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Developing entangled photon sources in the near- and mid-IR

The QuantIC Enhanced Imaging Hub is led by The University of Glasgow and brings together industry and academia in a collaborative project to revolutionise imaging across industrial, scientific and consumer markets.  

Quantum technologies using single and entangled photons underpin developments in computing, information processing, sensing and imaging. Application areas span defence and security, healthcare, intelligent transport systems, space and low orbit, and climate change. Development of efficient single and entangled photon sources is therefore a key area of research.  

Spontaneous parametric down-conversion (SPDC) is an important nonlinear optical process for the generation of single photons and entangled photon pairs. This is routinely achieved using bulk non-linear crystals. Process conversion rates and spectral response are dictated by the crystal symmetry and bulk electronic structures which limit custom tunability and design. Non-linear metamaterials and metasurfaces represent a novel and versatile choice for enhancing light-matter interaction at the nanoscale. The design and engineering of meta-atoms in photonic crystals improve SPDC rates and enable device operation in a wider/tuneable spectral range. The application of these structures could enable new and improved quantum imaging methods for specific single and entangled photon studies.  

NPL is working in collaboration with the Experimental Solid State Physics group (Prof Rupert Oulton and Prof Chris Phillips) at Imperial College London. We are undertaking research and development on gold-based metasurfaces for their use as non-linear photonic crystals for SPDC. Our efforts include near-field optical characterisation of gold-based single antenna and antenna/waveguide metasurfaces. This is used to evaluate coupling efficiency of far-field mid-infrared light, using our cross-polarised s-SNOM facilities. These studies provide insight into the performance of the designed metasurfaces for their optimisation and subsequent evaluation for SPDC which can lead to applications in many quantum technologies. One such example is quantum imaging with undetected photons using entangled photons generated via SPDC photonic crystals. Expensive infrared and even THz detectors could thus be replaced with cheaper standard visible cameras in applications such as biosensing, chemical identification, MIR-THz device development and quantum information processing.   

Find out more about the QuantIC Enhanced Imaging Hub

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The cross-polarised scattering scanning near field optical microscopy (s-SNOM) capabilities at NPL have been developed to allow the sub-wavelength resolution imaging of coupled modes in:

  • single nano-antennas at targeted resonances (on left above), and
  • nano-antennas/waveguides arrays to evaluate coupling efficiency in a broad spectral range in the mid- infra red region (on right above).


Imaging of mid-infrared light in nanoantenna arrays