QUANTUM SENSING FOR UNDERSEA DOMAIN AWARENESS IMPLICATIONS FOR ANTI-SUBMARINE WARFARE IN THE IOR

Abstract: This paper examines quantum enabled sensing as an emerging application for undersea surveillance, with particular emphasis on its potential relevance to Anti-Submarine Warfare and related maritime security tasks. Focusing on Quantum Magnetometry and Gravimetric sensing at the level of operational application, the study avoids foundational quantum theory and instead assesses how these sensing approaches differ from traditional acoustic methods. The analysis highlights the prospective utility of passive, non-acoustic sensing for persistent monitoring in geographically constrained and acoustically complex maritime environments. The paper argues that, while quantum enabled sensing remains niche and largely experimental, limited deployment in high-value areas may offer incremental improvements in Undersea Domain Awareness. It further emphasises that any operational value will depend on careful integration with existing surveillance architectures rather than standalone use. By adopting a restrained and application focused perspective, the paper aims to inform naval planners and policymakers about realistic pathways for experimentation and future capability development.

Introduction

Anti-Submarine warfare (ASW) has historically relied on acoustic detection. Passive sonar, active sonar and their Avariants have shaped naval doctrine for decades. These systems were effective when submarines were louder, faster and less constrained by stealth requirements. That context no longer holds. Modern submarines are significantly quieter. Advances in hull design, propulsion systems, vibration isolation and anechoic coatings have reduced radiated noise levels to a point where passive detection ranges have contracted sharply, particularly in shallow and cluttered waters.¹ Diesel electric submarines operating on batteries and nuclear submarines running at low speeds can remain acoustically elusive for extended periods. Active sonar can extend detection but it comes with its own drawbacks as it reveals the searcher’s position, increases the risk of counter detection. These challenges are particularly pronounced in the Indian Ocean Region. Littoral zones, narrow straits, variable salinity and complex seabed topography degrade acoustic performance and complicate signal interpretation. In such environments, reliance on acoustics alone creates gaps in undersea awareness. These gaps are increasingly exploited by both manned and unmanned underwater platforms.

Against this background, non-acoustic sensing has re-emerged as a serious operational requirement rather than a technological curiosity. Among non-acoustic approaches, quantum enabled sensing has advanced most rapidly toward practical deployment. Quantum magnetometers and gravimeters do not rely on detecting emissions from a target.² They respond instead, to disturbances in the surrounding physical environment created by the presence and movement of large submerged objects. Recent advances in atomic magnetometry have pushed sensitivity beyond what was previously achievable outside laboratory settings. Modern optically pumped magnetometers can register very small variations in the Earth’s magnetic field, including anomalies associated with metallic submarine hulls and their magnetic wakes.³ Compared with legacy magnetic anomaly detection  systems, these sensors offer higher sensitivity and greater flexibility in deployment, including use on unmanned platforms and fixed seabed installations.

Similar progress has been made in quantum gravimetry. Atom interferometric gravimeters are now available for applications such as geophysical survey and navigation research and can detect subtle changes in local gravitational fields caused by mass displacement.⁴ In an undersea context, this raises the possibility of detecting submarines that move slowly or remain stationary, even when their acoustic and magnetic signatures are carefully managed. From a naval standpoint, the importance of quantum sensing lies less in its physics and more in the operational options it introduces. Quantum sensors are passive. They do not emit signals. They can support persistent surveillance and operate in environments where acoustics are unreliable. They also expand the detectable target set to Quantum Sensing for Undersea Domain Awareness Implications include unmanned underwater vehicles, seabed installations and mines.

This paper examines quantum sensing strictly as an applied capability for ASW. It focuses on how quantum magnetometry and gravimetry alter detection concepts, how they can be integrated with existing ASW architectures and what their adoption implies for naval operations in contested maritime spaces.⁵ The emphasis is on operational relevance and  near term applicability, not on foundational quantum theory.

