arXiv subjects

Saimon Filipe Covre da Silva

Publications and source records attributed to Saimon Filipe Covre da Silva.

At least 19 recordsLinked to original sources

arXiv2026

Towards Stirling cooler operable single-photon sources based on low-noise GaAs quantum dots

For photonic quantum technology applications, sources capable of emitting photons with indistinguishability close to unity are essential. Ideally, these sources should not require demanding cooling systems. Here, we present temperature-dependent two-photon-interference measurements on photons produced by the radiative decay of the negative trion in a low-noise GaAs quantum dot, which are in quantitative agreement with theoretical calculations accounting for carrier-phonon interactions and coupling to excited states. While at at the lowest explored temperatures the emission linewidth reaches values only 6(2) % above the Fourier limit and the indistinguishability I between subsequently emitted photons reaches 0.966(6), the latter drops to 0.05(4) at 55 K. We show that this loss can be explained with the coupling with energetically close excited trion states and suggest that the photon indistinguishability at elevated temperatures can be increased by employing Purcell enhancement of the emission rate or by increasing the energy separation of the excited states. Using cavity-enhanced emission, we experimentally verify the first route and demonstrate an improvement in photon indistinguishability from 0.314(25) to 0.80(3) at 32 K, which - to our knowledge - is the highest reported value at such temperature.

quant-ph↗

arXiv2026

Planar metal-semiconductor Yagi-Uda type antennas for tunable narrow-linewidth quantum dot emitters

Tunable photonic architectures that improve the extraction efficiency of light from embedded epitaxial quantum dots across a wide spectral range are key enablers for developing bright sources of single and indistinguishable photons. In this study, we experimentally demonstrate planar multilayer antenna structures consisting of epitaxially grown AlGaAs and InGaAs membranes containing quantum dots sandwiched between metallic Au (or Ag) reflector and director layers together with Al$_2$O$_3$ spacer layers. We show that the linewidths and fine-structure splitting of the neutral exciton emission remain comparable to those measured in the corresponding unprocessed samples, demonstrating that the fabrication process preserves the optical quality of the emitters. In addition to broadband operation, we demonstrate that the planar architecture is compatible with electrical tuning via integrated diode structures, and strain tuning using piezoelectric actuators. In spite of limitations related to optical losses in the ultrathin metallic layers, the demonstrated fabrication simplicity, scalability, and compatibility with tunable quantum emitters establish planar antennas as a promising platform for solid-state quantum photonic devices.

physics.optics↗

arXiv2026

Picosecond-resolved entanglement distribution over an urban free-space channel

Time-evolving entangled states describe quantum particles whose correlations evolve in time according to a well-defined dynamics. Such states can be generated in a variety of physical systems and are promising resources for several quantum technologies, ranging from quantum clock synchronization to quantum communication. However, their full potential is currently limited by the fact that the entanglement dynamics often occur on timescales comparable to the achievable synchronization precision, especially in experiments aimed at distributing entanglement through noisy urban channels. In this context, accurate timing is not merely a technical detail, but a fundamental requirement for faithfully observing and exploiting the underlying quantum correlations. Here, we demonstrate the faithful distribution of a fast-evolving entangled state over a 270 m free-space channel connecting two buildings in the center of Rome. The developed system incorporates a synchronization device capable of achieving sub-50 ps timing accuracy between the two ends of the link while simultaneously supporting channel stabilization. Our results demonstrate that time-evolving entanglement can be reliably transmitted through a noisy urban free-space channel, representing an important benchmark toward long-distance free-space quantum communication and the future implementation of time-correlated entangled states in demanding scenarios such as satellite-based quantum networks.

quant-ph↗

arXiv2026

Automated Vector-Scanning Spectroscopy for Large-Scale Characterization of Single Quantum Emitters

The inherent spatial randomness and broad spectral heterogeneity of epitaxial quantum dots (QDs) -- one of the most mature classes of solid-state quantum emitters -- remains a major obstacle to their scalable deployment in integrated photonic quantum technologies. Overcoming this challenge requires deterministic fabrication strategies capable of precisely aligning nanophotonic structures with high-quality emitters, which in turn demands efficient and automated single-QD characterization. Despite substantial progress in optical measurement techniques, a platform capable of autonomous, data-efficient, and sufficiently versatile characterization of single quantum dots at the chip scale remains lacking. Here, we introduce an automated cryogenic measurement platform that combines wide-field photoluminescence imaging with vector-stage-scanning confocal spectroscopy to enable high-throughput, chip-scale targeted optical characterization of individual QDs. Using this platform, we automatically acquire photoluminescence data from thousands of GaAs/AlGaAs QDs on a single chip. We demonstrate how this extensive dataset enables identification of high-performance emitters for future deterministic device fabrication, while simultaneously revealing statistical trends across the QD ensemble. By uniting data-efficient targeted measurements with scalable automation, our platform establishes a foundation for large-scale quantum photonic integration and the high throughput characterization framework needed to accelerate materials optimization.

