  We describe a new biasing scheme for single photon detectors based on
superconducting tunnel junctions. It replaces a single detector junction with a
circuit of three junctions and achieves biasing of a detector junction at
subgap currents without the use of an external magnetic field. The biasing
occurs through the nonlinear interaction of the three junctions, which we
demonstrate through numerical simulation. This nonlinear state is numerically
stable against external fluctuations and is compatible with high fidelity
electrical readout of the photon-induced current. The elimination of the
external magnetic field potentially increases the capability of these types of
photon detectors and eases constraints involved in the fabrication of large
detector arrays.
