Adaptive Interleaved Sampling for Interactive High‐Fidelity Rendering

Recent advances have made interactive ray tracing (IRT) possible on consumer desktop machines. These advances have brought about the potential for interactive global illumination (IGI) with enhanced realism through physically based lighting. IGI, unlike IRT, has a much higher computational complexity. Furthermore, since non‐primary rays constitute the majority of the computation, the rays are predominantly incoherent, making impractical many of the methods that have made IRT possible. Two methods that have already shown promise in decreasing the computational time of the GI solution are interleaved sampling and adaptive rendering. Interleaved sampling is a generalized sampling scheme that smoothly blends between regular and irregular sampling while maintaining coherence. Adaptive rendering algorithms adjust rendering quality, non‐uniformally, using a guidance scheme. While adaptive rendering has shown to provide speed‐up when used for off‐line rendering it has not been utilized in IRT due to its naturally incoherent nature. In this paper, we combine adaptive rendering and interleaved sampling within a component‐based solution into a new approach we term adaptive interleaved sampling. This allows us to tailor new adaptive heuristics for interleaved sampling of the individual components of the GI solution significantly improving overall performance. We present a novel component‐based IGI framework for which we achieve interactive frame rates for a range of effects such as indirect diffuse lighting, soft shadows and single scatter homogeneous participating media.     

Weak continuous measurements of multiqubits systems

In this review we summarize our recent experiments on the investigation on superconducting qubits. Instead of strong projective measurement used by other groups in their first pioneering experiments we have proposed and realized a weak continuous readout which belongs to the class of quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at the so called sweet (or magic) point where a qubit is in a superposition of two classical states and its sensitivity to external noise is minimized. In this scheme, which is widely used nowadays, the superconducting oscillator coupled to superconducting qubit is used as a detector of the qubit’s state. Such system is analogue to a system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics in artificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused by energy exchange between an oscillator and a flux qubit. Using the Sisyphus effect we show consistency between the adiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us to characterize the more complicated system of coupled qubits by making use of the same method. We have realized and studied fixed ferromagnetic, antiferromagnetic as well as tunable qubit–qubit coupling. We argue that ground state measurements can be used for characterization of entangled states in coupled flux qubits.     

两千兆高速数据采集电路设计

本文采用美国国家半导体公司的高速双通道模数转换器(ADC08D1000),以及Altera公司CycloneII系列的FPGA(EP2C70F896C8)实现对双路信号的高速采样,每片ADC通过交叉采样对每路信号的采样率达到2GSPS。本文着重介绍电路的设计,以及PCB制版过程当中的技巧问题。     

参数稀疏信号非均匀采样性能分析

提出了一种参数稀疏信号的时间交替周期非均匀采样方案。相对于非均匀采样,周期非均匀采样可以在降低系统复杂度的前提下依然保持较高的转换速率。通过仿真证明,非均匀采样样本的超分辨率特性可以提高非线性最小二乘周期图谱估计的重构性能。     

非均匀采样系统的修正与补偿

提出一种针对非均匀采样失真的修正补偿方法.用正弦波激励与波形拟合,获得各子A/D的增益、直流偏移和相对于参考子A/D的延迟时间差.将各子A/D的采样序列叠加直流偏移修正因子使各直流偏移一致,补偿偏移采样失真,将各子A/D的样本序列乘以增益修正因子使各增益一致,补偿增益采样失真,通过等间隔采样插值运算,补偿采样延迟失真,获得均匀采样结果.在一组16个子A/D的仿真数据上的补偿实验验证了方法的正确性.在具有8个子A/D的一个数据采集系统的实测数据上的补偿实验,验证了方法的可行性.     

Negativity fonts, multiqubit invariants and four qubit maximally entangled states

Recently, we introduced negativity fonts as the basic units of multipartite entanglement in pure states. We show that the relation between global negativity of partial transpose of N?qubit state and linear entropy of reduced single qubit state yields an expression for global negativity in terms of determinants of negativity fonts. Transformation equations for determinants of negativity fonts under local unitaries (LU??s) are useful to construct LU invariants such as degree four and degree six invariants for four qubit states. The difference of squared negativity and N?tangle is an N qubit invariant which contains information on entanglement of the state caused by quantum coherences that are not annihilated by removing a single qubit. Four qubit invariants that detect the entanglement of specific parts in a four qubit state are expressed in terms of three qubit subsystem invariants. Numerical values of invariants bring out distinct features of several four qubit states which have been proposed to be the maximally entangled four qubit states.     

