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Color-center-based single-photon emitters in hexagonal boron nitride (h-BN) have shown promising photophysical properties as sources for quantum light emission. Despite significant advances toward such a goal, achieving lifetime-limited quantum light emission in h-BN has proven to be challenging, primarily due to various broadening mechanisms, including spectral diffusion. Here, we propose and experimentally demonstrate suppression of spectral diffusion by applying an electrostatic field. We observe both Stark shift tuning of the resonant emission wavelength and emission line width reduction (down to 89 MHz) nearly to the homogeneously broadened lifetime limit. Finally, we find a cubic dependence of the line width with respect to temperature at the homogeneous broadening regime. Our results suggest that field tuning in electrostatically gated heterostructures is promising as an approach to control the emission characteristics of h-BN color centers, removing spectral diffusion and providing the energy tunability necessary for integrate of quantum light emission in nanophotonic architectures.

Compact sources in the mid-wave infrared (MWIR) are needed for applications ranging from spectroscopy to free-space communication. Ultrathin incandescent metasurfaces are promising candidates, offering the possibility to tune the emission spectrum, directivity, and modulation speed. However, control over polarization remains a challenge, especially when it comes to the emission of circularly polarized light. Here, we report the emission of polarized MWIR radiation from a 700 nm thick incandescent chiral metasurface. The degree of polarization is above 0.5 with degree of circular polarization of 0.38 at 5 µm. The metasurface is heated by the Joule effect, and the emission can be modulated beyond 10 MHz. This could enable detection techniques that use polarization as an additional degree of freedom.

We report an experimental and theoretical study of light emission by a patterned ensemble of colloidal quantum dots (cQDs). This system modifies drastically the emission spectrum and polarization as compared to a planar layer of cQDs. It exhibits bright, directional and polarized emission including a degree of circular polarization in some directions. We introduce a model of light emission based on a local Kirchhoff law which reproduces accurately all the features of the experiment. The model provides a figure of merit to assess quantitatively the emitted power. This work paves the way to the systematic design of efficient ultrathin light emitting metasurfaces with controlled polarization, spectrum and directivity.

The authors propose a general absorption-coherence relation to show that spatial coherence emission by molecules on a metallic film is due to the excitation of surface plasmon polaritons and is reduced in the presence of strong coupling.

While spatially coherent emission has been experimentally observed for several photoluminescent devices composed of metallic nanostructures, no model is currently able to compute the spatial coherence function of the emitted fields, and thus to explain its origin. We introduce a model of light emission by thermalized ensembles of emitters which connects the coherence of the fields at two positions to the power absorbed by the system when illuminated by two sources. We can apply it to the study of the spatial coherence properties of the light emitted by a layer of molecular dyes deposited on top of a silver layer.

We report a reduction in the linewidth and suppression of spectral diffusion of quantum emitters in hexagonal boron nitride supported on a conductive substrate. We observe a temperature-dependent reduction in the spectral emission linewidth for CVD-grown and exfoliated crystals on conductive ITO relative to those seen on silicon dioxide (${\mathrm{Si}\mathrm{O}}_{2}$) substrates. We show that the inhomogeneous linewidth can be suppressed by 45% as a result of using a conductive substrate. We investigate the zero-phonon line profile at temperatures ranging from 4 to 300 K and decompose the effects of thermal broadening and spectral diffusion at each temperature by Voigt fitting. The temperature dependence of homogeneous and inhomogeneous components of the broadening is discussed.

Optical antennas have become ubiquitous tools to enhance the spontaneous emission of atoms, molecules and quantum dots. In this presentation, we report a series of experimental results investigating the emission of light by ensembles of interacting emitters coupled to resonators. First, we report the observation of a strong plasmon−exciton coupling regime in a system consisting of a layer of nanoplatelets on top of a gold planar surface. Reflectometry measurements and mode analysis lead to the non-ambiguous derivation of a Rabi splitting between two polaritonic branches. Secondly, we investigate the polarized and directional emission of light by a patterned layer of nanoplatelets optically pumped. Models based on the paradigm of the Purcell effect mediated radiation fail to fully explain spectral and spatial features observed in such experiments, such as the emergence of spatial coherence or the suppression of quenching. We discuss and highlight the differences between emission by a single emitter and by a thermalized assembly of quantum emitters to show that a statistical framework is required to understand their interactions with optical antennas. Based on these considerations, we introduce a model of light emission by thermalized ensembles of emitters, and find good agreement between our model and experimental data.

