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arXiv:cond-mat/0702480 · Physical Review B

Macroscopic quantum tunneling and quasiparticle-tunneling blockade effect in s -wave/ d -wave hybrid junctions

Shiro Kawabata, Alexander A. Golubov, Ariando Ariando, C.J.M. Verwijs, Hans Hilgenkamp, John R. Kirtley

Published Aug 6, 2007• 18 citations
arXivHTMLPDF

Abstract

We have theoretically investigated macroscopic quantum tunneling (MQT) and the influence of nodal quasiparticles and zero energy bound states (ZESs) on MQT in $s$-wave/$d$-wave hybrid Josephson junctions. In contrast to $d$-wave/$d$-wave junctions, the low-energy quasiparticle dissipation resulting from nodal quasiparticles and ZESs is suppressed due to a quasiparticle-tunneling blockade effect in an isotropic $s$-wave superconductor. Therefore, the inherent dissipation in these junctions is found to be weak. We have also investigated MQT in a realistic $s$-wave/$d$-wave $(\mathrm{Nb}∕\mathrm{Au}∕\mathrm{YBCO})$ junction in which Ohmic dissipation in a shunt resistance is stronger than the inherent dissipation and find that MQT is observable within the current experimental technology. This result suggests the high potential of $s$-wave/$d$-wave hybrid junctions for applications in quantum information devices.

DOI
10.1103/physrevb.76.064505

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We have theoretically investigated macroscopic quantum tunneling (MQT) and the influence of nodal quasiparticles and zero energy bound states (ZES) on MQT in s-wave/d-wave hybrid Josephson junctions. In contrast to d-wave/d-wave junctions, the low-energy quasiparticle dissipation resulting from nodal quasiparticles and ZES is suppressed due to a quasiparticle-tunneling blockade effect in an isotropic s-wave superconductor. Therefore, the inherent dissipation in these junctions is found to be weak. This result suggests high potential of s-wave/d-wave hybrid junctions for applications in quantum information devices.
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The escape rate from the zero voltage state in a superconducting Josephson junction (JJ) is determined by the temperature, but it saturates at low temperature due to macroscopic quantum tunneling (MQT). Complications due to d-wave symmetry in a high temperature superconductor, like low energy quasiparticles and an unconventional current-phase relation, may influence the escape rate. We report, for the first time to our knowledge, the observation of MQT in a YBa(2)Cu(3)O(7-delta) grain boundary biepitaxial JJ. This proves that dissipation can be significantly reduced by a proper junction configuration, which is of significance for quantum coherence.
We study macroscopic quantum tunneling (MQT) in ccc-axis twist Josephson junctions made of high-Tc{T}_{c}Tc​ superconductors in order to clarify the influence of the anisotropic order parameter symmetry (OPS) on MQT. The dependence of the MQT rate on the twist angle $\ensuremath{\gamma}$ about the ccc axis is calculated by using the functional integral and the bounce method. Due to the ddd-wave OPS, the $\ensuremath{\gamma}$ dependence of standard deviation of the switching current distribution and the crossover temperature from thermal activation to MQT are found to be given by $\mathrm{cos}\phantom{\rule{0.2em}{0ex}}2\ensuremath{\gamma}$ and $\sqrt{\mathrm{cos}\phantom{\rule{0.2em}{0ex}}2\ensuremath{\gamma}}$, respectively. We also show that a dissipative effect resulting from the nodal quasiparticle excitation on MQT is negligibly small, which is consistent with recent MQT experiments using ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ intrinsic junctions. These results indicate that MQT in ccc-axis twist junctions becomes a useful experimental tool for testing the OPS of high-Tc{T}_{c}Tc​ materials at low temperature, and suggest high potential of such junctions for qubit applications.
While Josephson-junction-like structures intrinsic to the layered cuprate high temperature superconductors offer an attractive stage for exploiting possible applications to new quantum technologies, the low energy quasiparticle excitations characteristically present in these d-wave superconductors may easily destroy the coherence required. Here we demonstrate for the first time the feasibility of macroscopic quantum tunneling in the intrinsic Josephson junctions of a high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8 + delta), and find it to be characterized by a high classic-to-quantum crossover temperature and a relatively weak quasiparticle dissipation.
We theoretically investigate the macroscopic quantum dynamics of a $\ensuremath{\pi}$ junction with a superconductor (S) and a multiferroic material or a ferromagnetic insulator (FI). By deriving the effective action from a microscopic Hamiltonian, a $\ensuremath{\pi}$-junction qubit (a S-FI-S superconducting quantum interference device ring) is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of the quasiparticle dissipation is found to be very weak. These features make it possible to realize a quiet qubit with high coherency. We also investigate macroscopic quantum tunneling (MQT) in current-biased S-FI-S $\ensuremath{\pi}$ junctions and show that the influence of the quasiparticle dissipation on MQT is negligibly small.