Measurement of Parity-Dependent Energy-Phase Relations in a Potential Artificial Kitaev Chain Utilizing a Transmon Qubit

Artificial Kitaev chains have emerged as a promising platform for realizing topological quantum computing. Once the chains are formed and Majorana zero modes are braided/fused, reading out the parity of the chains is essential for verifying the non-Abelian property of Majorana zero modes. Here, we demonstrate a transmon-based microwave probe for a four-site quantum dot–superconductor chain based on a Ge/Si nanowire. One end of the chain is incorporated into a superconducting transmon circuit, enabling spectroscopic identification of the chain’s singlet/doublet ground state and thereby inference of its total Fermion parity. We also demonstrate that, for multiple-dot chains, there are two types of 0−π transitions between different charging states: the parity-flip 0−π transition and the parity-preserved 0−π transition. Furthermore, we demonstrate electrostatic tunability of the interdot coupling. This phase-sensitive microwave platform provides a tool for studying complex hybrid superconducting quantum dot systems and for future extended artificial Kitaev chains.