Employing coaxmon-based qudits for quantum information processing - Shuxiang Cao

Superconducting circuits have emerged as a promising platform for quantum information processing. However, scalability remains a challenge, and one of the difficulties is the complexities of packaging and wiring large qubit arrays. To address this, "coaxmon", a variant of transmon qubits, was developed. It offers an off-chip wiring solution while maintaining high coherence [1]. This presentation reports the recent progress in coaxmon design and our efforts in employing coaxmons as qudits, utilizing more than two levels of a transmon for quantum computation. We share our research on qutrit and qudit gate benchmarking analyses using Gate-Set Tomography [2,3]. Additionally, we demonstrate a qutrit quantum classifier for quantum machine learning with the coaxmon qudit. We have also utilized four transmon levels to emulate a two-qubit system and demonstrate a variational quantum eigensolver algorithm on this emulator [3]. We analyze the noise affecting the quantum algorithm and report the strategies we have adopted for error mitigation.
[1] P. A. Spring et al., High coherence and low cross-talk in a tileable 3D integrated superconducting circuit architecture, Science Advances, vol. 8, no. 16. American Association for the Advancement of Science (AAAS), Apr. 22, 2022.
[2] S. Cao et al., "Efficient qutrit gate-set tomography on a transmon." arXiv, 2022.
[3] S. Cao et al., "Emulating two qubits with a four-level transmon qudit for variational quantum algorithms." arXiv, 2023.