Recently, a new generation of experiments with ultracold quantum gases has emerged where the many-body properties are probed and manipulated using ultra-narrow “clock” transitions. We describe here our experimental project, which aims at engineering a special kind of optical lattice realizing an effective magnetic field coupling to the atomic motion - the Hofstadter optical lattice. Our specific experimental scheme uses the ultra-narrow optical transition linking the ground state to a metastable excited state of 174 Ytterbium atoms. We present the current status of the experiment, including the observation of coherent Rabi oscillations between the ground and excited states.
Recently, a new generation of experiments with ultracold quantum gases has emerged where the many-body properties are probed and manipulated using ultra-narrow “clock” transitions. We describe here our experimental project, which aims at engineering a special kind of optical lattice realizing an effective magnetic field coupling to the atomic motion - the Hofstadter optical lattice. Our specific experimental scheme uses the ultra-narrow optical transition linking the ground state to a metastable excited state of 174 Ytterbium atoms. We present the current status of the experiment, including the observation of coherent Rabi oscillations between the ground and excited states.
Recent development of cooling and manipulating Ytterbium atoms opens a new avenue to investigate unprecedented atomic systems with SU(N) spin symmetry and orbital degrees of freedom. The available metastable states and narrow-line optical transitions of Ytterbium atoms allow for the versatile control of the system. Here, we first describe our apparatus for producing ultracold Ytterbium-173 quantum gases in an optical lattice. A gas of 3 × 104 Ytterbium173 atoms is routinely produced at T /TF ∼ 0.3, and loaded into an optical lattice potential. Then we report our recent progress on the spin orbital (SO) coupling interaction realized in optical lattice. As a novel quantum simulator, cold Ytterbium atoms with SO coupling provide a platform to explore the intriguing topological physics.
In this manuscript I present an experimental investigation of the dynamics of an ultracold gas of bosonic ytterbium loaded into optical lattices and exposed to resonant light. The interaction between atoms and light makes it possible to study the coherence properties of the gas. The resonant driving is performed on the relevant optical transitions featured by ytterbium. On the one hand, I demonstrate the coherent driving of the internal state of the atoms on the clock transition, the excited state of which is metastable and can not spontaneously decay, thus preserving the coherence of the gas. The temporal internal dynamics in a deep lattice allows me to measure the collisional properties at low temperature for both clock states. On the other hand, I use the spontaneously emitted photons of the intercombination transition excited level to induce a coupling to the atomic external degrees of freedom. I present the momentum diffusion of a superfluid excited on this transition. Strong interactions between atoms slow down the decoherence and lead to an anomalous sub-diffusive relaxation. A simple model comprising atomic motion, interactions and dissipation accounts for our observations. A theoretical study of the dissipative dynamics in optical lattices sheds light on complementary phenomena such as induced dipole-dipole interactions or collective effects in spontaneous emission.
We demonstrate the experimental implementation of an optical lattice that allows for the generation of large homogeneous and tunable artificial magnetic fields with ultracold atoms. Using laser-assisted tunneling in a tilted optical potential, we engineer spatially dependent complex tunneling amplitudes. Thereby, atoms hopping in the lattice accumulate a phase shift equivalent to the Aharonov-Bohm phase of charged particles in a magnetic field. We determine the local distribution of fluxes through the observation of cyclotron orbits of the atoms on lattice plaquettes, showing that the system is described by the Hofstadter model. Furthermore, we show that for two atomic spin states with opposite magnetic moments, our system naturally realizes the time-reversal-symmetric Hamiltonian underlying the quantum spin Hall effect; i.e., two different spin components experience opposite directions of the magnetic field.
Im “Ytterbium Quantengas”-Experiment untersuchen wir stark korrelierte Quantenvielteilchenphysik mit einem System aus ultrakaltem Ytterbium in einem optischen Gitter durch Spektroskopie an einem extrem schmalen “Uhrenubergang” mit einem stabilen, schmalbandigen Laser.
Ultrakalte Quantengase aus Erdalkali-ahnlichen (AEL) Atomen eignen sich hervorragend als Quantensimulator-Systeme zur Untersuchung stark korrelierter Vielteilchenphysik. Fermionische AELs, wie z.B. 173Yb, weisen viele gunstige Eigenschaften fur Experimente auf: einen schmalen Uhrenubergang, der prazise spektroskopische Messungen ermoglicht, einen tief liegenden, langlebigen metastabilen Zustand, eine Entkopplung von Kernspin und elektronischem Zustand und eine SU(N)-Symmetrie. Ultrakalte Quantengase von AEL-Atomen in einem optischen Gitter ermoglichen die experimentelle Realisierung komplexer Systeme wie das Kondo-Gitter-Modell oder die Untersuchung von Korrelationen in stark dissipativen Systemen.
