Description
Digital quantum simulations (DQS) model complex quantum systems by discretising continuous, complex time evolution into sequences of implementable physical gates. For example, the quantum Rabi model has been simulated in circuit QED by interleaving Jaynes-Cummings (JC) interaction gates with fast single-qubit π-gates [1]. Achieving outsized computational complexity relative to processor complexity, the circuit QED quantum Rabi system provides a highly versatile digital quantum simulator that can demonstrate interesting physics phenomena such as quantum phase transitions and enable exploration of advanced DQS techniques. Ideally, this requires high-fidelity but also highly controllable Jaynes-Cummings gates, with fine control, including for short or negative interaction times. In circuit QED platforms, qubit-cavity interactions can be implemented via magnetic flux tuning of qubit frequencies, but achieving short, fine-tunable interaction times using variable bandwidth-limited cryogenic control lines challenges the limits of typical microwave pulse control performance.
In this work, we demonstrate a new approach to smooth-profile flux-pulse control, using guided optimisation techniques to develop robust families of low-bandwidth entangling qubit-resonator gates with fine-tunable and ultrashort interaction times. Building on recent applications of a geometric framework which characterised frequency-time pulse profiles as geometric trajectories of complex interaction coefficients [2, 3], our approach delivers practical, bandwidth-limited pulses that have higher fidelity and are more robust to tuning than conventional brute-force optimisation. Using experimentally relevant system parameters, we find nanosecond-scale smooth qubit-cavity interaction pulses delivering fidelities above 99.9% (up to 99.999%) for positive and negative effective durations up to 0.175π radians. Such pulses extend the qubit-cavity control toolbox for circuit QED systems, with potential applications for novel digital quantum simulations, and for quantum computing platforms exploiting bosonic modes, such as bosonic quantum error correction codes.
[1] Langford et al., Nature Communications 8, 1715 (2017).
[2] Zeng et al., Phys. Rev. A 99, 052321 (2019).
[3] Manatuly, PhD thesis, UTS (2026).
| I am the presenting author | Yes |
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