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Demonstrating a Continuous Set of Two-qubit Gates for Near-term Quantum Algorithms

Brooks Riley Foxen
Charles Neill
Andrew Dunsworth
Ben Chiaro
Anthony Megrant
Jimmy Chen
Rami Barends
Frank Carlton Arute
Kunal Arya
Yu Chen
Roberto Collins
Edward Farhi
Austin Fowler
Rob Graff
Trent Huang
Sergei Isakov
Zhang Jiang
Kostyantyn Kechedzhi
Alexander Korotkov
Fedor Kostritsa
Dave Landhuis
Xiao Mi
Masoud Mohseni
Josh Mutus
Vadim Smelyanskiy
Amit Vainsencher
Jamie Yao
John Martinis
arXiv:2001.08343 (2020)

Abstract

Quantum algorithms offer a dramatic speedup for computational problems in machine learning, material science, and chemistry. However, any near-term realizations of these algorithms will need to be heavily optimized to fit within the finite resources offered by existing noisy quantum hardware. Here, taking advantage of the strong adjustable coupling of gmon qubits, we demonstrate a continuous two qubit gate set that can provide a 5x reduction in circuit depth. We implement two gate families: an iSWAP-like gate to attain an arbitrary swap angle, $\theta$, and a CPHASE gate that generates an arbitrary conditional phase, $\phi$. Using one of each of these gates, we can perform an arbitrary two qubit gate within the excitation-preserving subspace allowing for a complete implementation of the so-called Fermionic Simulation, or fSim, gate set. We benchmark the fidelity of the iSWAP-like and CPHASE gate families as well as 525 other fSim gates spread evenly across the entire fSim($\theta$, $\phi$) parameter space achieving purity-limited average two qubit Pauli error of $3.8 \times 10^{-3}$ per fSim gate.

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