Affleck-Kennedy-Lieb-Tasaki state on a honeycomb lattice is a universal quantum computational resource

Universal quantum computation can be achieved by simply performing single-qubit measurements on a highly entangled resource state, such as cluster states. The family of Affleck-Kennedy-Lieb-Tasaki states has recently been intensively explored and shown to provide restricted computation. Here, we show that the two-dimensional Affleck-Kennedy-Lieb-Tasaki state on a honeycomb lattice is a universal resource for measurement-based quantum computation.     

Universal quantum computation with continuous-variable cluster states

We describe a generalization of the cluster-state model of quantum computation to continuous-variable systems, along with a proposal for an optical implementation using squeezed-light sources, linear optics, and homodyne detection. For universal quantum computation, a nonlinear element is required. This can be satisfied by adding to the toolbox any single-mode non-Gaussian measurement, while the initial cluster state itself remains Gaussian. Homodyne detection alone suffices to perform an arbitrary multimode Gaussian transformation via the cluster state. We also propose an experiment to demonstrate cluster-based error reduction when implementing Gaussian operations.     

A proposal for preparation of cluster states with linear optics

Measurement-based quantum computation in an optical setup shows great promise towards the implementation oflarge-scale quantum computation. The difficulty of measurement-based quantum computation lies in the preparation ofcluster state. In this paper, we propose the method of generating the large-scale cluster state, which is a platform formeasurement-based quantum computation. In order to achieve more complex quantum circuits, the preparation protocolof N-photon cluster state will be proposed as a generalization of the preparation of four- and five-photon cluster states.Furthermore, our proposal is experimentally feasible.     

Generation of non-classical states from an optical parametric oscillator/amplifier and their applications

Quantum information and quantum optics are rapidly advancing areas of modern physics. As an important device in quantum optics and quantum information, the optical parametric amplifier/oscillator (OPA/O) has been extensively studied and applied to the generation of non-classical state since the 1980s. This article reviews the progress in the generation of non-classical state from an OPO/A and application of twin beams in quantum optics and quantum information.     

低分析频率压缩光的实验制备

基于PPKTP晶体的阈值以下光学参量振荡(OPO)过程,制备了共振于铷原子D1线795 nm的压缩真空态光场,研究了分析频率处于千赫兹范围的主要噪声来源,特别是795 nm激光及其二次谐波397.5 nm激光在晶体内吸收引起的非线性损耗增加和系统热不稳定的问题(397.5 nm激光处于PPKTP晶体透光范围边缘,具有高于其他波长数倍的吸收系数).以795 nm和1064 nm为例,分析了非线性损耗及晶体内热效应对压缩度的影响.受限于以上因素,795 nm压缩光很难得到1064 nm波段同样的压缩度.探测系统中的噪声耦合则限制了压缩频带.实验上对分析频率为千赫兹的经典噪声进行了有效控制,通过使用真空注入的OPO、垂直偏振及反向传输的腔长锁定光、低噪声的平衡零拍探测器、高稳定度的实验系统及量子噪声锁定等方法,最终在2.6—100 kHz的分析频段得到了约2.8 dB的795 nm压缩真空.该压缩光可用作磁场测量系统的探测光以提高测量灵敏度.     

Generation of non-classical states from an optical parametric oscillator/amplifier and their applications

Quantum information and quantum optics are rapidly advancing areas of modern physics. As an important device in quantum optics and quantum information, the optical parametric amplifier/oscillator (OPA/O) has been extensively studied and applied to the generation of non-classical state since the 1980s. This article reviews the progress in the generation of non-classical state from an OPO/A and application of twin beams in quantum optics and quantum information      

Efficient preparation of a four-photon cluster state with homodyne measurement via cross-Kerr nonlinearity

A scheme is proposed for generating a multiphoton entangled cluster state among four modes. The scheme only uses Kerr medium, beam splitter and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. The photon in the signal mode is prepared in a superposition state of the vacuum state and one-photon state while the probe beam is initially set in a coherent state superposition. The strong probe mode interacts successively with multiple signal-mode photo...     

