Robin Cote

Fast quantum gates for neutral atoms

We propose several schemes for implementing a fast two-qubit quantum gate for neutral atoms with the gate operation time much faster than the time scales associated with the external motion of the atoms in the trapping potential. In our example, the large interaction energy required to perform fast gate operations is provided by the dipole-dipole interaction of atoms excited to low-lying Rydberg states in constant electric fields. A detailed analysis of imperfections of the gate operation is given.

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.

Long-range interactions between alkali Rydberg atom pairs correlated to the ns–ns, np–np and nd–nd asymptotes

We have calculated the long-range interaction potential curves of highly excited Rydberg atom pairs for the combinations Li–Li, Na–Na, K–K, Rb–Rb and Cs–Cs in a perturbative approach. The dispersion C-coefficients are determined for all symmetries of molecular states that correlate to the ns–ns, np–np and nd–nd asymptotes. Fitted parameters are given for the scaling of the C-coefficients as a function of the principal quantum number n for all homonuclear pairs of alkali metal atoms.

Macrodimers: Ultralong Range Rydberg Molecules

We study long range interactions between two Rydberg atoms and predict the existence of ultralong range Rydberg dimers with equilibrium distances of many thousands of Bohr radii. We calculate the dispersion coefficients C5, C6, and C8 for two rubidium atoms in the same excited level np and find that they scale like n(8), n(11), and n(15), respectively. We show that for certain molecular symmetries these coefficients lead to long range potential wells that can support molecular bound levels. Such macrodimers would be very sensitive to their environment and could probe weak interactions. We suggest experiments to detect these macrodimers.

Mesoscopic molecular ions in Bose-Einstein condensates.

We study the possible formation of large (mesoscopic) molecular ions in an ultracold degenerate bosonic gas doped with charged particles (ions). We show that the polarization potentials produced by the ionic impurities are capable of capturing hundreds of atoms into loosely bound states. We describe the spontaneous formation of these hollow molecular ions via phonon emission and suggest an optical technique for coherent stimulated transitions of condensate atoms into a specific bound state. These results open up new possibilities for manipulating tightly confined ensembles.

MECHANISM FOR THE PRODUCTION OF VIBRATIONALLY EXCITED ULTRACOLD MOLECULES OF 7LI2

Abstract A scheme is described by which translationally cold molecules can be created in specific rotational and vibrational levels and it is suggested they be employed to test Wigners threshold laws for inelastic collisions. Calculations are presented of the spontaneous emission probabilities and the absorption oscillator strengths of transitions between the vibrational energy levels of the ground and excited triplet states of the molecules 7 Li 2 . The fractions of transitions into the continuum and into the discrete levels are estimated and it is shown that the translationally cold molecules can be produced efficiently in photoassociation experiments. The photoabsorption rate coefficients are computed.

Two-photon photoassociative spectroscopy of ultracold 88Sr

We present results from two-photon photoassociative spectroscopy of the least-bound vibrational level of the X

Photoassociative Spectroscopy at Long Range in Ultracold Strontium

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SUPERFLUIDITY IN SYMPATHETIC COOLING WITH ATOMIC BOSE-EINSTEIN CONDENSATES

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Efficient formation of ground-state ultracold molecules via STIRAP from the continuum at a Feshbach resonance

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