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Ronen Rapaport

Publications and source records attributed to Ronen Rapaport.

At least 37 records · Page 2Linked to original sources
arXiv2018

Attractive dipolar coupling between stacked exciton fluids

The interaction between aligned dipoles is long-ranged and highly anisotropic: it changes from repulsive to attractive depending on the relative positions of the dipoles. We report on the observation of the attractive component of the dipolar coupling between excitonic dipoles in stacked semiconductor bilayers. We show that the presence of a dipolar exciton fluid in one bilayer modifies the spatial distribution and increases the binding energy of excitonic dipoles in a vertically remote layer. The binding energy changes are explained by a many-body polaron model describing the deformation of the exciton cloud due to its interaction with a remote dipolar exciton. The results open the way for the observation of theoretically predicted new and exotic collective phases, the realization of interacting dipolar lattices in semiconductor systems as well as for engineering and sensing their collective excitations.

cond-mat.quant-gas↗
arXiv2018

Fast and accurate functionalization of opaque conductive samples with single nano particles

Single quantum emitters coupled to different plasmonic and photonic structures are key elements for integrated quantum technologies. In order to fully exploit these elements, e.g. for quantum enhanced sensors or quantum repeaters, a reliable fabrication method as enabling technology is crucial. In this work, we present a method that allows for positioning of individual nano crystals containing single quantum light sources on non-transparent conductive samples with sub-micrometer precision. We induce long-range electrostatic forces between an atomic force microscope (AFM) tip, which carries a nano particle, and the target surface. This allows for mapping of the target area in non contact mode. Then, the placement site can be identified with high accuracy without any tip approach, eliminating the risk of a particle loss. We demonstrate the strength of the method by transferring a diamond nano crystal containing a single nitrogen-vacancy defect to the center of a micrometer-sized silver bullseye antenna with nanometer resolution. Our approach provides a simple and reliable assembling technology for positioning single nano objects on opaque substrates with high reproducibility and precision.

physics.optics↗
arXiv2018

Dynamical formation and interaction-induced stabilization of dark condensates of dipolar excitons

The formation of a dense Bose-Einstein condensate in dark spin states of two-dimensional dipolar excitons is shown to be driven by a dynamical transition to the long-lived dark states. The condensate is stabilized by strong dipole-dipole interactions up to densities high enough for a dark quantum liquid to form. The persistence of dark condensation was observed in recent experiments. A model describing the non-equilibrium dynamics of externally driven coupled dark and bright condensates reproduces the step-like dependence of the exciton density on the pump power or on temperature. This unique condensate dynamics demonstrates the possibility of observing new unexpected collective phenomena in coupled condensed Bose systems, where the particle number is not conserved.

cond-mat.quant-gas↗
arXiv2018

Strongly interacting dipolar-polaritons

Exciton-polaritons are mutually interacting quantum hybridizations of confined photons and electronic excitations. Here we demonstrate a system of optically guided, electrically polarized exciton-polaritons ('dipolaritons') that displays up to 200-fold enhancement of the polariton-polariton interaction strength compared to unpolarized polaritons. The magnitude of the dipolar interaction enhancement can be turned on and off and be easily tuned over a very wide range by varying the applied polarizing electric-field. The very large interaction strengths and the very long propagation distances of these fully-guided dipolaritons open up new opportunities for realizing complex quantum circuitry and quantum simulators, as well as topological states based on exciton-polaritons, for which the interactions between polaritons need to be large and spatially or temporally controlled. The results also raise fundamental questions on the origin of such large enhancements.

cond-mat.mes-hall↗
arXiv2017

Transition from spin-orbit to hyperfine dominated spin relaxation in a cold fluid of dipolar excitons

We measure the spin-resolved transport of dipolar excitons in a biased GaAs double quantum well structure. From these measurements we extract both spin lifetime and mobility of the excitons. We find that below a temperature of $4.8$K, there is a sharp increase in the spin lifetime of the excitons, together with a sharp reduction in their mobility. Below a critical power the spin lifetime increases with increasing mobility and density, while above the critical power the opposite trend is observed. We interpret this transition as an evidence of the interplay between two different spin dephasing mechanisms: at low mobility the dephasing is dominated by the hyperfine interaction with the lattice nuclei spins, while at higher mobility the spin-orbit interaction dominates, and a Dyakonov-Perel spin relaxation takes over. The excitation power and temperature regime where the hyperfine interaction induced spin dephasing is observed correlates with the regime where a dark dipolar quantum liquid was reported recently on a similar sample.

cond-mat.quant-gas↗
arXiv2017

Quantum emitters coupled to circular nanoantennas for high brightness quantum light sources

