The cluster states and Greenberger-Horne-Zeilinger (GHZ) states are two different types of multipartite quantum entangled states. We present the first experimental results generating continuous variable quadripartite cluster and GHZ entangled states of electromagnetic fields. Utilizing two amplitude-quadrature and two phase-quadrature squeezed states of light and linearly optical transformations, the two types of entangled states for amplitude and phase quadratures of light are experimentally produced. The combinations of the measured quadrature variances prove the full inseparability of the generated four subsystems. The presented experimental schemes show that the multipartite entanglement of continuous variables can be deterministically generated with the relatively simple implementation.

The unconditional entanglement swapping for continuous variables is experimentally demonstrated. Two initial entangled states are produced from two nondegenerate optical parametric amplifiers operating at de-amplification. Through implementing the direct measurement of the Bell-state between two optical beams from each amplifier the remaining two optical beams, which have never directly interacted with each other, are entangled. The quantum correlation degrees of 1.23 and 1.12 dB below the shot noise limit for the amplitude and phase quadratures resulting from the entanglement swapping are measured straightly.

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A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. Understanding how quantum resources can be quantified and distributed over many parties has profound applications in quantum communication. As one of the most intriguing features of quantum mechanics, Einstein-Podolsky-Rosen (EPR) steering is a useful resource for secure quantum networks. By reconstructing the covariance matrix of a continuous variable four-mode square Gaussian cluster state subject to asymmetric loss, we quantify the amount of bipartite steering with a variable number of modes per party, and verify recently introduced monogamy relations for Gaussian steerability, which establish quantitative constraints on the security of information shared among different parties. We observe a very rich structure for the steering distribution, and demonstrate one-way EPR steering of the cluster state under Gaussian measurements, as well as one-to-multimode steering. Our experiment paves the way for exploiting EPR steering in Gaussian cluster states as a valuable resource for multiparty quantum information tasks.

Measurement-based one-way quantum computation using cluster states as resources provides an efficient model to perform computation and information processing of quantum codes. Arbitrary Gaussian quantum computation can be implemented sufficiently by long single-mode and two-mode gate sequences. However, continuous variable gate sequences have not been realized so far due to an absence of cluster states larger than four submodes. Here we present the first continuous variable gate sequence consisting of a single-mode squeezing gate and a two-mode controlled-phase gate based on a six-mode cluster state. The quantum property of this gate sequence is confirmed by the fidelities and the quantum entanglement of two output modes, which depend on both the squeezing and controlled-phase gates. The experiment demonstrates the feasibility of implementing Gaussian quantum computation by means of accessible gate sequences.

The preparation of multipartite entangled states is the prerequisite for exploring quantum information networks and quantum computation. In this letter, we present the first experimental demonstration of eight-partite spatially separated CV entangled states. The initial resource quantum states are eight squeezed states of light, through the linearly optical transformation of which two types of the eight-partite cluster entangled states are prepared, respectively. The generated eight entangled photonic qumodes are spatially separated, which provide valuable quantum resources to implement more complicated quantum information task.PACS numbers: 03.67. Bg, 03.67.Lx, 03.65.Ud, 42.50.Dv Developing quantum information (QI) science have exhibited unusual potentiality [1, 2]. Optical QI based on exploiting discrete-variable (DV) of single-photon states (photonic qubits) and continuous-variable (CV) of optical modes (photonic qumodes) plays important role in QI development. The one-way quantum computation(QC) based on multipartite cluster entanglement is initially proposed by Raussendorf and Briegel in the DV model [3], then it is extended to the CV regime by Menicucci et al [4]. For one-way QC model the qubits (qumodes) are initialized in a multipartite cluster entangled state firstly, then a variety of quantum logical operations can be achieved only via the single-qubit (qumode) projective measurement and the classical feedforward of the measured outcomes, in which the order and choices of measurements are determined by the required algorithm [3]. The basic logical operations of one-way DVQC has been experimentally demonstrated by several groups [5][6][7].Parallelly, the theoretical and experimental explorations on one-way CVQC were also proceeding continually [8][9][10][12][13][14][15]. In contrast of the probabilistic generation of photonic qubits in most cases, CV cluster states are produced in an unconditional fashion and thus the one-way QC with CV cluster entangled photonic qumodes can be implemented deterministically [12][13][14][15][16][17][18][19]. Following the theoretical proposals on one-way CVQC the principally experimental demonstrations of various one-way QC logical operations over CVs were achieved by utilizing bipartite and four-partite cluster entangled photonic qumodes, respectively [12][13][14][15]. To develop more complicated QC larger cluster states with more numbers of entangled qubits (qumodes) are desired. However, the numbers of spatially separable entangled qumodes generated by experiments still stay below four-partites, so far [16][17][18]. In the paper, we present the first experimental achievement on producing CV eight-partite entangled states for photonic qumodes. Using eight squeezed states of light to be the initial resource quantum states and passing through the linearly optical transformation on a specially designed beam-splitter network, the eight-partite linear and two-diamond shape cluster states for photonic qumodes are prepared, respectively. The entanglement feature among the ...