Ich stelle einen Aufbau einer volloptischen 2D/3D MOT mit optischer Dipolfalle vor. Wir erzeugen saubere, ultrakalte Ytterbium-Quantengase mit Kontrolle uber die Spin-Population. Wir konnen einige 104 Atome in das unterste Band eines tiefen dreidimensionalen optischen Gitters laden, das bei der magischen Wellenlange von 578 nm arbeitet. Ein Abbildungssystem mit einem Repumping-Laser ermoglicht die getrennte Detektion von grundzustands- und angeregten Atomen.
Koharente Kontrolle uber den metastabilen elektronischen Zustand und eine hohe spektroskopische Auflosung erfordern ein hochstabiles, schmalbandiges Lasersystem, das im Zentrum dieser Arbeit steht. Ich prasentiere eine detaillierte Charakterisierung unseres uberarbeiteten 578 nm “Uhren”-Lasersystems, welches durch einen Pound-Drever-Hall (PDH) Lock auf einen Resonator mit hoher Finesse stabilisiert wird. Wesentliche Neuerungen sind der vollstandig aus ULE Glas bestehende Resonator, der einen Betrieb mit geringer Empfindlichkeit gegenuber Temperatur- und Strahlleistungsschwankungen ermoglicht, ein wellenleiterbasierter, fasergekoppelter EOM fur optimale Modulationstiefen des PDH-Lock, eine verbesserte Strahlleistungs-Stabilisierung im Lock-Aufbau und eine verbesserte phasenstabile Faserverbindung zum Experiment. In einer Stabilitatsanalyse mit einem unabhangig auf einen zweiten Resonator stabilisierten Strahl zeigt der Uhrenlaser eine kurzzeitige Linienbreite von 1 Hz uber 2 s. Das kombinierte System zeigt Ein-Stunden lange Zeitfenster mit annahernd linearem Drift und verbleibende Frequenzschwankungen von bis zu 50 Hz. Die Messungen der atomaren Resonanzfrequenz ergab einen langfristigen linearen Drift des Resonators von 318 ± 1 mHz/s. Dieses Lasersystem ist ein wichtiges Werkzeug fur die Praparation, Manipulation und Untersuchung von stark korrelierten Vielteilchensysteme aus ultrakaltem Ytterbium.
In koharenten Uhrenspektroskopie an Spin-polarisiertem 173Yb erreichten wir eine hohe Auflosung von 50 ± 2 Hz FWHM (sinc²-Funktions-Fit) und uber 80% Anregung in dem metastabilen 3P0-Zustand. Wir prasentierten Ubergange in hohere Bandern des optischen Gitters. In Spektroskopie-Messungen an Zwei-Spin-Komponenten-Mischungen konnten wir ein Merkmal von Spin-Austausch-Wechselwirkungen zwischen interorbitalen Zwei-Teilchen-Zustanden auflosen.
Der vorgestellte Aufbau und die entwickelten Techniken zur Praparation und koharenten Kontrolle von Ytterbium bieten einen idealen Ausgangspunkt fur die Erforschung neuer Quantensysteme.
In the “Ytterbium quantum gas” experiment, we investigate strongly correlated quantum many-body physics with a system of ultracold Ytterbium in an optical lattice by performing spectroscopy on an ultra-narrow “clock” transition using a stable, narrow-linewidth laser.
Ultracold quantum gases of alkaline-earth-like (AEL) elements are highly suitable as “quantum simulator” systems for the investigation of strongly-correlated many-body physics. Fermionic AELs, such as 173Yb, exhibit many favourable features for experiments: a narrow clock transition enabling precision spectroscopy measurements, a low-lying, long-lived metastable state, a decoupled nuclear spin- and electronic state and an SU(N) symmetry. Ultracold quantum gases of AEL atoms in an optical lattice enable experimental realizations of complex systems, such as the Kondo lattice model, or the study of correlations emerging in strongly dissipative systems.
I show an experimental apparatus of an all-optical 2D/3D MOT setup with three-beam optical dipole trap. We prepare clean, ultracold Ytterbium quantum gases with control over the spin population. We can load several 104 atoms into the lowest band of a three-dimensional, deep optical lattice, operating at the magic-wavelength of 578 nm. An imaging system with a repumping laser enables the separate detection of ground- and excited state atoms.