Classical Non-Acoustic Detection to Persistent Quantum Sensing

Non-acoustic sensors refer to a class of submarine detection technologies that operate without relying on sound propagation. They exploit secondary physical effects generated by a submarine as it moves through the ocean. These include disturbances in magnetic, electromagnetic, thermal, hydrodynamic, or chemical domains. The principal non-acoustic sensor categories currently in use or under near term consideration include Magnetic Anomaly Detection (MAD), electromagnetic and ELF/VLF field disturbances, wake detection using radar, infrared, or optical methods, chemical or particulate sensing and pressure based hydrodynamic sensors. All of these are fundamentally classical sensors, measuring macroscopic effects using conventional physics and signal processing techniques.

Magnetic Anomaly Detection (MAD) identifies localised distortions in Earth’s magnetic field caused by a submarine’s ferromagnetic hull, but its effective range is limited to a few hundred meters and requires low altitude platforms such as maritime patrol aircraft or UAVs. Advances in degaussing, low magnetic materials and stealth design have further reduced its effectiveness, confining MAD largely to tactical confirmation rather than wide area search. Wake and hydrodynamic detection methods use radar, light detection and ranging (lidar), infrared or pressure sensors to identify disturbances caused by submarine motion, However their performance is highly dependent on sea state, offers only short lived detection as wakes dissipate rapidly and are ineffective against deep or slow moving submarines. Electromagnetic and chemical sensing approaches seek to detect ionization effects, trace chemicals, or electromagnetic leakage, yet these methods are highly environment sensitive, difficult to attribute uniquely to submarines and remain largely experimental or niche in operational deployment.

Quantum sensors including quantum gravimeters, quantum magnetometers and quantum accelerometers measure fundamental physical fields by observing phase shifts in controlled quantum states. These measurements are intrinsically absolute, passive and stealth compatible and far less reliant on emissions or proximity compared to classical approaches. Quantum gravimeters measure extremely small variations in the local gravitational field caused directly by changes in mass distribution. For submarine detection, this is significant because gravity cannot be shielded by stealth coatings; degaussing and reduced speed do not eliminate mass. In principle, this allows for passive and covert detection of submerged platforms. However, gravitational signals from submarines are extraordinarily weak and are masked by substantial environmental noise from tides, seabed structures and ocean dynamics. As a result, practical detection ranges remain very limited and operational deployment is still experimental.

Quantum magnetometers exploit atomic spin states to achieve sensitivities that can exceed those of MAD sensors by an order of magnitude or more. This enables the detection of weaker magnetic signatures at greater distances. Nevertheless, quantum magnetometers remain subject to magnetic countermeasures and environmental interference and their operational advantage is best characterized as evolutionary rather than revolutionary.

The United States remains a global leader in quantum sensing research and early prototyping, driven by agencies such as DARPA, the National Science Foundation and the Department of Energy.⁶  U.S. programmes 6focus on atomic interferometry, quantum magnetometry and quantum inertial navigation, with direct relevance to defence applications including submarine detection, GPS denied navigation and underwater intelligence, surveillance and reconnaissance. While advanced laboratory prototypes of quantum gravimeters, magnetometers and inertial sensors have been demonstrated, most systems are still transitioning toward field deployable configurations through defence contractors and remain in development or demonstration phases rather than full operational deployment. China has pursued quantum sensing, positioning to counter stealth technologies and reliance on GPS. Research led by the Chinese Academy of Sciences and military laboratories has reportedly produced high sensitivity, drone Quantum Sensing for Undersea Domain Awareness Implications mounted quantum magnetometers designed to detect magnetic anomalies associated with submarine movement. In parallel, China is advancing quantum navigation technologies, including quantum gyroscopes and gravimeters for GPS independent positioning applicable both to submarine operations and to their detection.⁷ Prototype systems have reportedly been tested in marine environments and on tactical platforms such as UAVs, with field trials underway, though wide operational deployment has not yet been confirmed. France is among the few countries pursuing quantum sensing with explicit naval intent and tangible deployment milestones.⁸ The French Navy has received its first serially produced quantum gravimeter, currently used for high precision seabed mapping, with longer term ambitions for navigation and submarine detection based on gravitational anomaly sensing^.9

