378 research outputs found
Multimode entanglement in coupled cavity arrays
We study a driven-dissipative array of coupled nonlinear optical resonators
by numerically solving the Von Neumann equation for the density matrix. We
demonstrate that quantum correlated states of many photons can be generated
also in the limit where the nonlinearity is much smaller than the losses,
contrarily to common expectations. Quantum correlations in this case arise from
interference between different pathways that the system can follow in the
Hilbert space to reach its steady state under the effect of coherent driving
fields. We characterize in particular two systems: a linear chain of three
coupled cavities and an array of eight coupled cavities. We demonstrate the
existence of a parameter range where the system emits photons with
continuous-variable bipartite and quadripartite entanglement, in the case of
the first and the second system respectively. This entanglement is shown to
survive realistic rates of pure dephasing and opens a new perspective for the
realization of quantum simulators or entangled photon sources without the
challenging requirement of strong optical nonlinearities.Comment: 20 pages, 7 figure
Critical behavior of dissipative two-dimensional spin lattices
We explore critical properties of two-dimensional lattices of spins
interacting via an anisotropic Heisenberg Hamiltonian and subject to incoherent
spin flips. We determine the steady-state solution of the master equation for
the density matrix via the corner-space renormalization method. We investigate
the finite-size scaling and critical exponent of the magnetic linear
susceptibility associated to a dissipative ferromagnetic transition. We show
that the Von Neumann entropy increases across the critical point, revealing a
strongly mixed character of the ferromagnetic phase. Entanglement is witnessed
by the quantum Fisher information which exhibits a critical behavior at the
transition point, showing that quantum correlations play a crucial role in the
transition even though the system is in a mixed state.Comment: Accepted for publication on Phys. Rev. B (6 pages, 5 figures
Polariton quantum blockade in a photonic dot
We investigate the quantum nonlinear dynamics of a resonantly excited
photonic quantum dot embedding a quantum well in the strong exciton-photon
coupling regime. Within a master equation approach, we study the polariton
quantum blockade and the generation of single photon states due to
polariton-polariton interactions as a function of the photonic dot geometry,
spectral linewidths and energy detuning between quantum well exciton and
confined photon mode. The second order coherence function is
calculated for both continuous wave and pulsed excitations
Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates
A theoretical prediction of the spin-dependent electron self-energy and
in-plane transport of a two-dimensional electron gas in proximity with a
ferromagnetic gate is presented. The application of the predicted
spin-dependent properties is illustrated by the proposal of a device
configuration with two neighboring ferromagnetic gates which produces a
magnetoresistance effect on the channel current generated by nonmagnetic source
and drain contacts. Specific results are shown for a silicon inversion layer
with iron gates. The gate leakage current is found to be beneficial to the spin
effects.Comment: 3 pages, 2 figures, Replaced with revised versio
Quantum squeezing generation versus photon localization in a disordered microcavity
We investigate theoretically the nonlinear dynamics induced by an intense
pump field in a disordered planar microcavity. Through a self-consistent
theory, we show how the generation of quantum optical noise squeezing is
affected by the breaking of the in-plane translational invariance and the
occurrence of photon localization. We find that the generation of single-mode
Kerr squeezing for the ideal planar case can be prevented by disorder as a
result of multimode nonlinear coupling, even when the other modes are in the
vacuum state. However, the excess noise is a non-monotonous function of the
disorder amplitude. In the strong localization limit, we show that the system
becomes protected with respect to this fundamental coupling mechanism and that
the ideal quadrature squeezing generation can be obtained
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