We report on the imaging of the in situ spatial distribution of deterministically prepared single-atom wave packets as they expand in a plane, finding excellent agreement with the scaling dynamics predicted by the Schrödinger equation. Our measurement provides a direct and quantitative observation of the textbook free expansion of a one-particle Gaussian wave packet, which we believe has no equivalent in the existing literature. Second, we utilize these expanding wave packets as a benchmark to develop a protocol for the controlled projection of a spatially extended wave function from continuous space onto the sites of a deep optical lattice and subsequent single-atom imaging using quantum gas microscopy techniques. By probing the square modulus of the wave function for various lattice ramp-up times, we show how to obtain a near-perfect projection onto lattice sites. Establishing this protocol represents a crucial prerequisite to the realization of a quantum gas microscope for continuum physics. The method demonstrated here for imaging a wave packet whose initial extent greatly exceeds the pinning lattice spacing, is designed to be applicable to the many-body wave function of interacting systems in continuous space, promising a direct access to their microscopic properties, including spatial correlation functions up to high order and large distances.
We report on the imaging of the in situ spatial distribution of deterministically prepared single-atom wave packets as they expand in a plane, finding excellent agreement with the scaling dynamics predicted by the Schrödinger equation. Our measurement provides a direct and quantitative observation of the textbook free expansion of a one-particle Gaussian wave packet, which we believe has no equivalent in the existing literature. Second, we utilize these expanding wave packets as a benchmark to develop a protocol for the controlled projection of a spatially extended wave function from continuous space onto the sites of a deep optical lattice and subsequent single-atom imaging using quantum gas microscopy techniques. By probing the square modulus of the wave function for various lattice ramp-up times, we show how to obtain a near-perfect projection onto lattice sites. Establishing this protocol represents a crucial prerequisite to the realization of a quantum gas microscope for continuum physics. The method demonstrated here for imaging a wave packet whose initial extent greatly exceeds the pinning lattice spacing, is designed to be applicable to the many-body wave function of interacting systems in continuous space, promising a direct access to their microscopic properties, including spatial correlation functions up to high order and large distances.
Cold atom experiments have traditionally employed bulk imaging techniques, such as absorption imaging, to measure atomic sample densities. However, in recent years, single-atom imaging methods have emerged as powerful tools to probe and manipulate quantum many-body systems at the level of individual particles. This work focuses specifically on quantum gas microscopy using Raman sideband cooling in an optical lattice. This technique, which has been used extensively in several cold atoms groups, has mostly been applied in the context of discrete systems, such as the celebrated Bose- and Fermi-Hubbard models and their generalization. In this thesis, we show how quantum gas microscopy can be extended beyond its original scope to probe continuous many-body systems in a quantitative manner. Our proposed protocol consists in a rapid ramp of the pinning lattice intensity, projecting atoms from the continuum onto discrete lattice sites, followed by a Raman sideband cooling stage that confines atoms near the motional ground state and prevents them from escaping during imaging. To validate the effectiveness of this new method, we characterize the pinning and imaging processes by using continuous quantum gas microscopy to reconstruct the wavefunction of a single-atom Gaussian wave packet during its free expansion. Under optimal conditions, we achieve an imaging fidelity in excess of 95%, defined as the probability of projecting an atom from the continuum to the nearest lattice site and successfully imaging it. We also apply this technique to a quasi-two-dimensional non-interacting Fermi gas, enabling us to extract two- and three-body correlation functions, g2 and g3, with unprecedented spatial resolution and finding an excellent agreement with the theoretical prediction. In particular, our measurements reveal a 90% reduction in the probability of finding two atoms in close proximity for the coldest samples, offering one of the most pristine in situ observations of the Pauli exclusion principle in a continuous system. Finally, we propose a thermometry method based on atom number fluctuations, which are readily obtained from our imaging procedure. Crucially, this thermometry technique could be generalized to strongly interacting systems, where temperature estimation is typically challenging. The quantum gas microscopy technique developed here opens new avenues for studying continuous many-body systems with unprecedented resolution, offering a powerful tool for future cold atom experiments.
