David E. Pritchard

Continuous and Pulsed Quantum Zeno Effect

Continuous and pulsed quantum Zeno effects were observed using a 87Rb Bose-Einstein condensate. Oscillations between two ground hyperfine states of a magnetically trapped condensate, externally driven at a transition rate omega(R), were suppressed by destructively measuring the population in one of the states with resonant light. The suppression of the transition rate in the two-level system was quantified for pulsed measurements with a time interval deltat between pulses and continuous measurements with a scattering rate gamma. We observe that the continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when gammadeltat=3.60(0.43), in agreement with the predicted value of 4. Increasing the measurement rate suppressed the transition rate down to 0.005 omega(R).

Phase Diagram for a Bose-Einstein Condensate Moving in an Optical Lattice

The stability of superfluid currents in a system of ultracold bosons was studied using a moving optical lattice. Superfluid currents in a very weak lattice become unstable when their momentum exceeds 0.5 recoil momentum. Superfluidity vanishes already for zero momentum as the lattice deep reaches the Mott insulator (MI) phase transition. We study the phase diagram for the disappearance of superfluidity as a function of momentum and lattice depth between these two limits. Our phase boundary extrapolates to the critical lattice depth for the superfluid-to-MI transition with 2% precision. When a one-dimensional gas was loaded into a moving optical lattice a sudden broadening of the transition between stable and unstable phases was observed.

Ion Balance Mass Spectrometry

We have developed a technique to simultaneously compare the cyclotron frequencies of two single ions to obtain atomic mass ratios with fractional accuracies at or below 10−11. Much like a balance scale, this two‐ion technique cancels many sources of noise and error — chief among them magnetic field noise. The new mass comparisons are used in combination with γ‐ray wavelength measurements, performed by the Institut Laue‐Langevin/National Institute of Standards and Technology, to perform the most direct test of Einstein’s mass‐energy relationship E = mc2. The increased precision and long measurement times also lead to the discovery of a new cyclotron frequency shift arising from polarization forces. This shift allowed the most accurate measurement of the dipole moment of a charged molecule (CO+), as well as a new method for non‐destructively measuring the quantum state of a single molecule.

Raman superradiance & and matter wave amplification in bose-einstein condensates

We observe superradiant light scattering on a Raman transition between different hyperfine levels in 87Rb Bose-Einstein condensates. This effect is used to demonstrate Raman matter wave amplification

Experiments with dilute bose-einstein condensates

Bose-Einstein condensates confined by a combination of gravitational and magnetic force exhibit very low peak density (5*1010 atoms*cm-3) and kinetic temperature (450 pK). Such ensembles are predicted to experience quantum reflection from material surfaces