This PDF file contains the front matter associated with SPIE Proceedings Volume 13204, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Matter-wave interferometers show great a potential for improving inertial sensing. The absence of drifts recommends them for a variety of applications in geodesy, navigation, or fundamental physics.

Here, ultracold atomic ensembles, featuring a velocity distribution well below the photon recoil velocity, open up new perspectives. In contrast to standard laser cooling methods, they allow to reach better beam-splitting efficiencies and, hence, a higher contrast as well as to reduce systematic uncertainties and biases.

Presently, Bose-Einstein condensates (BECs) provide the means to achieve the lowest expansion energies of few picokelvin. Indeed, the momentum distribution of a BEC can be further narrowed after reaching the regime of ballistic expansion, where all mean field energy is converted to kinetic energy, by the application of the delta-kick collimation technique.

With such ensembles, Bragg processes can be driven with an efficiency of above 95% as well as Bloch oscillations performed without large atomic losses or dephasing. Both enable efficient large momentum transfer in interferometers to enhance their sensitivity for inertial effects. In a so-called twin-lattice atom interferometers more than thousand photon recoils are used to form compact but sensitive atom interferometers.

These methods not only bring in reach extremely accurate gravimeters and accelerometers but also gyroscopes. Like the Sagnac effect in ring laser or fiber gyroscopes, the sensitivity of atom interferometers to rotations increases with the space-time area enclosed by the interferometer. In the case of light interferometers, the latter can be enlarged by forming multiple fiber loops. However, the equivalent for matter-wave interferometers remains an experimental challenge. An atom interferometer with scalable area may be formed in a twin lattice combined with a relaunch mechanism to obtain multi loops as well. Due to this scalability, it offers the perspective of reaching unprecedented sensitivities for rotations in comparably compact sensor head setups.

Moreover, atom-chip technologies offer the possibility to generate a BEC and perform delta-kick collimation in a fast and reliable away, paving the way for field-deployable miniaturized atomic devices. Last but not least, the extremely low expansion energies of BECs open up to extend the time atoms spend in the interferometer to tens of seconds. This brings in reach unprecedented sensitivities in space-borne applications such as satellite geodesy.

Optically pumped magnetometers (OPMs) exploiting alkali metal vapours for accurate, precise magnetometry have benefited from improvements in components and techniques in recent years. Microfabrication of alkali cells and chip-scale lasers allow mass-production of compact sensors, and feedback an spin-preparation techniques, such as light-narrowing, allow enhanced performance, comparable with cryogenic SQUID magnetometers. I will introduce two OPM modalities developed at Strathclyde for geomagnetic operation- the digital alkali-spin maser and geophysical free-precession magnetometer. I will discuss the potential impacts of using these sensors for geophysical applications, including Global Navigation Satellite System (GNSS)-denied positioning, monitoring of space weather and magnetic anomaly detection. I will present developments in microfabrication and digital signal processing which will enable their widespread adoption.

Military and civilian operations worldwide heavily rely on accurate position estimation provided by global navigation satellite systems (GNSS). However, in recent years, it has become apparent that GNSS is vulnerable to jamming and spoofing, necessitating the development of alternative solutions. Novel quantum-sensing technology offers promising alternatives, notably the Magnetic Aided Inertial Navigation System (MAINS). MAINS employs a combination of scalar (e.g. optically pumped magnetometers, or OPMs) and vector magnetometers (e.g. fluxgate sensors) to measure the ambient magnetic field. By correlating these measurements with a pre-established map of magnetic values in the region of navigation, the system can correct the accumulated errors of the inertial navigation system. In Spring 2024 a shared trial was organized by the NATO Centre for Maritime Research and Experimentation (CMRE), the University of Pisa and the Netherlands Organisation for Applied Scientific Research (TNO) in La Spezia, Italy. In this presentation, we will demonstrate the performance of MAINS using the magnetic data acquired in this trial.

We present an advanced quantum ghost imaging (QGI) setup that enables low-noise, three-dimensional imaging and ranging of distant objects. A key technical innovation is asynchronous detection by independent single photon detectors, which significantly simplifies existing setups and allows imaging at arbitrary distances. Recent experimental results demonstrate low-noise imaging and efficient object ranging. An important quantum advantage with regard to secure active sensing is indistinguishability from background noise for external parties.

