Two-particle correlations and

Larry McLerran

Dong Zhou

We identify the correlation in a state of two identical particles as the residual information beyond what is already contained in the 1-particle reduced density matrix, and propose a correlation measure based on the maximum entropy principle. We obtain the analytical results of the correlation measure, which make it computable for arbitrary two-particle states. We also show that the degrees of correlation in the same two-particle states with different particle types will decrease in the following order: bosons, fermions, and distinguishable particles.

A. K. Chaudhuri

Benedikt B. Brandt, Constantine Yannouleas, Uzi Landman

Identification and understanding of the evolution of interference patterns in two-particle momentum correlations as a function of the strength of interatomic interactions are important in explorations of the nature of quantum states of trapped particles. Together with the analysis of two-particle spatial correlations, they offer the prospect of uncovering fundamental symmetries and structure of correlated many-body states, as well as opening vistas into potential control and utilization of correlated quantum states as quantum information resources. With the use of the two-particle density matrix constructed via configuration-interaction (CI) exact diagonalization of the microscopic Hamiltonian, we explored here the systematic evolution of characteristic, damped, interference patterns in the two-particle momentum and spatial correlation maps of two ultracold fermionic atoms trapped in a double-well potential, over the entire range of variation of the contact repulsive interatomic interaction strength. For the singlet ground state the two-particle momentum maps were found to transform from a square-plaid pattern for non-interacting particles, to a system of striped interference fringes, with the most intense fringe lying along the main diagonal indicating bunching. Two-particle momentum correlation maps for low-lying excited states were also analyzed, with the triplet excited state found to exhibit antibunching. A modified Hubbard-type effective model is shown to reproduce well the microscopic CI results. This led to uncovering of analytic expressions capturing the full evolution of the two-particle momentum correlation maps over the entire range of interparticle interactions, from the independent particle limit with a substantial site-double-occupancy fraction, to the Mott insulating regime.

A. K. Chaudhuri

Claudia Benedetti, Fabrizio Buscemi, Paolo Bordone

We evaluate the degree of quantum correlation between two fermions (bosons) subject to continuous-time quantum walks in a one-dimensional (1D) ring lattice with periodic boundary conditions. In our approach, no particle-particle interaction is considered. We show that the interference effects due to exchange symmetry can result into the appearance of nonclassical correlations. The role played onto the appearance of quantum correlations by the quantum statistics of the particles, the boundary conditions, and the partition of the system is widely investigated. Quantum correlations have also been investigated in a model mimicking the ballistic evolution of two indistinguishable particles in a 1D continuous-space structure. Our results are consistent with recent quantum optics and electron quantum optics experiments where the showing up of two-particle nonclassical correlations has been observed even in the absence of mutual interaction between the particles.