Warfare Evolved: Quantum Radar

By Alessandro Gagaridis

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When it was first introduced by the US armed forces toward the end of the Cold War, stealth technology represented a major shift in the conduct of military operations. Low radar observability – a more appropriate term for ‘stealth’ – allowed American aircraft to safely penetrate into heavily defended areas without being detected by enemy sensors; and it demonstrated its operational value for the first time during the 1991 Gulf War. It then became an integral part of US military operations, one that was gradually applied to other platforms, including ships. While today it is no longer a US monopoly, since other powers like Russia and China have also deployed hardware with purported low-observability features, the technology remains the exclusive domain of advanced militaries and provides a significant operational advantage.

New experimental technologies, however, hold the potential to change the status quo. A new kind of sensor, called ‘quantum radar,’ holds the promise of detecting stealth platforms. While this technology is still in its early stages and currently presents notable technical limitations, if successful it could usher in the next chapter in the everlasting dialectic between defense and offense in warfare.

BACKGROUND

What are quantum radars?

The first step to assess the potential strategic impact of quantum radars is to understand how they work and how they differ from traditional models.

‘Radar’ is actually an acronym for ‘radio detection and ranging,’ a term which reveals its basic functioning principle. Radars emit radio waves that, when they hit an object, are reflected back to the source. By analyzing this return signal, radars are able to detect and track the object. To avoid this kind of tracking, there are two possible solutions. The first is jamming, which means producing a signal in the same wavelength as the radar to interfere with it so that it cannot distinguish the return signal from the spoofing emission, thus ‘blinding’ it. The second is using stealth systems which exploit design features like radar-reflecting shapes and radar-absorbent materials to reduce their radar cross-section (RCS, the amount of radio energy reflected to the source) and render them harder to detect. Even though no stealth platform is completely ‘invisible’ to radar, as sensors operating in the very high / ultra frequencies (VHF / UHF) band can successfully detect a low-RCS object, this remains a complex endeavour that does not result in a sufficiently precise localization that allows for targeting.

The functioning principle of quantum radars is different. Such systems exploit a particular physical property known as quantum entanglement. When two particles are entangled, they have the same quantum state and any change in the status of one particle results in a parallel change in the status of the other, even if the they are considerably distant from one another. The quantum radar exploits this property by generating a visible light beam of entangled photons which then splits in two. One half is converted into the microwave band without changing its quantum state and is then emitted by the radar. When the signal hits an object, it is reflected back to the source and converted back to the visible wavelength in order to be compared with the other half of the original beam. Since the quantum state of its particles changed when it collided with the object, the system can detect its presence by observing the differences in the quantum status of the particles present in the two beams and by filtering out those from other sources. A properly-functioning quantum radar would therefore make both jamming and stealth technology useless. Since the jamming system cannot know the quantum state of the radar signal, the characteristics of the spoofing emission will not match and will automatically be ignored. As for stealth platforms, they would still retain their ability to disperse most of the incoming radar signal, but a small part – not sufficient to be detected by conventional radars – will still come back to the source and the observation of changes in the particle’s quantum status will result to detection.

Naturally, quantum radars also have their limits. Apart from the fact that they are an experimental technology that needs to be significantly perfected before becoming operational, the main problem lies in their limited range. As a matter of fact, particles lose their entanglement properties at some point due to a phenomenon called quantum decoherence, meaning that quantum radars also lose their ability to detect targets. In 2015, a study concluded that the effective range of quantum radars would be under 7 miles, but the following year a Chinese team claimed to have manufactured a quantum radar of 61 miles of range. While the ability to detect stealth platforms at such distance would still be a considerable feat, it remains much lower than the range of conventional radars. Nevertheless, the prospected introduction of quantum radars in the years ahead may have deep consequences in both military and geopolitical terms.

Quantum radars: Three possible scenarios

Given the importance of stealth systems in the US military, any power determined to counter its superiority would be interested in quantum radars. As of today, China seems to be leading the way in the field; but the same logic also applies to Russia. Quantum radars would represent a significant enhancement to their anti-access / area denial (A2/AD) strategy conceived to prevent US forces from operating close to their territory. As stealth technology and electronic warfare (EW) techniques such as jamming played a central role in US military operations to penetrate into heavily-defended environment to strike the enemy’s command & control (C&C) centers and critical logistical infrastructures, quantum radars would significantly affect the attack capabilities of US forces. At the same time, the low range of quantum radars also limits their value as anti-stealth solutions; even though sensor fusion – the sharing of data between different platforms to have a greater view of the battlespace – could offset this problem at least to a certain degree. If quantum radars were able to send detailed enough data on the position (including altitude for aircraft), speed and direction to missile launchers, the latter could use the information to guide their weapons to the target; but this solution presents its own technical challenges.

