Quantum gas microscopes have become a major element for quantum simulations using ultra-cold atoms in optical lattices. They are for example used to observe long-range order such as anti-ferromagnetic correlations in far field optical lattices using density and spin resolved microscopy. Decreasing the period of such lattice offer interesting perspective to increase atom-atom interaction energies and engineer atom-light coupling that our group tackles via the hybridization of cold atoms and nano-structured surfaces.In this poster, we will present how such type of sub-wavelength lattice potentials can be generated by trapping atoms in proximity (tens to hundreds of nanometers) of a nano-structured surface. At such atom to surface distance, the attractive Casimir-Polder force can be compensated by a doubly dressed state trapping method that I will discuss. Such method additionally offers solutions to overcome the diffraction limit of conventional imaging that become critical for sub-wavelength lattices. In this work, I will present the experimental characterization of a sub-wavelength resolution absorption imaging applicable to quantum gas detection. This method requires a quantitative determination of the atom number of dense clouds which has been characterized in this work and demonstrate that the scattering cross section reduces linearly with the optical density. Modelling the propagation of light in dense cloud we show that this reduction can be attributed to re-scattering of the incoherent part of the resonant fluorescence spectrum.The poster will additionally present an update on our recent work on the spectroscopy of Acetylene in sealed hollow core fibers.
Quantum gas microscopes have become a major element for quantum simulations using ultra-cold atoms in optical lattices. They are for example used to observe long-range order such as anti-ferromagnetic correlations in far field optical lattices using density and spin resolved microscopy. Decreasing the period of such lattice offer interesting perspective to increase atom-atom interaction energies and engineer atom-light coupling that our group tackles via the hybridization of cold atoms and nano-structured surfaces.In this poster, we will present how such type of sub-wavelength lattice potentials can be generated by trapping atoms in proximity (tens to hundreds of nanometers) of a nano-structured surface. At such atom to surface distance, the attractive Casimir-Polder force can be compensated by a doubly dressed state trapping method that I will discuss. Such method additionally offers solutions to overcome the diffraction limit of conventional imaging that become critical for sub-wavelength lattices. In this work, I will present the experimental characterization of a sub-wavelength resolution absorption imaging applicable to quantum gas detection. This method requires a quantitative determination of the atom number of dense clouds which has been characterized in this work and demonstrate that the scattering cross section reduces linearly with the optical density. Modelling the propagation of light in dense cloud we show that this reduction can be attributed to re-scattering of the incoherent part of the resonant fluorescence spectrum.The poster will additionally present an update on our recent work on the spectroscopy of Acetylene in sealed hollow core fibers.
Recently, cold atoms in lattices blossomed as good candidates to mimic the prop- erties of electrons in solid state systems and to simulate other quantum systems. However, experimental techniques currently use optical lattices in the far-field. This limit the lattice spacing to λ/2, thus the relevant energy scale (tunneling and interaction), making it difficult to enter deeply into the proper quantum regimes to observe magnetic quantum correlations or strongly correlated phases. Our project aims at reducing the lattice period to bridge the gap between solid state ( ̊A) and far field lattice (500nm) by developing an hybrid quantum system of Bose and Fermi quantum gas in close proximity of a nano-structured surface generating sub-wavelength lattice potentials. To push toward this goal, we first developed a novel method to transport and then trap an ultracold atomic cloud in close vicinity of a surface. We will discuss about the early stage atom-chip produced, and report on some tests about the transport sequence. By measuring the power spectral density of the trap parameters, we can predict the noise- induce heating of the trapped cloud. In order to work with such system, one need to be able to address individually each sites with a resolution under the standard PSF limit. We implemented a tunable sub-wavelength imaging system with a theoretical resolution of 30nm that we used to resolve the wave-packet of a cloud in a single lattice site. This scheme involves two superimposed optical lattices, one at 1064nm and one at 1529nm, whose interfringe can be tuned. We present hereafter the experimental setup in detail and show interesting results we obtained.
