Quantum sensing schemes based on multi-photon interference

Abstract

The recent advances in the field of quantum mechanics have been incessantly stimulating the development of increasingly ingenious and innovative technologies which exploit the laws and rules of the microscopic world. Ranging from computing to biology, medicine, cosmology, imaging, sensing, cryptography and neural networks, quantum technologies appear to consistently outperform their classical counterparts. In particular, the fields of quantum sensing and quantum metrology propose schemes for the estimation of physical properties, such as lengths, time intervals, temperatures, and more, achieving enhanced levels of precision. However, such an enhanced sensitivity usually comes at a price: the use of probes in highly fragile states, the need to adaptively optimise the estimation schemes to the value of the unknown property we want to estimate, and the limited working range, are some examples of challenges which prevent quantum sensing protocols to be practical for applications.
This thesis addresses these challenges, proposing feasible estimation schemes employing easily realisable resources, such as squeezed light or single photons, which achieve the desired metrological quantum advantage. More in detail, it is here shown that, in the estimation of any parameter affecting multiple components of an arbitrary M-channel linear optical network, the need to adaptively optimise the network can be reduced to a requirement of prior knowledge on the parameter which can be achieved through a classical estimation strategy, while it can be completely removed at the price of simultaneously employing multiple detectors. In this way, schemes for the quantum enhanced estimation of a parameter distributed in a linear network, or linear and non-linear functions of multiple parameters are proposed. Moreover, it is shown that resolving the frequencies of two independent photons, after they impinge on a beam-splitter, unveils information on their delay in time also in the regime of small temporal overlap between the photons, to which instead non-resolving strategies are insensitive. The sensitivity to the time delays here stems from interference which can be observed through frequency-resolving detectors regardless of the distinguishability in time of the photons.

Date of Award	Dec 2021
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Vincenzo Tamma (Supervisor)