Macroscopic quantum tunneling in globally coupled series arrays of Josephson junctions

Abstract

We present a quantitative analysis of an escape rate for switching from the superconducting state to a resistive one in series arrays of globally coupled Josephson junctions. A global coupling is provided by an external shunting impedance. Such an impedance can strongly suppress both the crossover temperature from the thermal fluctuation to quantum regimes, and the macroscopic quantum tunneling (MQT) in short Josephson junction series arrays. However, in large series arrays we obtain an enhancement of the crossover temperature, and a giant increase of the MQT escape rate. The effect is explained by excitation of a spatial-temporal charge instanton distributed over a whole structure. The model gives a possible explanation of recently published experimental results on an enhancement of the MQT in single crystals of high-Tc superconductors.Great attention has been devoted to an experimental and theoretical study of dc biased series arrays of Josephson junctions [1, 2, 3, 4]. Such a system displays diverse fascinated nonlinear classical and macroscopic quantummechanical phenomena. E.g. a resistive state of Josephson junction series arrays can show synchronized behavior [1, 2], and this effect has been used in Josephson voltage standard devices [3]. As we turn to a region of small dc bias currents and low temperatures, the macroscopic quantum-mechanical phenomena start to play a role. Thus, a quantum phase superconductor-insulator transition has been observed in artificially prepared series arrays of a small size Al/Al 2 0 3 /Al junctions [4]. All these effects strongly depend on the interaction between Josephson junctions. This field of research, i.e. the macroscopic quantum phenomena in spatially extended superconducting systems, has been boosted even further by recent discovery of macroscopic quantum tunneling (MQT) in single crystals of layered high-T c superconductors [5,6]. At low temperatures the MQT determines the escape rate of the switching from the superconducting state to a resistive one. Although the MQT of a single Josephson phase has been found long time ago in low-T c lumped Nb Josephson junctions [7,8], MQT in layered high-T c superconductors has shown many novel features. A most unexpected result is that the MQT escape rate Γ MQT in high-T c superconductors is four order of magnitude larger than the MQT escape rate for a lumped Josephson junction having the same parameters [6]. Moreover, the crossover temperature T * from the thermal fluctuation regime to the MQT regime increases in respect to a lumped Josephson junction. In these experiments it was also found that the escape rate Γ T in the thermal fluctuation regime did not differ from the escape rate of a single Josephson junction.Layered high-T c superconductors can be modelled as a stack (a series array) of intrinsic Josephson junctions [9].A modern fabrication technique allows to prepare single crystals of layered high-T c superconductors with an extremely homogeneous distribution of critical currents of intrinsic Josephson junctions, and a low...

Resonant enhancement of macroscopic quantum tunneling in Josephson junctions: Influence of coherent two-level systems

“…Notice here, that in Eqs. (9) and (11) we neglect a small suppression of the function G(t) that is due to the back influence of the Josephson phase dynamics on the dynamics of TLSs. This is valid as the energy difference between two low-lying states is much smaller than other characteristic energies.…”

“…The interaction of a Josephson phase with other degrees of freedom can result in the reduction of the potential barrier and, therefore, lead to an enhancement of the MQT [8][9][10][11][12][13]. E.g., in the presence of a magnetic field the intrinsic cavity modes are excited, and an enhancement of the MQT has been obtained [10,11].…”

“…It is well known that at low temperatures switching from the superconducting (the zero-voltage) state to a resistive one occurs in the form of macroscopic quantum tunneling (MQT) of a Josephson phase [1,3,4,[6][7][8][9]. At high temperatures the so-called Josephson phase escape phenomenon is determined by thermal fluctuations.…”

“…Currently there is a great interest in experimental and theoretical studies of macroscopic quantum phenomena in diverse Josephson systems [1][2][3][4][5][6][7][8][9]. It is well known that at low temperatures switching from the superconducting (the zero-voltage) state to a resistive one occurs in the form of macroscopic quantum tunneling (MQT) of a Josephson phase [1,3,4,[6][7][8][9].…”

Chaos Synchronization in Josephson Junctions

“…The complex dynamics of Josephson-Junction extended to large arrays of coupled junction [4,5] since such an array has been found very useful in generating large output power in the millimeter and sub-millimeter wave range. It is known that chaos is generated in different configurations of Josephson junction.…”