The ability to control the population of ground-state magnetic sublevels in ultracold atomic gasses of fermionic87Sr is critical for experiments studying quantum magnetism in systems with many spin-components. This thesis describes the design and construction of hardware allowing the manipulation of spin populations via optical pumping. The apparatus operates using light scattering on the 1S0 to 3P1, F=9/2 to F'=9/2 transition in strontium, near 689nm.
The ability to control the population of ground-state magnetic sublevels in ultracold atomic gasses of fermionic87Sr is critical for experiments studying quantum magnetism in systems with many spin-components. This thesis describes the design and construction of hardware allowing the manipulation of spin populations via optical pumping. The apparatus operates using light scattering on the 1S0 to 3P1, F=9/2 to F'=9/2 transition in strontium, near 689nm.
This thesis presents progress on a path to Rubidium-85 Feshbach molecules that could be used for magnetometery and other experiments. An apparatus including a magneto-optical trap, magnetic trap, and dual laser dipole trap has been modified for studies of the 155 G Feshbach resonance and associated production of ultracold Rubidium-85 molecules. Modifications include changes in the optical pumping technique to spin-polarize Rubidium-85 atoms in the F=2, mF =-2 hyperfine state. In addition, we constructed a dual 6.8 GHz and 3.0 GHz source and a 3 GHz microwave amplifier to evaporatively cool Rubidium-87 and Rubidium-85 and allow for more control of the atomic spin. These modifications and techniques will aid in manipulating the atomic spins in future experiments. As an example, we perform microwave spectroscopy on Rubidium-85 atoms from which we infer a residual magnetic field in the MOT cell of 170 +/- 5 mG. We also found the |F=2, mF = 0> to |F=3, mF = 0> transition to have a Rabi Frequency of 8.9 +/- 0.5 kHz, the |F=2, mF = 0> to |F=3, mF = -1> transition to have a Rabi frequency of 10.1 +/- 0.5 kHz, and the |F=2, mF = 0> to |F=3, mF = +1> transition to have a Rabi frequency of 11.0 +/- 0.5 kHz.
Lanthanides, like erbium and dysprosium, have emerged as powerful platforms for quantum-gas research due to their diverse properties, including a significant large spin manifold in their absolute ground state. However, effectively exploiting the spin richness necessitates precise manipulation of spin populations, a challenge yet to be fully addressed in this class of atomic species. In this work, we present an all-optical method for deterministically controlling the spin composition of a dipolar bosonic erbium gas, based on a clocklike transition in the telecom window at 1299 n m . The atoms can be prepared in just a few tens of microseconds in any spin-state composition using a sequence of Rabi-pulse pairs, selectively coupling Zeeman sublevels of the ground state with those of the long-lived clocklike state. Finally, we demonstrate that this transition can also be used to create spin-selective light shifts, thus fully suppressing spin-exchange collisions. These experimental results unlock exciting possibilities for implementing advanced spin models in isolated, clean, and fully controllable lattice systems. Published by the American Physical Society 2024
Abstract : Ultracold molecules provide an exciting testing ground for studies of fundamental interactions, new states of matter, and metrology. Diatomic molecules based on two-electron atoms are especially suitable for precise tests of interatomic interactions, molecular quantum electrodynamics, electron-proton mass ratio variations, and other measurements in molecular and fundamental physics. This thesis describes the construction of a new strontium apparatus, from initial vacuum system setup through characterization of ultracold atom samples, followed by a new method of efficient, all-optical production of ultracold 88Sr2 molecules in an optical lattice, with detection via optical fragmentation. High-Q spectra of the weakly bound molecules in magnetic fields are studied, yielding precise binding energies, anomalously large molecular g factors resulting from large nonadiabatic effects, and strongly enhanced magnetic susceptibility. The thesis then concludes with an outlook on future experiments in our lab, including studies of forbidden molecular transitions, and longer term studies of fundamental physics from deeply bound Sr2.
