Hybrid InAs–Al Josephson Architectures for Exploring Quantum Phase Transitions
ORAL
Abstract
Hybrid superconductor–semiconductor Josephson junctions (JJs) provide a highly tunable platform that bridges superconducting qubit architectures and mesoscopic quantum phenomena. Beyond their role as building blocks for next-generation qubits, such as strongly-anharmonic transmons and high-impedance Josephson junction (JJ) chains, these hybrid circuits offer an opportunity to experimentally access quantum phase transitions in low-dimensional superconductors, including the metal–insulator [1] and Schmid–Bulgadaev transitions [2].
To this end, we first briefly discuss two complementary approaches that provide distinct control knobs for tuning the Josephson coupling energy. The first is a flux-tunable split-junction InAs-Al transmon [3], where the Josephson energy is modulated through magnetic flux in a SQUID loop. By engineering the junction transparency and loop geometry, we achieve anharmonicities exceeding 100% without any increase in the flux-noise sensitivity, enabling Rabi frequencies above 100 MHz without complex pulse-shaping protocols. In addition, the second approach incorporates large-inductance InAs–Al JJ chains to form “gatemonium” qubit [4], where electrostatic gating enables in-situ control of the Josephson energy and circuit impedance. This provides a complementary route—via carrier density tuning—to explore impedance-driven phase transitions.
Together, these flux- and gate-tunable hybrid circuits establish a unified framework for engineering controllable, high-impedance superconducting environments. This tunability opens a direct pathway from high-coherence hybrid qubits to the controlled study of quantum phase transitions, where we report our ongoing efforts towards realizing the superconductor–insulator Schmid–Bulgadaev transition, in gate-tunable mesoscopic superconducting circuits.
[1] C.G.L. Bøttcher et. al., Nature Physics 14, 1138–1144 (2018)
[2] R. Kuzmin et. al., Nature Physics 21, 132–136 (2025)
[3] S. Liu et. al., arXiv:2503.12288 (2025)
[4] W.M. Strickland et. al., PRX Quantum 6, 010326 (2025)
To this end, we first briefly discuss two complementary approaches that provide distinct control knobs for tuning the Josephson coupling energy. The first is a flux-tunable split-junction InAs-Al transmon [3], where the Josephson energy is modulated through magnetic flux in a SQUID loop. By engineering the junction transparency and loop geometry, we achieve anharmonicities exceeding 100% without any increase in the flux-noise sensitivity, enabling Rabi frequencies above 100 MHz without complex pulse-shaping protocols. In addition, the second approach incorporates large-inductance InAs–Al JJ chains to form “gatemonium” qubit [4], where electrostatic gating enables in-situ control of the Josephson energy and circuit impedance. This provides a complementary route—via carrier density tuning—to explore impedance-driven phase transitions.
Together, these flux- and gate-tunable hybrid circuits establish a unified framework for engineering controllable, high-impedance superconducting environments. This tunability opens a direct pathway from high-coherence hybrid qubits to the controlled study of quantum phase transitions, where we report our ongoing efforts towards realizing the superconductor–insulator Schmid–Bulgadaev transition, in gate-tunable mesoscopic superconducting circuits.
[1] C.G.L. Bøttcher et. al., Nature Physics 14, 1138–1144 (2018)
[2] R. Kuzmin et. al., Nature Physics 21, 132–136 (2025)
[3] S. Liu et. al., arXiv:2503.12288 (2025)
[4] W.M. Strickland et. al., PRX Quantum 6, 010326 (2025)
–
Presenters
-
Arunav Bordoloi
- University of Maryland College Park
- New York University (NYU)
- New York University