arXiv subjects

Emmanuel Lassalle

Publications and source records attributed to Emmanuel Lassalle.

16 recordsLinked to original sources

arXiv2026

Dicke Superradiance in Extended 2D Quantum Arrays Coupled to Metasurface Bound States in the Continuum

Dicke superradiance is a collective phenomenon where the emission from ensembles of quantum emitters is coherently enhanced beyond the sum of each emitter's independent emission. Here, we propose a platform that exploits the delocalised nature of a high-Q, non-local mode supported by a dielectric metasurface (a so-called bound-state-in-the-continuum or BIC) to induce superradiant behaviour within an extended two-dimensional array of distant quantum emitters. We show that these BIC-mediated emitter interactions can span several wavelengths, thus overcoming the traditional subwavelength separation between emitters required in free space. We further show that reaching the idealised Dicke limit is possible in this system, provided that the emitters are coupled to the BIC mode efficiently enough, as quantified through the $\beta$-factor. Moreover, we demonstrate its experimental viability by analysing its robustness to realistic experimental imperfections. This work puts forward optical metasurfaces supporting BICs as a physically viable platform for realising the upper limits of cooperative emission in physically extended quantum emitter arrays.

quant-ph↗

arXiv2026

Sampling methods to describe superradiance in large ensembles of quantum emitters

Superradiance is a quantum phenomenon in which coherence between emitters results in enhanced and directional radiative emission. Many quantum optical phenomena can be characterized by the two-time quantum correlation function $g^{(2)}(t,\tau)$, which describes the photon statistics of emitted radiation. However, the critical task of determining $g^{(2)}(t,\tau)$ becomes intractable for large emitter ensembles due to the exponential scaling of the Hilbert space dimension with the number of emitters. Here, we analyse and benchmark two approximate numerical sampling methods applicable to emitter arrays embedded within electromagnetic environments, which generally provide upper and lower bounds for $g^{(2)}(t,0)$. We also introduce corrections to these methods (termed offset corrections) that significantly improve the quality of the predictions. The optimal choice of method depends on the total number of emitters, such that taken together, the two approaches provide accurate descriptions across a broad range of important regimes. This work therefore provides new theoretical tools for studying the well-known yet complex phenomenon of superradiance in large ensembles of quantum emitters.

quant-ph↗

arXiv2025

Neural network enabled wide field-of-view imaging with hyperbolic metalenses

The ultrathin form factor of metalenses makes them highly appealing for novel sensing and imaging applications. Amongst the various phase profiles, the hyperbolic metalens stands out for being free from spherical aberrations and having one of the highest focusing efficiencies to date. For imaging, however, hyperbolic metalenses present significant off-axis aberrations, severely restricting the achievable field-of-view (FOV). Extending the FOV of hyperbolic metalenses is thus feasible only if these aberrations can be corrected. Here, we demonstrate that a Restormer neural network can be used to correct these severe off-axis aberrations, enabling wide FOV imaging with a hyperbolic metalens camera. Importantly, we demonstrate the feasibility of training the Restormer network purely on simulated datasets of spatially-varying blurred images generated by the eigen-point-spread function (eigenPSF) method, eliminating the need for time-intensive experimental data collection. This reference-free training ensures that Restormer learns solely to correct optical aberrations, resulting in reconstructions that are faithful to the original scene. Using this method, we show that a hyperbolic metalens camera can be used to obtain high-quality imaging over a wide FOV of 54{\deg} in experimentally captured scenes under diverse lighting conditions.

physics.optics↗

arXiv2025

Long-range quantum emitter interactions mediated by a non-local metasurface: Application to qubit-qubit entanglement

Scalable quantum technologies demand long-range interactions between many distant quantum emitters (QEs). We introduce non-local metasurfaces supporting bound-states-in-the-continuum (BICs) as a promising platform to achieve this goal. We show that efficient QE interactions depend almost entirely on emitter-BIC coupling efficiencies ($\beta$-factors), which in our system can exceed $80\%$ even without additional mode engineering. These values rival those of 1D waveguides but are achieved here in a geometry that naturally accommodates large 2D QE arrays. Using this platform, we explore entanglement generation between two remote QEs, finding that it develops faster than in free space, is significantly amplified, and persists over separations spanning several emission wavelengths. Optimal inter-QE interactions require large $\beta$-factors but only moderately small Purcell factors, both within experimentally achievable ranges. Our results establish non-local metasurfaces as a practical and scalable platform for leading-edge quantum nanophotonics.

