arXiv subjects

Yi-Hsien Wu

Publications and source records attributed to Yi-Hsien Wu.

6 recordsLinked to original sources

arXiv2026

Simultaneous High-Fidelity Single-Qubit Gates in a Spin Qubit Array

Silicon spin qubits offer a promising path to scalable quantum computing due to their compatibility with industrial semiconductor manufacturing and recent advances in multi-qubit integration. A key requirement for scaling quantum processors is the ability to perform high-fidelity operations in parallel across many qubits. In silicon spin systems, however, simultaneous control remains a major challenge, as fidelities typically degrade under parallel operation. In a five-qubit silicon spin array, we identify microwave-drive-induced AC Stark shifts as the dominant source of this degradation. We address this by introducing a scalable mitigation protocol based solely on pairwise phase calibrations. Using tailored control pulses on a shared control line, we achieve primitive $π/2$ gate fidelities well above 99.99% for each qubit individually, with some approaching 99.999%, surpassing previously reported fidelities in silicon spin qubits. Crucially, these fidelities are preserved above 99.99% during simultaneous operation of up to three qubits. During parallel five-qubit operation, fidelities remain at the practical fault-tolerant threshold of 99.9%, with the loss attributed to drive-induced decoherence resulting from increased microwave power. This effect can be mitigated through device-level improvements. By demonstrating that high-fidelity control is maintained during simultaneous operation, we overcome a central challenge in silicon spin qubits and highlight the potential of shared qubit-control lines for scaling.

quant-ph↗

arXiv2026

Scaling of silicon spin qubits under correlated noise

The path to fault-tolerant quantum computing hinges on hardware that scales while remaining compatible with quantum error correction (QEC). Silicon spin qubits are a leading hardware candidate because they combine industrial fabrication compatibility with a nanoscale footprint that could accommodate millions of qubits on a chip. However, their suitability for QEC remains uncertain since spatially correlated noise naturally emerges from the resulting close proximity of qubits. These correlations increase the likelihood of simultaneous errors and erode the redundancy that QEC depends on. Here we quantify the spatial extent of noise correlations in a five-qubit silicon array and assess their impact on QEC. We identify two distinct sources of correlated noise: global magnetic field drifts that generate perfectly correlated fluctuations, and charge noise from two-level fluctuators that produces short-range correlations decaying within neighboring qubits. While magnetic drifts represent a critical correlated noise source that can compromise QEC, they can be mitigated. In contrast, the measured charge noise correlations are moderate, electrically tunable, and compatible with fault-tolerant operation with minimal qubit overhead. Our results establish quantitative benchmarks for correlated noise and clarify how such correlations impact the viability of quantum error correction in scalable qubit arrays.

cond-mat.mes-hall↗

arXiv2026

Weight-four parity checks with silicon spin qubits

Recent advances in coherent spin shuttling have made sparse semiconductor spin qubit arrays an appealing solid-state platform to realize quantum processors. The dynamic and long-range connectivity enabled by shuttling is also essential for many quantum error-correction (QEC) schemes. Here, we demonstrate a silicon spin-qubit device that comprises a shuttling bus for coherently transporting qubits that can interact at four isolated locations we call bus stops. We dynamically populate the array and tune all single- and two-qubit operations using shuttling and quantum non-demolition (QND) spin measurements, without access to charge sensing in most of the device. We achieve universal control of the effective five-qubit processor and select the connectivity required to form a surface-code stabilizer plaquette that supports X- and Z-type parity checks up to weight-four. We use the parity checks to generate multi-qubit entanglement between all qubit combinations in the array and report the genuine entanglement of a five-qubit Greenberger-Horne-Zeilinger (GHZ) state, constituting the largest such state ever constructed with gate-defined semiconductor spins. This work opens immediate opportunities to pursue QEC experiments with spin qubits, and the protocols developed here lay the groundwork for the modular calibration and operation of sparse spin qubit arrays.

cond-mat.mes-hall↗

arXiv2025

Effect of Stochastic Charge Noise in Si/SiGe Quantum-Dot Spin Qubits

In Si/SiGe quantum dots, the decoherence behavior of spin qubits usually comes from the non-Markovian effect of the charge noise. To improve the performance of using the coherent noise models in the decoherence simulation and tomography analysis, here we propose a spin-phonon model derived from the electric dipole spin resonance to characterize the decoherence behavior of the spin qubit in a Si/SiGe quantum dot. Utilizing a 1/f spectrum to characterize quantum noise correlation, our stochastic model can yield a more precise prediction of decoherence compared to a random coherence model. We also use gate set tomography (GST) to address the error generator and analyze the model violation coming from the non-Markovian effect. Based on the results, we attribute certain error generators of this model to the incoherence error, which avoids the scenario of using too large a coherent noise strength in the previous study to account for the experimentally observed decoherence times, and thus underestimates the gate fidelity. We also perform a gate optimization and show that our optimized control pulse can substantially reduce the error contribution of the incoherent non-Markovian 1/f charge noise. We further demonstrate that the optimized pulse against incoherent noise is more robust against coherent noise than the regular Gaussian pulse through a filter function analysis in a CPMG protocol, demonstrating the significant effectiveness of the optimized pulse.

quant-ph↗

arXiv2025

Noise cross-correlations from single-shot measurements

We introduce a novel method that we call Single-Shot Cross-Spectroscopy (SSCS), for extracting the auto- and cross-power spectral densities of dephasing noise of a qubit pair. The method uses straightforward input, namely single-shot readouts from single-qubit Ramsey-type experiments, and is resilient against errors in state preparation and measurement. We apply it to experimental data from a semiconductor spin-qubit device and obtain noise spectra over five orders of magnitude in frequency (5 mHz--500 Hz). Compared to other techniques, SSCS enables access to noise correlations in the previously inaccessible intermediate-frequency range (1--500 Hz) for spin qubits, and can be further extended with faster readout. More broadly, the frequency range accessible with SSCS is limited only by the experiment repetition rate, and scales accordingly on other platforms.

quant-ph↗

arXiv2023

Hamiltonian Phase Error in Resonantly Driven CNOT Gate Above the Fault-Tolerant Threshold

Because of their long coherence time and compatibility with industrial foundry processes, electron spin qubits are a promising platform for scalable quantum processors. A full-fledged quantum computer will need quantum error correction, which requires high-fidelity quantum gates. Analyzing and mitigating the gate errors are useful to improve the gate fidelity. Here, we demonstrate a simple yet reliable calibration procedure for a high-fidelity controlled-rotation gate in an exchange-always-on Silicon quantum processor allowing operation above the fault-tolerance threshold of quantum error correction. We find that the fidelity of our uncalibrated controlled-rotation gate is limited by coherent errors in the form of controlled-phases and present a method to measure and correct these phase errors. We then verify the improvement in our gate fidelities by randomized benchmark and gate-set tomography protocols. Finally, we use our phase correction protocol to implement a virtual, high-fidelity controlled-phase gate.

cond-mat.mes-hall↗