2,013 research outputs found
Quantum Entanglement in Nanocavity Arrays
We show theoretically how quantum interference between linearly coupled modes
with weak local nonlinearity allows the generation of continuous variable
entanglement. By solving the quantum master equation for the density matrix, we
show how the entanglement survives realistic levels of pure dephasing. The
generation mechanism forms a new paradigm for entanglement generation in arrays
of coupled quantum modes.Comment: 5 pages, 3 figure
Single photons from coupled quantum modes
Single photon emitters often rely on a strong nonlinearity to make the
behaviour of a quantum mode susceptible to a change in the number of quanta
between one and two. In most systems the strength of nonlinearity is weak, such
that changes at the single quantum level have little effect. Here, we consider
coupled quantum modes and and that they can be strongly sensitive at the single
quantum level, even if nonlinear interactions are modest. As examples, we
consider solid-state implementations based on the tunneling of polaritons
between quantum boxes or their parametric modes in a microcavity. We find that
these systems can act as promising single photon emitters.Comment: 4 pages, 3 figure
Optically erasing disorder in semiconductor microcavities with dynamic nuclear polarization
The mean squared value of the photonic disorder is found to be reduced by a
factor of 100 in a typical GaAs based microcavity, when exposed to a circularly
polarized continuous wave optical pump without any special spatial patterning.
Resonant excitation of the cavity mode excites a spatially non-uniform
distribution of spin-polarized electrons, which depends on the photonic
disorder profile. Electrons transfer spin to nuclei via the hyperfine contact
interaction, inducing a long-living Overhauser magnetic field able to modify
the potential of exciton-polaritons.Comment: 4 pages, 3 figure
Optically induced transparency in bosonic cascade lasers
Bosonic cascade lasers are terahertz (THz) lasers based on stimulated
radiative transitions between bosonic condensates of excitons or
exciton-polaritons confined in a trap. We study the interaction of an incoming
THz pulse resonant in frequency with the transitions between neighboring energy
levels of the cascade. We show that at certain optical pump conditions the
cascade becomes transparent to the incident pulse: it neither absorbs nor
amplifies it, in the mean field approximation. The populations of intermediate
levels of the bosonic cascade change as the THz pulse passes, nevertheless. In
comparison, a fermionic cascade laser does not reveal any of these properties.Comment: 4 pages, 5 figure
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
Exciton-Polariton Oscillations in Real Space
We introduce and model spin-Rabi oscillations based on exciton-polaritons in
semiconductor microcavities. The phase and polarization of oscillations can be
controlled by resonant coherent pulses and the propagation of oscillating
domains gives rise to phase-dependent interference patterns in real space. We
show that interbranch polariton-polariton scattering controls the propagation
of oscillating domains, which can be used to realize logic gates based on an
analogue variable phase.Comment: 6 page
Spontaneous polariton currents in periodic lateral chains
We predict spontaneous generation of superfluid polariton currents in planar
microcavities with lateral periodic modulation of both potential and decay
rate. A spontaneous breaking of spatial inversion symmetry of a polariton
condensate emerges at a critical pumping, and the current direction is
stochastically chosen. We analyse the stability of the current with respect to
the fluctuations of the condensate. A peculiar spatial current domain structure
emerges, where the current direction is switched at the domain walls, and the
characteristic domain size and lifetime scale with the pumping power.Comment: 6+6 pages, 4+1 figures (with supplemental material
Ballistic spin transport in exciton gases
Traditional spintronics relies on spin transport by charge carriers, such as
electrons in semiconductor crystals. This brings several complications: the
Pauli principle prevents the carriers from moving with the same speed; Coulomb
repulsion leads to rapid dephasing of electron flows. Spin-optronics is a
valuable alternative to traditional spintronics. In spin-optronic devices the
spin currents are carried by electrically neutral bosonic quasi-particles:
excitons or exciton-polaritons. They can form highly coherent quantum liquids
and carry spins over macroscopic distances. The price to pay is a finite
life-time of the bosonic spin carriers. We present the theory of exciton
ballistic spin transport which may be applied to a range of systems where
bosonic spin transport has been reported, in particular, to indirect excitons
in coupled GaAs/AlGaAs quantum wells. We describe the effect of spin-orbit
interaction of electrons and holes on the exciton spin, account for the Zeeman
effect induced by external magnetic fields, long range and short range exchange
splittings of the exciton resonances. We also consider exciton transport in the
non-linear regime and discuss the definitions of exciton spin current,
polarization current and spin conductivity.Comment: 16 pages, 10 figures to be published in Phys. Rev.
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