Björn Hessmo

Controlling cold atoms using nanofabricated surfaces: atom chips

Atoms can be trapped and guided using nanofabricated wires on surfaces, achieving the scales required by quantum information proposals. These atom chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

Beam splitter for guided atoms

We have designed and experimentally studied a simple beam splitter for atoms guided on an Atom Chip, using a current carrying Y-shaped wire and a bias magnetic field. This beam splitter and other similar designs can be used to build atom optical elements on the mesoscopic scale, and integrate them in matterwave quantum circuits. PACS numbers: 03.75.Be, 03.65.Nk Typeset using REVTEX

A single-atom detector integrated on an atom chip: fabrication, characterization and application

We describe a robust and reliable fluorescence detector for single atoms that is fully integrated on an atom chip. The detector allows spectrally and spatially selective detection of atoms, reaching a single-atom detection efficiency of 66%. It consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multi-mode fiber to collect the fluorescence. The fibers are mounted in lithographically defined holding structures on the atom chip. Neutral 87Rb atoms propagating freely in a magnetic guide are detected and the noise of their fluorescence emission is analyzed. The variance of the photon distribution allows us to determine the number of detected photons per atom and from there the atom detection efficiency. The second-order intensity correlation function of the fluorescence shows near-perfect photon anti-bunching and signs of damped Rabi oscillations. With simple improvements, one can increase the detection efficiency to 95%.

Simple integrated single-atom detector

We present a reliable and robust integrated fluorescence detector capable of detecting single atoms. The detector consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multimode fiber to collect the fluorescence. Both are mounted in lithographically defined SU-8 holding structures on an atom chip. 87Rb atoms propagating freely in a magnetic guide are detected with an efficiency of up to 66%, and a signal-to-noise ratio in excess of 100 is obtained for short integration times.

Detecting magnetically guided atoms with an optical cavity

We show that a low-finesse cavity can be efficient for detecting neutral atoms. The low finesse can be compensated for by decreasing the mode waist of the cavity. We have used a near-concentric resonator with a beam waist of 12 microm and a finesse of only 1100 to detect magnetically guided Rb atoms with a detection sensitivity of 0.1 atom in the mode volume. For future experiments on single-atom detection and cavity QED applications, it should be beneficial to use miniaturized optical resonators integrated on atom chips.

Integrated atom detector: Single atoms and photon statistics

Physikalisches Institut, Universita¨t Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany(Dated: March 23, 2009)We demonstrate a robust fiber optics based fluorescence detec tor, fully integrated on an atom chip, whichdetects single atoms propagating in a guide with 66% efficien cy. We characterize the detector performance andthe atom flux by analysing the photon statistics. Near-perfect photon antibunching proves that single atoms aredetected, and allows us to study the second-order intensitycorrelation function of the fluorescence over threeorders of magnitude in atomic density.

Nanofabricated atom optics: Atom chips

Abstract Small tight trapping and guiding potentials can be created for neutral atoms moving microns above surfaces patterned with nanofabricated charged and current-carrying structures. Surfaces holding such structures form atom chips which, for coherent matter wave optics, may form the basis for a variety of novel applications and research tools, similar to integrated circuits in electronics. In this paper we describe the basic principles of atom chip experiments.

Atoms and wires: toward atom chips

Atoms can be trapped and guided using nanofabricated wires on surfaces, achieving the scales required by quantum information proposals. These atom chips form the basis for robust and widespread application of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

Limits to modulation rates of electroabsorption modulators

We analyze the speed limitations of optical electroabsorption modulators. We argue that modulation rate limits are closely related to quantum mechanical adiabaticity. By analyzing the breakdown of the adiabatic approximation, analytical expressions for modulation limits are found. These expressions are numerically validated. Furthermore, we discuss the constraints on the allowable modulation rate set by losses from the quantum well and transition linewidth.

Realization of adiabatic Aharonov–Bohm scattering with neutrons

The adiabatic Aharonov-Bohm (AB) effect is a manifestation of the Berry phase acquired when some slow variables take a planar spin around a loop. While the effect has been observed in molecular spectroscopy, direct measurement of the topological phase shift in a scattering experiment has been elusive in the past. Here, we demonstrate an adiabatic AB effect by explicit simulation of the dynamics of unpolarized very slow neutrons that scatter on a long straight current-carrying wire.