Currently, there are no cheap and compact sources in the mid-infrared range that can be modulated at high frequencies. Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications, but for detection or communication applications where fast temperature modulation are desirable, thermal inertia quickly becomes a limiting factor. Besides, such incandescent sources are typically unpolarized, isotropic, broadband and have a low efficiency. However, these properties are not imposed by fundamental limitations stemming from physics laws, except for the low brightness dictated by Bose-Einstein distribution. Here, we introduce a metasurface that combines nanoscale heaters to ensure fast thermal response and nanophotonic resonances to provide large spectrally selective and polarized emissivity. We report a peak emissivity of 0.8 and an operation up to 20 MHz, six orders of magnitude faster than commercially available hot membranes.

To bunch or to antibunch Particles of matter can be classed as either as bosons or fermions. Their subsequent behavior in terms of their physical properties and interactions depends on which quantum statistics they obey. Photons, for instance, are bosons and tend to bunch. Electrons are fermions and tend to antibunch. Vest et al. show that surface plasmon polaritons, a hybrid excitation of light and electrons, can exhibit both kinds of behavior (see the Perspective by Faccio). By tuning the level of loss in their system, bunching and antibunching of interfering plasmons can be seen. Science , this issue p. 1373 ; see also p. 1336

Nanoplatelets are strongly anisotropic colloidal nanocrystals confined in only one direction. Perfect thickness control and large lateral dimensions enable a large exciton coherence area that exhib...

Quantum plasmonics experiments have on multiple occasions resulted in the observation of quantum coherence of discrete plasmons, which exhibit remarkable preservation of quantum interference visibility, a seemingly surprising feature for systems mixing light and matter with high Ohmic losses during propagation. However, most experiments to date used essentially weakly confined plasmons, which experience limited light-matter hybridization, thus limiting the potential for decoherence. In this paper, we investigate experimentally the robustness of coherence preservation in a plasmonic system: our setup is based on a hole-array chip supporting plasmons near the surface plasma frequency, where plasmonic dispersion and confinement are much stronger than in previous experiments, making the plasmons much more susceptible for decoherence processes. We, however, report preservation of quantum coherence even in these extreme conditions. We generate polarization-entangled pairs of photons using type-I spontaneous parametric down-conversion and transmit one of the photons through a plasmonic hole array that is numerically designed to convert incident single photons into highly dispersive single surface-plasmon polaritons. Our results show that the quality of photon entanglement after the plasmonic channel is unperturbed by the introduction of a highly dispersive plasmonic element. Our findings provide a lower bound of 100 fs for the pure dephasing time for dispersive plasmons in gold, and show that even in a highly dispersive regime surface plasmons preserve quantum mechanical correlations, making possible harnessing of the power of extreme light confinement for integrated quantum photonics.

International audience; Fabry-Perot (FP) like resonances have been widely described in nanoantennas. In the original Fabry-Perot resonator, a third mirror can be added, resulting in a multimirror interferometer. However, in the case of combination of nanoantennas, it has been reported that each cavity behaves independently. Here, we evidence the interferences between two FP absorbing nanoantennas through a common mirror, which has a strong impact on the optical behavior. While the resonance wavelength is only slightly shifted, the level of absorption reaches nearly 100 \%. Moreover, the quality factor increases up to factor 7 and can be chosen by geometric design over a range from 11 to 75. We first demonstrate thanks to a simple analytical model that this coupling can be ascribed to a double FP cavity resonance, with the unique feature that each cavity is separately coupled to the outer medium. Based on this principle, we experimentally illustrate the existence of a high-Q factor resonance originating from the interference between two under-coupled ribbon-shaped nano Fabry-Perot.; Les résonances de type Fabry-Perot (FP) ont été largement décrites dans les nanoantennes. Dans le résonateur Fabry-Perot original, un troisième miroir peut être ajouté, ce qui donne un interféromètre à miroir multiple. Cependant, dans le cas d'une combinaison de nanoantennes, il a été rapporté que chaque cavité se comporte indépendamment. Ici, nous mettons en évidence les interférences entre deux nano-antennes absorbant la PF à travers un miroir commun, ce qui a un fort impact sur le comportement optique. Alors que la longueur d'onde de résonance n'est que légèrement décalée, le niveau d'absorption atteint près de 100 \%. De plus, le facteur de qualité augmente jusqu'à un facteur 7 et peut être choisi par conception géométrique sur une plage de 11 à 75. Nous démontrons d'abord grâce à un modèle analytique simple que ce couplage peut être attribué à une résonance à double cavité FP, avec la particularité unique que chaque cavité est couplée séparément au milieu extérieur. Sur la base de ce principe, nous illustrons expérimentalement l'existence d'une résonance à facteur Q élevé provenant de l'interférence entre deux nano Fabry-Perot en forme de ruban sous-couplé.

