Packaged circuit board containing the chip placed under a microscope. [Image: Boston University]
Currently, the major challenge facing quantum technologies—including quantum computing, secure communication and sensing—is a scalable way of building large systems. Feasibility has already been shown with numerous proof-of-concept devices, and the next step is tackling scalability so that quantum information systems can be made large enough to perform useful functions.
“Think about it like the difference between the first transistor in 1947 versus the integrated circuits developed over the following decades that were needed to make computers useful and ubiquitous,” said Danielius Kramnik, University of California, Berkeley, USA. “One of the promising approaches being used to build scalable components for quantum computers is silicon photonics, which uses CMOS-compatible manufacturing to build quantum systems based on manipulating light instead of matter.”
By leveraging a silicon photonics platform, Kramnik and his colleagues have created what they believe is the world’s first electronic-photonic quantum system-on-chip fabricated in a commercial 45-nm CMOS microelectronics foundry (Nat. Electron., doi: 10.1038/s41928-025-01410-5). They say their approach paves the way for silicon quantum photonics to achieve the massive scale required for future generations of quantum information systems.
A single silicon chip
Semiconductor fabrication techniques developed in the CMOS microelectronics industry routinely produce chips with billions of transistors in high volumes. Naturally, CMOS-compatible silicon photonic integration is a promising path to building scalable quantum information systems. While previous work has reported CMOS-compatible methods in principle, the current study is the first to actually implement quantum photonics in a commercial CMOS foundry.
The US-based interdisciplinary team—with researchers at the University of California, Berkeley; Boston University and Northwestern University—combined their expertise in electronic-photonic integration and quantum optics to design, build and characterize the quantum system-on-a-chip. They monolithically integrated microring-resonator photon-pair sources and spectral filtering resonators with analog and digital control electronics, all on a single silicon chip.
The quantum-correlated photon-pair sources are stabilized via on-chip feedback control circuits that calibrate and stabilize the production of photon pairs.
The quantum-correlated photon-pair sources are stabilized via on-chip feedback control circuits that calibrate and stabilize the production of photon pairs. The pairs can be used to create a stream of heralded single photons that form the basis for most types of photonic quantum information systems. As a result, they maintain consistent performance even under temperature fluctuations and during the simultaneous operation of multiple nearby microrings.
Next steps
The resulting array of “quantum light factories” on a chip, each less than 1 mm × 1 mm in dimension, can already be used to build prototype quantum networks used for distributing quantum information and interconnecting quantum computers. Next, Kramnik and his colleagues plan to demonstrate more functionality from the chips for quantum network applications and perform quantum interference experiments between multiples of chips.
“One immediate practical application we envision is to build a pluggable fiber-optic quantum communication module based on our chip, which is analogous to the SFP [small form-factor pluggable] fiber optic modules used in data centers for classical rack-to-rack data communication, that would allow any computer to tap into a quantum-secured network,” he said. “In the longer term, this platform can be used to build large numbers of heralded single-photon sources needed for photonic quantum computers.”
