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arxiv: 2606.21452 · v1 · pith:WVR5AIIOnew · submitted 2026-06-19 · ❄️ cond-mat.mes-hall · quant-ph

Spin qubit operations by conveyor-mode shuttling

M. De Smet , Y. Matsumoto , D. Fern\'andez-Fern\'andez , L. Tryputen , S.L. de Snoo , D.J. Michalak , H.G.J. Eenink , G. Platero
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S. Bosco G. Scappucci L.M.K. Vandersypen
This is my paper

Pith reviewed 2026-06-26 13:25 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall quant-ph
keywords conveyor-mode shuttlingspin qubitsEDSRdiabatic gatesqubit routingsemiconductor quantum processorstwo-qubit interactionsdynamic control
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The pith

Conveyor-mode shuttling performs coherent single- and two-qubit control on spin qubits by motion through field gradients and axis tilts.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that traveling-wave conveyor potentials can move electrons while enabling qubit operations directly through the motion. Two methods are shown: resonant shuttling through magnetic gradients at the Larmor frequency for rotations, and diabatic control from quantization-axis tilts for bang-bang gates. Combining the transport with motion-activated exchange produces selectable two-qubit interactions. A reader would care because this merges qubit routing with gate execution in one mechanism, potentially reducing the need for separate static control structures in semiconductor processors. If correct, it supports architectures where qubits are reconfigured dynamically during operation.

Core claim

Conveyor electric-dipole spin resonance achieves high-fidelity rotations by resonantly shuttling spins through transverse magnetic-field gradients at their mean Larmor frequency, while conveyor diabatic gates exploit quantization-axis tilts for tunable bang-bang control; combining diabatic conveyor transport with exchange activation controlled by the motion directly yields a variety of effective two-qubit interactions selectable via the shuttling speed and distance.

What carries the argument

Conveyor-mode shuttling using traveling-wave potentials that move charge carriers while the induced motion through gradients or tilts supplies the coherent control.

If this is right

  • Single-qubit rotations become possible solely by resonant shuttling without additional microwave drives.
  • Two-qubit interactions become tunable by choosing shuttling speed and distance during exchange activation.
  • Qubit routing and gate operations can be performed by the same conveyor mechanism in one device.
  • Semiconductor processors gain reconfigurability where connections are set dynamically by transport paths.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The approach may reduce wiring density by moving qubits to shared interaction regions instead of routing control signals to fixed locations.
  • Different conveyor velocities could be tested to separate coherent motion effects from velocity-dependent noise sources.
  • Integration with existing quantum-dot arrays might allow conveyor segments to act as both highways and gate zones without new fabrication layers.

Load-bearing premise

Traveling-wave conveyor potentials preserve spin state with high fidelity during shuttling so motion-induced gradients and tilts can produce coherent control without dominant decoherence.

What would settle it

Failure to observe the predicted rotation angles or two-qubit interaction strengths when shuttling at the mean Larmor frequency through calibrated gradients, with coherence times instead limited by the transport itself.

Figures

Figures reproduced from arXiv: 2606.21452 by D. Fern\'andez-Fern\'andez, D.J. Michalak, G. Platero, G. Scappucci, H.G.J. Eenink, L.M.K. Vandersypen, L. Tryputen, M. De Smet, S. Bosco, S.L. de Snoo, Y. Matsumoto.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: d clearly shows that shuttling-induced Larmor pre￾cession around a new quantization axis appears only when the electron is displaced beyond 40 nm, as expected. Fur￾thermore, we see that the contrast of the oscillations vanishes if the conveyor velocity is reduced. The qubit dynamics thus depends not only on the shuttling distance but also on the shut￾tle velocity, which in the present experiment can be tun… view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

Dynamic qubit routing is emerging as a promising architectural path for semiconductor quantum processors. Charge carriers can be rapidly moved around on a chip using traveling-wave potentials known as conveyors, preserving the spin state with high fidelity. Originally developed for spin transport, conveyor-mode shuttling may also offer opportunities for performing qubit operations directly controlled by the motion itself. Here, we demonstrate coherent single- and two-qubit control by conveyor-mode electron shuttling, using two conceptually different approaches. First, conveyor electric-dipole spin resonance (conveyor EDSR) achieves high-fidelity rotations by resonantly shuttling spins through transverse magnetic-field gradients at their mean Larmor frequency. Second, conveyor diabatic gates exploit quantization-axis tilts for tunable bang-bang control. Combining diabatic conveyor transport with exchange activation controlled by the motion directly yields a variety of effective two-qubit interactions selectable via the shuttling speed and distance. These experimental results motivate an architectural paradigm of reconfigurable and transport-driven spin qubits.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript claims to experimentally demonstrate coherent single- and two-qubit control via conveyor-mode electron shuttling in two approaches: conveyor EDSR, which uses resonant shuttling through transverse magnetic gradients at the mean Larmor frequency for high-fidelity rotations, and conveyor diabatic gates, which exploit quantization-axis tilts for tunable bang-bang control; the latter is combined with motion-controlled exchange to produce selectable two-qubit interactions.

