Atomic lattices bound by light

Meacher

Andreas Hemmerich, Theodor W. Hänsch

Matthias Weidemüller, Andreas Hemmerich, Axel Görlitz +2 more

We observe Bragg diffraction of blue (422 nm) radiation from ultracold rubidium atoms bound in an infrared (780 nm) optical lattice thus demonstrating the long range periodic order in these atomic lattices. The blue light is reflected from the [201] planes of a cubic body-centered lattice at an incidence angle of 57\ifmmode^\circ\else\textdegree\fi{}. The angular breadth of the Bragg resonance is limited by the size of the atomic lattice to less than 0.26 mrad. We use Bragg diffraction in combination with an additional weak infrared probe beam as a novel tool to selectively study the motion of atoms deeply bound in the potential wells.

Christopher R. Monroe

Matthias Weidemüller, Axel Görlitz, Theodor W. Hänsch +1 more

We explore Bragg diffraction from atomic lattices bound by light as a diagnostic tool for studying properties of optical lattices not accessible so far. A weak laser beam at a wavelength of about half the wavelength of the lattice field is diffracted from the (100) and (130) lattice planes of a Rb optical lattice. The observation of well-defined Bragg spots confirms the long-range order in optical lattices. From the acceptance angle for Bragg diffraction we deduce the range over which crystalline order is preserved. The comparison of two Bragg spots diffracted from different lattice planes allows us to directly measure the position spread of the atomic wave packets oscillating in the light-induced potential wells. By combining conventional probe transmission spectroscopy with Bragg diffraction we study the motion of atoms that are deeply bound inside the potential wells. We show experimentally and theoretically how backaction of the bound atoms on the trapping field influences the lattice constant. We develop a model for the modification of the refractive index by the highly ordered atomic medium. Based on first-order scattering theory the model explicitly includes the influence of atomic localization on the resulting lattice constant. By measuring the change of the Bragg angle, we observe a decrease of the lattice plane separation for increasing atomic density. We report experimental evidence for the correction to the refractive index due to the finite position spread of the atoms.

Bhuvanesh Sundar, Kaden R. A. Hazzard