Frequency entangled W states and quantum frequency translation protocols via forward Brillouin interactions (2412.06641v1)

Abstract: Complex quantum states of light are not only central to advancing our understanding of quantum mechanics, but are also necessary for a variety of quantum protocols. High-dimensional, or multipartite, quantum states are of specific interest, as they can exhibit unique properties both fundamentally and in application. The synthesis of high-dimensional, entangled photonic states can take the form of various schemes, which result in varying forms of entanglement. Frequency-entanglement is specifically attractive due to compatibility with integrated systems and resistance to decoherence in fiber transportation; however, increasing the dimension of frequency-entangled states requires a system that offers quantum interactions between a large set of distinct frequencies. Here, we show how the phonon-photon interactions of forward Brillouin scattering, which offer access to a ladder of optical resonances permitted by a single mechanical mode, can be used for fast-synthesis of frequency-entangled, single-photon W states. In our proposed system, simultaneous laser pulses of different frequencies dynamically evolve either an injected single photon or a heralded single phonon, generating W states of selected dimension and output frequency. This method enables the synthesis of `perfect' W states by adjusting the pulse amplitudes. In addition, we show how this system can be used for quantum frequency translation.