171 research outputs found
Oriented polaritons in strongly-coupled asymmetric double quantum well microcavities
Replacing independent single quantum wells inside a strongly-coupled
semiconductor microcavity with double quantum wells produces a special type of
polariton. Using asymmetric double quantum wells in devices processed into
mesas allows the alignment of the electron levels to be voltage-tuned. At the
resonant electronic tunnelling condition, we demonstrate that `oriented
polaritons' are formed, which possess greatly enhanced dipole moments. Since
the polariton-polariton scattering rate depends on this dipole moment, such
devices could reach polariton lasing, condensation and optical nonlinearities
at much lower threshold powers.Comment: 3 figure
Dynamic virtual machine allocation in cloud server facility systems with renewable energy sources
Bragg Polaritons: Strong Coupling and Amplification in an Unfolded Microcavity
Periodic incorporation of quantum wells inside a one--dimensional Bragg
structure is shown to enhance coherent coupling of excitons to the
electromagnetic Bloch waves. We demonstrate strong coupling of quantum well
excitons to photonic crystal Bragg modes at the edge of the photonic bandgap,
which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg
polariton branches are in good agreement with the theory and allow
demonstration of Bragg polariton parametric amplification.Comment: 4 pages, 4 figure
Polariton Condensate Transistor Switch
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits
Optical control of spin textures in quasi-one-dimensional polariton condensates
We investigate, through polarization-resolved spectroscopy, the spin
transport by propagating polariton condensates in a quasi one-dimensional
microcavity ridge along macroscopic distances. Under circularly polarized,
continuous-wave, non-resonant excitation, a sinusoidal precession of the spin
in real space is observed, whose phase depends on the emission energy. The
experiments are compared with simulations of the spinor-polariton condensate
dynamics based on a generalized Gross-Pitaevskii equation, modified to account
for incoherent pumping, decay and energy relaxation within the condensate.Comment: 10 pages, 9 figure
Phase diagrams of magnetopolariton gases
The magnetic field effect on phase transitions in electrically neutral
bosonic systems is much less studied than those in fermionic systems, such as
superconducting or ferromagnetic phase transitions. Nevertheless, composite
bosons are strongly sensitive to magnetic fields: both their internal structure
and motion as whole particles may be affected. A joint effort of ten
laboratories has been focused on studies of polariton lasers, where
non-equilibrium Bose-Einstein condensates of bosonic quasiparticles,
exciton-polaritons, may appear or disappear under an effect of applied magnetic
fields. Polariton lasers based on pillar or planar microcavities were excited
both optically and electrically. In all cases a pronounced dependence of the
onset to lasing on the magnetic field has been observed. For the sake of
comparison, photon lasing (lasing by an electron-hole plasma) in the presence
of a magnetic field has been studied on the same samples as polariton lasing.
The threshold to photon lasing is essentially governed by the excitonic Mott
transition which appears to be sensitive to magnetic fields too. All the
observed experimental features are qualitatively described within a uniform
model based on coupled diffusion equations for electrons, holes and excitons
and the Gross-Pitaevskii equation for exciton-polariton condensates. Our
research sheds more light on the physics of non-equilibrium Bose-Einstein
condensates and the results manifest high potentiality of polariton lasers for
spin-based quantum logic applications.Comment: 21 pages, 11 figure
Strain-assisted optomechanical coupling of polariton condensate spin to a micromechanical resonator
We report spin and intensity coupling of an exciton-polariton condensate to
the mechanical vibrations of a circular membrane microcavity. We optically
drive the microcavity resonator at the lowest mechanical resonance frequency
while creating an optically-trapped spin-polarized polariton condensate in
different locations on the microcavity, and observe spin and intensity
oscillations of the condensate at the vibration frequency of the resonator.
Spin oscillations are induced by vibrational strain driving, whilst the
modulation of the optical trap due to the displacement of the membrane causes
intensity oscillations in the condensate emission. Our results demonstrate
spin-phonon coupling in a macroscopically coherent condensate
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