使用非最大纠缠态远程执行部分未知量子操作

建议一个使用非最大纠缠态通道远程执行部分未知量子操作的协议,并且显示,当采用非最大纠缠粒子对作为量子通道时,由引进一个集中的幺正变换使得部分未知的量子操作能够被概率地远程执行.讨论了在这种情况下,部分未知的量子操作远程执行的成功概率以及所需要的资源.     

未知二粒子纠缠态的辅助克隆

提出一个以三粒子GHZ态为量子信道的未知二粒子纠缠态及其正交态的概率克隆方案.此方案中,发送方Alice和接收方Bob对未知态的信息一无所知.首先Alice对他的粒子实施贝尔测量,在得知Alice的测量结果后,通过引入辅助粒子并执行控制非门操作后,Bob可成功地接收未知态.随后在态的制备方Victor的帮助下,Alice以一定的概率获得未知二粒子纠缠态及其正交态的复制.该方案同样适合量子信道是非最大纠缠态的情况.此外,量子纠缠资源和经典信息损耗在该方案中均得到了节省.     

基于4粒子纠缠态的未知3粒子态概率量子隐形传态

使用4粒子纠缠态作为量子信道,在对4粒子纠缠态的纠缠系数方面并没有做确切要求的前提下,完成了未知3粒子纠缠态的隐形传态.在传输过程中,发送方对2对粒子进行Bell测量并公布结果,然后再对4粒子中的一个粒子作Hadamard操作之后,也对其进行测量,且将测量结果通过经典信道公布.接收方引进2个辅助粒子并实施一次控制非操作,再进行一组适当的幺正变换,便可实现未知3粒子纠缠态的概率量子隐形传态.     

二能级多粒子任意纠缠态的超空间传送

在二能级单粒子未知量子态的超空间传送方案和有控制者参与的受控二能级单粒子量子态超空间传送方案的基础上,分析了一般情况和受控情况下二能级二粒子量子态的超空间传送,并给出了详细的计算结果.同时简要讨论了这2种情况下任意数目的二能级系统的任意未知量子态的超空间传输问题.     

未知二粒子纠缠态及其正交态的概率克隆

提出一个实现二粒子纠缠态及其正交态的概率克隆方案.此方案分为两个步骤,第一步通过一个四粒子簇态作为量子信道实现未知二粒子纠缠态的量子隐形传输,第二步在态的制备者的帮助下实现二粒子纠缠态及其正交态的概率克隆.     

在QED腔中实现一个未知的三粒子W态的隐形传输方案

量子隐形传输在量子信息科学中有着重要的地位,很多方案被设计出来用于实现隐形传输,但在实际中,存在着很多困难,例如EPR对的制备,联合Bell测量,腔衰减和热场的影响等.在本文中,首先介绍了一个单模腔,原子4、5,原子6、7和原子8、9的最大纠缠态被制备出来,从它的有效哈密顿量的形式,可以看出,热场和腔衰减可以消除掉,其次我们设计了一个未知的三粒子W态的隐形传输方案,从中可以发现,这个过程中不需要联合Bell测量,而且实现这个过程成功的概率是1.     

利用超导量子干涉仪制备N比特团簇态（英文）

利用两个超导量子干涉仪与腔场的相互作用,提出一种实现标准两比特量子相位门的方案。利用构造的两比特相位门,还提出了一种制备N比特团簇态的方案。在此方案中,量子信息被编码在两个超导量子干涉仪的相对稳定的基态上。在两个超导量子干涉仪与单模腔场的相互作用过程中,由于超导量子干涉比特的激发态被绝热地消去,激发态所引起的消相干得到了有效的抑制。此外,还讨论方案的实验可行性。     

极小最大量子态区分

得到在未知先验概率的情况下,区分三个非正交量子态的最优概率,给出了求解这类问题的公式,同时,把这类区分和Bayesian非正交量子态的区分相比较。该方法可以推广到N个非正交量子态问题的区分。     

利用腔-QED进行两原子任意态量子隐态传输方案

基于腔QED技术,我们提出一种无需Bell态联合测量的两原子任意态量子隐态传输方案．在传输过种中,在一个强经典场驱动下,原子与非共振的单模腔场相互作用,对原子的分离测量来代替实验上难以实现的联合Bell态测量,且不受腔泄漏及环境热库的影响,     

