Surpassing the Thermal Cramer-Rao Bound with Collisional Thermometry

Abstract

In collisional thermometry, a system in contact with the thermal bath is probed by a stream of ancillas. Coherences and collective measurements were shown to improve the Fisher information in some parameter regimes, for a stream of independent and identically prepared (i.i.d.) ancillas in some specific states [Seah et al., Phys. Rev. Lett., 180602 (2019)]. Here we refine the analysis of this metrological advantage by optimising over the possible input ancilla states, also for block-i.i.d.~states of block size b=2. For both an indirect measurement interaction and a coherent energy exchange channel, we show when the thermal Cramér-Rao bound can be beaten, and when a collective measurement of $N>1$ ancilla may return advantages over single-copy measurements.

arXiv comment6 pages, 5 figures

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• Invasiveness of non-equilibrium quantum thermometry
• Stochastic collisional quantum thermometry
• Machine classification for probe based quantum thermometry
• Harnessing coherence generation for precision single- and two-qubit quantum thermometry
• Correlations break homogenization
• Fisher information rates in sequentially measured quantum systems
• Bayesian estimation for collisional thermometry
• Quantum thermometry for ultralow temperatures using probe and ancilla qubit chains
• Thermometric machine for ultraprecise thermometry of low temperatures
• Universal bounds for quantum metrology in the presence of correlated noise
• Non-positive energy quasidistributions in coherent collision models
• Queued quantum collision models
• Coherence-enhanced single-qubit thermometry out of equilibrium
• Information flow-enhanced precision in collisional quantum thermometry
• Simulating quantum collision models with Hamiltonian simulations using early fault-tolerant quantum computers
• Performance Evaluations of Signed and Unsigned Noisy Approximate Quantum Fourier Arithmetic
• Nonequilibrium thermometry via an ensemble of initially correlated qubits