Overview
Quantum technologies are based on the physics of quantum mechanics, which emerged early in the twentieth century. While there are many potential technologies based on quantum principles, the three most mature are quantum computing, quantum communication, and quantum sensing.
Quantum Computing Quantum computing constitutes a fundmentally new computational paradigm. Classical computers use individual bits as the smallest unit of information, with each being 0 or 1. In contrast, qubits—the smallest unit of information for a quantum computer—can be in multiple states simultaneously; that is, they can exist in superposition. This is one aspect of what allows quantum computers to simultaneously process a vast number of possibilities, a phenomenon called quantum parallelism.
Quantum computers promise major speedups for factoring large numbers and simulating quantum particles and processes—essential for breaking certain kinds of encryption and for accelerating innovation in chemistry and materials science. Quantum computing will remain a specialized, niche technology, rather than one with broad real-world impact, unless and until practical and effective algorithms for finance and other fields are developed.
All known applications of quantum computers will require error correction to outperform traditional, classical computers. Quantum computing hardware has now reached the “break-even” point (i.e., where meaningful error correction is feasible), enabling practical scaling.
The main scaling challenge is not simply in increasing numbers of qubits but also in controlling individual qubits. Scaling of quantum computers comparable to that achieved for classical computers depends on the availability of robust errorcorrection approaches—expected within the next few years—and on leveraging established techniques from semiconductor and photonics engineering.
Quantum Communication Quantum communication uses the principles of quantum mechanics, such as superposition and entanglement, to encode, transmit, and secure information between separate systems. It has two primary applications: data security and networking.
Today’s secure data communication relies upon the difficulty of factoring large numbers (or other related problems). Cryptographers are developing quantumresistant algorithms based on different types of hard problems. Quantum key distribution (QKD) provides an alternative approach. QKD prevents the undetectable interception of encryption keys being distributed, enabling the secure sharing of such keys and the establishment of secure communication channels. However, it does not guarantee secure communication because it does not secure a communication system’s physical endpoints.
QKD provides a hedge against a failure to develop public-key encryption algorithms resistant to being broken by quantum computers. However, the cryptographic community has considerable confidence that such algorithms will be successfully developed.
Quantum networking focuses on how to transfer quantum information between quantum computers or other quantum devices without loss. One approach depends on the computers involved being of the same design. This eliminates the need to convert information from one quantum form to another, thus avoiding losses inherent in any such conversion. The second approach is transduction, which converts quantum information from one physical quantum system to another kind without losing the data’s quantum properties. Both present technical challenges, especially when long-distance quantum communication is involved.
Quantum Sensing Quantum sensing is the most mature of quantum technologies. It exploits quantum mechanics to achieve greater sensitivity than classical sensors and can detect extremely small signals previously inaccessible to classical methods.
Classical sensors achieve their sensitivity by utilizing the average response of many independent atoms and are impacted by noise associated with random fluctuations in the overall system. Quantum sensors, however, achieve their superior sensitivity through precise measurement of individual quantum systems and through leveraging quantum correlations between them (a phenomenon known as entanglement). But true quantum advantage can be demonstrated only by a well-engineered system that outperforms an optimized classical sensor with the same requirements for size, weight, power, and integration time.
Application areas for quantum sensors include astronomy (which requires capture of dim images), bioimaging (which requires that the light source not damage delicate specimens), and ultra-low-power platforms. Quantum sensing demonstrably excels in areas where classical probes are impractical, invasive, or inadequate, including gravitational-wave detection, precision timekeeping, and nanoscale field sensing.
