Quantum

Source: Defense Primer, Quantum Technology, Congressional Research Service, Oct 2021

Quantum technology translates the principles of quantum physics into technological applications. In general, quantum technology has not yet reached maturity; however, it could hold significant implications for the future of military sensing, encryption, and communications, as well as for congressional oversight, authorizations, and appropriations.

Quantum applications rely on a number of key concepts, including superposition, quantum bits (qubits), and entanglement. Superposition refers to the ability of quantum systems to exist in two or more states simultaneously. A qubit is a computing unit that leverages the principle of superposition to encode information.(A classical computer encodes information in bits that can represent binary states of either 0 or 1, whereas a quantum computer encodes information in qubits, each of which can represent0, 1, or a combination of 0 and 1at the same time. Thus, the power of a quantum computer increases exponentially with the addition of each qubit.)

Entanglement is defined by the National Academy of Sciences (NAS) as a property in which “two or more quantum objects in a system can be intrinsically linked such that measurement of one dictates the possible measurement outcomes for another, regardless of how far apart the two objects are.” Entanglement underpins a number of potential military applications of quantum technology. Both superposition and entanglement are, however, difficult to sustain due to the fragility of quantum states, which can be disrupted by minute movements, changes in temperature, or other environmental factors.

The Defense Science Board (DSB), an independent Department of Defense (DOD) board of scientific advisors, has concluded that three applications of quantum technology hold the most promise for DOD: quantum sensing, quantum computers, and quantum communications. The DSB concluded that quantum radar, hypothesized to be capable of identifying the performance characteristics (e.g., radar cross-section, speed) of objects- including low observable, or stealth, aircraft-“will not provide upgraded capability to DOD.”

Quantum sensing uses the principles of quantum physics within a sensor. According to the DSB, this is the most mature military application of quantum technologies and is currently “poised for mission use.” Quantum sensing could provide a number of enhanced military capabilities. For example, it could provide alternative positioning, navigation, and timing options that could in theory allow militaries to continue to operate at full performance in GPS degraded or GPS-denied environments. In addition, quantum sensors could potentially be used in an intelligence, surveillance, and reconnaissance (ISR) role.

Successful development and deployment of such sensors could lead to significant improvements in submarine detection and, in turn, compromise the survivability of sea based nuclear deterrents. Quantum sensors could also enable military personnel to detect underground structures or nuclear materials due to their expected “extreme sensitivity to environmental disturbances.” The sensitivity of quantum sensors could similarly potentially enable militaries to detect electromagnetic emissions, thus enhancing electronic warfare capabilities and potentially assisting in locating concealed adversary forces.

According to NAS, “quantum computers are the only known model for computing that could offer exponential speedup over today's computers.” While quantum computers are in a relatively early stage of development, advances-many of which are driven by the commercial sector-could hold implications for the future of artificial intelligence (AI), encryption, and other disciplines. For example, some analysts have suggested that quantum computers could enable advances in machine learning, a subfield of AI. Such advances could spur improved pattern recognition and machine-based target identification. This could in turn enable the development of more accurate lethal autonomous weapon systems, or weapons capable of selecting and engaging targets without the need for manual human control or remote operation. AI-enabled quantum computers potentially could be paired with quantum sensors to further enhance military ISR applications.

In addition, quantum computers could potentially decrypt classified or controlled unclassified information stored on encrypted media, allowing adversaries to gain access to sensitive information about U.S. military or intelligence operations. Some analysts note that significant advances in quantum computing would likely be required to break current encryption methods. Their estimates suggest that a quantum computer with around 20 million qubits would be required to break current encryption methods; however, the most advanced quantum computers today generally have no more than 100 qubits.

The practical applications of quantum computers will likely be realized only after improvement in error rates and development of new quantum algorithms, software tools, and hardware. While, as NAS notes, “there is no guarantee that [these technical challenges] will be overcome,” some analysts believe that an initial quantum computer prototype capable of breaking current encryption methods could be developed in the 2030 to 2040 timeframe. For this reason, NAS concludes that “the development, standardization, and deployment of post-quantum cryptography is critical for minimizing the chance of a potential security and privacy
disaster.” (Information intercepted prior to the deployment of post-quantum cryptography would not be protected.)

Quantum communications-excluding quantum key distribution ([QKD], discussed below)-are in a nascent stage of development. Quantum communications could theoretically enable the secure networking of quantum military sensors, computers, and other systems, thus improving performance over that of a single quantum system or classical communications network. Networking could additionally strengthen the robustness of such systems at range, thus expanding the potential environments in which they could be deployed (i.e., outside of the laboratory settings generally required to sustain fragile quantum states).This could significantly expand the military utility of quantum communications.

Quantum key distribution is a subset of quantum communications that uses the principles of quantum physics to encrypt information that is then sent over classical networks. QKD enables secure communications that cannot be covertly intercepted during transmission.(QKD communications can, however, be intercepted at the relay stations currently required for long-distance transmissions.)

China is reportedly investing heavily in QKD and completed construction of an approximately 1,250 mile Beijing-Shanghai quantum network in 2016. Nonetheless, the DSB concluded that “QKD has not been implemented with sufficient capability or security to be deployed for DOD mission use."