  The terahertz (THz) spectral domain offers a myriad of applications spanning
chemical spectroscopy, medicine, security and imaging[1]. It has also recently
become a playground for fundamental studies of light-matter interactions [2-6].
THz science and technology could benefit from optomechanical approaches, which
harness the interaction of light with miniature mechanical resonators [7,8]. So
far, optomechanics has mostly focused on the optical and microwave domains,
leading to new types of quantum experiments [9-11] and to the development of
optical-microwave converters [12-14]. Here we demonstrate an integrated
meta-atom [15] THz resonator with a flexible part acting as a mechanical
oscillator. In this device free space THz photons are collected by the
resonator and induce high frequency currents and charges that, in turn, couple
to the mechanical degrees of freedom. The resulting mechanical motion is
read-out optically, allowing our device to function as a compact and efficient
terahertz detector at room temperature. Furthermore the device operates at high
modulation frequencies (>10MHz), well beyond the cut-off frequencies of Golay
cells, pyroelectric detectors and cryogenic semiconductor bolometers [16,17].
Notably, our experiments unambiguously reveal an instantaneous THz detection
mechanism arising from a nano-scale Coulomb interaction, with a Noise
Equivalent Power that is potentially frequency independent. Alongside this
effect, our compact geometry allows for an uncooled bolometric detection [18]
with extremely short heat diffusion times (few microseconds) and high
detectivity.
