Rarity Group

Research interests and activities

Quantum communications

We work on free space quantum key distribution (QKD) from short distance (hand held) consumer applications to satellite to ground scenarios (500km). Key ongoing projects involve designing and building ultra-compact quantum key transmitters for use in small satellite (CUBESAT) applications. We are involved in three separate missions with planned launches in 2023 and 2024 funded by EPSRC, UK space agency and Innovate UK.

Also within the EPSRC Quantum communications technology hub we work on measurement device independent (MDI) QKD, tamper proof quantum key exchange, chip-scale entanglement sources, and novel quantum counterfactual communications schemes where information is exchanged without photons arriving at the receiver.

Quantum sensing and imaging

We have developed a range of quantum enhanced measurements:

  • Sub-shot noise Imaging: We demonstrate imaging with noise level below the shot noise limit by creating quantum identical photon beams. Using one beam as a reference and the other passing through a sample allows an estimate of sample transmission with better signal to noise than classical methods.
  • Quantum illumination rangefinding: Here we use a bright pair photon sources to make a heralded source of single photons for rangefinding featuring strong background light suppression compared to equivalent weak coherent sources. By using energy-time correlations in the source we have demonstrated a covert spread spectrum heralded source that could achieve significantly higher brightness and loss tolerance. We are now developing ‘quantum inspired’ random pulse spread spectrum LIDAR demonstrator to reach several kilometre range.   
  • Short wave infrared gas sensing and gas sensing without detection: We have developed Carbon dioxide and Methane remote sensing systems that exploit the single photon sensitivity of photon counting detectors and classical random modulation differential absorption LIDAR. This has been extremely successful and led to a start-up company QLM (qlmtec.com). In In the group we continue research aspects of this work developing mid infra-red gas sensing using the techniques of non-linear interferometry to transfer a sensing signal at 3.28 um onto a 1.55 um beam detected using single photon sensitive detectors.

Light matter interactions

We are interested in developing the concept of spin photon interfaces. We are developing 1D cavity model where the scattering of photons by single emitters has near unit efficiency. When such an emitter carries a spin and has spin dependent interactions with photons we can entangle spins and photons thus generating a fundamental quantum gate. To realise such a concept in the laboratory we are working with:

  • NV-centres (with Prof Balram’s group): We have worked on measuring spin in bulk diamond in the past but now focus on fabricating ordered arrays of nano-diamonds. These are embedded into silicon nitride waveguides for efficient collection of emitted light enabling rapid spin readout (QCSCALE project).
  • Quantum dots (with Prof Oulton’s group): We are studying micropillar microcavities containing single dots carrying a single electronic charge. These systems are engineered to have high coupling efficiency to incoming light. Reflected light from these ‘1D’ cavities carries information on the electron spin due to spin selectivity of the transitions. We can see evidence of spin-photon entanglement in these systems.

Wavelength scale structures

We are looking to enhance photon ‘atom’ interactions by confining light in wavelength scale structures. These are 1D, 2D and 3D crystals with crystal lattice periods arranged to reflect near infra-red light. We have fabricated 3D materials showing full photonic bandgaps at communications wavelengths. Structures are fabricated using 3D nano-lithography to make 3D polymer photonic crystals. These crystals can then be backfilled with high index materials using vapour deposition methods. We visualise the band structure of these crystalline materials using the technique of Fourier imaging spectroscopy.

Major research topics

  • Quantum Communication
  • Quantum Imaging and sensing
  • Light matter interactions
  • Wavelength scale structures
  • Diamond NV-centres and Quantum dots
  • Integrated quantum photonics

(pictured above: example of sub-shot noise imaging)

Current postdocs and research fellows

Current PhD students

Active grants

Confocal microscope for characterising the spin of diamond colour centres

Selected publications

Full publication list, including patents list can be found in Google Scholar and Bristol Research

Back filled photonic crystal structure designed for full photonic bandgap at 1.55 µm wavelength.
Measuring gas absorption at 3.28 µm using 1.55 µm photons via non-linear interferometry.
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