Individual quantum probes for optimal thermometry

Understand

The unknown temperature of a sample may be estimated with minimal disturbance by putting it in thermal contact with an individual quantum probe.

• If the interaction time is sufficiently long so that the probe thermalizes, the temperature can be read out directly from its steady state.
• Here we prove that the optimal quantum probe, acting as a thermometer with maximal thermal sensitivity, is an effective two-level atom with a maximally degenerate excited state.
• When the total interaction time is insufficient to produce full thermalization, we optimize the estimation protocol by breaking it down into sequential stages of probe preparation, thermal contact and measurement.