Fig. 4: Inducing photonic entanglement by post-selecting the electron’s energy.

a A scheme of the proposed experiment, where an (unshaped) electron interacts with two Fock states of light and is then measured with an electron energy spectrometer. The electron spectrometer enables post-selection of events in which an integer number of photons k were emitted by the electron. b Each electron energy is entangled to a different photonic state after the interaction. c A map of the probability to post-select the electron with energy E₀ − ℏω (i.e., k = 1) after one interaction for different initial parameters. The x axis is the number of photons in each photonic Fock state. The y axis is the interaction strength g_Q. d A map of the entropy of entanglement between the two states of light after post-selecting on electrons with energy E₀ − ℏω (i.e., k = 1). The axes are the same as in b. In both panels, we mark interesting initial parameters (one of them is discussed in the text and represents the creation of a Bell state).