Thermal quantum metrology in memoryless and correlated environments

Abstract

In bosonic quantum metrology, the estimate of a loss parameter is typically performed by means of pure states, such as coherent, squeezed or entangled states, while mixed thermal probes are discarded for their inferior performance. Here we show that thermal sources with suitable correlations can be engineered in such a way to approach, or even surpass, the error scaling of coherent states in the presence of general Gaussian decoherence. Our findings pave the way for practical quantum metrology with thermal sources in optical instruments (e.g., photometers) or at different wavelengths (e.g., far infrared, microwave or X-ray) where the generation of quantum features, such as coherence, squeezing or entanglement, may be extremely challenging.

Quantum illumination with a generic Gaussian source

“…It is worth noting that, although Gaussian entanglement is the main resource of QI, previous literature has also considered the use of separable non-Gaussian sources with nonpositive P representations, finding an advantage over a restricted classical benchmark [11]. More generally, quantum correlations beyond entanglement have also been considered for a number of other quantum information and computation tasks [12][13][14][15]. However, our current study is specifically focused on Gaussian states because they are, so far, the only sources showing a quantum advantage over the best classical benchmark.…”

Detecting and tracking bacteria with quantum light

“…This performance can equivalently be achieved in a double-beam configuration where a two-mode correlated thermal state is prepared in a very asymmetric way, so that one mode is faint and the other is highly energetic (see Ref. [20] for more details on this equivalence). The faint mode is sent through the sample while the energetic one is directly sent to the output measurement, where both the output modes are subject to photon counting (see Methods for more details).…”

“…where the classical Fisher information h η,n,x is [20] h η,n,x = γ n η , γ := 1 + (1 − x)nx −1 1 + (1 − x + xη)nx −1 ≤ 1. (20) Using Eq. ( 3), we therefore find σ A 1 ln 10…”

Quantum Illumination with a generic Gaussian source

“…It is worth noting that, although Gaussian entanglement is the main resource of QI, previous literature has also considered the use of separable non-Gaussian sources with non-positive P-representations, finding an advantage over a restricted classical benchmark [11]. More generally, quantum correlations beyond entanglement have also been considered for a number of other quantum information and computation tasks [12][13][14][15]. However, our current study is specifically focused on Gaussian states because they are, so far, the only sources showing a quantum advantage over the best classical benchmark.…”