https://crsreports.congress.gov
Updated August 14, 2024
Defense Primer: Quantum Technology
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.
Key Concepts in Quantum Technology
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 represent 0, 1, or a
combination of 0 and 1 at 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.
Military Applications of
Quantum Technology
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
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.
Quantum Computers
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 1,088 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
