Generation of non-classical light in a photon-number superposition

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Generating light in a pure quantum state is essential for advancing optical quantum technologies. However, controlling its photon number remains elusive. Optical fields with zero and one photon can be produced by single atoms, but, so far, this has been limited to generating incoherent mixtures or coherent superpositions with a very small one-photon term. Here, we report the on-demand generation of quantum superpositions of zero, one and two photons via coherent control of an artificial atom. Driving the system up to full atomic inversion leads to quantum superpositions of vacuum and one photon, with their relative populations controlled by the driving laser intensity. A stronger driving of the system, with 2π pulses, results in a coherent superposition of vacuum, one and two photons, with the two-photon term exceeding the one-photon component, a state allowing phase super-resolving interferometry. Our results open new paths for optical quantum technologies with access to the photon-number degree of freedom.

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Fig. 1: Coherent control of an artificial atom.
Fig. 2: Quantum superposition of vacuum and one photon.
Fig. 3: Quantum superposition of vacuum, one and two photons.

Data availability

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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This work was partially supported by ERC Starting Grant no. 277885 QD-CQED, the French Agence Nationale pour la Recherche (grant ANR SPIQE and USSEPP), the French RENATECH network and a public grant overseen by the French National Research Agency (ANR) as part of the Investissements d’Avenir programme (Labex NanoSaclay, reference ANR-10-LABX-0035). J.C.L. and C.A. acknowledge support from Marie Skłodowska-Curie Individual Fellowships SMUPHOS and SQUAPH, respectively. We thank N. Carlon Zambon for providing technical assistance throughout the project.

Author information

The experiments were conducted by J.C.L. and C.A. with help from P.H., C.M., H.O. and L.D.S. Data analysis was carried out by C.A. and J.C.L. The theoretical modelling was done by A.A., B.R., O.K., C.A. and J.C.L. The cavity devices were fabricated by A.H. and N.S. from samples grown by A.L., and the etching was done by I.S. The manuscript was written by J.C.L., C.A. and P.S. with input from all authors. The project was supervised by L.L., A.A., O.K. and P.S.

Correspondence to J. C. Loredo or C. Antón or P. Senellart.

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Competing interests

N.S. is co-founder, and P.S. is scientific advisor and co-founder, of the single-photon-source company Quandela.

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Loredo, J.C., Antón, C., Reznychenko, B. et al. Generation of non-classical light in a photon-number superposition. Nat. Photonics 13, 803–808 (2019) doi:10.1038/s41566-019-0506-3

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