Microwave-controlled universal entangling gate for fixed-frequency superconducting qubits

A basic requirement for fault tolerant quantum computing is a universal set of nearly perfect single- and two-qubit gates. As high-fidelity single-qubit operations on superconducting qubits become routine1,2, the focus shifts onto developing robust and scaleable two-qubit gates. Already, rapid progress has been made, including a controlled-NOT gate with fixed coupled qubits3, and highly entangled states of two4,5 and three6,7 qubits generated from tuning the qubits to explicit resonance conditions. However, as superconducting systems scale up, fixed-coupled systems become difficult to individually address, and tuning to resonances in a spectrally crowded frequency space is problematic. Here we demonstrate a new microwave controlled two-qubit gate8-10 on capacitively-shunted flux qubits11 parked at locations of optimal coherence and coupled via a quantum bus. The effective interaction is tunable via irradiation of one qubit at them other qubit's transition frequency. We use this cross-resonance (CR) gate to generate Bell states with a maximal fidelity of 90% and concurrence of 0:88, limited by qubit relaxation. Quantum process tomography gives a gate fidelity of 81%. This gate scheme is readily extendable to systems of more than two qubits and would permit coupling of qubits which are non-nearest neighbours in frequency.

By: Jerry M. Chow, A. D. Corcoles, Jay M. Gambetta, Chad Rigetti, B. R. Johnson, John A. Smolin, J. R. Rozen, George A. Keefe, Mary E. Rothwell, Mark Ketchen, M. Steffen

Published in: RC25189 in 2011


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