Current noise in a quantum point contact

The current correlation is evaluated for a ballistic quantum point contact interacting with a classical time-dependent field. The formula of low-frequency current noise spectra is obtained and is evaluated analytically for a very short defect and numerically for a smooth potential. In contract to the previous study, there is a parameter region where the current noise with a weak random field is smaller than the Johnson–Nyquist/shot noise expected for a static potential.