Engineering the directionality and emission rate of quantum light sources is essential in the development of modern quantum applications.In this work we use numerical calculations to optimize the brightness of a broadband quantum emitter positioned in a hybrid metal-dielectric circular periodic nanoantenna. The optimized structure features a photon collection efficiency of 74% (82%) and a photon flux enhancement of over 10 (6) into a numerical aperature of 0.22 (0.50) respectively, corresponding to a direct coupling into two types of multimode fibers. In order to enhance the emission rate, we present a new circular nanoantenna design where a quantum emitter is attached to a silver nanocone at the center of the antenna. After optimization, we find a collection efficiency of 61% (78%) into a numerical aperature of 0.22 (0.50), giving a brightness enhancement of 1000 (600) for an unpolarized emitter. The enhancements in both structures are broadband due to the low quality factor of the device and are therefore ideal for room-temperature sources. This type of a scalable design can be utilized towards on-chip, high brightness quantum light sources operating at room temperature.

physics.optics↗
arXiv2017

Condensation to a strongly correlated dark fluid of two dimensional dipolar excitons

Recently we reported on the condensation of cold, electrostatically trapped dipolar excitons in GaAs bilayer heterostructure into a new, dense and dark collective phase. Here we analyze and discuss in detail the experimental findings and the emerging evident properties of this collective liquid-like phase. We show that the phase transition is characterized by a sharp increase of the number of non-emitting dipoles, by a clear contraction of the fluid spatial extent into the bottom of the parabolic-like trap, and by spectral narrowing. We extract the total density of the condensed phase which we find to be consistent with the expected density regime of a quantum liquid. We show that there are clear critical temperature and excitation power onsets for the phase transition and that as the power further increases above the critical power, the strong darkening is reduced down until no clear darkening is observed. At this point another transition appears which we interpret as a transition to a strongly repulsive yet correlated $e$-$h$ plasma. Based on the experimental findings, we suggest that the physical mechanism that may be responsible for the transition is a dynamical final-state stimulation of the dipolar excitons to their dark spin states, which have a long lifetime and thus support the observed sharp increase in density. Further experiments and modeling will hopefully be able to unambiguously identify the physical mechanism behind these recent observations.

cond-mat.quant-gas↗
arXiv2016

Radiative lifetimes of dipolar excitons in double quantum-wells

Spatially indirect excitons in semiconducting double quantum wells have been shown to exhibit rich collective many-body behavior that result from the nature of the extended dipole-dipole interactions between particles. For many spectroscopic studies of the emission from a system of such indirect excitons, it is crucial to separate the single particle properties of the excitons from the many-body effects arising from their mutual interactions. In particular, knowledge of the relation between the emission energy of indirect excitons and their radiative lifetime could be highly beneficial for control, manipulation, and analysis of such systems. Here we study a simple analytic approximate relation between the radiative lifetime of indirect excitons and their emission energy. We show, both numerically and experimentally, the validity and the limits of this approximate relation. This relation between the emission energy and the lifetime of indirect excitons can be used to tune and determine their lifetime and their resulting dynamics without the need of directly measuring it, and as a tool for design of indirect exciton based devices.

cond-mat.quant-gas↗
arXiv2016

Electrically controlled mutual interactions of flying waveguide dipolaritons

We show that with a system of electrically-gated wide quantum wells embedded inside a simple dielectric waveguide structure, it is possible to excite, control, and observe waveguided exciton polaritons that carry an electric dipole moment. We demonstrate that the energy of the propagating dipolariton can be easily tuned using local electrical gates, that their excitation and extraction can be easily done using simple evaporated metal gratings, and that the dipolar interactions between polaritons and between polaritons and excitons can also be controlled by the applied electric fields. This system of gated flying dipolaritons thus exhibit the ability to locally control both the single polariton properties as well as the interactions between polaritons, which should open up opportunities for constructing complex polaritonic circuits and for studying strongly-interacting, correlated polariton gases.

cond-mat.quant-gas↗
arXiv2016

A dark incompressible dipolar liquid of excitons

The possible phases and the nano-scale particle correlations of two-dimensional interacting dipolar particles is a long-sought problem in many-body physics. Here we observe a spontaneous condensation of trapped two-dimensional dipolar excitons with internal spin degrees of freedom from an interacting gas into a high density, closely packed liquid state made mostly of dark dipoles. Another phase transition, into a bright, highly repulsive plasma is observed at even higher excitation powers. The dark liquid state is formed below a critical temperature $T_c \approx 4.8K$, and it is manifested by a clear spontaneous spatial condensation to a smaller and denser cloud, suggesting an attractive part to the interaction which goes beyond the purely repulsive dipole-dipole forces. Contributions from quantum mechanical fluctuations are expected to be significant in this strongly correlated, long living dark liquid. This is a new example of a two-dimensional atomic-like interacting dipolar quantum liquid, but where the coupling of light to its internal spin degrees of freedom plays a crucial role in the dynamical formation and the nature of resulting ground state.

