Abstract
We investigate the indistinguishability of single photons retrieved from collective Rydberg excitations in cold atomic ensembles. The Rydberg spin waves are created either by off resonant two-photon excitation to the Rydberg state or by Rydberg electromagnetically induced transparency. To assess the indistinguishability of the generated single photons, we perform Hong-Ou-Mandel experiments between the single photons and weak coherent states of light. We analyze the indistinguishability of the single photons as a function of the detection window and for photons generated by off-resonant excitation we infer high value of indistinguishability going from 89% for the full waveform to 98% for small detection windows. In the same way, we also investigate for the first time the indistinguishability of single photons generated by Rydberg EIT, showing values lower than those corresponding to single photons generated by off-resonant excitation. These results are relevant for the use of Rydberg atoms as quantum network nodes.
Highlights
Collective Rydberg atomic excitations are an interesting system for realizing quantum network nodes [1], due to the strong long-range interaction between two Rydberg atoms [2]
We study the overlap between the single photons and weak coherent states as a function of the detection window, and we find that the photons generated under Rydberg electromagnetically induced transparency (EIT) conditions show lower overlap than the ones generated by OR excitation
(normalized coincidences larger than 1), which can be explained by the creation of long-lived pollutants [26,31], which are nonretrievable Rydberg excitations that block the generation of retrievable Rydberg spin waves for several trials
Summary
Collective Rydberg atomic excitations are an interesting system for realizing quantum network nodes [1], due to the strong long-range interaction between two Rydberg atoms [2]. In most of the proposed quantum repeater architectures, including the ones based on Rydberg interactions [22,23], the remote nodes are entangled by a measurement-induced process which involves interference of single photons emitted by the nodes and a Bell state measurement. For this process to be successful, the single photons must be indistinguishable, which means the information about the path is erased. We discuss possible reasons for the lower indistinguishability observed for EIT photons
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