False-colored scanning electron microscope image of a three-site Kitaev chain device. A semiconducting nanowire (green), placed on top of an array of electrostatic gates (red), is contacted by two superconducting strips (blue) and two gold probes (yellow). Credit: QuTech
An innovative leap in quantum computing has emerged from a pioneering international research team led by QuTech, which successfully created a **three-site Kitaev chain** using **semiconducting quantum dots** linked by superconducting segments. This breakthrough not only showcases the **scalability** of quantum-dot-based Kitaev chains but also **enhances the stability of Majorana zero modes** (MZMs), potentially reshaping the future of quantum technology. The research findings were recently published in the esteemed journal Nature Nanotechnology.
Decoding Majorana Zero Modes
Majorana zero modes (MZMs) are not just quasiparticles; they are the **cornerstone of topological superconductivity** and promise a revolution in **decoherence-free quantum computing**. Their non-Abelian exchange statistics make them prime candidates for **high-fidelity quantum gates**, positioning topological superconductors as essential players in the quest for scalable quantum computing solutions.
The Kitaev model forms the backbone of one-dimensional topological superconductors, comprised of chains of spinless fermions united through **p-wave superconductivity** and **electron hopping**. As anticipated, extending the Kitaev chains has led to significant advancements, particularly the transition from **two-site to three-site chains**, which markedly improves the stability of zero-energy modes.
Scaling Up: The Journey to Three Sites
Over the past decade, there has been tremendous excitement in the lab as researchers explored various platforms to achieve topological superconductivity. The transition from a rudimentary two quantum dot system to a **three-site Kitaev chain** marks a significant milestone. This evolving framework highlights the potential for **Majorana zero modes** to thrive in a more stable environment.
Under the guidance of renowned scientists like Leo Kouwenhoven and Grzegorz Mazur, alongside first authors **Alberto Bordin** and **Chun-Xiao Liu**, QuTech has achieved something remarkable. Their three-site Kitaev chain, crafted from **semiconducting quantum dots** and embedded within a **hybrid InSb/Al nanowire**, demonstrates that **longer chains equate to greater stability** for MZMs, which previously struggled under the more constrained two-site model.
Strong tn and Δn couplings between all the three QDs of the device. Credit: Nature Nanotechnology (2025). DOI: 10.1038/s41565-025-01894-4
Mazur enthusiastically notes, "By scaling our previous two-site Kitaev chain to three sites, we confirmed that Majorana zero modes gain stability in this new setup. This demonstrates our path forward to achieving stable MZMs at even larger scales." Similarly, Bordin stresses the implications of their findings, stating, "Though we previously detected MZMs in a two-site setup, their lack of protection limited their practical application. Our research now proves that extending the chain's length enhances their robustness, indicating that reaching five or six sites could lead to breakthrough technologies."
The Synthesis of Knowledge
This research is an integral part of an expansive endeavor initiated at QuTech three years ago. According to Mazur, "Our founding success involved constructing a unit cell linking two quantum dots via superconducting pairing. While this stage didn’t qualify as a topological superconductor, it housed two MZMs at its periphery. Transitioning to a topological regime required stacking multiple unit cells accurately, necessitating extensive study on effectively coupling these components."
Augmenting the device’s complexity required integrating knowledge from several prior studies, including pivotal findings about triplet Cooper pair splitting, the visualization of the two-site Kitaev chain, and methods to fine-tune these systems.
"Bringing all these components together with heightened precision allowed us to create a larger functional device," explains Bordin. The fabrication process proved complex yet rewarding, resulting in the successful creation of multiple operational devices, all of which displayed robust three-site chains resilient to external perturbations. "I was ecstatic when I found that our measurements across devices yielded virtually identical results," remarked Mazur.
Second Device. Credit: Nature Nanotechnology (2025). DOI: 10.1038/s41565-025-01894-4
Next Steps: Expanding Futures
The researchers now turn their gaze toward quantum information experiments. "We aim to scrutinize the behaviors of these Kitaev chains in a qubit context," Mazur elaborates. The goal is to understand how the **length of the Kitaev chain** influences qubit lifetimes. Notably, two-site chains exhibited limited stability, whereas the three-site model shows promising resilience against gate noise and disturbances.
Bordin underscores the potential for future advancements, proposing that **machine learning** could facilitate automatic tuning of the Kitaev chains to attain **topological protection** effectively. If these setups continue to improve, they could significantly transform quantum computing methodologies.
In Kouwenhoven's words, "With every step, we are assembling the framework for a topological qubit." Furthermore, new research involving three-site Kitaev chains coupled to an additional quantum dot is already underway and set to publish shortly.
For further details:
Alberto Bordin et al, Enhanced Majorana stability in a three-site Kitaev chain, Nature Nanotechnology (2025). DOI: 10.1038/s41565-025-01894-4
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