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Continuous generation of single photons with controlled waveform in an ion-trap cavity system

Abstract

The controlled production of single photons is of fundamental and practical interest; they represent the lowest excited quantum states of the radiation field, and have applications in quantum cryptography1 and quantum information processing2. Common approaches use the fluorescence of single ions3, single molecules4,5, colour centres6,7 and semiconductor quantum dots8,9,10,11,12. However, the lack of control over such irreversible emission processes precludes the use of these sources in applications (such as quantum networks13) that require coherent exchange of quantum states between atoms and photons. The necessary control may be achieved in principle in cavity quantum electrodynamics. Although this approach has been used for the production of single photons from atoms14,15,16, such experiments are compromised by limited trapping times, fluctuating atom–field coupling and multi-atom effects. Here we demonstrate a single-photon source based on a strongly localized single ion in an optical cavity. The ion is optimally coupled to a well-defined field mode, resulting in the generation of single-photon pulses with precisely defined shape and timing. We have confirmed the suppression of two-photon events up to the limit imposed by fluctuations in the rate of detector dark counts. The stream of emitted photons is uninterrupted over the storage time of the ion, as demonstrated by a measurement of photon correlations over 90 min.

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Acknowledgements

We gratefully acknowledge the financial support of the European Commission through the QUEST, QUBITS and QGATES networks.

Author information

Correspondence to Wolfgang Lange.

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Competing interests

The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figure

Cross-correlations between four sets of measured raw data, which were used in determining the two-photon correlation function shown in Figure 3. Legend included. (PDF 79 kb)

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Figure 1: Experimental set-up, outlining the excitation and detection scheme for single photons.
Figure 2: Single-photon pulse shapes for different pump laser profiles, indicated by the green dotted line (not to scale).
Figure 3: Cross-correlations of photon arrival times at the two detectors (counts in 100-ns time bins) around zero delay.
Figure 4: Long-term correlations of photon arrival times at the two detectors.

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