Soft-pulse dynamical decoupling in a cavity

TL;DR

This paper demonstrates how properly designed soft-pulse sequences can effectively implement dynamical decoupling in cavity systems, reducing errors and heating, with theoretical analysis and numerical validation.

Contribution

It introduces a method to construct soft refocusing pulses that suppress errors in cavity quantum systems, extending dynamical decoupling techniques.

Findings

Second-order error cancellation achieved with shaped pulses

Numerical simulations show high qubit fidelity

Strong suppression of oscillator heating

Abstract

Dynamical decoupling is a coherent control technique where the intrinsic and extrinsic couplings of a quantum system are effectively averaged out by application of specially designed driving fields (refocusing pulse sequences). This entails pumping energy into the system, which can be especially dangerous when it has sharp spectral features like a cavity mode close to resonance. In this work we show that such an effect can be avoided with properly constructed refocusing sequences. To this end we construct the average Hamiltonian expansion for the system evolution operator associated with a single ``soft'' pi-pulse. To second order in the pulse duration, we characterize a symmetric pulse shape by three parameters, two of which can be turned to zero by shaping. We express the effective Hamiltonians for several pulse sequences in terms of these parameters, and use the results to analyze the structure of error operators for controlled Jaynes-Cummings Hamiltonian. When errors are cancelled to second order, numerical simulations show excellent qubit fidelity with strongly-suppressed oscillator heating.