Quantum technology is moving from the domain of fundamental physics towards a strategic technology with implications for secure communications, precision navigation, sensing, computation and electronic warfare. Its importance for defence arises not from a single “quantum weapon”, but from the possibility of creating military systems that are more secure, more precise and more resilient than those based exclusively on classical technologies.
The defence significance of quantum technology rests on exploiting the behaviour of matter and light at the quantum scale. The same properties that make quantum systems delicate, that is, superposition, entanglement and the measurement sensitivity of quantum states, can also provide unprecedented advantages in communications, timing, navigation and detection. However, the transition from laboratory demonstrations to rugged, deployable military systems remains a substantial engineering challenge.
Superposition enables quantum computers to process certain classes of problems in ways that are fundamentally different from conventional computers. It does not mean that a quantum computer simply tries every answer simultaneously and automatically produces the correct one. Rather, quantum algorithms manipulate probability amplitudes so that desired answers are amplified and undesirable ones cancelled.
The second critical property is entanglement. Two or more quantum particles can become correlated in such a way that the state of one is linked to the state of the other, even when separated by a considerable distance. Measuring one particle provides information about the corresponding state of its entangled partner.
A third important feature is quantum measurement. The act of measuring a quantum state generally disturbs it. This is the foundation of quantum security: an adversary attempting to intercept or measure a quantum signal can introduce detectable errors.
These properties support four broad technological areas:
- Quantum computing, which may solve selected optimisation, simulation and cryptanalytic problems more efficiently than classical machines.
- Quantum communication, including quantum key distribution and future quantum networks.
- Quantum sensing and metrology, which exploit quantum states for highly precise measurements of time, acceleration, gravity, magnetic fields and electromagnetic phenomena.
- Quantum materials and devices, which provide the physical components required for quantum processors, sensors, lasers, detectors and communication systems.
For defence planners, the relevant question is not whether quantum technology will replace existing systems. It is how quantum capabilities will be integrated with satellites, fibre networks, inertial systems, artificial intelligence, electronic warfare architectures and conventional sensors.
Quantum Key Distribution
Quantum key distribution, or QKD, is currently the most mature defence-related application of quantum communication. Its purpose is not to transmit the entire message through a quantum channel. Instead, it allows two authorised users to generate a shared cryptographic key whose interception can be detected.
In a basic QKD system, information is encoded in the properties of individual photons, such as their polarisation. The sender transmits photons using different, non-orthogonal measurement bases. The receiver measures them using randomly selected bases. After the transmission, both parties publicly compare the bases, but not the measurement results, and retain only the compatible events. This produces a shared raw key, which is then subjected to error correction and privacy amplification.
The security advantage derives from the fact that an unknown quantum state cannot be copied perfectly. This is known as the no-cloning principle. An eavesdropper who tries to measure and resend the photons inevitably disturbs their states, increasing the quantum bit error rate. If the error exceeds an agreed threshold, the users can discard the key.
For defence forces, QKD could protect strategic command-and-control communications, links between national command authorities and military headquarters, satellite control, and missile-warning networks, intelligence databases and sensitive diplomatic traffic, communications between naval task groups and shore commands and data exchanged between defence laboratories, weapons-test ranges and production facilities.
QKD is not a complete cybersecurity solution. It secures key exchange, but endpoint devices, authentication systems, network management and user terminals remain vulnerable. A compromised terminal can expose information before encryption or after decryption. QKD also requires trusted infrastructure, specialised photon sources and detectors, and secure authentication. It must therefore be deployed alongside post-quantum cryptography, hardened networks and conventional cyber defence.
India’s Free-Space Demonstrations
India has made important progress in quantum communication. In January 2022, scientists from the Space Applications Centre and the Physical Research Laboratory demonstrated entanglement-based QKD over a 300-metre atmospheric free-space channel. The demonstration included quantum-secure text and image transmission as well as quantum-assisted two-way video communication. ISRO describes this as the country’s first free-space quantum communication demonstration over that distance.
The experiment is significant because free-space QKD is essential for satellite-to-ground and inter-satellite quantum links. Fibre-based QKD is useful for fixed terrestrial networks, but optical losses increase with distance. Satellites can potentially connect distant ground stations through free-space optical paths, thereby creating the foundation for national and eventually international quantum networks.
The 300-metre demonstration should nevertheless be understood as a technology validation rather than an operational satellite capability. Atmospheric turbulence, cloud cover, pointing errors, background light, photon loss and the requirement for extremely accurate optical alignment become more severe over longer distances. Defence applications will require compact terminals, resilient acquisition and tracking systems, high-performance single-photon detectors and secure integration with existing military networks.
