Quantum-state transfer on spin-chain channels with random imperfections

We investigate the quantum-state transfer on spin-chain channels with random imperfections. Through combining the advantages of two known schemes, the dual-rail spin-chain channels [9] and the particular ihhomogenous spin-chain channel [10], we propose a protocol that can avoid the quantum noises introduced by many unnecessary measurements and can enhance the anti-decoherence ability. The results show that our protocol is more efficient to transfer an arbitrary quantum state than the original one. In particular, we discuss the effects of couplings fluctuations and imperfect initialization on both of the improved scheme and original one.     

Teleportation of a multiqubit state by an entangled qudit channel

We investigate the problem of teleportation of an M-qubit state by using an entangled qudit pair as a quantum channel and show that the teleportation of a multiparticle state can correspond to the teleportation of a multi-dimensional state. We also introduce a quantum-state converter composed of beamsplitter arrays, on/off-detectors and cross-Kerr couplers and demonstrate that the state conversion from an M-qubit to an N-dimensional qudit and vice versa can be implemented with this converter, where N=2^M. Based on this, an experimentally feasible scheme for the teleportation of an M-qubit via an entangled N-level qudit pair channel is proposed.     

A multiperipheral model with continued cross channel unitarity

We derive, by using a spectral representation in momentum transfer, t, an integral equation, similar in structure to a multipheral equation, with continued cross channel unitarity, for the absorptive part for a composite particle scattering amplitude from a Bethe-Salpeter equation describing composite particle scattering in the s channel. At high energy in the t channel, the equation becomes homogeneous and has a Reggeized solution. We indicate how this equation may be solved using determinental techniques. We also show how the composite particle amplitude resulting from the original equation may be used to construct production and three body amplitudes. We also infer the possibility of studying, using the amplitude from the cross channel problem, the effect of extra unitarity on Reggeon-Reggeon-particle vertices.     

利用信息流方法优化多激发自旋链中的量子态传输

研究了量子态在一条均匀耦合的反铁磁自旋链中传输时, 信道中自旋激发数变化对其传输性质的影响. 利用信息流方法分析输出端粒子的算符演化动力学, 获得了量子态传输的平均保真度与信道自旋初态之间的关系. 结果表明, 平均保真度的大小只依赖于信道中自旋激发数的奇偶性. 通过比较在奇偶激发信道中获得的最大平均保真度, 构建了优化信道来提升量子态在自旋链中的传输质量. 进一步分析了纠缠在激发信道中的传输情况, 发现纠缠的传输质量不仅和信道中自旋激发的具体个数有关, 还取决于激发自旋的初始排列. 特别地, 当信道中自旋无激发或全部激发时, 纠缠传输的大小和持续时间都优于其他的激发信道. 上述研究结果有助于在实际系统中搭建适合量子态和纠缠传输的量子信道.     

A Quantum-Bayesian Route to Quantum-State Space

In the quantum-Bayesian approach to quantum foundations, a quantum state is viewed as an expression of an agent’s personalist Bayesian degrees of belief, or probabilities, concerning the results of measurements. These probabilities obey the usual probability rules as required by Dutch-book coherence, but quantum mechanics imposes additional constraints upon them. In this paper, we explore the question of deriving the structure of quantum-state space from a set of assumptions in the spirit of quantum Bayesianism. The starting point is the representation of quantum states induced by a symmetric informationally complete measurement or SIC. In this representation, the Born rule takes the form of a particularly simple modification of the law of total probability. We show how to derive key features of quantum-state space from (i) the requirement that the Born rule arises as a simple modification of the law of total probability and (ii) a limited number of additional assumptions of a strong Bayesian flavor.     

Biased tomography schemes: an objective approach

We report on an intrinsic relationship between the maximum-likelihood quantum-state estimation and the representation of the signal. A quantum analogy of the transfer function determines the space where the reconstruction should be done without the need for any ad hoc truncations of the Hilbert space. An illustration of this method is provided by a simple yet practically important tomography of an optical signal registered by realistic binary detectors.     