低频压缩态光场的制备

低频压缩态光场可用于提高引力波探测器灵敏度, 近年来受到人们的广泛关注. 相对于高频段而言, 低频压缩态的产生更容易受到外界环境噪声的干扰而不易被观察到. 本文采用全固化单频倍频Nd: YVO4/KTP激光器作为光源, 利用双波长共振的光学参量振荡器实现参量过程, 以1064 nm波长的红外作为基频光, 激光器腔内倍频产生的532 nm绿光作为抽运光, 通过调节周期性极化磷酸氧钛钾晶体温度使光学参量振荡器达到双波长同时共振, 采用真空注入的方式, 利用Pound-Drever-Hall锁腔技术锁定抽运场. 输出压缩光通过平衡零拍探测, 最终在实验上获得了频率低至3 kHz的真空压缩, 所直接观察到的压缩度为2 dB.     

Fine tuning of a triply resonant OPO for generating frequency degenerate CV entangled beams at low pump powers

A method of achieving triple resonance in a frequency-degenerate but polarization-non-degenerate optical parametric oscillator (OPO) with external mirrors is illustrated. The OPO is brought to the triple-resonance condition by tuning the non-linear crystal temperature and tilting the cavity axis. The interplay among temperature and tilting mismatch and gain is analyzed together with the allowed ranges of variation of these parameters. The method has been successfully applied to an OPO based on a periodically poled KTP crystal. Calibration of the system is reported together with parametric gain and squeezing measurements below threshold as a test of reliability and efficiency. PACS 42.50.-p; 42.65.-k     

Vortices in the microcavity optical parametric oscillator

A theoretical treatment is presented for a novel from of optical vortex state, in a microcavity optical parametric oscillator (OPO). The state comprises a vortex/anti-vortex pair in the signal and idler beams, with a Gaussian pump. A numerical solution of the microcavity OPO equations shows that such a vortex can be stable.     

A FULL QUANTUM THEORY OF THE THREE-MODE INTERACTIONS INSIDE AN OPO CAVITY

A full quantum treatment about the process of parametric down-conversion with frequency degenerate but polarization pon-degenerate in an optical parametric oscillator (OPO) cavity is presented. Using the linearized Langevin equations and spectral matrix, we calculated the squeezing spectra of the coupled mode in the output field. The squeezing as a function of driving field and detection frequency is obtained. The resuits obtained, which are compared with those found semiclassically by Reynaud et al., indicate that it is possible to generate a two-mode coherent squeezed state with large amplitude. The quantum correlation between the signal and the idler modes is also discussed. It is shown that there is an inseparable relationship between the two-mode squeezing and the intermode quantum correlation.     

Percolation, renormalization, and quantum computing with nondeterministic gates

We apply a notion of static renormalization to the preparation of entangled states for quantum computing, exploiting ideas from percolation theory. Such a strategy yields a novel way to cope with the randomness of nondeterministic quantum gates. This is most relevant in the context of optical architectures, where probabilistic gates are common, and cold atoms in optical lattices, where hole defects occur. We demonstrate how to efficiently construct cluster states without the need for rerouting, thereby avoiding a massive amount of conditional dynamics; we furthermore show that except for a single layer of gates during the preparation, all subsequent operations can be shifted to the final adapted single-qubit measurements. Remarkably, cluster state preparation is achieved using essentially the same scaling in resources as if deterministic gates were available.     

Generation of Four-Photon Cluster State with Coherent Light via Cross-Kerr Nonlinearity

We propose two schemes for preparing four-photon cluster state through cross-Kerr nonlinearity. Two coherent fields interact when they enter a nonlinear Kerr medium. If the interaction time is chosen appropriately in each Kerr medium, four-photon cluster state can be generated based on the results of two homodyne detectors in the first scheme. These schemes only use Kerr medium and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. In addition, weak cross-Kerr nonlinearity is sufficient. All of the properties make these schemes feasible in experiments.     

Broadly tunable noncritically phase-matched ZnGeP2 optical parametric oscillator with a 2-microJ pump threshold

We report a high-repetition-rate (1-10-kHz) optical parametric oscillator (OPO) based on noncritically phase-matched ZnGeP2 (ZGP). The pump source was an OPO based on periodically pole lithium niobate that was pumped in turn by a Q-switched diode-pumped 1-microm Nd:YAG laser. The ZGP OPO yielded continuously tunable output from 3.7 to 10.2 microm by tuning of the pump wavelength from 2.3 to 3.7 microm. At the optimal pump focusing, the minimum ZGP OPO threshold achieved was 2 microJ, which is to our knowledge the lowest ever reported for a singly resonant OPO. The output energy in the 6-8-microm range was > 20 microJ, and the quantum efficiency of converting 1-microm radiation to the mid IR exceeded 10%.     

