Measurement of parity-dependent energy-phase relation of the low-energy states in a potential artificial Kitaev chain utilizing a transmon qubit

TL;DR

This study demonstrates a method to detect the parity of artificial Kitaev chains using a superconducting transmon qubit, revealing parity-dependent energy-phase relations and transitions crucial for topological quantum computing.

Contribution

The paper introduces a novel approach to directly measure chain parity via a transmon qubit in a Ge/Si nanowire-based artificial Kitaev chain, including analysis of 0-π transitions and tunable inter-dot couplings.

Findings

Successful detection of singlet/doublet states indicating chain parity.

Identification of two types of 0-π transitions related to parity changes.

Demonstration of electrostatic gating to control inter-dot coupling.

Abstract

Artificial Kitaev chains have emerged as a promising platform for realizing topological quantum computing. Once the chains are formed and the Majorana zero modes are braided/fused, reading out the parity of the chains is essential for further verifying the non-Abelian property of the Majorana zero modes. Here we demonstrate the feasibility of using a superconducting transmon qubit, which incorporates an end of a four-site quantum dot-superconductor chain based on a Ge/Si nanowire, to directly detect the singlet/doublet state, and thus the parity of the entire chain. We also demonstrate that for multiple-dot chains there are two types of 0-{\pi} transitions between different charging states: the parity-flip 0-{\pi} transition and the parity-preserved 0-{\pi} transition. Furthermore, we show that the inter-dot coupling, hence the strengths of cross Andreev reflection and elastic cotunneling of electrons, can be adjusted by local electrostatic gating in chains fabricated on Ge/Si core-shell nanowires. Our exploration would be helpful for the ultimate realization of topological quantum computing based on artificial Kitaev chains.