We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1 S 0 -1 P 1 88 Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkalineearth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88 Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87 Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87 Sr MOT. A dual-isotope ( 87 Sr and 88 Sr) MOT is also demonstrated.

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Ring exchange is an elementary interaction for modeling unconventional topological matters which hold promise for efficient quantum information processing. We report the observation of fourbody ring-exchange interactions and the topological properties of anyonic excitations within an ultracold atom system. A minimum toric code Hamiltonian in which the ring exchange is the dominant term, was implemented by engineering a Hubbard Hamiltonian that describes atomic spins in disconnected plaquette arrays formed by two orthogonal superlattices. The ring-exchange interactions were resolved from the dynamical evolutions in the spin orders, matching well with the predicted energy gaps between two anyonic excitations of the spin system. A braiding operation was applied to the spins in the plaquettes and an induced phase 1.00(3)π in the four-spin state was observed, confirming 1 2 -anynoic statistics. This work represents an essential step towards studying topological matters with many-body systems and the applications in quantum computation and simulation.Exploiting the laws of quantum mechanics, quantum information processing can be exponentially faster than the classical counterpart [1]. To make this technology a reality, scientists have to solve the crucial problem of decoherence and systematic errors in real quantum systems, which is very difficult due to the request of an extremely small error threshold to enable error corrections [2,3]. A very encouraging solution to this problem is the Kitaev model [4] of fault-tolerant quantum computation by anyons, a sort of topological quasiparticles being neither bosons nor fermions [5]. In this model, anyons are exploited to encode and manipulate information in a manner which is resistant to errors, the so-called topological protection. Unfortunately, except that signatures of anyonic statistics emerged in the fractional quantum Hall systems [6,7], there has been no conclusive observation of anyons in any existing matters. A proposal suggests to solely mimic anyonic statistics with non-interacting qubits [8] and experimental demonstrations were achieved with entangled photons [9, 10] and ions [11]. However, because the background interacting Hamiltonian does not exist in such systems, it is not possible to define anyonic excitations [12]. Therefore, the observation of anyons remains challenging.To construct the appropriate Hamiltonian for studying anyons, a practical scheme [13] was proposed to create artificial topological matters by manipulating ringexchange interactions [14] among ultracold atoms in optical lattices [15,16]. Although a large category of manybody models [17][18][19][20][21] have been realized with optical lattices, implementing the ring-exchange Hamiltonian is notoriously difficult due to its nature of the fourth-order spin interaction, which is greatly suppressed compared to the lower order processes, such as superexchange interactions [19,20]. So, generation and observation of the ring-exchange interactions and the correlated anyonic excitations become the ...

We report the first experimental study of sub-Doppler cooling in alkaline earth atoms (87Sr) enabled by the presence of nuclear spin-originated magnetic degeneracy in the atomic ground state. Sub-Doppler cooling in a sigma(+)-sigma(-) configuration is achieved despite the presence of multiple, closely spaced excited states. This surprising result is confirmed by an expanded multilevel theory of the radiative cooling force. Detailed investigations of system performance have shed new insights into (sigma(+)-sigma(-)) cooling dynamics and will likely play an important role in the future development of neutral atom-based optical frequency standards.

Ultracold atoms in optical lattices offer a great promise to generate entangled states for scalable quantum information processing owing to the inherited long coherence time and controllability over a large number of particles. We report on the generation, manipulation and detection of atomic spin entanglement in an optical superlattice. Employing a spin-dependent superlattice, atomic spins in the left or right sites can be individually addressed and coherently manipulated by microwave pulses with near unitary fidelities. Spin entanglement of the two atoms in the double wells of the superlattice is generated via dynamical evolution governed by spin superexchange. By observing collisional atom loss with in-situ absorption imaging we measure spin correlations of atoms inside the double wells and obtain the lower boundary of entanglement fidelity as 0.79±0.06, and the violation of a Bell's inequality with S = 2.21±0.08. The above results represent an essential step towards scalable quantum computation with ultracold atoms in optical lattices. arXiv:1507.05937v1 [cond-mat.quant-gas] 21 Jul 2015

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The collision of two ultracold atoms results in a quantum mechanical superposition of the two possible outcomes: each atom continues without scattering, and each atom scatters as an outgoing spherical wave with an s-wave phase shift. The magnitude of the s-wave phase shift depends very sensitively on the interaction between the atoms. Quantum scattering and the underlying phase shifts are vitally important in many areas of contemporary atomic physics, including Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic clocks and magnetically tuned Feshbach resonances. Precise experimental measurements of quantum scattering phase shifts have not been possible because the number of scattered atoms depends on the s-wave phase shifts as well as the atomic density, which cannot be measured precisely. Here we demonstrate a scattering experiment in which the quantum scattering phase shifts of individual atoms are detected using a novel atom interferometer. By performing an atomic clock measurement using only the scattered part of each atom's wavefunction, we precisely measure the difference of the s-wave phase shifts for the two clock states in a density-independent manner. Our method will enable direct and precise measurements of ultracold atom-atom interactions, and may be used to place stringent limits on the time variations of fundamental constants.

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