Efficient tools for quantum metrology with uncorrelated noise

TL;DR

This paper develops efficient methods to determine the ultimate precision bounds in quantum metrology under uncorrelated noise, bridging finite and asymptotic regimes, and applies these to various noisy estimation models.

Contribution

It extends existing techniques to finite particle regimes and provides a unified framework for comparing quantum metrological bounds under decoherence.

Findings

Derived explicit hierarchy of quantum bounds under noise.

Extended techniques to finite particle regimes.

Applied methods to noisy phase, frequency, and decoherence estimation.

Abstract

Quantum metrology offers an enhanced performance in experiments such as gravitational wave-detection, magnetometry or atomic clocks frequency calibration. The enhancement, however, requires a delicate tuning of relevant quantum features such as entanglement or squeezing. For any practical application the inevitable impact of decoherence needs to be taken into account in order to correctly quantify the ultimate attainable gain in precision. We compare the applicability and the effectiveness of various methods of calculating the ultimate precision bounds resulting from the presence of decoherence. This allows us to put a number of seemingly unrelated concepts into a common framework and arrive at an explicit hierarchy of quantum metrological methods in terms of the tightness of the bounds they provide. In particular, we show a way to extend the techniques originally proposed in Demkowicz-Dobrzanski et al 2012 Nat. Commun. 3 1063, so that they can be efficiently applied not only in the asymptotic but also in the finite-number of particles regime. As a result, we obtain a simple and direct method, yielding bounds that interpolate between the quantum enhanced scaling characteristic for small number of particles and the asymptotic regime, where quantum enhancement amounts to a constant factor improvement. Methods are applied to numerous models including noisy phase and frequency estimation, as well as the estimation of the decoherence strength itself.