QUANTUM 101
a particular element (e.g., rubidium or cesium). Te well-defined transition frequency makes them excellent standards for clocks, with far better performance than quartz crystal oscillators such as those used in wristwatches. A second reason is that qubits can be exquisitely sensitive to environmental fields, such as magnetic or electric fields. While this sensitivity is one of the reasons build- ing a quantum computer is difficult, it is also the reason qubits can be excellent sensors.
Quantum communication networks require the precise synchro- nization and stabilization that atomic clocks provide. When combined with quantum sensors for acceleration, rotation and gravity, these clocks will also ensure robust navigation in GPS-denied environments. Together, quantum-enabled enhancements such as these contribute to the assured posi- tion, navigation and timing capabilities crucial to the Army’s future success.
Te application of quantum information science to general problems in sensing and metrology has shown that measure- ments can surpass classical detection limits. Tis enhanced sensitivity is of interest to the Army for a variety of applications, ranging from ultra-precise magnetometry to distinguish tank and submarine decoys from the real things, to precise chemical detection with limited sample volumes.
1 or 0?) that can enable exponential processing improvements that make quantum computing so fundamentally different from classical computing.
“Quantum”
refers to the fundamental discreteness of nature— that, at the smallest scales, measurements of energy, of light, of matter, and so on, come in indivisible packets.
Several physical platforms are viable candidates for building quan- tum computers. Although qubits based on trapped atomic ions, superconducting and semiconducting systems seem to hold the most promise for large-scale implementations, they are not the only ones, and the question is still open as to what type or types of qubits will enable the first quantum computer capable of solving classically intractable problems. While quantum computers large enough to run Shor’s algorithm for code breaking are decades away, when we have these computers they will be able to attack multiple problems of interest to the Army in addition to code breaking, like resource optimization, optimal war- gaming, efficient command, control, communications and intelligence, and maximal logistical support.
Quantum simulators can be thought of as special-purpose quantum comput- ers suited to understanding specific problems, such as the design of novel materials. Quantum simulators are expected to solve some long-standing problems in physics and chemistry, including the origin of certain types of
As a result of these varied applications, the Army has research programs related to quantum metrology and sensing, and is now targeting assured position, navigation and timing as a crucial area for increased investment.
Quantum Computation and Simulation Quantum computers function via controlled initialization and manipulation of qubits to execute quantum algorithms like Shor’s. During these operations, qubits are placed in superpositions and entangled with one another. Recalling that quantum phenomena are tied to probabilities of being in certain states, we can under- stand that during a quantum computation, all of the possible results exist with some probability. Quantum algorithms func- tion such that the probability of getting the correct answer upon measurement is enhanced while the probabilities of all of the incorrect answers are suppressed. It is these enhancements and suppressions together with state sampling (is the electronic state
84 Army AL&T Magazine October-December 2018
superconductivity, and for chemical (e.g., pharmaceutical drug or energetic material) design. Tis specialization removes many of the constraints that make general-purpose quantum computers decades away from realization, and, as a result, near-term quan- tum simulators may have a more immediate impact on Army capabilities, especially in materials design.
CONCLUSION Quantum information science provides unprecedented advan- tages that are impossible under classical laws of physics. Some of these advantages that rely on superposition or matter-wave dual- ity are already in the early stages of application in quantum clocks and sensors, while some involving multiparticle entanglement are further off, including quantum networks. Some will require decades of additional development, such as complex quantum computers.
Quantum mechanics has proven over and over that with each included quantum ingredient, revolutionary capabilities occur, and we should be confident that this will continue to occur.
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