Two-qubit entangling gates for superconducting quantum computers

Abstract

Noisy intermediate-scale quantum computers (NISQ) have demonstrated superior performance compared to conventional computing schemes. Nonetheless, errors associated with two-qubit entangling gates remain a substantial obstacle in fully harnessing the potential of current superconducting quantum computers. The achievement of quantum computation and quantum information processing critically depends on the presence of entangled states. These states are indispensable for quantum computers to surpass classical computers in terms of computational power. This paper presents a comprehensive characterization of a two-qubit entangling gate, known as Dagwood Bumstead (DB) gate, to investigate the challenges posed by errors in the DB gate on NISQ devices. Firstly, we propose a scheme for the realization of the DB gate using two capacitively coupled Josephson Superconducting qubits, based on the experimental setup carried out in Bialczak et al. (2010). Additionally, we introduce and characterize a novel two-qubit quantum gate. Our proposed gate showcases an impressive average gate fidelity of 0.85450. The DB gate's performance is fully described through quantum process tomography (QPT) and quantum state tomography (QST) experiments conducted in three different environments: noisy, noiseless, and on a real IBM quantum computer. The process fidelity of the DB gate is measured to be 0.8069705, and the state fidelity is determined to be 0.8858750. This study offers valuable insights into the performance of the DB gate on a NISQ device, showcasing its potential for executing intricate algorithms and operations on an authentic quantum computer.

Keywords: Dagwood Bumstead gate; Entangling gates; IBM's NISQ quantum computers; Novel two-qubit quantum gates; Quantum process tomography; Quantum state tomography