S. M. Farooqi

Local Blockade of Rydberg Excitation in an Ultracold Gas

In the laser excitation of ultracold atoms to Rydberg states, we observe a dramatic suppression caused by van der Waals interactions. This behavior is interpreted as a local excitation blockade: Rydberg atoms strongly inhibit excitation of their neighbors. We measure suppression, relative to isolated atom excitation, by up to a factor of 6.4. The dependences of this suppression on both laser irradiance and atomic density are in good agreement with a mean-field model. These results are an important step towards using ultracold Rydberg atoms in quantum information processing.

Four-level polarization beats with broadband noisy light

Four-level polarization beats (FLPBs) with broadband noisy light are investigated by use of chaotic field, phase-diffusion, and Gaussian-amplitude models. The polarization beat signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light fields with arbitrary bandwidth. Different stochastic models of the laser field affect only the fourth-order coherence functions. The constant background of the beat signal originates from the amplitude fluctuation of the Markovian stochastic fields. The Gaussian-amplitude field shows fluctuations larger than the chaotic field, which in turn exhibits fluctuations much larger than for the phase-diffusion field with pure phase fluctuations caused by spontaneous emission. It is also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced dispersion effects between the two arms of an interferometer and to the Doppler width do not affect the overall accuracy when FLPBs are used to measure the energy-level difference between two states that are dipolar forbidden from the ground state.

Observation of electric quadrupole transitions to Rydberg nd states of ultracold rubidium atoms

We report the observation of dipole-forbidden, but quadrupole-allowed, one-photon transitions to high-Rydberg states in Rb. Using pulsed uv excitation of ultracold atoms in a magneto-optical trap, we excite 5s{yields}nd transitions over a range of principal quantum numbers n=27-59. Compared to dipole-allowed (E1) transitions from 5s{yields}np, these E2 transitions are weaker by a factor of approximately 2000. We also report measurements of the anomalous np{sub 3/2}:np{sub 1/2} fine-structure transition strength ratio for n=28-75. Both results are in agreement with theoretical predictions.

Long-range interactions in a cold Rydberg gas

The excitation of cold Rydberg atoms is significantly influenced by long-range van der Waals interactions. Avoided crossings between interatomic potentials lead to molecular resonances, while energy level shifts from neighboring atoms suppress resonant Rydberg excitation.

Excitation suppression in an ultracold rydberg gas due to a local van der waals blockade

We observe an excitation suppression effect due to van der Waals interactions between ultracold Rydberg atoms. The observed dependence of this effect on sample density suggests a viable blockade mechanism for realizing quantum gates