Wave function collapse in a mesoscopic device

We determine the nonlocal in time and space current-current cross correlator $⟨\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{I}({x}_{1},{t}_{1})\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{I}({x}_{2},{t}_{2})⟩$ 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 ${t}_{1}\ensuremath{-}{t}_{2}\ensuremath{-}(\ensuremath{\mid}{x}_{1}\ensuremath{\mid}\ensuremath{-}\ensuremath{\mid}{x}_{2}\ensuremath{\mid})∕{v}_{F}$, with ${v}_{F}$ the Fermi velocity. The nonmonotonic dependence of the retardation on ${x}_{1}$ and its absence at the symmetric position ${x}_{1}=\ensuremath{-}{x}_{2}$ is a signature of an instantaneous wave function collapse, which thus becomes amenable to observation in a mesoscopic solid state device.