Qubit spectroscopy of the Fraunhofer-modulated modes in InAs 2DEG Josephson Weak Links

Josephson junction (JJ) with a 2D Electron Gas (2DEG) weak link hosts localized phase-dependent bound states - Andreev bound states (ABSs). When a perpendicular magnetic field is applied to the weak link, the phase across a planar JJ has a gradient along the width of the JJ. The supercurrent carried by the ABSs displays spatial interference that can give rise to the Fraunhofer pattern. Qubits using ABS-based JJs usually use the collective modes of all the ABSs in the JJ to build up the two-level artificial atom. However, the dynamic of the collective ABS modes within a perpendicular field remains unclear. Here we present the magnetic-field-dependent spectroscopy of qubits that uses 2DEG weak link JJs realized on an InAs-EpiAl heterostructure. The spectrum collected near the frequency local minima shows strong positive anharmonicity contrary to the prediction from an ideal junction model which predicts negative anharmonicity. The spectrum closely resembles SQUID-based qubits despite the supercurrent interference occurring in only one JJ. We investigate and model the spectrum to explain the unique single-junction interference behavior.