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.
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. The great majority of optical tweezers are actually optimized for trapping particles in suspension, allowing for example working with biological cells such as bacteria. Optical trapping of small particles in air is a more challenging task as one has to compensate the stronger Brownian motion and consider the very strong adhesion forces of particles on a surface. Very recently we have succeed to trap efficiently sub-micron sized dielectric particles in air.
In 1948, Hendrik Casimir predicted that quantum fluctuations of the vacuum, so-called zero-point fluctuations, could give rise to an attractive force between objects. Casimir’s calculations were idealized – he considered two perfectl conducting parallel mirrors facing each other in the vacuum at absolute-zero temperature. Since then, this prediction has been confirmed experimentally but many questions remain, among which the possibility of achieving a repulsive Casimir force.
Quantum mechanics is well known for its apparent weirdness. But at the beginning of quantum history, the likes of Einstein, de Broglie, and later Bohm tried to decipher the meaning behind it through the use of classical analogies and mechanisms that were well understood at the time. The aim of our approach is to venture back to this lost realm of clarity in classical physics without renouncing the great achievements of modern quantum mechanics. Works by de Broglie, Bohm, and Einstein will serve as a foundation to study how some (if not all) quantum effects can be experimentally reproduced using adequately locked and fine-tuned mechanical oscillators interacting within a wavy background.
Exploring new strategies for decision making is a major need in view of scaling up the capability to manage extended numbers of “bandits” (players in the theory game language), but also to deal with complex choices with an arbitrary number of outcomes. At the same time, maintaining the ability to remotely control the type of interactions among players is the cornerstone of this project. To fulfill these global challenges, all resources offered by the quantum nature of photons have to be exploited: coherence (allowing correlated responses among players), quantum superposition (providing unique properties driving the player choices), and all degrees of freedom associated with mass-less particles (scaling the available phase space). In this view, new aspects will be introduced in decision-making strategies: (i) photons multiplets will be generated for emulating larger player assemblies (ii) orbital angular momenta (OAM) will widen the number of degrees of freedom (available choices) compared to polarization-based strategies, (iii) the level of discernibility will be exploited to control the coherence of the player choices and (iv) the full spectrum between factorizable states to quantum-entangled ones will select the type of rules introduced among players. For this proposal, we aim to conduct research on parallel exploration-exploitation optimization on all theoretical, numerical, and experimental fronts, expanding previous works to more “arms” (choices in the game theory language), more realistic situations and with quantitative comparison with existing conventional algorithms. Based on the fundamental quantum nature of light, this work is foreseen to bring significant advances in various domains such as resource sharing, reinforcement learning, and parallel quantum processing.
In this thesis, we propose to address the Casimir effect with a hydrodynamic approach based on an acoustical analog of the quantum vacuum. Experimentally, an isotropic random acoustic noise in a liquid is used to mimic the quantum fluctuations of the vacuum Zero-point field (ZPF). The advantages of using an analog approach are manyfold: (i) fluctuation spectra can be fine-tuned and shaped at will to match that of the quantum, (ii) the orders of magnitude of the length-scales and forces are larger than their quantum counterparts, (iii) the experiments do not require heavy instrumentation (when compared with cryogenic and vacuum conditions) and (iv) most parameters can therefore easily be varied, allowing for quick exploration of any effect. Most importantly, the (acoustic) field itself can be probed and even imaged, unlike the vacuum field.
