High fidelity gates and states in a 5 Xmon qubit Josephson quantum processor, part II: multiqubit logic
ORAL
Abstract
One of the critical challenges in quantum computing is to employ simultaneous, high fidelity quantum logic gates across a system. Here, we show how a novel implementation of a fast, adiabatic controlled-phase gate achieves fidelities between 99.0 and 99.4 \% across all pairs in a 5 Xmon qubit quantum processor. We also show that nearest as well as next nearest neighbor qubits can be operated simultaneously without sacrificing fidelity. This, combined with low Z control crosstalk allows for direct control of single or multiqubit subspaces. To showcase the addressability of the qubits and modularity of the logic set, we use single and two-qubit gates to construct N=3, 4 and 5 Greenberger-Horne-Zeilinger states with fidelities of 96 \%, 86 \% and 82 \%, characterized by quantum state tomography.
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