Abstract:The quantum entanglement of amplitude and phase quadratures between two intense optical beams with the total intensity of 22mW and the frequency difference of 1nm, which are produced from an optical parametric oscillator operating above threshold, is experimentally demonstrated with two sets of unbalanced Mach-Zehnder interferometers.The measured quantum correlations of intensity and phase are in reasonable agreement with the results calculated based on a semi-classical analysis of the noise characteristics given by C. Fabre et al. OCIS codes: 190.4410, 270.6570 In recent years quantum information with continuous variables (CV) where f is the noise frequency, S 0 is the shot noise limit (SNL), B and ξ =T/(T+δ) are the cavity bandwidth and the output coupling efficiency of NOPO respectively (T -the transmission coefficient of the output coupling mirror; δ -extra intracavity losses), η is the detection efficiency,is the pump parameter (P -the pump power, P 0 -the threshold pump power of NOPO). The intensity difference quantum correlations of twin beams were experimentally measured with self-homodyne detectors by different groups and were effectively applied [7][8][9][10][11][12] . However, the phase correlation of the twin beams was not observed for a long time Almost at a parallel period we were also devoting our efforts to measure the quantum entanglement of twin beams from NOPO above threshold. The measurement scheme used by us is basically same with that presented by O. Glockl et al. inRef.[15], where they performed sub-shot-noise measurement of the phase quadratures of intense pulsed light 16 . Considering that the phase correlation will be significantly affected by the phase fluctuation of the pump laser 6 and the restricted condition deducing Eqs. (1) and (2) in Ref. [4] requires the finesse of the NOPO cavity for the pump laser much lower than that for the twin beams, in our design the ratio of the cavity finesses for the pump and the twin beams is 16/164 which is much smaller than that in Refs.[13] and [14]. Due to the lower finesse the resonant peak of the pump laser in the cavity is relatively flat and thus the threshold power is higher (~120mW).At first, using a pair of Mach-Zehnder (M-Z) interferometers with unbalanced arm-lengths we detected the amplitude and phase noise of signal and idler output fields from a NOPO above threshold at a certain analysis frequency (20MHz), respectively. Then, the quantum correlations were denoted by the noise levels of the intensity difference and the phase sum of the photocurrents measured by two unbalanced interferometers. wave plate P1 (P2). Rotating the polarization orientation of P1 (P2) we can conveniently switch between phase and amplitude measurements 15 . In our system, the distance difference of two arms ∆L is 7.5m which matches the analysis frequency of 20MHz to make θ=π. The difference of the 5 dc photocurrents of D1 and D2 (D3 and D4) serves as the error signal and is fed back onto the PZT mounted on one of mirrors of the interferometer to...

The deterministic teleportation of optical modes over a 6.0-km fiber channel is realized with continuous variable entanglement.