arXiv subjects

Ronen Rapaport

Publications and source records attributed to Ronen Rapaport.

At least 19 recordsLinked to original sources

arXiv2025

Quadrupolar and dipolar phases of excitons in transition-metal dichalcogenide trilayer heterostructures

Recent experiments on trilayer transition-metal dichalcogenide heterostructures have revealed the rich behavior of dipolar excitons. Motivated by these experimental observations, we investigate the collective dynamics of planar quantum dipoles whose orientation fluctuates due to charge tunneling between the outer layers. Using large-scale quantum Monte Carlo simulations, we map out the low-temperature phase diagram as a function of experimentally tunable parameters. We uncover a diverse landscape of phases driven by dipolar correlations. Under strong dipole fluctuations, a quadrupolar superfluid emerges. Suppressing charge tunneling nucleates a droplet state stabilized by the attractive interaction between antiparallel dipoles. At high exciton densities, the system gives way to a partially fragmented condensate, characterized by competing quadrupolar and dipolar superfluid states. Furthermore, at a large exciton mass and high density, we find a staggered dipolar crystal. Our detailed study of the dependence of exciton energy shifts on an external electric field directly interprets existing experimental data and underscores the crucial role of the antiparallel dipolar configuration. Our results provide a guide for future experimental explorations of quantum phases of trilayer excitons.

cond-mat.mes-hall↗

arXiv2025

Approaching Unity Photon Collection from NV Centers via Ultra-Precise Positioning of Nanodiamonds in Hybrid Nanoantennas

Efficient readout of nitrogen-vacancy (NV) centers in diamond is crucial for various quantum information technologies. However, achieving high-fidelity, single-shot readout at room temperature remains challenging due to limited photon collection efficiency (CE) and background noise. In this work, we enhance the readout efficiency of NV centers by integrating them into hybrid metal-dielectric bullseye nanoantennas using ultra-precise deterministic positioning. This approach enables highly directional emission while minimizing optical losses, resulting in a measured CE of 82\% into a numerical aperture (NA) as low as 0.5, and approaching unity for NA$>$0.8. This marks a substantial improvement over previous realizations using nanodiamonds, highlighting the advantage of combining hybrid nanoantennas with precise positioning. Our results mark a substantial advancement towards efficient single-shot readout of NV centers by significantly improving readout fidelity and efficiency in a simple on-chip configuration.

physics.optics↗

arXiv2025

Ultrafast electrical control of dipolariton-based optical circuits with a few femto-joul per bit power consumption

The next generation of photonic circuits will require programmable, ultrafast, and energy-efficient components on a scalable platform for quantum and neuromorphic computing. Here, we present ultrafast electrical control of highly nonlinear light-matter hybrid quasi-particles, called waveguide exciton-dipolaritons, with extremely low power consumption. Our device performs as an optical transistor with a GHz-rate electrical modulation at a record-low total energy consumption $\sim$3 fJ/bit and a compact active area of down to 25 $\mu$m$^2$. This work establishes waveguide-dipolariton platforms for scalable, electrically reconfigurable, ultra-low power photonic circuits for both classical and quantum computing and communication.

physics.optics↗

arXiv2024

Electrically tunable quantum correlations of dipolar polaritons with micrometer-scale blockade radii

An extreme yet reconfigurable nonlinear response to a single photon by a photonic system is crucial for realizing a universal two-photon gate, an elementary building block for photonic quantum computing. Yet such a response, characterized by the photon blockade effect, has only been achieved in atomic systems or solid states ones that are difficult to scale up. Here we demonstrate electrically tunable partial photon blockade in dipolar waveguide polaritons on a semiconductor chip, measured via photon-correlations. Remarkably, these "dipolar photons" display a two-orders-of-magnitude stronger nonlinearity compared to unpolarized polaritons, with an extracted dipolar blockade radius up to more than 4 $\mu$m, significantly larger than the optical wavelength, and comparable to that of atomic Rydberg polaritons. Furthermore, we show that the dipolar interaction can be electrically switched and locally configured by simply tuning the gate voltage. Finally we show that with a simple modification of the design, a full photon blockade is expected, setting a new route towards scalable, reconfigurable, chip-integrated quantum photonic circuits with strong two-photon nonlinearities.

quant-ph↗

arXiv2024

Decoy state and purification protocols for superior quantum key distribution with imperfect quantum-dot based single photon sources: Theory and Experiment