Significance. If the experimental results hold, the work would be significant for semiconductor spin-qubit architectures by showing that traveling-wave conveyor potentials can be used not only for transport but also to directly implement coherent operations, potentially enabling reconfigurable, motion-driven qubit routing with reduced static control overhead.

major comments (2)
  1. [Abstract] Abstract: the central experimental claim of 'high-fidelity rotations' and 'coherent single- and two-qubit control' is stated without any fidelity numbers, error bars, raw data, or methods details, rendering the claim unverifiable from the manuscript text.
  2. [Abstract] Abstract: the load-bearing premise that 'traveling-wave potentials known as conveyors, preserving the spin state with high fidelity' is asserted as background without independent shuttling-fidelity or transport-T2 measurements that would separate spin preservation from the claimed motion-induced control effects.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments on the abstract. We address each point below and have revised the manuscript accordingly to improve the verifiability of our claims while respecting length constraints.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the central experimental claim of 'high-fidelity rotations' and 'coherent single- and two-qubit control' is stated without any fidelity numbers, error bars, raw data, or methods details, rendering the claim unverifiable from the manuscript text.

    Authors: We agree that the abstract would benefit from quantitative support. The main text (Sections III and IV) and figures report specific fidelities with error bars (e.g., from randomized benchmarking and Ramsey experiments) along with raw data traces. We have revised the abstract to include key fidelity values and a brief reference to the experimental methods used. revision: yes

  2. Referee: [Abstract] Abstract: the load-bearing premise that 'traveling-wave potentials known as conveyors, preserving the spin state with high fidelity' is asserted as background without independent shuttling-fidelity or transport-T2 measurements that would separate spin preservation from the claimed motion-induced control effects.

    Authors: This background statement is drawn from our prior experimental characterization of conveyor transport (cited in the manuscript), which separately quantified shuttling fidelity and transport-induced dephasing via T2 measurements. To address the concern, we have added an explicit citation to those independent measurements directly in the revised abstract. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental claims rest on measurements, not derivations or self-referential fits

full rationale

The paper reports experimental demonstrations of coherent single- and two-qubit operations via conveyor-mode shuttling. No equations, derivations, fitted parameters renamed as predictions, or load-bearing self-citations appear in the provided abstract or described content. The central claims are supported by new measurements of rotations and interactions, with the spin-preservation premise treated as a background experimental condition rather than a result derived from the control effects themselves. This is the expected non-finding for an experimental methods paper without theoretical reduction steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The abstract relies on established semiconductor spin physics without introducing new free parameters, ad-hoc axioms, or invented entities; all mechanisms are framed as extensions of known EDSR and exchange effects.

axioms (1)
  • standard math Standard quantum mechanics and semiconductor physics assumptions for electron spin in quantum dots and magnetic gradients
    Invoked implicitly in the description of Larmor frequency, quantization-axis tilts, and exchange activation.

pith-pipeline@v0.9.1-grok · 5753 in / 1253 out tokens · 29558 ms · 2026-06-26T13:25:24.421530+00:00 · methodology

discussion (0)

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Reference graph

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    Two-tone conveyor shuttling In the main text of this work, we employ a two-tone con- veyor [23] to shuttle qubit 2 or qubit 5. Each gate in the conveyor, therefore, receives two sinusoidal pulses, given by Vn(t)=V DC n + An 2 sin(2πf t−ϕ n) +sin (πf t−θ n) . Here, the DC voltageV DC n is tuned individually for each gate, while the amplitudesA n are shared...

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    A simple estimate of the resulting infidelity 1−F≈ ⟨δϕ 2⟩/6=9×10 −5 shows that these phase errors are an order of magnitude smaller than theX90 shuttling gate error, supporting the conclusion from the interleaved ran- domized benchmarking measurements. FIG. S9.Conveyor EDSR subharmonics when shuttling with a block-like motion profile.The one-way shuttle t...

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    The left qubit is shuttled towards the right qubit, which remains static

    Model Hamiltonian The starting point is a minimal Hamiltonian for two electron-spin qubits subject to a spatially varying magnetic field vector, resulting from the vector sum of the externally ap- plied magnetic field and the stray magnetic field from the mi- cromagnet. The left qubit is shuttled towards the right qubit, which remains static. We set thez-...

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    We therefore analyze a single electron-spin qubit shuttled along a one-dimensional channel in the presence of the total magnetic field ⃗B

    Single-qubit calibration The calibration begins in the simplest regime, where ex- change is absent, and the magnetic-field profile can be probed directly. We therefore analyze a single electron-spin qubit shuttled along a one-dimensional channel in the presence of the total magnetic field ⃗B. In this step, the left qubit is initial- ized in |↑⟩, shuttled ...

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    The Hamiltonian is still given by Eq

    Two-qubit calibration Having fixed the field sampled by the moving qubit, we now turn to the interacting two-qubit system. The Hamiltonian is still given by Eq. (S2), but the magnetic field at the position of the left qubit is now fixed by the single-qubit reconstruction. The remaining unknowns are the exchange couplingJ(d) and the magnitude and polar ang...

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    Predicted Two-Qubit Gate Set We now use the calibrated Hamiltonian to assess which two-qubit gates the model predicts are accessible with the shuttling protocol. Because the magnetic field shows some dataset-to-dataset variability, we fix the global shift to∆x=2 nm and the right-qubit Larmor frequency to fR =102.2 MHz, i.e., the values extracted from the ...