This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As quantum computers grow more ambitious, many researchers believe the best way forward is to build them in multiple interconnected parts. In these modular designs, separate quantum processors are linked so they can work together as one larger machine.
For this to happen, however, connections must carry fragile quantum information without destroying it. For superconducting processors, this means building reliable links around a meter (3.3 feet) long inside equipment chilled to just above absolute zero. A team at IBM Research has now achieved this for the first time: joining two large superconducting processors using four separate high-quality quantum links, all installed after both chips were already in place.
Their work is detailed in a new paper published on the arXiv preprint server. So far, quantum links between superconducting chips have mostly involved a single connection between small experimental processors. These links have allowed researchers to transfer quantum states from one chip to another, and to create quantum entanglement.
To build larger machines, however, engineers will need to install many connections between processors that are already mounted in their refrigerators. These attachments must be packed closely together, lose very little of the signal passing through them, and keep working as the system is repeatedly warmed and cooled. To tackle this challenge, the IBM team linked two of its 120-qubit Nighthawk R1 processors.
In each link, a qubit inside one processor passed its information to a dedicated 'interface' qubit. An adjustable coupler then fed this information into an 80 cm (31-inch) superconducting aluminum cable, which carried it to a matching set of components on the other chip. To allow for denser packing in the cables, the team plugged each one into its chip from directly above, rather than from the side.
With their setup complete, researchers tested how well it could pass quantum states between the chips, and carry out logic operations involving qubits on both processors. Across the four links, quantum states were transferred with an average accuracy of 99%, reaching 99.29% on the best link. Two-qubit logic operations spanning both processors reached an average accuracy of 94.75%.
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