Quantum Components Now Stably Combined Despite Conflicting Magnetic Field Needs

Scientists are tackling a significant hurdle in the development of hybrid quantum computing, integrating the distinct requirements of superconducting circuits and spin ensembles. Lukas Vogl, Gerhard B. P. Huber, and Ana Strinić, working with colleagues at the Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, present a novel experimental setup designed to address this challenge. Their research details a cryogenic system featuring spatially and magnetically decoupled volumes, one for flux-tunable superconducting circuits and another for a spin ensemble controlled by a superconducting solenoid generating fields up to 50 mT. This innovative configuration, incorporating multiple layers of Cryophy shielding and a superconducting aluminum shield, demonstrably suppresses magnetic crosstalk by over eight orders of magnitude, ensuring stable operation and representing a crucial advancement towards scalable hybrid quantum architectures.

This breakthrough addresses a fundamental challenge; superconducting qubits demand magnetically quiet environments, while spin ensembles require substantial magnetic fields for operation. The work details the first experimentally verified setup that simultaneously satisfies both conditions, paving the way for more scalable and powerful quantum processors. This innovative design employs multiple layers of Cryophy® shielding alongside a superconducting aluminum shield, suppressing magnetic crosstalk by over eight orders of magnitude. This level of isolation ensures the stability of the qubits, preventing performance degradation from the magnetic fields used to control the spin ensemble. The system incorporates a superconducting solenoid capable of generating fields up to 50 mT, while minimising additional thermal load on the refrigerator’s critical cooling stages. By leveraging the unique properties of both superconducting circuits and spin-based quantum memories, future devices could overcome limitations in qubit density and enhance overall computational performance. Magnetic crosstalk suppression exceeding eight orders of magnitude has been experimentally demonstrated, enabling the stable operation of spatially proximal superconducting qubits and a spin ensemble within a single dilution refrigerator. The research details a cryogenic setup featuring magnetically decoupled volumes, one housing flux-tunable superconducting qubits and the other a spin ensemble controlled by a superconducting solenoid generating fields up to 50 mT. Several layers of Cryophy® shielding, combined with a superconducting aluminum shield, were instrumental in achieving this exceptional level of magnetic isolation. The implemented shielding effectively confines the magnetic field generated by the solenoid, preventing interference with the sensitive superconducting circuits. Superconducting qubits are highly susceptible to magnetic field fluctuations, which can lead to decoherence and necessitate frequent recalibration. The solenoid’s operation introduces minimal additional thermal load onto the dilution refrigerator stages, preserving the ultracold environment essential for qubit coherence. Furthermore, the study confirms the feasibility of integrating components with inherently incompatible magnetic field requirements within a compact cryogenic architecture. Spin ensembles typically require moderate to high magnetic fields, ranging from 300 mT to 1.5 T, to facilitate control and maintain long coherence times, particularly at Zero First-Order Zeeman points. A superconducting solenoid magnet, meticulously wound with 4360 turns of 101μm-thick NbTi wire, forms the core of this work’s hybrid quantum architecture. Each winding layer, and the solenoid body itself, received a coating of GE Varnish, a cryogenic adhesive ensuring both electrical insulation and enhanced thermal contact. This careful construction was essential to generate stable magnetic fields up to 50 mT while minimising thermal load on the dilution refrigerator. The coil constant was initially calculated numerically to optimise the winding pattern, and then experimentally verified at both room temperature and cryogenic conditions using an AS-UAP GEO-X axial probe at positions P1, the coil’s geometrical centre, and P0, the identified optimal sample location. To achieve precise calibration at low temperatures, low-temperature electron spin resonance (ESR) measurements were performed on a 2,2-Diphenyl-1-Picrylhydrazyl (DPPH) sample, a well-established reference material in spin resonance spectroscopy. By exploiting the linear relationship between resonance frequency and magnetic field, defined by Bohr’s magneton and Planck’s constant, the actual magnetic field strength and, consequently, the coil constant, could be accurately determined. A custom-engineered cryogenic magnetic shielding (CMS) system, constructed from 1mm-thick Cryophy® sheet metal, was implemented to address the challenge of magnetically decoupling superconducting qubits from the spin ensemble. This nickel-iron-molybdenum alloy effectively attenuates static magnetic fields at cryogenic temperatures. The CMS comprises three cylindrical shielding cans, each with a 4mm gap, providing an inner working volume of 88mm diameter and 256mm height, and was initially designed with three Cryophy® shields before the outermost layer was replaced with a superconducting aluminum shield of identical dimensions. Comsol Multiphysics® simulations validated the shielding’s performance, demonstrating a suppression of magnetic crosstalk exceeding eight orders of magnitude and ensuring the stability required for integrated hybrid quantum systems. The persistent challenge of scaling quantum computing isn’t simply about building better qubits, but about building them together. For years, the field has grappled with the inherent incompatibility of leading qubit technologies, superconducting circuits, promising for their scalability, and quantum memories, essential for long-duration storage and processing. These components operate under opposing conditions; superconducting qubits demand isolation from magnetic interference, while quantum memories often rely on controlled magnetic fields for manipulation. This work doesn’t offer a revolutionary qubit design, but a crucial piece of engineering that bridges this divide. What’s particularly notable is the demonstrated level of magnetic shielding, reducing crosstalk by over eight orders of magnitude. This isn’t merely incremental improvement, but a fundamental enabling step, allowing for the close proximity of these disparate quantum systems within a single cryostat. The minimal additional thermal load from the control solenoid is also a significant practical achievement, addressing a common bottleneck in complex cryogenic setups. However, the architecture remains a proof-of-principle demonstration. Scaling this setup to encompass a larger number of qubits and memory units will undoubtedly present new challenges in terms of wiring complexity and maintaining uniform shielding. Furthermore, the performance characteristics of the quantum memory itself, coherence times, and readout fidelity, are not addressed here and remain critical factors. The next phase will likely focus on integrating this shielding technology with specific quantum memory materials and exploring the impact of this integration on overall system performance, potentially paving the way for more complex quantum algorithms and applications.