Quantum Sensing as a Detection Paradigm in Undersea Warfare

Quantum enabled sensors do not rely on emissions. A submerged platform cannot avoid interacting with the Earth’s magnetic and gravitational fields. Hull materials, onboard machinery and the displacement of large volumes of water all alter local field conditions. These changes are subtle but they persist and can be measured. Acoustic systems look for what a submarine does. Quantum sensors instead respond to what a submarine is. Magnetic disturbance has long been recognised as a detection pathway, but earlier methods were limited by sensitivity, platform stability and noise.¹⁰ Classical magnetic anomaly detection required close proximity and was largely confined to airborne use. Its effectiveness declined as submarines adopted degaussing and improved signature management. Recent advances in quantum magnetometry¹¹ shift this balance. Even a carefully degaussed submarine cannot avoid disturbing surrounding water and ions as it moves. Atomic magnetometers operating at pico-tesla or femto-tesla sensitivity can register signals that older systems would treat as background noise.

Quantum gravimeters add a parallel capability by measuring small changes in local gravitational acceleration caused by mass displacement. A submarine is a concentrated mass moving through a fluid medium. Whether moving slowly, stationary or operating near the seabed, it continues to perturb the local gravitational field. Unlike acoustic or magnetic signatures, gravitational effects cannot be engineered away.¹² They arise from mass  itself. Moving from emission based to disturbance based detection changes familiar ASW trade-offs. Extreme quieting becomes less decisive, though not irrelevant. Quantum sensing does not replace existing ASW sensors; its value lies in how it complements them. Acoustic systems remain better suited for classification and tracking once contact is established, while quantum sensors are more useful for initial detection, area denial and persistent monitoring in constrained spaces.¹³ When combined with sonar, intelligence inputs and environmental models, they can reduce uncertainty and narrow search areas.¹⁴

From a force design perspective, this approach favours distributed sensing over platform centric detection. Fixed seabed nodes, unmanned platforms and air deployed sensors can operate together within layered surveillance networks. The focus shifts away from episodic search missions toward continuous measurement of the environment. Detection becomes less about a single signal and more about observing how the undersea environment departs from its expected physical state.

Quantum Magnetometry in Anti-Submarine Warfare Operations

Magnetic field disturbance has long been recognised as a non-acoustic indicator of a submerged platform. Submarines interact with the Earth’s magnetic field through their metallic hulls, onboard electrical systems and movement through seawater. For many years this interaction was exploited through magnetic anomaly detection, mainly from fixed wing aircraft and helicopters. Over time, the effectiveness of these systems declined as submarines adopted signature reduction measures and detection ranges remained limited.

Quantum magnetometry changes the operational relevance of magnetic sensing by offering higher sensitivity, improved stability and greater flexibility in deployment. Even when performance is reduced by motion and environmental noise, sensitivity remains well above that of older fluxgate and induction based sensors. This translates into better discrimination of weak signals against background variation. As a submarine moves through seawater, it generates a magnetic wake through the interaction of its conductive hull, water flow and the ambient geomagnetic field. This wake can persist after the platform has passed. Quantum Sensing for Undersea Domain Awareness Implications Diesel electric submarines running on batteries are acoustically quiet but still contain ferromagnetic materials and electrical systems. Nuclear powered submarines, although quieter than earlier designs, retain larger hulls and higher displacement, increasing their magnetic footprint. In both cases, magnetic disturbance cannot be fully eliminated.

Quantum magnetometers also broaden deployment options. Unlike traditional MAD systems, which are limited by size, power and integration constraints, atomic magnetometers can be compact and energy efficient. This enables use on unmanned platforms such as UAVs, USVs and AUVs, as well as on fixed seabed installations. In operational terms, quantum magnetometry is best suited to area surveillance and initial cueing rather than precise classification. Magnetic data alone rarely provides high confidence on target type, but when fused with environmental models, acoustic data or intelligence inputs, it can narrow search areas.¹⁵ Its passive nature is particularly relevant in contested or politically sensitive waters, where active sonar use carries escalation risks. Overall, quantum magnetometry represents a substantive advance over earlier magnetic sensing, shifting it from a short range, platform bound tool toward a more distributed and persistent means of observing how submarines interact with the Earth’s magnetic environment.

