P. L. Gould

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.

Laser cooling of molecules: A sequential scheme for rotation, translation, and vibration

A novel scheme is proposed for sequential cooling of rotation, translation, and vibration of molecules. More generally, this scheme manipulates and controls the states and energies of molecules. The scheme, while somewhat complex, is simpler and more feasible than simply providing a large number of synchronously but independently tunable lasers. The key component is a multiple single frequency laser (MSFL) in which a single narrow band pump laser generates an ensemble of resonant ‘‘stimulated Raman’’ (RSR) sidebands (subsequently amplified and selected) in a sample of the molecules to be cooled. Starting with a relatively cold molecular sample (e.g., a supersonic beam of Cs2), the rotation of molecules is cooled by sequential application of P branch electronic transition frequencies transverse to the molecular beam beginning at higher rotational angular momentum J. Then translation of molecules is cooled by application of multiple low J, P, and R branch transition frequencies which counterpropagate with t...

Photoassociative Production and Trapping of Ultracold KRb Molecules

We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb+. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to 91 cm(-1) below the K(4s)+Rb(5p(1/2)) asymptote have been obtained. We have made assignments to all eight of the attractive Hunds case (c) KRb* potential curves in this spectral region.

Formation of Cold (T ⩽ 1 K) Molecules

Publisher Summary This chapter illustrates that the formation of low-temperature molecules with translational energy distributions characterized by T ≤ K is reviewed. Such molecules can in principle be produced optically or nonoptically or by photoassociation of ultracold atoms. Recent results producing cold - and especially ultracold - alkali metal dmers and producing cold paramagnetic molecules are highlighted, along with their potential applications and scientific significance. It clarifies and summarizes the many proposals for formation of gas-phase molecules with subKelvin translational and internal temperatures (or average energies (divided by Boltzmanns constant k ) if not in a thermal distribution) and to discuss the exciting and very recent results achieved in implementing these proposals. However, for low-density, low-temperature atomic and molecular gases, the time required to reach true equilibrium (a solid) can be much longer than the corresponding experimental studies. Only the translational degrees of freedom clearly equilibrate thermally on a short time scale. The possibilities for nonthermal distributions among other (internal) degrees of freedom are great, as discussed in the chapter.

Long-range interaction of the 39K(4s)+39K(4p) asymptote by photoassociative spectroscopy. I. The 0g− pure long-range state and the long-range potential constants

This paper reports on a comprehensive study of the long-range interaction of the 39K(4s)+39K(4p) asymptotic system. We present a detailed discussion of the R-dependent angular momentum couplings and correlation between the Hund’s case (a) and case (c) molecular states. Analytical expressions for the 16 adiabatic Hund’s case (c) long-range potential curves are derived including the higher order dispersion forces and the effects of retardation. Experimentally, six Hund’s case (c) long-range molecular states (0u+, 1g, and 0g− dissociating to the 4 2S1/2+4 2P3/2 asymptote and 0u+, 1g, and 0g− to the 4 2S1/2+4 2P1/2 limit) are observed with rovibrational resolution by photoassociative spectroscopy of ultracold 39K atoms in a high density magneto-optical trap (MOT). Among the six observed long-range states, the upper 0g− “pure long-range” state has negligible short-range chemical exchange contributions and the measured molecular binding energies (v=0–26) are used to precisely determine the long-range potential ...

Measurements of temperature and spring constant in a magneto-optical trap

We have measured the low-density characteristics of a magneto-optical trap for both isotopes of rubidium. Trapped-atom temperatures are measured by the time-of-flight technique and are similar to temperatures in optical molasses. They are below the Doppler limit in most cases and increase linearly with the ratio of laser intensity to laser detuning. A slight difference between the two isotopes is observed. The data agree well with three-dimensional, multistate, semiclassical simulations. Spring constants of the trap are inferred from careful measurements of the size of the trapped-atom cloud. The spring constant is seen to increase with intensity at low intensity, becoming independent of intensity at high intensity. This trend is consistent with sub-Doppler cooling mechanisms.

Use of trapped atoms to measure absolute photoionization cross sections.

We describe a new technique for accurate measurement of absolute photoionization cross sections. By measuring the loss rateof atoms from a laser trap in the presence of ionizing light, we directly measure the photoionization rate. The only quantities requiring absolute calibration are the ionizing laser intensity and the fractional population in the relevant state. Our technique is capable of detecting extremely small ionization rates, which means that low-power cw sources can be used. We have applied this method to photoionization from the 5P(3/2) state of rubidium at wavelengths of 413 and 407 nm.The cross sections are 1.36(12) x 10(-17) and 1.25(11) x 10(-17) cm(2) , respectively.

Narrow linewidth, highly stable, tunable diode laser system

Abstract We describe a simple method for long term stabilization and tuning of a diode laser which is locked to an external cavity by optical feedback. The cavity-locked laser is stabilized to a saturated absorption resonance in rubidium which is modulated and shifted by a combination of ac and dc magnetic fields. We achieve a linewidth of 15 kHz, long term stability of 10 kHz, and tunability over 80 MHz with no laser frequency modulation.

Observation of a Resonant Four-Body Interaction in Cold Cesium Rydberg Atoms

Cold Rydberg atoms subject to long-range dipole-dipole interactions represent a particularly interesting system for exploring few-body interactions and probing the transition from 2-body physics to the many-body regime. In this work we report the direct observation of a resonant 4-body Rydberg interaction. We exploit the occurrence of an accidental quasicoincidence of a 2-body and a 4-body resonant Stark-tuned Förster process in cesium to observe a resonant energy transfer requiring the simultaneous interaction of at least four neighboring atoms. These results are relevant for the implementation of quantum gates with Rydberg atoms and for further studies of many-body physics.

Two-photon two-color diode laser spectroscopy of the Rb 5D5/2 state

We report on spectroscopic measurements of the Rb 5D5/2 state performed using two-photon excitation with a resonant intermediate state. With the two beams (5S1/2 → 5P3/2 at 780 nm and 5P3/2 → 5D5/2 at 776 nm) counterpropagating, the spectra are Doppler-free and the signals are very robust, even in a room temperature vapor. This is due to the near match of the transition wavelengths. The 5D5/2 hyperfine constants have been measured and compared to previous determinations. We have also performed the excitation in a sample of laser-cooled atoms and compare these results to those obtained at room temperature. The fact that the 5P3/2 → 5D5/2 transition is narrow, robust, diode-laser accessible, and relatively immune to AC-Stark shifts, may make it a promising candidate for a frequency reference at 776 nm.