A Single Atom as a Mirror of an Optical Cavity

By tightly focussing a laser field onto a single cold ion trapped in front of a far-distant dielectric mirror, we could observe a quantum electrodynamic effect whereby the ion behaves as the optical mirror of a Fabry-P\'erot cavity. We show that the amplitude of the laser field is significantly altered due to a modification of the electromagnetic mode structure around the atom in a novel regime in which the laser intensity is already changed by the atom alone. e propose a direct application of this system as a quantum memory for single photons.Comment: 7 pages, 3 figures, to appear in Physical Review Letter

Vacuum-Stimulated Raman Scattering based on Adiabatic Passage in a High-Finesse Optical Cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counter-intuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a sub-natural linewidth. The results are in excellent agreement with numerical simulations.Comment: 4 pages, 5 figure

QED with a spherical mirror

We investigate the Quantum-Electro-Dynamic properties of an atomic electron close to the focus of a spherical mirror. We first show that the spontaneous emission and excited state level shift of the atom can be fully suppressed with mirror-atom distances of many wavelengths. A three-dimensional theory predicts that the spectral density of vacuum fluctuations can indeed vanish within a volume $\lambda^3$ around the atom, with the use of a far distant mirror covering only half of the atomic emission solid angle. The modification of these QED atomic properties is also computed as a function of the mirror size and large effects are found for only moderate numerical apertures. We also evaluate the long distance ground state energy shift (Casimir-Polder shift) and find that it scales as $(\lambda/R)^2$ at the focus of a hemi-spherical mirror of radius $R$, as opposed to the well known $(\lambda/R)^4$ scaling law for an atom at a distance $R$ from an infinite plane mirror. Our results are relevant for investigations of QED effects, and also free space coupling to single atoms using high-numerical aperture lenses.Comment: 12 pages, 4 figure

Electromagnetically Induced Transparency from a Single Atom in Free Space

We report an absorption spectroscopy experiment and the observation of electromagnetically induced transparency from a single trapped atom. We focus a weak and narrowband Gaussian light beam onto an optically cooled Barium ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.3 %. We demonstrate electromagnetically induced transparency of the ion by tuning a strong control beam over a two-photon resonance in a three-level lambda-type system. The probe beam extinction is inhibited by more than 75 % due to population trapping.Comment: 4 pages, 3 figure

Transition from antibunching to bunching in cavity QED

The photon statistics of the light emitted from an atomic ensemble into a single field mode of an optical cavity is investigated as a function of the number of atoms. The light is produced in a Raman transition driven by a pump laser and the cavity vacuum [M.Hennrich et al., Phys. Rev. Lett. 85, 4672 (2000)], and a recycling laser is employed to repeat this process continuously. For weak driving, a smooth transition from antibunching to bunching is found for about one intra-cavity atom. Remarkably, the bunching peak develops within the antibunching dip. For saturated driving and a growing number of atoms, the bunching amplitude decreases and the bunching duration increases, indicating the onset of Raman lasing.Comment: 4 pages, 4 figure

Chirality distribution and transition energies of carbon nanotubes

From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, the radial breathing mode frequency and Raman intensity of both metallic and semiconducting tubes. We unambiguously assigned the chiral index (n_1,n_2) of approximately 50 nanotubes based solely on a third-neighbor tight-binding Kataura plot and find omega_RBM=214.4cm^-1nm/d+18.7cm^-1. In contrast to luminescence experiments we observe all chiralities including zig-zag tubes. The Raman intensities have a systematic chiral-angle dependence confirming recent ab-initio calculations.Comment: 4 pages, to be published in Phys. Rev. Let

Interferometric thermometry of a single sub-Doppler cooled atom

Efficient self-interference of single-photons emitted by a sideband-cooled Barium ion is demonstrated. First, the technical tools for performing efficient coupling to the quadrupolar transition of a single $^{138}$Ba$^{+}$ ion are presented. We show efficient Rabi oscillations of the internal state of the ion using a highly stabilized 1.76 $\mu m$ fiber laser resonant with the S$_{1/2}$-D$_{5/2}$ transition. We then show sideband cooling of the ion's motional modes and use it as a means to enhance the interference contrast of the ion with its mirror-image to up to 90%. Last, we measure the dependence of the self-interference contrast on the mean phonon number, thereby demonstrating the potential of the set-up for single-atom thermometry close to the motional ground state.Comment: 6 pages, 6 figure

Contacting single bundles of carbon nanotubes with alternating electric fields

Single bundles of carbon nanotubes have been selectively deposited from suspensions onto sub-micron electrodes with alternating electric fields. We explore the resulting contacts using several solvents and delineate the differences between Au and Ag as electrode materials. Alignment of the bundles between electrodes occurs at frequencies above 1 kHz. Control over the number of trapped bundles is achieved by choosing an electrode material which interacts strongly with the chemical functional groups of the carbon nanotubes, with superior contacts being formed with Ag electrodes.Comment: 4 pages, RevTe