Two-dimensional macroscopic quantum dynamics in YBCO Josephson junctions

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBCO Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.Comment: 9 pages, 2 figure

Effect of zero energy bound states on macroscopic quantum tunneling in high-Tc superconductor junctions

The macroscopic quantum tunneling (MQT) in the current biased high-Tc superconductor Josephson junctions and the effect of the zero energy bound states (ZES) on the MQT are theoretically investigated. We obtained the analytical formula of the MQT rate and showed that the presence of the ZES at the normal/superconductor interface leads to a strong Ohmic quasiparticle dissipation. Therefore, the MQT rate is noticeably inhibited in compared with the c-axis junctions in which the ZES are completely absent.Comment: 4 pages, 1 figure, comment and reference about recent experiment adde

Theory of Macroscopic Quantum Tunneling in High-T_c c-Axis Josephson Junctions

We study macroscopic quantum tunneling (MQT) in c-axis twist Josephson junctions made of high-T_c 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 $\gamma$ about the c-axis is calculated by using the functional integral and the bounce method. Due to the d-wave OPS, the $\gamma$ dependence of standard deviation of the switching current distribution and the crossover temperature from thermal activation to MQT are found to be given by $\cos2\gamma$ and $\sqrt{\cos2\gamma}$, 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 Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8 + \delta}$ intrinsic junctions. These results indicate that MQT in c-axis twist junctions becomes a useful experimental tool for testing the OPS of high-T_c materials at low temperature, and suggest high potential of such junctions for qubit applications.Comment: 15 pages, 8 figures, 1 tabl

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

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 very weak. We have also investigated MQT in a realistic s-wave/d-wave (Nb/Au/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 high potential of s-wave/d-wave hybrid junctions for applications in quantum information devices.Comment: 4 pages, 3 figure

Quasi-Superradiant Soliton State of Matter in Quantum Metamaterials

Strong interaction of a system of quantum emitters (e.g., two-level atoms) with electromagnetic field induces specific correlations in the system accompanied by a drastic insrease of emitted radiation (superradiation or superfluorescence). Despite the fact that since its prediction this phenomenon was subject to a vigorous experimental and theoretical research, there remain open question, in particular, concerning the possibility of a first order phase transition to the superradiant state from the vacuum state. In systems of natural and charge-based artificial atome this transition is prohibited by "no-go" theorems. Here we demonstrate numerically a similar transition in a one-dimensional quantum metamaterial - a chain of artificial atoms (qubits) strongly interacting with classical electromagnetic fields in a transmission line. The system switches from vacuum state with zero classical electromagnetic fields and all qubits being in the ground state to the quasi-superradiant (QS) phase with one or several magnetic solitons and finite average occupation of qubit excited states along the transmission line. A quantum metamaterial in the QS phase circumvents the "no-go" restrictions by considerably decreasing its total energy relative to the vacuum state by exciting nonlinear electromagnetic solitons with many nonlinearly coupled electromagnetic modes in the presence of external magnetic field.Comment: 6 pages, 4 figure

Large Polarization Degree of Comet 2P/Encke Continuum Based on Spectropolarimetric Signals During Its 2017 Apparition

Spectropolarimetry is a powerful technique for investigating the physical properties of gas and solid materials in cometary comae without mutual contamination, but there have been few spectropolarimetric studies to extract each component. We attempt to derive the continuum polarization degree of comet 2P/Encke, free from influence of molecular emissions. The target is unique in that it has an orbit dynamically decoupled from Jupiter like main-belt asteroids, while ejecting gas and dust like ordinary comets. We observed the comet using the Higashi-Hiroshima Optical and Near-Infrared Camera attached to the Cassegrain focus of the 150-cm Kanata telescope on UT 2017 February 21 when the comet was at the solar phase angle of 75.7 deg. We find that the continuum polarization degree with respect to the scattering plane is 33.8+/-2.7 % at the effective wavelength of 0.815 um, which is significantly higher than those of cometary dust in a high-Pmax group at similar phase angles. Assuming that an ensemble polarimetric response of 2P/Encke's dust as a function of phase angle is morphologically similar with those of other comets, its maximum polarization degree is estimated to > 40 % at the phase angle of ~100 deg. In addition, we obtain the polarization degrees of the C2 swan bands (0.51-0.56 um), the NH2 alpha bands (0.62-0.69 um) and the CN-red system (0.78-0.94 um) in a range of 3-19 %, which depend on the molecular species and rotational quantum numbers of each branch. The polarization vector aligns nearly perpendicularly to the scattering plane with the average of 0.4 deg over a wavelength range of 0.50-0.97 um. From the observational evidence, we conjecture that the large polarization degree of 2P/Encke would be attributable to a dominance of large dust particles around the nucleus, which have remained after frequent perihelion passages near the Sun.Comment: 9 pages, 4 figures, accepted for publication in Astronomy & Astrophysic