Atom-based quantum simulators offer a unique platform that enables the imaging of each particle in a many-body system. Until now, however, this capability has been limited to quantum systems in discretized space such as optical lattices and tweezers, where spatial degrees of freedom are quantized. Here, we introduce a novel method for imaging atomic quantum many-body systems in the continuum, allowing for in situ resolution of every particle. We demonstrate the capabilities of our approach on a two-dimensional atomic Fermi gas. We probe the density correlation functions, resolving their full spatial functional form, and reveal the shape of the Fermi hole arising from Pauli exclusion as a function of temperature. Our method opens the door to probing strongly correlated quantum gases in the continuum with unprecedented spatial resolution, providing in situ access to spatially resolved correlation functions of arbitrarily high order across the entire system.
Quantum gas microscopy provides single-shot access to many-body configurations, yet has so far relied on pinning atoms to a discrete lattice during fluorescence readout. Here, we realize ultrafast atom-resolved fluorescence microscopy of an ultracold 162Dy gas directly in free space, with all external confinement removed during imaging. Exploiting the large mass and broad optical transition of dysprosium together with a high numerical aperture in-vacuum objective, we detect single atoms within 4μs while maintaining an effective point-spread function with a full width at half maximum of 254.8(3)nm. We achieve a single-atom conditional classification fidelity of 99.72(3)% for identified fluorescence candidates. We use the measured single-atom response to construct a statistical configuration-inference model that recovers atomic positions and multiplicities, coming from overlapping atoms, directly from single fluorescence snapshots. We further benchmark our reconstruction algorithm through end-to-end Monte Carlo simulations with known ground-truth atomic configurations, obtaining a reconstruction fidelity of 98.7%. Our approach, applicable to a wide variety of atomic species, extends quantum gas microscopy beyond predefined detection lattices, enabling atom-resolved measurements of counting statistics and higher-order spatial correlations directly on the intrinsic length scales of continuum many-body systems.
This thesis details the complete upgrade and renovation of an existing experimental platform into a high-resolution quantum gas microscope for ultracold 87Rb atoms. Quantum gas microscopes enable site-resolved imaging, providing unprecedented access to quantum statistical effects and many-body phenomena. While such instruments are often employed to study physics in optical lattices, we have innovatively adapted our apparatus to investigate bulk system behavior. A major part of this project involved upgrading the scientific apparatus and retrofitting the previous system. We introduced new optical components, including a high-NA objective, and improved the vacuum system for better optical access. Extensive lab renovations, from upgrading the optical table to reorganizing the laser and imaging setups, were carried out to enhance mechanical and thermal stability. Rigorous optical benchmarking confirmed that the objective achieves diffractionlimited imaging, which is critical for resolving single atoms. This capability allowed us to detect density fluctuations at the scale of the thermal de Broglie wavelength in a quasi-two-dimensional gas of 87Rb atoms. In an experiment resembling Hanbury Brown and Twiss interferometry, we measured a 30% enhancement in the second-order correlation function in situ, demonstrating strong bosonic bunching. This outcome underscores the microscope’s precision and the importance of high-resolution imaging in capturing subtle quantum statistical effects. The successful realization of this apparatus demonstrates the utility of quantum gas microscopes in probing bulk systems. With this new platform in place, future studies can explore critical phenomena, many-body correlations, matter-wave emission, and quantum simulations with cold atoms.
We demonstrate a method to determine the position of single atoms in a three-dimensional optical lattice. Atoms are sparsely loaded from a far-off-resonant optical tweezer into a few vertical planes of a cubic optical lattice positioned near a high-resolution microscope objective. In a single realization of the experiment, we pin the atoms in deep lattices and then acquire multiple fluorescence images with single-site resolution. The objective is translated between images, bringing different vertical planes of the lattice into focus. The applicability of our method is assessed using simulated fluorescence images where the atomic filling fraction in the lattice is varied. This opens up the possibility of extending the domain of quantum simulation using quantum gas microscopes from two to three dimensions.
We demonstrate high-resolution in situ imaging of density-wave ordering induced by cavity-mediated interactions in a unitary Fermi gas. We observe long-range spatial correlations throughout the formation of density waves, both for adiabatic preparation and following a quench, with a pattern controlled by the cavity mode structure. Our single-shot microscopic images together with the real-time readout of the cavity photons provide access to atom-photon correlations. We use this capability to investigate order fluctuations as a function of time following a quench and to directly confirm the correspondence between optical and atomic observables. Our system opens rich perspectives, from local patterning to correlation measurements in long-range interacting quantum gases.