arXiv subjects

Marcel Walter

Publications and source records attributed to Marcel Walter.

9 recordsLinked to original sources

arXiv2026

Practical HPCQC Integration with QDMI: A Real-Hardware Case Study with IQM Systems

Quantum computers are moving into HPC centers, and the main challenge is now integration rather than pure hardware access. Many current software paths still depend on vendor-specific adapter chains between user SDKs, schedulers, and backend APIs. This pattern makes operations more complex than necessary and slows the transition from pilots to production workflows. We present a practical integration path centered on the Quantum Device Management Interface (QDMI). Using IQM superconducting systems as a hardware case study, we implement an IQM-backed QDMI layer and connect it to two software layers that HPC centers working with quantum computers already care about: Slurm-based job execution and Qiskit-facing user workflows. The implementation is publicly available at https://github.com/iqm-finland/QDMI-on-IQM. The key message is simple: integrating quantum hardware into HPC does not have to be a bespoke engineering effort for each backend. Once the software-hardware boundary is standardized, large parts of the stack become reusable across providers and deployment styles. Our results do not claim that standardization eliminates all HPCQC challenges. They show that this specific boundary can already be standardized today in a way that is practical for users, operators, and vendors.

quant-ph↗

arXiv2025

Accelerated ultrafast demagnetization of an interlayer-exchange-coupled Co/Mn/Co trilayer

We investigate the ultrafast magnetization dynamics of an interlayer-exchange-coupled Co/Mn/Co trilayer system after excitation with an ultrafast optical pump. We probe element- and time-resolved ferromagnetic order by X-ray magnetic circular dichroism in resonant reflectivity. We observe an accelerated Co demagnetization time in the case of weak total parallel interlayer coupling at 9.5 ML Mn thickness for antiparallel alignment of both Co layers compared to parallel alignment as well as for parallel alignment in the case of strong parallel interlayer coupling at 11 ML of Mn. From ab initio time-dependent density functional theory calculations, we conclude that optically induced intersite spin transfer of spin-polarized electrons from Co into Mn acts as a decay channel to enhance and accelerate ultrafast demagnetization. This spin transfer can only take place in case of a collinear Mn spin structure. We argue that this is the case for antiparallel alignment of both Co layers at 9.5 ML Mn thickness and parallel alignment in case of 11 ML of Mn. Our results point out that an antiferromagnetic spacer layer and its spin structure have a significant effect on the magnetization dynamics of adjacent ferromagnetic layers. Our findings provide further insight into fundamental mechanisms of ultrafast demagnetization and may lead to improve dynamics in multilayered systems for faster optical switching of magnetic order.

cond-mat.mtrl-sci↗

arXiv2025

A Fully Planar Approach to Field-coupled Nanocomputing: Scalable Placement and Routing Without Wire Crossings

Field-coupled Nanocomputing (FCN) is a class of promising post-CMOS technologies that transmit information through electric or magnetic fields instead of current flow. They utilize basic building blocks called cells, which can form gates that implement Boolean functions. However, the design constraints for FCN circuits differ significantly from those for CMOS. One major challenge is that wires in FCN have to be realized as gates, i.e., they are constructed from cells and incur the same costs as gates. Additionally, all FCN technologies are fabricated on a single layer, e.g., a silicon surface, requiring all elements -- gates and wires -- to be placed within that same layer. Consequently, FCN employs special gates, called wire crossings, to enable signals to cross. While existing wire-crossing implementations are complex and were previously considered costly, initial efforts have aimed at minimizing their use. However, recent physical simulations and experiments on a quantum annealing platform have shown that currently used wire crossings in FCN significantly compromise signal stability, to the extent that circuits cannot function reliably. This work addresses that issue by introducing the first placement and routing algorithm that produces fully planar FCN circuits, eliminating the need for all wire crossings. For a comparative evaluation, a state-of-the-art placement and routing algorithm was also modified to enforce planarity. However, our proposed algorithm is more scalable and can handle inputs with up to 149k gates, enabling it to process circuits that are 182x more complex than those handled by the modified state-of-the-art algorithm.

cs.ET↗

arXiv2024

Element-selective probing of ultrafast ferromagnetic--antiferromagnetic order dynamics in Fe/CoO bilayers

The ultrafast magnetization dynamics of an epitaxial Fe/CoO bilayer on Ag(001) is examined in an element-resolved way by resonant soft-x-ray reflectivity. The transient magnetic linear dichroism at the Co L2 edge and the magnetic circular dichroism at the Fe L3 edge measured in reflection in a pump-probe experiment with 120 fs temporal resolution show the loss of antiferromagnetic and ferromagnetic order in CoO and Fe, respectively, both within 300 fs after excitation with 60 fs light pulses of 800 and 400 nm wavelengths. Comparison to spin-dynamics simulations using an atomistic spin model shows that direct energy transfer from the laser-excited electrons in Fe to the magnetic moments in CoO provides the dominant demagnetization channel in the case of 800-nm excitation.

