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Deterministic creation of entangled atom–light Schrödinger-cat states

Nature Photonicsvolume 13pages110115 (2019) | Download Citation

Abstract

Quantum physics allows for entanglement between microscopic and macroscopic objects, described by discrete and continuous variables, respectively. As in Schrödinger’s famous cat gedanken experiment, a box enclosing the objects can keep the entanglement alive. For applications in quantum information processing, however, it is essential to access the objects and manipulate them with suitable quantum tools. Here we reach this goal and deterministically generate entangled light–matter states by reflecting a coherent light pulse with up to four photons on average from an optical cavity containing one atom. The quantum light propagates freely and reaches a remote receiver for quantum state tomography. We produce a plethora of quantum states and observe negative-valued Wigner functions, a characteristic sign of non-classicality. As a first application, we demonstrate a quantum-logic gate between an atom and a light pulse, with the photonic qubit encoded in the phase of the light field.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors thank J.I. Cirac, S. Dürr and O. Morin for valuable ideas and discussions. This work was supported by the Deutsche Forschungsgemeinschaft via the excellence cluster Nanosystems Initiative Munich (NIM) and the EU flagship project Quantum Internet Alliance (QIA). S.W. was supported by Elitenetzwerk Bayern (ENB) through the doctoral program Exploring Quantum Matter (ExQM).

Author information

Author notes

    • Stephan Ritter

    Present address: TOPTICA Photonics AG, Gräfelfing, Germany

    • Lin Li

    Present address: School of Physics, Huazhong University of Science and Technology, Wuhan, China

Affiliations

  1. Max-Planck-Institut für Quantenoptik, Garching, Germany

    • Bastian Hacker
    • , Stephan Welte
    • , Severin Daiss
    • , Armin Shaukat
    • , Stephan Ritter
    • , Lin Li
    •  & Gerhard Rempe

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Contributions

Experimental data were taken and analysed by B.H., S.W., S.D. and L.L. The homodyne detection set-up was built by B.H., S.W., S.D., A.S., S.R. and L.L. The manuscript was written by B.H., S.W. and G.R., with input from all authors.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Bastian Hacker.

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DOI

https://doi.org/10.1038/s41566-018-0339-5

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