Reversible simulation of bipartite product Hamiltonians

Consider two quantum systems A and B interacting according to a product Hamiltonian H=H/sub A//spl ominus/H/sub B/. We show that any two such Hamiltonians can be used to simulate each other reversibly (i.e., without efficiency losses) with the help of local unitary operations and local ancillas. Accordingly, all nonlocal features of a product Hamiltonian - including the rate at which it can be used to produce entanglement, transmit classical or quantum information, or simulate other Hamiltonians - depend only upon a single parameter. We identify this parameter and use it to obtain an explicit expression for the entanglement capacity of all product Hamiltonians. Finally, we show how the notion of simulation leads to a natural formulation of measures of the strength of a nonlocal Hamiltonian.     

关于量子非局域逻辑门的研究

对几种类型的量子非局域逻辑门进行了讨论,并且研究了信道为非最大纠缠态的情况,此时量子非局域控制-非门只能概率性实现.     

On quantum fidelities and channel capacities

For the discrete memoryless quantum channel, we show the equivalence of two different notions of quantum channel capacity: that which uses the entanglement fidelity as its criterion for success in transmission, and that which uses the minimum fidelity of pure states in a subspace of the input Hilbert space as its criterion. As a corollary, any source with entropy rate less than the capacity may be transmitted with high entanglement fidelity. We also show that a restricted class of encodings is sufficient to transmit any quantum source which may be transmitted on a given channel. This enables us to simplify a known upper bound for the channel capacity. It also enables us to show that the availability of an auxiliary classical channel from encoder to decoder does not increase the quantum capacity     

On the optimum design of unitary cyclic group space-time codes

In this letter, based on the exact pairwise-error probability, we derive the union bound on the symbol-error probability (SEP) of the differential unitary space-time (DUST) modulation employing group codes. Instead of using the rank-and-determinant or Euclidean distance criteria, we optimize the cyclic group codes such that the union bound on the SEP is minimized for a predetermined scenario, taking into account the number of transmit and receive antennas and the operating signal-to-noise ratio (SNR). Our simulation results show that for a wide range of SNRs, the codes with the minimum union bound for a particular SNR outperform the codes designed based on rank-and-determinant or Euclidean distance criteria.     

On the design robustness of threshold logic gates using multi-inputfloating gate MOS transistors

In this paper, the design robustness of logic circuits implemented as threshold logic gates with multi-input floating gate transistors is analyzed. The parameter variations of the basic components, namely the coupling capacitances of the floating gate MOSFETs and the sensing circuits for obtaining full logic levels, are investigated separately using appropriate array test structures. It is found that the dominant mismatch originates from the input offset voltage variations of the sensing circuits. Methods are presented for estimating the yield of a given logic circuit from the measured parameter distributions. The estimations are verified with measured data of a multiplier cell and of the encoding logic in a parallel fingerprint sensor architecture. Considerations are given for robust design of circuits based on threshold logic gates that use floating gate transistors     

On a lower bound for the redundancy of reliable networks with noisy gates

A proof is provided that a logarithmic redundancy factor is necessary for the reliable computation of the parity function by means of a network with noisy gates. This result was first stated by R.L. Dobrushin and S.I. Ortyukov (1977). However, the authors believe that the analysis given by Dobrushin and Ortyukov is not entirely correct. The authors establish the result by following the same steps and by replacing the questionable part of their analysis with entirely new arguments.<>     

On performance analysis and design criteria for trellis coded unitary space-time modulation

In this letter, we present formulas for the pairwise error-event probability (PEP) and bit error probability (BEP) of trellis-coded unitary space-time modulation (TC-USTM) operated in a piecewise constant Rayleigh fading channel. From these analyses we discovered design criteria for the TC-USTM encoder to achieve an optimal BEP performance. We conduct simulations and verify that our analyzes are accurate, especially at high signal-to-noise ratio (SNR).     

On the robustness of decision-feedback detection of DPSK and differential unitary space-time modulation in Rayleigh-fading channels

Decision-feedback differential detection (DFDD) of differential phase-shift keying (DPSK) and differential unitary space-time modulation (DUST) in Rayleigh-fading channels exhibits significant performance improvement over standard single-symbol maximum-likelihood detection. However, knowledge of channel fading correlation and signal-to-noise ratio (SNR) is required at the receiver to compute the feedback coefficients used in DFDD. In this letter, we investigate the robustness of the DFDD to imperfect knowledge of the feedback coefficients by modeling the mismatch between estimated feedback coefficients and ideal coefficients in terms of mismatch between the estimated values of fading correlation and SNR and the true values. Under the assumption of a block-fading channel when nondiagonal DUST constellations are used and a continuous fading channel otherwise, we derive exact and Chernoff bound expressions for pair-wise word-error probability and then use them to approximate the bit-error rate (BER), finding close agreement with simulation results. The relationships between BER performance and various system parameters, e.g., DFDD length and Doppler mismatch, are also explored. Furthermore, the existence of an error floor in the BER-vs-SNR curve is investigated for the infinite-length DFDD. For the special case of Jakes' fading model, it is shown that the error floor can be removed completely even when the Doppler spread is over-estimated.     

Testing of complex gates

A systematic scheme for testing NMOS complex gates is presented. A minimal complete test set for all single and multiple detectable s-open, s-on and bridging faults is obtained. The scheme can easily be extended to test any general NMOS complex gate.     

