Quantum sensors and submarine invulnerability
Quantum Sensors and Submarine Invulnerability
WRITTEN BY SAMANVYA HOODA
16 October 2023
The past two years have seen various developments that point to an uncertain nuclear future. These include China’s nuclear modernisation, Russia’s sabre-rattling, and even South Korea’s nuclear ambitions. This is amidst technological developments that make nuclear arsenals less secure, and future technologies that could threaten nuclear deterrence even more. Since nuclear-armed submarines serve as the cornerstone of nuclear deterrence because of their survivability, it is important to consider emerging technologies that pose a threat to them. Easy detection of ballistic missile submarines (SSBNs) has caused destabilising behaviour in the past, and would be particularly dangerous in situations involving multiple actors. Quantum sensors are one of the technologies that could improve submarine detection over the next two or three decades, and it is hence important to consider their policy implications. Quantum sensors are unlikely to increase submarine vulnerability to the point of threatening nuclear deterrence, but only if there is continued research into these technologies. Though all nuclear-weapon states have armed or are attempting to arm submarines with nuclear weapons, this analysis uses the US-China dyad as a representative example. This dyad is also relevant because it will see significant geopolitical competition in the coming years, including in nuclear technologies.
Why submarines?
The United States currently fields 14 SSBNs, which can be armed with about 50 per cent of its nuclear stockpile. The forthcoming Columbia-class SSBNs will be in service until the 2070s. China is also allotting more nuclear responsibilities to its forthcoming Type 096 submarines. Considering their longevity, studying technologies that could threaten these expensive and seemingly indispensable vessels is vital. The other eight nuclear weapon states (NWS) similarly field, or hope to field, a second-strike capability on submarines. Submarine survivability is crucial for NWS, and technology that threatens this would negatively impact nuclear stability.
As long as research into quantum sensing technologies is guided by realistic expectations and sober policy discussions, quantum sensors will not make SSBNs vulnerable to the point of threatening nuclear deterrence.
Until now, the relative ease of hiding submarines has hindered submarine detection. Other parts of the nuclear triad (air-, sea-, and land-based nuclear delivery systems) could also be vulnerable; quantum sciences can improve detection of stealth bombers and silo- and mobile-launched missiles. However, as submarines are seen as the ultimate guarantors of a nuclear second-strike, it is important to first study how quantum sensors would affect SSBN operations.
It is important not to exaggerate submarine vulnerability — there have always been fears about ‘transparent oceans’ leading to second-strike instability. These fears have not materialised because of technological constraints, and the United States still leads compared to its adversaries in submarine and anti-submarine warfare. This advantage stems from US successes in submarine quietening, as well as using extremely sensitive acoustic sensors to locate other submarines. The United States may be reaching the physical limits of improving these sensors, while China and Russia are trying to quieten their submarines further.
Some other technologies like laser sensing (LIDAR) and magnetic detection have seen limited success. However, their relatively low sensitivity, limited range, and impractical size and costs make them difficult to employ at scale like US acoustic sensor networks. For new technologies to render submarines vulnerable, they need to offer better detection at reasonable costs, while keeping to militarily practical size, weight, and power (SWaP) specifications.
Quantum sensors: hype or substance?
Quantum sensors can potentially meet these SWaP specifications, while also detecting electrical, magnetic, or even gravitational fields far beyond what is possible with other modern sensors. These sensors span different technologies at different levels of viability and their military use depends on several factors. For instance, cold-atom interferometers offer excellent precision to aid navigation and conceal submarines but require large unwieldy cooling systems to function properly. Despite this, the US government predicts they could “work in their final form and in expected conditions’ for inertial measurements by 2029. Nitrogen-vacancy centre diamonds are extremely promising for practical use; they combine high sensitivity with a robustness to environmental changes that quantum sensors usually do not have. However, their sensitivity makes it difficult to separate signals from noise. Superconducting Quantum Interference Devices (SQUIDs) are a proven technology, but have a limited range for devices that can be militarily practical. The examples illustrate that the military value of quantum sensors should not be assumed or dismissed without careful consideration of all the pitfalls involved — especially the supporting technologies required.
Using quantum sensors in militarily practical ways can be aided by several adjacent technologies, ranging from AI advances to miniaturising supporting systems. Some of these sensors may show promising results only in laboratories. Moreover, most military technologies also spawn innovative workarounds — quantum sensors may be no different. For example, submarine magnetic signatures can be masked through degaussing and non-magnetic materials. Changing a submarine’s mass distribution could help deceive gravimeters. Increased sensitivity could also mean these sensors are susceptible to jamming or decoys.
However, technology often advances faster than expected. For example, engineers in the 1970s were tasked with reducing an aircraft’s radar cross-section by a factor of 10,000. Despite daunting challenges, these engineers successfully delivered the F-117 in time for precision strikes against Iraq in 1991. For quantum sensors, one cannot discount AI as a crucial enabler for quantum technology. Nuclear stability between adversaries exists in a complex system where even small changes cause emergent effects. For example, improving Trident missile accuracy in the 1980s shifted perceptions of US SSBNs being stabilising second-strike platforms, to destabilising first-strike platforms instead. The main driver of this change was improving missile accuracy by a few hundred metres, but it drastically changed the balance of power between Soviet and US nuclear forces. Considering the speed of AI advances, quantum-enabled AI (or AI-enabled quantum) would allow the exponential growth of critical technologies. In the context of nuclear deterrence, this growth could have strong destabilising effects.
Turbulent implications
An adversary detecting US submarines would have turbulent implications — diminished US military hegemony, increased allied fears about US extended deterrence, and significant shifts in the world order. Even a low probability of an adversary ‘making the oceans transparent’ demands consideration, because its hypothetical impact has significant consequences. Quantum technologies are still immature, which makes it difficult to compare the relative strengths of different companies or countries. Counting the number of academic publications devoted to quantum technologies can reflect the resources devoted to R&D, and can help forecast a country’s technology development by indicating its research and workforce capabilities. Take the example of China, which leads in the number of publications about quantum sensors, and is marginally second for highly-cited quantum sensor research, for all applications. It leads in total number of AI-related publications, and has collaborated on several highly-cited AI publications. Although the US has imposed some export controls, China is also pursuing novel forms of AI research. Were China to make AI-enabled breakthroughs in quantum sensing, the United States would have to significantly re-evaluate its regional security policies, force structure, and military doctrine.
Quantum sensing technologies are too novel and nascent to make strong predictions about their efficacy. Concurrently, their successful use will have significant implications for how nuclear-weapon states perceive the reliability and safety of their nuclear deterrent. In the Indo-Pacific, this means quantum sensors could have a significant bearing on US and Chinese military strategies, as well as those of US allies and partners under extended deterrence commitments. Whether for offensive or defensive use cases, countries operating (or planning to operate) submarines need to research quantum sensors for realistic perspectives about the technology—quantum sensors are no silver bullet, nor should they be dismissed easily. They have limitations in how they can be currently deployed and defended against. As long as research into quantum sensing technologies is guided by realistic expectations and sober policy discussions, quantum sensors will not make SSBNs vulnerable to the point of threatening nuclear deterrence.
DISCLAIMER: All views expressed are those of the writer and do not necessarily represent that of the 9DASHLINE.com platform.
Author biography
Samanvya Hooda is a graduate student in the Security Studies Program at Georgetown University. He is also a 2023 CSIS Nuclear Scholar, and a Visiting Researcher at the Institute of Chinese Studies, New Delhi. Image credit: Flickr/ U.S. Indo-Pacific Command.