David Weld

New experimental constraints on non-Newtonian forces below 100 microm.

We have searched for large deviations from Newtonian gravity by means of a finite-frequency microcantilever-based experiment. Our data eliminate from consideration mechanisms of deviation that posit strengths approximately 10(4) times Newtonian gravity at length scales of 20 microm. This measurement is 3 orders of magnitude more sensitive than others that provide constraints at similar length scales.

Spin Gradient Thermometry for Ultracold Atoms in Optical Lattices

We demonstrate spin gradient thermometry, a new general method of measuring the temperature of ultracold atoms in optical lattices. We realize a mixture of spins separated by a magnetic field gradient. Measurement of the width of the transition layer between the two spin domains serves as a new method of thermometry which is observed to work over a broad range of lattice depths and temperatures, including in the Mott insulator regime. We demonstrate the thermometry using ultracold rubidium atoms, and suggest that interesting spin physics can be realized in this system. The lowest measured temperature is 1 nK, indicating that the system has reached the quantum regime, where insulating shells are separated by superfluid layers.

Bragg Scattering as a Probe of Atomic Wave Functions and Quantum Phase Transitions in Optical Lattices

We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence.

Feedback control and characterization of a microcantilever using optical radiation pressure

The authors describe a simple method for feedback regulation of the response of a microcantilever using the radiation pressure of a laser. A modified fiber-optic interferometer uses one laser to read out the position of the cantilever and another laser of a different wavelength to apply a force that is a phase-shifted function of that position. The method does not require a high-finesse cavity, and the feedback force is due solely to the momentum of the photons in the second laser. The feedback phase can be adjusted to increase or decrease the microcantilever’s effective quality factor Qeff and effective temperature Teff. The authors demonstrate a reduction of both Qeff and Teff of a silicon nitride microcantilever by more than a factor of 15 using a root-mean-square optical power variation of ∼2μW. Additionally, the authors suggest a method for determination of the spring constant of a cantilever using the known force exerted on it by radiation pressure.

New apparatus for detecting micron-scale deviations from Newtonian gravity

We describe the design and construction of a new apparatus for detecting or constraining deviations from Newtonian gravity at short length scales. The apparatus consists of a new type of probe with rotary mass actuation and cantilever-based force detection which is used to directly measure the force between two micromachined masses separated by tens of microns. We present the first data from the experiment, and discuss the prospects of more precisely constraining or detecting non-Newtonian effects using this probe. Currently, the sensitivity to attractive mass-dependent forces is equal to the best existing limits at length scales near

Effusive atomic oven nozzle design using an aligned microcapillary array

5\text{ }\text{ }\ensuremath{\mu}\mathrm{m}

Self-assembled Zeeman slower based on spherical permanent magnets

. No non-Newtonian effects are detected at that level.

Adiabatic cooling of bosons in lattices to magnetically ordered quantum states

We present a simple and inexpensive design for a multichannel effusive oven nozzle which provides improved atomic beam collimation and thus extended oven lifetimes. Using this design, we demonstrate an atomic lithium source suitable for trapped-atom experiments. At a nozzle temperature of 525 °C, the collimated atomic beam flux directly after the nozzle is 1.2 × 10(14) atoms/s with a peak beam intensity greater than 5.0 × 10(16) atoms/s/sr. This suggests an oven lifetime of several decades of continuous operation.

Fibonacci optical lattices for tunable quantum quasicrystals

We present a novel type of longitudinal Zeeman slower. The magnetic field profile is generated by a 3D array of permanent spherical magnets, which are self-assembled into a stable structure. The simplicity and stability of the design make it quick to assemble and inexpensive. In addition, as with other permanent magnet slowers, no electrical current or water cooling is required. We describe the theory, assembly, and testing of this new design.

Quantum Emulation of Extreme Non-equilibrium Phenomena with Trapped Atoms

We suggest and analyze a scheme to adiabatically cool bosonic atoms to picokelvin temperatures which should allow the observation of magnetic ordering via superexchange in optical lattices. The starting point is a gapped phase called the spin Mott phase, where each site is occupied by one spin-up and one spin-down atom. An adiabatic ramp leads to an xy-ferromagnetic phase. We show that the combination of time-dependent density matrix renormalization group methods with quantum trajectories can be used to fully address possible experimental limitations due to decoherence, and demonstrate that the magnetic correlations are robust for experimentally realizable ramp speeds. Using a microscopic master equation treatment of light scattering in the many-particle system, we test the robustness of adiabatic state preparation against decoherence. Due to different ground-state symmetries, we also find a metastable state with xy-ferromagnetic order if the ramp crosses to regimes where the ground state is a z ferromagnet. The bosonic spin Mott phase as the initial gapped state for adiabatic cooling has many features in common with a fermionic band insulator, but the use of bosons should enable experiments with substantially lower initial entropies.