Entanglement in a quantum annealing processor

TLDR: In this paper, a series of scalable quantum annealing (QA) processors consisting of networks of manufactured interacting spins (qubits) were built and the authors used qubit tunneling spectroscopy to measure the energy eigenspectrum of two and eight qubit systems.

Abstract: Entanglement lies at the core of quantum algorithms designed to solve problems that are intractable by classical approaches. One such algorithm, quantum annealing (QA), provides a promising path to a practical quantum processor. We have built a series of scalable QA processors consisting of networks of manufactured interacting spins (qubits). Here, we use qubit tunneling spectroscopy to measure the energy eigenspectrum of two- and eight-qubit systems within one such processor, demonstrating quantum coherence in these systems. We present experimental evidence that, during a critical portion of QA, the qubits become entangled and that entanglement persists even as these systems reach equilibrium with a thermal environment. Our results provide an encouraging sign that QA is a viable technology for large-scale quantum computing.