Superconducting qubit-qutrit circuit: A toolbox for efficient quantum gates*

We propose a superconducting circuit which implements an effective tunable spin chain consisting of a qutrit (three-level system) coupled to two qubits (spin-1/2).
In our paper [1] we show the derivation leading to an effective spin-model system which has highly tunable qutrit energy levels and Heisenberg XXZ -like interactions between the three effective degrees of freedom.
Our system can very efficiently accomplish various quantum information tasks, including entanglement of the two qubits and conditional three-qubit quantum gates such as the Toffoli and Fredkin gates. Furthermore, our system realizes a double-conditional non-adiabatic holonomic quantum gate.
The efficiency, robustness, and universality of our circuit makes it a promising candidate to serve as a building block for larger spin networks capable of performing involved quantum computational tasks.
We are currently working on a system implementing two qutrits, realizing an effective AKLT spin model.

[1] T. Bækkegaard, L. B. Kristensen, N. J. S. Loft, C. K. Andersen, D. Petrosyan, and N. T. Zinner. Superconducting qutrit-qubit circuit: A toolbox for efficient quantum gates. ArXiv e-prints, feb 2018.