The original proposal of quantum key distribution (QKD) was based on ideal single photon sources, which 40 years later, are still challenging to develop. Therefore, the development of decoy state protocols using weak coherent states (WCS) from lasers, set the frontier in terms of secure key rates and distances. Here, we propose and experimentally demonstrate two simple-to-implement QKD protocols that allow practical, far from ideal sub-Poissonian photon sources to outperform state-of-the-art WCS. By engineering the photon statistics of a biexciton-exciton cascade in room temperature single photon sources based on giant colloidal quantum dots coupled to nanoantennas, we show that either a truncated decoy state protocol or a heralded purification protocol can be employed to achieve a significantly increased performance in terms of the maximal allowed channel loss for secure key creation, which can exceed even that of ideal WCS by more than 3dB. We then experimentally emulate a BB84 QKD using such a quantum dot source, verifying the superiority of our protocols over the best possible BB84 WCS performance. These protocols can be utilized efficiently on a host of various quantum emitters having controllable photon statistics with a finite photon-number basis, offering a practical approach to QKD without the hindering requirements on the single photon purity of the photon source.

quant-ph↗

arXiv2024

High-dimensional quantum key distribution using orbital angular momentum of single photons from a colloidal quantum dot at room temperature

High-dimensional quantum key distribution (HDQKD) is a promising avenue to address the inherent limitations of basic QKD protocols. However, experimental realizations of HDQKD to date have relied on indeterministic photon sources that limit the achievable key rate. In this paper, we demonstrate a full emulation of a HDQKD system using a single colloidal giant quantum dot (gQD) as a deterministic, compact and room-temperature single-photon source (SPS). We demonstrate a practical protocol by encoding information in a high-dimensional space ($d = 3$) of the orbital angular momentum of the photons. Our experimental configuration incorporates two spatial light modulators for encoding and decoding the spatial information carried by individual photons. Our experimental demonstration establishes the feasibility of utilizing high radiative quantum yield gQDs as practical SPSs for HDQKD. We also demonstrate experimentally secure qudit transmission exceeding one secure bit per photon, thus already beating the traditional d=2 QKD capacity.

quant-ph↗

arXiv2024

Ultrafast and highly collimated radially polarized photons from a colloidal quantum dot in a hybrid nanoantenna at room-temperature

To harness the potential of radially polarized single photons in applications such as high-dimensional quantum key distribution (HD-QKD) and quantum communication, we demonstrate an on-chip, room-temperature device, which generates highly directional radially polarized photons at very high rates. The photons are emitted from a giant CdSe/CdS colloidal quantum dot (gQD) accurately positioned at the tip of a metal nanocone centered inside a hybrid metal-dielectric bullseye antenna. We show that due to the large and selective Purcell enhancement specifically for the out-of-plane optical dipole of the gQD, the emitted photons can have a very high degree of radial polarization (>93%), based on a quantitative metric. Our study emphasizes the importance of accurate gQD positioning for optimal radial polarization purity through extensive experiments and simulations, which contribute to the fundamental understanding of radial polarization in nanostructured devices and pave the way for implementation of such systems in practical applications using structured quantum light.

physics.optics↗

arXiv2023

Electrically controlled photonic circuits of field-induced dipolaritons with huge nonlinearities

Electrically controlled photonic circuits hold promise for information technologies with greatly improved energy efficiency and quantum information processing capabilities. However, weak nonlinearity and electrical response of typical photonic materials have been two critical challenges. Therefore hybrid electronic-photonic systems, such as semiconductor exciton-polaritons, have been intensely investigated for their potential to allow higher nonlinearity and electrical control, with limited success so far. Here we demonstrate an electrically-gated waveguide architecture for dipolar-polaritons that allows enhanced and electrically-controllable polariton nonlinearities, enabling an electrically-tuned reflecting switch (mirror) and transistor of the dipolar-polaritons. The polariton transistor displays blockade and anti-blockade by compressing a dilute dipolar-polariton pulse exhibiting very strong dipolar interactions. The large nonlinearities are explained using a simple density-dependent polarization field that very effectively screens the external electric field, with an order of magnitude enhancement of the nonlinearities as compared to fixed dipoles. We project that a quantum blockade at the single polariton level is feasible in such a device.

physics.optics↗

arXiv2023

Room Temperature Fiber-Coupled single-photon devices based on Colloidal Quantum Dots and SiV centers in Back Excited Nanoantennas

We demonstrate an important step towards on chip integration of single photon sources operating at room temperature fiber coupling of a directional quantum emitter with back-excitation. Directionality is achieved with a hybrid metal-dielectric bullseye antenna, while back-excitation is permitted by placement of the emitter at or in a sub-wavelength hole positioned at the bullseye center. Overall, the unique design enables a direct laser excitation from the back of the on-chip device and very efficient coupling of the highly collimated photon emission to either low numerical aperture (NA) free space optics or directly to an optical fiber from the front. To show the versatility of the concept, we fabricate devices containing either a colloidal quantum dot or a silicon-vacancy center containing nanodiamond, which are accurately coupled to the nano-antenna using two different nano-positioning methods. Both back-excited devices display front collection efficiencies of about 70 % at NAs as low as 0.5. Moreover, the combination of back-excitation with forward low-NA directionality enables direct coupling of the emitted photons into a proximal optical fiber without the need of any coupling optics, thereby facilitating and greatly simplifying future integration.

