NederlandsQuantum error correction
Quantum error correction is the technique by which a quantum computer detects and repairs its own errors while it computes. Many qubits work together as one reliable qubit.
Quantum error correction is the detection and repair of errors in a quantum computer while it is computing. It is needed because qubits, the computing units of a quantum computer, are very sensitive. A little heat, a vibration or an imprecise laser pulse is enough to disturb them.
How does it work?
In an ordinary computer you can store a piece of data three times and let the majority decide when in doubt. That does not work with qubits: you cannot copy quantum information, and anyone who looks at a qubit disturbs it.
That is why the information is spread across a group of qubits. Together they form one reliable qubit, a logical qubit. Helper qubits keep checking whether their neighbours still agree with each other, without looking at the information itself. A computing program, the decoder, deduces from those checks where an error is and how to repair it. One such round of checking and repairing is called a check round. It has to happen extremely fast, because the computer must know which error it is repairing while it is still computing.
Why it matters
Error correction is the threshold between quantum computers as an experimental setup and quantum computers as a useful tool. Useful calculations require millions to billions of steps. Quantinuum's Helios quantum computer set a new record: on average only five in a million check rounds still went wrong, ten times better than the previous record. The errors also decreased as the group of qubits got larger. The next step is to show this for more complex calculations too (link).
Another component is steering during computation. Researchers at Rutgers, IBM and other institutions had a 100-qubit quantum computer check and reset itself thousands of times while it was computing. It is not yet a working fault-tolerant quantum computer, but it is an important building block for one (link). AI can help here: at Quantinuum, neural networks read out the check measurements in under a millisecond per round.
Articles about Quantum error correction
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PSI: AI found proof of a 2008 conjecture on the limits of quantum computers
The US company Physical Superintelligence says its AI system found a proof of the Aaronson-Ambainis conjecture, an open question from 2008 about when quantum computers are much faster. The program Lean has approved the proof; fellow researchers are now checking it.
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Google demonstrates magic state cultivation on Willow: 40 times fewer errors
Google Quantum AI tested a new way to make magic states on its Willow chip: special states that a quantum computer needs for its hardest operations. The errors in them became about 40 times smaller. The result is published in Science.
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German company makes a molecule that stores quantum information and can pass it on with light
The German company NVision and researchers from Ulm and Jerusalem describe in Nature a molecule of carbon and hydrogen that stores quantum information and can pass it on with light. Such a building block could later link quantum computers together.
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IBM links two quantum chips with 80-centimetre cables
IBM researchers connected two quantum chips of 120 qubits each with four superconducting links of 80 centimetres. The quantum information came across with an average fidelity of 99 per cent. It is a step towards quantum computers built from separate modules.
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Japanese researchers control five quantum bits in silicon at once, with almost no errors
Researchers at RIKEN in Japan controlled five quantum bits on a silicon chip at the same time, through one shared control line. They found the biggest source of errors and kept accuracy at around 99.9 per cent. That helps to build larger quantum computers.
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Quantum computer keeps chaos under control on 100 qubits: a step towards fault-tolerant computing
Researchers from Rutgers, IBM and other institutions had a quantum computer check and correct itself thousands of times while it was computing. It is not yet a working fault-tolerant quantum computer, but it is an important building block for one.
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Quantum computer catches its own errors so well that only 5 in a million remain
Quantinuum's Helios quantum computer set a new record in error correction: on average, something went wrong five times in a million checking rounds. That is ten times better than the previous record. The next step is to show this for more complex calculations too.
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Nvidia simulates a 104-qubit quantum circuit on a European supercomputer, real errors included
Nvidia and the German research centre Jülich used the JUPITER supercomputer to simulate how a 104-qubit quantum computer makes an important building block, including the errors that real hardware makes. This lets designs be tested before they are built.
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Stanford builds a grid of more than 600 light traps to link quantum computers made of atoms
Physicists at Stanford built a grid of more than 600 tiny light traps, each of which can catch the light of a single atom. That helps to read out quantum computers made of atoms faster and later to link them together.
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Oxford keeps a quantum link between atoms in two places alive for more than ten seconds
Physicists at the University of Oxford linked atoms of strontium and calcium in two places into a single quantum state. By passing the link on to calcium, it lasted more than ten seconds instead of milliseconds. A step towards networks of quantum computers.
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Electron pairs survive after superconductivity is gone
Physicists saw that electrons in a metal keep forming pairs even when it is just too warm for superconductivity. That helps to understand how electricity without losses comes about. The next step is to see whether it also happens inside the material.
