Sensing high-frequency ac fields via a two-qubit sensor

TL;DR

This paper introduces a two-qubit quantum sensing scheme for high-frequency ac fields that avoids the limitations of rapid pulse sequences, using interaction strength changes to estimate the field with quantified precision.

Contribution

It proposes a novel two-qubit sensing method that does not require short-interval control pulses, enhancing high-frequency field measurement accuracy.

Findings

The scheme effectively estimates high-frequency ac fields by measuring interaction strength changes.

Fisher information quantifies the precision of the field estimation.

Control pulses can mitigate noise impact without needing very short intervals.

Abstract

Quantum sensors allow us to measure weak oscillating fields with incredible precision. One common approach is to use the time evolution of a single two-level system (or a qubit) in conjunction with applied control pulses to measure the oscillating field. For high-frequency fields, the time interval required between the applied pulses decreases, meaning that errors due to the finite width of the pulses can become important. This paper presents an alternative scheme that does not rely on applying pulses with short time intervals. Our scheme uses two interacting qubits. In the presence of an oscillating field, the interaction strength changes. The oscillating field can be estimated by measuring the change in this interaction strength. We quantify the precision of this estimate by calculating the Fisher information. We show the effect of noise on our scheme and discuss how control pulses can be applied to mitigate the impact of noise. Importantly, the time interval between these pulses need not be very short.