quant-ph↗

arXiv2023

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Preliminary investigations on dielectric nanoantennas have been carried out for a trifecta of enhancements, i.e., simultaneous enhancements in absorption, emission directionality and radiative decay rates of quantum emitters. However, these investigations are limited by fragile substrates or low Purcell factor, which is extremely important for exciting quantum emitters electrically. In this paper, we present a Si mix antenna array to achieve the trifecta enhancement of ~1200 fold with a Purcell factor of ~47. The antenna design incorporates ~10 nm gaps within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS compatible platforms for enhancing fluorescence for biological and chemical applications.

physics.optics↗

arXiv2023

Dual-resonance nanostructures for colour down-conversion of colloidal quantum emitters

Linear colour conversion is a process where an emitter absorbs a photon and then emits another photon with either higher or lower energy, corresponding to up- or down conversion, respectively. In this regard, the presence of a volumetric cavity plays a crucial role in enhancing absorption and photoluminescence (PL), as it allows for large volumes of interaction between the exciting photons and the emissive materials, maximising the colour conversion efficiency. Here, we present a dual resonance nanostructure made of a titanium dioxide (TiO2) subwavelength grating to enhance the colour down-conversion efficiency of green light at ~530 nm emitted by gradient alloyed CdxZn1-xSeyS1-y colloidal quantum dots (QDs) when excited with a blue light at ~460 nm. A large mode volume can be created within the QD layer by the hybridisation of the grating resonances and waveguide modes. This allows increasing mode overlap between the resonances and the QDs, resulting in large absorption and tailored emission enhancements. Particularly, we achieved polarized light emission with maximum photoluminescence enhancement of ~140 times at a specific angular direction, and a total enhancement of ~34 times within 0.55 numerical aperture (NA) of the collecting objective. The enhancement encompasses absorption enhancement, Purcell enhancement and directionality enhancement (i.e., outcoupling). We achieved total absorption of 35% for green QDs with a remarkably thin colour conversion layer of ~ 400 nm (inclusive of the TiO2 layer). This work provides a guideline for designing large-volume cavities for practical application in absorption/fluorescence enhancement, such as down colour conversion in microLED displays, detectors or photovoltaics.

physics.optics↗

arXiv2023

Single atom in a superoscillatory optical trap

Optical tweezers have become essential tools to manipulate atoms or molecules at a single particle level. However, using standard diffracted-limited optical systems, the transverse size of the trap is lower bounded by the optical wavelength, limiting the application range of optical tweezers. Here we report trapping of single ultracold atom in an optical trap that can be continuously tuned from a standard Airy focus to a subwavelength hotspot smaller than the usual Abbe's diffraction limit. The hotspot was generated using the effect of superoscillations, by the precise interference of multiple free-space coherent waves. We argue that superoscillatory trapping and continuous potential tuning offer not only a way to generate compact and tenable ensembles of trapped atoms for quantum simulators but will also be useful in single molecule quantum chemistry and the study of cooperative atom-photon interaction within subwavelength arrays of quantum emitters.

physics.atom-ph↗

arXiv2023

Large field-of-view and multi-color imaging with GaP quadratic metalenses

Metalenses, in order to compete with conventional bulk optics in commercial imaging systems, often require large field of view (FOV) and broadband operation simultaneously. However, strong chromatic and coma aberrations present in common metalens designs have so far limited their widespread use. Stacking of metalenses as one of the possible solutions increases the overall complexity of the optical system and hinders the main benefit of reduced thickness and light weight. To tackle both issues, here we propose a single-layer imaging system utilizing a recently developed class of metalenses providing large field of view. Using it, we demonstrate full-color imaging with a FOV of 100 degrees. This approach, empowered by computational imaging techniques, produce high quality images, both in terms of color reproduction and sharpness. Suitable for real-time unpolarized light operation with the standard color filters present in prevalent camera systems, our results might enable a pathway for consumer electronics applications of this emerging technology.

