Physical Society Colloquium

Sharper Images Through Quantum Imaging

Robert W. Boyd

Department of Physics, University of Ottawa &
Institute of Optics, University of Rochester

Quantum imaging is a research area that seeks to produce “better” images using quantum methods. The image can be better in one of several different ways. It might possess better spatial resolution, it might display better signal-to-noise ratio, or it might be able to be formed using a very small number of photons. From an operational standpoint, we can consider quantum imaging to be an imaging modality that seeks to exploit the quantum properties of the transverse structure of light fields. In this presentation, we describe several different recent examples of advances in the field of quantum imaging.

Figure 1. Typical quantum imaging setup

One such example is afforded by quantum phase imaging. Many biological materials, especially cellular materials, possess very small contrast in terms of the amplitude of a light field transmitted through the material. However, the transmitted field does show significant structure in terms of the phase of the transmitted light. Many of these materials are optically quite fragile and cannot withstand a high intensity light field. High intensities are required for certain applications such as short-exposure imaging to monitor the dynamical changes in the structure of the material. The problem with optical damage is aggravated through use of short illumination wavelengths, which are normally required in order to obtain good spatial resolution of the image. These difficulties can largely be mitigated through use of quantum imaging methods. For example, quantum imaging can make optimum use of a small number of photons in an image-bearing field. Also, the spatial resolution can be limited not by the wavelength of light being used but by some fraction 1/N of this wavelength, where N is the number of photons in the quantum state that interrogates the object to be imaged. A quantum phase-imaging setup similar to the one used in our recent work is shown in Fig. 1. In our work, we were able to achieve a spatial resolution 1.7 times better than that of a classical imaging system with the same numerical aperture. Moreover, the measured phase shift of the light transmitted through the sample was 2.0 times larger than that of a classical imaging system.

Reference:
[1] Black, A. N., L. D. Nguyen, B. Braverman, K. T. Crampton, J. E. Evans, and R. W. Boyd, “Quantum-enhanced phase imaging without coincidence counting”, Optica Vol.10, 952-958, 2023.