Quantum Gravimetry for Mass Anomaly Detection

Gravitational sensing or gravimetry, responds directly to mass. A submarine, because of its size and density has inherent mass anomaly and the same can be detected by gravimetry. Recent progress in quantum gravimetry has been driven mainly by cold atom interferometry. Clouds of ultra cold atoms act as test masses and their interference patterns shift with changes in gravitational acceleration. Over the past decade, these instruments have moved from laboratory settings to transportable systems used in geophysical surveys, mineral exploration and precision navigation, signalling improved robustness and deployability of interest for defence applications.

For ASW, the appeal of gravimetric sensing lies in its resistance to conventional stealth measures. Acoustic quieting, speed reduction and seabed masking are intended to suppress emissions or reflections, but they do not affect gravitational interaction. A submarine that slows or remains stationary may evade sonar more effectively, yet it continues to disturb the surrounding gravitational field. In some cases, reduced movement can prolong the anomaly within a sensor’s field of view. Gravimetric approaches are therefore most relevant in shallow and littoral waters, where sonar performance often degrades and submarines operate close to the seabed. Quantum gravity gradiometers,¹⁶ an advanced form of gravimetric 16 sensing measure spatial variations in the gravitational field and improve sensitivity to localised mass anomalies while suppressing common mode noise. Although less mature than quantum magnetometers, they point toward possible mobile and seabed based surveillance roles. Gravimetry does not offer rapid, long range detection akin to acoustics under ideal conditions. The range of detection is limited and its interpretation is computationally demanding. Its strength lies in persistence particularly for monitoring harbour approaches, seabed infrastructure, constrained transit routes and for detecting slow moving or stationary platforms such as unmanned vehicles or clandestine seabed installations.

Operational Applications of Quantum Enabled Non Acoustic Sensing

The operational relevance of quantum enabled sensing is best understood through its potential applications rather than through sensor performance alone. These capabilities remain experimental and niche, but they point to different ways of approaching undersea surveillance compared with platform centric ASW concepts. One clear feature is silent detection. Quantum magnetometers and gravimetric sensors operate passively and do not transmit energy into the environment. This allows surveillance and cueing without revealing the position or posture of the detecting force, a useful attribute in contested or politically sensitive waters.¹⁷

Quantum sensing also lends itself to persistent area monitoring. When deployed on the seabed or in long endurance unmanned platforms, sensors can maintain continuous observation of selected maritime spaces. This differs from patrol-based ASW, where coverage is intermittent and tied to platform availability. Such persistence is most relevant in chokepoints, harbour approaches and other constrained areas where submarine and unmanned movement is channelled.

The potential application extends beyond crewed submarines. Current Quantum Sensing for Undersea Domain Awareness Implications maritime competition increasingly involves unmanned underwater vehicles, covert seabed sensors and deployed naval mines. These systems are often small and acoustically quiet, limiting the effectiveness of sonar. They still contain magnetic materials and create mass anomalies, which disturb the local physical environment and may be detectable in monitored zones. Quantum sensing may therefore also support harbour security and protection of undersea infrastructure. Ports, naval bases, seabed cables and offshore installations are vulnerable to covert activity that produces little acoustic signature. Persistent monitoring with the help of established fixed magnetic or gravitational sensors can provide early warning. Taken together, these capabilities suggest quantum sensing as an adjunct rather than a central element of undersea surveillance, with limited deployment in high-value areas offering a way to gain experience and inform future practice.¹⁸

Integration into Naval Force Structure and Sensor Architectures

The operational utility of quantum enabled sensing is determined largely by how it is integrated into existing naval force structures rather than by standalone sensor performance. In practice, these capabilities matter most when they are built into layered undersea surveillance systems that mix fixed, mobile and manned assets.¹⁹ One approach is the use of fixed seabed installations. In constrained areas such as chokepoints, harbour approaches and narrow straits, seabed sensors can provide persistent monitoring with a small operational footprint. Fixed placement also simplifies calibration and baseline establishment, which are essential for magnetic and gravimetric sensing. Such installations are best suited for early warning and anomaly detection rather than continuous tracking.