physics.optics↗

arXiv2023

Hybrid Dielectric-Plasmonic Nanoantenna with Multiresonances for Subwavelength Photon Sources

The enhancement of the photoluminescence of quantum dots induced by an optical nanoantenna has been studied considerably, but there is still significant interest in optimizing and miniaturizing such structures, especially when accompanied by an experimental demonstration. Most of the realizations use plasmonic platforms, and some also use all-dielectric nanoantennas, but hybrid dielectric-plasmonic (subwavelength) nanostructures have been very little explored. In this paper, we propose and demonstrate single subwavelength hybrid dielectric-plasmonic optical nanoantennas coupled to localized quantum dot emitters that constitute efficient and bright unidirectional photon sources under optical pumping. To achieve this, we devised a silicon nanoring sitting on a gold mirror with a 10 nm gap in-between, where an assembly of colloidal quantum dots is embedded. Such a structure supports both (radiative) antenna mode and (nonradiative) gap mode resonances, which we exploit for the dual purpose of out-coupling the light emitted by the quantum dots into the far-field with out-of-plane directivity, and for enhancing the excitation of the dots by the optical pump. Moreover, almost independent control of the resonance spectral positions can be achieved by simple tuning of geometrical parameters such as the ring inner and outer diameters, allowing us to conveniently adjust these resonances with respect to the quantum dots emission and absorption wavelengths. Using the proposed architecture, we obtain experimentally average fluorescence enhancement factors up to $654\times$ folds mainly due to high radiative efficiencies, and associated with a directional emission of the photoluminescence into a cone of $\pm 17\degree$ in the direction normal to the sample plane. We believe the solution presented here to be viable and relevant for the next generation of light-emitting devices.

physics.optics↗

arXiv2021

Imaging properties of large field-of-view quadratic metalenses and their applications to fingerprint detection

Dielectric metasurfaces, extremely thin nanostructured dielectric surfaces, hold promise to replace conventional refractive optics, such as lenses, due to their high performance and compactness. However, designing large field-of-view (FOV) metalenses, which are of particular importance when imaging relatively big objects at short distances, remains one of the most critical challenges. Recently, metalenses implementing a quadratic phase profile have been put forward to solve this problem with a single element, but despite their theoretical ability to provide $180^\circ\,$FOV, imaging over very large FOV has not been demonstrated yet. In this work, we provide an in-depth analysis of the imaging properties of quadratic metalenses and, in particular, show that due to their intrinsic barrel distortion or fish-eye effect, there is a fundamental trade-off between the FOV achievable in a given imaging configuration and the optical resolution of the metalens and/or the detector resolution. To illustrate how to harness the full potential of quadratic metalenses, we apply these considerations to the fingerprint detection problem, and demonstrate experimentally the full imaging of a $5\,$mm fingerprint with features of the order of $100\,μ$m, with a metalens ten times smaller in size and located at a distance of only $2.5\,$mm away from the object. This constitutes the most compact system reported so far for the fingerprint detection.

physics.optics↗

arXiv2020

Predicting Stock Returns with Batched AROW

We extend the AROW regression algorithm developed by Vaits and Crammer in [VC11] to handle synchronous mini-batch updates and apply it to stock return prediction. By design, the model should be more robust to noise and adapt better to non-stationarity compared to a simple rolling regression. We empirically show that the new model outperforms more classical approaches by backtesting a strategy on S\&P500 stocks.

