Flux-Tunable Hybridization in a Double Quantum Dot Interferometer*

Tuning the hybridization between fermionic modes with magnetic flux to distinguish parity states is crucial for topological quantum computation [1,2]. We demonstrate tuning of the tunnel coupling between two such modes with flux, implemented in a phase-coherent loop comprising two quantum dots in an InSbAs two-dimensional electron gas. Using reflectometry at radio frequencies on the dots’ plunger gate electrodes, we extract the inter-dot tunnel coupling as a function of flux through the loop, observing oscillations of the coupling with a periodicity of a flux quantum across numerous inter-dot charge transitions. This is found to be consistent with reflectometry measurements of the Aharonov-Bohm effect in the open loop measured with the tunnel barriers lowered. Next, in different tunnel coupling regimes we benchmark the contrast of these hybridization oscillations, observing that they vary depending on the modes involved, but are generally not suppressed at their minima. These results establish the feasibility and contrast limitations of conducting parity readout of hybrid qubits with tunnel couplings tuned by flux.

[1] T. B. Smith, M. C. Cassidy, D. J. Reilly, S. D. Bartlett, and A. L. Grimsmo, Dispersive Readout of Majorana Qubits, PRX Quantum 1, 10.1103/prxquantum.1.020313 (2020).

[2]  M. Leijnse and K. Flensberg, Parity qubits and poor man's Majorana bound states in double quantum dots, Physical Review B 86, 10.1103/PhysRevB.86.134528 (2012).