Estimating the coherence of noise in quantum control of a solid-state qubit

TL;DR

This paper demonstrates methods to distinguish and quantify coherent and incoherent noise in quantum control of solid-state qubits, using purity and randomized benchmarking, and discusses how optimal control pulses can reduce these errors.

Contribution

It introduces a combined approach using purity and randomized benchmarking to differentiate and quantify noise types in quantum systems, providing bounds on achievable fidelity.

Findings

Purity benchmarking and randomized benchmarking effectively distinguish noise types.

Optimal control pulses reduce both coherent and incoherent errors.

Bounds on fidelity and diamond norm are established for error correction.

Abstract

To exploit a given physical system for quantum information processing, it is critical to understand the different types of noise affecting quantum control. Distinguishing coherent and incoherent errors is extremely useful as they can be reduced in different ways. Coherent errors are generally easier to reduce at the hardware level, e.g. by improving calibration, whereas some sources of incoherent errors, e.g. T2* processes, can be reduced by engineering robust pulses. In this work, we illustrate how purity benchmarking and randomized benchmarking can be used together to distinguish between coherent and incoherent errors and to quantify the reduction in both of them due to using optimal control pulses and accounting for the transfer function in an electron spin resonance system. We also prove that purity benchmarking provides bounds on the optimal fidelity and diamond norm that can be achieved by correcting the coherent errors through improving calibration.