This PDF file contains the front matter associated with SPIE Proceedings Volume 12795, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Quantum technology promises improvements in imaging, computing, and communication, for example using the resource of entanglement between photons with spatial correlations. Detecting spatial correlations, or coincidences, between entangled photons scalably, efficiently, and affordably is therefore an essential capability. However, this task is non-trivial for existing camera technologies, which require low illumination intensities or low detection duty cycles to count coincidences at high signal-to-noise ratios, resulting in long acquisition time, or use expensive custom electronic components. Here, we present an entanglement imaging system based around a novel Single-Photon Avalanche Diode (SPAD) array camera, optimized for sparse illumination with correlated photon pairs. The system is capable of maintaining a duty cycle close to 100%, while simultaneously detecting spatially resolved coincidences with high SNR, enabling the acquisition of real-time entanglement videos at a ~Hz frame rate. We use our system to demonstrate real-time monitoring of entanglement interference visibility, optical system point spread function, as well as real-time widefield entanglement-enhanced phase imaging. Our results show that SPAD array cameras represent a natural choice for scalable entanglement detection and imaging applications.

Gas leaks pose a prevalent issue in industry and can have pressing impacts on individual safety and the environment. There is demand for new technologies that can ease, and reduce the cost of, detection of the source of leaks, both on a large and small scale. We present a device capable of visualizing the gas involved in the leaks allowing for an accessible tool in source location. Our current device can image methane leaks from ranges of up to 10m. By imaging a scene illuminated using a laser diode tuned to an absorption band of methane, followed by imaging at a similar but non-absorbed wavelength one can build a differential image of the scene and identify the presence of methane. This differential signal is then processed and assigned a false colour, in order to be overlaid upon an accompanying visible live feed. This system is adaptable and could be used to detect other gas species with modification to light source and detector. Future candidate gases would be based upon industry interest with acetylene, a common and flammable welding gas, being an example. The system is also robust enough to be drone mounted, we present data from conducted test flights. These flights demonstrate new ways in which the system can be used, such as in monitoring of difficult to access pipe geometries and for preset flight paths along expansive pipelines. This can allow for a more automated gas detection process, that is straightforward to review.

Parametric down-conversion converts pump photons in pairs of correlated signal and idler photons. Even when pumped by a single-mode laser, the signal and idler photons are spread over several thousand spatial modes yet strongly correlated with each other in their position and transverse momentum. These correlations enable applications in imaging, sensing, communication, and optical processing. Here we show that, using a photon number resolving camera, spatial correlations can be observed after only a few 10s seconds measurement time. Photon number resolving camera technologies are likely to find wide use in quantum enhanced low-light imaging systems.

Quantum imaging experiments rely on the detection of correlated photon-pairs. Due to experimental configuration the detected strength of correlations can be larger than a single detector pixel and as such may not be collected by a simple algorithm. Here we show the improvement offered by integrating over the correlation peak to enhance the pixel-by-pixel AND operation and demonstrate an enhancement of over approximately 43%. This technique to collect an increased proportion of correlated photon-pairs can be used to improve the output of quantum enhanced imaging techniques for use in low-light imaging systems to improve noise rejection, image contrast, and image resolution.

We review recent experimental and theoretical results of photon interferometry on rotating platforms. Quantum phenomena such as two-photon interference and entanglement can be controlled with mechanical rotations in a regime accessible to table-top experiments. We first discuss experiments demonstrating how low-frequency mechanical rotations affect the bunching behavior of frequency-entangled photon pairs. It was shown that low-frequency mechanical rotations can affect the temporal distinguishability of photons and can transform photonic behavior from perfectly indistinguishable (bosonic behavior) to perfectly distinguishable (fermionic behavior). We then give a future outlook for testing the generation of entanglement from mechanical rotation. A recent theoretical work showed that generating path-polarization entanglement from mechanical rotations could be verified with present technology. These works make a strong case for further exploration of quantum phenomena at the interface with non-inertial (rotational) motion.

Quantum technologies containing key GaN laser components will enable a new generation of precision sensors, optical atomic clocks and secure communication systems for many applications such as next generation navigation, gravity mapping and timing since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from the U.V. to the visible. We report our latest results on a range of AlGaInN diode-lasers targeted to meet the linewidth, wavelength and power requirements suitable for quantum sensors such as optical clocks and cold-atom interferometry systems. This includes the [5s²S_1/2-5p²P_1/2] cooling transition in strontium⁺ ion optical clocks at 422 nm, the [5s₂ ¹S₀-5p¹P₁] cooling transition in neutral strontium clocks at 461 nm and the [5s² s_1/2 – 6p²P_3/2] transition in rubidium at 420 nm. Several approaches are taken to achieve the required linewidth, wavelength and power, including an Extended Cavity Laser Diode (ECLD) system and an on-chip grating, distributed feedback (DFB) GaN laser diode.

Quantum Key Distribution (QKD) uses quantum states in an optical channel to grow a key with guaranteed security. Satellite QKD (SatQKD) is a proposed topology for QKD which provides unlimited terrestrial range for links and allows mobile access. SatQKD (and generally satellite optical communications) Optical Ground Stations (OGSs) require an optical beacon, a beam from OGS to satellite to assist pointing the satellite’s telescope(s). Beaconing is challenging for SatQKD due to the single-photon sensitivity of the receiver to back-reflected beacon light and the need to point the outgoing beacon ahead of the downlink channel (the Point-Ahead Angle (PAA)). Hence, beacon light is often propagated through separate telescopes, increasing complexity. We describe a spatially separated beacon which reduces back-reflection errors and how its PAA is achieved. The far field beams of this and other beacon architectures are compared. Beaconing in this way can give greater up-time (due to less maintenance) and a lower cost barrier to development. A related system could have similar benefits for laser-guide-star telescopes.

The security provided by Quantum Key Distribution (QKD) can be strongly compromised by interception of the raw and sifted key through side channels, such as the practical characteristics of electronic components used in the transmitter and receiver modules. Some out-of-band electromagnetic attacks have already been identified and tested in components used in QKD, such as quantum random number generators. In this presentation, we explore out-of-band electromagnetic attacks of other components used in a quantum receiver, such as Single Photon Avalanche Diodes (SPADs), and the time-correlated single-photon counting module. We measured the electromagnetic (EM) radiated emissions of the components to quantify the emanation levels and evaluate the vulnerability that this QKD side channel may present. The test was conducted in an anechoic chamber up to 1 GHz, at 3 m distance, and rotating the SPAD to provide radiation from four azimuth angles. Results show that measurable radiated pulses are generated by the SPAD in this frequency range due to dark count pulses and due to incoming Single-Photon level pulses. Dark counts of few kHz and Single-Photon level counts of hundreds of kHz were considered in the tests. EM radiation frequency bands with main emissions and electric field strengths are identified for both operation conditions.

A limitation of free-space optical communications is the ease with which the information can be intercepted. Overcoming this limitation is possible by hiding the information within the background optical noise that is present in all real-world situations. We demonstrate the limitations of our experimental system for transferring images over free-space using a photon-pair source emitting two correlated beams. The system uses spontaneous parametric down-conversion to create photon-pairs, where one photon contains the spatial information and the other the heralding information.