Modelling the operation of pass transistor and CPL gates

Pass transistor logic and complementary pass-transistor logic (CPL) are becoming increasingly important in the design of a specific class of digital integrated circuits owing to their speed and power efficiency as compared with conventional CMOS logic. In this paper, a simple and very accurate technique for the timing analysis of gates that involve pass transistor logic is presented. This investigation offers for the first time the possibility of simulating pass transistor and CPL gates by partitioning the behaviour of complex structures into well defined subcircuits whose interaction is studied separately. Using the proposed analysis, which is validated by results for two submicron technologies, most pass-transistor logic styles can be modelled efficiently. Consequently, a significant speed advantage can be gained compared with simulation tools that employ numerical methods such as SPICE.     

加强整体协调 提高服务意识 强化监管 开拓创新

过去的一年,广东省无线电管理工作按照年初提出的工作思路,努力推动“从重审批向重监管转变”。围绕着无线电台专项整顿和无线电管理信息网、无线电监测网、800MHz数字集群共用平台“三网”建设,不断强化无线电监管能力,积极开展无线电监测、通信保障和粤港无线电管理协调工作。同时,在技术设施建设方面也加快了步伐。随着无线通信技术的应用,无线电管理工作所处的国际、国内大环境在不断发生变化:无线电频率资源日益紧张紧张;无线电管理业务和技术设施建设经费大幅度减少。就广东省而言,无线电管理工作还存在有法不依的现象;无线电管理系…     

涨落对几何量子门的影响

研究了几何量子门抵抗控制外场随机涨落的能力.在用周期微扰近似代替随机涨落下的研究表明:无论是绝热的Berry几何相还是非绝热的Aharonov-Anandan(A-A)几何相,其抗涨落的能力都和其对应的动力学相位的抗涨落能力相当.而Berry相位(几何相位,动力学相位)的抗涨落能力要远强于A-A位相,可视为由绝热近似导致这种差别.此外验证了利用正交态方案构造的量子门具有很强的抗涨落能力.     

Parallel and pipeline computation of fast unitary transforms

The letter discusses the parallel and pipeline organisation of fast-unitary-transform algorithms such as the fast Fourier transform, and points out the efficiency of a combined parallel-pipeline processor of a transform such as the Haar transform, in which 2n?1 hardware `butterflies? generate a transform of order 2n every computation cycle.     

Existence and construction of noncoherent unitary space-time codes

We consider transmission using N transmit and reception using M receive antennas in a wireless environment assuming that neither the transmitter nor the receiver knows the channel coefficients. For the scenario that the transmission employs noncoherent T /spl times/ N unitary space-time codes and for a block-fading channel model where the channel is static during T channel uses and varies from T channel uses to the other, we establish the bound r /spl les/ min(T-N, N) on the diversity advantage rM provided by the code. In order to show that the requirement r /spl les/ min(T-N, N) cannot be relaxed, for any given R, N, T, and r /spl les/ min(T-N, N), we then construct unitary T /spl times/ N space-time codes of rate R that guarantee diversity advantage rM. Two constructions are given that are also amenable to simple encoding and noncoherent maximum-likelihood (ML) decoding algorithms.     

Systematic design of unitary space-time constellations

We propose a systematic method for creating constellations of unitary space-time signals for multiple-antenna communication links. Unitary space-time signals, which are orthonormal in time across the antennas, have been shown to be well-tailored to a Rayleigh fading channel where neither the transmitter nor the receiver knows the fading coefficients. The signals can achieve low probability of error by exploiting multiple-antenna diversity. Because the fading coefficients are not known, the criterion for creating and evaluating the constellation is nonstandard and differs markedly from the familiar maximum-Euclidean-distance norm. Our construction begins with the first signal in the constellation-an oblong complex-valued matrix whose columns are orthonormal-and systematically produces the remaining signals by successively rotating this signal in a high-dimensional complex space. This construction easily produces large constellations of high-dimensional signals. We demonstrate its efficacy through examples involving one, two, and three transmitter antennas     

7 Gbit/s optical JK flip flop design with two optical AND gates and NOR gates

This study presents a simple methodology for implementation of all optical JK flip flop for future optical high speed networks. The scheme utilizes electronic model of JK flip flop for implementation of all optical JK flip flop at the bit rate of 7 Gbit/s. Firstly, all-optical AND and NOR gates are implemented. Furthermore, with the combination of these basic gate structures, the optical model of JK flip flop is verified. This structure makes use of two optical AND gates and two optical NOR gates. This technique uses a semiconductor optical amplifier (SOA) as the nonlinear medium to produce considerable amount of cross gain and cross phase modulation to attain truth table conditions of optical JK flip flop. In this method, the number of gates is reduced as compared to earlier schemes. Rise time and fall time of 5.6 ps with contrast ratio more than 60 dB are achieved in this design.     

Design strategies of cascaded CML gates

In this paper, a strategy to design paths consisting of cascaded bipolar current-mode logic gates is proposed. In particular, explicit design criteria are derived both for low-power non-critical paths and high-speed critical paths. The analytical results are simple to be applied to actual circuits avoiding the usual time-consuming approach based on iterative simulations with a trial-and-error procedure. Moreover, it provides the designer with a deeper understanding of the power-delay trade-off. Design examples based on a 20-GHz bipolar process are introduced to validate the procedure and clarify its application.     

Computer modelling of bipolar logic gates

A basic approach to the computer modelling of large arrays of bipolar gates using continuous analytic expressions is presented. A program has been written which applies this principle. It can handle complex situations and is justified on grounds of efficiency with l.s.i. circuits.     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.