Negativity of the excess noise in a quantum wire capacitively coupled to a gate

The electrical current noise of a quantum wire is expected to increase with increasing applied voltage. We show that this intuition can be wrong. Specifically, we consider a single channel quantum wire with impurities and with a capacitive coupling to nearby metallic gates and find that its excess noise, defined as the change in the noise caused by the finite voltage, can be negative at zero temperature. This feature is present both for large (c ≫ cq) and small (c ≪ cq) capacitive coupling, where c is the geometrical and cq the quantum capacitance of the wire. In particular, for c ≫ cq, negativity of the excess noise can occur at finite frequency when the transmission coefficients are