Plate Nº 46 · recorded November 15, 2026
PhysicsReported finding
Physicists Propose a Supercurrent Way to Read Qubits Without Wrecking Them
A theoretical study in Physical Review B says oscillating supercurrents from Andreev qubits could reveal quantum states without destroying them. Nobody has built it yet.
By James Calloway4 min read713 words
In brief
- Researchers from China and Brazil published the theoretical work in Physical Review B in 2026.
- Modeling suggests qubit readout accuracy of up to 99.85 percent.
- The method reads oscillating supercurrents from Andreev qubits instead of measuring the qubit directly.
- The technique would avoid auxiliary qubits, or ancillas, used in existing non-destructive readout protocols.
- No experiments have been performed; the findings are purely computational modeling.
Physicists from China and Brazil say a qubit could be read with up to 99.85 percent accuracy — without destroying the delicate quantum state that makes it useful. That's the headline figure from a new theoretical study published in Physical Review B in 2026.
Here's the caveat, and it's a big one: nobody has built the device. This is pure modeling, calculations on paper, not a lab result. Still, the idea is intriguing enough to take seriously.
Why is reading a qubit so hard?
A qubit is the quantum cousin of a classical computer bit. A regular bit is a 1 or a 0. A qubit can be a 1, a 0, or a blend of both at once — a state physicists call superposition. That flexibility is exactly what promises to make quantum computers so powerful.
The catch is brutal. The moment you measure a qubit, its superposition collapses into a plain 1 or 0. Check the value, and you've destroyed the very thing you wanted to know.
"If a qubit has been prepared in a certain superposition of 0 and 1, its direct measurement tends to destroy that superposition and, consequently, the information it contained," said physicist Jose Carlos Egues of the University of São Paulo in Brazil.
What's the new trick?
Current quantum computers partially dodge the problem using auxiliary qubits, known as ancillas — helper qubits that accept the information so the original stays untouched. It works. But it costs time and adds complexity.
The new approach skips the middleman entirely.
"Our strategy is different," Egues said. "Instead of transferring the information to an auxiliary qubit, we seek to obtain it from a signal produced by the qubit under study itself."
Think of it as peripheral vision. You don't look at the thing directly; you read the shadow it casts.
The team's proposal centers on Andreev qubits, which are built from Andreev states that form at the boundary between superconducting materials — materials that carry electricity without resistance. Like any qubit, they can encode 0s, 1s, and superpositions of the two.
According to the researchers' calculations, Andreev qubits in superposition generate oscillating electrical currents with no external voltage required. The quantum behavior itself powers the signal. Those oscillations produce a magnetic field, and that field reveals the qubit's state — a signature you can record instead of a measurement you can't undo.
The physical setup involves a quantum dot — a nanoscale structure where electrons are trapped in a tiny space — formed in an indium arsenide (InAs) nanowire, connected to superconducting materials on both sides. "It's in this environment that the states characterizing the Andreev qubit are formed," Egues said.
How does the readout actually work?
As the qubit shifts between states, its electrical current changes. A separate detector device tracks those variations over time. The researchers liken it to two compasses: one points the way, the other interprets the directions.
"Thus, by measuring how the current varies over time, it's possible to reconstruct the initial state of the qubit," Egues said.
Andreev qubits themselves are not new; physicists have studied them extensively. What's new is the suggestion that their oscillating electrical behavior — the "supercurrent" — can serve as a readable signal. The authors say it's the first time this kind of oscillating signature has been proposed as a way to decode qubits.
There's a practical bonus, too. After each measurement, the usual qubit reset step would apparently be unnecessary.
What does this change for quantum computing?
Right now, nothing concrete — and Egues is admirably blunt about that. "Our method doesn't eliminate the fundamental problem of quantum measurement," he said. "But it can approach the limit of a non-destructive readout and, at the same time, avoid the use of auxiliary qubits — the ancillas — employed in other non-destructive quantum measurement protocols."
The obvious next step is building the thing and testing whether reality agrees with the math. If it does, reading qubits could become simpler and more reliable, pushing quantum computers closer to their potential.
If it doesn't, this joins the long shelf of elegant quantum ideas that looked better in simulation than on a bench. The paper, by Zhang and colleagues, is published in Physical Review B.
via sciencealert.com (Source)
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Staff writer covering regulation, policy and their impact on general science news at SciBeat.
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