  Bipolar thermoelectricity in tunnel junctions between superconductors of
different energy gap has been recently predicted and experimentally
demonstrated. This effect showed thermovoltages up to $\pm150\;\mu$V at
milliKelvin temperatures. Thus, superconducting tunnel junctions can be
exploited to realize a passive single-photon thermoelectric detector $TED$
operating in the broadband range 15 GHz - 50 PHz. In particular, this detector
is expected to show a signal-to-noise ratio of about 15 down to $\nu=50$ GHz
and a operating window of more than 4 decades. Therefore, the $TED$ might find
applications in quantum computing, telecommunications, optoelectronics,
spectroscopy and astro-particle physics.
