126 research outputs found
Solid-state quantum optics with quantum dots in photonic nanostructures
Quantum nanophotonics has become a new research frontier where quantum optics
is combined with nanophotonics in order to enhance and control the interaction
between strongly confined light and quantum emitters. Such progress provides a
promising pathway towards quantum-information processing on an all-solid-state
platform. Here we review recent progress on experiments with single quantum
dots in nanophotonic structures. Embedding the quantum dots in photonic
band-gap structures offers a way of controlling spontaneous emission of single
photons to a degree that is determined by the local light-matter coupling
strength. Introducing defects in photonic crystals implies new functionalities.
For instance, efficient and strongly confined cavities can be constructed
enabling cavity-quantum-electrodynamics experiments. Furthermore, the speed of
light can be tailored in a photonic-crystal waveguide forming the basis for
highly efficient single-photon sources where the photons are channeled into the
slowly propagating mode of the waveguide. Finally, we will discuss some of the
surprises that arise in solid-state implementations of quantum-optics
experiments in comparison to their atomic counterparts. In particular, it will
be shown that the celebrated point-dipole description of light-matter
interaction can break down when quantum dots are coupled to plasmon
nanostructures.Comment: Review. 15 pages, 9 figure
Interfacing single photons and single quantum dots with photonic nanostructures
Photonic nanostructures provide means of tailoring the interaction between
light and matter and the past decade has witnessed a tremendous experimental
and theoretical progress in this subject. In particular, the combination with
semiconductor quantum dots has proven successful. This manuscript reviews
quantum optics with excitons in single quantum dots embedded in photonic
nanostructures. The ability to engineer the light-matter interaction strength
in integrated photonic nanostructures enables a range of fundamental
quantum-electrodynamics experiments on, e.g., spontaneous-emission control,
modified Lamb shifts, and enhanced dipole-dipole interaction. Furthermore,
highly efficient single-photon sources and giant photon nonlinearities may be
implemented with immediate applications for photonic quantum-information
processing. The review summarizes the general theoretical framework of photon
emission including the role of dephasing processes, and applies it to photonic
nanostructures of current interest, such as photonic-crystal cavities and
waveguides, dielectric nanowires, and plasmonic waveguides. The introduced
concepts are generally applicable in quantum nanophotonics and apply to a large
extent also to other quantum emitters, such as molecules, nitrogen vacancy
ceters, or atoms. Finally, the progress and future prospects of applications in
quantum-information processing are considered.Comment: Updated version resubmitted to Reviews of Modern Physic
Mapping the local density of optical states of a photonic crystal with single quantum dots
We use single self-assembled InGaAs quantum dots as internal probes to map
the local density of optical states of photonic crystal membranes. The employed
technique separates contributions from non-radiative recombination and
spin-flip processes by properly accounting for the role of the exciton fine
structure. We observe inhibition factors as high as 55 and compare our results
to local density of optical states calculations available from the literature,
thereby establishing a quantitative understanding of photon emission in
photonic crystal membranes.Comment: 4 pages, 3 figure
Unraveling the mesoscopic character of quantum dots in nanophotonics
We provide a microscopic theory for semiconductor quantum dots that explains
the pronounced deviations from the prevalent point-dipole description that were
recently observed in spectroscopic experiments on quantum dots in photonic
nanostructures. At the microscopic level the deviations originate from
structural inhomogeneities generating a large circular quantum current density
that flows inside the quantum dot over mesoscopic length scales. The model is
supported by the experimental data, where a strong variation of the multipolar
moments across the emission spectrum of quantum dots is observed. Our work
enriches the physical understanding of quantum dots and is of significance for
the fields of nanophotonics, quantum photonics, and quantum-information
science, where quantum dots are actively employed.Comment: 6 pages, 5 figure
Designing Photonic Topological Insulators with Quantum-Spin-Hall Edge States using Topology Optimization
Designing photonic topological insulators is highly non-trivial because it
requires inversion of band symmetries around the band gap, which was so far
done using intuition combined with meticulous trial and error. Here we take a
completely different approach: we consider the design of photonic topological
insulators as an inverse design problem and use topology optimization to
maximize the transmission through an edge mode with a sharp bend. Two design
domains composed of two different, but initially identical,
C-symmetric unit cells define the geometrical design problem.
