Quantum Codes for Simplifying Design and Suppressing Decoherence in Superconducting Phase-Qubits

We introduce simple qubit-encodings and logic gates which eliminate the need for certain difficult single-qubit operations in superconducting phase-qubits, while preserving universality. The simplest encoding uses two physical qubits per logical qubit. Two architectures for its implementation are proposed: one employing N physical qubits out of which N/2 are ancillas fixed in the |1 state, the other employing N/2+1 physical qubits, one of which is a bus qubit connected to all others. Details of a minimal set of universal encoded logic operations are given, together with recoupling schemes, that require nanosecond pulses. A generalization to codes with higher ratio of number of logical qubits per physical qubits is presented. Compatible decoherence and noise suppression strategies are also discussed. PACS: 03.67.Lx; 85.25.Hv; 03.67.-a; 89.70.+c     

辐照加固集成电路

本文叙述了辐照加固集成电路在军事武器及航天设备中的意义，重点介绍了已有的辐照加固集成电路，如微处理器系列电路、数字电路、接口电路，最后通过对这些电路所用的加工技术的分析，提出了我国发展辐照加固集成电路的建议。     

Implementing a Quantum Algorithm with Exchange-Coupled Quantum Dots: A Feasibility Study

We present Monte Carlo wavefunction simulations for quantum computations employing an exchange-coupled array of quantum dots. Employing a combination of experimentally and theoretically available parameters, we find that gate fidelities greater than 98% may be obtained with current experimental and technological capabilities. Application to an encoded 3 qubit (nine physical qubits) Deutsch-Josza computation indicates that the algorithmic fidelity is more a question of the total time to implement the gates than of the physical complexity of those gates. PACS: 81.07.Ta, 02.70.Ss, 03.67.Lx, 03.65.Yz     

An Explicit Universal Gate-Set for Exchange-Only Quantum Computation

A single physical interaction might not be universal for quantum computation in general. It has been shown, however, that in some cases it can achieve universal quantum computation over a subspace. For example, by encoding logical qubits into arrays of multiple physical qubits, a single isotropic or anisotropic exchange interaction can generate a universal logical gate-set. Recently, encoded universality for the exchange interaction was explicitly demonstrated on three-qubit arrays, the smallest nontrivial encoding. We now present the exact specification of a discrete universal logical gate-set on four-qubit arrays. We show how to implement the single qubit operations exactly with at most 3 nearest neighbor exchange operations and how to generate the encoded controlled-NOT with 27 parallel nearest neighbor exchange interactions or 50 serial gates, obtained from extensive numerical optimization using genetic algorithms and Nelder–Mead searches. We also give gate-switching times for the three-qubit encoding to much higher accuracy than previously and provide the full speci.cation for exact CNOT for this encoding. Our gate-sequences are immediately applicable to implementations of quantum circuits with the exchange interaction. PACS: 03.67.Lx, 03.65.Ta, 03.65.Fd, 89.70.+c     

Implementation Schemes for the Factorized Quantum Lattice-Gas Algorithm for the One Dimensional Diffusion Equation using Persistent-Current Qubits

We present two experimental schemes that can be used to implement the Factorized Quantum Lattice-Gas Algorithm for the 1D Diffusion Equation with Persistent-Current (PC) Qubits. One scheme involves biasing the PC Qubit at multiple flux bias points throughout the course of the algorithm. An implementation analogous to that done in Nuclear Magnetic Resonance (NMR) Quantum Computing is also developed. Errors due to a few key approximations utilized are discussed and differences between the PC Qubit and NMR systems are highlighted     

Improved Gap Estimates for Simulating Quantum Circuits by Adiabatic Evolution

We use elementary variational arguments to prove, and improve on, gap estimates which arise in simulating quantum circuits by adiabatic evolution. Partially supported by the National Science Foundation under Grant DMS-0314228 and by the National Security Agency and Advanced Research and Development Activity under Army Research Office contract number DAAD19-02-1-0065.     

多量子位量子小波变换逻辑线路及仿真实现

由于量子计算相比于经典计算的突出优越性,量子小波变换的实现对于小波变换的理论完善和实际应用具有重要的意义,而逻辑线路是该变换实现的基础。应用多量子算符代数理论设计了3量子位Haar和D^（4）小波变换的逻辑线路,进而将逻辑线路转化成核磁共振系统可以实现的脉冲序列,并在量子计算仿真器（QCE）上进行了模拟实现,验证了逻辑线路的合理性。     

模拟集成电路三维互连电容的改进层次式提取

层次式直接边界元方法可一次性计算出整个互连寄生电容矩阵,具有较高的计算效率．针对模拟集成电路的特点,对层次式三维电容提取的三维块切割方式、非均匀边界元划分和程序组织等方面进行了改进,显著地提高了算法的效率．数值实验表明,改进的层次式互连电容提取在保证高精度的同时,速度提高了数倍,适用于实际的模拟集成电路设计．     

量子遗传算法研究现状

Quantum Genetic Algorithm (QGA)is the combination of quantum computation and genetic algorithm. In this paper, actuality of research on QGA is summarized. QGA and Multi-universe Parallel Quantum Genetic Algorithm (MPQGA)are discussed in detail. Application progenies in respective regions are introduced. The subsequent research on QGA is also prospected.     

