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A MODULAR HIGH-DENSITY CRYOGENIC ARCHITECTURE FOR 10⁴–10⁵ QUBIT SUPERCONDUCTING QUANTUM

Sahraoui, Nadia

Published Nov 18, 2025• 0 citations
Publisher

Abstract

Title A Modular High-Density Cryogenic Architecture for 10⁴–10⁵ Qubit Superconducting Quantum Computers (Version 1.0 – Open Proposal, December 2025) Abstract (copy-paste this in the abstract field) This document proposes a practical, fully specified cryogenic wiring and packaging architecture that enables 10 000 to 40 000 high-quality superconducting qubits inside a single commercial dilution refrigerator (Bluefors XLD or Oxford Triton class) using only components and fabrication processes demonstrated in 2024–2025. The central idea is a large vertical “Wall” panel at the 10 mK stage combined with a vertical coaxial routing scheme that reduces conductive heat load to ≤ 0.58 µW per line (measured on NbTi/CuNi aerogel-filled lines with two-point anchoring). No new materials, no unproven refrigeration cycles, and no speculative physics are required. The design is deliberately conservative and offered as an open contribution for community validation. Description (copy-paste this in the “Notes” / description box on Zenodo) I am an independent researcher sharing this detailed engineering proposal in the hope that groups with real dilution refrigerators and clean-room access will find it useful enough to test. Key points that I believe make this worth a quick look: Uses only off-the-shelf cryogenic coax, PEEK 3D printing, OFHC braids, Kevlar suspension, and standard 2025 transmon/fluxonium processes. The thermal budget calculations and the ≤ 0.58 µW/line number are derived from publicly available NbTi/CuNi data and simple two-point anchoring – nothing exotic. A subscale prototype (e.g. 0.5 m × 0.5 m sector, 2 000–5 000 lines) could be built and cooled down in 2026 by almost any serious lab. Full mechanical drawings, spacer STL files, cabling lists, and test protocols will be uploaded here as soon as at least one group expresses interest in trying it. I am not claiming that everything will work perfectly on the first try – only that the path looks technically conservative and testable today. Feedback, criticism, and especially experimental results (positive or negative) are very warmly welcomed. If you run a quantum hardware lab and would like the CAD files or discuss a small joint prototype, please feel free to reach out, I am easy to find. License: CC-BY-4.0 (share, adapt, and publish results freely, just attribute). The specific vertical routing geometry may be patentable, but I am happy to grant royalty-free use for academic and non-commercial research. Thank you for your time, Nadia Sahraoui Independent researcher ORCID 0009-0002-7049-9794 December 2025

