arXiv subjects

Jiheng Duan

Publications and source records attributed to Jiheng Duan.

5 recordsLinked to original sources

arXiv2026

Mitigating Residual Exchange Coupling in Resonant Singlet-Triplet Qubits

We propose methods to mitigate single- and two-qubit control errors due to residual exchange coupling in systems of exchange-coupled resonant singlet-triplet qubits. Commensurate driving, where the pulse length is an integer multiple of the drive period, can mitigate errors from residual intra-qubit exchange, including effects from counter rotating terms and off-axis rotations, as well as leakage errors during two-qubit operations. Residual inter-qubit exchange creates crosstalk errors that reduce single-qubit control fidelities. We show that using a single-spin coupler between two resonant singlet-triplet qubits can reduce this crosstalk error by an order of magnitude. Assuming perfect coupler state preparation and realistic charge and hyperfine noise, we predict that coupler-assisted two-qubit gate errors can be below $3\times10^{-3}$ for gate times as short as $66~\text{ns}$, even in the presence of residual exchange levels exceeding several hundred kHz. Our results suggest the potential of utilizing coupler-based architectures for large scale fault-tolerant spin qubit processors based on resonant singlet-triplet qubits.

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arXiv2026

Measuring and correcting nanosecond pulse distortions in quantum-dot spin qubits

Gate-defined semiconductor quantum dots utilize fast electrical control to manipulate spin and charge states of individual electrons. Electrical pulse distortions can limit control fidelities but are difficult to measure at the device level. Here, we use detuning-axis pulsed spectroscopy to characterize baseband pulse distortions in a silicon double quantum-dot. We extract the gate-voltage impulse response and apply a digital pre-distortion filter to eliminate pulse distortions on timescales longer than 1~ns. With the pre-distortion, we reduce the frequency chirp of coherent exchange oscillations in a singlet-triplet qubit. Our results suggest a scalable and tuning-efficient method for characterizing pulse distortions in quantum-dot spin qubits.

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arXiv2026

Drive-Only Interaction Engineering via Dynamical Freezing

Freezing is usually used to suppress unwanted dynamics, but it can also be used to engineer interactions. We introduce freezing-induced interaction engineering, a drive-only control paradigm in which dynamically freezing an auxiliary subsystem reshapes the effective Hamiltonian of the remaining degrees of freedom. As a concrete realization, we consider a three-qubit architecture where a driven modulator $M$ is coupled to one of two target qubits, $Q_1$, while $Q_1$ and $Q_2$ retain a fixed native exchange-type interaction. When $M$ is frozen in a dressed eigenstate, its projection renormalizes the local Hamiltonian of $Q_1$. This makes the dressed-frame detuning between $Q_1$ and $Q_2$ controllable by the drive frequency. The native interaction can then be switched between two regimes: an interaction-off regime with large dressed-frame detuning, and an interaction-on regime with resonant exchange. In the interaction-on regime, the protocol realizes an iSWAP gate using the native $Q_1Q_2$ coupling. Full lab-frame simulations show high-fidelity iSWAP dynamics and strong interaction suppression in the interaction-off regime. By combining native-coupling gate speed with drive-only operational simplicity, freezing-induced interaction engineering provides a route toward fast, drive-controlled entangling gates in fixed-frequency quantum architectures.

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arXiv2024

Neural network based time-resolved state tomography of superconducting qubits

Superconducting qubits have emerged as a premier platform for large-scale quantum computation, yet the fidelity of state readout is often hindered by random noise and crosstalk, especially in multi-qubit systems. While neural networks trained on labeled data have shown promise in reducing crosstalk effects during readout, their current capabilities are limited to binary discrimination of joint-qubit states due to architectural constraints. Here we introduce a time-resolved modulated neural network capable of full-state tomography for individual qubits, enabling detailed time-resolved measurements like Rabi oscillations. This scalable approach, with a dedicated module per qubit, mitigated readout error by an order of magnitude under low signal-to-noise ratios and substantially reduced variance in Rabi oscillation measurements. This advancement bolsters quantum state discrimination with neural networks, and propels the development of next-generation quantum processors with enhanced performance and scalability.

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arXiv2022

A quantum algorithm for finding collision-inducing disturbance vectors in SHA-1

Modern cryptographic protocols rely on sophisticated hash functions to generate quasi-unique numbers that serve as signatures for user authentication and other security verifications. The security could be compromised by finding texts hash-mappable to identical numbers, forming so-called collision attack. Seeding a disturbance vector in the hash mapping to obtain a successful collision is that a major focus of cryptography study in the past two decades to improve hash protocols. We propose an algorithm that takes advantage of entangled quantum states for concurrent seeding of candidate disturbance vectors, out of which the one entailing collision is selected through a combination of quantum search, phase gating, diffusion gating, and information feedbacks from classical computing machinery. The complexity reduction is shown to be on the order of $\mathcal{O}(2^{n/2+1})$ where $n$ is the number of qubits encoding addresses. We demonstrate the practicality of the proposed by an implementation scheme based on degenerate optical parametric oscillators.

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