physics.optics↗

arXiv2022

Thickness mapping and layer number identification of exfoliated van der Waals materials by Fourier imaging micro-ellipsometry

As properties of mono- to few layers of exfoliated van der Waals heterostructures are heavily dependent on their thicknesses, accurate thickness measurement becomes imperative in their study. Commonly used atomic force microscopy and Raman spectroscopy techniques may be invasive and produce inconclusive results. Alternatively, spectroscopic ellipsometry is limited by tens-of-microns lateral resolution and/or low data acquisition rates, inhibiting its utilization for micro-scale exfoliated flakes. In this work, we demonstrate a Fourier imaging spectroscopic micro-ellipsometer with sub-5 microns lateral resolution along with fast data acquisition rate and present angstrom-level accurate and consistent thickness mapping on mono-, bi- and trilayers of graphene, hexagonal boron nitride and transition metal dichalcogenide (MoS2, WS2, MoSe2, WSe2) flakes. We show that the optical microscope integrated ellipsometer can also map minute thickness variations over a micro-scale flake. In addition, our system addresses the pertinent issue of identifying monolayer thick hBN.

physics.optics↗

arXiv2022

Mapping single-shot angle-resolved spectroscopic micro-ellipsometry with sub-5 microns lateral resolution

Spectroscopic ellipsometry is a widely used optical technique both in industry and research for determining the optical properties and thickness of thin films. The effective use of spectroscopic ellipsometry on micro-structures is inhibited by technical limitations on lateral resolution and data acquisition rate. Here we introduce a spectroscopic micro-ellipsometer (SME), capable of measuring spectrally resolved ellipsometric data at many angles of incidence in a single-shot with a lateral resolution down to 2 microns. The SME can be easily integrated into generic optical microscopes by addition of a few stock optics. We demonstrate complex refractive index and thickness measurements by the SME which are in excellent agreement with a commercial spectroscopic ellipsometer. As an application for its accuracy and high lateral resolution, the SME can characterize the optical properties and number of layers of exfoliated transition-metal dichalcogenides and graphene, for structures that are a few microns in size.

physics.optics↗

arXiv2022

Collective interlayer pairing and pair superfluidity in vertically stacked layers of dipolar excitons

Layered bosonic dipolar fluids have been suggested to host a condensate of interlayer molecular bound states. However, its experimental observation has remained elusive. Motivated by two recent experimental works [Hubert et al., Phys. Rev. X 9, 021026 (2019) and D. J. Choksy et al., Phys. Rev. B 103 045126 (2021)], we theoretically study, using numerically exact quantum Monte Carlo calculations, the experimental signatures of collective interlayer pairing in vertically stacked indirect exciton (IX) layers. We find that IX energy shifts associated with each layer evolve non trivially as a function of density imbalance following a nonmonotonic trend with a jump discontinuity at density balance, identified with the interlayer IX molecule gap. This behavior discriminates between the superfluidity of interlayer bound pairs and independent dipole condensation in distinct layers. Considering finite temperature and finite density imbalance conditions, we find a cascade of Berezinskii--Kosterlitz--Thouless (BKT) transitions, initially into a pair superfluid and only then, at lower temperatures, into complete superfluidity of both layers. Our results may provide a theoretical interpretation of existing experimental observations in GaAs double quantum well (DQW) bilayer structures. Furthermore, to optimize the visibility of pairing dynamics in future studies, we present an analysis suggesting realistic experimental settings in GaAs and transition metal dichalcogenide (TMD) bilayer DQW heterostructures where collective interlayer pairing and pair superfluidity can be clearly observed.

cond-mat.mes-hall↗

arXiv2021

A Robust Coherent Single-Photon Interface for Moderate- NA Optics Based on SiV Center in Nanodiamonds and a Plasmonic Bullseye Antenna

Coherent exchange of single photons is at the heart of applied Quantum Optics. The negatively-charged silicon vacancy center in diamond is among most promising sources for coherent single photons. Its large Debye-Waller factor, short lifetime and extraordinary spectral stability is unique in the field of solid-state single photon sources. However, the excitation and detection of individual centers requires high numerical aperture optics which, combined with the need for cryogenic temperatures, puts technical overhead on experimental realizations. Here, we investigate a hybrid quantum photonics platform based on silicon-vacancy center in nanodiamonds and metallic bullseye antenna to realize a coherent single-photon interface that operates efficiently down to low numerical aperture optics with an inherent resistance to misalignment.

