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arXiv:2605.00611

Suppressing spin qubit decoherence during shuttling via confinement modulation

Daniel Q. L. Nguyen, Maximilian Rimbach-Russ, Stefano Bosco

cond-mat.mes-hallquant-phSubmitted May 1, 2026• Announced May 4, 2026• 0 citations
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Abstract

Reliable long-range qubit shuttling is a powerful tool for scalable quantum computing architectures. We investigate strategies to improve the coherence of moving spin qubits by performing continuous dynamical decoupling by modulating their confinement potential. Specifically, we introduce temporal and spatial breathing shuttling protocols that leverage spin-orbit interactions in hole-spin systems to electrically drive the qubit while moving. This enables efficient dressed-state shuttling, where the spin is continuously rotated during transport, suppressing the effect of low-frequency noise. Using the filter function formalism, we identify driving regimes that efficiently mitigate both global and local magnetic and electric noise sources. We find that confinement-modulated shuttling can significantly enhance coherence during transport, while revealing distinct limitations depending on the correlation length of the noise. Applying our framework to germanium hole-spin qubits, we show that these protocols provide a practical route toward noise-resilient long-range coherent quantum links.

Comments
main 13 pages, 6 figures, 1 table appendix 5 pages

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Reliable long-range qubit shuttling is a powerful tool for scalable quantum computing architectures. We investigate strategies to improve the coherence of moving spin qubits by performing continuous dynamical decoupling by modulating their confinement potential. Specifically, we introduce temporal and spatial breathing shuttling protocols that leverage spin-orbit interactions in hole-spin systems to electrically drive the qubit while moving. This enables efficient dressed-state shuttling, where the spin is continuously rotated during transport, suppressing the effect of low-frequency noise. Using the filter function formalism, we identify driving regimes that efficiently mitigate both global and local magnetic and electric noise sources. We find that confinement-modulated shuttling can significantly enhance coherence during transport, while revealing distinct limitations depending on the correlation length of the noise. Applying our framework to germanium hole-spin qubits, we show that these protocols provide a practical route toward noise-resilient long-range coherent quantum links.
Mobile spin qubit architectures promise flexible connectivity for efficient quantum error correction and relaxed device layout constraints, but their viability rests on preserving spin coherence during transport. While shuttling transforms spatial disorder into time-dependent noise, its net impact on spin coherence remains an open question. Here we demonstrate systematic noise mitigation during spin shuttling in a linear 28^{28}28Si/SiGe quantum dot device. First, by passively reducing magnetic field gradients, we minimize charge-noise coupling to the spin and double the spatially averaged dephasing time T2∗(xn)T_2^*(x_n)T2∗​(xn​) from 4.44.44.4 to 8.5 μs8.5\,μ\text{s}8.5μs. Next, we exploit motional narrowing by periodically shuttling the qubit, achieving a further enhancement in coherence time up to T2∗,sh=11.5 μsT_{2}^{*,sh} = 11.5\,μ\text{s}T2∗,sh​=11.5μs. Finally, we incorporate dynamical decoupling techniques while periodically shuttling over distances exceeding 200 nm200\,\text{nm}200nm, reaching T2H,sh=32 μsT_\text{2}^{H,sh}= 32\,μ\text{s}T2H,sh​=32μs. For the same setup, we demonstrate that dressed-state shuttling provides robust protection against low-frequency noise with a decay time TRsh=21 μsT_R^{\text{sh}} = 21\,μ\text{s}TRsh​=21μs, without the overhead of pulsed control and allowing protection during one-way spin transport. By preserving coherence over timescales exceeding typical gate and readout operations, the demonstrated strategies establish mobile spin qubits as a viable solution for scalable silicon quantum processors.
