Josephson Junction π-0 Transition Induced by Orbital Hybridization in a Double Quantum Dot

Area of Science:

• Condensed Matter Physics
• Quantum Information Science
• Mesoscopic Physics

Background:

• Josephson junctions are fundamental in quantum electronics.
• Quantum dots (QDs) offer tunable electronic properties.
• Controlling the current-phase relation is key for quantum devices.

Purpose of the Study:

• To investigate the manipulation of Josephson junction phase shift using a parallel double quantum dot (QD) system.
• To determine the impact of orbital hybridization and detuning on the current-phase relation within the Coulomb blockade regime.
• To explore the conditions leading to π junction characteristics and π-0 transitions.

Main Methods:

• Utilized a superconducting quantum interference device (SQUID) to probe the current-phase relation.
• Employed a parallel double quantum dot (QD) setup to control phase shifts.
• Analyzed behavior in the Coulomb blockade regime with varying hybridization and detuning.

Main Results:

• Observed π junction characteristics when at least one QD had an unpaired electron under weak hybridization.
• Found a higher critical current with odd electron occupation in both QDs.
• Demonstrated a reduction in critical current and a π-0 transition with increased inter-QD hybridization or QD level detuning.

Conclusions:

• Phase-shift transitions are linked to an increased weight of double occupancy states in the ground state.
• Cooper pair transport is dominated by local Andreev reflection during these transitions.
• The study provides a framework for understanding and controlling quantum transport in hybrid QD-superconductor systems.