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Joining the quantum state of two photons into one

Nature Photonics volume 7, pages 521–526 (2013)Cite this article

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Abstract

Photons are the ideal carriers of quantum information for communication1,2. Each photon can have a single or multiple qubits encoded in its internal quantum state, as defined by optical degrees of freedom such as polarization, wavelength, transverse modes and so on3,4. However, as photons do not interact, multiplexing and demultiplexing the quantum information across photons has not been possible hitherto. Here, we introduce and demonstrate experimentally a physical process, named ‘quantum joining’, in which the two-dimensional quantum states (qubits) of two input photons are combined into a single output photon, within a four-dimensional Hilbert space. The inverse process is also proposed, in which the four-dimensional quantum state of a single photon is split into two photons, each carrying a qubit. Both processes can be iterated, and hence provide a flexible quantum interconnect to bridge multiparticle protocols of quantum information with multidegree-of-freedom ones, with possible applications in future quantum networking5.

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Figure 1: Quantum joining concept and implementation schemes.
Figure 2: Schematics of the photon quantum joining apparatus.
Figure 3: Experimental set-up used to implement and test the quantum joining.
Figure 4: Experimental results and model predictions.

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Acknowledgements

This work was supported by the 7th Framework Programme of the European Commission, within the Future Emerging Technologies programme, under grant No. 255914, PHORBITECH, and by the Italian Ministry for Education, University and Research, within the Futuro in Ricerca programme, under grant HYTEQ.

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Authors and Affiliations

  1. Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma, I-00185, Italy

    Chiara Vitelli, Nicolò Spagnolo, Lorenzo Aparo & Fabio Sciarrino

  2. Center of Life NanoScience at La Sapienza, Istituto Italiano di Tecnologia, Viale Regina Elena, 255, Roma, I-00185, Italy

    Chiara Vitelli

  3. Dipartimento di Fisica, Università di Napoli Federico II, Complesso Universitario di Monte S. Angelo, via Cintia, Napoli, 80126, Italy

    Enrico Santamato & Lorenzo Marrucci

  4. CNR-SPIN, Complesso Universitario di Monte S. Angelo, via Cintia, Napoli, 80126, Italy

    Lorenzo Marrucci

Authors
  1. Chiara Vitelli
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  2. Nicolò Spagnolo
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  3. Lorenzo Aparo
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  4. Fabio Sciarrino
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Contributions

L.M., with contributions from F.S. and E.S., developed the qubit joining/splitting concept and the corresponding optical schemes. C.V., N.S. and F.S. designed the experimental layout and methodology and, with L.A., carried out the experiments. N.S., C.V. and F.S. developed the model of partial photon distinguishability. All authors discussed the results and participated in preparing the manuscript.

Corresponding authors

Correspondence to Fabio Sciarrino or Lorenzo Marrucci.

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The authors declare no competing financial interests.

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Vitelli, C., Spagnolo, N., Aparo, L. et al. Joining the quantum state of two photons into one. Nature Photon 7, 521–526 (2013). https://doi.org/10.1038/nphoton.2013.107

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