Quantum technologies rely on qubits, units of information that can exist in combinations of the states 0 and 1 instead of being limited to one or the other like conventional bits. Qubits can become entangled, which means their states become linked in ways that cannot be explained by considering each qubit separately.
A promising platform for realizing and studying entangled qubits is a nitrogen-vacancy center. This is a tiny defect in diamond in which a nitrogen atom sits beside a missing carbon atom.
In these diamond-based systems, researchers typically entangle groups of qubits through a series of gates (i.e., controlled operations), linking an electron at the defect to the nucleus of one carbon atom at a time. This process takes time and can cause crosstalk, a phenomenon in which an operation also affects qubits it was not supposed to target.
Researchers at the University of Pennsylvania recently introduced a new approach for implementing a gate that links multiple qubits in diamond at room temperature. Their method, outlined in a paper published in Nature Nanotechnology, allowed them to realize a four-qubit Greenberger–Horne–Zeilinger state, a type of entanglement in which the four qubits share a quantum combination of two collective arrangements, such as all 0s and all 1s.
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