This thesis reviews our implementation of a quantum simulator for the Fermi-Hubbard modelwith strontium 87. Closed-shell 87 Sr with large nuclear spin I=9/2 benefits from a 7.4 kHz narrowintercombination line that played a central role in this thesis. It offers ideal conditions for the realizationof spin orbit coupling schemes to coherently manipulate the 10 nuclear spin states with minimalspontaneous emission. First, we demonstrated a method to measure local densities smaller than theresolution limit of our imaging system. We overcome the limits due to aberrations and fast variationsof the density profiles. Derived from the Beer-Lambert law, the non-linear correction lets us infer sizesas small as 1/4 pixel. Then, we prepare polarized Fermi seas of 87 Sr at T /TF ≃ 0.25, with a spinpurification by optical pumping. The spin populations are measured with a spin orbit coupling schemeassociated with the narrow line, realizing a spin dependent momentum transfer. We then demonstratea method to coherently and selectively flip the spin states. The degeneracy of the ground state is liftedwith a quadratic light shift. With a Raman adiabatic passage, the spins are flipped with 80 % efficiencythat will be improved up to 95 %. Designed as an optical super lattice, this scheme will permit to writedeterministic spin textures that will be the initial state for the quantum simulator. Finally, we studythe loading of Fermi gases into the ground band of a 1D lattice with large sites spacing 2 µm. Ourexperiment highlights the critical importance of maintening a sufficient collision rate to adiabaticallyfollow the 3D to 2D dimensionnality cross-over, and we simultaneously produce four 2D Fermi seas.
The subject of this thesis is the construction and characterization of an experimental setup for studying the interaction of an ensemble of 10^5 - 10^6 cold 87 Rb atoms held in a far off-resonance optical dipole trap with a probe detuned by about 100 natural line widths, a regime in which refractive effects are resonantly enhanced but absorption is small. An important feature of this type of atom-light interface is that it facilitates quantum non-demolition measurements which in turn have numerous applications in quantum information technology, as well as in the field of ultra-precise metrology where they allow the measurements to overcome the so-called standard quantum limit.
The use of a dipole trap has several advantages over more conventional approaches in which vapor cells or magneto-optical traps (MOT) have been used. Most importantly interaction strength of comparable magnitude can be achieved with a far lower number of atoms and with longer coherence times. The elongated geometry that can be realized in a dipole trap maximizes the interaction strength. One of the complications that arise is that the achievable interaction strength is highly sensitive to the mode-matching between the trapped ensemble and the probe beam.
The theoretical description of the interaction between a trapped ensemble and a freely-propagating probe beam is provided in the framework of continuous variables. The relevant quantities are a pseudo-spin, defined for an ensemble of atoms in their ground state, and the Stokes vector that characterizes the polarization state of light. In practice the experiment consists of four main blocks: the atom traps, the optical pumping setup, the probe laser setup, and the photodetection.
Before loading into the dipole trap, atoms are cooled in a MOT. An existing MOT setup has been improved by implementing a new, more powerful laser system. A dedicated dipole trap, which had been constructed in collaboration with another project, has been thoroughly characterized and the results are presented in this thesis. Setups for optical pumping and for the probe have been built, characterized and incorporated into the apparatus.
Several experimental techniques have been developed and tested in order to optimize the alignment of the probe with the trapped ensemble. The effect of the geometrical overlap on the achievable signal to noise ratio is discussed and illustrated using simple, intuitive models.
Photo-detection is a critical part of the setup. In order to facilitate detection of non-classical (squeezed) states of the atomic (pseudo-) spin, the detection system must be shot-noise limited within the range of photon numbers used in the experiments. Such a system has been constructed and tested, and is described in detail. It employs a charge-sensitive amplifier (CSA) but, unlike earlier implementations, it does not use a pulse-shaping stage. Instead, an algorithm has been devised and implemented that derives the quantities of interest directly from the output signal of the CSA. This novel approach avoids the technical problems that arise in systems using hardware-based pulse shaping. It also makes the detector more flexible in terms of the shape and timing of the probe pulses that can be used.
The atomic states produced in the setup are intrinsically sensitive to stray magnetic fields. Therefore an efficient cancellation of stray fields is essential. On the other hand having the possibility to apply a fully controlled, external magnetic field makes the experimental setup more versatile. Both goals can be achieved with a magnetic field control unit that has been built during this project. It facilitates active cancellation of stray magnetic fields at the frequency of the mains and in addition allows to apply an arbitrary waveform magnetic fields along all three axes. One of the main results reported in this thesis is the observation of polarization rotation caused by population imbalance created in the process of optical pumping and, in a separate series of measurements, due to an applied magnetic field. These measurements have allowed us to assess the strength of the atom-light interaction available in the current setup. They indicate that with the necessary modifications to the optical pumping scheme the system should prove successful in implementing quantum information protocols, in particular quantum memory for light.
An interesting off-shoot has been the spectroscopic characterization of the atomic state in the dipole trap. In these measurements Doppler free spectra are recorded in a very simple setup without the need to use nonlinear techniques. Apart from providing a method to characterize the efficiency of the optical pumping into the hyperfine level of interest, the acquired spectra are a very direct illustration of the power of the laser cooling techniques developed in the recent years and without which this work would not have been possible.