Josephson junctions

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Dissipative phase transition

In a mesoscopic Josephson junction, the quantum mechanical nature of charge has to be taken into account. According to the quantum prescription, the Coulomb energy $\frac{Q^{2}}{2C}$ leads to a term

               

in the Hamiltonian. Therefore, the quantum behavior of a superconducting junction is described by the Schrödinger equation

 

where the Josephson coupling energy plays a role of a periodic potential.

Presently, we are working mostly on noise spectroscopy applications to detect higher order moments of noise and counting statistics using Coulomb blockaded junctions in the regime E_J/E_C << 1.

Energy levels $\lambda =\frac{E}{E_{c}}$ of the Mathieu equation as a function of E_J/E_C. Labels a_n and b_n denote the sine- and cosine-type solutions. The functions corresponding to an even value of $n$ are $\pi $-periodic and those with odd index are 2$\pi $-periodic. The energy bands (shaded regions) of the Schrödinger equation appear between a_{0}- a_{1}, b_{1}-b_{2}, a_{2}-a_{3}, etc.



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Last updated: 10/13/04.