Optimized pulse shapes for a resonator-induced phase gate

TL;DR

This paper develops optimized pulse shapes for a resonator-induced phase gate in superconducting qubits, aiming to minimize decoherence and residual entanglement, thereby enabling faster and more reliable multi-qubit quantum gates.

Contribution

It introduces spline and optimized pulse shaping techniques that reduce gate duration and residual entanglement, improving the fidelity of resonator-induced phase gates.

Findings

Shaped pulses can achieve ~212 ns gate times with ~6e-4 infidelity.

Spline pulses are robust to parameter uncertainties.

Optimized pulses further shorten gate duration without residual entanglement.

Abstract

The resonator-induced phase gate is a multi-qubit controlled-phase gate for fixed-frequency superconducting qubits. Through off-resonant driving of a bus resonator, statically coupled qubits acquire a state-dependent phase. However, photon loss leads to dephasing during the gate, and any residual entanglement between the resonator and qubits after the gate leads to decoherence. Here we consider how to shape the drive pulse to minimize these unwanted effects. First, we review how the gate's entangling and dephasing rates depend on the system parameters and validate closed-form solutions against direct numerical solution of a master equation. Next, we propose spline pulse shapes that reduce residual qubit-bus entanglement, are robust to imprecise knowledge of the resonator shift, and can be shortened by using higher-degree polynomials. Finally, we present a procedure that optimizes over the subspace of pulses that leave the resonator unpopulated. This finds shaped drive pulses that further reduce the gate duration. Assuming realistic parameters, we exhibit shaped pulses that have the potential to realize ~212 ns spline pulse gates and ~120 ns optimized gates with ~6e-4 average gate infidelity. These examples do not represent fundamental limits of the gate and in principle even shorter gates may be achievable.