Exploiting one-dimensional exciton-phonon coupling for tunable and efficient single-photon generation with a carbon nanotube

Condensed-matter emitters offer enriched cavity quantum electrodynamical effects due to the coupling to external degrees of freedom. In the case of carbon nanotubes a very peculiar coupling between localized excitons and the one-dimensional acoustic phonon modes can be achieved, which gives rise to pronounced phonon wings in the luminescence spectrum. By coupling an individual nanotube to a tunable optical micro-cavity, we show that this peculiar exciton-phonon coupling is a valuable resource to enlarge the tuning range of the single-photon source while keeping an excellent exciton-photon coupling efficiency and spectral purity. Using the unique flexibility of our scanning fiber cavity, we are able to measure the efficiency spectrum of the very same nanotube in the Purcell regime for several mode volumes. Whereas this efficiency spectrum looks very much like the free-space luminescence spectrum when the Purcell factor is small (large mode volume), we show that the deformation of this spectrum at lower mode volumes can be traced back to the strength of the exciton-photon coupling. It shows an enhanced efficiency on the red wing that arises from the asymmetry of the incoherent energy exchange processes between the exciton and the cavity. This allows us to obtain a tuning range up to several hundred times the spectral width of the source

Unifying the low-temperature photoluminescence spectra of carbon nanotubes: the role of acoustic phonon confinement

At low temperature the photoluminescence of single-wall carbon nanotubes show a large variety of spectral profiles ranging from ultra narrow lines in suspended nanotubes to broad and asymmetrical line-shapes that puzzle the current interpretation in terms of exciton-phonon coupling. Here, we present a complete set of photoluminescence profiles in matrix embedded nanotubes including unprecedented narrow emission lines. We demonstrate that the diversity of the low-temperature luminescence profiles in nanotubes originates in tiny modifications of their low-energy acoustic phonon modes. When low energy modes are locally suppressed, a sharp photoluminescence line as narrow as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with specific temperature dependence show the presence of confined phonon modes

A telecom band single-photon source using a grafted carbon nanotube coupled to a fiber Fabry-Perot cavity in the Purcell regime

We report on the coupling of a reconfigurable high Q fiber micro-cavity to an organic color center grafted to a carbon nanotube for telecom wavelength emission of single photons in the Purcell regime. Using three complementary approaches we assess various figures of merit of this tunable single photon source and of the cavity quantum electrodynamical effects : the brightening of the emitter is obtained by comparison of the count rates of the very same emitter in free-space and cavity coupled regimes. We demonstrate a fiber coupled single-photon output rate up to 20 MHz at 1275~nm. Using time-resolved and saturation measurements, we determine independently the radiative quantum yield and the Purcell factor of the system with values up to 30 for the smallest mode volumes. Finally, we take advantage of the tuning capability of the cavity to measure the spectral profile of the brightness of the source which gives access to the vacuum Rabi splitting $g$ with values up to $25 \; \mu$eV

Intraband and intersubband many-body effects in the nonlinear optical response of single-wall carbon nanotubes

International audienceWe report on the nonlinear optical response of a mono-chiral sample of (6,5) single-wall carbon nanotubes by means of broad-band two-color pump-probe spectroscopy with selective excitation of the S11 excitons. By using a moment analysis of the transient spectra, we show that all the nonlinear features can be accurately accounted for by elementary deformations of the linear absorption spectrum. The photo-generation of S11 excitons induces a broadening and a blue shift of both the S11 and S22 excitonic transitions. In contrast, only the S11 transition shows a reduction of oscillator strength, ruling out population up-conversion. These nonlinear signatures result from many-body effects, including phase-space filling, wave-function renormalization and exciton collisions. This framework is sufficient to interpret the magnitude of the observed nonlinearities and stress the importance of intersubband exciton interactions. Remarkably, we show that these intersubband interactions have the same magnitude as the intraband ones and bring the major contribution to the photo-bleaching of the S22 excitonic transition upon S11 excitation through energy shift and broadening

Photonique pour les lasers à cascade quantique térahertz

So-called "terahertz" waves, which lie between infrared and microwaves, have the property of penetrating skin, clothing, paper, wood, cardboard or plastic. These advantages offer numerous applications in medical imaging, spectroscopy, security, and the environment. This is why terahertz quantum cascade lasers - a new family of semiconductor lasers that emit in the frequency range of the terahertz - raise such interest. However, although they are now almost the only compact sources operating within this frequency range, they have two major drawbacks : First, they operate only at cryogenic temperatures. In order to develop stra- tegies to their maximum operating temperature (Tmax), we have developed a comparative study, as a function of the laser emission frequency, which allowed us to elucidate the main factors which limit the devices Tmax (parasitic channel and emission of activated longitudinal-optical phonons). Secondly, the best Tmax are obtained to date by using metal-metal wave- guides. However in such waveguides, the resulting emission is strongly divergent, a drawback which prevents their widespread use. We have overcome this issue by using 2D photonic crystals, defined by the sole metal patterning. This approach yields an angularly narrow surface emission, which is also spectrally single mode, with reasonably high maximum operating temperatures.Situées entre l'infrarouge et les micro-ondes, les ondes dites "terahertz" (THz) ont les propriétés de passer aussi bien à travers la peau et les vêtements que les papiers, le bois, le carton ou encore le plastique. Autant d'atouts qui permettent d'envisager de multiples applications dans les secteurs de l'imagerie médicale, de la spectroscopie, de la sécurité et de l'environnement. D'où l'intérêt que suscitent les lasers à cascade quantique terahertz, une récente famille de lasers semi-conducteurs qui émettent à des fréquences de l'ordre du terahertz. Pourtant, s'ils sont aujourd'hui les seules sources compactes fonctionnant dans cette gamme de fréquences, ils présentent deux inconvénients : Premièrement, ils ne fonctionnent qu'à des températures cryogéniques. En vue d'une augmentation future de la température maximale de fonctionnement (Tmax), nous avons développé une étude comparative en fonction de la fré- quence d'émission, ce qui a permis de déterminer les mécanismes principaux limitant la Tmax (courant parasite ainsi que l'émission de phonons optiques lon- gitudinaux activés thermiquement). Deuxièmement, afin d'obtenir les meilleures Tmax, l'utilisation d'un guide métal- métal est nécessaire. Néanmoins, dans un tel guide, l'émission obtenue est fortement divergente, ce qui s'avère rédhibitoire pour une utilisation généralisée. Pour résoudre ce point, nous avons intégrés des cristaux photoniques bidimensionnels définis uniquement par la géométrie du métal supérieur, ce qui a permis l'obtention d'une émission directive par la surface, spectralement mono-mode, tout en maintenant des températures de fonctionnement assez élevées

