Detection of single phonons via phonon drag in two-dimensional materials

The capacity to electrically detect phonons, ultimately at the single-phonon limit, is a key requirement for many schemes for phonon-based quantum computing; so-called quantum phononics. Here, we predict that by exploiting the strong coupling of their electrons to surface-polar phonons, van der Waals heterostructures can offer a suitable platform for phonon sensing, capable of resolving energy transfer at the single-phonon level. The geometry we consider is one in which a drag momentum is exerted on electrons in a graphene layer, by a single out-of-equilibrium phonon in a dielectric layer of hexagonal boron nitride, giving rise to a measurable induced voltage (Vdrag). Our numerical solution of the Boltzmann transport equation shows that this drag voltage can reach a level of a few hundred microvolts per phonon, well above experimental detection limits. Furthermore, we predict that Vdrag should be highly insensitive to the mobility of carriers in the graphene layer and to increasing the temperature to at least 300 K, offering the potential of a versatile material platform for single-phonon sensing.