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Squeezing of quantum fluctuations by means of entanglement is a well-recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between 2-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for ≳105 cold caesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A 2-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared with a single-color QND measurement. [ABSTRACT FROM AUTHOR]

We demonstrate the first guiding of cold atoms through a 88mm long piece of photonic band gap fiber. The guiding potential is created by a far-off resonance dipole trap propagating inside the fiber with a hollow core of 12μm. We load the fiber from a dark spot 85Rb magneto-optical trap and observe a peak flux of more than 105 atoms s-1 at a velocity of 1.5m s-1. With an additional reservoir optical dipole trap, a constant atomic flux of 1.5 × 104 atoms s-1 is sustained for more than 150 ms. These results open up interesting possibilities to study nonlinear light-matter interaction in a nearly one-dimensional geometry and pave the way for guided matter wave interferometry. [ABSTRACT FROM AUTHOR]

We report on the collapse and revival of Ramsey fringe visibility when a spatially dependent phase is imprinted in the coherences of a trapped ensemble of two-level atoms. The phase is imprinted via the light shift from a Gaussian laser beam which couples the dynamics of internal and external degrees of freedom for the atoms in an echo spectroscopy sequence. The observed revivals are directly linked to the oscillatory motion of atoms in the trap. An understanding of the effect is important for quantum state engineering of trapped atoms. [ABSTRACT FROM AUTHOR]

Magnetism plays a key role in modern science and technology, but still many open questions arise from the interplay of magnetic many-body interactions. Deeper insight into complex magnetic behaviour and the nature of magnetic phase transitions can be obtained from, for example, model systems of coupled XY and Ising spins. Here, we report on the experimental realization of such a coupled system with ultracold atoms in triangular optical lattices. This is accomplished by imposing an artificial gauge field on the neutral atoms, which acts on them as a magnetic field does on charged particles. As a result, the atoms show persistent circular currents, the direction of which provides an Ising variable. On this, the tunable staggered gauge field, generated by a periodic driving of the lattice, acts as a longitudinal field. Further, the superfluid ground state presents strong analogies with the paradigm example of the fully frustrated XY model on a triangular lattice. [ABSTRACT FROM AUTHOR]

We present a universal method to create a tunable, artificial vector gauge potential for neutral particles trapped in an optical lattice. The necessary Peierls phase of the hopping parameters between neighboring lattice sites is generated by applying a suitable periodic inertial force such that the method does not rely on any internal structure of the particles. We experimentally demonstrate the realization of such artificial potentials, which generate ground-state superfluids at arbitrary nonzero quasimomentum. We furthermore investigate possible implementations of this scheme to create tunable magnetic fluxes, going towards model systems for strong-field physics. [ABSTRACT FROM AUTHOR]

Magnetism plays a key role in modern technology and stimulates research in several branches of condensed matter physics. Although the theory of classical magnetism is well developed, the demonstration of a widely tunable experimental system has remained an elusive goal. Here, we present the realization of a large-scale simulator for classical magnetism on a triangular lattice by exploiting the particular properties of a quantum system. We use the motional degrees of freedom of atoms trapped in an optical lattice to simulate a large variety of magnetic phases: ferromagnetic, antiferromagnetic, and even frustrated spin configurations. A rich phase diagram is revealed with different types of phase transitions. Our results provide a route to study highly debated phases like spin-liquids as well as the dynamics of quantum phase transitions. [ABSTRACT FROM AUTHOR]

In solid-state materials, the static and dynamic properties as well as the magnetic and electronic characteristics are crucially influenced by the crystal symmetry. Hexagonal structures play a particularly important role and lead to novel physics, such as that of carbon nanotubes or graphene. Here we report on the realization of ultracold atoms in a spin-dependent optical lattice with hexagonal symmetry. We show how the combined effects of the lattice and interactions between atoms lead to a forced antiferromagnetic Néel order when two spin-components localize at different lattice sites. We also demonstrate that the coexistence of two components-one Mott-insulating and the other one superfluid-leads to an interaction-induced modulation of the superfluid density, which is observed spectroscopically. Our studies reveal the vast impact of the interaction-induced modulation on the superfluid-to-Mott-insulator transition. The observations are consistent with theoretical predictions using Gutzwiller mean-field theory. [ABSTRACT FROM AUTHOR]

We employ light-induced double Bragg diffraction of delta-kick collimated Bose-Einstein condensates to create three symmetric Mach-Zehnder interferometers. They rely on (i) first-order, (ii) two successive first-order, and (iii) second-order processes which demonstrate the scalability of the corresponding momentum transfer. With respect to devices based on conventional Bragg scattering, these symmetric interferometers double the scale factor and feature a better suppression of noise and systematic uncertainties intrinsic to the diffraction process. Moreover, we utilize these interferometers as tiltmeters for monitoring their inclination with respect to gravity. [ABSTRACT FROM AUTHOR]