The entry into the new millennium was marked in the quantum community by the first experimental realizations of the Bose-Einstein condensation of atoms in a vapor, achieved in different research groups. Twenty-five years later, such systems are 'routinely' produced and are the core of many experiments. At the frontier between condensed matter their y, quantum optics, and atomic physics, ultra-cold atoms are subjects of high scientific interest.Ultra-cold gas can be trapped in optical lattices, giving a realistic way of experimentally realizing a new range of lattice Hamiltonians, that are used to simulate condensed matter systems. In these simulations, ultra-cold atoms are used to mimic the behavior of electrons in a solid-state material and could be used to simulate a wide range of complex condensed matter phenomena, such as the fractional quantum Hall effect, topological insulators, and high-temperature superconductivity.In order to study such systems, diffraction-limited quantum gas microscopes have emerged as a way to manipulate and detect atoms trapped in lattice potentials. Using far-field interference, experiments have mainly been restricted to a lattice spacing of 500 nm. This limits the speed of dynamics of all physical processes.Higher energy regimes could be accessed by reducing the lattice spacing. For this purpose, one of the long-term goals of the team is to trap atoms in the near-field of a surface and to make use of the Casimir-Polder forces to shape sub-wavelength potentials. Thanks to nano-fabrication capabilities, the spacing can be reduced to a few tens of nanometers. However, this requires to adapt the imaging techniques to observe cold-atoms with sub-wavelength spatial resolutions.In this PhD thesis, I report first on the advances toward implementing an atom chip in our experiment, which will serve as an integrated platform to manipulate the quantum gas. I present simulations and study an experimental solution allowing the cloud to be transported to the near-field. The method is based on the interference of a laser radiation in the near field of a rotating surface. It has been fully simulated, and the limitations have been numerically and experimentally assessed. I conclude this part by presenting the first model of chip that has been fabricated.In a second part, I report on the development of a sub-wavelength imaging method of cold Rubidium 87 atoms which is based on excited state dressing. I detail the concept of this nano-metric spatial resolution method and apply it to super-resolve a single longitudinal wave function trapped in a tight lattice that exhibits a width below 30 nm.
Cold atoms are a quantum system well-isolated from the environment. Since the 80s, they have been used to make high-sensitivity atomic sensors and to deepen the understanding of quantum physics phenomena. At low temperatures, degenerate atomic gas regimes can be reached. They are characterized by a macroscopic quantum state that can be manipulated and controlled by lasers. Placing such atomic wave function in optical lattices provide a way to study the dynamics of complex many-body systems. In this context, diffraction-limited quantum gas microscopes have emerged as standard tools to probe such complex systems and to measure atomic density correlations between lattice sites. By further reducing the optical lattices dimensions, the energy scales are strongly enhanced and favor novel quantum phases. Such reduction of optical lattice dimensions requires novel trapping and imaging techniques to manipulate cold-atoms with subwavelength spatial resolutions.In this PhD thesis, we experimentally perform subwavelength imaging of ultra-cold atoms of Rubidium 87 using a dressed excited state method, initially proposed for generating subwavelength trapping potentials. The measurement are performed using in situ absorption imaging. A quantitative comparison of data and theory lead us to reinterprete and modify a method for atom number calibrations that is commonly used in the community. This reinterpretation requires a fine understanding of the interaction of a single quantum multi-level system and a coherent saturating field. The measurement of the in situ transmission of a coherent probe shows a linear reduction of the single-atom scattering cross-section with the optical density for which we propose a physical interpretation and a model. Once calibrated, we use our subwavelength imaging method that reaches down to 20 nm resolution in a few microseconds to super-resolve a tiny quantum object : the longitudinal wave function of a BEC in a very tight lattice.
