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arXiv:2004.02124 · Physical Review Research

Readout of Majorana qubits

Jacob F. Steiner, Felix von Oppen

Published Aug 17, 2020• 57 citations
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Abstract

This work develops a quantum measurement theory for practical readout protocols relying on charge sensing using a tunnel-coupled quantum dot. The authors analyze the conditions for successful readout protocols and identify the conditions for implementing robust measurements of Majorana qubits.
DOI
10.1103/physrevresearch.2.033255

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Reading out Majorana bound states (MBSs) is essential both to verify their non-Abelian property and to realize topological quantum computation. Here, we construct a protocol to measure the parity of two MBSs in a Majorana island coupled to a double quantum dot (DQD). The parity information is mapped to the charge state of the DQD through Landau-Zener transition. The operation needed is sweeping the bias of the DQD, which is followed by charge sensing. In the case without fine-tuning, a single run of sweep and detection implements a weak measurement of the parity. We find that in general a sequence of about ten runs would completely project a superposition state to either parity, and the charge detection in each run records how the state of the MBSs collapses step by step. Remarkably, this readout protocol is a nondemolition measurement and robust to low-frequency charge fluctuation.
High-fidelity readout of semiconductor-based qubits (in particular, Majorana qubits of the future) could be accomplished by dispersive readout, as already used with superconducting qubits. So far, though, the dispersive signals have been small, and the required integration times much longer than typical qubit coherence times. This work shows that signal amplitude can be vastly increased by strongly coupling a sensing gate to a readout quantum dot. This coupling allows readout of this system in the microsecond regime, which is on par with the state of the art for other qubits. Here the chief limiting factor of the signal-to-noise ratio is tunnel coupling.