Macroscopic quantum tunneling in "small" Josephson junctions in a magnetic field

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Superconductivity

Background:

• Macroscopic quantum tunneling (MQT) is a quantum phenomenon observed in systems like Josephson junctions (JJ).
• Applied magnetic fields introduce Fraunhofer-type modulations in JJ, affecting tunneling behavior.
• Understanding MQT in JJ is crucial for developing quantum technologies.

Purpose of the Study:

• To investigate MQT in small Josephson junctions (JJ) subjected to an external magnetic field.
• To analyze the impact of magnetic field-induced Fraunhofer modulations on tunneling dynamics.
• To derive key parameters governing the transition between quantum and thermal tunneling regimes.

Main Methods:

• The study models MQT in point-like JJ as a quantum particle in a washboard potential.
• For finite-size JJ, MQT is analyzed in a potential dependent on spatial variables and phase.
• Analytical calculations were performed to determine crossover temperature and escaping time.

Main Results:

• Derived a general expression for the crossover temperature (T0) between thermally activated and macroscopic quantum tunneling regimes.
• Calculated the escaping time (tau(esc)) characterizing the tunneling process.
• The Fraunhofer modulation's effect on MQT in finite-size JJ was theoretically addressed.

Conclusions:

• The findings provide a theoretical framework for understanding MQT in Josephson junctions under magnetic fields.
• The calculated crossover temperature and escaping time are critical parameters for designing and controlling quantum devices.
• This research contributes to the fundamental understanding of quantum phenomena in superconducting circuits.