Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding
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arXiv
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| Main Authors: | , , , |
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| Format: | Preprint |
| Published: |
2026
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| _version_ | 1866910146368634880 |
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| author | Sarkar, Anindita Chaki, Paranjoy Saha, Debarupa Sen, Ujjwal |
| author_facet | Sarkar, Anindita Chaki, Paranjoy Saha, Debarupa Sen, Ujjwal |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_17537 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding Sarkar, Anindita Chaki, Paranjoy Saha, Debarupa Sen, Ujjwal Quantum Physics 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. |
| title | Surpassing thermal-state limit in thermometry via non-completely positive quantum encoding |
| topic | Quantum Physics |
| url | https://arxiv.org/abs/2604.17537 |