Quantum computing may feel like a departure from the traditional world of semiconductors, but at its core lies a shared demand for precision fabrication. The bridge connecting silicon logic and quantum superposition is lithography, the art and science of etching patterns at the nanometer scale. Erik Hosler, a lithography expert and photonics strategist at PsiQuantum, highlights how the fabrication demands of quantum systems have reawakened and redirected advanced lithographic techniques. His perspective makes clear that the future of quantum computing will include refining old tools to meet even more exacting standards.
As photon-based quantum computing accelerates toward practical realization, the spotlight turns to how qubits, delicate, noise-sensitive building blocks of quantum logic, can be manufactured with the uniformity, precision, and scalability that modern computation demands. Lithography, developed and perfected in the semiconductor industry for decades, is suddenly center stage again, tasked with fabricating quantum architectures that push beyond its original intent.
A Converging Craft: Lithography in Classical and Quantum Domains
Traditional silicon chips rely on transistor architectures shrunk down to just a few nanometers. In comparison, quantum photonic circuits might work with feature sizes in the hundreds of nanometers or microns. But what matters in quantum isn’t size. It’s stability. Patterning quantum components requires meticulous attention to detail, as even small imperfections in a waveguide’s edge or the placement of a coupler can introduce phase noise, scattering loss, or qubit decoherence.
In both domains, lithography governs performance fidelity. But quantum circuits have a slimmer margin for error. Classical circuits can compensate for imperfections through error-checking logic or redundancy; quantum circuits, governed by fragile quantum states, offer no such luxuries.
The Demands of Quantum Photonics
Photon-based quantum computers, like those developed at PsiQuantum, route and process individual photons through integrated photonic circuits. These circuits contain:
- Waveguides to carry quantum information
- Interferometers to perform logic gates
- Detectors to read results
- Sources to generate entangled photons
Every one of these elements depends on sub-micron precision for correct operation. A waveguide that’s too narrow scatters light; one that’s slightly wider may shift the photon’s phase. Misalignments of 20–30 nanometers can distort interference patterns and compromise computation.
It places intense pressure on patterning processes, not just in initial design but in the reproducibility of the final product across hundreds or thousands of wafers.
Why EUV Matters in a Quantum World
Extreme Ultraviolet Lithography (EUV) was developed for the 7 nm and 5 nm nodes in classical computing. It uses 13.5 nm wavelength light to produce ultra-fine patterns with exceptional edge definition. In the quantum context, the logic features may not be that small, but the need for smoothness and uniformity is just as great, sometimes greater.
Erik Hosler notes, “Patterning techniques developed for advanced EUV… might be needed in a photon-based quantum computer.” It reflects a fundamental truth: quantum systems benefit as much from reduced variation as classical systems do from reduced size. EUV’s ability to pattern cleaner lines with less proximity effect, line-edge roughness, and edge placement error makes it a valuable, if not essential, tool in the quantum fabrication toolkit.
Patterning Perfection and Quantum Fidelity
In a quantum system, optical path length differences as small as a few nanometers can alter interference patterns. That’s why photonic quantum systems require the following:
- Low Line-Edge Roughness (LER): to maintain phase coherence
- Accurate Overlay: to align different layers for detectors, control electronics, and routing
- Tight Critical Dimension Control: to guarantee consistent gate behavior across large-scale chips
These requirements aren’t just academic. They’re tied directly to qubit fidelity. For quantum systems operating on a scale, even a 1% performance drop per gate or component can lead to cascading failure across a computation.
EUV Beyond the Classical Roadmap
While EUV has become essential for classical logic at single-digit nanometer nodes, quantum computing introduces a new use case. As quantum devices grow more complex and approach commercial deployment, the need to eliminate fabrication-induced variability grows alongside them.
It shifts the EUV narrative. No longer is it simply about density and transistor count; it’s about building a platform where each photonic structure behaves identically, from the first chip to the tenth. Quantum doesn’t demand smaller; it demands better.
Foundry Integration and Process Standardization
Quantum photonic startups working with foundry partners must ensure that EUV-based process flows are compatible with their device architectures. Foundries, in turn, adapt their photonic platforms to accommodate tighter etch control, reduced LER, and more uniform overlay precision.
Standard Process Development Kits (PDKs) for quantum photonics are beginning to include EUV-optimized components, waveguides, couplers, and modulators that can be simulated and fabricated using industry-grade tools. This integration opens the door to scalable quantum chip production on the same lines that currently serve advanced logic and memory fabrication.
The result is a convergence of quantum design needs with classical process excellence.
Patterning Beyond Lithography
Lithography is only one part of the patterning equation. The etch process that follows must also preserve the high fidelity of features defined by the exposure tool. Etch selectivity, anisotropy, and sidewall roughness all influence final device performance.
In quantum systems, waveguide roughness translates directly into photon scattering, while vertical misalignment in etched gratings can cause wavelength shifts and insertion loss. Thus, patterning perfection involves a synchronized litho-etch-deposition sequence, all governed by tight process control loops and real-time metrology.
EUV alone doesn’t guarantee success, but when paired with advanced process tuning, it becomes a cornerstone of quantum reliability.
The Future: Toward Fault-Tolerant Patterning
As fault-tolerant quantum systems become the next benchmark, the demand for lithographic consistency will only rise. Error correction in quantum computing requires enormous numbers of physical qubits, and each one must behave predictably. That means wafer-level uniformity is no longer a nice-to-have necessity.
The semiconductor industry, with its legacy of scaling and standardization, is well-equipped to meet this challenge. But the effort will require more than repurposing classical tools. It will demand quantum-specific patterning targets, tighter error budgets, and a more symbiotic relationship between designers and process engineers.
The Lithographic Thread Linking Two Eras
From shrinking transistors to guiding entangled photons, lithography has quietly developed into the enabling force behind two computing developments. The same light-driven patterning technologies that made smartphones possible are now shaping quantum chips destined for cryogenic vacuum chambers and optical labs.
As quantum computing shifts toward commercial scale, lithography stands as a common denominator, quietly connecting the precision of silicon logic to the fragility of quantum information. From silicon to superposition, the tools of the past are being redefined to meet the future. And once again, it all begins with light.