Enhancement of Josephson phase diffusion by microwaves

Area of Science:

• Condensed matter physics
• Quantum electronics
• Superconductivity

Background:

• Josephson junctions are crucial in quantum electronics.
• Understanding phase diffusion is key to controlling superconducting devices.
• Microwave irradiation effects on Josephson junctions are complex and require detailed study.

Purpose of the Study:

• To experimentally and theoretically investigate phase diffusion in small Josephson junctions under microwave irradiation.
• To characterize the peculiar enhancement of phase diffusion induced by microwaves.
• To elucidate the underlying physical mechanisms, including multiphoton absorption.

Main Methods:

• Experimental measurements of current-voltage characteristics of small Josephson junctions.
• Applying microwave irradiation with varying power and frequency.
• Theoretical modeling incorporating incoherent superconducting current and multiphoton absorption.

Main Results:

• Observed a peculiar enhancement of phase diffusion by microwaves.
• Identified a pronounced current peak in current-voltage characteristics.
• Found the peak voltage scales with the square root of microwave power (V(top) ∝ sqrt[P]).
• Noted the peak current amplitude weakly decreases with increasing microwave power.
• Observed the peak feature evolving into Shapiro steps with finite slope as microwave frequency increased.

Conclusions:

• Microwave irradiation significantly enhances phase diffusion in small Josephson junctions.
• The observed phenomena are well-explained by a theoretical model including multiphoton absorption.
• The study provides insights into controlling and understanding superconducting quantum devices.