Roger C. Brown

Anomalous broadening in driven dissipative Rydberg systems

We observe interaction-induced broadening of the two-photon 5s-18s transition in ^{87}Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly 2 orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with blackbody induced population in nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms.

Quantum interference and light polarization effects in unresolvable atomic lines: Application to a precise measurement of the6,7LiD2lines

We characterize the effect of quantum interference on the line shapes and measured line positions in atomic spectra. These effects, which occur when the excited state splittings are of order the excited state line widths, represent an overlooked but significant systematic effect. We show that excited state interference gives rise to non-Lorenztian line shapes that depend on excitation polarization, and we present expressions for the corrected line shapes. We present spectra of 6,7 Li D lines taken at multiple excitation laser polarizations and show that failure to account for interference changes the inferred line strengths and shifts the line centers by as much as 1 MHz. Using the correct lineshape, we determine absolute optical transition frequencies with an uncertainty of <= 25kHz and provide an improved determination of the difference in mean square nuclear charge radii between 6 Li and 7 Li. This analysis should be important for a number of high resolution spectral measurements that include partially resolvable atomic lines.

Multiphoton Magnetooptical Trap

We demonstrate a magnetooptical trap (MOT) configuration which employs optical forces due to light scattering between electronically excited states of the atom. With the standard MOT laser beams propagating along the x and y directions, the laser beams along the z direction are at a different wavelength that couples two sets of excited states. We demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and sub-Doppler cooling on both the red and blue sides of the two-photon resonance. The technique demonstrated in this work may have applications in background-free detection of trapped atoms, and in assisting laser cooling and trapping of certain atomic species that require cooling lasers at inconvenient wavelengths.

Magic wavelengths for the 5s-18s transition in rubidium

Magic wavelengths, for which there is no differential ac Stark shift for the ground and excited state of the atom, allow trapping of excited Rydberg atoms without broadening the optical transition. This is an important tool for implementing quantum gates and other quantum information protocols with Rydberg atoms, and reliable theoretical methods to find such magic wavelengths are thus extremely useful. We use a high-precision all-order method to calculate magic wavelengths for the 5s−18s transition of rubidium, and compare the calculation to experiment by measuring the light shift for atoms held in an optical dipole trap at a range of wavelengths near a calculated magic value.

Pulsed Sisyphus Scheme for Laser Cooling of Atomic (Anti)Hydrogen

We propose a laser cooling technique in which atoms are selectively excited to a dressed metastable state whose light shift and decay rate are spatially correlated for Sisyphus cooling. The case of cooling magnetically trapped (anti)hydrogen with the 1S-2S-3P transitions by using pulsed ultraviolet and continuous-wave visible lasers is numerically simulated. We find a number of appealing features including rapid three-dimensional cooling from ∼1 K to recoil-limited, millikelvin temperatures, as well as suppressed spin-flip loss and manageable photoionization loss.

Photonic-Chip Supercontinuum with Tailored Spectra for Counting Optical Frequencies

Supercontinuum generation using chip-integrated photonic waveguides is a powerful approach for spectrally broadening pulsed laser sources with very low pulse energies and compact form factors. When pumped with a mode-locked laser frequency comb, these waveguides can coherently expand the comb spectrum to more than an octave in bandwidth to enable self-referenced stabilization. However, for applications in frequency metrology and precision spectroscopy, it is desirable to not only support self-referencing, but also to generate low-noise combs with customizable broadband spectra. In this work, we demonstrate dispersion-engineered waveguides based on silicon nitride that are designed to meet these goals and enable precision optical metrology experiments across large wavelength spans. We perform a clock comparison measurement and report a clock-limited relative frequency instability of

Faraday-Shielded dc Stark-Shift-Free Optical Lattice Clock

3.8\times10^{-15}

Absolute Transition Frequencies and Quantum Interference in a Frequency Comb Based Measurement of the ^{6,7}Li D Lines

at

2D Superexchange mediated magnetization dynamics in an optical lattice

\tau = 2

Hyperpolarizability and operational magic wavelength in an optical lattice clock

seconds between a 1550 nm cavity-stabilized reference laser and NISTs calcium atomic clock laser at 657 nm using a two-octave waveguide-supercontinuum comb.