A related DRDO-supported project with IIT Delhi demonstrated entanglement-based free-space quantum-secure communication over more than one kilometre in 2025. It achieved a secure key rate of approximately 240 bits per second with a quantum bit error rate below 7 per cent. This represents a meaningful step from campus-scale experimentation towards more practical free-space links, although substantial work remains before such systems can support high-volume operational traffic.
Quantum Radar
The expression “quantum radar” covers several different concepts. The most widely discussed is Quantum Illumination. In this approach, a source generates pairs of correlated photons. One photon is transmitted towards a suspected target while the other is retained locally as a reference. Reflections from the target are extremely weak and may be mixed with thermal noise. By comparing the returning signal with the retained reference, the system may detect a target under conditions in which a conventional radar would have difficulty distinguishing the return from background noise.
The theoretical advantage of quantum illumination can survive even when the original entanglement is destroyed by loss and environmental interaction. The retained reference and the returned photon remain statistically correlated in a way that can improve target detection in certain low-signal-to-noise conditions.
For defence, potential applications would comprise detecting low-observable aircraft or unmanned systems, improving performance against electronic jamming, detecting small maritime targets in cluttered environments, supporting passive or low-probability-of-intercept sensing and enhancing short-range surveillance in dense electromagnetic environments.
However, quantum radar should not be presented as an imminent replacement for conventional radar. The quantum advantage is difficult to preserve over operational distances because photons are lost rapidly, entanglement sources are imperfect, and the returned signal is extremely weak. Quantum radar remains largely at the laboratory and experimental stage, with no publicly established evidence of a mature operational system capable of routinely detecting stealth aircraft at long ranges. The immediate defence value is more likely to emerge in specialised sensing, low-light detection and quantum-enhanced signal processing than in a revolutionary standalone radar.
Quantum Navigation and Timing
Modern armed forces depend heavily on satellite-based positioning, navigation and timing. Global Navigation Satellite Systems are vulnerable to jamming, spoofing, cyberattack, anti-satellite operations and signal denial. A force operating in a contested theatre needs alternatives that can function without continuous access to satellite signals.
Quantum navigation seeks to exploit highly precise measurements of acceleration, rotation, gravity and magnetic fields. One important approach is the quantum accelerometer, which uses cold atoms. Atoms are cooled to very low temperatures and interrogated with laser pulses. Their matter-wave interference provides a highly accurate measurement of acceleration. Combining quantum accelerometers and gyroscopes can produce an inertial navigation system that drifts much more slowly than conventional systems.
A second approach is quantum gravimetry. Small variations in the local gravitational field can reveal information about location and terrain. Gravity maps can support navigation beneath the surface, underground or in regions where satellite signals are unavailable.
Quantum magnetic navigation uses highly sensitive magnetometers to measure variations in the Earth’s magnetic field. These variations can be compared with a pre-existing magnetic map to estimate position. Such a system may be valuable for submarines, aircraft and ground forces operating in GNSS-denied environments.
The military advantages would include navigation when GPS or other GNSS signals are jammed, reduced exposure to spoofing and electromagnetic detection, improved submarine navigation without frequent surfacing, More accurate guidance for long-range missiles and autonomous platforms, better synchronisation of distributed sensors and weapons and resilient positioning for aircraft, naval vessels and unmanned systems.
The principal challenge is that extreme laboratory precision does not automatically translate into field performance. Temperature changes, vibration, vehicle motion, magnetic interference and component size can degrade the measurement. The priority is therefore not merely to build the most sensitive sensor, but to create a sensor that remains sufficiently accurate on a helicopter, submarine, armoured vehicle or spacecraft.
Underwater Applications
Underwater environments are particularly attractive for quantum sensing because conventional navigation and communication systems face severe limitations. Radio-frequency signals do not propagate efficiently through seawater, satellite navigation is unavailable underwater, and acoustic systems can reveal the presence of a submarine.
Quantum technologies could contribute in three main areas: Navigation, Detection and Communication.
Quantum inertial navigation could allow submarines to maintain accurate position for longer periods without surfacing or deploying a mast. Quantum gravimeters and magnetometers could support navigation by comparing local measurements with detailed ocean-floor and magnetic maps. These systems could also assist autonomous underwater vehicles that must operate in deep water or under sea ice.
Quantum magnetometers may detect subtle disturbances caused by ferromagnetic objects, including submarines and underwater infrastructure. Quantum gravimeters could identify variations associated with geological structures, tunnels, voids or submerged objects. In anti-submarine warfare, these systems would not replace sonar, but could complement acoustic sensors by providing a passive measurement channel.
Underwater quantum communication is more difficult. Absorption and scattering limit the propagation of optical photons in seawater, while radio communication requires very low frequencies and large antennas. A realistic near-term architecture may therefore combine quantum-secure links at surface or satellite nodes with conventional acoustic or optical underwater networks. Quantum sensors, rather than quantum communications, are likely to produce the earliest underwater defence benefits.
