Wave function collapse in a mesoscopic device

We determine the nonlocal in time and space current-current cross correlator ⟨Î(x₁,t₁)Î(x₂,t₂)⟩ in a mesoscopic conductor with a scattering center at the origin. Its excess part appearing at finite voltage exhibits a unique dependence on the retarded variable t₁-t₂-(∣x₁∣-∣x₂∣)/v_F , with v_F the Fermi velocity. The nonmonotonic dependence of the retardation on x₁ and its absence at the symmetric position x₁=-x₂ is a signature of an instantaneous wave function collapse, which thus becomes amenable to observation in a mesoscopic solid state device.