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Advancing Imaging Technology with Quantum Optical Imaging Techniques - Federica Villa’s Team at Polytechnic University of Milan


  1. Quantum coherence and entanglement can push the resolution and sensitivity limits of quantum imaging and microscopy well beyond what is possible with traditional optics.
  2. To realize these quantum techniques, detectors with specific capabilities are required.
  3. This paper aims to highlight the importance of single photon avalanche diode (SPAD) based sensors for quantum imaging and microscopy applications, paving the way towards next-generation ideal quantum imagers.
  4. After reviewing the main quantum physics-based techniques for enhancing image resolution and sensitivity, the pros and cons of various sensors like avalanche photodiodes (APDs), intensified and electron-multiplying CCDs (ICCDs and EMCCDs) are outlined.
  5. The analysis then focuses on SPAD-based detectors, identified as prime candidates for quantum imaging, critically discussing requirements and performance and drawing connections to existing SPAD architectures with capabilities fitting the application.
  6. Ultimately, next-generation quantum imagers should integrate all the best architectural choices presented here for coincident photon detection and efficient event-driven readout, also exploiting suitable technologies and SPAD designs to optimize the detection performance.

A Quantum Revolution in Resolution

Leveraging unique quantum entanglement and coherence, quantum optical techniques push the resolution and sensitivity limits of traditional optics. By manipulating individual photons and photon pairs, quantum imaging systems visualize nano-scale cellular and material structures. This breakthrough harnessing the particle nature of light opens up new horizons for biological and medical applications.

Essential Single Photon Detection

Fundamental to quantum optical imaging is efficient single photon sensing. Unlike conventional APDs or ICCDs, single photon avalanche diodes (SPADs) can accurately detect individual photons and their arrival times to probe inter-photon coherence. This unique strength makes SPAD sensors ideal solutions.

Quantum Tagging of Photon Coincidences

Quantum imaging often relies on photon entanglement and coherence, requiring coincident photon detection across multiple optical paths. With timing resolution down to picoseconds, SPAD sensors can effectively tag coincident photons, extracting vital quantum information through event-driven readout.

Enlitech’s SPD2200 stands as the pioneering commercial-grade SPD characterization system, specializing in the analysis and testing of crucial SPADs essential for LiDAR advancements. Recently successfully sold to one of the top three global wafer fabs for SPAD. With its offering of Spectral and Time Domain Characterization Modules, it adeptly caters to diverse measurement requirements in dToF module development, allowing adaptable module selection or combined utilization for a comprehensive characterization approach.

Quantum Effects Across Length Scales

Single photon detection facilitates quantum imaging techniques across microscopic to macroscopic length scales – from optical coherence tomography for cellular/tissue 3D imaging to single photon self-correlation spectroscopy for non-invasive deep tissue sensing. As detection methods progress, the potential grows for quantum imaging in life and medical sciences.

Awaiting New Quantum Visions

Today, quantum microscopes and cameras harnessing single photon detection remain in proof-of-concept stages but already far exceed conventional resolution and sensitivity. Fully utilizing quantum principles, quantum optical imaging will lead a revolution that reveals unseen facets of our world and expands human perception. Let’s look forward to the new quantum vision!

Figure 20
Pixel architecture of the gated SPAD imager.[64] Reproduced with permission.[64] Copyright 2018, SPIE.

Figure 26
PDP comparison among SPADs fabricated in different technologies.[54, 65, 81, 82] For completeness, PDPs related to ICCD PI-MAX4-III Gen and EMCCD ANDOR iXon3 are added.