SCB Quantum Computers Using iSWAP and 1-Qubit Rotations
- Wednesday, 06 December 2006
Practical implementation in the SCB context appears to be feasible.
Units of superconducting circuitry that exploit the concept of the single-Cooper-pair box (SCB) have been built and are undergoing testing as prototypes of logic gates that could, in principle, constitute building blocks of clocked quantum computers. These units utilize quantized charge states as the quantum information-bearing degrees of freedom.
An SCB is an artificial two-level quantum system that comprises a nanoscale superconducting electrode connected to a reservoir of Cooperpair charges via a Josephson junction. The logical quantum states of the device, are implemented physically as a pair of charge-number states that differ by (where e is the charge of an electron). Typically, some 109 Cooper pairs are involved. Transitions between the logical states are accomplished by tunneling of Cooper pairs through the Josephson junction. Although the two-level system contains a macroscopic number of charges, in the superconducting regime, they behave collectively, as a Bose-Einstein condensate, making possible a coherent superposition of the two logical states. This possibility makes the SCB a candidate for the physical implementation of a qubit.
Unlike in prior experimental quantum computer circuits, neither the starting time nor the duration of a gate operation is used as a control parameter to determine the nature of the operation. Instead, quantum gate operations are controlled by applying sequences of voltages and magnetic fluxes to single qubits or pairs of qubits: hence, quantum logic operations can be performed in predictable, fixed, time intervals; that is, they can be clocked. Hence, further, it is easier to integrate these units into large-scale circuits. The feasibility of fabricating such gates and large-scale quantum circuits by use of electron-beam lithography has been demonstrated.
This work was done by Colin Williams and Pierre Echternach of Caltech forNASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category.
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Refer to NPO-30213, volume and number of this
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