physics.optics↗

arXiv2024

Many-body quantum register for a spin qubit

Quantum networks require quantum nodes with coherent optical interfaces and multiple stationary qubits. In terms of optical properties, semiconductor quantum dots are highly compelling, but their adoption as quantum nodes has been impaired by the lack of auxiliary qubits. Here, we demonstrate a functional quantum register in a semiconductor quantum dot leveraging the dense, always-present nuclear spin ensemble. We prepare 13,000 host nuclear spins into a single many-body dark state to operate as the register logic state $|0\rangle$. The logic state $|1\rangle$ is defined as a single nuclear magnon excitation, enabling controlled quantum-state transfer between the electron spin qubit and the nuclear magnonic register. Using 130-ns SWAP gates, we implement a full write-store-retrieve-readout protocol with 68.6(4)% raw overall fidelity and a storage time of 130(16) $μ$s in the absence of dynamical decoupling. Our work establishes how many-body physics can add step-change functionality to quantum devices, in this case transforming quantum dots into multi-qubit quantum nodes with deterministic registers.

quant-ph↗

arXiv2023

Intermediate Field Coupling of Single Epitaxial Quantum Dots to Plasmonic Waveguides

Key requirements for quantum plasmonic nanocircuits are reliable single-photon sources, high coupling efficiency to the plasmonic structures and low propagation losses. Self-assembled epitaxially grown GaAs quantum dots are close to ideal stable, bright and narrowband single-photon emitters. Likewise, wet-chemically grown monocrystalline silver nanowires are among the best plasmonic waveguides. However, large propagation losses of surface plasmons on the high-index GaAs substrate prevent their direct combination. Here, we show by experiment and simulation that the best overall performance of the quantum plasmonic nanocircuit based on these building blocks is achieved in the intermediate field regime with an additional spacer layer between the quantum dot and the plasmonic waveguide. High-resolution cathodoluminescence measurements allow a precise determination of the coupling distance and support a simple analytical model to explain the overall performance. The coupling efficiency is increased up to four times by standing wave interference near the end of the waveguide.

cond-mat.mes-hall↗

arXiv2023

Highly indistinguishable single photons from droplet-etched GaAs quantum dots integrated in single-mode waveguides and beamsplitters

The integration of on-demand quantum emitters into photonic integrated circuits (PICs) has drawn much of attention in recent years, as it promises a scalable implementation of quantum information schemes. A central property for several applications is the indistinguishability of the emitted photons. In this regard, GaAs quantum dots (QDs) obtained by droplet etching epitaxy show excellent performances with visibilities close to one for both individual and remote emitters. Therefore, the realization of these QDs into PICs is highly appealing. Here, we show the first implementation in this direction, realizing the key passive elements needed in PICs, i.e. single-mode waveguides (WGs) with integrated GaAs-QDs, which can be coherently controlled, as well as beamsplitters. We study both the statistical distribution of wavelength, linewidth and decay times of the excitonic line of multiple QDs, as well as the quantum optical properties of individual emitters under resonant excitation. Here, we achieve single-photon purities as high as $1-\text{g}^{(2)}(0)=0.929\pm0.009$ as well as two-photon interference visibilities of up to V$_{\text{TPI}}=0.939\pm0.004$ for two consecutively emitted photons.

quant-ph↗

arXiv2023

Compact Chirped Fiber Bragg Gratings for Single-Photon Generation from Quantum Dots

A scalable source of single photons is a key constituent of an efficient quantum photonic architecture. To realize this, it is beneficial to have an ensemble of quantum emitters that can be collectively excited with high efficiency. Semiconductor quantum dots hold great potential in this context, due to their excellent photophysical properties. Spectral variability of quantum dots is commonly regarded as a drawback introduced by the fabrication method. However, this is beneficial to realize a frequency-multiplexed single-photon platform. Chirped pulse excitation, relying on the so-called adiabatic rapid passage, is the most efficient scheme to excite a quantum dot ensemble due to its immunity to individual quantum dot parameters. Yet, the existing methods of generating chirped laser pulses to excite a quantum emitter are bulky, lossy, and mechanically unstable, which severely hampers the prospects of a quantum dot photon source. Here, we present a compact, robust, and high-efficiency alternative for chirped pulse excitation of solid-state quantum emitters. Our simple plug-and-play module consists of chirped fiber Bragg gratings (CFBGs), fabricated via femtosecond inscription, to provide high values of dispersion in the near-infrared spectral range, where the quantum dots emit. We characterize and benchmark the performance of our method via chirped excitation of a GaAs quantum dot, establishing high-fidelity single-photon generation. Our highly versatile chirping module coupled to a photon source is a significant milestone toward realizing practical quantum photonic devices.

