Issue 1 | Physical Review Research, published 14 October 2026

Spin qubits that leapfrog over each other

Our understanding

Slide 1: Qubits that leapfrog over each other. Theory and simulation. Schematic: on a track of five tiny traps, a blue moving qubit passes along the track through the middle trap, which already holds a white parked qubit; both sit in that trap together.Slide 2: In silicon chips, qubits travel. Schematic: one electron moved along a track of tiny traps.Slide 3: Some spots on the track cause trouble. Schematic: a moving electron is stopped before a spot with small valley splitting.Slide 4: The idea: pass through, and link up. Schematic in three steps: before, passing through the occupied trap with both electrons in it, after, with both electrons linked.Slide 5: In simulations, the leapfrog works. Simulated for several sets of device parameters; the pass acts as an entangling two-qubit gate, a γ gate. Schematic circuit: lines for the moving and the parked qubit run through one shared γ gate during the pass.Slide 6: Next step: a real chip. It would turn weak spots into extra routes and give a two-qubit gate without extra hardware. Schematic chip outline around the track with the moving qubit passing through the occupied trap, labelled real chip: still open. Link to anyon.news.
Slide 1 of 6

In silicon quantum chips, each qubit is a single electron, and electrons are moved along the chip like cars on a lane. Some spots on the chip are troublesome and are normally avoided. The authors show in simulations that a moving electron can hop over a parked one, right at such a spot. While it passes, the two electrons become linked, which is a basic step of quantum computing. Nobody has done this in a real chip yet.

The details

Schematic: a row of quantum dots in a silicon channel; a mobile electron is shuttled from left to right and passes through a dot occupied by a stationary electron, picking up an entangling two-qubit gate; the region of low valley splitting is marked.
Schematic drawn for this newsletter (anyon, CC BY 4.0), illustrating Meineke and Burkard, Phys. Rev. Research (2026), DOI 10.1103/l1vq-9zhr. Not a figure from the paper.

What they did

In silicon quantum chips, a qubit is a single electron’s spin, and electrons are moved across the chip (“shuttled”) to connect distant parts of the processor. Silicon has an extra quantum property called the valley degree of freedom; in regions where the “valley splitting” is small, the usual shuttling protocols run into trouble, and how to handle such regions has been an open problem. Instead of avoiding them, the authors propose using exactly this valley property to let a moving electron pass through a quantum dot that is already occupied by a stationary electron, hopping over it. In the same step the two electrons undergo an entangling two-qubit operation (a so-called γ gate). Simulations for several parameter sets show that the leapfrog is feasible.

Why it matters

It turns a weak spot of the chip into a feature: more routing paths for qubits, and a two-qubit gate without extra hardware, in regions that would otherwise be avoided.

What is still open

This is theory and simulation. Which device will show it first, and how robust is the leapfrog against the charge noise and valley-splitting variations of real silicon devices? (The robustness question is our inference; the abstract does not discuss noise.)

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