Hole spins in silicon quantum dots are a promising platform for quantum computing due to their strong intrinsic spin-orbit coupling (SOC), which enables fast, all-electrical control. However, this coupling also increases their susceptibility to charge noise, thereby limiting coherence times. Moreover, holes in silicon are also affected by hyperfine interactions with residual nuclear spins in the silicon substrate, introducing a non-negligible source of low-frequency noise. Here, we implement a phase-modulated concatenated continuous driving (CCD) technique for hole spin qubits to suppress low-frequency noise through microwave phase modulation. This approach stabilizes Rabi oscillations and extends the oscillation decay time compared to the conventional method. Furthermore, by defining a qubit in the CCD frame, we achieve coherent control while simultaneously protecting the qubit from noise, confirming coherence protection during gate operations. These results demonstrate a viable route toward noise-robust hole spin qubits.
Electron shuttling is emerging as a key mechanism for enabling long-range coupling in scalable spin-qubit architectures. Bringing shuttling waveform generation into the cryostat can improve scalability, but imposes strict area and power constraints on the control electronics. Concurrently, shuttling in Si/SiGe is further limited by a spatially varying valley splitting that induces spin--valley mixing and degrades coherence. Here, we make three contributions that address these limitations jointly: (i) an end-to-end co-simulation framework that combines disorder-informed valley maps with transistor-level cryogenic circuit simulations including electronic noise; (ii) a fully integrated cryogenic shuttling-signal generator tailored to velocity modulation, enabling period-wise waveform shaping through discrete circuit settings stored in on-chip memory; and (iii) a noise-aware optimization procedure that tunes only these implementable circuit controls, using one of four discrete resistor settings per period, to generate high-fidelity shuttling sequences. Across simulated valley and noise realizations in our co-simulation framework, the optimized velocity-modulation waveforms improve transport performance, achieving an average shuttling fidelity of 99.99±0.007%99.99 \pm 0.007\%99.99±0.007% at vavg=20 m s−1v_{\mathrm{avg}} = 20~\mathrm{m\,s^{-1}}vavg​=20 ms−1 over a distance of 10 μm10~μ\mathrm{m}10 μm, while maintaining active analog power consumption in the tens of μWμ\mathrm{W}μW during shuttling. This validates on-chip storage and replay of optimized control settings as a practical strategy to mitigate valley disorder in scalable shuttling architectures.
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.
Entangled qubits transported through space is a key element in many prospective quantum information systems, from long-distance quantum communication to large modular quantum processors. The moving qubits are decohered by time- and space-dependent noises with finite extent of correlations. Since the qubit paths are interrelated, the phase fluctuations experienced by the qubits exhibit peculiar correlations, which are difficult to analyze with the conventional theory of random processes. We propose an approach to this problem based on the concept of trajectories on random sheets. We establish its efficacy with a specific example of the electron spins shuttled in semiconductor structures, and derive explicit solutions, revealing the role of unusual noise correlations. We also demonstrate how the analysis of noise correlations can enhance the shuttling fidelity, by studying transport of two entangled spins encoding a logical qubit. The proposed approach enabled us to specify the favorable conditions for this encoding, and find a particularly beneficial shuttling regime. We also describe application of this approach to other shuttling scenarios, and explain its utility for analysis of other types of systems, such as atomic qubits and photons in quantum networks.
Exchange-based two-qubit gates in semiconductor spin qubits are sensitive to low-frequency detuning noise and control errors. Here, we extend concatenated continuous driving (CCD), implemented by phase modulation of a global microwave drive, to exchange-based SWAP and SWAP\sqrt{\mathrm{SWAP}}SWAP​ operations between double-dressed spin qubits and investigate its effectiveness for protecting two-qubit gates. We find that CCD retains strong protection against quasistatic common-mode detuning errors while substantially improving robustness against Rabi-frequency errors and qubit-to-qubit Rabi-frequency mismatch compared with conventional continuous dressing. By contrast, the gate fidelity is impacted by differential detuning errors. By modeling partially correlated quasistatic detuning noise, we further show that the noise-averaged gate fidelity depends strongly on the spatial correlation of the qubit-frequency fluctuations, with positive correlations enhancing CCD protection by suppressing the differential-noise component. These results identify the symmetry and spatial correlation of qubit-frequency noise as key factors governing continuous-drive protection in coupled spin-qubit systems.