One of the central challenges for practical applications of single-photon sources is the ability to efficiently extract light from a single quantum emitter. A useful single-photon source must emit into a well-defined direction because in practice one can collect light only in a finite solid angle. Here, we propose to harness the exceptional light molding capabilities of photonic metasurfaces to engineer the emission from quantum emitters and achieve highly directional emission. We have designed a phase gradient reflectarray metasurface, which efficiently collects spontaneous emission from a quantum emitter, located in the far-field (d~5 wavelengths), and redirects it back to the source. By controlling the phase imprinted by the metasurface on the incident light, we control the emission properties of the emitters. We apply this concept to design a metasurface for use with hexagonal boron nitride (hBN) single photon emitters operating at 620 nm. We have observed experimentally bright single photon emission at 620 nm with a remarkably narrow spectral width of zero-phonon line emission from multilayer hBN films synthesized by chemical vapor deposition. Simulations show that at a wavelength of 620 nm, the reflection efficiency of our metasurface is greater than 85%, and that the emission from these emitters are highly directional with deviation from emission in the surface-normal direction of 2∆θ ~ 20°. We will report on experimental measurements of hBN quantum emitters coupled to metasurfaces and describe metasurface designs for coupling of multiple quantum emitters.

The growing field of quantum plasmonics lies at the intersection between nanophotonics and quantum optics. QUantum plasmonics investigate the quantum properties of single surface plasmons, trying to reproduce fundamental and landmark quantum optics experiment that would benefit from the light-confinement properties of nanophotonic systems, thus paving the way towards the design of basic components dedicated to quantum experiments with sizes inferior to the diffraction limit. Several groups have recently reproduced fundamental quantum optics experiments with single surface plasmons polaritons (SPPs). We have investigated two situations of quantum interference of single SPPs on lossy beamsplitters : a plasmonic version of the Hong-Ou-Mandel experiment, and the observation of plasmonic N00N states interferences. We numerically designed and fabricated several beamsplitters that reveal new quantum interference scenarios, such as the coalescence and the anti-coalescence of SPPs, or quantum non-linear absorption. Our work show that losses can be seen as a new degree of freedom in the design of plasmonic devices.

Two-photon absorption (TPA) is a third order non-linear process that relies on the quasi-simultaneous absorption of two photons. Therefore, it has been proved to be an interesting tool to measure ultra-fast correlations 1 or to design all-optical switches. 2 Yet, due to the intrinsically low efficiency of the non-linear processes, these applications rest upon high peak power light sources such as femtosecond and picosecond pulsed laser. However TPA has also been noticed as an appealing new scheme for quantum infrared detection. 3, 4 Indeed, typical quantum detection of IR radiation is based on small gap semiconductors that need to be cooled down to cryogenic temperature to achieve sufficient detectivity. TPA enables the absorption of IR photons by wide gap semiconductors when pump photons are provided to complete optical transitions across the gap. Still, the low efficiency of TPA represents a difficulty to detect usual infrared photon fluxes. To tackle this issue, we combined three strategies to improve the detection efficiency. First, it has been proved theoretically and experimentally that using different pump and signal photon energies which is known as non degenerate TPA (NDTPA) help increasing the TPA efficiency by several orders of magnitude. 5 Thus we decided to work with different pump and signal wavelength. Secondly, since TPA is a local quasi-instantaneous process, both pump and signal photons must be temporarily and spatially co-localized inside the active medium. We made sure to maximize the overlap of the fields inside our device. Finally, it is well known that TPA has a quadratic dependence with the signal electric fields modulus, so we designed a specific nanostructure to enhance the signal field inside the active medium of the detector.

