Multiparameter Quantum Metrology based on Squeezed Light Interferometry

Abstract

The aim of this thesis is developing interferometric schemes which are scalable
and can be implemented with current quantum optical technologies and yet
achieve quantum-enhanced metrological sensitivity. The fundamental precision
limit in classical interferometric schemes is the so-called standard quantum
limit. Harnessing distinctively quantum-mechanical features such as entanglement, quantum technologies have the potential to take us beyond what
is fundamentally impossible in a classical setting. Unfortunately, while it is
well known this is possible in theory, current optical technology can only produce
quantum resources which would not produce any appreciable quantum
advantage over classical methods.
The work presented in this thesis shows how squeezed states of light can
be used to overcome some of the most pressing technological limitations in
quantum metrology and can be used as a basis for an experimental demonstration of a quantum advantage in sensitivity with a significantly high mean photon number. The use of squeezed states allows us to forego the production of Fock states and difficult post-selection techniques for the creation of NOON states. It foregoes the reliance on entanglement to use as quantum
resource, except perhaps for the one that can be generated simply by running
photons through a linear optical network. Squeezed states also offer the technological advantage of foregoing number-resolving detectors in favour of more accessible on-off photodetectors.
A novel scheme for the estimation of a linear combination of phase shifts
with arbitrary non-negative weights is proposed which achieves the Heisenberg
limit. An intuitive graphical interpretation of the 2-mode scenario is found.
It turns out a Mach-Zehnder configuration can actually estimate either the
sum of the phase shifts associated to the two arms of the optical network–
provided the relative phase of the squeezers is known– with Heisenberg-limited
sensitivity, or the difference of the same phases at the standard quantum
limit. By introducing photon losses it is proven that the estimation protocol
in both cases is robust to detector inefficiencies. The interaction between
photon losses at the optical network level and at the detection level reveals
an unexpected dithering effect which can provide an advantage in the highlosses
regime.

Date of Award	12 Mar 2023
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Vincenzo Tamma (Supervisor) & Andrew Lundgren (Supervisor)