Influence from Cavity Decay on Entanglement Evolution of Three Superconducting Charge Qubits Coupled to a Cavity

We investigate the entanglement dynamics of a quantum system consisting of three Superconducting charge qubits （SCQs） interacting with a single-mode cav- ity field. Considering the Rotating wave approximation （RWA） and the resonance condition, we give the effective Hamiltonian of the system involving cavity decay. The dy- namical evolution is studied in terms of the entanglements in the different bipartite partitions of the system, as quan- tified by the square concurrence. With the choice of the appropriate initial states, a four-qubit W-entangled state can be obtained. We study the effect of cavity decay on various square concurrences in the system, the results show that the peak value of the square concurrence declines with the increase of cavity decay when the other parameters are fixed, but the cavity decay does not change the period of the square concurrence. We also find a natural entangle- ment transfer and entanglement invariant under evolution of the effective Hamiltonian.     

高温超导材料研究近况

近两年高温超导又取得了巨大的进展，特别是在：（１）新的更高温度超导体系的探索，这包括进一步提高Ｔｃ值和合成新结构、新类型的超导材料；（２）材料的应用基础研究，主要指超导块材、线材、带材、膜材料的制备和改进，包括ＳＱＵＩＤ、Ｊｏｓｅｐｈｓｏｎ结和微波无源器件；（３）对高温超导现象的解释和机理的研究方面尤为显著。本文重点介绍过去一年高温超导在材料研究方面的主要进展。     

量子计算机存储器中的解相干

量子计算机中的解相干，破坏量子态中的信息，是量子计算难以实现的主要原因之一。     

量子逻辑门中的编码量子位研究

本文提出在量子编码中用量子字节控制量子字节的设想,具体分析了字节被控编码法防止或纠正逻辑运算错误的量子线路,该编码既适用于量子逻辑门的防错和纠错,也适用于防止量子计算机存储单元的解相干。该编码法量子位使用效率为５０％,且防错和纠错过程简单明了,并有单个逻辑双态双轨技术提供实验基础,因此该方案实现的可能性大。     

柱形量子点中量子比特的消相干时间

通过求解柱形量子点的能量本征方程,得到极化子的基态和第一激发态的本征能量以及本征波函数,进而根据基态和第一激发态构造一个量子比特。数值计算讨论了消相干时间与色散系数、电子-体纵光学声子耦合强度、柱形量子点的半径及柱高的变化关系。     

High Tc Superconducting Materials for Strong Current Applications： Approach at the First Stage

Strong current and large-scale application is the most important prospect of high Te superconductors （HTS）. Practical HTS samples in various forms have been produced with high critical currents operated at economic cryogenic temperatures. Engineering applications of those HTS materials have been studied with various HTS prototype devices. The applicable HTS materials produced in different forms are verified in this paper with regard to their strong current characterizations, and the HTS applications are summarized along with the HTS prototypes made.     

热辐射场中两能级原子的消相干

本文将两能级原子视为量子位。当量子位置于外部环境（热库）中,研究两个量子位约化密度矩阵非对角元的时间演化,分析量子位消相干规律。如果仅考虑振幅阻尼,结果表明热辐射与量子噪声对量子位的消相干产生影响。     

硅基自旋量子比特技术研究进展

量子芯片是运用量子力学基本原理构建实用化计算机的基础.各国研究团队通过近几年的卓越研究工作,将硅基量子比特芯片技术发展成量子计算的核心方向之一.文章重点归纳了Si自旋量子比特的主要类型,分析了可靠量子计算实现所要求的高保真度、长程耦合等指标的关键技术.这些技术的研究表明,硅是一个能实现全面量子计算发展的可行平台.     

