Why Micron-Scale Precision Still Matters in Quantum Fabrication

In an industry obsessed with scaling toward the atomic level, it might seem counterintuitive to focus on feature sizes that span hundreds of nanometers or even microns. But in the world of quantum computing, especially in photonic architectures, those larger dimensions carry just as much significance. Erik Hosler, a quantum systems engineer with a background in lithography and semiconductor physics, highlights that precision is not a relic of past manufacturing goals; it remains central to quantum’s future.

There’s a persistent assumption that because quantum devices operate under different principles than classical ones, they must also require a new set of fabrication priorities. Yet the opposite is often true. As fabrication moves from research-grade chips to high-yield production, micron-scale features, waveguides, beam splitters, and couplers must be patterned with an exactness that leaves no room for error. Even if the scale shifts, the demand for control doesn’t.

What Microns Mean in the Quantum Context

Unlike logic transistors in classical computing, which are below 10 nm in size, many quantum components, particularly in photonics, are comfortably in the hundreds of nanometers to micrometer range. It includes the width of optical waveguides, the gaps in interferometers, and the dimensions of photon detectors.

But their generous size doesn’t make it easier to fabricate. On the contrary, quantum optical devices are extraordinarily sensitive to imperfections. A slight edge roughness, a shift in feature alignment, or a non-uniform sidewall can degrade the performance of the entire circuit.

These small imperfections can lead to phase errors, signal loss, or photon misrouting, all of which disrupt quantum computation at the most fundamental level.

The Myth of “Large = Easy”

It’s tempting to assume that larger feature sizes are more forgiving. After all, micron-scale patterns don’t push the limits of today’s most advanced lithography systems. But in practice, quantum photonic devices demand a different kind of precision, one centered on uniformity, repeatability, and structural integrity across the entire wafer. Here’s why that matters:

• Waveguide uniformity: Variations in width or height can shift the optical path, altering interference and degrading entanglement.
• Edge placement errors: Misalignments can misdirect photon flows or break symmetry in essential components.
• Overlay accuracy: Multi-layer alignment is critical for coupling quantum circuits with control electronics or detectors.

So, while the feature sizes may be larger, the tolerance for variation remains just as strict, if not more so.

Striving for Perfection: A Design Principle

This uncompromising demand for fabrication excellence is echoed by those who build these systems. Erik Hosler remarks, “We’d like to see perfection in our patterning, but we’ll settle for striving for perfection.” That statement encapsulates the mindset needed to make quantum computing scalable. It’s not enough for a handful of chips to work in a lab. Thousands, or even millions, must be manufactured with near-identical characteristics.

It is especially vital when those chips are part of modular quantum architectures, where each photonic unit must perform identically to its neighbor to ensure system-wide coherence and synchronization.

Process Control and Lithography Discipline

Modern photonic quantum chips are fabricated using semiconductor-grade processes, often in commercial foundries. These facilities rely on extreme consistency governed by tightly controlled photolithography, etching, and deposition steps. Key parameters that must be maintained include:

• Critical Dimension (CD) control: Ensures that waveguides and couplers perform as designed.
• Line Edge Roughness (LER): Reduces scattering losses and maintains photon fidelity.
• Etch depth uniformity: Affects mode of confinement and coupling efficiency.

Foundries can typically achieve these parameters through EUV lithography, DUV immersion, or multi-patterning techniques, depending on the required geometry. But even with innovative tools, the push for micron-scale perfection still requires robust process monitoring, inline metrology, and constant calibration.

Optical Quantum Circuits Aren’t Forgiving

The physics of photonic quantum computing is unforgiving. Unlike classical bits, which can be buffered, corrected, or refreshed, quantum bits must operate in lockstep. If a single photon strays due to a patterning flaw, it can collapse a computation or introduce an untraceable error.

The design of quantum optical circuits often relies on interference-based operations, where two or more paths must be perfectly aligned in both distance and phase. Small geometric differences, measured in tens of nanometers, can cause outputs to shift from constructive to destructive interference.

These small deviations accumulate across a large system, which is why, even when features span microns, the acceptable margin of error remains small.

Scaling Without Compromise

As quantum hardware moves toward commercial viability, scalability is a central concern. But scaling without consistency is self-defeating. If manufacturing yield drops as chip size increases, or if too many components fail post-fabrication, the cost per working device quickly becomes unsustainable.

That’s why quantum foundry strategies are developing to prioritize not just feature count but feature integrity. It includes:

• Automate alignment and overlay processes
• Implementing predictive quality control
• Using test structures to validate process corners in real-time

In this way, micron-scale precision becomes a cost-control measure, not just a performance booster.

Toward Fault-Tolerant Fabrication

In the longer term, quantum computing will need to develop from handcrafted systems to fault-tolerant, mass-produced platforms. Just as transistors become standardized across billions of devices, quantum components must become reproducible across billions of circuits.

That transition depends heavily on mastering micron-scale patterning. Even if qubit design changes or new materials are introduced, the underlying discipline of patterning with near-perfection will remain essential.

More than any specific tool or platform, that mindset, striving for perfection even when it’s elusive, may be the most valuable technology in a quantum engineer’s arsenal.

Precision Isn’t Going Away

The future of quantum computing is often described in terms of abstract breakthroughs and high-level milestones. But beneath those achievements lies a quiet but essential reality: the path to quantum usefulness is paved with disciplined fabrication.

Micron-scale features may lack the glamour of atomic-scale gates or exotic physics, but they hold the key to whether quantum hardware can scale, perform, and deliver on its promise. Precision still matters, not because it looks good on paper but because the machines we build can only be as reliable as the patterns we etch into silicon.

In quantum fabrication, as in classical physics, striving for perfection is the only way forward. Even when perfection is impossible, refusing to accept less makes innovation possible.