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

Atom-atom entanglement by single-photon detection

A scheme for entangling distant atoms is realized, as proposed in the seminal paper by Cabrillo et al. [Phys. Rev. A 59, 1025 (1999)]. The protocol is based on quantum interference and detection of a single photon scattered from two effectively one meter distant laser-cooled and trapped atomic ions. The detection of a single photon heralds entanglement of two internal states of the trapped ions with high rate and with a fidelity limited mostly by atomic motion. Control of the entangled state phase is demonstrated by changing the path length of the single-photon interferometer

Deterministic single-photon source from a single ion

We realize a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity. Photons are created in the cavity with efficiency (88 +- 17)%, a tenfold improvement over previous cavity-ion sources. Results of the second-order correlation function are presented, demonstrating a high suppression of two-photon events limited only by background counts. The cavity photon pulse shape is obtained, with good agreement between experiment and simulation. Moreover, theoretical analysis of the temporal evolution of the atomic populations provides relevant information about the dynamics of the process and opens the way to future investigations of a coherent atom-photon interface

Resonant interaction of a single atom with single photons from a down-conversion source

We observe the interaction of a single trapped calcium ion with single photons produced by a narrow-band, resonant down-conversion source [A. Haase et al., Opt. Lett. 34, 55 (2009)], employing a quantum jump scheme. Using the temperature dependence of the down-conversion spectrum and the tunability of the narrow source, absorption of the down-conversion photons is quantitatively characterized.Comment: 4 pages, 3 figure

Entanglement transfer from dissociated molecules to photons

We introduce and study the concept of a reversible transfer of the quantum state of two internally-translationally entangled fragments, formed by molecular dissociation, to a photon pair. The transfer is based on intracavity stimulated Raman adiabatic passage and it requires a combination of processes whose principles are well established.Comment: 5 pages, 3 figure

Heralded single photon absorption by a single atom

The emission and absorption of single photons by single atomic particles is a fundamental limit of matter-light interaction, manifesting its quantum mechanical nature. At the same time, as a controlled process it is a key enabling tool for quantum technologies, such as quantum optical information technology [1, 2] and quantum metrology [3, 4, 5, 6]. Controlling both emission and absorption will allow implementing quantum networking scenarios [1, 7, 8, 9], where photonic communication of quantum information is interfaced with its local processing in atoms. In studies of single-photon emission, recent progress includes control of the shape, bandwidth, frequency, and polarization of single-photon sources [10, 11, 12, 13, 14, 15, 16, 17], and the demonstration of atom-photon entanglement [18, 19, 20]. Controlled absorption of a single photon by a single atom is much less investigated; proposals exist but only very preliminary steps have been taken experimentally such as detecting the attenuation and phase shift of a weak laser beam by a single atom [21, 22], and designing an optical system that covers a large fraction of the full solid angle [23, 24, 25]. Here we report the interaction of single heralded photons with a single trapped atom. We find strong correlations of the detection of a heralding photon with a change in the quantum state of the atom marking absorption of the quantum-correlated heralded photon. In coupling a single absorber with a quantum light source, our experiment demonstrates previously unexplored matter-light interaction, while opening up new avenues towards photon-atom entanglement conversion in quantum technology.Comment: 10 pages, 4 figure

Trapped Rydberg Ions: From Spin Chains to Fast Quantum Gates

We study the dynamics of Rydberg ions trapped in a linear Paul trap, and discuss the properties of ionic Rydberg states in the presence of the static and time-dependent electric fields constituting the trap. The interactions in a system of many ions are investigated and coupled equations of the internal electronic states and the external oscillator modes of a linear ion chain are derived. We show that strong dipole-dipole interactions among the ions can be achieved by microwave dressing fields. Using low-angular momentum states with large quantum defect the internal dynamics can be mapped onto an effective spin model of a pair of dressed Rydberg states that describes the dynamics of Rydberg excitations in the ion crystal. We demonstrate that excitation transfer through the ion chain can be achieved on a nanosecond timescale and discuss the implementation of a fast two-qubit gate in the ion chain.Comment: 26 pages, 9 figure

Determinisitic Optical Fock State Generation

We present a scheme for the deterministic generation of N-photon Fock states from N three-level atoms in a high-finesse optical cavity. The method applies an external laser pulsethat generates an $N$-photon output state while adiabatically keeping the atom-cavity system within a subspace of optically dark states. We present analytical estimates of the error due to amplitude leakage from these dark states for general N, and compare it with explicit results of numerical simulations for N \leq 5. The method is shown to provide a robust source of N-photon states under a variety of experimental conditions and is suitable for experimental implementation using a cloud of cold atoms magnetically trapped in a cavity. The resulting N-photon states have potential applications in fundamental studies of non-classical states and in quantum information processing.Comment: 25 pages, 9 figure