Nat. Photonics: Wein et al.


Photon-number entanglement generated by sequential excitation of a two-level atom

Wein, S. C., Loredo, J. C., Maffei, M., Hilaire, P., Harouri, A., Somaschi, N., Lemaitre, A., Sagnes, I., Lanco, L., Krebs, O., Auffeves, A., Simon, C., Senellart, P. & Anton-Solanas, C.



Entanglement and spontaneous emission are fundamental quantum phenomena that drive many applications of quantum physics. During the spontaneous emission of light from an excited two-level atom, the atom briefly becomes entangled with the photonic field. Here we show that this natural process can be used to produce photon-number entangled states of light distributed in time. By exciting a quantum dot—an artificial two-level atom—with two sequential π-pulses, we generate a photon-number Bell state. We characterize this state using time-resolved intensity and phase correlation measurements. Furthermore, we theoretically show that applying longer sequences of pulses to a two-level atom can produce a series of multi-temporal mode entangled states with properties intrinsically related to the Fibonacci sequence. Our results on photon-number entanglement can be further exploited to generate new states of quantum light with applications in quantum technologies.