Ultracold atomic gas is a quantum system well-isolated from the environment, whose interaction with light is well understood. The ultracold gas thus becomes a highly performant quantum simulator to place under tailored potential generated by light. Observation of atom dynamics give answers to many quantum phenomena, such as the fractional quantum Hall effect, topological insulators, and superconductivity. In this context, diffraction-limited quantum gas microscopes have emerged as standard tools to probe such complex systems and to measure atomic density correlations between lattice sites. In addition, capability of manipulating the quantum gas microscopically opens the access to non-equilibrium many-body physics. In this PhD thesis, we investigate sub-wavelength control upon ultracold atoms using a dressed excited state method. We first characterized the excited state spectrum. From Lindblad master equations, a new form of ground state potential has been proposed to explain the coherent dynamics of the atomic wavefunction. We experimentally confirmed the correctness of the proposal through Kapitza-Dirac scattering. We then performed sub-wavelength microscopy on the smallest quantum object we could realize: the atomic wavefunction compressed in a tight optical lattice. Based on this microscopy technique, we could spatially resolve the coherent tunneling dynamics between lattice sites. By introducing site-resolved decay channel, quantum Zeno effect has been observed during the tunneling, opening the way to coherent control of an atomic wavefunction at sub-wavelength scales.
The main objective of this research is to study a particular case of light-matter interaction: the scattering of light in dense atomic samples.The regime of high atomic densities is represented by samples where the distance between neighboring atoms is on the order of the wavelength associated with the atomic transition.In this regime, short-range atomic interactions cannot be neglected, and in these systems, we expect to observe significant modifications in collective effects such as subradiance or superradiance.Overall, the propagation of light through this type of system is not well-known to the scientific community, and the existing models work to describe very specific situations.To pave the way for achieving our overall goal, this work proposes an experimental setup to obtain a dense cloud of 88 Sr, which is the chemical species we work with in our laboratory.For this purpose, atoms previously trapped using a Magneto-Optical Trap are transferred to a Crossed Optical Dipole Trap.During the optimization and characterization of the optical trap, problems were encountered in producing an image with quantitative information of the atomic ensemble and in transferring a large number of atoms in a very small trapping volume.These problems were resolved with the implementation of a Phase Contrast Imaging system and the implementation of an Optical Molasses as an additional cooling step.Under these conditions, we obtained a cloud that can be suitable for conducting studies on collective effects, transitioning from the dilute to the dense regime.The initial experiments, once our atomic ensemble was prepared, involve measuring the coherent transmission of a low-intensity beam through the cloud.For this purpose, incident light near the resonance of a dipolar transition of the type J = 0 ↔ J = 1 of 88 Sr is used, interacting with a homogeneous region of the sample.Simulations of this type of process can be performed using the Coupled Dipole Model, which describes the overall response of light scattering by the sample considering dipole-dipole interactions mediated by light.With this work, we aim to advance the understanding of density effects by comparing the coherent optical response of the dense cloud with the theory based on the Coupled Dipole Model.
Abstract Ultracold atoms in optical lattices are a very promising quantum simulation platform, as they provide a very clean system (almost defect free) and allow control over many parameters such as tunneling coupling or interaction strength. Because the typical lattice spacing lies in the sub-micron range, it is technically demanding to resolve exactly the position of the atoms in the lattice using high-resolution optics such as quantum gas microscopy. Here we review the matter-wave protocol of quantum gas magnification that we developed for magnifying the atomic density distribution in the lattice (Asteria et al 2021 Nature 599 571). The atomic cloud, thus magnified by a factor of up to ∼ 90 , can then be imaged in a single-shot even with sub-lattice resolution with standard absorption imaging techniques. Furthermore, the protocol was demonstrated for 3D systems with high filling factors, which are typically impossible to measure with high-resolution imaging. In this tutorial, we will review how this technique can be used for high-resolution imaging of the density distribution and present the results obtained using it as a method to access new observables. We conclude with an outlook focusing on how this technique could be beneficial for a wide variety of physical systems which can be realized using cold atoms. This tutorial expands on the topic of my presentation for the SAMOP 2023 PhD Prize finalist symposium.