Photonique pour les lasers à cascade quantique térahertz

Situées entre l'infrarouge et les micro-ondes, les ondes dites "terahertz" (THz) ont les propriétés de passer aussi bien à travers la peau et les vêtements que les papiers, le bois, le carton ou encore le plastique. Autant d'atouts qui permettent d'envisager de multiples applications dans les secteurs de l'imagerie médicale, de la spectroscopie, de la sécurité et de l'environnement. D'où l'intérêt que suscitent les lasers à cascade quantique terahertz, une récente famille de lasers semi-conducteurs qui émettent à des fréquences de l'ordre du terahertz. Pourtant, s'ils sont aujourd'hui les seules sources compactes fonctionnant dans cette gamme de fréquences, ils présentent deux inconvénients: Premièrement, ils ne fonctionnent qu'à des températures cryogéniques. En vue d'une augmentation future de la température maximale de fonctionnement (Tmax), nous avons développé une étude comparative en fonction de la fréquence d'émission, ce qui a permis de déterminer les mécanismes principaux limitant la Tmax (courant parasite ainsi que l'émission de phonons optiques longitudinaux activés thermiquement). Deuxièmement, afin d'obtenir les meilleures Tmax, l'utilisation d'un guide métal-métal est nécessaire. Néanmoins, dans un tel guide, l'émission obtenue est fortement divergente, ce qui s'avère rédhibitoire pour une utilisation généralisée. Pour résoudre ce point, nous avons intégrés des cristaux photoniques bidimensionnels définis uniquement par la géométrie du métal supérieur, ce qui a permis l'obtention d'une émission directive par la surface, spectralement mono-mode, tout en maintenant des températures de fonctionnement assez élevées.So-called terahertz waves, which lie between infrared and microwaves, have the property of penetrating skin, clothing, paper, wood, cardboard or plastic. These advantages offer numerous applications in medical imaging, spectroscopy, security, and the environment. This is why terahertz quantum cascade lasers - a new family of semiconductor lasers that emit in the frequency range of the terahertz - raise such interest. However, although they are now almost the only compact sources operating within this frequency range, they have two major drawbacks: First, they operate only at cryogenic temperatures. In order to develop strategies to their maximum operating temperature (Tmax), we have developed a comparative study, as a function of the laser emission frequency, which allowed us to elucidate the main factors which limit the devices Tmax (parasitic channel and emission of activated longitudinal-optical phonons). Secondly, the best Tmax are obtained to date by using metal-metal waveguides. However in such waveguides, the resulting emission is strongly divergent, a drawback which prevents their widespread use. We have overcome this issue by using 2D photonic crystals, defined by the sole metal patterning. This approach yields an angularly narrow surface emission, which is also spectrally single mode, with reasonably high maximum operating temperatures.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Tuning the electron-phonon coupling in carbon nanotubes through nano confinement of phonons : a photoluminescence study.

International audienc

Optical properties of core-shell systems based on carbon nanotubes

International audienceSingle-walled carbon nanotubes exhibit unique physical properties and in particular, single-photon emission at room temperature has been recently reported . This has been achieved by surface chemistry that creates point-like defects that localize the nanotube's exciton. The design of these defects allows creating potential well with deepness far above kT leading to the antibunching at room T. The last achievement reports g$^2$(0)<0.01 at room T and in the telecom wavelength bands . Concomitantly, first Cavity Quantum Electrodynamics experiments have been carried out using nanotubes as the quantum emitter. These experiments exhibit Purcell effect and cavity feeding. In order to integrate nanotubes in devices, efforts have to be made on the material side. Nanotubes are only made of surface atoms, the consequence is an uncontrolled sensitivity to their local environment. Our main problem is blinking and spectral diffusion processes at low temperature. The important influence of the environment does not allow us to do lithography that is needed to build real photonics devices. Our strategy is to protect carbon nanotubes from the environment to have a more stable emission and a suitable material for real devices. To do that, we synthesize core/shell nanostructures: the nanotube is the active core, while a polymer acts as protective shell. Here, we will discuss our preliminary results about the influence of the shell on the emission properties of single nanotubes investigated by microphotoluminescence experiments at low temperature

Phonon-Photon Mapping in a Color Center in Hexagonal Boron Nitride

International audienceWe report on the ultraviolet optical response of a color center in hexagonal boron nitride. We demonstrate a mapping between the vibronic spectrum of the color center and the phonon dispersion in hexagonal boron nitride, with a striking suppression of the phonon assisted emission signal at the energy of the phonon gap. By means of nonperturbative calculations of the electron-phonon interaction in a strongly anisotropic phonon dispersion, we reach a quantitative interpretation of the acoustic phonon sidebands from cryogenic temperatures up to room temperature. Our analysis provides an original method for estimating the spatial extension of the electronic wave function in a point defect