On the excitability of two-level atoms by spectrally encoded single-photon wave packets

Single-photon wave packets are utilized as quantum information carriers within quantum information science and quantum communication applications. Here, we analyze the time-dependent interaction of a two-level atom with a spectrally encoded single-photon wave packet and obtain the excitation probability of the atom based on the Heisenberg-Langevin equations. Our results show that the spectral encoding process causes the single-photon wave packet to spread in the time domain, and the intensity of the wave packet decreases. Therefore, an encoded single-photon wave packet excites a two-level atom much weaker than an uncoded one. These results are crucial for understanding how encoded quantum light interacts with quantum nodes in realistic quantum networks. In particular, they reveal limitations and trade-offs in using spectrally encoded photons for secure, multiplexed quantum communication. The findings offer insights into optimizing encoding strategies for efficient atom-photon interactions and contribute to the development of scalable and secure quantum networking protocols.