AbstractOptical shot-noise is a limiting factor common to all classical imaging and spectroscopy applications. Using quantum-intensity-correlated light beams generated via processes such as downconversion and four-wave mixing, one may surpass this classical limit and obtain greater measurement precision for a given photon flux. However, previous work in quantum-enhanced parameter estimation has primarily used single-photon intensities and infrared-wavelength sources, sometimes obtaining a precision advantage only in a post-selected regime rather than per exposed photon. These specifications are not practical for many applications that require greater optical power and visible wavelengths. In this thesis, we push quantum metrology technologies towards real-world applications with the development of a non-post-selected correlated-intensity photon source at blue and red wavelengths and picowatts to microwatts average power. The photon source which we develop employs a silica, few-mode fiber to produce twin beams via four-wave mixing, demonstrating a low-cost method of accessing novel visible wavelengths.
We first discuss the theoretical foundations of classical and quantum parameter estimation, developing a full theoretical model of our experiment, which includes realistic experimental effects such as loss, optical and detector noise, and thermal intensity fluctuations. We compare three absorption estimators and show how loss and optical noise may reduce their efficacy. This theory is confirmed with experimental data and characterizations of our source and detector. We also show that the photonic crystal fiber and single-mode fiber which we use to generate correlated beams via four-wave mixing can reliably produce visible-wavelength beams at microwatts of average power due to exponential parametric gain. Using this source, we perform an absorption measurement at the shot-noise limit, and show that sub-Poissonian intensity correlations are necessary, though not sufficient, for sub-shot-noise parameter estimation. The main experimental results of this work are a successful demonstration of twin-beam intensity correlations 3 dB below the coherent-state limit, overcoming challenges of using silica fibers such as optical noise from Raman scattering and precise mode coupling.
|Date of Award||23 Jan 2020|
|Supervisor||John G Rarity (Supervisor) & Jonathan C F Matthews (Supervisor)|