Depending on the cost and capabilities of quantum radars, three theoretical scenarios are possible, which may coincide with different phases of their development.

If they will turn out to be highly expensive and limited-range systems, as is likely over the short term, they will hardly have any operational value, as enemy stealth platforms would be able to engage their target with long-range standoff weapons well before entering into the quantum radars’ detection zone.

If their cost will diminish without significant improvements to their range (possible medium-term scenario), quantum radars will probably be deployed to form dense’ grids’ of networked sensors to ensure an extensive coverage at least over sensitive target-rich areas. Even though it would complicate the C&C structure of the defenders, this kind of scenario would also present significant challenges to the attacker due to the difficulty of locating and neutralizing a large number of radars and thus disrupting the grid’s efficacy. This would be a time-consuming and resource-intensive endeavor, which may be simplified only with accurate intelligence on the location of the individual stations (which would not be easy to obtain) or possibly by using drone swarms to carry out a complex search & destroy operation.

Finally, in the long term the detection range of quantum radars may increase, resulting in a similar use as conventional radars; with the cost influencing only the number of stations deployed. By ensuring detection of enemy aircraft or surface ships over whole regions (for instance the South China Sea), this would have deep strategic consequences. Another possible implication of long-range but low-cost systems would be their miniaturization, allowing them to be mounted on mobile ground vehicles, fighter planes, and so on. This would provide anti-stealth and anti-EW capabilities to expeditionary forces and may potentially lead to a proliferation and a ‘normalization’ of quantum radars that would significantly change warfare.

The strategic implications of quantum radars

These are of course archetypical scenarios, and reality is likely to take in-between forms also depending on the user’s specific strategic environment. Yet, they allow to make some predictions on the impact of quantum radars on international stability. Thanks to their ability to ignore RCS-reducing features and jamming techniques, they would make it much harder for an attacker to launch a surprise attack with the intent of debilitating its adversary. By reducing the appeal of such an escalatory move, quantum radars would therefore have a stabilizing effect. Yet, warfare is a dialectic process where any advance in defence results in efforts to circumvent it.

To bypass China’s and Russia’s A2/AD ‘bubbles’ that quantum radars create alongside other systems, the US will reasonably place greater emphasis on submarines, which can be neither detected by radars (as long as they stay submerged) nor hit by the majority of missiles (though there are examples of anti-submarine missiles); even though another quantum-related technology – namely quantum magnetometers known as superconducting quantum interference device, or SQUID – may offset the benefits of this solution. Unsurprisingly, China seems determined to develop this technology as well.

Hypersonic weapons are another solution since they are nearly impossible to intercept and could be used to neutralize quantum radars (as well as other critical targets); but this may have destabilizing effects by triggering a ‘shoot first’ dynamic where the US would be tempted to use them to quickly overcome Chinese/Russian defences and the latter would consider a preemptive hypersonic strike out of fear of being the victims of one. In this sense, quantum radars may indirectly have destabilizing effects; but this is mainly the consequence of hypersonic missiles themselves, also because their influence on the decision to launch a hypersonic first strike would be limited by the fact that, to be effective, such an attack would require complete and accurate intelligence on the location of the quantum radars to be targeted, which is hard to obtain and would require many missiles (especially in the ‘grid’ scenario described above, which implies a large number of stations to destroy). On this basis, quantum radars will probably have a globally stabilizing effect; but much depends on their actual capabilities and the specific strategic environment where they will be deployed.

To conclude, quantum radars represent a promising technology with the potential to significantly transform warfare in the 21st century by making stealth technology and jamming obsolete in hypothetical great power conflicts. Yet, for the time being they remain experimental systems that are still far from reaching operational use; and as with all new technologies, a considerable margin of uncertainty remains, meaning that only time will tell how quantum radars will affect warfare in the decades ahead.