Remarkably, the optimization results in a photonic topological insulator
reminiscent of the shrink-and-grow approach to quantum-spin-Hall photonic
topological insulators but with notable differences in the topology of the
crystal as well as qualitatively different band structures and with
significantly improved performance as gauged by the band-gap sizes, which are
at least 50 \% larger than previous designs. Furthermore, we find a directional
beta factor exceeding 99 \%, and very low losses for sharp bends. Our approach
allows for the introduction of fabrication limitations by design and opens an
avenue towards designing PTIs with hitherto unexplored symmetry constraints.Comment: 7 pages, 5 figure
Two mechanisms of disorder-induced localization in photonic-crystal waveguides
Unintentional but unavoidable fabrication imperfections in state-of-the-art
photonic-crystal waveguides lead to the spontaneous formation of
Anderson-localized modes thereby limiting slowlight propagation and its
potential applications. On the other hand, disorder-induced cavities offer an
approach to cavity-quantum electrodynamics and random lasing at the nanoscale.
The key statistical parameter governing the disorder effects is the
localization length, which together with the waveguide length determines the
statistical transport of light through the waveguide. In a disordered
photonic-crystal waveguide, the localization length is highly dispersive, and
therefore, by controlling the underlying lattice parameters, it is possible to
tune the localization of the mode. In the present work, we study the
localization length in a disordered photonic-crystal waveguide using numerical
simulations. We demonstrate two different localization regimes in the
dispersion diagram where the localization length is linked to the density of
states and the photon effective mass, respectively. The two different
localization regimes are identified in experiments by recording the
photoluminescence from quantum dots embedded in photonic-crystal waveguides.Comment: Accepted for publication in Physical Review
Probing electric and magnetic vacuum fluctuations with quantum dots
The electromagnetic-vacuum-field fluctuations are intimately linked to the
process of spontaneous emission of light. Atomic emitters cannot probe
electric- and magnetic-field fluctuations simultaneously because electric and
magnetic transitions correspond to different selection rules. In this paper we
show that semiconductor quantum dots are fundamentally different and are
capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole
transitions on a single electronic resonance. As a consequence, quantum dots
can probe electric and magnetic fields simultaneously and can thus be applied
for sensing the electromagnetic environment of complex photonic nanostructures.
Our study opens the prospect of interfacing quantum dots with optical
metamaterials for tailoring the electric and magnetic light-matter interaction
at the single-emitter level.Comment: 6 pages, 4 figure
Two regimes of confinement in photonic nanocavities: bulk confinement versus lightning rods
We present a theoretical study of dielectric bowtie cavities and show that
they are governed by two essentially different confinement regimes. The first
is confinement inside the bulk dielectric and the second is a local
lightning-rod regime where the field is locally enhanced at sharp corners and
may yield a vanishing mode volume without necessarily enhancing the mode inside
the bulk dielectric. We show that while the bulk regime is reminiscent of the
confinement in conventional nanocavities, the most commonly used definition of
the mode volume gauges in fact the lightning-rod effect when applied to
ultra-compact cavities, such as bowties. Distinguishing between these two
regimes will be crucial for future research on nanocavities, and our insights
show how to obtain strongly enhanced light-matter interaction over large
bandwidths.Comment: 9 pages, 5 figures, 39 reference
Impact of transduction scaling laws on nanoelectromechanical systems
We study the electromechanical transduction in nanoelectromechanical
actuators and show that the differences in scaling for electrical and
mechanical effects lead to an overall non-trivial scaling behavior. In
particular, the previously neglected fringing fields considerably increase
electrical forces and improve the stability of nanoscale actuators. This shows
that electrostatics does not pose any limitations to downscaling of
electromechanical systems, in fact in several respects, nanosystems outperform
their microscale counterparts. As a specific example, we consider in-plane
actuation of ultrathin slabs and show that devices consisting of a few layers
of graphene are feasible, implying that electromechanical resonators operating
beyond 40 GHz are possible with currently available technology
Exciton spin-flip rate in quantum dots determined by a modified local density of optical states
The spin-flip rate that couples dark and bright excitons in self-assembled
quantum dots is obtained from time-resolved spontaneous emission measurements
in a modified local density of optical states. Employing this technique, we can
separate effects due to non-radiative recombination and unambiguously record
the spin-flip rate. The dependence of the spin-flip rate on emission energy is
compared in detail to a recent model from the literature, where the spin flip
is due to the combined action of short-range exchange interaction and acoustic
phonons. We furthermore observe a surprising enhancement of the spin-flip rate
close to a semiconductor-air interface, which illustrates the important role of
interfaces for quantum dot based nanophotonic structures. Our work is an
important step towards a full understanding of the complex dynamics of quantum
dots in nanophotonic structures, such as photonic crystals, and dark excitons
are potentially useful for long-lived coherent storage applications.Comment: 5 pages, 4 figure
- …