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

TL;DR

This paper demonstrates how sequential excitation of a two-level atom, like a quantum dot, can generate photon-number entangled states over time, with potential applications in quantum technology.

Contribution

It introduces a method to produce photon-number Bell states using sequential pulses on a two-level atom and explores multi-temporal entangled states related to the Fibonacci sequence.

Findings

Generation of photon-number Bell states with two sequential pulses

Time-resolved measurements confirm entanglement properties

Theoretical prediction of Fibonacci-related multi-temporal entangled states

Abstract

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 $\pi$ pulses, we generate a photon-number Bell state. We characterise 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.