Entangled quantum state of magnetic dipoles

Free magnetic moments usually manifest themselves in Curie laws, where weak external magnetic fields produce magnetizations that vary as the reciprocal of the temperature (1/T). For a variety of materials that do not display static magnetism, including doped semiconductors and certain rare-earth intermetallics, the 1/T law is replaced by a power law T(-alpha) with alpha < 1. Here we show that a much simpler material system-namely, the insulating magnetic salt LiHo(x)Y(1-x)F(4)-can also display such a power law. Moreover, by comparing the results of numerical simulations of this system with susceptibility and specific-heat data, we show that both energy-level splitting and quantum entanglement are crucial to describing its behaviour. The second of these quantum mechanical effects-entanglement, where the wavefunction of a system with several degrees of freedom cannot be written as a product of wavefunctions for each degree of freedom-becomes visible for remarkably small tunnelling terms, and is activated well before tunnelling has visible effects on the spectrum. This finding is significant because it shows that entanglement, rather than energy-level redistribution, can underlie the magnetic behaviour of a simple insulating quantum spin system.     

量子态的非局域关联性

在普遍的两个自旋1/2粒子量子态下证明了局域实在论与量子力学是不相容的,推广了Hardy在两个粒子非最大纠缠态下关于Bell 定理的证明.通过纠缠态下广义量子不可克隆定理中的正交条件的转移证明了量子力学非局域关联性.     

基于量子扩散理论的量子动力学过程仿真

在分析系统和环境的相互作用的基础上,首先研究了主方程模型描述的开放量子系统的随机动力学特征,得到了表征系统消相干因素的Lindblad算符和描述系统量子态演化规律的量子随机微分方程;然后根据微分方程的形式,采用了一种迭代算法,实现了表征系统演化特征的约化密度算符的数值模拟,并给出一个卖例,与经典Runge-Kutta迭代算法的比较,验证了其实用性和优越性;最后分析了仿真算法的收敛性．     

Measuring-basis-encrypted six?state quantum key distribution scheme

A six-state quantum key distribution scheme with measuring-basis encryption technique, which is based on the six?state protocol and the MBE protocol, is proposed. In this modified six-state quantum key distribution protocol, Alice and Bob use a control key to synchronize the use of their measuring-basis so that they always use the same measuring?basis. This modified six-state quantum key distribution protocol retains the advantage of higher security and at the same time has a higher efficiency.     

Observation of a quarter of an electron charge at the nu = 5/2 quantum Hall state

The fractional quantum Hall effect, where plateaus in the Hall resistance at values of h/nue2 coexist with zeros in the longitudinal resistance, results from electron correlations in two dimensions under a strong magnetic field. (Here h is Planck's constant, nu the filling factor and e the electron charge.) Current flows along the sample edges and is carried by charged excitations (quasiparticles) whose charge is a fraction of the electron charge. Although earlier research concentrated on odd denominator fractional values of nu, the observation of the even denominator nu = 5/2 state sparked much interest. This state is conjectured to be characterized by quasiparticles of charge e/4, whose statistics are 'non-abelian'-in other words, interchanging two quasiparticles may modify the state of the system into a different one, rather than just adding a phase as is the case for fermions or bosons. As such, these quasiparticles may be useful for the construction of a topological quantum computer. Here we report data on shot noise generated by partitioning edge currents in the nu = 5/2 state, consistent with the charge of the quasiparticle being e/4, and inconsistent with other possible values, such as e/2 and e. Although this finding does not prove the non-abelian nature of the nu = 5/2 state, it is the first step towards a full understanding of these new fractional charges.     

Optical coherent state discrimination using a closed-loop quantum measurement

Quantum mechanics hinders our ability to determine the state of a physical system in two ways: individual measurements provide only partial information about the observed system (because of Heisenberg uncertainty), and measurements are themselves invasive-meaning that little or no refinement is achieved by further observation of an already measured system. Theoretical methods have been developed to maximize the information gained from a quantum measurement while also minimizing disturbance, but laboratory implementation of optimal measurement procedures is often difficult. The standard class of operations considered in quantum information theory tends to rely on superposition-basis and entangled measurements, which require high-fidelity implementation to be effective in the laboratory. Here we demonstrate that real-time quantum feedback can be used in place of a delicate quantum superposition, often called a 'Schr?dinger cat state', to implement an optimal quantum measurement for discriminating between optical coherent states. Our procedure actively manipulates the target system during the measurement process, and uses quantum feedback to modify the statistics of an otherwise sub-optimal operator to emulate the optimal cat-state measurement. We verify a long-standing theoretical prediction and demonstrate feedback-mediated quantum measurement at its fundamental quantum limit over a non-trivial region of parameter space.     

