English

Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding

Quantum Physics 2026-04-21 v1

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.

Keywords

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

R2 v1 2026-07-01T12:17:07.564Z