Speaker
Description
In noisy quantum metrology, information about an unknown parameter is lost to the environment and thus inaccessible for any measurement on the system alone. Continuously monitoring the reservoir's output allows to partially recover the lost information, quantified by the unraveling quantum Fisher information (QFI) [1]. This unraveling strategy is particularly relevant for cavity- and circuit-QED platforms, where a quantum system can interact with a structured non-Markovian bath whose Markovian output can be continuously measured. However, to fully capture the memory effects of the non-Markovian bath, standard stochastic methods rely on propagating the joint system-pseudomode state [2,3], requiring the simulation of exponentially large Hilbert spaces. Here, we overcome this limitation by formulating continuous quantum parameter estimation within the framework of the conditioned hierarchical equations of motion (cHEOM) [4]. Our approach directly maps the unraveling QFI onto the hierarchy, reducing the exponential bosonic dimensionality to a highly efficient combinatorial scaling. Applying this framework, we demonstrate that non-Markovian memory effects significantly enhance the unraveling QFI compared to Markovian limits, thereby extending the regime in which continuous environmental monitoring yields a metrological advantage.
References:
[1] F. Albarelli, M. A. Rossi, D. Tamascelli, and M. G. Genoni, “Restoring heisenberg scaling in noisy quantum metrology by monitoring the environment”, Quantum 2, 110 (2018).
[2] B. M. Garraway, “Nonperturbative decay of an atomic system in a cavity”, Phys. Rev. A 55, 2290–2303 (1997).
[3] G. Pleasance, B. M. Garraway, and F. Petruccione, “Generalized theory of pseudomodes for exact descriptions of non-markovian quantum processes”, Phys. Rev. Res. 2, 043058 (2020).
[4] V. Link, K. M¨uller, R. G. Lena, K. Luoma, F. Damanet, W. T. Strunz, and A. J. Daley, “Non-markovian quantum dynamics in strongly coupled multimode cavities conditioned on continuous measurement”, PRX Quantum 3, 020348 (2022).