4 research outputs found
Quantum Coherence and Correlations of optical radiation by atomic ensembles interacting with a two-level atom in microwave cavity
We examine quantum statistics of optical photons emitted from atomic
ensembles which are classically driven and simultaneously coupled to a
two-level atom via microwave photon exchange. Quantum statistics and
correlations are analyzed by calculating second order coherence degree, von
Neumann entropy, spin squeezing for multi-particle entanglement, as well as
genuine two and three-mode entanglement parameters for steady state and
non-equilibrium situations. Coherent transfer of population between the
radiation modes and quantum state mapping between the two-level atom and the
optical modes are discussed. A potential experimental realization of the
theoretical results in a superconducting coplanar waveguide resonator
containing diamond crystals with Nitrogen-Vacancy color centers and a
superconducting artificial two-level atom is discussed.Comment: 15 pages, 17 figures, submitted to Phys. Rev.
Spin squeezing and pairwise entanglement for symmetric multiqubit states
We show that spin squeezing implies pairwise entanglement for arbitrary
symmetric multiqubit states. If the squeezing parameter is less than or equal
to 1, we demonstrate a quantitative relation between the squeezing parameter
and the concurrence for the even and odd states. We prove that the even states
generated from the initial state with all qubits being spin down, via the
one-axis twisting Hamiltonian, are spin squeezed if and only if they are
pairwise entangled. For the states generated via the one-axis twisting
Hamiltonian with an external transverse field for any number of qubits greater
than 1 or via the two-axis counter-twisting Hamiltonian for any even number of
qubits, the numerical results suggest that such states are spin squeezed if and
only if they are pairwise entangled.Comment: 6 pages. Version 3: Small corrections were mad