**Useful quantum computers are one step closer, thanks to the latest demonstration of a technique designed to stop them making mistakes.**

**Quantum computers store information as quantum bits, or qubits. Unlike binary bits, which store a 0 or a 1, qubits can hold a mixture of both states at the same time, boosting their computing potential for certain types of problems. But qubits are fragile – their quantum nature means they can’t hold data for long before errors creep in.**

**So researchers wanting to build large-scale computers invented quantum error correction (QEC). This technique encodes a bit of quantum information using many physical qubits.**

**The code is designed to provide wiggle-room, making it possible to recover from errors. A similar concept is used to handle errors in binary bits on hard drives and DVDs, but things are more difficult in the quantum realm. The rules of quantum mechanics mean you can’t directly read the state of a qubit without destroying it – it’s like opening the box to take a look at Schrödinger’s cat. That means we need more sophisticated codes for quantum computers than for DVDs.**

**Demonstrations of QEC so far haven’t been able to extend the lifetime of the data stored on a qubit, as the extra complexity of running the corrections introduced new errors that eliminated any benefit. “There’s kind of a chicken-and-egg thing, as to do error correction you need a larger collection of quantum bits,” says Rob Schoelkopf of Yale University. “Then, unfortunately, there are more things that can go wrong.”**

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