Quantum illumination is one of the main paradigms for implementing quantum radar in the low-frequency spectrum. Here, we discuss how to ease the open-air application of the protocol. I first define an experimentally feasible receiver for an entangled signal-idler transmitter. This consists of measuring heterodyne the received signal and adaptively measuring homodyne the idler, reaching a maximal quantum advantage of 3 dB in the error probability exponent with respect to the optimal classical strategy. Our receiver requires only a single tunable JPA. To relax the bandwidth requirement at the transmitter level, we discuss a sequential protocol that uses patches of modes sequentially to probe the target region. We show that, in a practical scenario, the sequential protocol needs two orders of magnitude less bandwidth with respect to the non-sequential protocol, while keeping the same quantum advantage. We finally briefly discuss possible applications of quantum illumination for backscatter communication and covert communication.

One of the advantages of Rydberg atom-based detection of microwave and THz fields is weak distortion of the measured field, allowing for precise and stealthy detection. However, recent developments focused on using Rydberg atoms as a RF mixer with a local oscillator field in a superheterodyne-type detection that is no longer all-optical, as the local oscillator antenna has to be a part of the detector. Here we undertake the task of developing an all-optical detection, where the phase reference is provided not in local oscillator, but instead in the polarization of atoms. To realize this feature, we access the 13.9 GHz Rydberg transition in rubidium with two separate optical excitation paths and measure the beating of probe field. We report an overall detection sensitivity of 176 nV/cm/ √Hz and reliable operation up to 3.5 mV/cm of RF field, results that are parallel to superheterodyne detection method demonstrated in the same setup. The results of this work are largely based on an earlier conducted study, published as a preprint.¹ The present manuscript is meant to serve as an appendix to this work, focusing on putting this research in the context of all-optical detection schemes.

Quantum computers have the potential to solve some complex problems much faster than classical equivalents. Significant research efforts are aimed at determining which algorithms give which advantages for different use-cases. An application where quantum computers can possibly bring great advantages is solving (partial) differential equations, which has a broad set of applications, for instance in wave-propagation models. Few differential equations admit an analytical solution. For most heuristic methods are required to approximate a solution. Well-known heuristic techniques include the finite element and finite difference method, where the considered space is partitioned and systems of linear equations resulting from this partitioning need to be solved. Quantum computing puts forward new methods to solve these systems of linear equations and hence these differential equations. First, the HHL algorithm gives an efficient way to solve a linear system of equations. The HHL algorithm comes with drawbacks, but in this specific use-case some of these objections might be circumvented. Quantum computers furthermore offer the variational approach: an optimization-based path to solving differential equations. With this approach, the devices might even ‘learn’ the noise patterns emerging in present day quantum computers and compensate for it. In this work we revisit quantum methods for solving partial differential equations and consider how well they work in solving differential equations in practice. We also discuss possible caveats and bottlenecks of the approaches.

Mission planning often involves optimising the use of ISR (Intelligence, Surveillance and Reconnaissance) assets in order to achieve a set of mission objectives within allowed parameters subject to constraints. The missions of interest here, involve routing multiple UAVs visiting multiple targets, utilising sensors to capture data relating to each target. Finding such solutions is often an NP-Hard problem and cannot be solved efficiently on classical computers. Furthermore, during the mission new constraints and objectives may arise, requiring a new solution to be computed within a short time period. To achieve this we investigate near term quantum algorithms that have the potential to offer speed-ups against current classical methods. We demonstrate how a large family of these problems can be formulated as a Mixed Integer Linear Program (MILP) and then converted to a Quadratic Unconstrained Binary Optimisation (QUBO). The formulation provided is versatile and can be adapted for many different constraints with clear qubit scaling provided. We discuss the results of solving the QUBO formulation using commercial quantum annealers and compare the solutions to current edge classical solvers. We also analyse the results from solving the QUBO using Quantum Approximate Optimisation Algorithms (QAOA) and discuss their results. Finally, we also provide efficient methods to encode to the problem into the Variational Quantum Eigensolver (VQE) formalism, where we have tailored the ansatz to the problem making efficient use of the qubits available.

