Two-qubit quantum probes for the temperature of an Ohmic environment

TL;DR

This paper investigates using two-qubit quantum probes to estimate the temperature of an Ohmic environment, highlighting how quantum correlations and coherence influence thermometry accuracy without disturbing the system.

Contribution

It introduces a method employing two-qubit probes with pure dephasing interactions to measure temperature, analyzing the roles of entanglement and coherence in quantum thermometry.

Findings

Entanglement enhances short-time thermometry accuracy.

Coherence becomes more important than entanglement for longer interaction times.

Pure dephasing avoids energy exchange, minimizing system perturbation.

Abstract

We address a particular instance where open quantum systems may be used as quantum probes for an emergent property of a complex system, as the temperature of a thermal bath. The inherent fragility of the quantum probes against decoherence is the key feature making the overall scheme very sensitive. The specific setting examined here is that of quantum thermometry, which aims to exploits decoherence as resource to estimate the temperature of a sample. We focus on temperature estimation for a bosonic bath at equilibrium in the Ohmic regime (ranging from sub-Ohmic to super- Ohmic), by using pairs of qubits in different initial states and interacting with different environments, consisting either of a single thermal bath, or of two independent ones at the same temperature. Our scheme involves pure dephasing of the probes, thus avoiding energy exchange with the sample and the consequent perturbation of temperature itself. We discuss the interplay between correlations among the probes and correlations within the bath, and show that entanglement improves thermometry at short times whereas, if the interaction time is not constrained, coherence rather than entanglement, is the key resource in quantum thermometry.