  NOR gate response in a double quantum ring, where each ring is threaded by a
magnetic flux $\phi$, is investigated. The double quantum ring is sandwiched
symmetrically between two semi-infinite one-dimensional metallic electrodes and
two gate voltages, namely, $V_a$ and $V_b$, are applied, respectively, in lower
arms of the two rings those are treated as the two inputs of the NOR gate. A
simple tight-binding model is used to describe the system and all the
calculations are done through the Green's function formalism. Here we exactly
calculate the conductance-energy and current-voltage characteristics as
functions of the ring-to-electrode coupling strengths, magnetic flux and gate
voltages. Our numerical study predicts that, for a typical value of the
magnetic flux $\phi=\phi_0/2$ ($\phi_0=ch/e$, the elementary flux-quantum), a
high output current (1) (in the logical sense) appears if both the inputs to
the gate are low (0), while if one or both are high (1), a low output current
(0) results. It clearly demonstrates the NOR gate behavior and this aspect may
be utilized in designing an electronic logic gate.