Sideband cooling of micromechanical motion to the quantum ground state

The advent of laser cooling techniques revolutionized the study of many atomic-scale systems, fuelling progress towards quantum computing with trapped ions and generating new states of matter with Bose-Einstein condensates. Analogous cooling techniques can provide a general and flexible method of preparing macroscopic objects in their motional ground state. Cavity optomechanical or electromechanical systems achieve sideband cooling through the strong interaction between light and motion. However, entering the quantum regime--in which a system has less than a single quantum of motion--has been difficult because sideband cooling has not sufficiently overwhelmed the coupling of low-frequency mechanical systems to their hot environments. Here we demonstrate sideband cooling of an approximately 10-MHz micromechanical oscillator to the quantum ground state. This achievement required a large electromechanical interaction, which was obtained by embedding a micromechanical membrane into a superconducting microwave resonant circuit. To verify the cooling of the membrane motion to a phonon occupation of 0.34?±?0.05 phonons, we perform a near-Heisenberg-limited position measurement within (5.1?±?0.4)h/2π, where h is Planck's constant. Furthermore, our device exhibits strong coupling, allowing coherent exchange of microwave photons and mechanical phonons. Simultaneously achieving strong coupling, ground state preparation and efficient measurement sets the stage for rapid advances in the control and detection of non-classical states of motion, possibly even testing quantum theory itself in the unexplored region of larger size and mass. Because mechanical oscillators can couple to light of any frequency, they could also serve as a unique intermediary for transferring quantum information between microwave and optical domains.     

借助于推广Bell态实现两体量子态隐形传态

两比特量子隐形传态的实现直接关系到量子计算机的实现,因此提出一个任意两比特量子态的隐形传态方案,发送者能成功地将此量子态几率地传送给接收者.此方案中,16个推广的非最大纠缠Bell态(简称G态)之一充当量子信道.发送者通过实行推广的Bell态测量(G态测量),接收者通过引入一个辅助粒子并实施适当的么正变换和单粒子测量,能将此任意两比特量子态以一定的几率发送给接收者.此种隐形传态方案的成功几率由量子信道系数绝对值的最小值所决定.

Abstract：

Two-qubit quantum teleportation is closely related to quantum computation, so a teleportation protocol in which an arbitrary bipartite quantum state is perfectly teleported probabilistically from sender to receiver is proposed. One of 16 generalized non-maximally entangled Bell states (G states for simplicity) functions as quantum channel. The teleportation can be successfully realized with a certain probability if sender performs generalized Bell state measurements (G measurements) and receiver introduces an auxiliary particle and operates appropriate unitary transformations and single-qubit measurements. The probability of successful teleportation is determined by the smallest one among the coefficients' absolute values of the quantum channel.     

Structure-based activity prediction for an enzyme of unknown function

With many genomes sequenced, a pressing challenge in biology is predicting the function of the proteins that the genes encode. When proteins are unrelated to others of known activity, bioinformatics inference for function becomes problematic. It would thus be useful to interrogate protein structures for function directly. Here, we predict the function of an enzyme of unknown activity, Tm0936 from Thermotoga maritima, by docking high-energy intermediate forms of thousands of candidate metabolites. The docking hit list was dominated by adenine analogues, which appeared to undergo C6-deamination. Four of these, including 5-methylthioadenosine and S-adenosylhomocysteine (SAH), were tested as substrates, and three had substantial catalytic rate constants (10(5) M(-1 )s(-1)). The X-ray crystal structure of the complex between Tm0936 and the product resulting from the deamination of SAH, S-inosylhomocysteine, was determined, and it corresponded closely to the predicted structure. The deaminated products can be further metabolized by T. maritima in a previously uncharacterized SAH degradation pathway. Structure-based docking with high-energy forms of potential substrates may be a useful tool to annotate enzymes for function.     

数据库表关联删除的遍历算法实现

对数据库表关联删除的需求作了详细分析，为其解决给出了一套完整的处理方案，使数据库管理更加方便合理。直接借助或使用该方案可以在软件中操作数据库，并可以由此编制一些触发器。此外，使用树形存储结构结合树的先根、后根遍历算法，提出了一种全新的松散先根遍历算法，从而有效地解决了数据库表的关联删除在占用空间及搜索处理上效率更高的关键问题。