Spectral Analysis and Identification of Noises in Quantum Systems

TL;DR

This paper introduces a novel noise-identification method for quantum systems that leverages non-Markovian responses, enabling noise spectrum recovery without additional quantum devices, and is validated on superconducting charge qubits.

Contribution

The paper presents a direct noise spectrum identification technique based on non-Markovian responses, applicable to various qubit types, and improves precision by utilizing transient response data.

Findings

Method recovers Fermi's golden rule in the Markovian limit.

Applicable to any qubit type, demonstrated on superconducting charge qubits.

Enhances noise identification accuracy by incorporating transient responses.

Abstract

In quantum information processing, knowledge of the noise in the system is crucial for high-precision manipulation and tomography of coherent quantum operations. Existing strategies for identifying this noise require the use of additional quantum devices or control pulses. We present a noise-identification method directly based on the system's non-Markovian response of an ensemble measurement to the noise. The noise spectrum is identified by reversing the response relationship in the frequency domain. For illustration, the method is applied to superconducting charge qubits, but it is equally applicable to any type of qubits. We find that the identification strategy recovers the well-known Fermi's golden rule under the lowest-order perturbation approximation, which corresponds to the Markovian limit when the measurement time is much longer than the noise correlation time. Beyond such approximation, it is possible to further improve the precision at the so-called optimal point by incorporating the transient response data in the non-Markovian regime. This method is verified with experimental data from coherent oscillations in a superconducting charge qubit.