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arXiv:2402.13157 · Physical Review Applied

Interferometry with few photons

Quimey Pears Stefano, Agustina G. Magnoni, Darío Rodrigues, Javier Tiffenberg, Claudio Iemmi

Published Jun 21, 2024• 0 citations
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Abstract

Optical phase determination using just a few photons is crucial for applications in biological imaging and quantum information processing, yet is hampered by shot noise from the source and readout noise from the sensor. Employing a skipper CCD, which can arbitrarily decrease readout noise, the authors investigate these noise sources individually and demonstrate a significant improvement in detection fidelity with reduced detector noise. With fewer than three photons per pixel, the accuracy of phase estimation suffers, regardless of detection noise. This insight highlights the skipper CCD's potential to enhance high-fidelity phase detection in ultralow-light scenarios.

DOI
10.1103/physrevapplied.21.064050

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Optical phase determination using just a few photons is crucial for applications in biological imaging and quantum information processing, yet is hampered by shot noise from the source and readout noise from the sensor. Employing a skipper CCD, which can arbitrarily decrease readout noise, the authors investigate these noise sources individually and demonstrate a significant improvement in detection fidelity with reduced detector noise. With fewer than three photons per pixel, the accuracy of phase estimation suffers, regardless of detection noise. This insight highlights the skipper CCD's potential to enhance high-fidelity phase detection in ultralow-light scenarios.
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Optimizing the sensitivity for interferometric measurement of optical phase involves maximizing the intensity of the illuminating light source and minimizing any noise sources. Limits to the light source intensity may arise from the availability of a stable high-power laser or from damage to the system being measured. For example, we describe here a scanning confocal polarization microscope designed to image the dynamics of nerve networks. In this case the light intensity limit is set by several factors, including the scanning rate, the required response time and damage limits of the biological system. Assuming a stable experimental configuration for the interferometer and light source, the limiting noise source for visible light interferometry is shot-noise associated with the quantum state of the light inputs to the interferometer. Shot-noise can be thought of as arising from vacuum fluctuations entering the dark input port of the interferometer.(1) These vacuum field fluctuations combine with the light entering the other port to cause shot-noise in the detected photocurrent at the output ports of the interferometer. This shot-noise current normally limits the measured phase variance Δϕ to a value of 1/N where N is the average number of photons detected in a measurement interval. We describe an experiment which demonstrates that this shot-noise limit can be improved by injecting squeezed vacuum into the normally dark input port.(2) In this case the phase variance is reduced below the 1/N limit by the degree of squeezing. In contrast to early experiments,(2) we are now operating the interferometer in a dark fringe mode(3–5) in order to avoid setting a limit to the light level caused by detector saturation (near 1 mW).
Quantum enhanced optical measurement protocols aim at reducing the uncertainty in the estimation of some physical quantities of a system below the shot-noise limit, classically unavoidable. In particular when small number of photons is used the shot noise can be the main source of uncertainty, in these cases the use of quantum light is of great interest. Note that there are several situations where the number of photons in the probe can not be increased arbitrarily, as when fragile biological samples are under investigation. Two different imaging protocols are discussed in the following.