(Phys.org) Researchers at the Joint Quantum Institute have discovered ways to implement robust, error-resistant gates using just a constant number of simple building blocks—achieving essentially the best reduction possible in a parameter called circuit depth. Their findings apply to quantum computers based on topological quantum error correcting codes, were reported recently.
Circuit depth counts the number of gates that affect each qubit, and a constant depth means that the number of gates needed for a given operation won’t increase as the computer grows—a necessity if errors are to be kept at bay. This is a promising feature for robust and universal quantum computers, says Maissam Barkeshli, a JQI Fellow and an associate professor of physics at the University of Maryland (UMD).
Unlike other kinds of quantum computers, quantum computers built atop topological error correction—which so far have only been studied theoretically—don’t store information in individual physical qubits. Instead, they smear a single qubit’s worth of information out among a network of many qubits—or, more exotically, across special topological materials.
This information smearing provides resilience against stray bits of light or tiny vibrations—quantum disturbances that may cause errors—and it allows small errors to be detected and then actively corrected during a computation. It’s one of the main advantages that quantum computers based on topological error correction offer. But the advantage comes at a cost: If noise can’t get to the information easily, neither can you.

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