Using Andreev bound states and spin to remove domain walls in a Kitaev chain

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Abstract
Quantum dot (QD)-superconductor hybrids have been established as a suitable platform for realizing Kitaev chains hosting Majorana bound states. Implementing these structures in a qubit architecture is expected to result in coherence times that scale exponentially with the lengths of the chains. To scale to longer systems, the phase differences between all superconducting segments in the chain need to be controlled. While this control has been demonstrated by using an external magnetic flux [ten Haaf , ; Bordin , ], ideally, it can be achieved with control over intrinsic system parameters [Liu , ]. In this work, we investigate whether the relevant phase differences can be tuned through the spin degree of freedom in each QD or the chemical potential of the discrete bound states in the hybrid sections. We confirm that both these tuning knobs allow for controlling the phase difference in the couplings between neighboring QDs, bypassing the requirement to tune an external flux. However, we find that the amplitude of the phase shifts can deviate from a discrete π shift. We introduce a spatial variation in the spin-orbit field as a possible mechanism to explain the observed behavior and comment on the consequences for experimentally creating long Kitaev chains.
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Funding Information
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek
  • Microsoft
  • Topconsortium voor Kennis en Innovatie
  • HORIZON EUROPE European Innovation Council (101115315)

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