Silicon photonics is a promising platform for integrating various optical components on a single chip. However, one of the major challenges is to develop efficient and compact light sources due to the poor light emission efficiency of silicon. Semiconducting transition metal dichalcogenide (TMD) shows great potential to address this issue by efficient band engineering with stacking of different TMD monolayers. In this work, we observe the bright-light emission from TMD heterobilayers (MoS2/WSe2), where interlayer excitons dominate the optical properties of materials even at room temperature. Through integrating the heterobilayers with silicon topological cavities, we observe a dominant single emission mode around 1230 nm that is outcoupled to an on-chip waveguide. Our work demonstrates a new architecture for realizing silicon photonic chip-scale integrated light sources at room temperature.
Strong field gradients in electromagnetic resonators can trap individual nanospheres. Moreover, the presence of the sphere in the resonator can give rise to self-induced back-action (SIBA), which increases the trap stiffness beyond standard dipolar force theory. In this work, we investigate SIBA in a system with a silica sphere of 16 nm in diameter in a dielectric nanocavity with a strongly localized electric field. We analyze the optical forces in a novel framework based on perturbation theory with quasi-normal modes, where modifications to the gradient and scattering forces are found to arise due to the presence of the particle, thus capturing the back-action effect. This gives closed-form expressions with clear insight into the mechanism of SIBA, and provides an efficient method of estimating optical forces when SIBA is present. We compare the results with reference calculations based on the Maxwell Stress Tensor formalism and find good agreement.
We investigate coherent perfect absorption (CPA) of squeezed coherent states of light by an absorbing beam splitter. First we derive the absorption coefficients for quantum coherence and for intensity, which generally differ. Secondly, we present the remarkable properties of a CPA-gate: two identical but otherwise arbitrary incoming squeezed coherent states can be completely stripped off their coherence, producing a pure entangled squeezed vacuum state at the output. Importantly, this output state of light is not entangled with the absorbing beam splitter by which it was produced. This makes the CPA gate potentially interesting for continuous-variable quantum state preparation.
Traditionally, the active material in a laser is modelled as independent emitters, but in recent years it has become increasingly clear that radiative coupling between emitters can significantly change the characteristics of small lasers. Collective effects in free space such as superradiance have been studied extensively [1,2], but the effects of inter-emitter correlation in micro- and nano-cavities need further examination to be put on firm theoretical ground. Several studies of collective effects in nano-cavities have been made [3-6], but the theoretical models employed are intricate, and numerical methods are needed both to generate the dynamic equations and to solve them. We propose a model where the complexity is strongly reduced, allowing analytical solutions [7].
We consider a collection of identical two-level emitters interacting with a single cavity mode. We start from Maxwell-Bloch equations, but instead of making the typical adiabatic elimination of the polarization, we allow the polarization decay rate to be of the same magnitude or smaller than other decay rates. Hence, the traditional laser rate equations for the photon number and the population inversion must be supplemented by equations for the emitter-field correlation and the emitter-emitter correlation. This gives us four generalized laser rate equations, which we solve analytically in steady state.
Comparing with the steady state results obtained from the traditional laser rate equations we see that inclusion of collective effects leads to a reduction of the photon number for small pump rates, similarly to what is found in [4]. From the generalized laser rate equations, we derive a measure of the strength of collective effects in terms of laser parameters: This describes the difference between results with and without inter-emitter correlations, and it goes smoothly to zero as we approach parameter values where the traditional laser rate equations become valid.
To gain insight into the photon statistics of the laser, we construct dynamic equations for higher order correlations of operators. We derive an analytical expression for the zero-delay photon auto-correlation function, and for low pump rates we find that the interaction of emitters results in super-thermal values of the auto-correlation. This feature is observed in experiments and numerical models [4-5], and with our analytical expressions, we are able to pinpoint the parameter combinations for which the collective effects have the largest impact.
Considering the same model in terms of the Fourier components of the operators, we find results for the photon number that agree well with the previous approach, while allowing computation of the linewidth. Thus, we can examine how emitter-emitter correlation affects the line broadening of the laser.
While typically designed to manipulate classical light, metamaterials have many potential applications for quantum optics as well. We argue why a quantum optical effective-medium theory is needed. We present such a theory for layered metamaterials that is valid for light propagation in all spatial directions, thereby generalizing earlier work for one-dimensional propagation. In contrast to classical effective-medium theory there is an additional effective parameter that describes quantum noise. Our results for metamaterials are based on a rather general Lagrangian theory for the quantum electrodynamics of media with both loss and gain. In the second part of this paper, we present a new application of transformation optics whereby local spontaneous-emission rates of quantum emitters can be designed. This follows from an analysis how electromagnetic Green functions trans- form under coordinate transformations. Spontaneous-emission rates can be either enhanced or suppressed using invisibility cloaks or gradient index lenses. Furthermore, the anisotropic material profile of the cloak enables the directional control of spontaneous emission.
