G. Edward Marti

Enhanced and Reduced Atom Number Fluctuations in a BEC Splitter

We measure atom number statistics after splitting a gas of ultracold 87Rb atoms in a purely magnetic double-well potential created on an atom chip. Well below the critical temperature for Bose-Einstein condensation Tc, we observe reduced fluctuations down to -4.9 dB below the atom shot noise level. Fluctuations rise to more than +3.8 dB close to Tc, before reaching the shot noise level for higher temperatures. We use two-mode and classical field simulations to model these results. This allows us to confirm that the supershot noise fluctuations directly originate from quantum statistics.

Coherent magnon optics in a ferromagnetic spinor Bose-Einstein condensate.

We measure the dispersion relation, gap, and magnetic moment of a magnon in the ferromagnetic F = 1 spinor Bose-Einstein condensate of (87)Rb. From the dispersion relation we measure an average effective mass 1.033(2)(stat)(10)(sys) times the atomic mass, as determined by interfering standing and running coherent magnon waves within the dense and trapped condensed gas. The measured mass is higher than theoretical predictions of mean-field and beyond-mean-field Beliaev theory for a bulk spinor Bose gas with s-wave contact interactions. We observe a magnon energy gap of h × 2.5(1)(stat)(2)(sys) Hz, which is consistent with the predicted effect of magnetic dipole-dipole interactions. These dipolar interactions may also account for the high magnon mass. The effective magnetic moment of -1.04(2)(stat)(8)(sys) times the atomic magnetic moment is consistent with mean-field theory.

Thermometry and cooling of a Bose gas to 0.02 times the condensation temperature

Ultracold gases promise access to many-body quantum phenomena at convenient length and time scales. However, it is unclear whether the entropy of these gases is low enough to realize many phenomena relevant to condensed matter physics, such as quantum magnetism. Here we report reliable single-shot temperature measurements of a degenerate Rb gas by imaging the momentum distribution of thermalized magnons, which are spin excitations of the atomic gas. We record average temperatures as low as 0.022(1)stat(2)sys times the Bose-Einstein condensation temperature, indicating an entropy per particle, S/N ≈ 0.001 kB at equilibrium, that is well below the critical entropy for antiferromagnetic ordering of a Bose-Hubbard system. The magnons themselves can reduce the temperature of the system by absorbing energy during thermalization and by enhancing evaporative cooling, allowing low-entropy gases to be produced within deep traps. Trapped quantum gases can be brought to impressively low temperatures. A single-component Bose gas was cooled to around 500 pK by adiabatic expansion [1], and a two-component lattice-trapped Bose gas was cooled to 350 pK using a spin demagnetization technique [2]. However, the entropies achieved in these systems are still much higher than would be required to observe many-body quantum effects such as magnetic ordering or d-wave superconductivity of atoms in optical lattices [3]. Estimated critical entropies required to achieve quantum magnetic ordering of atoms in optical lattices include S/N ∼ 0.3 kB and S/N ∼ 0.03 kB for bosons in statedependent threeand two-dimensional lattices, respectively [4], and similar values for Néel ordering of latticetrapped Fermi gases [5], with lower entropy needed for less strongly interacting gases. In many experiments on strongly interacting atomicgas systems, the low-entropy regime is reached by first preparing a weakly interacting bulk Bose gas at the lowest possible temperature, and then slowly transforming the system to become strongly interacting [6–10]. To discern whether the transformation is adiabatic and to de-

Collective excitation interferometry with a toroidal Bose-Einstein condensate

The precision of most compact inertial sensing schemes using trapped- and guided-atom interferometers has been limited by uncontrolled phase errors caused by trapping potentials and interactions. Here we propose an acoustic interferometer that uses sound waves in a toroidal Bose-Einstein condensate to measure rotation, and we demonstrate experimentally several key aspects of this type of interferometer. We use spatially patterned light beams to excite counterpropagating sound waves within the condensate and use in situ absorption imaging to characterize their evolution. We present an analysis technique by which we extract separately the oscillation frequencies of the standing-wave acoustic modes, the frequency splitting caused by static imperfections in the trapping potential, and the characteristic precession of the standing-wave pattern due to rotation. Supported by analytic and numerical calculations, we interpret the noise in our measurements, which is dominated by atom shot noise, in terms of rotation noise. While the noise of our acoustic interferometric sensor, at the level of

Two-element Zeeman slower for rubidium and lithium

\ensuremath{\sim}\text{rad}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1}/\sqrt{\text{Hz}}

A Fermi-degenerate three-dimensional optical lattice clock

, is high owing to rapid acoustic damping and the small radius of the trap, the proof-of-concept device does operate at the high densities and small volumes of trapped Bose-Einstein condensed gases.

Imaging Optical Frequencies with 100 1microHz Precision and 1.1 micro m Resolution

We demonstrate a two-element oven and Zeeman slower that produce simultaneous and overlapped slow beams of rubidium and lithium. The slower uses a three-stage design with a long, low-acceleration middle stage for decelerating rubidium situated between two short, high-acceleration stages for aggressive deceleration of lithium. This design is appropriate for producing high fluxes of atoms with a large mass ratio in a simple, robust setup.

Imaging Optical Frequencies with 100 μHz Precision and 1.1 μm Resolution

Making a denser optical lattice clock Some of todays most advanced clocks are made up of large numbers of atoms lined up in a one-dimensional (1D) optical lattice. The numbers improve clock stability, but atomic interactions can limit accuracy. Campbell et al. loaded their fermionic strontium atoms into a 3D optical lattice. The low temperatures and strong interactions ensured that the atoms avoided one another, resulting in a neat pattern where each lattice site was occupied by exactly one atom. This ordering reduced the influence of interactions on the clocks accuracy, whereas the high density of atoms enabled by the 3D geometry improved the precision. Science, this issue p. 90 Dense packing of strontium atoms leads to a measurement precision of 5 × 10–19 in 1 hour of averaging time. Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 × 1017. Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 × 10–19 in 1 hour of averaging time.