423 research outputs found
Macroscopic Quantum Phenomena in High Critical Temperature Superconducting Josephson Junctions
No full textYBa2Cu3O7-delta grain boundary bi-epitaxial Josepshon junctions (JJs) allow a very clear demonstration of Josephson current variation with the misorientation angle, consistent with the d-wave symmetry of the superconducting order parameter in cuprate, high temperature superconductors. Our bi-epitaxial junctions show a strong suppression of the first harmonic, I-1 sin phi, of the current phase relation when tunneling from a lobe into a node of the superconducting gap function. In these configurations, the contribution of the second harmonic, I-2 sin 2 phi, becomes of the same magnitude as the first one, giving rise to a characteristic two-well Josephson potential as a function of phase phi instead of the usual single well. This characteristic intrinsic property has suggested proposals of a new class of qu-bit named "quiet" because of the existence a spontaneously degenerate fundamental state without the need of applying an external field. Our experiments probe the macroscopic quantum properties in a d-wave Josephson junction by measuring macroscopic quantum tunneling and energy level quantization. The switching current out of the zero voltage state is measured as a function of temperature down to 20 mK. The temperature variation of the width of an ensemble of switching events goes over from one, which is characteristic of a thermal activation of phase fluctuations to a temperature independent width which is a token of quantum tunneling of the phase. The transition regime is affected by the two-well potential in a 45 degrees misorientation junction as the second harmonic term gives rise to additional thermal transitions. The difference between quantized energy levels in the harmonic potential was determined by microwave spectroscopy. From the broadening of energy levels, it was possible to extract a Q-value of about 40 for the phase oscillations. The relatively high Q indicates quantum coherence over a sizeable time in d-wave junctions and gives hopes for a realization of a "quiet" high-T-c qu-bit. The contributions of V. L. Ginzburg to several different fields of physics are impressive and long standing. In superconductivity the Ginzburg-Landau theory, for instance, still represents a very powerful approach to model a huge number of different physical systems. High Temperature Superconductors (HTS) have strongly influenced research of the last 20 years and their d-wave order parameter symmetry represents one of the most intriguing features from both the fundamental point of view and some types of innovative long-term applications
Quantum dynamics of a d-wave Josephson junction
No full textHere we present the direct observation of macroscopic quantum properties in an all high-criticaltemperature superconductor d-wave Josephson junction. Although dissipation caused by low-energy excitations is expected to strongly suppress macroscopic quantum effects, we demonstrate energy level quantization in our d-wave Josephson junction. The result indicates that the role of dissipation mechanisms in high-temperature superconductors has to be revised, and it may also have consequences for the class of solid-state ‘‘quiet’’ quantum bits with superior coherence time
Macroscopic quantum tunneling in d-wave YBaCuO Josephson junctions
No full textThe 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 YBa2Cu3O7 grain boundary biepitaxial JJ.
This proves that dissipation can be significantly reduced by a proper junction configuration, which is of significance for quantum coherence
Tunnel barriers for an all-high-Tc single electron tunneling transistor
No full textWe have studied possible implementations of high-resistance tunnel barriers for an all-YBa2Cu3O7-delta superconducting single-electron transistor (SSET). The step-edge and biepitaxial techniques have been employed to fabricate the junctions. Both technologies appear very promising for the implementation of all-high-T-c SSET
Energy level quantization in a YBaCuO Josephson Junction
No full textWe have observed energy level quantization in an all high critical temperature superconductor d-wave Josephson junction. From the
measurements we have also extracted the quality factor Q of the junction which is of the order of 40. These results indicate that the role
of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for the class of solid
state ‘‘quiet’’ quantum bit with longer coherence time
Macroscopic Quantum Phenomena in High Critical Temperature Superconducting JOSEPHSON JUNCTIONS;
No full textEnergy level quantization in a YBaCuO Josephson Junction
No full textWe have observed energy level quantization in an all high critical temperature superconductor d-wave Josephson junction. From the measurements we have also extracted the quality factor Q of the junction which is of the order of 40. These results indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for the class of solid state "quiet" quantum bit with longer coherence time
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