FC-72在竖直壁面上及微小三角型通道内的沸腾传热

本文对浸在FC-72液池中的竖直壁面及两个微小三角形通道进行了沸腾实验研究,考虑了管道尺寸对沸腾传热特性的影响。两个微小三角形通道的边长分别为1.5和2.5 mm,水力直径分别为0.87和1.44 mm,长度50 mm,采用铜块上开V型沟槽,再覆盖上透明的玻璃片构成。热流密度由贴在铜块背后的膜状加热器提供。实验得到了沸腾曲线和传热系数,并用DV摄影机拍摄到了沸腾状况。实验结果显示,管道尺寸对沸腾传热特性有显著的影响,CHF值随通道尺寸的减小而减小,小通道在低热流密度时传热系数较大。     

Supersonic <Emphasis Type="Italic">N</Emphasis>-Crowdions in a Two-Dimensional Morse Crystal

An interstitial atom placed in a close-packed atomic row of a crystal is called crowdion. Such defects are highly mobile; they can move along the row, transferring mass and energy. We generalize the concept of a classical supersonic crowdion to an N-crowdion in which not one but N atoms move simultaneously with a high velocity. Using molecular dynamics simulations for a close-packed two-dimensional Morse crystal, we show that N-crowdions transfer mass much more efficiently, because they are capable of covering large distances while having a lower total energy than that of a classical 1-crowdion.     

Permutation approach to finite-alphabet stationary stochastic processes based on the duality between values and orderings

The duality between values and orderings is a powerful tool to discuss relationships between various information-theoretic measures and their permutation analogues for discrete-time finite-alphabet stationary stochastic processes (SSPs). Applying it to output processes of hidden Markov models with ergodic internal processes, we have shown in our previous work that the excess entropy and the transfer entropy rate coincide with their permutation analogues. In this paper, we discuss two permutation characterizations of the two measures for general ergodic SSPs not necessarily having the Markov property assumed in our previous work. In the first approach, we show that the excess entropy and the transfer entropy rate of an ergodic SSP can be obtained as the limits of permutation analogues of them for the N-th order approximation by hidden Markov models, respectively. In the second approach, we employ the modified permutation partition of the set of words which considers equalities of symbols in addition to permutations of words. We show that the excess entropy and the transfer entropy rate of an ergodic SSP are equal to their modified permutation analogues, respectively.     

Quantum information processing with nuclear spins mediated by a weak-mechanically controlled electron spin

We propose a scheme to achieve nuclear-nuclear indirect interactions mediated by a mechanically driven nitrogen-vacancy (NV) center in a diamond. Here we demonstrate two-qubit entangling gates and quantum-state transfer between two carbon nuclei. When the dipole-dipole interaction strength is much larger than the driving field strength, the scheme is robust against decoherence caused by coupling between the NV center (nuclear spins) and the environment. Conveniently, precise control of dipole coupling is not required so this scheme is insensitive to fluctuating positions of the nuclear spins and the NV center. Our scheme provides a general blueprint for multi-nuclear-spin gates and for multi-party communication.     

Asymptotically Well-Behaved Input States Do Not Violate Additivity for Conjugate Pairs of Random Quantum Channels

It is now well-known that, with high probability, the additivity of minimum output entropy does not hold for pairs of the random quantum channel and its complex conjugate. We investigate asymptotic behavior of output states of r-tensor powers of such pairs, as the dimension of inputs grows. We compute the limit output states for any sequence of well-behaved inputs, which consist of a large class of input states having a nice set of parameters. Then, we show that among these input states tensor products of Bell states give asymptotically the least output entropy, giving positive mathematical evidence towards additivity of above pairs of channels.     

The effect of gradually constricted channel on the I–V characteristics of graphene sheets

Ideal graphene is a gapless semiconductor consisting of a single layer of carbon atoms regularly arranged in a honeycomb lattice having infinite spatial extent in the (x,y)-plane, in which electrons behave as Dirac massless fermions. Even neglecting interactions with the anchoring substrate, a graphene sheet in real world has finite extent, leading to distinctive features in the conductivity of a given sample. In this letter we study the effect of a gradual channel constriction in graphene nanoribbons on their I–V characteristics, using non-equilibrium Green's function formalism. The constriction width and the border cutting angle are the main parameters to be varied. We found that transmission through the channel is considerably affected by these parameters, presenting sharp peaks at specific energies, which can be attributed to a resonance due to the tuning of energy eigenvalues.     

Laminar free convection heat transfer between vertical isothermal plates

The paper represents results on numerical investigation of flow and heat transfer between two isothermal vertical plates under laminar natural convection. A system of complete Navier–Stokes equations is solved for a two-dimensional gas flow between the plates along with additional rectangular regions (connected to inlet and outlet sections), whose characteristic sizes are much greater than the spacing between the plates. The calculations were performed over very wide ranges of Rayleigh number Ra = 10 ÷ 10⁵ and a relative channel length AR = L/w = 1 ÷ 500. The influence of the input parameters on the gas-dynamic and thermal structure of thermogravitational convection, the local and mean heat transfer, and also the gas flow rate between the plates (convective draft. We determined sizes of the regions and regime parameters when the local heat flux on the walls tends to zero due to the gas temperature approach to the surface temperature. It is shown that the mean heat transfer decreases as the relative channel length AR grows, whereas the integral gas flow rate (convective draft) and Reynolds number in the channel Re = 2wUm/ν increase. The use of a modified Rayleigh number Ra* = Ra · (w/L) (Elenbaas number) leads to generalization of calculation data on mean heat transfer. These data are in good agreement with the correlations for heat transfer [1, 2] and gas flow rate [3]. The reasons of variation of the data in the range of low Rayleigh numbers are discussed in detail.     