基于K60和FPGA的四相交错并联Boost变换器效率优化设计

设计了一种基于K60单片机和FPGA为主控制器的四相交错并联Boost变换器,变换器可以根据输出电流的变化,自动改变工作相数,以提高变换器的效率.采用数字PID控制算法实现输出电压无静差调节,提高负载变化时电压调节的响应速度.设计了电压/电流采样电路、MOSFET驱动电路、存储电路以及软件控制策略,并制作了实验样机,对实验数据进行分析,验证了设计的可行性.     

多片AD并行采样技术在软件无线电中的应用

介绍了软件无线电和多片AD时间交替采样技术的基本原理,并分析了采用这种技术会产生的通道失配误差。给出了校正的基本方法和基于2片ADS5474的实现。     

Quantum teleportation between a single-rail single-photon qubit and a coherent-state qubit using hybrid entanglement under decoherence effects

We study quantum teleportation between two different types of optical qubits using hybrid entanglement as a quantum channel under decoherence effects. One type of qubit employs the vacuum and single-photon states for the basis, called a single-rail single-photon qubit, and the other utilizes coherent states of opposite phases. We find that teleportation from a single-rail single-photon qubit to a coherent-state qubit is better than the opposite direction in terms of fidelity and success probability. We compare our results with those using a different type of hybrid entanglement between a polarized single-photon qubit and a coherent state.     

Lower bounds of concurrence for <Emphasis Type="Italic">N</Emphasis>-qubit systems and the detection of <Emphasis Type="Italic">k</Emphasis>-nonseparability of multipartite quantum systems

Concurrence, as one of the entanglement measures, is a useful tool to characterize quantum entanglement in various quantum systems. However, the computation of the concurrence involves difficult optimizations and only for the case of two qubits, an exact formula was found. We investigate the concurrence of four-qubit quantum states and derive analytical lower bound of concurrence using the multiqubit monogamy inequality. It is shown that this lower bound is able to improve the existing bounds. This approach can be generalized to arbitrary qubit systems. We present an exact formula of concurrence for some mixed quantum states. For even-qubit states, we derive an improved lower bound of concurrence using a monogamy equality for qubit systems. At the same time, we show that a multipartite state is k-nonseparable if the multipartite concurrence is larger than a constant related to the value of k, the qudit number and the dimension of the subsystems. Our results can be applied to detect the multipartite k-nonseparable states.     

DIAL,a system for atmospheric methane measurement over Guwahati: development and results

The article discusses the development and operational details of Differential Absorption LiDAR (DIAL) for the measurement of methane concentration in the semi-urban environment of Gauhati University. The system comprises two specifically selected wavelengths in 3 μm range: one is an absorbing wavelength (λ_on) and the other is non-absorbed (λ_off) by methane molecules. Pulses of 10 ns for the two wavelengths are transmitted alternately for interleaved sampling of differential absorption. The pulse repetition rate is variable between 1 and 20 Hz. The slope and integrated target approaches are adopted to calculate the methane concentration, and observed figures are compared with globally reported values.     

Improving quantum state transfer efficiency and entanglement distribution in binary tree spin network through incomplete collapsing measurements

We propose a mechanism for quantum state transfer (QST) over a binary tree spin network on the basis of incomplete collapsing measurements. To this aim, we perform initially a weak measurement (WM) on the central qubit of the binary tree network where the state of our concern has been prepared on that qubit. After the time evolution of the whole system, a quantum measurement reversal (QMR) is performed on a chosen target qubit. By taking optimal value for the strength of QMR, it is shown that the QST quality from the sending qubit to any typical target qubit on the binary tree is considerably improved in terms of the WM strength. Also, we show that how high-quality entanglement distribution over the binary tree network is achievable by using this approach.     

Overcoming experimental limitations in a nonlinear two-qubit gate through postselection

We introduce a modular-value two-qubit gate and explore its advantages in experimentally limited situations. The gate is defined such that the final state of a qubit is fully controlled by a pre- and postselection procedure in an ancillary qubit given an (imperfect or technically limited) intermediate conditional qubit–qubit interaction. As an example of the gate and its benefit, we make the connection to a postselected cross-phase modulation scenario when a undesired absorption is present. Probabilistic amplification of a small cross phase while mitigating relative absorption is possible, and a complementary behavior between phase and amplitude emerges.     

A quantum probability splitter and its application to qubit preparation

This paper presents a quantum probability splitter, i.e. a quantum circuit that modifies the probability amplitudes of a qubit so that the probability on the selected basis state is halved. It also presents a potential application of this circuit related to qubit preparation: it shows how a qubit is prepared to a superposition of any valid pair of basis states probabilities, by repeated application of the quantum probability splitter.     

