The Magic at the Heart of Quantum Computers Has Finally Worked

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Here’s what you’ll learn when you read this story:

Making quantum computers fault-tolerant (and scaling effective error correction to enable this) is a key barrier to a new era of quantum supremacy.
A new study demonstrates for the first time that a process known as ‘magic state distillation,’ which expands the number of operations a quantum system can do, can occur within logical qubits (the more fault-tolerant cousins of physical qubits).
This breakthrough, and others like it, could help unleash quantum computing’s potential and allow scientists to ponder ways that these machines could actually be useful.

The future of quantum computers holds a lot of promise, but as of today, that’s all it is—promise. While breakthroughs seemingly push us ever forward in our quest to create a true universal quantum computer capable of exceeding the abilities of even our very best supercomputers, scientists haven’t quite crossed that enviable threshold.

One major barrier standing between today and this future computational eden is an idea known as “quantum error correction.” Qubits are easily disrupted by “noise,” which can come in the form of electromagnetic radiation and even just temperature. This noise eventually leads to decoherence of the system, transforming our nifty quantum computer into just a run-of-the-mill classical one. While the error-rate of normal bits is extremely minuscule, quantum error rates average around one in 1,000, which basically turns computations into an unusable mess pretty quick.

A new study—published in the journal Nature by a research team from MIT, Harvard, and the quantum computing company QuEra—aims to improve this error-correction by demonstrating what’s called “magic state distillation” in logical qubits.

…yeah, that sentence might need some unpacking.

First, logical qubits aren’t the same physical qubits, which are the basic building blocks of quantum systems. Logical qubits are groups of physical qubits that share the same information and are protected by layers of error-correcting code. The idea goes that if one logical qubit produces and error, it won’t disrupt the whole system, as that information is contained.

For more than 20 years, scientists have known about so-called “magic states,” which are highly refined resources that are key to scaling fault-tolerant quantum systems. In a press release accompanying the study, QuEra compares “magic states” to jet fuel.

Think of magic state distillation as the quantum equivalent of refining crude oil into aviation fuel: it transforms the fragile, noisy raw materials produced by today’s quantum systems into the high‑octane resource required to run any quantum algorithm reliably. Raw magic states are imperfect, so engineers combine multiple copies and “distill” the batch into a single, cleaner version.

For the first time, researchers performed this distillation process within logical qubits using the QuEra’s neutral-atom computer. They created logical qubit bundles of sizes known as Distance-3 and Distance-5—essentially, the higher the number, the better the logical qubit (it’s more capable of correcting errors, for example). They then distilled five imperfect magic states into one cleaner magic states—refining that “crude oil” into high-octane jet fuel. The results showed that the final magic state contained a higher fidelity than any of the inputs, proving that fault-tolerant magic state distillation is possible.

“This experiment leverages the unique strengths of neutral‑atom arrays…to tackle one of the most demanding sub‑routines in quantum error correction,” Mikhail Lukin, a co-author of the study from Harvard University, said in a press statement. “It is a very important step toward practical, universal quantum processors.”

QuEra’s chief commercial officer Yuval Boger, speaking with Live Science, said that this breakthrough is a true step forward. In years past, scientists had pondered whether quantum computers were even possible, and recently, universities and tech companies have been searching for ways to make those computers less prone to errors. Boger says that the question has now become: “Can we make these computers truly useful?”

If history is any indicator, we might already know that answer.

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