Harnessing Floquet dynamics for selective metrology in few-qubit systems

TL;DR

This paper demonstrates how Floquet dynamics in a three-qubit system can be used to selectively enhance sensitivity for estimating specific parameters, such as interaction strength or magnetic field, by exploiting a period-doubling phase.

Contribution

It introduces the concept of using a period-doubling Floquet phase for targeted quantum metrology, showing how dynamical regimes can be harnessed for selective parameter sensing in finite-size quantum systems.

Findings

The period-doubling phase enhances sensitivity to Ising interaction strength.

Non-PD regimes are optimal for sensing transverse magnetic fields.

The filtering effect is robust and measurable with accessible observables.

Abstract

Periodically driven quantum systems can function as highly selective parameter filters. We demonstrate this capability in a finite-size, three-qubit system described by the transverse-field Floquet Ising model. In this system, we identify a period-doubling (PD) dynamical phase that exhibits a stark asymmetry in metrological sensitivity to the magnetic field applied on the qubits and to the coupling strength between the qubits. The PD phase originates from $\pi$-pairing, where the initial state exhibits strong overlap with $\pi$-paired Floquet eigenstates, leading to robust period-doubled dynamics and enhanced metrological sensitivity. The analysis of quantum Fisher information reveals that the PD regime significantly enhances precision for estimating the Ising interaction strength while simultaneously suppressing sensitivity to the transverse magnetic field. Conversely, non-PD regimes are optimal for sensing the transverse field. This filtering effect is robust for larger system sizes and is quantifiable using experimentally accessible observables, such as magnetization and two-qubit correlations, via the classical Fisher information. Our work shows that distinct dynamical regimes in finite-size Floquet systems can be harnessed for targeted quantum sensing.