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Over the last decade Quantum Technologies (QT) have evolved from a relatively nascent area of experimental research to an international strategic priority. Global government funding in QT is estimated as between $34bn (McKinsey) and $55bn (Quantum Intelligence), with private investment gradually following suit in the $5-10bn range. This investment is truly global, with public funding in excess of $1bn in China, the EU, US, Japan, UK, Canada, and India. However, the strategies underpinning these investments vary greatly. Whilst the US and China lead in total investment, China’s focus is on large government-funded centres of excellence with limited private equity. In contrast, the US (and western powers more broadly) pursues greater parity between private and public investment and has won a dominant position in QT start-ups, with over a third of quantum companies based in North America.
The rationale for investment has been both the potential for substantial economic prizes for those who realise disruptive technologies, and the clear link between the promises of QT and the needs of defence and security. The most often cited example is the impact of Quantum Computing on cyber security, rendering certain forms of classically secure cryptography vulnerable, necessitating a change of cryptographic standards, and creating a credible opportunity for powers to collect and store encrypted data today with the expectation of decrypting in the future. This is a tangible threat in domains where sensitive information may have a data lifespan of decades and elevates quantum to a strategic priority.
However, quantum computing is not the only area of QT with strong relevance to defence. Quantum sensing has the potential to provide disruptive capabilities in land, sea, air and space – offering both step-changes in current sensing modalities and new modes of sensing that may enhance battlefield awareness. These technologies are not distant concepts; real systems are reaching demonstration in representative environments (TRL 6-7) and progressing towards platform integration for use. Supporting supply chains are also maturing, however there remain large gaps in areas such as standards, assurance, and certification.
Understanding of Quantum Systems Engineering (QSE) is an especially notable gap. Systems engineering and associated processes are deeply embedded in defence engineering, and it is quite clear that Quantum Systems Engineering will require new concepts. These fall across the system life cycle processes (as defined in ISO 15288), for example including additions to reliability engineering due to quantum-unique failure modes and effects, new notions of interfaces and system-of-interest boundaries due to quantum entanglement, significant limitations in current approaches to modelling and simulation (necessary for Model-Based Systems Engineering), and, for some systems, changes in approach to test, verification and validation (particularly towards statistical black-box methods). The leap from demonstration to scalable, widely deployable products will require progress across all of these gaps.
With these caveats of maturity in mind, let us consider a few specific areas of quantum sensing in more detail.
Quantum Position, Navigation and Timing (PNT)
Resilience in PNT is an established strategic imperative. Over-reliance on Global Navigation Satellite System (GNSS) derived signals for position and timing has become an acute problem, resulting in significant vulnerabilities to wide-area denial and to more subtle attacks like spoofing. In the worst cases this risks platforms operating with hazardously misleading information, but even in less severe cases can result in a loss of accurate knowledge of position, and more crucially loss of accurate synchronised time. A loss of time inevitably results in a loss of communications, and as reliance on remote assets grows so does reliance on guaranteed resilient connectivity. Quantum sensing solutions are seeking to address all aspects of this problem.
Quantum Timing
Firstly, Quantum Clocks present one of the most mature areas of QT, and many of the aforementioned gaps have been addressed for clocks specifically. Quantum optical clocks that improve upon current widely used rack-mounted clocks by 2-4 orders of magnitude in performance – notably extending timing holdover in case of denial – are now reaching market. More interesting is that these architectures show promise for significant miniaturisation without major degradation in performance. Whilst unlikely to reach a chip-scale formfactor, board-scale products could be realised within the next 5 years providing resilient timing options to a much wider range of platforms such as small autonomous systems and dismounted applications.
Quantum Navigation
Timing aside, positioning and navigation are also being advanced by quantum technologies. In the absence of an external positioning signal (whether GNSS or terrestrial, e.g. eLoran) navigation is performed by dead reckoning from a known initial location. An Inertial Navigation System (INS), consisting of accelerometers and a gyroscope, continuously measures platform motion and uses this to determine changes to position and heading over time – enabling navigation from a known location without additional external references. Dead reckoning is very susceptible to errors in measurement, so sensor drift, accuracy and measurement rate all limit the hold-over time inertial systems offer.
