Quantum Optical Techniques for Biomedical Imaging

TL;DR

Biomedical imaging seeks higher resolution and lower radiation dose without sacrificing safety. This paper surveys quantum optical imaging modalities that exploit entanglement, squeezing, and quantum correlations—such as QOCT, sub shot-noise imaging, entangled fluorescence, ghost imaging, induced coherence, and multi-parameter imaging—alongside quantum-inspired classical approaches. Key findings include potential gains in axial resolution, SNR at low light, and the ability to image through scattering media or perform ultraweak photon emission sensing, while recognizing substantial practical hurdles like decoherence, limited photon flux, detector tradeoffs, and standardization gaps. The authors argue for hybrid, integrated photonics, and machine-learning–assisted strategies to translate these quantum techniques from laboratory demonstrations to clinically relevant imaging tools, with significant impact in neuroscience, ophthalmology, and regenerative medicine.

Abstract

Quantum imaging is emerging as a transformative approach for biomedical applications, applying nonclassical properties of light, such as entanglement, squeezing, and quantum correlations, to overcome fundamental limits of conventional techniques. These methods promise superior spatial resolution, enhanced signal-to-noise ratios, improved phase sensitivity, and reduced radiation dose, for potentially safer and more precise imaging for delicate biological samples. Here, we present an overview of quantum optical biomedical imaging technologies as well as quantum-inspired imaging methods, including quantum optical coherence tomography, quantum optical microscopy, ghost imaging, multi-parameter quantum imaging, and imaging with quantum-grade cameras. We describe the operating principles, biomedical applications, and unique advantages of each approach, along with the specific challenges for their translation into real-life practice. This review aims to guide future research toward advancing quantum imaging from experimental demonstrations to impactful biomedical tools.

Figures (8)

• Figure 1: Schematic of a SPDC-based quantum entangled light beams generation, where the conservation of the total energy and momentum in the SPDC process are held
• Figure 2: (a) A QOCT setup, where two-dimensional transverse (xy) images (C-scans) of an onion-skin sample (coated with gold nanoparticles) acquired at various axial depths (z). Two-dimensional axial (xz) images (B-scans) of the onion-skin are recorded at different transverse positions (y). A pronounced response, corresponding to a reflecting surface, is evidenced by a reduction in the measured coincidence rate. (b) C-scan of onion skin sample in different depths, (c) B-scan of onion skin bib197.
• Figure 3: (a) A scheme of entangled microscopy in a multi-photon fluorescence microscope where two entangled photons are directed at fluorophores, resulting in photon-pair absorption bib202. Multi-photon absorption by fluorophores reduces the number of photons needed to illuminate the sample with a fixed SNR, minimizing potential damage. (b) Quantum measuring using N00N states, where two correlated light beams illuminate slightly different sections of a sample bib208.
• Figure 4: Quantum imaging with a very low intensity light of SPDC (a) Full imaging experiment setup where a 355 nm laser pumps a BBO crystal, generating collinear down-converted photon pairs at 710 nm. The crystal’s output facet is imaged onto both the microscope slide (holding the sample) and then onto the ICCD camera. An image-preserving delay line is included to compensate for electronic delays in the triggering system bib115. (b) Ghost imaging - The object (sample) is positioned in the heralding arm, and the camera is triggered by photon detections at the heralding detector. (c) Heralded imaging – The object is placed in the camera arm, while heralding detector events still trigger the camera. (d) Direct imaging – The object remains in the camera arm, but the camera is triggered internally at a rate matched to the single-photon counts measured by the counter in the heralding arm. (e) Ghost image (reconstructed) from non-local imaging of setup (b) from a light-sensitive biological sample, from a weakly absorbing wasp wing with the scale bar of 400 $\mu$m bib115.
• Figure 5: Quantum imaging with undetected photons. Left) Green laser light is divided by the beam splitter BS1 into two paths, modes $a$ and $b$. Path $a$ pumps the nonlinear crystal NL1, where collinear SPDC may generate a pair of photons at different wavelengths, referred to as the signal (yellow) and idler (red). After traversing the object O, the idler photon is reflected by the dichroic mirror D2 so that it becomes indistinguishable from the idler produced in NL2. As a result, the final emerging idler state $\lvert f \rangle_{i}$ carries no information about which crystal generated the photon pair. Consequently, the signal states $\lvert c \rangle_{s}$ and $\lvert e \rangle_{s}$ interfere at the beam splitter BS2, and the output signal beams $\lvert g \rangle_{s}$ and $\lvert h \rangle_{s}$ reveal the idler’s transmission properties through the object O. Right) Inside the interferometer, placing the cardboard cut-out leads to constructive and destructive interference at the outputs of the beam splitter (BS).bib116