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Portrait of Martin Leijnse; Photo: Kennet Ruona

Martin Leijnse

Professor, Member of NanoLund Management Group

Portrait of Martin Leijnse; Photo: Kennet Ruona

Four-Majorana qubit with charge readout : Dynamics and decoherence

Author

  • Tommy Li
  • William A. Coish
  • Michael Hell
  • Karsten Flensberg
  • Martin Leijnse

Summary, in English

We present a theoretical analysis of a Majorana-based qubit consisting of two topological superconducting islands connected via a Josephson junction. The qubit is operated by electrostatic gates which control the coupling of two of the four Majorana zero modes. At the end of the operation, readout is performed in the charge basis. Even though the operations are not topologically protected, the proposed experiment can potentially shed light on the coherence of the parity degree of freedom in Majorana devices and serve as a first step towards topological Majorana qubits. We discuss in detail the charge-stability diagram and its use for characterizing the parameters of the devices, including the overlap of the Majorana edge states. We describe the multilevel spectral properties of the system and present a detailed study of its controlled coherent oscillations, as well as decoherence resulting from coupling to a non-Markovian environment. In particular, we study a gate-controlled protocol where conversion between Coulomb-blockade and transmon regimes generates coherent oscillations of the qubit state due to the overlap of Majorana modes. We show that, in addition to fluctuations of the Majorana coupling, considerable measurement errors may be accumulated during the conversion intervals when electrostatic fluctuations in the superconducting islands are present. These results are also relevant for several proposed implementations of topological qubits which rely on readout based on charge detection.

Department/s

  • Solid State Physics
  • NanoLund: Center for Nanoscience

Publishing year

2018-11-05

Language

English

Publication/Series

Physical Review B

Volume

98

Issue

20

Document type

Journal article

Publisher

American Physical Society

Topic

  • Condensed Matter Physics

Status

Published

ISBN/ISSN/Other

  • ISSN: 2469-9950