Quantum accelerometers go some way to addressing these issues. They provide highly accurate measurements that exceed classical systems, but more importantly they very substantially reduce issues of drift since measurements are made on physically identical atoms. Conversely, they suffer major limitations in measurement rates (1-10Hz), which is significantly less than the hundreds of Hertz required for dead reckoning. Because of this, current quantum inertial sensors cannot be used for navigation by themselves. However, they can provide powerful drift-correction for classical systems, reducing their primary source of error and extending hold-over. Quantum-Classical INS are currently reaching demonstration and trial, TRL 6-7. Key integration and sensor fusion work is required to bring them to maturity, but productisation is expected within the next 5 years. First generation devices will have high SWAP-C and likely be suited to large critical platforms such as those in surface and sub-surface maritime domains, and there is a strong impetus to then bring these to aircraft (a goal stated, for example, in the UK quantum missions which explicitly seeks to achieve this by 2030).
Quantum Gravity Gradiometry
Quantum also introduces new mechanisms for position fixing across platforms. The most notable approach here is quantum gravity sensing and gravity gradiometry. Using a technology very similar to the aforementioned quantum accelerometers, it is possible to make ultra-accurate measurements of the earth’s gravitational field strength and field gradient. Furthermore, the unique properties of quantum entanglement can be used to make these measurements highly resilient to vibrations and noise, and hence accurate even if made from an operational platform.
The earth’s gravitational field is far from constant, and detailed maps can be drawn of field strength or gradient (coarse global gravity maps can be made from space, but fine-grained maps are often derived from sensors flown over a region, or carried by hydrographic vessels). If such a map is available, quantum gravity sensing can be used as a completely passive means of localising one’s position through map matching. Quantum gravity gradiometers are high SWAP-C devices with strong similarities to quantum accelerometers, but pose fewer integration challenges since they do not need to be part of a quantum-classical hybrid system. Currently solutions for land, sea and air domains are being matured, with strong dual-use motivation driven by use-cases in civil engineering (site surveying) and oil, gas and mineral prospecting. This reveals a second key use-case for quantum gravity sensors – remote void and object detection. A measurement of the gravity gradient is, essentially, a measurement of how mass underneath the sensor is changing over a region. Therefore, measurements of gravity features and anomalies may be used to detect and map underground infrastructure, or to detect buried objects that are heavier than their surroundings, providing new insights into the battlefield.
Quantum Magnetometry
Quantum sensors also enable very accurate magnetic field measurements. The use of Superconducting Quantum Interference Devices (SQUIDs) for magnetic measurement is well established, and whilst being costly due to the need for cryogenic operation, they are effective magnetic anomaly detectors. In the same manner as gravity sensors this may be used for magnetic map matching if there are magnetic landmarks to position against. However, a more interesting use-case may be for anti-submarine warfare, with SQUID systems on patrol aircrafts looking to detect magnetic anomalies over open ocean.
Quantum RF Sensing
Moving away from the PNT context, QT is also making strides into ultra-wideband RF sensing. Rydberg atom-based RF sensors provide a new mechanism of receiving RF signals, with the promise of detecting very low intensity modulated signals over a very large spectral range (from Hz to THz), enabling wide swathe monitoring of the RF spectrum. There is prominent defence-led investment in these systems, which are currently at prototype stage. Notably comparative analysis of early prototype systems against established RF sensors already shows competitive sensitivity. Whilst less mature than some of the previously mentioned technologies, Rydberg sensors have the potential to significantly enhanced RF sensing capabilities both for monitoring purposes and potentially for communications with lower signal strength requirements.
Conclusion
Quantum sensing shows convincing promise to provide key enhancements to defence and security capabilities over the next 5 years. Quantum clocks are leading productisation, with quantum inertial systems maturing rapidly but requiring more complex engineering, and gravity gradiometry and RF sensing following. Their combined potential impact is profound, improving resilience in all domains, and providing new ways to investigate and monitor the battlefield. However, transitioning from compelling demonstrators to fully integrated, deployed systems presents substantial challenges.
There is a rapidly increasing need to better interface the expertise of the defence engineering and system integration communities with the quantum technology sector, including establishing pathways to on-platform trials and demonstration, agreeing system requirements, and defining the value chain for productised quantum sensors.
The defence community has played a key role in elevating Quantum Technologies to an area of strategic importance. The fruition of these efforts is now within sight, but their realisation will require a proactive collaborative approach to align global advancements with the needs of defence, ensuring quantum-backed superiority in the battlefields of tomorrow.
