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Unformatted text preview: 1 Design and optimisation of quantum logic circuits for a threequbit DeutschJozsa algorithm implemented with opticallycontrolled, solidstate quantum logic gates A Del Duce, S Savory and P Bayvel Optical Networks Group, Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK Email: a.delduce@ee.ucl.ac.uk Abstract. We analyse the design and optimisation of quantum logic circuits suitable for the experimental demonstration of a threequbit quantum computation prototype based on opticallycontrolled, solidstate quantum logic gates. In these gates, the interaction between two qubits carried by the electronspin of donors is mediated by the optical excitation of a control particle placed in their proximity. First, we use a geometrical approach for analysing the entangling characteristics of these quantum gates. Then, using a genetic programming algorithm, we develop circuits for the refined DeutschJozsa algorithm investigating different strategies for obtaining short total computational times. We test two separate approaches based on using different sets of entangling gates with the shortest possible gate computation time which, however, does not introduce leakage of quantum information to the control particles. The first set exploits fast approximations of controlledphase gates as entangling gates, while the other one arbitrary entangling gates with a shorter gate computation time compared to the first set. We have identified circuits with consistently shorter total computation times when using controlledphase gates. 1 Introduction During the last years a new model of quantum computer has been developed which is based on the opticallycontrolled, solidstate quantum logic gates proposed by Stoneham, Fisher and Greenland in [1] and typically referred to as SFG gates[2]. In this proposal the qubits are carried by the electronspin of donors in a solidstate substrate while twoqubit interactions are mediated by a socalled control particle placed in proximity of the qubits and triggered by the excitation and deexcitation of the control particle through optical pulses. The potential of this implementation lies in the optical control of the twoqubit interactions which allows to remove noisy electrical circuitry from the quantum register and to avoid highprecision fabrication processes for the exact placement of control electrodes. After its first proposal presented in [1], further theoretical studies on the dynamics of SFG gates have been presented in [3], while in [2] gate parameters were identified which allow the fast implementation of entangling gates such as the CNOT gate, for example, with minor leakage of quantum information from the qubits to the control particles. Recently, important measurements of the lifetimes of potential control particles in a silicon substrate have been obtained [4]. These results are a fundamental step towards the implementation of a quantum computation prototype based on SFG quantum logic gates which represents an essential test...
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 Spring '11
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