Mach–Zehnder interferometer with quantum beamsplitters
N. G. de Almeida, T. Werlang, D. Valente · Journal of the Optical Society of America B · 2019
The quantum beamsplitter—a two-level system (TLS) coupled to a one-dimensional continuum of electromagnetic modes—is the most elementary version of a beamsplitter that may not only refract and reflect, but also absorb and then reemit a photon. This raises the question of whether a single-photon pulse, once split by a first quantum beamsplitter, could be made to interfere with a second one. Here, we propose and theoretically analyze a quantum Mach–Zehnder interferometer (QMZ) as formed by two concatenated quantum beamsplitters. The distinctive feature of our QMZ is its considerable saturability for a single photon, arising from the broadband nature of the pulse. We show that (i) off-resonant monochromatic photons produce classical interference patterns, whereas (ii) resonant broadband pulses erase these patterns, and that (iii) off-resonant broadband pulses always preserve some degree of interference if the two TLSs are oppositely detuned.