A second approach is integration on mobile unmanned platforms, including surface and underwater vehicles. Mobility allows coverage to shift in response to intelligence cues and changing priorities. Though the motion in the sensor introduces noise and stability challenges, improvements in vibration isolation, signal processing and data correction would lead to achieving useful performance. These platforms are therefore suited for gap filling roles and extending coverage beyond fixed sensor fields. Airborne integration offers a complementary option. Quantum magnetometers on maritime patrol aircraft or helicopters can be used to investigate cues from seabed or unmanned sensors, supporting confirmation and localisation rather than persistent surveillance.

Across all deployment modes, sensor fusion remains critical. Magnetic and gravitational data must be interpreted using environmental models, historical baselines and inputs from other sensors, placing demands on data processing, communications and command and control systems. Integration also raises questions of resilience and survivability. Fixed sensors require concealment or protection, while mobile systems rely on dispersion and redundancy. For these reasons, integration of quantum enabled sensing is likely to be incremental in application and technology absorption.

Strategic Implications for the Indian Ocean Region

The strategic significance of quantum enabled non acoustic sensing is most apparent when examined in the context of geography. The Indian Ocean Region is a mix of confined seas, narrow approaches and busy maritime corridors. Many of these spaces restrict submarine manoeuvre and at the same time reduce the effectiveness of acoustic detection. This combination makes the region well suited to non-acoustic ASW approaches. Narrow straits, choke points and island passages pose difficulties for acoustics because of shallow water, high background noise and seabed conditions. From a quantum sensing standpoint, these constraints are favourable for the applications. Submarines moving through restricted waters, and monitored zones can be picked up by fixed magnetic and gravitational sensors. Persistent sensing in such locations shifts the operational balance from episodic detection to continuous awareness.

Littoral waters present a similar dynamic. Submarines operating close to shore often rely on terrain masking and reduced speed to evade sonar. These tactics are effective against active and passive acoustics but do not eliminate environmental disturbance. In fact, operating close to the seabed increases interaction with local geological features, making deviations from baseline conditions more pronounced. Quantum sensing fits more naturally around coastal defence than with blue water power geography. Submarine operations depend on uncertainty about detection and even a partial reduction of that uncertainty raises operational risk. In this sense, deterrence arises from uncertainty imposed on the intruder rather than from

Quantum Sensing for Undersea Domain Awareness Implications the threat of immediate engagement. Quantum sensing may also support asymmetric advantage. High end ASW task groups are costly to build and sustain. By contrast, persistent seabed installations and unmanned sensing networks offer a lower cost means of monitoring selected areas over extended periods. For a navy operating across a wide maritime space with limited assets, this trade-off matters. It allows high value platforms to be reserved for response and prosecution rather than routine surveillance.

The IOR also contains extensive undersea infrastructure, including communication cables and energy installations. The protection of these assets are linked to national security. When integrated into broader undersea domain awareness systems, quantum sensing can contribute to aware and early warning of interference. Strategic competition in the region often remains below the threshold of open conflict, involving covert patrols and unmanned deployments with little public visibility. In such settings, the ability to observe without revealing one’s own presence is valuable. The relevance of quantum sensing in the IOR therefore stems less from technological novelty than from strategic fit, governed by geography, traffic patterns and the character of regional competition.