DOI
10.5281/zenodo.17641169

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Title A Modular High-Density Cryogenic Architecture for 10⁴–10⁵ Qubit Superconducting Quantum Computers (Version 1.0 – Open Proposal, December 2025) Abstract (copy-paste this in the abstract field) This document proposes a practical, fully specified cryogenic wiring and packaging architecture that enables 10 000 to 40 000 high-quality superconducting qubits inside a single commercial dilution refrigerator (Bluefors XLD or Oxford Triton class) using only components and fabrication processes demonstrated in 2024–2025. The central idea is a large vertical “Wall” panel at the 10 mK stage combined with a vertical coaxial routing scheme that reduces conductive heat load to ≤ 0.58 µW per line (measured on NbTi/CuNi aerogel-filled lines with two-point anchoring). No new materials, no unproven refrigeration cycles, and no speculative physics are required. The design is deliberately conservative and offered as an open contribution for community validation. Description (copy-paste this in the “Notes” / description box on Zenodo) I am an independent researcher sharing this detailed engineering proposal in the hope that groups with real dilution refrigerators and clean-room access will find it useful enough to test. Key points that I believe make this worth a quick look: Uses only off-the-shelf cryogenic coax, PEEK 3D printing, OFHC braids, Kevlar suspension, and standard 2025 transmon/fluxonium processes. The thermal budget calculations and the ≤ 0.58 µW/line number are derived from publicly available NbTi/CuNi data and simple two-point anchoring – nothing exotic. A subscale prototype (e.g. 0.5 m × 0.5 m sector, 2 000–5 000 lines) could be built and cooled down in 2026 by almost any serious lab. Full mechanical drawings, spacer STL files, cabling lists, and test protocols will be uploaded here as soon as at least one group expresses interest in trying it. I am not claiming that everything will work perfectly on the first try – only that the path looks technically conservative and testable today. Feedback, criticism, and especially experimental results (positive or negative) are very warmly welcomed. If you run a quantum hardware lab and would like the CAD files or discuss a small joint prototype, please feel free to reach out, I am easy to find. License: CC-BY-4.0 (share, adapt, and publish results freely, just attribute). The specific vertical routing geometry may be patentable, but I am happy to grant royalty-free use for academic and non-commercial research. Thank you for your time, Nadia Sahraoui Independent researcher ORCID 0009-0002-7049-9794 December 2025
Scaling superconducting quantum processors to hundreds of qubits is essential for demonstrating quantum advantage and implementing quantum error correction codes with larger distances. A key challenge is integrating control and readout wiring without compromising cryogenic or electronic performance. To address this, we performed a systematic analysis of the thermal budget within a dilution refrigerator and developed high-density 0.5 mm SCuNi-CuNi coaxial cable sets optimized for heat load management. This enables the integration of 696 control lines and 40 readout amplification chains into a dilution refrigerator with a cooling power of 1 mW at 100 mK, maintaining a stable base temperature of ∼8 mK for over a year. We validated the platform's performance with two large-scale quantum processors: a 540-qubit processor with an average T1 of 35 μs and a 156-qubit processor with 182 tunable couplers, achieving average fidelities of 99.9% for single-qubit gates and 99.0% for two-qubit gates. This study demonstrates a viable high-density wiring solution for controlling and measuring processors at the 500-qubit scale and provides critical engineering insights for larger-scale quantum computing systems.
A robust cryogenic infrastructure in form of a wired, thermally optimized dilution refrigerator is essential for solid-state based quantum processors. Here, we engineer a cryogenic setup, which minimizes passive and active heat loads, while guaranteeing rapid qubit control and readout. We review design criteria for qubit drive lines, flux lines, and output lines used in typical experiments with superconducting circuits and describe each type of line in detail. The passive heat load of stainless steel and NbTi coaxial cables and the active load due to signal dissipation are measured, validating our robust and extensible concept for thermal anchoring of attenuators, cables, and other microwave components. Our results are important for managing the heat budget of future large-scale quantum computers based on superconducting circuits.
Abstract Superconducting quantum computers require microwave control lines running from room temperature to the mixing chamber of a dilution refrigerator. Adding more lines without preliminary thermal modeling to make predictions risks overwhelming the cooling power at each thermal stage. In this paper, we investigate the thermal load of SC-086/50-SCN-CN semi-rigid coaxial cable, which is commonly used for the control and readout lines of a superconducting quantum computer, as we increase the number of lines to a quantum processor. We investigate the makeup of the coaxial cables, verify the materials and dimensions, and experimentally measure the total thermal conductivity of a single cable as a function of the temperature from cryogenic to room temperature values. We also measure the cryogenic DC electrical resistance of the inner conductor as a function of temperature, allowing for the calculation of active thermal loads due to Ohmic heating. Fitting this data produces a numerical thermal conductivity function used to calculate the static heat loads due to thermal transfer within the wires resulting from a temperature gradient. The resistivity data is used to calculate active heat loads, and we use these fits in a cryogenic model of a superconducting quantum processor in a typical Bluefors XLD1000-SL dilution refrigerator, investigating how the thermal load increases with processor sizes ranging from 100 to 225 qubits. We conclude that the theoretical upper limit of the described architecture is approximately 200 qubits. However, including an engineering margin in the cooling power and the available space for microwave readout circuitry at the mixing chamber, the practical limit is approximately 140 qubits.
Scaling superconducting quantum computers to the fault-tolerant regime calls for a commensurate scaling of the classical control and readout stack. Today's systems largely rely on room-temperature, rack-based instrumentation connected to dilution-refrigerator cryostats through many coaxial cables. Looking ahead, superconducting fault-tolerant quantum computers (FTQCs) will likely adopt a heterogeneous quantum-classical architecture that places selected electronics at cryogenic stages -- for example, cryo-CMOS at 4~K and superconducting digital logic at 4~K and/or mK stages -- to curb wiring and thermal-load overheads. This review distills key requirements, surveys representative room-temperature and cryogenic approaches, and provides a transparent first-order accounting framework for cryoelectronics. Using an RSA-2048-scale benchmark as a concrete reference point, we illustrate how scaling targets motivate constraints on multiplexing and stage-wise cryogenic power, and discuss implications for functional partitioning across room-temperature electronics, cryo-CMOS, and superconducting logic.
This work presents a conceptual architecture and technological roadmap for a scalable superconducting quantum computing platform based on modular design principles. Rather than introducing a new qubit technology, the proposal focuses on addressing critical engineering bottlenecks that currently limit the large-scale deployment of quantum processors, including wiring complexity, electromagnetic crosstalk, fabrication yield, and latency in error-correction feedback loops.The proposed framework introduces a modular hybrid architecture (“Quantum Mesh”), where medium-scale quantum chiplets containing 25–50 superconducting transmon qubits are interconnected through advanced 3D packaging and cryogenic infrastructure. This approach aims to improve manufacturing yield, reduce wiring density, and enable rack-level integration of quantum processing units while maintaining high gate fidelities and manageable thermal loads.A second central element of the proposal is the integration of a high-fidelity digital twin environment capable of simulating qubit dynamics, noise sources, control latency, and thermal constraints at nanosecond resolution. This predictive framework is intended to support hardware iteration cycles prior to fabrication, potentially accelerating design optimization and system validation.The document outlines a three-year development pathway targeting 100–200 physical qubits and several logical qubits using surface code error correction, followed by a longer-term scaling strategy toward quantum fabrics exceeding one thousand qubits. By combining modular quantum chiplets, partial cryogenic electronics, and predictive digital twin modeling, the proposed architecture explores a plausible industrial pathway toward large-scale quantum computing systems.
Large-scale quantum computers with more than 10510^5105 qubits will likely be built within the next decade. Trapped ions, semiconductor devices, and superconducting qubits among other physical implementations are still confined in the realm of medium-scale quantum integration (∼100\sim 100∼100 qubits); however, they show promise toward large-scale quantum integration. Building large-scale quantum processing units will require truly scalable control and measurement classical coprocessors as well as suitable wiring methods. In this blue paper, we introduce a fully vertical interconnect that will make it possible to address ∼105\sim 10^5∼105 superconducting qubits fabricated on a single silicon or sapphire chip: Pin-chip bonding. This method permits signal transmission from DC to ∼10\sim 10∼10 GHz, both at room temperature and at cryogenic temperatures down to ∼10\sim 10∼10 mK. At temperatures below ∼1\sim 1∼1 K, the on-chip wiring contact resistance is close to zero and all signal lines are in the superconducting state. High-density wiring is achieved by means of a fully vertical interconnect that interfaces the qubit array with a network of rectangular coaxial ribbon cables. Pin-chip bonding is fully compatible with classical high-density test board applications as well as with other qubit implementations.