Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding
Abstract
Conventional quantum thermometry assumes completely positive (CP) encoding maps, where the probe is initially uncorrelated with the environment. We consider realistic scenarios with initial probe-environment correlations leading to physically realizable non-completely positive (NCP) encoding, and show how such encodings can significantly impact temperature estimation of the environment. We first consider pure entangled probe-environment initial states (Type-I NCP encoding) and analytically show that for probes and environments of equal but arbitrary dimension, the maximum achievable precision matches the thermal-state bound, as in the CP case. However, upon relaxing the constraint of pure probe-environment states and considering general correlated initial states (Type-II NCP encoding), we demonstrate that the estimation precision can surpass the thermal-state limit. This establishes a clear advantage of NCP encoding in enhancing thermometric performance. We illustrate the results using qubit probes interacting with qubit environments via XY interactions.
Cite
@article{arxiv.2604.17537,
title = {Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding},
author = {Anindita Sarkar and Paranjoy Chaki and Debarupa Saha and Ujjwal Sen},
journal= {arXiv preprint arXiv:2604.17537},
year = {2026}
}
Comments
11 pages, 2 figures