16,968 research outputs found

    Multipartite quantum correlation and entanglement in four-qubit pure states

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    Based on the quantitative complementarity relations, we analyze thoroughly the properties of multipartite quantum correlations and entanglement in four-qubit pure states. We find that, unlike the three-qubit case, the single residual correlation, the genuine three- and four-qubit correlations are not suited to quantify entanglement. More interestingly, from our qualitative and numerical analysis, it is conjectured that the sum of all the residual correlations may constitute a good measure for the total multipartite entanglement in the system.Comment: 7 pages, 3 figue

    Testing linear hypotheses in high-dimensional regressions

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    For a multivariate linear model, Wilk's likelihood ratio test (LRT) constitutes one of the cornerstone tools. However, the computation of its quantiles under the null or the alternative requires complex analytic approximations and more importantly, these distributional approximations are feasible only for moderate dimension of the dependent variable, say p20p\le 20. On the other hand, assuming that the data dimension pp as well as the number qq of regression variables are fixed while the sample size nn grows, several asymptotic approximations are proposed in the literature for Wilk's \bLa including the widely used chi-square approximation. In this paper, we consider necessary modifications to Wilk's test in a high-dimensional context, specifically assuming a high data dimension pp and a large sample size nn. Based on recent random matrix theory, the correction we propose to Wilk's test is asymptotically Gaussian under the null and simulations demonstrate that the corrected LRT has very satisfactory size and power, surely in the large pp and large nn context, but also for moderately large data dimensions like p=30p=30 or p=50p=50. As a byproduct, we give a reason explaining why the standard chi-square approximation fails for high-dimensional data. We also introduce a new procedure for the classical multiple sample significance test in MANOVA which is valid for high-dimensional data.Comment: Accepted 02/2012 for publication in "Statistics". 20 pages, 2 pages and 2 table

    Asymptotic properties of eigenmatrices of a large sample covariance matrix

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    Let Sn=1nXnXnS_n=\frac{1}{n}X_nX_n^* where Xn={Xij}X_n=\{X_{ij}\} is a p×np\times n matrix with i.i.d. complex standardized entries having finite fourth moments. Let Yn(t1,t2,σ)=p(xn(t1)(Sn+σI)1xn(t2)xn(t1)xn(t2)mn(σ))Y_n(\mathbf {t}_1,\mathbf {t}_2,\sigma)=\sqrt{p}({\mathbf {x}}_n(\mathbf {t}_1)^*(S_n+\sigma I)^{-1}{\mathbf {x}}_n(\mathbf {t}_2)-{\mathbf {x}}_n(\mathbf {t}_1)^*{\mathbf {x}}_n(\mathbf {t}_2)m_n(\sigma)) in which σ>0\sigma>0 and mn(σ)=dFyn(x)x+σm_n(\sigma)=\int\frac{dF_{y_n}(x)}{x+\sigma} where Fyn(x)F_{y_n}(x) is the Mar\v{c}enko--Pastur law with parameter yn=p/ny_n=p/n; which converges to a positive constant as nn\to\infty, and xn(t1){\mathbf {x}}_n(\mathbf {t}_1) and xn(t2){\mathbf {x}}_n(\mathbf {t}_2) are unit vectors in Cp{\Bbb{C}}^p, having indices t1\mathbf {t}_1 and t2\mathbf {t}_2, ranging in a compact subset of a finite-dimensional Euclidean space. In this paper, we prove that the sequence Yn(t1,t2,σ)Y_n(\mathbf {t}_1,\mathbf {t}_2,\sigma) converges weakly to a (2m+1)(2m+1)-dimensional Gaussian process. This result provides further evidence in support of the conjecture that the distribution of the eigenmatrix of SnS_n is asymptotically close to that of a Haar-distributed unitary matrix.Comment: Published in at http://dx.doi.org/10.1214/10-AAP748 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

    Multipartite entanglement in four-qubit cluster-class states

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    Based on quantitative complementarity relations (QCRs), we analyze the multipartite correlations in four-qubit cluster-class states. It is proven analytically that the average multipartite correlation EmsE_{ms} is entanglement monotone. Moreover, it is also shown that the mixed three-tangle is a correlation measure compatible with the QCRs in this kind of quantum states. More arrestingly, with the aid of the QCRs, a set of hierarchy entanglement measures is obtained rigorously in the present system.Comment: 7 pages, 3 figs, version 3, some refs. are adde

    Quantum state redistribution based on a generalized decoupling

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    We develop a simple protocol for a one-shot version of quantum state redistribution, which is the most general two-terminal source coding problem. The protocol is simplified from a combination of protocols for the fully quantum reverse Shannon and fully quantum Slepian-Wolf problems, with its time-reversal symmetry being apparent. When the protocol is applied to the case where the redistributed states have a tensor power structure, more natural resource rates are obtained
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