402 research outputs found
Making a case for introspection
Defending first-person introspective access to own mental states, we argue against Carruthers' claim of mindreading being prior to meta-cognition and for a fundamental difference between how we understand our own and others' mental states. We conclude that a model based on one mechanism but involving two different kinds of access for self and other is sufficient and more consistent with the evidence
Quantum networks with chiral light--matter interaction in waveguides
We propose a scalable architecture for a quantum network based on a simple
on-chip photonic circuit that performs loss-tolerant two-qubit measurements.
The circuit consists of two quantum emitters positioned in the arms of an
on-chip Mach-Zehnder interferometer composed of waveguides with chiral
light--matter interfaces. The efficient chiral light--matter interaction allows
the emitters to perform high-fidelity intranode two-qubit parity measurements
within a single chip, and to emit photons to generate internode entanglement,
without any need for reconfiguration. We show that by connecting multiple
circuits of this kind into a quantum network, it is possible to perform
universal quantum computation with heralded two-qubit gate fidelities achievable in state-of-the-art quantum dot systems.Comment: 5 pages plus supplementary materia
Optical refrigeration with coupled quantum wells
Refrigeration of a solid-state system with light has potential applications
for cooling small-scale electronics and photonics. We show theoretically that
two coupled semiconductor quantum wells are efficient cooling media for optical
refrigeration because they support long-lived indirect electron-hole pairs.
Thermal excitation of these pairs to distinct higher-energy states with faster
radiative recombination allows an efficient escape channel to remove thermal
energy from the system. This allows reaching much higher cooling efficiencies
than with single quantum wells. From band-diagram calculations along with an
experimentally realistic level scheme we calculate the cooling efficiency and
cooling yield of different devices with coupled quantum wells embedded in a
suspended nanomembrane. The dimension and composition of the quantum wells
allow optimizing either of these quantities, which cannot, however, be
maximized simultaneously. Quantum-well structures with electrical control allow
tunability of carrier lifetimes and energy levels so that the cooling
efficiency can be optimized over time as the thermal population decreases due
to the cooling.Comment: 10 pages, 5 figure
Large quantum dots with small oscillator strength
We have measured the oscillator strength and quantum efficiency of excitons
confined in large InGaAs quantum dots by recording the spontaneous emission
decay rate while systematically varying the distance between the quantum dots
and a semiconductor-air interface. The size of the quantum dots is measured by
in-plane transmission electron microscopy and we find average in-plane
diameters of 40 nm. We have calculated the oscillator strength of excitons of
that size and predict a very large oscillator strength due to Coulomb effects.
This is in stark contrast to the measured oscillator strength, which turns out
to be much below the upper limit imposed by the strong confinement model. We
attribute these findings to exciton localization in local potential minima
arising from alloy intermixing inside the quantum dots.Comment: 4 pages, 3 figures, submitte
Cavity Quantum Electrodynamics with Anderson-localized Modes
A major challenge in quantum optics and quantum information technology is to
enhance the interaction between single photons and single quantum emitters.
Highly engineered optical cavities are generally implemented requiring
nanoscale fabrication precision. We demonstrate a fundamentally different
approach in which disorder is used as a resource rather than a nuisance. We
generate strongly confined Anderson-localized cavity modes by deliberately
adding disorder to photonic crystal waveguides. The emission rate of a
semiconductor quantum dot embedded in the waveguide is enhanced by a factor of
15 on resonance with the Anderson-localized mode and 94 % of the emitted
single-photons couple to the mode. Disordered photonic media thus provide an
efficient platform for quantum electrodynamics offering an approach to
inherently disorder-robust quantum information devices
Photon Sorting, Efficient Bell Measurements and a Deterministic CZ Gate using a Passive Two-level Nonlinearity
Although the strengths of optical non-linearities available experimentally
have been rapidly increasing in recent years, significant challenges remain to
using such non-linearities to produce useful quantum devices such as efficient
optical Bell state analysers or universal quantum optical gates. Here we
describe a new approach that avoids the current limitations by combining strong
non-linearities with active Gaussian operations in efficient protocols for Bell
state analysers and Controlled-Sign gates
Observation of twin beam correlations and quadrature entanglement by frequency doubling in a two-port resonator
We demonstrate production of quantum correlated and entangled beams by second
harmonic generation in a nonlinear resonator with two output ports. The output
beams at wavelength 428.5 nm exhibit 0.9 dB of nonclassical intensity
correlations and 0.3 dB of entanglement.Comment: 5 pages, 7 figure
Efficient out-coupling of high-purity single photons from a coherent quantum dot in a photonic-crystal cavity
We demonstrate a single-photon collection efficiency of from
a quantum dot in a low-Q mode of a photonic-crystal cavity with a single-photon
purity of recorded above the saturation power. The high
efficiency is directly confirmed by detecting up to kilocounts per
second on a single-photon detector on another quantum dot coupled to the cavity
mode. The high collection efficiency is found to be broadband, as is explained
by detailed numerical simulations. Cavity-enhanced efficient excitation of
quantum dots is obtained through phonon-mediated excitation and under these
conditions, single-photon indistinguishability measurements reveal long
coherence times reaching ns in a weak-excitation regime. Our work
demonstrates that photonic crystals provide a very promising platform for
highly integrated generation of coherent single photons including the efficient
out-coupling of the photons from the photonic chip.Comment: 13 pages, 8 figures, submitte
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