Quantum learning control using differential evolution with equally-mixed strategies

Learning control has been recognized as a powerful approach in quantum information technology. In this paper, we extend the application of differential evolution (DE) to design optimal control for various quantum systems. Various DE methods are introduced and analyzed, and EMSDE featuring in equally mixed strategies is employed for quantum control. Two classes of quantum control problems, including control of four-level open quantum ensembles and quantum superconducting systems, are investigated to demonstrate the performance of EMSDE for learning control of quantum systems. Numerical results verify the effectiveness of the EMSDE method for various quantum systems and show the potential for complex quantum control problems.     

Estimation of Quantum Channels with Finite Resources

We examine the problem of determining the parameters that describe a quantum channel. It is assumed that the users of the channel have at best only partial knowledge of it and make use of a finite amount of resources to estimate it. We discuss simple protocols for the estimation of the parameters of several classes of channels that are studied in the current literature. A quantitative measures of the quality of the estimation schemes can be given on the basis of the standard deviation or of the fidelity. Protocols that employ entangled particles are also discussed. The use of entangled particles as a nonclassical resource enhances the estimation quality of some classes of quantum channel. Further, the methods presented here can be extended to higher dimensional quantum systems. PACS: 03.67.Hk     

On the Role of Hadamard Gates in Quantum Circuits

We study a reduced quantum circuit computation paradigm in which the only allowable gates either permute the computational basis states or else apply a “global Hadamard operation”, i.e. apply a Hadamard operation to every qubit simultaneously. In this model, we discuss complexity bounds (lower-bounding the number of global Hadamard operations) for common quantum algorithms: we illustrate upper bounds for Shor’s Algorithm, and prove lower bounds for Grover’s Algorithm. We also use our formalism to display a gate that is neither quantum-universal nor classically simulable, on the assumption that Integer Factoring is not in BPP.     

Quantum Computing and Information Extraction for Dynamical Quantum Systems

We discuss the simulation of complex dynamical systems on a quantum computer. We show that a quantum computer can be used to efficiently extract relevant physical information. It is possible to simulate the dynamical localization of classical chaos and extract the localization length with quadratic speed up with respect to any known classical computation. We can also compute with algebraic speed up the diffusion coefficient and the diffusion exponent, both in the regimes of Brownian and anomalous diffusion. Finally, we show that it is possible to extract the fidelity of the quantum motion, which measures the stability of the system under perturbations, with exponential speed up. The so-called quantum sawtooth map model is used as a test bench to illustrate these results. PACS: 03.67.Lx, 05.45.Mt     

具有主客观信息集成特征的人才需求预测方法及其应用

针对经济体制转归时期的特殊情况，提出了适应经济体制转轨时期的具有主客观信息集成特征的人才需求预测方法，并预测了Ｌ省２０００－２０１０年的人才需求量及补充量。     

Quantum Computer Development with Single Ion Implantation

Spins of single donor atoms are attractive candidates for large scale quantum information processing in silicon. Formation of devices with a few qubits is crucial for validation of basic ideas and development of a scalable architecture. We describe our development of a single ion implantation technique for placement of single atoms into device structures. Collimated highly charged ion beams are aligned with a scanning probe microscope. Enhanced secondary electron emission due tohigh ion charge states (e.g., ³¹P¹³⁺, or ¹²⁶Te³³⁺)allows efficient detection of single ion impacts. Studies of electrical activation of low dose, low energy implants of ³¹P in silicon show a drastic effect of dopant segregation to the SiO₂/Si interface,while Si₃N₄/Si retards ³¹P segregation. We discuss resolution limiting factors in ion placement, and process challenges forintegration of single atom arrays with control gates and single electron transistors. PACS: 03.67.Lx, 34.50.Dy, 85.35.Gv, 73.23, 61.72, 86.40.py, 07.79.-v     

Ion Trap Quantum Computing with Ca+ Ions

The scheme of an ion trap quantum computer is described and the implementation of quantum gate operations with trapped Ca⁺ ions is discussed. Quantum information processing with Ca⁺ ions is exemplified with several recent experiments investigating entanglement of ions. PACS: 03.67.Lx, 03.67.Mn, 32.80.Pj