  Single-photon superradiance can emerge when a collection of identical
emitters are spatially separated by distances much less than the wavelength of
the light they emit, and is characterized by the formation of a superradiant
state that spontaneously emits light with a rate that scales linearly with the
number of emitters. This collective phenomena has only been demonstrated in a
few nanomaterial systems, all requiring temperatures below 10K. Here, we
rationally design a single colloidal nanomaterial that hosts multiple (nearly)
identical emitters that are impervious to the fluctuations which typically
inhibit room temperature superradiance in other systems such as molecular
aggregates. Specifically, by combining molecular dynamics, atomistic electronic
structure calculations, and model Hamiltonian methods, we show that the faces
of a heterostructure nanocuboid mimic individual quasi-2D nanoplatelets and can
serve as the robust emitters required to realize superradiant phenomena at room
temperature. Leveraging layer-by-layer colloidal growth techniques to
synthesize a nanocuboid, we demonstrate single-photon superfluorescence via
single-particle time-resolved photoluminescence measurements at room
temperature. This robust observation of both superradiant and subradiant states
in single nanocuboids opens the door to ultrafast single-photon emitters and
provides an avenue to entangled multi-photon states via superradiant cascades.