Decision making in a complex and fast moving environment can be challenging for both humans and autonomous systems. Many operational decisions can be expressed as combinatorial optimisation problems, which allows them to be expressed mathematically but can incur high computational overheads to solve. Quantum information processing promises the capability of solving large combinatorial optimisation problems such as positioning of tens to hundreds of sensor carrying drones within a set of complex objectives and constraints to create a connected ISR swarm. Whilst the mathematical approach for this optimisation is well characterised, extant quantum computers can also address the problem but do not currently have the scale to address medium to large complexity. Digital annealers are GPU-based devices that bridge the gap between quantum and classical computing in that they run quantum annealing-like algorithms with the accompanying problem complexity and speed benefits, but using the decades of scale advantage provided by a conventional silicon platform. This provides the opportunity to apply quantum information processing to existing ISR platforms reaping benefits in planning, resilience and rapid changing of objectives. This presentation will describe the application of digital annealing to control an ISR swarm and its implications on the requirements for future quantum information processing approaches and the potential route to near-term testing.

Many quantum technologies are dual-use technologies that can introduce new capabilities to defence and security-related applications or increase their effectiveness. In particular, diamond-based quantum sensors have great potential due to the high robustness of this material in conjunction with quantum effects accessible at room temperature. The negatively charged nitrogen vacancy centre (NV^-), an atomic defect within the diamond matrix, carries an electron spin that can be actively addressed and read-out via optical and electrical means at room temperature. This electron spin is highly sensitive to external magnetic fields, temperature, and pressure and thus well-suited for quantum sensing in defence and security.

Nowadays, diamond is reliably produced by means of chemical vapour deposition, allowing for tailored sensor elements, such as with oriented NV centres in layers and in microstructures that are highly interesting for vector magnetometry. Sensitive magnetometry is useful in global magnetic navigation, detecting metallic objects like submarines, human-machine interfaces and more. Apart from that, radiofrequency signals are detected in real-time with GHz spectral coverage in radar analysis. Recently, the use of these diamond-based quantum sensing technologies for side-channel attacks has come into focus, for example, to gather information on implementation of algorithms for cryptosystems. These technologies are introduced along with the fabrication of the underlying diamond sensor element.

Global Navigation Satellite System (GNSS) serves as a critical tool for both military and civilian operations worldwide. However, its limitations in certain operational environments and vulnerability to interference or jamming have become increasingly apparent in recent years. Quantum technology has emerged as a crucial enabler of alternative solutions. In this presentation, our focus will be on the magnetic aided inertial navigation system (MAINS), which has shown promise as a navigation alternative in GNSS-denied environments. MAINS leverages anomalies in the Earth’s magnetic field, often referred to as magnetic anomaly maps, to assist inertial navigation systems and correct drift. In general, optically pumped magnetometers (OPMs) in combination with classical vector sensors are employed to measure the magnetic field. OPMs collect precise and accurate measurements of the magnetic field intensity, while vector sensors provide information on its direction. This directional information is crucial for successfully estimating and removing the platform’s own magnetic field. Additionally, to minimize the magnetic influence of the navigation platform, these sensors should be situated as far as possible from the platform itself, such as on a stinger behind the aircraft. However, integrating these sensors into smaller platforms like drones presents significant challenges, particularly in mitigating the platform’s own magnetic interference, which may overshadow magnetic anomalies. In this paper, we will discuss the challenges associated with using quantum sensors for drone navigation and explore noise compensation algorithms. Additionally, we will share the results of our measurement campaign conducted on a fixed-wing drone. Lastly, we will examine how NV magnetometers could potentially improve noise compensation algorithms by employing more accurate vector measurements.

Spontaneous Parametric Down-conversion (SPDC) is now routinely used to generate photon pairs for imaging, spectroscopy, and quantum information and metrology. However, the peculiar spectro-spatial properties of SPDC beams are not always known from the largest audience: they can give rise to ring-like beams, depending on the temperature, the wavelengths and pump focusing. This has to be considered for imaging or long-range applications. We will show examples of such beams created in 532-pumped PPLN or PPKTP and 1064-nm-pumped PPLN crystals. With a simple model of noncolinear phase matching we will give physical insight into the phenomena and explain the role of the signal/idler group delay. We will also explain how aperiodic crystals could be useful.

As quantum communications (QC), in particular quantum key distribution (QKD) transitions from lab curiosity to commercial implementation, cost reduction will become essential to increase the user number and thus make commercialisation viable. QC is hardware intensive, meaning new and novel techniques and technologies are essential to that cost reduction strategy. We present an experimental demonstration of a polarisation-based decoy-state BB84 QKD protocol utilising a single laser source (enabled by application of cascaded electro-optic modulator to perform the pulse-carving and encoding) and single single-photon avalanche diode (enabled by the application of space-to-time multiplexing), which reduced the hardware requirements for the QKD transmitter and receiver, is presented.