1694 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 15, NO. 6, NOVEMBER/DECEMBER 2009 Quantum Logic Circuits and Optical Signal Generation for a Three-Qubit, Optically Controlled, Solid-State Quantum Computer Andrea Del Duce and Polina Bayvel, Senior Member, IEEE Abstract—We analyze the preparation of an experimental demonstration for a three-qubit, optically controlled, solid-state quantum computational system. First, using a genetic program- ming approach, we design quantum logic circuits, specifically tai- lored for our computational model, which implement a three-qubit refined Deutsch–Jozsa algorithm. Aiming at achieving the short- est possible computational time, we compare two design strategies based on exploiting two different sets of entangling gates. The first set comprises fast approximations of controlled-phase gates, while in the second case, we exploit arbitrary entangling gates with gate computational times shorter than those of the first set. Then, con- sidering some recently proposed material implementations of this quantum computational system, we discuss the generation of the near-midinfrared, multiwavelength and picosecond optical pulse sequences necessary for controlling the presented quantum logic circuits. Finally, we analyze potential sources of errors and assess the impact of random fluctuations of the parameters controlling the entangling gates on the overall quantum computational system performance. Index Terms—Near-midinfrared picosecond pulse generation, quantum circuit design, refined Deutsch–Jozsa algorithm, solid- state quantum computation. I. INTRODUCTION A LTHOUGH during the past years many different proposals of quantum computational systems have been developed or even experimentally demonstrated, the task of building a large-scale quantum computer is still unresolved [1]. One group of implementations that is believed to have the potential for high scalability is the one of solid-state quantum computers, which could benefit from the vast expertise and knowledge acquired through the successes of classical microelectronics [2], [3]. Among these implementations, Kane’s idea of storing qubits in the nuclear spin of phosphorus atoms embedded in silicon [4] has attracted much attention [5]. Although significant break- throughs have been reported during the past years [6], one of the challenges of Kane’s proposals lies in the high precision required for the fabrication techniques of the control electrodes used for manipulating the qubits [7]. Manuscript received February 19, 2009; revised April 10, 2009. First published October 20, 2009; current version published December 3, 2009. This work was supported by the Research Councils U.K. (RCUK) and the Engi- neering and Physical Sciences Research Council (EPSRC), through the Basic Technology Programme, and by the Royal Society. The authors are with the Optical Networks Group, Department of Electronic and Electrical Engineering, University College London (UCL), London WC1E 7JE, U.K. (e-mail: a.delduce@ee.ucl.ac.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSTQE.2009.2024326 Building on Kane’s idea, a variation was presented that pro- posed to exploit, rather than the nuclear spin, the electron spin of donors [8]. Further, the potential of qubits carried by the elec- tron spin of donors in semiconductors has been confirmed, for example, by the results presented in [9], which reported deco- herence times of up to 60 ms for electron spins of phosphorus atoms in silicon. In this paper, we focus on the quantum computation model proposed by Stoneham et al. [10] that is based on optically controlled, solid-state quantum logic gates. In this proposal, the qubits are stored in the spin of electrons from donors in a solid- state (possibly silicon) substrate. Interactions between two adja- cent qubits are mediated by a third particle, termed control parti- cle, placed in their proximity, and are triggered by the excitation and deexcitation of the control particle through optical pulses. The strength of this control atom-mediated (CAM) quantum computation model lies in the optical control of the two-qubit interactions that allows noisy electrical circuitry to be removed from the quantum register as well as avoiding high-precision fabrication processes for placing control electrodes. While it is expected that patches of up to 20 qubits may be controlled with this system, scalable quantum registers may then be built by interconnecting different patches [11]. In [12], these gates were referred to as SFG gates, since they were first presented in the paper by Stoneham, Fisher, and Greenland [10]. For generality, they are referred to as CAM gates throughout this paper, even though the technology and interaction mechanism is the same. The quantum computation model based on CAM gates has been studied intensively during the past years, both, theoretically and experimentally. The details on the dynamics of the CAM quantum gate are described in [13], which also compared how accurately this model was able to produce two-qubit entangling gates typically used in literature, such as the controlled-phase or the √ SWAP gates. In [12], these studies were further developed and results were presented that aimed at identifying gate param- eters able to produce, both, highly accurate and fast two-qubit entangling gates. From the experimental point of view, important measurements of the lifetimes of two control particle candidates in a silicon substrate have been recently reported [14]. These re- sults represent essential steps toward the implementation of a quantum computer based on CAM gates that lead the way to an experimental demonstration of a complete few-qubit quantum computation prototype. Here, we work toward this aim by analyzing the prepara- tion of an experimental demonstration of a three-qubit quantum computation prototype based on the CAM model. Particularly, 1077-260X/$26.00 © 2009 IEEE