开放量子系统中消相干及其控制策略

从开放量子系统的起因入手,就量子系统中消相干现象的产生、类型以及所产生的影响进行了分析和阐述。在此基础上,针对不同类型抑制消相干控制研究的方法与策略,进行了比较详细的综述,并以对比的方式揭示了开放量子系统消相干控制策略中的优缺点。最后对抑制消相干研究的发展方向进行了展望。     

High Tc Superconducting Materials for Strong Current Applications: Approach at the First Stage

Strong current and large-scale application is the most important prospect of high Tc superconductors (HTS). Practical HTS samples in various forms have been produced with high critical currents operated at economic cryogenic temperatures. Engineering applications of those HTS materials have been studied with various HTS prototype devices. The applicable HTS materials produced in different forms are verified in this paper with regard to their strong current characterizations, and the HTS applications are summarized along with the HTS prototypes made.     

简并双光子过程中两能级原子的消相干

两能级原子置于外部环境（热库）时,将两能级原子视为量子位,通过分析简并双光子过程中量子位约化密度算符非对角元的时间演化,研究量子位消相干规律。     

压缩真空场中量子存储单元的消相干特性

两能级原子作为量子存储单元，当存储单元置于压缩真空库（人工制备的库）时，利用存储单元约化密度算符非对角元的时间演化，研究单光子过程和工双光子过程中存储单元的消相干特性。在压缩真空库中，可以消除量子存储单元的消相干。     

Microstructural Origins of High Piezoelectric Performance: A Pathway to Practical Lead‐Free Materials

Piezoelectric materials interconvert between electrical energy and mechanical strain and are widely used for electronic and electromechanical devices. Owing to growing environmental concerns, development of lead‐free piezoelectric materials with enhanced properties becomes of great interest. Key to the academic problem is a lack of fundamental understanding on the actual mechanisms involved at the microscopic (unit cell) level. While it is well known that giant responses occur near structural phase boundaries, and it has long been proposed that polarization rotation and nanodomains are major determinants, so far, atomistic understanding of the origin of the response has come mostly from theoretical simulations. Recently, notable breakthroughs have been achieved in improving the properties of piezoceramics and thin films. Precise mapping of atomic displacements by atomically resolved Z‐contrast imaging has demonstrated that gradual polarization rotation bridges the coexisting nanophases. These structural features, which take place on a length scale of just a few nanometers, now visible through aberration‐corrected microscopy, provide a new pivotal understanding on the outstanding piezoelectric behavior that has been obtained in all systems. They also provide key guiding principles for the development of lead‐free piezoelectrics, especially in the form of thin films, which remain far behind bulk ceramics at the time being. Coexistence of nanophases with flexible interconversion, introduced via phase boundary engineering, holds much promise for achieving high performance in other material systems with phase transitions.     

超导技术在测量雷达中的应用

空间目标探测对测量雷达威力提出了更高的要求,当雷达功率孔径积增大到其极限值时,需要挖掘其他潜力来提高雷达作用距离.文中介绍了超导接收前端的组成、原理和特点,通过对雷达威力的分析和计算,比较了不同噪声系数条件下,雷达作用距离与发射功率、天线口径的关系,将噪声系数极低的超导接收前端应用于雷达可以显著提高其作用距离.     

Superconducting properties of silicon nanostructures

Superconducting properties of silicon sandwich nanostructures on the n-Si (100) surface, which represent the ultra-narrow p-type silicon quantum wells confined by heavily boron-doped δ barriers, manifest themselves in the measurements of the temperature and field dependences of resistivity, thermopower, heat capacity, and static magnetic susceptibility. The cyclotron-resonance, scanning-tunneling-microscopy, and ESR data identify the presence of the single trigonal negative-U dipole boron centers in nanostructured δ barriers B ⁺-,B ^?, which are formed due to the reconstruction of shallow boron acceptors, 2B ⁰ ? B ⁺ + B ^?. The obtained results indicate that these negative-U centers are responsible for the transport of small-radius hole bipolarons, which is likely the basis of the mechanism of high-temperature superconductivity with T _C = 145 K. The superconductor-gap value of 0.044 eV determined from the measurements of the critical temperature using the above techniques is almost identical to the data on the tunneling spectroscopy and direct record of tunneling I–V characteristics. The quantization of the superconductive characteristics for silicon sandwich nanostructures manifests itself in the temperature and field dependences of the heat capacity and static magnetic susceptibility, which show the oscillations of the second critical field and critical temperature arising due to the supercurrent quantization.     

