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European Quantum Electronics Conference (EQEC)

Controlled single-photon pulses from an ion in a cavity

Matthias Keller, Birgit Lange, HERBERT WALTHER, W. Lange, K. Hayasaka

Published Jan 18, 2006• 0 citations
Publisher

Abstract

The paper reports on the single-photon pulses produced using a single /sup 40/Ca/sup +/-ion stored in a radio-frequency trap localizing the ion well in the Lamb-Dicke regime. In this case, the temporal structure of each single-photon pulse is determined exclusively by the shape of the pump pulse. The examples presented show the perfect correspondence of the measured pulse shapes with a theoretical model of single-photon emission from the system. The properties of the single photons continuously emitted from the cavity over times on the order of hours are reported and ways to further enhance the efficiency of the source are also presented.

DOI
10.1109/eqec.2005.1567432

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The paper reports on the single-photon pulses produced using a single /sup 40/Ca/sup +/-ion stored in a radio-frequency trap localizing the ion well in the Lamb-Dicke regime. In this case, the temporal structure of each single-photon pulse is determined exclusively by the shape of the pump pulse. The examples presented show the perfect correspondence of the measured pulse shapes with a theoretical model of single-photon emission from the system. The properties of the single photons continuously emitted from the cavity over times on the order of hours are reported and ways to further enhance the efficiency of the source are also presented.
Summary form only given. In a recent experiment, we have investigated the interaction between a single /sup 40/Ca/sup +/-ion stored in a radio-frequency trap and the field of an optical cavity. One mode of the cavity was tuned to the S/sub 1/2/ to P/sub 1/2/ transition of singly ionized calcium at a wavelength of /spl lambda/ = 397 nm. Using laser Doppler cooling in conjunction with the strong confinement of the ion in an effective harmonic potential (frequency 1.1 MHz), the extension of the ion's wave packet was reduced to 60 nm, corresponding to /spl lambda//7, in the direction of the cavity axis. The position of the ion in the cavity was determined by observing the fluorescent light emitted by the ion after excitation in the cavity field. A large fluorescent rate indicated a position of high intracavity intensity. An image of the standing wave pattern obtained in this way is shown. Note that throughout the measurement the ion remains stationary and the cavity is moved to scan the relative position of ion and field.
We have employed radio-frequency trapping to localize a single 40 Ca + -ion in a high-finesse optical cavity. By means of laser Doppler cooling, the position spread of the ion's wavefunction along the cavity axis was reduced to 42 nm, a fraction of the resonance wavelength of ionized calcium (λ = 397 nm). By controlling the position of the ion in the optical field, continuous and completely deterministic coupling of ion and field was realized. The precise three-dimensional location of the ion in the cavity was measured by observing the fluorescent light emitted upon excitation in the cavity field. The single-ion system is ideally suited to implement cavity quantum electrodynamics under cw conditions. To this end we operate the cavity on the D 3/2 –P 1/2 transition of 40 Ca + (λ = 866 nm). Applications include the controlled generation of single-photon pulses with high efficiency and two-ion quantum gates.
We have demonstrated high-speed controlled generation of single photons in a coupled atom-cavity system. A single 85Rb atom, pumped with a nanosecond-pulse laser, generates a single photon into the cavity mode, and the photon is then emitted out the cavity rapidly. By employing cavity parameters for a moderate coupling regime, the single-photon emission process was optimized for both high efficiency and fast bit rates up to 10 MHz. The temporal single-photon wave packet was studied by means of the photon-arrival-time distribution relative to the pump pulse and the efficiency of the single-photon generation was investigated as the pump power. The single-photon nature of the emission was confirmed by the second-order correlation of emitted photons.
We present a single calcium ion, coupled to a high-finesse cavity, as an almost ideal system for the controlled generation of single photons. Photons from a pump beam are Raman-scattered by the ion into the cavity mode, which subsequently emits the photon into a well-defined output channel. In contrast with comparable atomic systems, the ion is localized at a fixed position in the cavity mode for indefinite times, enabling truly continuous operation of the device. We have performed numeric calculations to assess the performance of the system and present the first experimental indication of single-photon emission in our set-up.
Summary form only given. Recently, cavity QED has produced spectacular advances exploiting the interaction of atoms and photons. A prominent example is the observation of atomic trajectories via the cavity field. In some cases however, the well determined atom-field coupling in those experiments is offset by the lack of control over the motion of the atom. This is detrimental, for example, to the implementation of deterministic dynamics in the system, since neither the arrival time nor the position (and hence the strength of interaction) of an atom is known in advance. These problems are avoided when a single trapped ion interacts with the optical field, as is the case in our cavity-QED system. For coupling to the optical field, we have chosen the D/sub 3/2/ to P/sub 1/2/ transition in /sup 40/Ca/sup +/.
Control over the internal states of trapped ions makes them the ideal system to generate single and two-photon states. Coupling a single ion to an optical cavity enables efficient emission of single photons into a single spatial mode and grants control over their temporal shape, phase and frequency. Using the long coherence time of the ion's internal states and employing a scheme to protect the coherence of the ion-cavity interaction, we demonstrate the generation of a two-photon entangled state with full control over the phase. Initially, ion-photon entanglement is generated. A second photon is subsequently generated, mapping the ion's state onto the second photon. By adjusting the drive field the phase of the entangled state can be fully controlled. We implement this scheme in the most resource efficient way by utilizing a single 40^{40}40Ca+^++ ion coupled to an optical cavity and demonstrate the generation of a two-photon entangled stated with full phase control with a fidelity of up to 82\%.