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New Journal of Physics

A calcium ion in a cavity as a controlled single-photon source

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

Published Jul 30, 2004• 85 citations
Publisher

Abstract

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.

DOI
10.1088/1367-2630/6/1/095

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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.
With a single trapped calcium ion, strongly localized in an optical resonator, we have realized a cavity-QED system operating under continuous coupling conditions. Ion and field interact via cavity-assisted Raman pulses, applied between the S1/2 ground state and the metastable D3/2 state. We have studied the long-term stability of this interaction at the single-photon level by monitoring the emission from the cavity output and analysing its fluctuations on time-scales up to s. The small Allan variances we find confirm that ion and cavity mode are continuously coupled in a deterministically controlled way. Applications include the generation of single photons on demand and an atom–photon interface for optical quantum networks.
A single rubidium atom trapped within a high-finesse optical cavity is an efficient source of single photons. We theoretically and experimentally study single-photon generation using a vacuum stimulated Raman adiabatic passage. We experimentally achieve photon generation efficiencies of up to 34% and 56% on the D1{D}_{1}D1​ and D2{D}_{2}D2​ line, respectively. Output coupling with 89% results in record-high efficiencies for single photons in one spatiotemporally well-defined propagating mode. We demonstrate that the observed generation efficiencies are constant in a wide range of applied pump laser powers and virtual level detunings. This allows for independent control over the frequency and wave packet envelope of the photons without loss in efficiency. In combination with the long trapping time of the atom in the cavity, our system constitutes a significant advancement toward an on-demand, highly efficient single-photon source for quantum information processing tasks.
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.