Introduction

Photonic integrated circuits (PICs) have become a central theme in nanophotonics because they compress optical functionalities, routing, modulation, filtering, frequency conversion, into compact, phase-stable, manufacturable systems. In the quantum context, integrated photonics is widely viewed as one of the most scalable approaches for generating, manipulating and detecting quantum states of light, enabling complexity growth from few-component circuits to highly programmable, large-component-count chips1, which charts the field’s progress toward dense, reconfigurable quantum photonic processors and the increasing emphasis on engineering yield and stability as circuits scale.

Crucially, “quantum PICs” are not a single platform but an evolving stack of materials and processes. Silicon and silicon nitride dominate passive routing and interferometry; thin-film lithium niobate (LNOI) is increasingly adopted for high-speed, low drive voltage electro-optic control; and heterogeneous integration with III–V semiconductors remains a leading route to on-chip gain and lasers. These platform trends-and the expectation that future quantum systems will be heterogeneous by design-are highlighted in the silicon nitride perspective2 and in major LNOI demonstrations3.

A particularly ambitious direction now gaining momentum is the pursuit of room-temperature quantum photonic chips-systems that can deliver quantum advantage without cryogenics. While “room temperature” is already realistic for some quantum sensing modalities (e.g., diamond NV centers)4, it is a much tougher systems problem for other quantum functions that demand ultralow noise and indistinguishable photons. The NV center literature makes clear why diamond is so attractive: long-lived spin states with optical readout at ambient conditions, enabling sensing that can function outside the lab.

What is holding quantum PICs back? Manufacturing-not just physics

As quantum photonic circuits scale, fabrication variation becomes a first-order limiter. Many key building blocks (interferometers, microring resonators, high-Q cavities) are exquisitely sensitive to nanometer-scale geometry changes, translating sidewall roughness and dimensional drift into excess scattering loss and phase errors. The scaling trajectory1 explicitly highlights the growing burden of calibration, trimming and control as circuits approach large component counts.

A second bottleneck is that quantum PICs increasingly demand 3D integration and complex mode engineering, while mainstream semiconductor photonics remains strongly planar. Even in classical photonics, practical systems need robust fiber-to-chip interfaces, vertical coupling, and packaging-tolerant mode converters. In quantum PICs, these requirements intensify because coupling loss and mode mismatch directly reduce multi-photon rates and circuit fidelity. The broader case for hybrid/heterogeneous integration as a route to functionality expansion (including III–V gain integration on otherwise passive platforms) is discussed in silicon nitride integration reviews and III–V-on-Si photonics progress literature.

Third, the field is converging on heterogeneous materials stacks because no single material “wins” on all axes. Silicon nitride offers ultra-low-loss passive routing and is increasingly used as a backbone platform2, while lithium niobate provides strong electro-optic response for fast control3, demonstrating CMOS-compatible-voltage LNOI modulators with very high bandwidth and illustrating why LN is now central to high-speed photonic control.

Laser nanoprinting: a precision-and-flexibility layer for quantum PICs

Laser direct writing has a long foundation in nanophotonics. The seminal work by Davis et al.5 showed that femtosecond lasers can write waveguides inside glass via nonlinear absorption, opening a path to true 3D photonic circuitry-a capability that remains strategically relevant today as PICs push beyond planar integration.

Since then, femtosecond laser direct writing (FLDW) has matured into a versatile platform for fabricating waveguides, couplers and more complex photonic circuits in transparent materials, with an increasingly refined understanding of process windows, morphology control and performance tradeoffs. Tan et al. provide a detailed review of improvements and recent progress in laser-written photonic circuits6, demonstrating that the field has developed beyond “proof of concept” and into an engineering discipline with reproducible design rules.

For quantum applications, FLDW is not only about fabricating entire circuits in glass; it is also emerging as an enabling tool for post-fabrication correction and local trimming-a critical need as photonic circuits scale. Permanent phase-error correction in silicon photonic circuits using single femtosecond laser pulses has been demonstrated by Bachman et al.7, directly addressing the “fabrication variation → phase error → yield loss” chain that becomes severe at scale.

