Dephasing in a Mach-Zehnder Interferometer by an Ohmic Contact

We study dephasing in an electronic Mach-Zehnder (MZ) interferometer based on quantum Hall edge states by a micrometer-sized Ohmic contact embedded in one of its arms. We find that at the filling factor ν=1, as well as in the case where an Ohmic contact is connected to a MZ interferometer by a quantum point contact that transmits only one electron channel, the phase coherence may not be fully suppressed. Namely, if the voltage bias Δμ and the temperature T are small compared to the charging energy of the Ohmic contact EC, the free fermion picture is manifested, and the visibility saturates at its maximum value. At large biases, ΔμEC, the visibility decays in a power-law manner.