Military applications of quantum physics

Here is a post by TTAC21 member Maziar Homayounnejad, who is studying for a PhD at Kings College London. His thesis is focussed on the legal issues of autonomous weapon systems.

This post looks at how breakthroughs in quantum physics could be applied to military technologies, specifically how it could lead to more accurate and discriminate targeting. Quantum physics (explained here) is basically a way of looking at particles in two states at once, for example seeing sun-light as waves, or photons.

How quantum physics applies to computing was rather wonderfully explained by Canadian Prime Minister Justin Trudeau at a recent press conference:

Anyway, here’s Maziar:

Military Applications of Quantum Physics

For this first post, I thought I would look at some of the security and defence applications of quantum physics (QP) and, in particular, gravity sensing, with specific reference to the ‘Technology Quarterly’ section of this week’s Economist. The supplement contains a series of articles on the coming of age of QP, and it gives us some clues on the direction that military innovation will soon be taking.

After decades of residing in textbook theory, some of the more far-reaching practical applications of QP are coming about and will continue to advance rapidly in the near-term. This is partly because of advances in various bits of hardware, which are needed for quantum capabilities to be put into effect.

Specific to counter-terrorism and defence, the article ‘Metrology – Sensing Sensibility’ is particularly interesting. It discusses how QP will boost the capabilities of all sorts of sensory devices, such as gravimeters, which are used to measure the strength of a gravitational field. Five applications are immediately apparent, some of which are in the article.

Firstly, accurate gravity sensing will enable attacking forces to detect underground and undersea movements, which will be a boon to detecting submarine movements from afar. Of course, this could mean the deterrent effect of the UK’s submarines and torpedoes could disappear, unless of course a counter-measure of some sort is discovered.

Secondly, in urban battlefields such as those in Gaza, insurgents and their military supplies often travel through underground tunnels, where they also maintain covert shelters. Here, gravity sensors will enable surveillance units to continue tracking suspected insurgents who disappear into a tunnel; and to obviate the risk of confusing the suspect with other ‘background noise’[1], powerful computers will separate and reconstruct the sensed movements of the person of interest. By the same token, gravity sensors will also provide valuable intelligence to both air and ground attack units, enabling them to intercept underground insurgents at the precise point of a tunnel’s exit; or to attack en route, to pre-empt both the insurgents and the underground movement of supplies[2]. Of course, a measure of precaution is needed as some tunnels may be accessible to civilians (which also form part of the ‘background noise’), rendering the battlefield status of underground movements less certain.

Thirdly, quantum gravimeters can precisely map geological features from the gravitational force they induce, thereby enabling military units to navigate in areas where satellite signals are weak (or in ‘GPS-denied’ environments). To illustrate the level of sensitivity, even the weight force of a human hair is measurable, thus facilitating precise mapping as a result of even minor variations across terrain. The article cites a British MoD scientist who aptly refers to this as “a kind of Google maps for gravitation”. This will be enormously important for the viability of lethal autonomous weapon systems (LAWS), which may at times have to operate in denied environments, or may have to shut off their own communication links to avoid enemy hacking.

Fourthly, the article goes on to explain that, as gravity is an example of acceleration, gravity sensors are effectively acceleration sensors too. This is a somewhat simplified statement of the Principle of Equivalence; yet its essence is clearly a boon to companies developing driverless vehicles, for which accurately sensing movements in their external environment and effective collision-avoidance will be a ‘make or break’. The same applies to LAWS, not just for collision avoidance – important as that is in a potentially chaotic battlefield – but also to make crucial assessments on the status of enemy forces. In some situations, the speed and acceleration of enemy movement towards you is one indicator (and may be a compelling one) in determining the likelihood of ‘hostile intent’. The faster the enemy is approaching and accelerating towards you, the more likely you will be attacked; the slower the movement and, especially, if that movement is decelerating, the less likely an attack may take place; retreat, or movement away from a LAWS unit, may even be taken as a sign of surrender, possibly requiring an autonomous system to be programmed to hold fire. Of course, gravity sensors will not be the only, or even necessarily the primary means of measuring external movement. Existing technologies that may help to confirm and enhance these data include Doppler radar, which uses the Doppler effect to generate its own velocity data on the movement of external objects[3].

Finally, the article mentions some of the civilian construction applications of gravity sensors, where contractors currently dig holes in roads and other plots of land but without really knowing what’s underneath; pebbles, pipes and underground wiring can all look the same to yesterday’s rudimentary technologies. Consequently, ‘underground surprises’ cause around half of all construction and roadwork delays, though this can be completely avoided with accurate and more penetrating gravity sensors based on QP. In the military sphere, this has obvious applications for collateral damage estimation (CDE). Currently, data-intensive CDE methodology is both sophisticated and accurate, but only in relation to what it can detect. Namely, by sensing the number and size of buildings, the likely material components of those buildings, and other objects and explosives around an intended strike site, and by applying this to the blast radius of the intended munition, CDE methodology can determine both a collateral effects radius and the severity of damage within that radius. From there, the system detects and includes (or is fed data estimates on) the number of people within the radius to produce a relatively accurate final assessment of collateral damage (including incidental injury to civilians). However, in cases where chemicals, explosives and other collateral effects-inducing objects are concealed or otherwise not taken into account, the CDE methodology will underestimate the true level of collateral damage that actually occurs from an attack. Gravity sensors will go some way to addressing this information gap, enabling those who are planning an attack to take into account underground objects, which may include heavy metallic items or even pipes liable to release dangerous forces, such as gas. It should be noted that the current situation of imperfect knowledge does not affect the legal assessment of proportionality, which hinges on the ‘expected’ and not the actual collateral damage caused. Nonetheless, being better-informed about underground objects that may increase the CDE assessments will undoubtedly improve the decision-making of commanders, and it gives them the opportunity to avoid PR disasters from heavy civilian casualties.

