Article

# Entropy of entanglement and multifractal exponents for random states

Physical Review A (Impact Factor: 2.99). 08/2008; DOI: 10.1103/PhysRevA.79.032308

Source: arXiv

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**ABSTRACT:**The entanglement between two arbitrary subsystems of random pure states is studied via properties of the density matrix's partial transpose, $\rho_{12}^{T_2}$. The density of states of $\rho_{12}^{T_2}$ is close to the semicircle law when both subsystems have dimensions which are not too small and are of the same order. A simple random matrix model for the partial transpose is found to capture the entanglement properties well, including a transition across a critical dimension. Log-negativity is used to quantify entanglement between subsystems and analytic formulas for this are derived based on the simple model. The skewness of the eigenvalue density of $\rho_{12}^{T_2}$ is derived analytically, using the average of the third moment over the ensemble of random pure states. The third moment after partial transpose is also shown to be related to a generalization of the Kempe invariant. The smallest eigenvalue after partial transpose is found to follow the extreme value statistics of random matrices, namely the Tracy-Widom distribution. This distribution, with relevant parameters obtained from the model, is found to be useful in calculating the fraction of entangled states at critical dimensions. These results are tested in a quantum dynamical system of three coupled standard maps, where one finds that if the parameters represent a strongly chaotic system, the results are close to those of random states, although there are some systematic deviations at critical dimensions.Physical Review A 02/2012; 85(6). · 2.99 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We investigate numerically the position- and momentum-space Shannon information entropies, S_{x}^{β} and S_{p}^{β}, respectively, of energy eigenstates |β〉 for an electron in four kinds of one-dimensional (1D) nonuniform systems, i.e., the Harper model, the slowly varying potential ones, the complex quasiperiodic potential ones, and the random-dimer potential ones. In the former three models, electronic localization properties are well-defined. For them, we find it interesting that, S_{x}^{β} is greater than, equal to, and less than S_{p}^{β} for delocalized, critical, and localized states in position-space, respectively, which can be used as signatures of the transition from a delocalized phase to a localized ones. With the criterion, we analyze the random-dimer potential model. We give another perspective and propose a consistent interpretation of discrepancies about the random-dimer potential model. Therefore, all these provide us a simple method to discern the nature of states in these 1D nonuniform systems.Physical Review E 12/2012; 86(6-1):061122. · 2.31 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We compute analytically the statistics of the Renyi and von Neumann entropies (standard measures of entanglement), for a random pure state in a large bipartite quantum system. The full probability distribution is computed by first mapping the problem to a random matrix model and then using a Coulomb gas method. We identify three different regimes in the entropy distribution, which correspond to two phase transitions in the associated Coulomb gas. The two critical points correspond to sudden changes in the shape of the Coulomb charge density: the appearance of an integrable singularity at the origin for the first critical point, and the detachement of the rightmost charge (largest eigenvalue) from the sea of the other charges at the second critical point. Analytical results are verified by Monte Carlo numerical simulations. A short account of some of these results appeared recently in Phys. Rev. Lett. {\bf 104}, 110501 (2010).Journal of Statistical Physics 06/2010; 142(2). · 1.28 Impact Factor

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