantum algorithms and inform the design of targeted error protection protocols. However, constructing effective noise models that are sparse in model parameters, yet predictive can be challenging. In this work, we present an approach for effective noise modeling of multi-qubit operations on transmon-based devices. Through a comprehensive characterization of seven devices offered by the IBM Quantum Platform, we show that the model can capture and predict a wide range of single- and two-qubit behaviors, including non-Markovian effects resulting from spatio-temporally correlated noise sources. The model's predictive power is further highlighted through multi-qubit dynamical decoupling demonstrations and an implementation of the variational quantum eigensolver. As a training proxy for the hardware, we show that the model can predict expectation values within a relative error of 0.5%; this is a 7$\times$ improvement over default hardware noise models. Through these demonstrations, we highlight key error sources in superconducting qubits and illustrate the utility of reduced noise models for predicting hardware dynamics.

quant-ph↗

arXiv2024

Suppressing Si Valley Excitation and Valley-Induced Spin Dephasing for Long-Distance Shuttling

We present a scalable protocol for suppressing errors during electron spin shuttling in silicon quantum dots. The approach maps the valley Hamiltonian to a Landau-Zener problem to model the nonadiabatic dynamics in regions of small valley splitting. An optimization refines the shuttling velocity profile over a single small segment of the shuttling path. The protocol reliably returns the valley state to the ground state at the end of the shuttle, disentangling the spin and valley degrees of freedom, after which a single virtual $z$-rotation on the spin compensates its evolution during the shuttle. The time cost and complexity of the error suppression is minimal and independent of the distance over which the spin is shuttled, and the maximum velocities imposed by valley physics are found to be orders of magnitude larger than current experimentally achievable shuttling speeds. This protocol offers a chip-scale solution for high-fidelity quantum transport in silicon spin-based quantum computing devices.

cond-mat.mes-hall↗

arXiv2023

Quantum Control Noise Spectroscopy with Optimal Suppression of Dephasing

We extend quantum noise spectroscopy (QNS) of amplitude control noise to settings where dephasing noise or detuning errors make significant contributions to qubit dynamics. Previous approaches to characterize amplitude noise are limited by their vulnerability to low-frequency dephasing noise and static detuning errors, which can overwhelm the target control noise signal and introduce bias into estimates of the amplitude noise spectrum. To overcome this problem, we leverage optimal control to identify a family of amplitude control waveforms that optimally suppress low-frequency dephasing noise and detuning errors, while maintaining the spectral concentration in the amplitude filter essential for spectral estimation. The waveforms found via numerical optimization have surprisingly simple analytic forms, consisting of oscillating sine waves obeying particular amplitude and frequency constraints. In numerically simulated QNS experiments, these waveforms demonstrate superior robustness, enabling accurate estimation of the amplitude noise spectrum in regimes where existing approaches are biased by low-frequency dephasing noise and detuning errors.

quant-ph↗

arXiv2023

Optimally Band-Limited Noise Filtering for Single Qubit Gates

We introduce a quantum control protocol that produces smooth, experimentally implementable control sequences optimized to combat temporally correlated noise for single qubit systems. The control ansatz is specifically chosen to be a functional expansion of discrete prolate spheroidal sequences, a discrete time basis known to be optimally concentrated in time and frequency, and quite attractive when faced with experimental control hardware constraints. We leverage the filter function formalism to transform the control problem into a filter design problem, and show that the frequency response of a quantum system can be carefully tailored to avoid the most relevant dynamical contributions of noise processes. Using gradient ascent, we obtain optimized filter functions and exploit them to elucidate important details about the relationship between filter function design, control bandwidth, and noise characteristics. In particular, we identify regimes of optimal noise suppression and in turn, optimal control bandwidth directly proportional to the size of the frequency bands where the noise power is large. In addition to providing guiding principles for filter design, our approach enables the development of controls that simultaneously yield robust noise filtering and high fidelity single qubit logic operations in a wide variety of complex noise environments.

quant-ph↗

arXiv2022

Quantum Crosstalk Robust Quantum Control

The prevalence of quantum crosstalk in current quantum devices poses challenges for achieving high-fidelity quantum logic operations and reliable quantum processing. Through quantum control theory, we develop an analytical condition for achieving crosstalk-robust single-qubit control of multi-qubit systems. We examine the effects of quantum crosstalk via a cumulant expansion and develop a condition to suppress the leading order contributions to the dynamics. The efficacy of the condition is illustrated in the domains of quantum state preservation and noise characterization through the development of crosstalk-robust dynamical decoupling and quantum noise spectroscopy (QNS) protocols. Using the IBM Quantum Experience, crosstalk-robust state preservation is demonstrated on 27 qubits, where a $3\times$ improvement in coherence decay is observed for single-qubit product and multipartite entangled states. Through the use of noise injection, we experimentally demonstrate crosstalk-robust dephasing QNS on a seven qubit processor, where a $10^4$ improvement in reconstruction accuracy over ``cross-susceptible" alternatives is found. Together, these experiments highlight the significant impact the crosstalk mitigation condition can have on improving multi-qubit characterization and control on current quantum devices.

quant-ph↗