Aside from gravity-sensing, QP has a whole host of other military applications, from communications and encryption to guard against cyber-attacks; to quantum computing and its effects on machine learning (the difference between quantum computers and today’s supercomputers apparently being like the difference between human intelligence and that of a ‘jellyfish’). Both of these are treated in separate articles in the Technology Quarterly. One more fascinating application of QP that is worth briefly mentioning is ‘ghost imaging’[4]. Put simply, this combines pictures of a target object (along with all the heat- and smoke-based distortions generated by military action) with light beams reflected directly from the target. Correlating those measurements derives an artificially-generated, but vastly improved holographic image of an object that might be two or so miles away on a smoky battlefield. Essentially, the system is computing the paths that light takes to the target and back to the sensors, and it corrects for distortions on the actual image. Undoubtedly, this will allow machines to more accurately classify persons as either combatants or civilians (as well as objects as being of a civilian or military nature) on a battlefield, thereby enabling it to fulfil the distinction task more effectively (all else being equal)[5].

One thing that is difficult to deny from all of this is that technological improvements are racing ahead in ways that can be unpredictable. Specifically in relation to LAWS, some of these capabilities can be integrated into autonomous systems, which may or may not be able to take lethal action more discriminately than humans on the battlefield. This all points towards a strong preference for regulating technological standards. In particular, for lawyers to set the legal and humanitarian requirements that a LAWS will have to meet before it is allowed to operate autonomously and without contemporaneous human control; beyond that, it should be for engineers to rise to the technical challenge of meeting extant legal standards. The current approach taken by some non-governmental organisations (i.e. advocating for a comprehensive and pre-emptive ban on LAWS) is often partly based on pre-emptively negative judgments about future technological capabilities, which of course they are not qualified to do[6]. Not only does this risk being a haphazard way to approach the situation, but to end the debate there could also possibly sacrifice the opportunity to bring greater precision onto the battlefield; in the same way that the advent and further refinement of precision-guided homing munitions have massively reduced collateral damage over the past 70 years or so.


[1] Background noise is more likely to be a problem in built-up urban areas, where underground civilian activity may add to the potential confusion. These include tube trains, vehicle and pedestrian underpasses, and civilian movements in basement facilities.

[2] See also Perkins, S ‘Tiny Gravity Sensor Could Detect Drug Tunnels’, Science, 30 March 2016:, describing the development towards miniaturised gravimeters that can be installed on drones to detect manmade tunnels used for drug smuggling, and also to detect underground chemicals or mineral deposits.

[3] This works by bouncing a microwave signal off an external object and analysing how the latter’s motion has altered the frequency of the returned signal. Doppler radars are commonly used in aviation – specifically, air traffic control radar, which establishes the speed of moving aircraft – and in police speed guns.

[4] See also ‘The Newest Thing in Quantum Imaging’, Department of Defense Armed with Science, 3 January 2014:

[5] For an in-depth and technical paper, reporting on the experimental and theoretical investigation of ghost imaging at the US Army Research Laboratory, see Meyers, RE. and Deacon, KS. (2015) ‘Space-Time Quantum Imaging’, Entropy, Vol. 17, 1508. Available at:

[6] Of course, if and for such time that a desired humanitarian standard is technically infeasible, the law will be imposing a de facto ban on LAWS; and it will continue to prohibit all LAWS models that do not meet the desired standard.

4 thoughts on “Military applications of quantum physics

  1. Very insightful and brings attention to the need for having a legal perspective of the enormous pace of technological progress and changes are having on how we work, live and also fight wars.


  2. Thanks for the article Maziar. For me, there still remains a question of accuracy vs precision in warfare, and the need to have more oversight of the decision making process that defines who to target and why. What is the criterion for defining a justifiable preemptive strike and how should the international community monitor this? It’s all well and good having better information, but it’s what we do with the information that’s the really important question. I just hope advances in QP as you’ve described above don’t become an instrumental cause for more attacks based on ‘more information’ (i.e. we know more about the ‘enemy’ and can define more ‘enemies’ so therefore we should preemptively strike etc…)


    1. Thanks for your comment. As with most technologies, QP applications can be used for both good and ill. In an international armed conflict (IAC), things are usually more (though not perfectly) clear-cut and it’s likely that these technologies will be used to enhance precision and overall legal compliance. The main aim of all armed forces is to defeat the enemy and no one else; for a rational commander this often goes hand-in-hand with civilian protection. After all, there’s no military utility to be gained from needless civilian deaths and, in fact, you’re more likely to aid enemy recruitment by doing so.

      Outside an IAC, I agree that boundaries get blurred and the definition of a legitimate target can begin to stretch the limits of credibility. As you imply, the key to containing overly broad targeting is to have more international discussion and greater clarity on key concepts like ‘imminence’, and how they should be applied, when exactly a territorial state is ‘unable and unwilling’ to cooperate, etc. The UK Attorney General’s speech in January of this year, as well as several speeches by the US administration in previous years, go some way towards this, but have also been criticised for stretching definitions too far and leaving too much down to discretion. Still, a step in the right direction…


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