CHARGE FLUCTUATIONS IN QUANTUM POINT CONTACTS AND CHAOTIC CAVITIES INTHE PRESENCE OF TRANSPORT

We analyze the frequency-dependent current fluctuations induced into a yale near a quantum point contact or a quantum chaotic cavity. We use a current-and charge-conserving effective scattering approach in whic h interactions are treated in tile: random-phase approximation. The cu rrent fluctuations measured at a nearby gate, coupled capacitively to the conductor, are determined by the screened charge fluctuations of t he conductor. Both the equilibrium and nonequilibrium current noise at the gate can be expressed with the help uf resistances which are rela ted to the charge dynamics on the conductor. We evaluate these resista nces for a point contact, and determine their distributions for an ens emble of chaotic cavities. For a quantum point contact these resistanc es exhibit pronounced oscillations with the opening of channels. For a chaotic cavity coupled to one-channel point contacts. the charge rela xation resistance shows a broad distribution between,een 1/4 and 1/2 o f a resistance quantum. The nonequilibrium resistance exhibits a broad distribution between zero and 1/4 of a resistance quantum.