Security & Sensors

Security & Sensors in Quantum Imaging

In addition to imaging through complex media, quantum phenomena will have impact in other areas of defence imaging, especially with respect to enhanced sensitivity, covert or unspoofable operations. Working in collaboration with industry partners, we will develop quantum LIDAR and radar and covert imaging systems. 

Quantum LIDAR and radar

Radar based on quantum correlations offers the advantages of increased range, counter-stealth and resistance to jamming. There is currently no consensus on which technologies will win out for practical implementation but a national approach to R&D is emerging, driven by both industry and government. Theoretical work will devise testable approaches to maximise the advantages across both long (>10km) and short (≈100m) range. A protocol proposed in the 1st phase of QuantIC8 will be applied to laserbased radar and LIDAR systems. This essentially exploits a random pulsed source and correlation detection to create unspoofable Lidar. It is even possible to use broad band random time-correlated pulses that can hide in the daylight modes realising a covert Lidar. We will collaborate with industry partners to demonstrate covert and unspoofable Lidar systems that use quantum or classical random number generation.

Few-photon spatio-temporally correlated imaging

CMOS-interfaced high-density and high (MHz) frame rate LED array technology – unique to QuantIC and interfaced to the programme’s novel SPAD imaging systems – can be modulated in time and space over a number of different timescales concurrently. This allows multi-mode operation (e.g. photometric stereo, spatial registration, data comms., time-of-flight) at the few photon level in novel schemes that are robust to background noise and are fully compatible with computational imaging/deep learning protocols to be developed in the programme. In addition, the technology can in principle operate at wavelengths spanning the deep ultraviolet to amber/red and by down-conversion into the infrared. We will explore these emerging hardware capabilities for application in covert imaging and imaging in a variety of scattering media/environments including surfaces and interfaces, water and air, in the latter case exploiting for the first time the properties of (solar blind) deep ultraviolet structured illumination.

Enhancing Backscatter Imaging Systems 

We are working to improve the sensitivity of systems that rely on the detection of backscattered light. Nowhere is this more critical than in systems relying upon the detection of backscattered photons. We will use complex beam shaping to enhance the number of backscattered photons. These techniques will increase the capabilities of techniques such as looking around corners, increase the sensitivity of trace gas detection and enable remote audio measurements.

Imaging Using Undetected Photons

Work pioneered by Zeilinger allows imaging with photons at different wavelengths to those that interact with the imaged object but are not detected. We aim to use spectroscopic imaging technologies in completely new parts of the spectrum. (3µm<λ<10µm). This spectral region is technologically challenging but is where bond-specific vibronic absorptions give distinctive fingerprints for IR analysis.  As well as using conventional bulk crystal SPDC sources, we will use narrowband photon generation in fibres, and nanophotonic designer non-linear elements. Underpinning theoretical work will investigate the classical limit, compared to that using quantum correlation to enhance performance beyond classical shot-noise and diffraction limits.

Wavelength-agile SPDC Sources and Wavelength Convertors

Bulk SPDC crystals are transparent only to ~3.5µm.  We are using nano-photonic SPDC sources to extend wavelength limitations to entanglement studies, and to exploit the correlations to enable single–photon imaging (using existing visible detector arrays) across the mid-IR. Using planar array structures on thin, transparent substrates avoids the absorption and phase matching limitations of bulk crystal SPDC sources and enables momentum filtering.

Gas Sensing Without Detection

We are engaging with industry to develop non-linear interferometry for gas sensing at ~3.3 µm but allow use of inherent more sensitive detectors at 1.55 µm. The long wavelength outgoing light will pass through the region where gas is to be sensed and returned to recombine with lasers at the crystal to allow more sensitive detection at short wavelength. We will extend this preliminary work to longer wavelengths incorporating novel nonlinear elements to extending operation to the 5-10µm wavelength region in collaboration with other source developments.