Quantum process tomography of two-qubit controlled-Z and controlled-NOT gates using superconducting phase qubits

TL;DR

This paper reports the experimental implementation and characterization of controlled-Z and controlled-NOT quantum gates using superconducting phase qubits, achieving fidelities of 0.70 and 0.56 respectively, and demonstrating a two-qubit Deutsch-Jozsa algorithm.

Contribution

First experimental quantum process tomography of two-qubit gates using superconducting phase qubits with detailed fidelity analysis.

Findings

Achieved process fidelities of 0.70 for controlled-Z and 0.56 for controlled-NOT gates.

Demonstrated a two-qubit Deutsch-Jozsa algorithm using the implemented gates.

Fidelity loss primarily due to single-qubit decoherence.

Abstract

We experimentally demonstrate quantum process tomography of controlled-Z and controlled-NOT gates using capacitively-coupled superconducting phase qubits. These gates are realized by using the $|2\rangle$ state of the phase qubit. We obtain a process fidelity of 0.70 for the controlled-phase and 0.56 for the controlled-NOT gate, with the loss of fidelity mostly due to single-qubit decoherence. The controlled-Z gate is also used to demonstrate a two-qubit Deutsch-Jozsa algorithm with a single function query.