Materials beyond silicon photonics emerge for scalable quantum photonic systems
Silicon photonics transformed optical integration by leveraging complementary metal-oxide semiconductor (CMOS)-compatible fabrication to enable dense, scalable optical circuits. Its success lies in manufacturing maturity, cost efficiency, and tight integration with electronics. But as photonics extends into quantum technologies, new constraints are emerging.
Quantum photonic systems demand performance parameters that stretch beyond those silicon alone can provide. The requirements for deterministic single-photon generation, low-loss routing, strong nonlinear interactions, and long coherence times introduce materials challenges that silicon photonics was never designed to address.
We are now at an inflection point: Scalable quantum photonic systems will not be built on silicon alone. Instead, they will emerge from a broader, heterogeneous materials ecosystem.
What does scalable mean in quantum photonics?
Scalability in quantum photonics is fundamentally different from scalability in classical optical interconnects. It involves maintaining quantum coherence across integrated circuits; generating indistinguishable single photons on demand; minimizing propagation loss to preserve interference fidelity; and enabling tunability and reconfigurability without introducing decoherence.
Every additional interface, defect, or scattering site affects quantum fidelity. Within this regime, materials selection is not just about optical properties but about quantum state preservation.
Silicon’s limits within the quantum domain
Silicon’s indirect bandgap restricts efficient light emission, which necessitates external sources for photon generation. While silicon can route photons with reasonable efficiency, it lacks intrinsic second-order nonlinearity, which limits its ability to generate entangled photon pairs through spontaneous parametric processes.
Moreover, silicon’s two-photon absorption and free-carrier effects can introduce noise at higher power densities problematic for quantum interference experiments.
These constraints have catalyzed the exploration of alternative and complementary materials.
Thin-film lithium niobate: Precision nonlinearity at scale
Lithium niobate (LiNbO3) has long been valued for its electro-optic properties. Within the context of quantum photonics, its strong second-order nonlinearity enables efficient photon pair generation and frequency conversion critical for entanglement distribution and quantum networking.
Recent advances in thin-film LiNbO3 platforms dramatically improved optical confinement and integration density. These thin-film architectures allow high-speed modulation and compact nonlinear devices that operate within photonic integrated circuits.
The challenge is no longer whether LiNbO3 can perform, but whether fabrication uniformity, poling precision, and waveguide loss can meet the stringent reproducibility demands of scalable systems.
III-V materials and integrated quantum emitters
While LiNbO3 excels at nonlinear interactions, III-V semiconductors excel at light generation. Direct bandgap materials such as gallium arsenide (GaAs) and indium phosphide (InP) enable integrated laser sources and quantum dot emitters. Quantum dots embedded within III-V hosts can act as deterministic single-photon sources with high brightness and narrow linewidth.
For scalable quantum systems, on-chip photon sources reduce alignment complexity and improve stability. But integration with passive photonic circuits requires heterogeneous bonding and careful thermal expansion matching.
The convergence of III-V active elements with passive routing platforms marks a significant step toward integrated quantum processors.
Diamond and solid-state defects: Long coherence, real-world potential
Diamond offers a fundamentally different advantage: Stable quantum defects with optically addressable spin states. Nitrogen-vacancy and silicon-vacancy centers exhibit long coherence times and compatibility with optical readout. These properties make diamond-based systems attractive for quantum repeaters, memory elements, and precision sensing.
From a materials standpoint, diamond’s thermal conductivity and mechanical stability are exceptional. The primary limitation lies in scalable fabrication and integration. Creating low-loss photonic structures within diamond requires precision machining and defect engineering at nanometer scales.
Nevertheless, diamond’s role in future quantum architectures may be pivotal where coherence time is paramount.
Silicon nitride: Ultralow-loss backbone
Silicon nitride (Si3N4) has emerged as a compelling low-loss platform for quantum photonics. Its propagation losses can be significantly lower than silicon, which makes it ideal for interference-based circuits where photon survival probability directly impacts performance.
Although it lacks strong second-order nonlinearity, its third-order nonlinear properties support four-wave mixing for photon pair generation. More importantly, Si3N4 provides a stable, scalable backbone for routing quantum states.
When combined with active materials for photon generation or modulation, Si3N4 enables hybrid architectures optimized for minimal loss.
2D materials and quantum flexibility
Two-dimensional (2D) materials introduce a new level of tunability in quantum photonics. Transition metal dichalcogenides and related layered materials exhibit strong excitonic effects and can host single-photon emission sites.
Because they are atomically thin, 2D materials can be transferred onto existing photonic circuits without major structural redesign. This enables post-fabrication integration of quantum emitters onto mature platforms.
The flexibility of 2D materials allows strain engineering, electrostatic tuning, and heterostructure stacking, expanding the design space for quantum photonic devices.
Heterogeneous integration: The real enabler
The future of scalable quantum photonic systems lies not in a single material breakthrough, but in heterogeneous integration.
Each material platform offers a specific strength: LiNbO3 is for nonlinear conversion; III-V semiconductors is for emission; diamond is for coherence; Si3N4 is for routing; and 2D materials are for tunable emitters.
The challenge is integrating them without compromising performance. Heterogeneous bonding, wafer-scale transfer printing, and precision alignment techniques are evolving to meet this need. Thermal expansion mismatch, interface scattering, and fabrication yield remain obstacles, but progress is steady.
Performance metrics will define the field
To transition from laboratory prototypes to scalable quantum photonic systems, materials must support measurable improvements in: Indistinguishability of emitted photons; on-chip coupling efficiency; propagation loss below critical quantum error thresholds; thermal stability under operational loads; and wafer-scale reproducibility.
Material systems that combine low loss, high nonlinearity, and integration compatibility will shape the next generation of devices.
Beyond silicon: Expansion, not replacement
The shift beyond silicon photonics does not represent abandonment of silicon. Instead, it reflects an expansion of the photonic materials toolkit.
Silicon remains valuable for electronic-photonic integration and certain passive functions. But scalable quantum photonic systems demand materials engineered specifically for quantum performance.
The field is entering a phase in which materials science and quantum engineering are inseparable. Photonics engineers must now think not only in terms of refractive index and waveguide confinement, but in terms of coherence time, decoherence channels, and quantum state fidelity.
The road ahead
As quantum technologies move from demonstration to deployment, material maturity will determine scalability. The most successful quantum photonic architectures will be those that integrate complementary materials into unified platforms capable of wafer-scale fabrication, stable operation, and reproducible performance.
Beyond silicon lies not a single successor, but a multi-material ecosystem designed to meet the unique demands of quantum photonics. The race is no longer just about photons, but also about the materials that sustain them.
About the Author
Pradyumna Gupta
Pradyumna (Prady) Gupta, Ph.D., is the founder and chief scientist of Infinita Lab and Infinita Materials, where he leads pioneering work in materials characterization, reliability engineering, and advanced manufacturing. With more than two decades of experience spanning semiconductors, electric mobility, and aerospace systems, he focuses on bridging material science with practical reliability needs. Gupta’s work centers on enabling high-performance, safe, and sustainable material architectures for next-generation technologies.