A spectrograph for exoplanet observations calibrated at the centimetre-per-second level.

The best spectrographs are limited in stability by their calibration light source. Laser frequency combs are the ideal calibrators for astronomical spectrographs. They emit a spectrum of lines that are equally spaced in frequency and that are as accurate and stable as the atomic clock relative to which the comb is stabilized. Absolute calibration provides the radial velocity of an astronomical object relative to the observer (on Earth). For the detection of Earth-mass exoplanets in Earth-like orbits around solar-type stars, or of cosmic acceleration, the observable is a tiny velocity change of less than 10 cm s(-1), where the repeatability of the calibration--the variation in stability across observations--is important. Hitherto, only laboratory systems or spectrograph calibrations of limited performance have been demonstrated. Here we report the calibration of an astronomical spectrograph with a short-term Doppler shift repeatability of 2.5 cm s(-1), and use it to monitor the star HD 75289 and recompute the orbit of its planet. This repeatability should make it possible to detect Earth-like planets in the habitable zone of star or even to measure the cosmic acceleration directly.

Short temporal coherence digital holography with a femtosecond frequency comb laser for multi-level optical sectioning.

In this paper, we demonstrate how short temporal coherence digital holography with a femtosecond frequency comb laser source may be used for multi-level optical sectioning. The object shape is obtained by digitally reconstructing and processing a sequence of holograms recorded during stepwise shifting of a mirror in the reference arm. Experimental results are presented.

Cavity-based single atom preparation and high-fidelity hyperfine state readout.

We prepare and detect the hyperfine state of a single 87Rb atom coupled to a fiber-based high-finesse cavity on an atom chip. The atom is extracted from a Bose-Einstein condensate and trapped at the maximum of the cavity field, resulting in a reproducibly strong atom-cavity coupling. We use the cavity reflection and transmission signal to infer the atomic hyperfine state with a fidelity exceeding 99.92% in a readout time of 100 µs. The atom is still trapped after detection.

Laser frequency combs for astronomical observations.

A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of approximately 1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of approximately 9 meters per second at approximately 1.5 micrometers-beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.

Strong atom-field coupling for Bose-Einstein condensates in an optical cavity on a chip.

An optical cavity enhances the interaction between atoms and light, and the rate of coherent atom-photon coupling can be made larger than all decoherence rates of the system. For single atoms, this 'strong coupling regime' of cavity quantum electrodynamics has been the subject of many experimental advances. Efforts have been made to control the coupling rate by trapping the atom and cooling it towards the motional ground state; the latter has been achieved in one dimension so far. For systems of many atoms, the three-dimensional ground state of motion is routinely achieved in atomic Bose-Einstein condensates (BECs). Although experiments combining BECs and optical cavities have been reported recently, coupling BECs to cavities that are in the strong-coupling regime for single atoms has remained an elusive goal. Here we report such an experiment, made possible by combining a fibre-based cavity with atom-chip technology. This enables single-atom cavity quantum electrodynamics experiments with a simplified set-up and realizes the situation of many atoms in a cavity, each of which is identically and strongly coupled to the cavity mode. Moreover, the BEC can be positioned deterministically anywhere within the cavity and localized entirely within a single antinode of the standing-wave cavity field; we demonstrate that this gives rise to a controlled, tunable coupling rate. We study the heating rate caused by a cavity transmission measurement as a function of the coupling rate and find no measurable heating for strongly coupled BECs. The spectrum of the coupled atoms-cavity system, which we map out over a wide range of atom numbers and cavity-atom detunings, shows vacuum Rabi splittings exceeding 20 gigahertz, as well as an unpredicted additional splitting, which we attribute to the atomic hyperfine structure. We anticipate that the system will be suitable as a light-matter quantum interface for quantum information.

Miniature fluorescence detector for single atom observation on a microchip.

We explore the feasibility of single atom detection on an atom chip by using a tiny fluorescence detector mounted on the chip. Resonant fluorescence from a trapped ultracold atom will be collected with a miniature aspheric lens and taken out of a vacuum chamber through a fiber. During detection, the atom can be held at the focus of the detector with a dipole trapping beam introduced through the same fiber. We have experimentally determined the optical performance of such a detector, taking into account effects such as stray light from the dipole trapping beam and chromatic aberration. The collection efficiency for isotropically emitted radiation is experimentally obtained to be 2.5%. From this, it is estimated that the fluorescence emitted from a single Rb atom will produce a photon count rate of 4.7x10(4) Hz, which is much larger than the shot noise limited background fluctuations.

Coherence in microchip traps.

We report the coherent manipulation of internal states of neutral atoms in a magnetic microchip trap. Coherence lifetimes exceeding 1 s are observed with atoms at distances of 5-130 microm from the microchip surface. The coherence lifetime in the chip trap is independent of atom-surface distance within our measurement accuracy and agrees well with the results of similar measurements in macroscopic magnetic traps. Because of the absence of surface-induced decoherence, a miniaturized atomic clock with a relative stability in the 10(-13) range can be realized. For applications in quantum information processing, we propose to use microwave near fields in the proximity of chip wires to create potentials that depend on the internal state of the atoms.

Magnetic microchip traps and single-atom detection.

Microchip traps provide a promising approach to quantum information processing and communication (QIPC) with neutral atoms: strong and complex potentials can be produced for acting on the qubit atoms, and the potentials can be scaled to higher qubit numbers by virtue of the microfabrication process. We describe experimental results that are relevant to use in QIPC, such as the transport of Bose-Einstein-condensed atomic ensembles along the chip surface with the help of a magnetic conveyor belt. The second part of the paper is devoted to single-atom detection on the chip.