Quantum Football

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Science  07 Aug 2009:
Vol. 325, Issue 5941, pp. 689-690
DOI: 10.1126/science.1178828

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Quantum information processing is usually based on two-level quantum systems, called quantum bits or qubits, but the use of additional quantum levels can simplify some quantum computations. It can also allow the emulation of other quantum systems, in which one quantum system acts as an analog of another and allows it to be better understood by reproducing its dynamics in a more controllable manner. On page 722 of this issue, Neeley et al. (1) demonstrate the operation of a superconducting circuit with five quantum levels, and show how to manipulate and measure its quantum states. They used this circuit to emulate the dynamics of single spins with various quantum numbers, including the measurement of their geometric phases that result from spin rotations. This extension of the two-level qubit to a multilevel “qudit” opens possibilities for richer quantum computing architectures and better emulations of other quantum systems.