q-fin.CP↗

arXiv2020

Long-lifetime coherence in a quantum emitter induced by a metasurface

An anisotropic quantum vacuum (AQV) has been predicted to induce quantum interferences during the spontaneous emission process in an atomic $V$-transition [G. S. Agarwal, Phys. Rev. Lett. 84, 5500 (2000)]. Nevertheless, the finite lifetime of the excited states is expected to strongly limit the observability of this phenomenon. In this paper, we predict that an AQV can induce a long-lifetime coherence in an atomic $Λ$-transition from the process of spontaneous emission, which has an additional advantage of removing the need for coherent laser excitation. We also carry out two metasurface designs and compare their respective efficiencies for creating an AQV over remote distances. The detection of this coherence induced by a metasurface, in addition to being yet another vindication of quantum electrodynamics, could pave the way towards the remote distance control of coherent coupling between quantum emitters, which is a key requirement to produce entanglement in quantum technology applications.

quant-ph↗

arXiv2018

Conditions for anti-Zeno effect observation in free-space atomic radiative decay

Frequent measurements can modify the decay of an unstable quantum state with respect to the free dynamics given by Fermi's golden rule. In a landmark article, Nature 405, 546 (2000), Kofman and Kurizki concluded that in quantum decay processes, acceleration of the decay by frequent measurements, called the quantum anti-Zeno effect (AZE), appears to be ubiquitous, while its counterpart, the quantum Zeno effect, is unattainable. However, up to now there have been no experimental observations of the AZE for atomic radiative decay (spontaneous emission) in free space. In this work, making use of analytical results available for hydrogen-like atoms, we find that in free space, only non-electric-dipolar transitions should present an observable AZE, revealing that this effect is consequently much less ubiquitous than first predicted. We then propose an experimental scheme for AZE observation, involving the electric quadrupole transition between D 5/2 and S 1/2 in the heaviest alkali-earth ions Ca + and Sr +. The proposed protocol is based on the STIRAP technique which acts like a dephasing quasi-measurement.

quant-ph↗

arXiv2018

Interplay between spontaneous decay rates and Lamb shifts in open photonic systems

In this letter, we describe the modified decay rate and photonic Lamb (frequency) shift of quantum emitters in terms of the resonant states of a neighboring photonic resonator. This description illustrates a fundamental distinction in the behaviors of closed (conservative) and open (dissipative) systems: the Lamb shift is bounded by the emission linewidth in closed systems while it overcomes this limit in open systems.

physics.optics↗

arXiv2018

Lamb shift multipolar analysis

It is now well established that radiative decay of quantum emitters can be strongly modified by their environment. In this paper we present an exact, within the weak-coupling approximation, multipole expression to compute the Lamb (frequency) shift induced by an arbitrary set of resonant scatterers on a nearby quantum emitter, using multi-scattering theory. We also adopt a Quasi-Normal Mode description to account for the line shape of the Lamb shift spectrum in the near-field of a plasmonic nanosphere. It is then shown that the Lamb shift resonance can be blue-shifted as the size of the nanoparticle increases, suggesting that nanoparticles may be used to tune this resonant interaction. Finally, a realistic calculation of the Lamb shift is made for a dimer configuration.

physics.optics↗

arXiv2014

Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields

The Gemini Multi-conjugate adaptive optics System (GeMS) is a facility instrument for the Gemini-South telescope. It delivers uniform, near-diffraction-limited image quality at near-infrared wavelengths over a 2 arcminute field of view. Together with the Gemini South Adaptive Optics Imager (GSAOI), a near-infrared wide field camera, GeMS/GSAOI's combination of high spatial resolution and a large field of view will make it a premier facility for precision astrometry. Potential astrometric science cases cover a broad range of topics including exo-planets, star formation, stellar evolution, star clusters, nearby galaxies, black holes and neutron stars, and the Galactic center. In this paper, we assess the astrometric performance and limitations of GeMS/GSAOI. In particular, we analyze deep, mono-epoch images, multi-epoch data and distortion calibration. We find that for single-epoch, un-dithered data, an astrometric error below 0.2 mas can be achieved for exposure times exceeding one minute, provided enough stars are available to remove high-order distortions. We show however that such performance is not reproducible for multi-epoch observations, and an additional systematic error of ~0.4 mas is evidenced. This systematic multi-epoch error is the dominant error term in the GeMS/GSAOI astrometric error budget, and it is thought to be due to time-variable distortion induced by gravity flexure.

astro-ph.IM↗