72 research outputs found
Antisymmetric PT-photonic structures with balanced positive and negative index materials
We propose a new class of synthetic optical materials in which the refractive
index satisfies n(-\bx)=-n^*(\bx). We term such systems antisymmetric
parity-time (APT) structures. Unlike PT-symmetric systems which require
balanced gain and loss, i.e. n(-\bx)=n^*(\bx), APT systems consist of
balanced positive and negative index materials. Despite the seemingly
PT-symmetric optical potential V(\bx)\equiv n(\bx)^2\omega^2/c^2, APT systems
are not invariant under combined PT operations due to the discontinuity of the
spatial derivative of the wavefunction. We show that APT systems can display
intriguing properties such as spontaneous phase transition of the scattering
matrix, bidirectional invisibility, and a continuous lasing spectrum.Comment: 5 pages, 4 figure
Spin-orbit interaction in quantum dots in the presence of exchange correlations
We discuss the problem of spin-orbit interaction in a 2D chaotic or diffusive
quantum dot in the presence of exchange correlations. Spin-orbit scattering
breaks spin rotation invariance, and in the crossover regime between different
symmetries of the spin-orbit coupling, the problem has no closed solution. A
conventional choice of a many-particle basis in a numerical diagonalization is
the set of Slater determinants built from the single-particle eigenstates of
the one-body Hamiltonian (including the spin-orbit terms). We develop a
different approach based on the use of a good-spin many-particle basis that is
composed of the eigenstates of the universal Hamiltonian in the absence of
spin-orbit scattering. We introduce a complete labelling of this good-spin
basis and use angular momentum algebra to calculate in closed form the matrix
elements of the spin-orbit interaction in this basis. Spin properties, such as
the ground-state spin distribution and the spin excitation function, are easily
calculated in this basis.Comment: 14 pages, 3 figure
Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks
The quantum dynamics of open many-body systems poses a challenge for
computational approaches. Here we develop a stochastic scheme based on the
positive P phase-space representation to study the nonequilibrium dynamics of
coupled spin-boson networks that are driven and dissipative. Such problems are
at the forefront of experimental research in cavity and solid state
realizations of quantum optics, as well as cold atom physics, trapped ions and
superconducting circuits. We demonstrate and test our method on a driven,
dissipative two-site system, each site involving a spin coupled to a photonic
mode, with photons hopping between the sites, where we find good agreement with
Monte Carlo Wavefunction simulations. In addition to numerically reproducing
features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we
also predict a novel steady state quantum dynamical phase transition for an
asymmetric configuration of drive and dissipation.Comment: 15 pages, 8 figure
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