Coherent control over the metastable electronic state and high spectroscopic resolution require a highly stable, narrow-linewidth laser system, which is at the focus of this thesis. I present a detailed characterisation of our revised 578 nm “clock” laser system stabilised by Pound-Drever-Hall (PDH) lock to a high-finesse cavity. Key features are the all-ULE glass cavity enabling operation with low sensitivities to temperature- and beam power fluctuations, a waveguide-based, fibre-coupled EOM providing optimal modulation depths for the PDH lock, an improved beam power stabilisation in the lock setup and an improved phase-stable fibre link to the experiment. In a stability evaluation with a beam independently locked to a second cavity, the clock laser shows a short-time linewidth of 1 Hz over 2 s. The combined system shows 1-hour long windows of approximately linear drift with remaining frequency fluctuations up to 50 Hz. Monitoring the atomic resonance frequency, we obtained a long-term linear drift of 318 ± 1 mHz/s of the cavity. This laser system is a crucial tool for the preparation, manipulation and probing of strongly-correlated many-body systems of ultracold Ytterbium.
In coherent clock spectroscopy measurements on single spin-component 173Yb, we achieved a high-resolution of 50 ± 2 Hz FWHM (sinc² curve fit) and over 80% excitation fraction to the metastable 3P0 state. We showed transitions to higher bands in the optical lattice. Performing spectroscopy on two spin-component mixtures, we resolved a feature of spin-exchange interactions between inter-orbital two-particle states.
The presented apparatus and the developed techniques for preparation and coherent control of Ytterbium provide an ideal starting point for the study of novel quantum systems.
In this work I present the development of a new experiment to produce quantum degenerate gases of ytterbium. This project aims at realizing artificial gauge fields with ultracold atoms in optical lattices. Combining intense gauge fields with strong on-site interactions is expected to open a new area for ultracold quantum gases, where for instance the atomic analogs of fractional quantum Hall systems could be realized.First I describe the experimental methods for the production of a Bose-Einstein condensate (BEC) of 174Yb. This implies magneto-optical trapping on the 1S0-3P1 intercombination transition and a transport of the atomic cloud in an optical dipole trap over a distance of 22 cm. Evaporative cooling in a crossed dipole trap results in the production of pure BECs of about 6x10^4 atoms.The planned implementation of artificial gauge fields requires the coherent driving of the 1S0-3P0 clock transition of ytterbium. For this purpose an ultrastable laser system at 578 nm, frequency locked to an ultralow expansion (ULE) cavity, has been realized. A precise determination of the temperature zero-crossing point of the ULE cavity allowed us to limit laser frequency drifts below 100 mHz/s. Spectroscopic measurements of the clock transition on a trapped and free falling BEC are presented, where typical linewidths in the kHz range are observed, limited by interatomic interactions. Finally I present a detailed discussion of the methods to achieve artificial gauge fields in optical lattices and their possible experimental implementation. This includes a scheme to realize a bichromatic state-dependent optical superlattice in a doubly-resonant cavity.
An optical lattice clock probes a spectrally narrow electronic transition in an ensemble of optically trapped, laser-cooled atoms, for use as a time and frequency standard. To date, several lattice clocks have been demonstrated with superior stability and accuracy compared to primary frequency standards based on microwave transitions. Yet, the question of which atomic system (including the element and isotope) performs best as a lattice clock remains unsettled. This thesis describes the first detailed investigation of an optical lattice clock using a spin-1/2 isotope of the ytterbium atom. A spin-1/2 system possesses several advantages over higher-spin systems, including a simplified level structure (allowing for straightforward manipulation of the nuclear spin state) and the absence of any tensor light shift from the confining optical lattice. Moreover, the ytterbium atom (Yb) stands among the leading lattice clock candidates, offering a high-performance optical clock with some degree of experimental simplicity. The frequency stability of the Yb clock is highlighted by resolving an ultra-narrow clock spectrum with a full-width at half-maximum of 1 Hz, corresponding to a record quality factor Q = ν0/Δν = 5 × 1014. Moreover, this system can be highly accurate, which is demonstrated by characterizing the Yb clock frequency at the 3 × 10-16 level of fractional uncertainty, with further progress toward a ten-fold improvement also presented. To reach this low level of uncertainty required careful consideration of important systematic errors, including the identification of the Stark-canceling wavelength, where the clock’s sensitivity to the lattice intensity is minimized, a precise determination of the static polarizability of the clock transition, and the measurement and control of atom-atom collisions.