Exploring Ququart Computation on a Transmon using Optimal Control

Abstract

Contemporary quantum computers encode and process quantum information in binary qubits (d = 2). However, many architectures include higher energy levels that are left as unused computational resources. We demonstrate a superconducting ququart (d = 4) processor and combine quantum optimal control with efficient gate decompositions to implement high-fidelity ququart gates. We distinguish between viewing the ququart as a generalized four-level qubit and an encoded pair of qubits, and characterize the resulting gates in each case. In randomized benchmarking experiments we observe gate fidelities greater 95% and identify coherence as the primary limiting factor. Our results validate ququarts as a viable tool for quantum information processing.

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Cited by in corpus (11)

• Systematic study of High $E_J/E_C$ transmon qudits up to $d=12$
• Emulating two qubits with a four-level transmon qudit for variational quantum algorithms
• Qu8its for Quantum Simulations of Lattice Quantum Chromodynamics
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• Synthesis of Single Qutrit Circuits from Clifford+R