physics.optics↗

arXiv2021

Single Photon Sources with Near Unity Collection Efficiencies by Deterministic Placement of Quantum Dots in Nanoantennas

Deterministic coupling between photonic nodes in a quantum network is an essential step towards implementing various quantum technologies. The omnidirectionality of free-standing emitters, however, makes this coupling highly inefficient, in particular if the distant nodes are coupled via low numerical aperture (NA) channels such as optical fibers. This limitation requires placing quantum emitters in nanoantennas that can direct the photons into the channels with very high efficiency. Moreover, to be able to scale such technologies to a large number of channels, the placing of the emitters should be deterministic. In this work we present a method for directly locating single free-standing quantum emitters with high spatial accuracy at the center of highly directional bullseye metal-dielectric nanoantennas. We further employ non-blinking, high quantum yield colloidal quantum dots (QDs) for on-demand single-photon emission that is uncompromised by instabilities or non-radiative exciton recombination processes. Taken together this approach results in a record-high collection efficiency of 85% of the single photons into a low NA of 0.5, setting the stage for efficient coupling between on-chip, room temperature nanoantenna-emitter devices and a fiber or a remote free-space node without the need for additional optics.

quant-ph↗

arXiv2020

Overcoming the rate-directionality tradeoff: a room-temperature ultrabright quantum light source

Deterministic GHz-rate single photon sources at room-temperature would be essential components for various quantum applications. However, both the slow intrinsic decay rate and the omnidirectional emission of typical quantum emitters are two obstacles towards achieving such a goal which are hard to overcome simultaneously. Here we solve this challenge by a hybrid approach, using a complex monolithic photonic resonator constructed of a gold nanocone responsible for the rate enhancement, and a circular Bragg antenna for emission directionality. A repeatable process accurately binds quantum dots to the tip of the antenna-embedded nanocone. As a result we achieve simultaneous 20-fold emission rate enhancement and record-high directionality leading to an increase in the observed brightness by a factor as large as 580 (120) into an NA = 0.22 (0.5). We project that such miniaturized on-chip devices can reach photon rates approaching 2.3*10^8 single photons/second thus enabling ultra-fast light-matter interfaces for quantum technologies at ambient conditions.

quant-ph↗

arXiv2020

Quantum phase transitions of tri-layer excitons in atomically thin heterostructures

We determine the zero temeperature phase diagram of excitons in the symmetric transition-metal dichalcogenide tri-layer heterosctructure WSe2/MoSe2/WSe2. First principle calculations reveal two distinct types of interlayer excitonic states, a lower energy symmetric quadrupole and a higher energy asymmetric dipole. While interaction between quadrupolar excitons is always repulsive, anti-parallel dipolar excitons attract at large distances. We find quantum phase transitions between a repulsive quadrupole lattice phase and a staggered (anti-parallel) dipolar lattice phase, driven by the competition between the exciton-exciton interactions and the single exciton energies. Remarkably, the intrinsic nature of each interlayer exciton is completely different in each phase. This is a striking example for the possible rich quantum physics in a system where the single particle properties and the many-body state are dynamically coupled through the particle interactions.

cond-mat.mtrl-sci↗

arXiv2018

Purification of single photons by temporal heralding of quantum dot sources

Efficient, high rate photon sources with high single photon purity are essential ingredients for quantum technologies. Single photon sources based on solid state emitters such as quantum dots are very advantageous for integrated photonic circuits, but they can suffer from a high two-photon emission probability, which in cases of non-cryogenic environment cannot be spectrally filtered. Here we propose two temporal purification-by-heralding methods for using a two photon emission process to yield highly pure and efficient single photon emission, bypassing the inherent problem of spectrally overlapping bi-photon emission. We experimentally demonstrate their feasibility on the emission from a single nanocrystal quantum dot, exhibiting single photon purities exceeding 99.5%, without a significant loss of single photon efficiency. These methods can be applied for any indeterministic source of spectrally broadband photon pairs.

quant-ph↗

arXiv2018

Fully guided electrically-controlled exciton polaritons

We demonstrate two types of waveguide structures which optically confine exciton- polaritons in two dimensions and act as polaritonic channels. We show a strong optical confinement in an etched rectangular waveguide, that significantly increases the propa- gation distance of the polaritons and allow to direct them in curved trajectories. Also, we show low-loss optical guiding over a record-high of hundreds of microns which is com- bined seamlessly with electrical control of the polaritons, in a strip waveguide formed by electrically conductive and optically transparent strips deposited on top of a planar waveguide. Both structures are scalable and easy to fabricate and offer new possibilities for designing complex polaritonic devices.

cond-mat.mes-hall↗