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

T. Bækkegaard, L. B. Kristensen, N. J. S. Loft, C. K. Andersen, D. Petrosyan, N. T. Zinner

Published:

As classical computers struggle to keep up with Moore's law, quantum
computing may represent a big step in technology and yield significant
improvement over classical computing for many important tasks. Building a
quantum computer, however, is a daunting challenge since it requires good
control but also good isolation from the environment to minimize decoherence.
It is therefore important to realize quantum gates efficiently, using as few
operations as possible, to reduce the amount of required control and operation
time and thus improve the quantum state coherence. Here we propose a
superconducting circuit for implementing a tunable spin chain consisting of a
qutrit (three-level system analogous to spin-1) coupled to two qubits
(spin-1/2). Our system can efficiently accomplish various quantum information
tasks, including generation of entanglement of the two qubits and conditional
three-qubit quantum gates, such as the Toffoli and Fredkin gates, which are
universal for reversible classical computations. Furthermore, our system
realizes a conditional geometric gate which may be used for holonomic
(non-adiabatic) quantum computing. 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.