Quark scattering amplitudes with quasi-elastic unitarity

We consider quark-quark scattering at high energies and fixed momentum transfer. In a model where in the s and u channel intermediate states only gluons with sufficiently small transverse momenta are emitted, the scattering amplitudes are expressed in terms of the S-matrix elements for exactly soluble two-dimensional field theories.     

微酒窝通道与圆柱面凹槽通道对流传热强化分析

结合对流传热场协同原理分析了微酒窝通道、圆柱面凹槽通道及低肋通道强化传热特点,研究发现酒窝与圆柱面凹槽强化传热主要原因为:1)增加近壁区流体扰动,促进酒窝或凹槽内部流体与主流之间的传热;2)酒窝与凹槽均可扩展传热面积,进而提高总传热量。与低肋通道相比,酒窝与圆柱面凹槽仅对其附近流体的流动产生影响,而对主流流体的流动影响较小,进而阻力增加较少。提出传热量单元性能参数PEC_A作为评价指标,酒窝通道综合性能参数略高于圆柱面凹槽通道,而远高于低肋通道。     

Wall heat transfer in static and rotating 180° turn channels by quantitative infrared thermography

The aim of the present study is to develop a new experimental methodology that allows one to perform accurate measurements of the local heat transfer distribution before, in, and after a 180° sharp turn in static and rotating channels. Preliminary measurements of convective heat transfer coefficients are performed by means of infrared thermography applied to the steady state ‘heated-thin-foil’ technique. Some preliminary results in terms of Nusselt number Nu distributions and profile, as well as averaged Nu profiles along the channel axis, are presented. Results prove that infrared thermography is capable of measuring heat flux coefficients and detecting particular phenomena linked to the fluid flow configuration such as location of separation bubbles, influence of the channel aspect ratio as well as the influence of the channel rotation.     

State reconstruction of one-dimensional wave packets

76 , 1985 (1996)] for quantum-state reconstruction of one-dimensional non-relativistic wave packets from position observations. We illuminate the theoretical background of the technique and show how to extend the procedure to the continuous part of the spectrum. Received: 7 July 1997     

Spectroscopy and reaction mechanism of the system90Zr→232Th in the vicinity of the Coulomb barrier

A study of few nucleon transfer reactions in conjunction with Coulomb excitation was performed by bombarding a²³²Th target with⁹⁰Zr projectiles at incident energies close to the Coulomb barrier. Particle-γ coincidence techniques using the Heidelberg-Darmstadt Crystal Ball were employed to select excited states of reaction products. Around the grazing angle roughly 2/3 of the total cross section goes into transfer channels, half of it formed by 1n...4n transfer. The enhancement of the 2n cross section is in accord with a sequential process with a highly excited intermediate state. A correlated pair transfer directly populating yrast states appears to be negligibly small. The excitation energy is almost equally distributed upon the outgoing reaction partners for the 1n channel and there are indications for a similar behaviour of the 2n channel.     

Two dimensional electron gas in a hybrid GaN/InGaN/ZnO heterostructure with ultrathin InGaN channel layer

We investigated the influence of an ultrathin InGaN channel layer on two-dimensional electron gas (2DEG) properties in a newly proposed hybrid GaN/In_xGa_1−xN/ZnO heterostructure using numerical methods. We found that 2DEG carriers were confined at InGaN/ZnO and GaN/InGaN interfaces. Our calculations show that the probability densities of 2DEG carriers at these interfaces are highly influenced by the In mole fraction of the InGaN channel layer. Therefore, 2DEG carrier confinement can be adjustable by using the In mole fraction of the InGaN channel layer. The influence of an ultrathin InGaN channel layer on 2DEG carrier mobility is also discussed. Usage of an ultrathin InGaN channel layer with a low indium mole fraction in these heterostructures can help to reduce the short-channel effects by improvements such as providing 2DEG with higher sheet carrier density which is close to the surface and has better carrier confinement.