Crosstalk-Robust Quantum Control in Multimode Bosonic Systems

TL;DR

This paper develops quantum optimal control techniques to create ancilla pulses that are robust against crosstalk errors in multimode bosonic systems, significantly improving gate fidelity for quantum information processing.

Contribution

It introduces a method to suppress crosstalk errors using optimized ancilla pulses integrated with an echo protocol, enhancing multimode bosonic quantum control.

Findings

Optimized pulses reduce crosstalk errors by orders of magnitude.

Numerical simulations demonstrate high-fidelity state preparation and entanglement.

Approach guides experimental realization of high-performance bosonic quantum processors.

Abstract

High-coherence superconducting cavities offer a hardware-efficient platform for quantum information processing. To achieve universal operations of these bosonic modes, the requisite nonlinearity is realized by coupling them to a transmon ancilla. However, this configuration is susceptible to crosstalk errors in the dispersive regime, where the ancilla frequency is Stark-shifted by the state of each coupled bosonic mode. This leads to a frequency mismatch of the ancilla drive, lowering the gate fidelities. To mitigate such coherent errors, we employ quantum optimal control to engineer ancilla pulses that are robust to the frequency shifts. These optimized pulses are subsequently integrated into a recently developed echoed conditional displacement (ECD) protocol for executing single- and two-mode operations. Through numerical simulations, we examine two representative scenarios: the preparation of single-mode Fock states in the presence of spectator modes and the generation of two-mode entangled Bell-cat states. Our approach markedly suppresses crosstalk errors, outperforming conventional ancilla control methods by orders of magnitude. These results provide guidance for experimentally achieving high-fidelity multimode operations and pave the way for developing high-performance bosonic quantum information processors.