cond-mat.quant-gas↗
arXiv2016

Vertically-coupled dipolar exciton molecules

While the interaction potential between two dipoles residing in a single plane is repulsive, in a system of two vertically adjacent layers of dipoles it changes from repulsive interaction in the long range to attractive interaction in the short range. Here we show that for dipolar excitons in semiconductor heterostructures, such a potential may give rise to bound states if two such excitons are excited in two separate layers, leading to the formation of vertically coupled dipolar exciton molecules. Our calculations prove the existence of such bound states and predict their binding energy as a function of the layers separation as well as their thermal distributions. We show that these molecules should be observed in realistic systems such as semiconductor coupled quantum well structures and the more recent van-der-Waals bound heterostructures. Formation of such molecules can lead to new effects such as a collective dipolar drag between layers and new forms of multi-particle correlations, as well as to the study of dipolar molecular dynamics in a controlled system.

cond-mat.quant-gas↗
arXiv2015

Purcell-enhanced optical spin readout of Nitrogen-Vacancy centers in diamond

Nitrogen-Vacancy (NV) color centers in diamond have emerged as promising quantum solid-state systems, with applications ranging from quantum information processing to magnetic sensing. One of the most useful properties of NVs is the ability to read their ground-state spin projection optically at room temperature. This work provides a theoretical analysis of Purcell enhanced NV optical coupling, through which we find optimal parameters for maximal Signal to Noise Ratio (SNR) of the optical spin-state readout. We conclude that a combined increase in spontaneous emission (through Purcell enhancement) and in optical excitation could significantly increase the readout SNR.

quant-ph↗
arXiv2013

Scalable interconnections for remote exciton systems

Excitons, quasi-particles consisting of electron-hole pairs bound by the Coulomb interaction, are a potential medium for processing of photonic information in the solid-state. Information processing via excitons requires efficient techniques for the transport and manipulation of these uncharged particles. We introduce here a novel concept for the interconnection of multiple remote exciton systems based on the long-range transport of dipolar excitons by a network of configurable interconnects driven by acoustic wave beams. By combining this network with electrostatic gates, we demonstrate an integrated exciton multiplexer capable of interconnecting, gating and routing exciton systems separated by millimeter distances. The multiplexer provides a scalable platform for the manipulation of exciton fluids with potential applications in information processing.

cond-mat.mes-hall↗
arXiv2013

Dynamics of indirect exciton transport by moving acoustic fields

We report on the modulation of indirect excitons (IXs) as well as their transport by moving periodic potentials produced by surface acoustic waves (SAWs). The potential modulation induced by the SAW strain modifies both the band gap and the electrostatic field in the quantum wells confining the IX, leading to changes in their energy. In addition, this potential capture and transports IXs over several hundreds of μm. While the IX packets keep to a great extent their spatial shape during transport by the moving potential, the effective transport velocity is lower than the SAW group velocity and increases with the SAW amplitude. This behavior is attributed to the capture of IXs by traps along the transport path, thereby increasing the IX transit time. The experimental results are well-reproduced by an analytical model for the interaction between trapping centers and IXs during transport.

cond-mat.mes-hall↗
arXiv2013

Particle correlations and evidence for dark state condensation in a cold dipolar exciton fluid

In this paper we show experimental evidence of a few correlation regimes of a cold dipolar exciton fluid, created optically in a semiconductor bilayer heterostructure. In the higher temperature regime, the average interaction energy between the particles shows a surprising temperature dependence which is an evidence for correlations beyond the mean field model. At a lower temperature, there is a sharp increase in the interaction energy of optically active excitons, accompanied by a strong reduction in their apparent population. This is an evidence for a sharp macroscopic transition to a dark state as was suggested theoretically.

cond-mat.quant-gas↗
arXiv2011

Remote Dipolar Interactions for Objective Density Calibration and Flow Control of Excitonic Fluids

In this paper we suggest a method to observe remote interactions of spatially separated dipolar quantum fluids, and in particular of dipolar excitons in GaAs bilayer based devices. The method utilizes the static electric dipole moment of trapped dipolar fluids to induce a local potential change on spatially separated test dipoles. We show that such an interaction can be used for a model- independent, objective fluid density measurements, an outstanding problem in this field of research, as well as for inter-fluid exciton flow control and trapping. For a demonstration of the effects on realistic devices, we use a full two-dimensional hydrodynamical model.

cond-mat.mes-hall↗
arXiv2010

Enhancement of two photon processes in quantum dots embedded in subwavelength metallic gratings

We show a large enhancement of two-photon absorption processes in nanocrystal quantum dots and of light upconversion efficiency from the IR to the near-IR spectral regime, using a hybrid optical device in which near-IR emitting InAs quantum dots were embedded on top a metallic nanoslit array. The resonant enhancement of these nonlinear optical processes is due to the strong local electromagnetic field enhancements inside the nanoslit array structure at the extraordinary transmission resonances. A maximal two-photon absorption enhancement of more than 20 was inferred. Different high field regions were identified for different polarizations, which can be used for designing and optimizing efficient nonlinear processes in such hybrid structures. Combining nanocrystal quantum dots with subwavelength metallic nanostructures is therfore a promising way for a range of possible nonlinear optical devices.

physics.optics↗