Low-temperature quantum thermometry boosted by coherence generation

TL;DR

This paper introduces a quantum thermometry method that enhances low-temperature measurement sensitivity and range by generating quantum coherence in a probe through a multi-qubit interface, without requiring direct contact with the sample.

Contribution

The work demonstrates a novel approach using ancilla qubits to induce nonthermal steady states in a probe, improving low-temperature sensitivity and measurement range compared to traditional methods.

Findings

Quantum Fisher information peaks at multiple low temperatures.

Quantum coherence increases with more ancilla qubits.

Nonthermal steady states enable enhanced temperature sensitivity.

Abstract

The precise measurement of low temperatures is significant for both the fundamental understanding of physical processes and technological applications. In this work, we present a method for low-temperature measurement that improves thermal range and sensitivity by generating quantum coherence in a thermometer probe. Typically, in temperature measurements, the probes thermalize with the sample being measured. However, we use a two-level quantum system, or qubit, as our probe and prevent direct probe access to the sample by introducing a set of ancilla qubits as an interface. We describe the open system dynamics of the probe using a global master equation and demonstrate that while the ancilla-probe system thermalizes with the sample, the probe \textit{per se} evolves into a nonthermal steady state due to nonlocal dissipation channels. The populations and coherences of this steady state depend on the sample temperature, allowing for precise and wide-range low-temperature estimation. We characterize the thermometric performance of the method using quantum Fisher information and show that the quantum Fisher information can exhibit multiple and higher peaks at different low temperatures with increasing quantum coherence and the number of ancilla qubits. Our analysis reveals that the proposed approach, using a nonthermal qubit thermometer probe with temperature-dependent quantum coherence generated by a multiple qubit interface between a thermal sample and the probe qubit, can enhance the sensitivity of temperature estimation and broaden the measurable low-temperature range.