Experimental evidence of a φ Josephson junction

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Quantum Electronics

Background:

• Josephson junctions are fundamental devices in superconductivity, exhibiting unique quantum phenomena.
• The control of quantum states in Josephson junctions is crucial for quantum computing and metrology.
• Previous theoretical work predicted the possibility of doubly degenerate ground states in specific Josephson junction designs.

Purpose of the Study:

• To experimentally demonstrate the existence of Josephson junctions with a doubly degenerate ground state.
• To investigate the properties of these junctions, including their critical currents and phase control mechanisms.
• To validate theoretical predictions regarding the behavior of 0-π Josephson junctions.

Main Methods:

• Fabrication of 0-π Josephson junctions with asymmetric 0 and π regions.
• Experimental measurement of critical currents.
• Control of the Josephson phase using external magnetic fields.
• Control of the Josephson phase using specific bias current sweep sequences.

Main Results:

• Experimental confirmation of a doubly degenerate ground state (ψ=±φ) in designed Josephson junctions.
• Observation of two distinct critical currents corresponding to phase escape from the ±φ states.
• Demonstration of tunable phase control using external magnetic fields.
• Successful phase manipulation through tailored bias current sweep protocols.

Conclusions:

• The experimental results confirm the existence and controllable nature of Josephson junctions with doubly degenerate ground states.
• These findings validate theoretical predictions and open new avenues for utilizing tunable quantum states in superconducting devices.
• The ability to set and control the Josephson phase offers potential for advanced applications in quantum information processing and sensing.