KEYWORDS: Metamaterials, Quantum optics, Quantum physics, Lab on a chip, Dielectrics, Metals, Near field optics, Near field, Homodyne detection, Multilayers
A well-known challenge for fabricating metamaterials is to make unit cells significantly smaller than the operating
wavelength of light, so one can be sure that effective-medium theories apply. But do they apply? Here we show
that nonlocal response in the metal constituents of the metamaterial leads to modified effective parameters
for strongly subwavelength unit cells. For infinite hyperbolic metamaterials, nonlocal response gives a very
large finite upper bound to the optical density of states that otherwise would diverge. Moreover, for finite
hyperbolic metamaterials we show that nonlocal response affects their operation as superlenses, and interestingly
that sometimes nonlocal theory predicts the better imaging. Finally, we discuss how to describe metamaterials
effectively in quantum optics. Media with loss or gain have associated quantum noise, and the question is whether
the effective index is enough to describe this quantum noise effectively. We show that this is true for passive
metamaterials, but not for metamaterials where loss is compensated by linear gain. For such loss-compensated
metamaterials we present a quantum optical effective medium theory with an effective noise photon distribution
as an additional parameter. Interestingly, we find that at the operating frequency, metamaterials with the same
effective index but with different amounts of loss compensation can be told apart in quantum optics.
Metamaterials with a hyperbolic dispersion curve, called hyperbolic metamaterials, exhibit an amazing broad-band singularity in the photonic density of states in the usual local-response approximation. In this paper, under
the framework of the hydrodynamic Drude model, we discuss the effects of the nonlocal response of the electron
gas in the metal on the hyperbolic metamaterials. By using mean field theory, we derive the effective material
parameters of the hyperbolic metamaterials. The original unbounded hyperbolic dispersion is found to be cut off
at the wavevector inverse to the Fermi velocity. By expanding the Green function in a plane-wave basis and using
the transfer matrix method to calculate the reflection coefficients, we study the local density of states (LDOS)
of hyperbolic metamaterials. We show that the nonlocal response of the electron gas in the metal removes the
singularity of both radiative and non-radiative local density of states, and also sets up a finite maximal value.
We also briefly discuss the effects of the nonlocal response on other plasmonic structures, such as a metallic
semi-infinite substrate and a metallic slab.
In tiny metallic nanostructures, quantum confinement and nonlocal response change the collective plasmonic
behaviour with resulting important consequences for e.g. field-enhancement and extinction cross sections. Here
we report on nonlocal resonances in the hydrodynamical Drude model for plasmonic nanostructures that have
no counterpart in the local-response Drude model. Even though there are no additional resonances in the visible
due to nonlocal response, plasmonic field enhancements are affected by nonlocal response. We present both
analytical results for simple geometries and our numerical implementation for arbitrary geometries, and address
computational issues related to the several length scales involved.
We point out an apparently overlooked consequence of the boundary conditions obeyed by the electric displacement vector at air-metal interfaces: the continuity of the normal component combined with the quantum mechanical penetration of the electron gas in the air implies the existence of a surface on which the dielectric function vanishes. This, in turn, leads to an enhancement of the normal component of the total electric field. We study this effect for a planar metal surface, with the inhomogeneous electron density accounted for by a Jellium model. We also illustrate the effect for equilateral triangular nanoislands via numerical solutions of the appropriate Maxwell equations, and show that the field enhancement is several orders of magnitude larger than what the conventional theory predicts.
We study the importance of taking the nonlocal optical response of metals into account for accurate determination
of optical properties of nanoplasmonic structures. Here we focus on the computational physics aspects of this
problem, and in particular we report on the nonlocal-response package that we wrote for state-of the art numerical
software, enabling us to take into account the nonlocal material response of metals for any arbitrarily shaped
nanoplasmonic structures, without much numerical overhead as compared to the standard local response. Our
method is a frequency-domain method, and hence it is sensitive to possible narrow resonances that may arise
due to strong electronic quantum confinement in the metal. This feature allows us to accurately determine which
geometries are strongly affected by nonlocal response, for example regarding applications based on electric field
enhancement properties for which metal nanostructures are widely used.
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