4,084 research outputs found
Polariton states bound to defects in GaAs/AlAs planar microcavities
We report on polariton states bound to defects in planar GaAs/AlAs
microcavities grown by molecular beam epitaxy. The defect types relevant for
the spatial polariton dynamics in these structures are cross-hatch misfit
dislocations, and point-like defects extended over several micrometers. We
attribute the latter defects to Ga droplets emitted occasionally by the Ga cell
during the growth. These defects, also known as oval defects, result in a
dome-like local modulation of surface, which is translated into the cavity
structure and leads to a lateral modulation of the cavity polariton energy of
up to 15\,meV. The resulting spatially localized potential landscape for the
in-plane polariton motion creates a series of bound states. These states were
characterized by spectrally resolved transmission imaging in real and
reciprocal space, and reveal the spatial potential created by the defects.
Interestingly, the defect states exhibit long lifetimes in the 10ps range,
which we attribute to a spatially smooth confinement potential
An alternative proposal for French negation
In this paper, I propose an analysis of the negative expression (ne) pas 'not' in Modern Standard French, set within the minimalist program of Chomsky (1995), whose goal is to keep only principles no theory can do without (Hornstein 1994: 62ff.; see also Abraham et al. 1996; Pollock
1997; etc. for introductions to the theory). The main characteristic of the present account is that it takes seriously the well-known fact that ne, traditionally thought of as the center of sentential negation, is no longer negative (Ashby 1981; Coveney 1996). Therefore, Pollock's (1989)
influential proposal of a specific negative functional category NEGP headed by ne with pas in its SPEC has to be revised. I will focus only on French, and leave for further research how my proposal could be extended to account for the structure of negation in other languages, especially in other Romance languages (see Zanuttini 1991)
A solid state spin-wave quantum memory for time-bin qubits
We demonstrate the first solid-state spin-wave optical quantum memory with
on-demand read-out. Using the full atomic frequency comb scheme in a \PrYSO
crystal, we store weak coherent pulses at the single-photon level with a signal
to noise ratio . Narrow-band spectral filtering based on spectral hole
burning in a second \PrYSO crystal is used to filter out the excess noise
created by control pulses to reach an unconditional noise level of photons per pulse. We also report spin-wave storage of
photonic time-bin qubits with conditional fidelities higher than a measure and
prepare strategy, demonstrating that the spin-wave memory operates in the
quantum regime. This makes our device the first demonstration of a quantum
memory for time-bin qubits, with on demand read-out of the stored quantum
information. These results represent an important step for the use of
solid-state quantum memories in scalable quantum networks.Comment: 10 pages, 10 figure
REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture
Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America
Coherent Storage of Temporally Multimode Light Using a Spin-Wave Atomic Frequency Comb Memory
We report on coherent and multi-temporal mode storage of light using the full
atomic frequency comb memory scheme. The scheme involves the transfer of
optical atomic excitations in Pr3+:Y2SiO5 to spin-waves in the hyperfine levels
using strong single-frequency transfer pulses. Using this scheme, a total of 5
temporal modes are stored and recalled on-demand from the memory. The coherence
of the storage and retrieval is characterized using a time-bin interference
measurement resulting in visibilities higher than 80%, independent of the
storage time. This coherent and multimode spin-wave memory is promising as a
quantum memory for light.Comment: 17 pages, 5 figure
Microcavity quantum-dot systems for non-equilibrium Bose-Einstein condensation
We review the practical conditions required to achieve a non-equilibrium BEC
driven by quantum dynamics in a system comprising a microcavity field mode and
a distribution of localised two-level systems driven to a step-like population
inversion profile. A candidate system based on eight 3.8nm layers of
In(0.23)Ga(0.77)As in GaAs shows promising characteristics with regard to the
total dipole strength which can be coupled to the field mode.Comment: 4 pages, 4 figures, to be published in J. Phys. Conf. Ser. for QD201
Emergence of thin shell structure during collapse in isotropic coordinates
Numerical studies of gravitational collapse in isotropic coordinates have
recently shown an interesting connection between the gravitational Lagrangian
and black hole thermodynamics. A study of the actual spacetime was not the main
focus of this work and in particular, the rich and interesting structure of the
interior has not been investigated in much detail and remains largely unknown.
We elucidate its features by performing a numerical study of the spacetime in
isotropic coordinates during gravitational collapse of a massless scalar field.
The most salient feature to emerge is the formation of a thin shell of matter
just inside the apparent horizon. The energy density and Ricci scalar peak at
the shell and there is a jump discontinuity in the extrinsic curvature across
the apparent horizon, the hallmark that a thin shell is present in its
vicinity. At late stages of the collapse, the spacetime consists of two vacuum
regions separated by the thin shell. The interior is described by an
interesting collapsing isotropic universe. It tends towards a vacuum (never
reaches a perfect vacuum) and there is a slight inhomogeneity in the interior
that plays a crucial role in the collapse process as the areal radius tends to
zero. The spacetime evolves towards a curvature (physical) singularity in the
interior, both a Weyl and Ricci singularity. In the exterior, our numerical
results match closely the analytical form of the Schwarzschild metric in
isotropic coordinates, providing a strong test of our numerical code.Comment: 24 pages, 10 figures. version to appear in Phys. Rev.
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