Breakthrough in SiC-based quantum platform enables entangled photon generation

Silicon carbide (SiC) as a platform is an unexplored frontier rich with hidden potential—digging into it might unveil pathways to advanced, scalable quantum technologies and set the course for future research.

Inspired by this vision, Xiao Tang and Oliver Slattery launched a SiC research project within the Quantum Communications group at the U.S. National Institute of Standards and Technology (NIST).

SiC has gained prominence in integrated electronic systems, particularly for green technologies like electric vehicles within the past few years. It’s also attracted significant interest for quantum applications due to its exceptional optical, electrical, and mechanical properties. Unlike traditional quantum photonic platforms such as silicon or lithium niobate, SiC is compatible with semiconductor fabrication processes—and it also offers properties uniquely favorable for quantum applications. But fully harnessing its potential is a challenge.

Collaboration to enable quantum applications

The NIST team initiated broad collaborations with other institutions and universities to develop high-quality SiC platforms, including 3C-SiC and 4H-SiC, with the goal of enabling a wide range of quantum technology applications.

“Entangled photon sources are milestones for scalable quantum technologies,” explains Lijun Ma, a member of NIST’s Quantum Communications group. “While several advanced capabilities have been demonstrated in silicon carbide, including entanglement of nuclear spins, an entangled photon source hasn’t yet been achieved on any SiC platform. Achieving such a demonstration would unlock the true potential of SiC for quantum technologies.”

Motivated by this, they launched a collaborative effort with Professor Qing Li’s group at Carnegie Mellon University to develop and design microring-resonator-based devices to demonstrate an entangled photon source using a four-wave mixing (FWM) process at telecom wavelengths.

“The 4H-SiC wafer is the highest-purity platform and is widely commercially available,” says Li, who draws upon his extensive expertise fabricating SiC integrated devices. “Its high Q-factors, demonstrated in several studies, including some of our own, make 4H-SiC a strong candidate for demonstrating entangled photon sources. We aim to optimize the microring resonator to generate photon combs aligned with the International Telecommunication Union’s (ITU) dense wavelength-division multiplexing (DWDM) grid, which will allow us to leverage existing DWDM filters and make the device compatible with current networking infrastructure.”

They successfully optimized their device fabrication of a compact 43-μm-radius SiC microring resonator to generate photon pairs within the telecom wavelength ~1550 nm, and optimized the free spectral range (FSR) to approximately 400 GHz (with an optical quality factor that exceeds one million).

Generating entangled photon pairs on SiC

Anouar Rahmouni, who led the optical setup and experimental measurements and characterization at NIST, was the first to observe the generation of entangled photon pairs on SiC.

“The main challenge observing entangled photons is filtering them from background noise, which is primarily generated by Raman scattering,” says Rahmouni. “This demands a filtering system with around 120 dB of isolation and minimal insertion loss. Aligning the optical coupling into and out of the chip, and precisely matching the pump wavelength and photon pairs with the filter passbands, also present significant technical challenges.”

The characterization results of their source “show a coincidence-to-accidental ratio (CAR) exceeding 600, photon-pair generation rates in the millions of counts per second, strong antibunching, and high entanglement visibility, which are comparable to the results achieved by more established nonlinear integrated photonic platforms,” Rahmouni adds. “These outcomes unequivocally demonstrate that the SiC-based entangled photon source is a promising candidate for chipscale quantum information processing.”

Because quantum photonics is a rapidly expanding field at the heart of secure communications, scalable quantum computing, and high-precision sensing technologies, a critical challenge now is to miniaturize these processes for scalability and stability by developing integrated optical devices capable of efficiently generating and manipulating quantum states of light. Within this context, the team believes their recent work marks an important milestone of demonstrating the first chipscale entangled photon source within SiC. It introduces a robust and scalable method for generating entangled photon pairs within a SiC photonic circuit.

The researchers' recent demonstration of entangled photon generation on a SiC microchip represents a breakthrough toward overcoming these challenges and unlocking SiC’s potential for quantum applications.

High-quality, high-purity entangled photon pairs

To generate the entangled photon pairs, they used a high-order quantum nonlinear optical process known as spontaneous four-wave mixing (SFWM) and an integrated optical microring resonator patterned onto a 4H-SiC-on-insulator platform. This process produced correlated signal and idler photon pairs at telecommunication wavelengths, which ensures compatibility with existing optical fiber networks (an essential requirement for practical quantum communication). And the generated photons exhibit time-energy entanglement, a foundational protocol for robust and scalable quantum information processing. The team demonstrated the generation of high-quality, high-purity entangled photon pairs, which underscores the effectiveness and promise of their SiC-based integrated photonic approach.

Integrating an entangled photon source within a SiC platform represents a crucial step toward fully integrated quantum photonic circuits. Achieving high-efficiency photon pair generation within a chipscale device significantly advances the scalability and feasibility of deploying SiC-based quantum communication systems and has profound implications for the future of quantum networks. SiC’s compatibility with telecom wavelengths makes it particularly well suited for long-distance quantum communication and holds the potential for seamless integration with existing fiber-optic infrastructure.

The team's future research will focus on integrating additional quantum functionalities—such as photon detectors, quantum converters, and quantum memories—within SiC photonic circuits. With continued progress, SiC-based quantum devices could soon play a pivotal role enabling practical and scalable quantum communication and networking—and bring us closer to achieving large-scale quantum technologies.

FURTHER READING

A. Rahmouni et al., Light Sci. Appl., 13, 110 (2024); https://doi.org/10.1038/s41377-024-01443-z.