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Title: Optimal gain sensing of quantum-limited phase-insensitive amplifiers
Authors: Nair, Ranjith
Tham, Guo Yao
Gu, Mile
Keywords: Science::Physics
Issue Date: 2022
Source: Nair, R., Tham, G. Y. & Gu, M. (2022). Optimal gain sensing of quantum-limited phase-insensitive amplifiers. Physical Review Letters, 128(18), 180506-.
Project: RG162/19 (S)
Journal: Physical Review Letters 
Abstract: Phase-insensitive optical amplifiers uniformly amplify each quadrature of an input field and are of both fundamental and technological importance. We find the quantum limit on the precision of estimating the gain of a quantum-limited phase-insensitive amplifier using a multimode probe that may also be entangled with an ancilla system. In stark contrast to the sensing of loss parameters, the average photon number N and number of input modes M of the probe are found to be equivalent and interchangeable resources for optimal gain sensing. All pure-state probes whose reduced state on the input modes to the amplifier is diagonal in the multimode number basis are proven to be quantum optimal under the same gain-independent measurement. We compare the best precision achievable using classical probes to the performance of an explicit photon-counting-based estimator on quantum probes and show that an advantage exists even for single-photon probes and inefficient photodetection. A closed-form expression for the energy-constrained Bures distance between two product amplifier channels is also derived.
ISSN: 0031-9007
DOI: 10.1103/PhysRevLett.128.180506
Schools: School of Physical and Mathematical Sciences 
Organisations: Centre for Quantum Technologies, National University of Singapore
Research Centres: Nanyang Quantum Hub
Complexity Institute 
Rights: © 2022 American Physical Society. All rights reserved. This paper was published in Physical Review Letters and is made available with permission of American Physical Society.
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:SPMS Journal Articles

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