Entanglement sudden death and birth in qubit–qutrit systems under Dzyaloshinskii–Moriya interaction

We study entanglement dynamics of qubit–qutrit pair under Dzyaloshinskii–Moriya (DM) interaction. The qubit–qutrit pair acts as a closed system and one external qubit serve as the environment for the pair. The external qubit interact with qubit of closed system via DM interaction. This interaction frequently kills the entanglement between qubit–qutrit pair, which is also periodically recovered. On the other hand two parameter class of state of qubit–qutrit pair also affected by DM interaction and one parameter class of state remains unaffected. The frequency of occurrence of entanglement sudden death and entanglement sudden birth in two parameter class of state is half than qubit–qutrit pure state. We used our quantification of entanglement as negativity measure.     

N-qubit quantum teleportation, information splitting and superdense coding through the composite GHZ–Bell channel

We introduce a general odd qubit entangled system composed of GHZ and Bell pairs and explicate its usefulness for quantum teleportation, information splitting and superdense coding. After demonstrating the superdense coding protocol on the five qubit system, we prove that ‘2N + 1’ classical bits can be sent by sending ‘N + 1’ quantum bits using this channel. It is found that the five-qubit system is also ideal for arbitrary one qubit and two qubit teleportation and quantum information splitting (QIS). For the single qubit QIS, three different protocols are feasible, whereas for the two qubit QIS, only one protocol exists. Protocols for the arbitrary N-qubit state teleportation and quantum information splitting are then illustrated.     

Multiprocessor pyramid architectures for bottom-up image analysis

This paper describes three hierarchical organizations of small processors for bottom-up image analysis:pyramids, interleaved pyramids, and pyramid trees. Progressively lower levels in the hierarchies process image windows of decreasing size. Bottom-up analysis is made feasible by transmitting up the levels quadrant borders and border-related information that captures quadrant interaction of interest for a given computation. The operation of the pyramid is illustrated by examples of standard algorithms for interior-based computations (e.g., area) and border-based computations of local properties (e.g., perimeter). A connected component counting algorithm is outlined that illustrates the role of border-related information in representing quadrant interaction. Interleaved pyramids are obtained by sharing processors among several pyramids. They increase processor utilization and throughput rate at the cost of increased hardware. Trees of shallow interleaved pyramids, calld pyramid trees, are introduced to reduce the hardware requirements of large interleaved pyramids at the expense of increased processing time, without sacrificing processor utilization. The three organizations are compared with respect to several performance measures.     

Quantum state control, entanglement, and readout of the Josephson persistent-current qubit

Quantum state control including entanglement, and readout of the Josephson persistent-current qubit, flux qubit, are reviewed. First, we mention our single-shot readout of quantum superposition state of a flux qubit by a current biased dc-SQUID. Second, we mention entangled state and vacuum Rabi oscillations of a flux-qubit LC-resonator system where qubit-resonator coupled state are controlled by a combination of microwave and DC-shift pulses, resulting in a controlling and measuring sequence analogous to atomic cavity QED. Third, we report our recent progress in high fidelity readout of a flux qubit state via Josephson bifurcation amplifier (JBA).     

Entanglement dynamics in two-parameter qubit–qutrit states under Dzyaloshinskii–Moriya interaction

We study entanglement dynamics in two-parameter qubit–qutrit states under the influence of Dzyaloshisnhkii–Moriya (DM) interaction. Our system consists of a qubit–qutrit pair as a closed system initially in two-parameter class of states, and one environmental qubit interacts with the qutrit of the closed system via DM interaction. We divide our analysis into two cases. In the first case, we study the entanglement dynamics in separable region, and in the second case we study the same in non-separable region. The DM interaction produces the entanglement in separable region with entanglement sudden death (ESD) and some states in this region remain unaffected by the same. In non-separable region, all the states are affected by DM interaction. The DM interaction excites the entanglement but does not produce ESD in this region. We observed that probability amplitude of environmental qubit does not affect the entanglement in two-parameter qubit–qutrit states in both the regions.     

Two-mode squeezing operator in circuit QED

We theoretically investigate the implementation of the two-mode squeezing operator in circuit quantum electrodynamics. Inspired by a previous scheme for optical cavities (Prado et al. in Phys Rev A 73:043803, 2006), we employ a superconducting qubit coupled to two nondegenerate quantum modes and use a driving field on the qubit to adequately control the resonator–qubit interaction. Based on the generation of two-mode squeezed vacuum states, firstly we analyze the validity of our model in the ideal situation and then we investigate the influence of the dissipation mechanisms on the generation of the two-mode squeezing operation, namely the qubit and resonator mode decays and qubit dephasing. We show that our scheme allows the generation of highly squeezed states even with the state-of-the-art parameters, leading to a theoretical prediction of more than 10 dB of two-mode squeezing. Furthermore, our protocol is able to squeeze an arbitrary initial state of the resonators, which makes our scheme attractive for future applications in continuous-variable quantum information processing and quantum metrology in the realm of circuit quantum electrodynamics.