Outlook of the Superconducting Maglev

The superconducting maglev has been developed as an ultra-high speed mass transport system. It makes use of modern superconducting magnets (SCMs), which enable a large gap electro-dynamic suspension and an efficient linear motor propulsion. Running tests have been conducted smoothly on the 18.4-km-long Yamanashi Maglev Test Line since 1997 and reaped the harvests such as the maximum speed of 581 km/h, relative speed of 1026 km/h on two trains' passing test and on-board high temperature SCM running tests. In March 2005 the Committee under the Ministry of Land, Infrastructure and Transport appreciated that “all the technologies of the Superconducting Maglev necessary for the future revenue service were established.” Based on this situation, JR Central has decided to expand the existing test line as well as renew the existing facilities and equipment into those of the future revenue service level. Furthermore, the company has decided to promote the Tokaido Shinkansen Bypass project utilizing the superconducting maglev system.      

Multiplexed Readout of Superconducting Bolometers

Studies of emission in the far-infrared and submillimeter from astrophysical sources require large arrays of detectors containing hundreds to thousands of elements. A multiplexed readout is necessary for practical implementation of such arrays, and can be developed using SQUIDS, such that, e.g., a 32 × 32 array of bolometers can be read out using ≈100 wires rather than the >2000 needed with a brute force expansion of existing arrays. These bolometer arrays are made by micromachining techniques, using superconducting transition edge sensors as the thermistors. We describe the development of this multiplexed superconducting bolometer array architecture as a step toward bringing about the first astronomically useful arrays of this design. This technology will be used in the SAFIRE instrument on SOFIA, and is a candidate for a wide variety of other spectroscopic and photometric instruments.     

Analytic Estimates of Magnetic Energy in Superconducting Quadrupoles

In this paper, we propose analytical formulae to determine the magnetic energy stored in superconducting quadrupoles made of sector coils. The study is based on the Fourier transformation of the current density flowing within the coils. The case of real magnets (i.e., magnets which are not made of pure sector coils) is treated and a heuristic corrective coefficient allowing taking into account the energy enhancement due to current grading is derived from a numerical study. We also introduce the effect of an unsaturated iron yoke on the stored energy and we discuss the issue of the yoke saturation.      

Superconducting Magnets and Cooling System in BEPCII

A pair of dual-purpose superconducting quadrupole magnets and a superconducting detector solenoid were fabricated and installed in Beijing Electron-Positron Collider Upgrade (BEPCII). The magnets are symmetrically inserted into the BESIII detector with respect to the interaction point. They are identical, iron-free, non-collared, multi-layered and active shielded superconducting magnets for the micro-beta focusing at the interaction region of the collider rings. Each quadrupole magnet is composed of seven coils at different operating currents wound layer by layer on a common cylindrical support. The magnet has an overall effective length of 0.96 m and provides a good field aperture of 65 mm in diameter. They are cooled by supercritical helium in order to eliminate the flow instabilities in constrained cooling channels. The BESIII superconducting solenoid magnet was designed to provide an axial magnetic field of about 1.0 T over the tracking volume and to meet the requirement of particle momentum resolution to particle detectors. A single layer of coil, in-direct cooling by forced two-phase helium, high purity aluminum based stabilizer and NbTi/Cu superconductor is adopted for the solenoid. The solenoid is 3.4 m in diameter and 3.89 m in length. This paper presents the design of the superconducting magnets in the BEPCII as well as their cryomodules. The cooling system for the magnets is also discussed.