physics.optics↗

arXiv2023

Coherent Quantum Interconnection between On-Demand Quantum Dot Single Photons and a Resonant Atomic Quantum Memory

Long-range quantum communication requires the development of in-out light-matter interfaces to achieve a quantum advantage in entanglement distribution. Ideally, these quantum interconnections should be as fast as possible to achieve high-rate entangled qubits distribution. Here, we demonstrate the coherent quanta exchange between single photons generated on-demand from a GaAs quantum dot and atomic ensemble in a $^{87}$Rb vapor quantum memory. Through an open quantum system analysis, we demonstrate the mapping between the quantized electric field of photons and the coherence of the atomic ensemble. Our results play a pivotal role in understanding quantum light-matter interactions at the short time scales required to build fast hybrid quantum networks.

quant-ph↗

arXiv2022

Beyond the four-level model: Dark and hot states in quantum dots degrade photonic entanglement

Entangled photon pairs are essential for a multitude of photonic quantum applications. To date, the best performing solid-state quantum emitters of entangled photons are semiconductor quantum dots operated around liquid-helium temperatures. To favor the widespread deployment of these sources, it is important to explore and understand their behavior at temperatures accessible with compact Stirling coolers. Here we study the polarization entanglement among photon pairs from the biexciton-exciton cascade in GaAs quantum dots at temperatures up to 65 K. We observe entanglement degradation accompanied by changes in decay dynamics, which we ascribe to thermal population and depopulation of hot and dark states in addition to the four levels relevant for photon pair generation. Detailed calculations considering the presence and characteristics of the additional states and phonon-assisted transitions support the interpretation. We expect these results to guide the optimization of quantum dots as sources of highly entangled photons at elevated temperatures.

quant-ph↗

arXiv2022

Fast and efficient demultiplexing of single photons from a quantum dot with resonantly enhanced electro-optic modulators

We report on a multi-photon source based on active demultiplexing of single photons emitted from a resonantly excited GaAs quantum dot. Active temporal-to-spatial mode demultipexing is implemented via resonantly enhanced free-space electro-optic modulators, making it possible to route individual photons at high switching rates of 38 MHz. We demonstrate routing into four spatial modes with a high end-to-end efficiency of 79% and measure a four-photon coincidence rate of 0.17 Hz mostly limited by the single-photon source brightness and not by the efficiency of the demultiplexer itself. We use the demultiplexer to characterize the pairwise indistinguishability of consecutively emitted photons from the quantum dot with variable delay time.

quant-ph↗

arXiv2022

Surface passivation and oxide encapsulation to improve optical properties of a single GaAs quantum dot close to the surface

Epitaxial GaAs quantum dots grown by droplet etching have recently shown excellent properties as sources of single photons as well as entangled photon pairs. Integration in some nanophotonic structures requires surface-to-dot distances of less than 100 nm. This demands a surface passivation scheme, which could be useful to lower the density of surface states. To address this issue, sulphur passivation with dielectric overlayer as an encapsulation is used for surface to QD distances of 40 nm, which results in the partial recovery of emission linewidths to bulk values as well as in the increase of the photoluminescence intensity.

physics.app-ph↗

arXiv2021

GaAs quantum dots grown by droplet etching epitaxy as quantum light sources

This paper presents an overview and perspectives on the epitaxial growth and optical properties of GaAs quantum dots obtained with the droplet etching method as high-quality sources of quantum light. We illustrate the recent achievements regarding the generation of single photons and polarization entangled photon pairs and the use of these sources in applications of central importance in quantum communication, such as entanglement swapping and quantum key distribution.

quant-ph↗

arXiv2020

The crux of using the cascaded emission of a 3-level quantum ladder system to generate indistinguishable photons