More recently, Wu et al. reviewed and demonstrated femtosecond-laser trimming approaches that compensate fabrication errors by modifying cladding effective indices, showing practical control of micro-ring resonator wavelengths and Mach–Zehnder phase bias with fast trimming times8,9. This class of work is important because it targets manufacturability: it treats tuning not as a lab workaround but as a controllable step toward uniformity in large-scale PICs.

Why this matters for “room-temperature quantum chips”

Room-temperature quantum photonic systems are likely to advance first in sensing and certain hybrid photonic–spin architectures, where ambient operation is already realistic in the underlying quantum material. The diamond NV center is the canonical example: Doherty et al.4 remains a cornerstone review that explains the NV center’s physics and the unresolved issues that still limit performance, while also underscoring why it is so compelling for practical quantum technologies.

However, “room temperature” in integrated quantum photonics is a systems-level challenge: it is not only about a quantum material operating at ambient conditions, but also about optical loss budgets, thermal stability, packaging, and integration of control2,3. Taken together, they outline a plausible architecture: ultra-low-loss passive backbones (e.g., SiN) combined with high-speed electro-optic control (e.g., LN) and material-specific quantum interfaces.

Laser nanoprinting becomes relevant in this context not because it is “another fabrication tool,” but because it can provide: (i) 3D photonic interconnects and mode transformers, (ii) localized tuning and correction for yield, and (iii) rapid iteration in hybrid stacks where conventional planar workflows can become slow and brittle. These strengths align directly with the engineering needs of room-temperature deployable quantum photonics: reproducibility, packaging tolerance, and reduced calibration overhead.

Key challenges for the field next

Despite real progress, several hard challenges remain. The first is loss and variability: as integrated quantum circuits scale, every interface and every millimeter of waveguide matters, and phase noise or small resonant shifts can accumulate into large performance penalties-hence the importance of permanent trimming and correction strategies (e.g., femtosecond-laser-based phase correction).

The second is heterogeneous integration at manufacturable yield. Hybrid stacks offer the best path to combine low-loss routing, fast modulation, on-chip gain and quantum interfaces, but they also multiply process steps, thermal budgets, and packaging complexities. This is why the community increasingly emphasizes co-design across materials, devices and process integration, as reflected in reviews of hybrid integration routes and in the platform roadmaps for SiN and LN photonics10,11,12.

The third is tooling and metrology: scalable quantum photonics needs wafer-level characterization, statistical process control, and standardized performance metrics that go beyond “hero devices.” Without robust metrology, the gap between laboratory demonstration and manufacturable system will persist, regardless of how strong individual device physics may be. The integrated photonic quantum technologies roadmap literature repeatedly emphasizes this systems transition and the need for scalable engineering.

What joint effort could unlock breakthroughs?

Breakthroughs will come fastest when the community treats quantum PICs as a full-stack engineering problem rather than a set of isolated device demonstrations. On the academic side, tighter coupling between device physics, nanofabrication and packaging research can reduce the number of “non-scalable” architectures that look impressive in a single chip but fail under process variation. On the industry side, process control, reliability testing and yield learning are essential-and these require early engagement, shared Process Design Kit (PDK)-like flows widely used in CMOS microelectronics, and realistic constraints built into research prototypes.

Equally important is shared infrastructure. Access to nanofabrication facilities, laser micro/nanofabrication tools, and standardized testbeds allows reproducibility and benchmarking across institutions. Laser nanoprinting sits naturally within this joint model: it can act as a rapid-iteration and post-processing layer that complements foundry processes, supporting both early-stage exploration and later-stage correction/standardization. The maturation of FLDW into an engineering platform6 supports the case for integrating laser nanoprinting into shared workflows rather than treating it as an artisanal one-off capability.

Finally, the field would benefit from community-level coordination around standards and reference designs-for example, agreed benchmark circuits and consistent reporting of loss, phase stability, tuning range, trimming permanence, and packaging robustness. Without common benchmarks, progress remains difficult to compare and cumulative learning slows. With benchmarks, joint efforts across photonics, quantum materials and manufacturing can converge more quickly toward room-temperature deployable quantum photonic systems.