One of the major challenges faced in the development of quantum computers and quantum communication is the integration of devices for generating single photons and photon pairs. In this context, a drastic reduction of the size of devices entails a significant drop in their efficiency of photon generation. One way to overcome this challenging obstacle is to excite local electric field by coupling the emitter to plasmonic nano-antennas.
Recently we have achieved this objective by coupling an emitter which is a non-linear nanocrystal to nano-antennas by placing it within the gap of two antennas. Hence, creating a hybrid nano-structure in order to generate an enhancement by a factor that is 1000 times higher than an isolated nanocrystal. Therefore, the objective of the project is to use experimental as well as theoretical or numerical tools to further optimize second order non-linear processes such as second harmonic generation (SHG) and spontaneous parametric down conversion (SPDC) to enhance their efficiency to several orders of magnitude higher than what is already demonstrated. If successful, this would enable the first ever detection of photon pairs with the so called hybrid plasmonic nanostructure using the experimental setup that we have built.
The groundwork towards achieving this goal has already been completed with the pioneering work conducted during the course of three thesis defended in 2018 and 2019. With the development of a quantitative and numerical tool, the optimal configuration to obtain a strong coupling between the non-linear crystal and plasmonic antenna can be determined. This step therefore involves adapting the developed numerical programmes to new plasmonic antenna configurations, in particular, bowtie and to also search for the best materials (Al, Au, Ag) to obtain plasmonic resonances as well as for nonlinear nanocrystals (in particular for nano-iodates developed by Géraldine Dantelle and organic crystals synthesized by Alain Ibanez at the Néel Institute or for other compounds developed by already established collaborations). In the next step, the hybrid structures will be fabricated at the NanoFab platform of the institute using a technique that was recently realized which allows to place the nano-antennas with precision around the desired non-linear crystal as per its efficiency. In the final step, the hybrid nano-structures will be characterized for SHG emission (using an experimental setup and a technique that has already been realized with extremely reliable results) as well as for SPDC if sufficient enhancement is obtained which will allow us to demonstrate for the first time the generation and detection of photon pairs in hybrid plasmonic nano-structures. While the last aspect is ambitious, its theoretical study would already constitute a significant advance towards applications in quantum engineering.
Since their introduction in 1986 optical tweezers become a standard tool for non-invasive manipulation in biology, chemistry, and soft-mater physics. Nowadays, optical tweezers are widely used for trapping dielectric micro-particles or biological cells. The paramount interest of optical tweezers was underlined by the attribution of Nobel Prize in 2018 to A. Ashkin, the inventor of optical tweezers.
The first optical fiber tweezers was proposed in 1993 by A. Constable. This complementary approach shows some interesting features such as the very straightforward experimental implementation and the eased realization of counter-propagatig beam tweezers with reduced light intensities. Moreover, the optical fibers emit the trapping beam close to the trapping position. Optical aberrations are, thus, reduced, the illuminated volume is constricted, and trapping can be realized at almost any position in a complex environment such as an biological cell. high flexibility. Finally, the use of nano-structured optical fiber allows us to tailor the emitted optical beams.
At Institut Néel we are developing different optical fiber tweezers in single and dual fiber geometries and using divergent or focused beams. Our tweezers are applied to trap efficiently dielectric particles of different sizes (60 nm to 1 µm) or shapes (spheres and rods). Furthermore, the anisotropy and polarization depended emission of free, only optically trapped, rare earth-doped nanorod is studied.
In collaboration with our French and international colleagues we are currently exploring optical trapping using advanced microstructured fibers. In particular, fibers with 3D printed optical elements are showing exceptional performances to realize single fiber tweezers or trapping beams with optical angular momentum. Concerning the trapped objects, we are extending our ongoing characterization of fluorescent dielectric particles to trapping of gold nanoparticles or biologic species such as E.colie bacteria or living alga.
A. Drezet and C. Poulain develop classical models that try to reproduce some features of the quantum realm. By combining adequately locked and fine tuned classical oscillators i.e., acoustic waves in vibrating mechanical media they create mechanical analogues that reproduce, at macro scale, effects believed to be exclusive to the quantum realm (e.g the wave-particle duality, the Unruh and the Casimir effect).
Their work is largely inspired by the foundations pioneered by de Broglie, Bohm, and Einstein, it also recalls the recent experiments of the bouncing droplets discovered by Y. Couder and E. Fort in the 2000s which serve as a great source of inspiration and comparison.
In particular, they consider different classical analogues based on fluid mechanics or acoustic waves . Their models relies on either a gas bubble acoustically excited and (in 1D) on a little bead freely sliding along a vibrating string. In all these systems, the particle acts as a defect of the propagating medium interacting with the incoming wave (in 1D, 2D or 3D), producing as scattered wave from which a radiation force emerges.
The complex non-linear dynamics at play in the interaction between a wave and a particle is reminiscent of the radiation force phenomenon, which could play a crucial role in the wave-particle nature. Consequently, this very fundamental subject of research is also very close to other issues studied in the group such as optical trapping on nanoparticles or nano resonators in optical cavity.
Goals
Our research activities are based on the electromagnetic and mechanical properties of matter where at least one spatial dimension is reduced to a few tense nanometers and therefore rely on near-fields. This includes the study of plasmonics, with chiral/nonlinear/quantum responses, opto-mechanics from optical tweezers to macroscopic (quantum) oscillators which are coupled to light and/or spins of NV centers, nanomagnets and skyrmions. These are examples of systems that we investigate in the team by combining experiments, simulations and theoretical approaches at the forefront of the international research.
This project is a combined experimental and theoretical effort aimed at understanding quantum and nonlinear optical processes in the presence of disorder that induces strong multiple scattering of light. In a typical experiment, a powerful light pulse will be sent into a suspension or a powder of sub-micron-sized particles and the nonlinear signal generated by the medium (e.g., second harmonics or parametrically generated entangled photon pairs) will be measured and its quantum statistics will be studied. Another configuration to consider is that of an entangled photon pair is transmitted through a strongly scattering nonlinear medium for analyzing the persistence of entanglement with clear applications to information transfer through foggy air. Most of experimental means are already available (pulsed laser for SHG, Signac loop for entangled photons generation as well as the detection based on four photon correlation measurements). The candidate will also have access to numerical resources (computing cluster) for finite element simulations of the light-matter interaction at the single particle level while large ensembles and multiple scattering will be treated with a combination of analytic diagrammatic theories and numerical simulations to provide a statistical characterisation of the nonlinear processes.
Since their introduction in 1986, optical tweezers become a standard tool for non-invasive manipulation in microbiology, chemistry, and solid state physics. The importance of this device was underlined by the attribution of the Nobel Prize 2018 to Athur Ashkin, the “Inventor” of the optical tweezers. One less known application of optical tweezers is the Photonic Force Microscope (PhFM). This device allows to measure a surface topology with sub-micron resolution by measuring the shift of a trapped object during scanning over the surface. Its principle is quite similar to that of an Atomic Force Microscope (AFM). In contrast to the AFM, the very small magnitude of the optical forces allows us, however, to characterize very soft samples, thus us biological cells.
