Microscopy with Quantum States of Light

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Microscopy is a technique to image samples, such as biological cells that cannot be seen unaided by the eye. Signal-to-noise ratio (SNR) and precision are important aspects for such imaging technique. The current methods for microscopy imaging rely on high intensity light that may degrade irreversibly the sample through photo-damage and photo-bleaching. In addition, the laws of quantum mechanics limit the performances of these imaging techniques due to the inherent noise of the electromagnetic field in the quadrature space.

In this thesis, I introduce two novel imaging techniques with quantum states of light acting as probes. First, I report the implementation of super-resolution microscopy with a two-photon interference: the Hong-Ou-Mandel effect. By measuring the time delay between a reference photon and a probe photon transmitting through the sample, the variation in thickness of a semi-transparent sample is evaluated in combination with two dimensional raster scanning. The wavelength separation between the signal and the idler of a two-colour entangled state controls the sensitivity of the microscope where sub-μm axial precision is reported using up to 12.3 nm of detuning and ∼ 104 detected photons pairs. Within the loss of the experimental setup, this corresponds to a sample illumination of fW level, corresponding from 8 to 12 order of magnitude below classical microscopes achieving similar performances. Consequently, the HOM microscope, reach higher Fisher information per photon, which can be an important consideration for photo-sensitive samples and can otherwise be a limiting factor for measurement precision.

In the second part, noise reduction within a coherent state due to Kerr squeezing with a photonic crystal fibre is used to enhance the precision for absorption microscopy. The classical noise is reduced by taking fast measurements and modulating the probe in time to be in a shot-noise limited bandwidth of the detector and the laser. Then, with the noise reduction of the amplitude squeezed light and despite the inherent noise of the laser, I report shot-noise precision on single-pixel measurements with squeezing of Φlog = −0.88 dB for ∼200 μW of light detected. Furthermore, a quantum advantage of 1.3 ± 0.1 with Φlog = −0.62 dB is demonstrated for confocal microscopy imaging, where I show that sub-shot noise precision can be possible with a higher squeezing value above Φlog ≤ −1.6 dB.

Applications for bio-imaging can be found for these two microscopes, where high sensitivity or enhancement in the precision can be done without photo-damaging or photo-bleaching the sample either by having a probe at the photon level or by taking fast measurements and limiting the sample illumination
Date of Award5 Dec 2023
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJonathan C F Matthews (Supervisor) & Alex R McMillan (Supervisor)


  • quantum imaging
  • microscopy
  • Hong-Ou-Mandel interference
  • Kerr squeezing

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