International audience; Quantum entanglement is a stunning consequence of the superposition principle. This universal property of quantum systems has been intensively explored with photons, atoms, ions, and electrons. Collective excitations such as surface plasmons exhibit quantum behaviors. We report the remote preparation of a single plasmon state through the projective measurement of a photon entangled with the plasmon. We achieved photon-plasmon entanglement by converting one photon of an entangled photon pair into a surface plasmon. The plasmon is tested on a plasmonic platform in a Mach-Zehnder interferometer. A projective measurement on the polarization of the photon allows the remote preparation of the interference state of the plasmon. Entanglement between particles of various nature paves the way to the design of hybrid systems in quantum information networks.

Surface plasmon polaritons (SPPs) are bosonic quasiparticles. In the last ten years, several groups have reproduced fundamental quantum optics experiments with surface plasmons. Observation of single-plasmon states, waveparticle duality, preservation of entanglement of photons in plasmon-assisted transmission [1,2], and more recently, two-plasmon interference has been reported, revisiting with success the famous Hong-Ou-Mandel (HOM) experiment[3]. Here we report the observation of two-plasmon quantum interference between two freely-propagating, non-guided SPPs interfering on lossy plasmonic beamsplitters. We find that, depending on the beamsplitter features, the reults of the experiment can be very different.

This letter is on the response of gallium arsenide p-i-n diodes to sub-bandgap photons (1.55 μm). We investigate the various regimes of sub-bandgap operation by using different light sources delivering pulses ranging from nanosecond to microsecond durations. We evidence two regimes : a regime of degenerate two-photon absorption, with a clear quadratic dependence with respect to the incident flux, and a sub-bandgap, temperature dependant linear regime, that drives photocurrent generation at lower power densities. Both processes are associated to a very low quantum efficiency, around 10–8. We then determine absorption coefficients as well as trap densities, thanks to a model involving a photo-assisted Shockley Read Hall effect.

International audience; Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-in diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°). This structure paves the way towards low-noise infrared detection, using non-degenerate TPA, involving two photons of vastly different energies in the same process of absorption in a large bandgap semiconductor material.

International audience; Fabry–Perot (FP)-like resonances have been widely described in nanoantennas. In the original FP resonator, a third mirror can be added, resulting in a multimirror interferometer. However, in the case of a combination of nanoantennas, it has been reported that each cavity behaves independently. Here, we evidence the interferences between two FP absorbing nanoantennas through a common mirror, which has a strong impact on the optical behavior. While the resonance wavelength is only slightly shifted, the level of absorption reaches nearly 100%. Moreover, the quality factor increases up to factor 7 and can be chosen by geometric design over a range from 11 to 75. We demonstrate, thanks to a simple analytical model, that this coupling can be ascribed to a double FP cavity resonance, with the unique feature that each cavity is separately coupled to the outer medium.

International audience; We investigate infrared detection at room temperature using non-degenerate two-photon absorption in a nanostructured indium phosphide photodiode. We designed the detector structure to achieve a good nonlinear absorption by combining three major ideas: first, we use the non-degenerate twophoton absorption process, which is known to be more efficient than the previously used degenerate two-photon absorption. Second, we ensured a correct spatial overlap of our pump field with our signal field. Third, we optimized the nanostructuration to increase the signal field amplitude locally within the active medium of the device. The resulting device consists of a PIN junction embedded between a back-reflecting gold mirror and a top grating. We experimentally characterized our diode with regard to reflectivity and two-photon absorption generated photocurrent for a continuouswave pump and a nanosecond pulsed signal of around 3.39 lm. Owing to the nanostructuration, the generated photocurrent shows a gain of 24 with respect to the bulk response of InP.