cond-mat.mtrl-sci↗

arXiv2023

Atomic Defect-Aware Physical Design of Silicon Dangling Bond Logic on the H-Si(100)2x1 Surface

Although fabrication capabilities of Silicon Dangling Bonds have rapidly advanced from manual labor-driven laboratory work to automated manufacturing in just recent years, sub-nanometer substrate defects still pose a hindrance to production due to the need for atomic precision. In essence, unpassivated or missing surface atoms, contaminants, and structural deformations disturb the fabricated logic or prevent its realization altogether. Moreover, design automation techniques in this domain have not yet adopted any defect-aware behavior to circumvent the present obstacles. In this paper, we derive a surface defect model for design automation from experimentally verified defect types that we apply to identify sensitivities in an established gate library in an effort to generate more robust designs. Furthermore, we present an automatic placement and routing algorithm that considers scanning tunneling microscope data obtained from physical experiments to lay out dot-accurate circuitry that is resilient against the presence of atomic surface defects. This culminates in a holistic evaluation on surface data of varying defect rates that enables us to quantify the severity of such defects. We project that fabrication capabilities must achieve defect rates of around 0.1 %, if charged defects can be completely eliminated, or < 0.1 %, otherwise. This realization sets the pace for future efforts to scale up this promising circuit technology.

physics.app-ph↗

arXiv2023

The Need for Speed: Efficient Exact Simulation of Silicon Dangling Bond Logic

The Silicon Dangling Bond (SiDB) logic platform, an emerging computational beyond-CMOS nanotechnology, is a promising competitor due to its ability to achieve integration density and clock speed values that are several orders of magnitude higher compared to current CMOS fabrication nodes. However, the exact physical simulation of SiDB layouts, which is an essential component of any design validation workflow, is computationally expensive. In this paper, we propose a novel algorithm called QuickExact, which aims to be both, efficient and exact. To this end, we are introducing three techniques, namely 1) Physically-informed Search Space Pruning, 2) Partial Solution Caching, and 3) Effective State Enumeration. Extensive experimental evaluations confirm that, compared to the state-of-the-art algorithm, the resulting approach leads to a paramount runtime advantage of more than a factor of 5000 on randomly generated layouts and more than a factor of 2000 on an established gate library.

physics.app-ph↗

arXiv2023

QuickSim: Efficient and Accurate Physical Simulation of Silicon Dangling Bond Logic

Silicon Dangling Bonds have established themselves as a promising competitor in the field of beyond-CMOS technologies. Their integration density and potential for energy dissipation advantages of several orders of magnitude over conventional circuit technologies sparked the interest of academia and industry alike. While fabrication capabilities advance rapidly and first design automation methodologies have been proposed, physical simulation effectiveness has yet to keep pace. Established algorithms in this domain either suffer from exponential runtime behavior or subpar accuracy levels. In this work, we propose a novel algorithm for the physical simulation of Silicon Dangling Bond systems based on statistical methods that offers both a time-to-solution and an accuracy advantage over the state of the art by more than one order of magnitude and a factor of more than three, respectively, as demonstrated by an exhaustive experimental evaluation.

physics.app-ph↗

arXiv2022

Simulating Charged Defects in Silicon Dangling Bond Logic Systems to Evaluate Logic Robustness

Recent research interest in emerging logic systems based on quantum dots has been sparked by the experimental demonstration of nanometer-scale logic devices composed of atomically sized quantum dots made of silicon dangling bonds (SiDBs), along with the availability of SiQAD, a computer-aided design tool designed for this technology. Latest design automation frameworks have enabled the synthesis of SiDB circuits that reach the size of $32\times10^3\,\text{nm}^{2}$ -- orders of magnitude more complex than their hand-designed counterparts. However, current SiDB simulation engines do not take defects into account, which is important to consider for these sizable systems. This work proposes a formulation for incorporating fixed-charge simulation into established ground state models to cover an important class of defects that has a non-negligible effect on nearby SiDBs at the $10\,\text{nm}$ scale and beyond. The formulation is validated by implementing it into SiQAD's simulation engine and computationally reproducing experiments on multiple defect types, revealing a high level of accuracy. The new capability is applied towards studying the tolerance of several established logic gates against the introduction of a single nearby defect to establish the corresponding minimum required clearance. These findings are compared against existing metrics to form a foundation for logic robustness studies.

cond-mat.mes-hall↗

arXiv2019

fiction: An Open Source Framework for the Design of Field-coupled Nanocomputing Circuits

As a class of emerging post-CMOS technologies, Field-coupled Nanocomputing (FCN) devices promise computation with tremendously low energy dissipation. Even though ground breaking advances in several physical implementations like Quantum-dot Cellular Automata (QCA) or Nanomagnet Logic (NML) have been made in the last couple of years, design automation for FCN is still in its infancy and often still relies on manual labor. In this paper, we present an open source framework called fiction for physical design and technology mapping of FCN circuits. Its efficient data structures, state-of-the-art algorithms, and extensibility provide a basis for future research in the community.

cs.ET↗