Nonclassical suppression of conductance fluctuation in a double stadium quantum system

Abstract

A double stadium quantum network of two quantum cavity stadiums with a tunable coupling by a ballistic quantum point contact in between was studied on universal properties of conductance fluctuation (CF) and weak localization (WL). Our experimental data of CF(Var(G)) and WL(deltaG) are best fitted by Var(G)/Var(G(U))=0.25(n/N)(alpha) and deltaG/deltaG(U)=0.42(n/N)(beta), respectively, with alpha =1.2 and beta = 1.8, where Var(G(U)) and deltaG(U) represent the universal magnitudes, n is a variable mode number at the point contact, and N is a fixed mode number at both the entrance and the exit gates. Our best fit exponents of alpha = 1.2 and beta = 1.8 are closer to those of quantum-mechanical theories (alpha = 1 and beta = 2) than those of Ohm's law analysis (alpha = beta = 2). This nonclassical suppression of conductance fluctuation in a simplest network of mesoscopic electronic elements suggests a quantum-mechanical importance in the network construction between mesoscopic quantum structures.