Challenges, Limitations, Countermeasures

Like any detection technology, quantum enabled sensing faces technical, environmental and operational limitation about its usage. A realistic view of these constraints is necessary if such systems are to be integrated credibly into naval practice rather than treated as speculative or overstated solutions. One major challenge is environmental noise and variability. Magnetic and gravitational fields are affected by geology, ocean dynamics and human activity. Seabed composition, tectonic features and nearby infrastructure can generate background signals and complicate anomaly detection. Therefore, effective use depends on detailed baseline mapping and regular calibration, favouring persistent deployment in well characterised areas.

Platform related challenges add further constraints. Quantum sensors, particularly gravimeters and gravity gradiometers are sensitive to motion, vibration and temperature changes. Despite advancement in signal processing, performance losses onboard mobile platforms are reality. In practice, this means that fixed and slow moving deployments are likely to mature earlier. Detection range and resolution also impose limits. Nonacoustic quantum sensors generally operate over shorter effective ranges than acoustic systems under favourable conditions, making them better suited to area monitoring and cueing than long range search. They can reduce uncertainty, but they do not remove the need for conventional ASW assets.

Data processing presents another challenge. Magnetic and gravitational measurements are not intuitive. Differentiating natural variation from benign activity requires advanced modelling and analysis. This increases reliance on computing capacity and specialised expertise. Although quantum sensors are becoming more accessible, they are still relatively complex and expensive.²⁰ Large scale deployment, especially of seabed networks, would demand sustained investment and maintenance. While quantum sensing offers persistence and complementarity, it also carries limitation in range, environmental sensitivity and integration effort. Recognising both sides is essential if experimentation and procurement are to stay aligned with operational reality.

Indian Context

Towards bolstering indigenous development of Quantum capabilities for defence and strategic applications DRDO has inaugurated Quantum Technology Research Centre (QTRC) on 27 May 2025. With Solid State Physics Laboratory, the centre is focussing on emerging technologies and development of Atomic Magnetometers using optically pumped magnetometry (OPM). This development is a critical requirement for ultra-sensitive persistent magnetic anomaly field detection in ASW. At present QTRC's infrastructure focuses heavily on micro fabricated alkali vapor cells and Vertical Cavity Surface Emitting Lasers (VCSELs). The broader pursuit of Quantum Gravimetry for gravity based navigation is primarily distributed across DRDO’s academic collaborations.

Parallel to these, National Quantum Mission (NQM) is undertaking research related to cold atom interferometry for gravimetric applications at Indian Institute of Science Educational and Research (IISER), Pune and IISER Bhopal.²² The synergy between QTRC’s hardware focus (vapor cells and lasers) and academic breakthroughs in atom optics is a Quantum Sensing for Undersea Domain Awareness Implications positive toward achieving persistent quantum sensing. However, it would require sustained research to turn it into a deployable product.

Conclusion

This paper has examined quantum enabled sensing as an emerging application for undersea surveillance, with particular reference to AntiSubmarine Warfare and related maritime security tasks. By looking at magnetometry and gravimetric sensing as operational tools rather than on underlying physics, this analysis shows how these approaches differ in practice from acoustic methods. Quantum enabled sensing remains niche and largely experimental. Its relevance is in enabling passive and persistent monitoring where acoustics perform poorly. These capabilities would yield substantial gain in undersea awareness. The utility of quantum sensing depends primarily on integration, not standalone performance. Fixed installations, unmanned platforms and limited airborne use appear to be the most plausible early pathways. Considering challenges w.r.t data fusion, calibration, command and control, its effectiveness will ultimately be governed by deployment context and supporting infrastructure.Atul Tripathi has over two decades of experience in Quantum Computing, AI having worked across industry, R&D, Prime Minister’s Office (NSCS). He was Artificial Intelligence consultant in Prime Minister’s Office (NSCS) and has extensive experience working across industry, R&D. Atul has been teaching at IIPA, Naval War College, various IIT’s, IIIT’s IIM’s. He serves on various academic councils, offering his expertise to multiple universities. He has authored a book titled Quantum Era Warfare. He has authored 2 books on AI and multiple articles in Quantum Computing, AI, Cyber security.