Abstract
We investigate theoretically and experimentally the environment-induced voltage shot noise in current biased Josephson junctions induced by phase particle tunneling. Quantum mechanical treatment based on the Caldeira-Leggett model with tight-binding formulation in local Wannier bases gives a clear picture of the voltage shot noise. A universal form of the zero-frequency noise spectrum is obtained, which exhibits a quadratic dependence on the mean voltage in small bias region. The quadratic dependence is verified experimentally on junctions covering a wide range of parameters, and is found also in junction arrays of various array sizes.
Highlights
There have been several studies on the voltage noise of current-biased JJs in the phase regime[4,5,6,7,8,9], early theoretical and experimental works mainly focused on the case in which the phase particle is driven in the running state or the phase diffusion state[4,5,6], where the shot noise picture based on quantized phase change is invalid
The treatment starts from the relationship between the voltage noise and phase particle tunneling in a current biased JJ
We would like to make further discussion on the quadratic feature of the voltage shot noise, since it is seemingly contradictive to the generally admitted viewpoint that the quadratic dependence is a feature representing the transition from shot noise to thermal noise in electronic tunnel devices
Summary
We investigate theoretically and experimentally the environment-induced voltage shot noise in current biased Josephson junctions induced by phase particle tunneling. The granularity required for the shot noise is granted by the fact that the voltage across JJs changes by a fixed amount for each tunneling event This alone does not warrant the existence of voltage shot noise, because it requests level spacings greater than the thermal energy to prevent tunneling stochasticity induced by thermal occupation distribution of the energy levels. Study on this issue relies on full quantum mechanical treatment, in which both voltage V and phase difference φ are treated as operators rather than classical variables. Dual case of the present current biased JJ circuit is a voltage biased JJ in an inductive environment, with which the Bloch band dynamics such as charge localization were studied[11]
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