We investigate the degree of indistinguishability of cascaded photons emitted from a 3-level quantum ladder system; in our case the biexciton-exciton cascade of semiconductor quantum dots. For the 3-level quantum ladder system we theoretically demonstrate that the indistinguishability is inherently limited for both emitted photons and determined by the ratio of the lifetimes of the excited and intermediate states. We experimentally confirm this finding by comparing the quantum interference visibility of non-cascaded emission and cascaded emission from the same semiconductor quantum dot. Quantum optical simulations produce very good agreement with the measurements and allow to explore a large parameter space. Based on our model, we propose photonic structures to optimize the lifetime ratio and overcome the limited indistinguishability of cascaded photon emission from a 3-level quantum ladder system.

cond-mat.mes-hall↗

arXiv2020

The Origin of Antibunching in Resonance Fluorescence

Epitaxial quantum dots have emerged as one of the best single-photon sources, not only for applications in photonic quantum technologies but also for testing fundamental properties of quantum optics. One intriguing observation in this area is the scattering of photons with subnatural linewidth from a two-level system under resonant continuous wave excitation. In particular, an open question is whether these subnatural linewidth photons exhibit simultaneously antibunching as an evidence of single-photon emission. Here, we demonstrate that this simultaneous observation of subnatural linewidth and antibunching is not possible with simple resonant excitation. First, we independently confirm single-photon character and subnatural linewidth by demonstrating antibunching in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy, respectively. However, when filtering the coherently scattered photons with filter bandwidths on the order of the homogeneous linewidth of the excited state of the two-level system, the antibunching dip vanishes in the correlation measurement. Our experimental work is consistent with recent theoretical findings, that explain antibunching from photon-interferences between the coherent scattering and a weak incoherent signal in a skewed squeezed state.

cond-mat.mes-hall↗

arXiv2019

Single-Particle-Picture Breakdown in laterally weakly confining GaAs Quantum Dots

We present a detailed investigation of different excitonic states weakly confined in single GaAs/AlGaAs quantum dots obtained by the Al droplet-etching method. For our analysis we make use of temperature-, polarization- and magnetic field-dependent $μ$-photoluminescence measurements, which allow us to identify different excited states of the quantum dot system. Besides that, we present a comprehensive analysis of g-factors and diamagnetic coefficients of charged and neutral excitonic states in Voigt and Faraday configuration. Supported by theoretical calculations by the Configuration interaction method, we show that the widely used single-particle Zeeman Hamiltonian cannot be used to extract reliable values of the g-factors of the constituent particles from excitonic transition measurements.

cond-mat.mes-hall↗

arXiv2019

A solid-state entangled photon pair source with high brightness and indistinguishability

The generation of high-quality entangled photon pairs has been being a long-sought goal in modern quantum communication and computation. To date, the most widely-used entangled photon pairs are generated from spontaneous parametric downconversion, a process that is intrinsically probabilistic and thus relegated to a regime of low pair-generation rates. In contrast, semiconductor quantum dots can generate triggered entangled photon pairs via a cascaded radiative decay process, and do not suffer from any fundamental trade-off between source brightness and multi-pair generation. However, a source featuring simultaneously high photon-extraction efficiency, high-degree of entanglement fidelity and photon indistinguishability has not yet been reported. Here, we present an entangled photon pair source with high brightness and indistinguishability by deterministically embedding GaAs quantum dots in broadband photonic nanostructures that enable Purcell-enhanced emission. Our source produces entangled photon pairs with a record pair collection probability of up to 0.65(4) (single-photon extraction efficiency of 0.85(3)), entanglement fidelity of 0.88(2), and indistinguishabilities of 0.901(3) and 0.903(3), which immediately creates opportunities for advancing quantum photonic technologies.

quant-ph↗

arXiv2019

Resonance fluorescence of GaAs quantum dots with near-unity photon indistinguishability

Photonic quantum technologies call for scalable quantum light sources that can be integrated, while providing the end user with single and entangled photons on-demand. One promising candidate are strain free GaAs/AlGaAs quantum dots obtained by droplet etching. Such quantum dots exhibit ultra low multi-photon probability and an unprecedented degree of photon pair entanglement. However, different to commonly studied InGaAs/GaAs quantum dots obtained by the Stranski-Krastanow mode, photons with a near-unity indistinguishability from these quantum emitters have proven to be elusive so far. Here, we show on-demand generation of near-unity indistinguishable photons from these quantum emitters by exploring pulsed resonance fluorescence. Given the short intrinsic lifetime of excitons confined in the GaAs quantum dots, we show single photon indistinguishability with a raw visibility of $V_{raw}=(94.2\pm5.2)\,\%$, without the need for Purcell enhancement. Our results represent a milestone in the advance of GaAs quantum dots by demonstrating the final missing property standing in the way of using these emitters as a key component in quantum communication applications, e.g. as an entangled source for quantum repeater architectures.

cond-mat.mes-hall↗