Creation of cluster state of four ions in ion-trap system by individual addressing

The cluster state is a special, highly entangled quantum state that forms the universal resource, on which measurement-based quantum computation can be performed. In this study, a new scheme is presented for creating four-ions cluster state in ion-trap system. This scheme is based on resonant sideband excitation in which the population is transferred to target states by precise control of pulse area. Meanwhile, the scheme is consist of combination of elementary stages belonging to a universal set whereby cluster state has been created in five interaction stages by individually addressed ions with red- or blue-sideband resonance laser pulses. The paper studies the population transfer of the system by numerical solutions of the master equation, considering the effect of decoherence channels due to dissipation in the phonon modes. The presented scheme does not require control of the turn-off ratio and time delay among pulses.     

Demonstration of eight-partite two-diamond shape cluster state for continuous variables

Multipartite entangled state is the basic resource for implementing quantum information networks and quantum computation. In this paper, we present the experimental demonstration of the eight-partite two-diamond shape cluster states for continuous variables, which consist of eight spatially separated and entangled optical modes. Eight resource squeezed states of light with classical coherence are produced by four nondegenerate optical parametric amplifiers and then they are transformed to the eight-partite two-diamond shape cluster states by a specially designed linear optical network. Since the spatially separated multipartite entangled state can be prepared off-line, it can be conveniently applied in the future quantum technology.     

Experimental realization of one-way quantum computing with two-photon four-qubit cluster states

We report an experimental realization of one-way quantum computing on a two-photon four-qubit cluster state. This is accomplished by developing a two-photon cluster state source entangled both in polarization and spatial modes. With this special source, we implemented a highly efficient Grover's search algorithm and high-fidelity two-qubit quantum gates. Our experiment demonstrates that such cluster states could serve as an ideal source and a building block for rapid and precise optical quantum computation.     

Resource-efficient linear optical quantum computation

We introduce a scheme for linear optics quantum computation, that makes no use of teleported gates, and requires stable interferometry over only the coherence length of the photons. We achieve a much greater degree of efficiency and a simpler implementation than previous proposals. We follow the "cluster state" measurement based quantum computational approach, and show how cluster states may be efficiently generated from pairs of maximally polarization entangled photons using linear optical elements. We demonstrate the universality and usefulness of generic parity measurements, as well as introducing the use of redundant encoding of qubits to enable utilization of destructive measurements--both features of use in a more general context.     

弱抽运下光学参量过程中压缩真空场的光子统计性质

在理论和实验上研究了光学参量振荡中产生的弱压缩真空场的光子统计行为. 弱压缩真空具有强烈的光子聚束效应,这种比热光场更强的聚束效应在量子光学和量子测量中具有重要的应用. 利用远离阈值的光学参量振荡(optical parametric oscillator, OPO )过程,在实验上产生了该弱压缩真空输出,运转波长在铯原子线附近. 通过Hanbury-Brown-Twiss(HBT)测量了OPO输出光场的二阶关联函数,实验结果与理论分析基本一致. 关键词： 压缩真空态 二阶相干度 光学参量振荡     

ZnGeP2 optical parametric oscillator with 3.8-12.4-mum tunability

A ZnGeP>(2) (ZGP) optical parametric oscillator (OPO) with wide mid-IR tunability has been demonstrated. The singly resonant angle-tuned ZGP OPO was pumped by 100-ns erbium laser pulses at lambda =2.93mum and yielded output that was continuously tunable from 3.8 to 12.4 mum (type I phase matching) and from 4 to 10 mum (type II phase matching). An OPO pump threshold was less than 1 mJ in the whole 4-12 mum range of the output, and the quantum conversion efficiency reached 35%. An OPO linewidth was typically a few wave numbers; however, with a single intracavity etalon (uncoated Si plate) in a type II OPO it was narrowed to <0.5cm(-1). We demonstrate the sensitive detection of N(2)O gas with the narrow-linewidth OPO.