Global Status: United States
The United States has developed a broad quantum ecosystem linking government laboratories, universities, defence agencies and private firms. Its priorities include quantum computing, quantum-resistant cryptography, atomic clocks, quantum sensing, secure communications and navigation in GPS-denied environments.
The US approach is strongly oriented towards military transition. It seeks to insert quantum components into existing platforms rather than wait for a fully developed “quantum battlefield”. The likely early advantages will be better timing, precision navigation, magnetic and gravitational sensing, and post-quantum cybersecurity.
Global Status: China
China has made quantum technology a national strategic priority and has pursued a state-led model combining civil research, military requirements and industrial policy. It has achieved major milestones in quantum communications, including satellite-based experiments and long-distance quantum links. China’s Micius satellite demonstrated the feasibility of quantum communication over space-based channels and helped establish the country as a leading power in quantum communications.
China’s advantage lies in the ability to mobilise national infrastructure, research institutions and state-owned enterprises around long-term objectives. Its civil–military fusion framework can accelerate the movement of dual-use technologies into defence applications. Its challenges include dependence on advanced semiconductor components, the complexity of scaling quantum computers and uncertainty over whether reported laboratory breakthroughs can withstand real operational conditions.
India’s National Quantum Mission
India approved the National Quantum Mission in April 2023 with an outlay of ₹6,003.65 crore for 2023–24 to 2030–31. The mission aims to develop capabilities in quantum computing, quantum communication, quantum sensing and metrology, and quantum materials and devices.
Its principal objectives include developing intermediate-scale quantum computers with 50 to 1,000 physical qubits; establishing satellite-based secure quantum communications over 2,000 kilometres within India; developing inter-city QKD networks; creating multi-node quantum networks with quantum memories; and building a national ecosystem of research institutions, industry and skilled personnel.
India has established thematic hubs for these domains. The Department of Space, DRDO, ISRO, IITs, the Department of Science and Technology and Indian industry are contributing to the effort. DRDO inaugurated a Quantum Technology Research Centre in Delhi in 2025 with facilities for single-photon sources, laser characterisation, atomic-vapour cells and QKD experimentation.
The financial allocation is important because quantum technology requires long-duration investment. Quantum laboratories need specialised fabrication, cryogenic systems, photonics, precision lasers and advanced detectors. A predictable funding structure can help retain researchers, support start-ups and create domestic manufacturing capacity.
Yet the allocation must be judged against the scale of the challenge. The United States and China operate with much larger technology ecosystems and defence budgets. India’s objective should therefore be selective technological leadership rather than attempting to reproduce every capability simultaneously.
The Way Forward
India should pursue a defence-oriented quantum strategy built around five priorities.
First, it should establish a quantum-secure migration plan. QKD should be developed for selected high-value links, but the broader national effort must include post-quantum cryptography across defence, government and critical infrastructure networks. Encryption migration can take decades, and adversaries may already be collecting encrypted data for future decryption.
Second, India should prioritise quantum PNT. GPS-denied navigation is a more immediate military requirement than large-scale quantum computing. Indigenous quantum inertial sensors, atomic clocks, magnetic navigation and gravimetry should be tested on aircraft, ships, submarines and unmanned systems.
Third, free-space and satellite QKD should move from demonstrations to operationally relevant trials. These trials should test turbulence, cloud, vibration, pointing errors, cyber intrusion, terminal reliability and interoperability with military networks.
Fourth, India needs a strong defense-industry-academia structure. Research contracts should reward measurable milestones, open test ranges and prototype demonstrations rather than only academic publications. Start-ups need access to defence users, clean procurement pathways and patient capital.
Finally, India must invest in human capital and standards. Quantum engineers need expertise in physics, electronics, optical communications, cryogenics, cybersecurity and systems integration. At the same time, standards are required for authentication, key management, quantum repeaters, satellite terminals and interoperability among the armed services.
Final Thoughts
Quantum technology will not make conventional military systems obsolete, nor will every claim about quantum radar or quantum communications translate into an immediate battlefield advantage. Its strategic importance lies in strengthening the foundations of military power: secure communications, resilient navigation, accurate timing, sensitive detection and decision-making under contested conditions.
For India, the National Quantum Mission provides an important institutional foundation. The country’s free-space QKD demonstrations by ISRO, DRDO and academic partners show that indigenous capability is possible. The next stage must be disciplined transition: from laboratory demonstrations to rugged systems tested in realistic operational environments.
The decisive advantage will belong not necessarily to the country that produces the most spectacular quantum experiment, but to the one that integrates quantum components into resilient military architectures. For India, that means linking quantum research with space systems, electronic warfare, cyber operations, underwater warfare, missile guidance and secure command networks. Quantum technology is best understood not as a single future weapon, but as a new layer of strategic advantage across the defence spectrum.
