Physicists have spent over a century exploring the peculiarities of quantum mechanics, particularly the interactions of subatomic particles like photons and electrons at minuscule scales. These investigations have unlocked groundbreaking phenomena that challenge our classical understanding of the universe. Engineers, in turn, have worked for decades to apply these findings to develop transformative technologies. One of the most intriguing phenomena uncovered during these efforts is quantum entanglement, a property of quantum particles that allows them to be “linked” in such a way that the state of one particle can instantaneously affect the state of its paired particle, no matter the distance between them.
This phenomenon was famously described by Albert Einstein in 1935 as “spooky action at a distance.” Despite Einstein’s skepticism about the implications of entanglement, this strange quantum property has since become a fundamental cornerstone of quantum research. Today, entanglement is not only a topic of deep scientific inquiry but also an essential feature in the development of quantum information systems, particularly in the creation and manipulation of qubits, the basic units of quantum computing.
As researchers continue to explore the potential of entanglement, creating photon pairs that can be entangled has become a crucial goal. In quantum communication, computing, and cryptography, these pairs play a critical role. However, until recently, the most efficient method for generating these photon pairs required the use of large crystals visible without a microscope. While effective, this approach was far from ideal due to its large scale and high energy consumption.
In a significant leap forward, a research team led by Columbia Engineering professor P. James Schuck has developed a new technique for generating photon pairs using a much smaller and more energy-efficient device. The team’s breakthrough, described in a recent publication in Nature Photonics, could lead to the integration of this technology into on-chip devices, advancing the scalability of quantum technologies.
A Breakthrough in Quantum Technology
The key to this breakthrough lies in nonlinear optics—a field of study that focuses on how light interacts with matter to produce new and often unusual properties. Nonlinear optics is critical for applications in telecommunications, laser technology, and more. By using these principles, the team has successfully created a device that can generate photon pairs using van der Waals materials, a class of materials known for their unique atomic layers that can be stacked in specific orientations.
Schuck, who is also the co-director of Columbia’s MS in Quantum Science and Technology program, describes the research as a crucial step toward bridging the gap between macroscopic (large-scale) and microscopic (quantum) systems. By integrating the generation of entangled photon pairs into smaller, more energy-efficient devices, the research lays the groundwork for the next generation of quantum devices. These new devices could be scalable, efficient, and fit into compact silicon chips, making them far more practical for real-world applications.
“Imagine a future where quantum systems that depend on photon pairs, such as those used in quantum computing or secure communication, could be integrated onto a single chip. This would drastically reduce the energy consumption of these devices and enhance their performance,” Schuck said. His team’s work has the potential to accelerate the development of quantum technologies, particularly in the fields of quantum communication, satellite-based networks, and mobile quantum communication.
The New Photon Pair Generation Technique
The new device created by Schuck and his team measures just 3.4 micrometers thick, making it thin enough to fit onto a silicon chip. This tiny size represents a major departure from earlier methods that required large crystals, sometimes visible without a microscope, to generate photon pairs. By leveraging the properties of molybdenum disulfide, a type of van der Waals material, the team was able to design a device that performs significantly better while using less energy.
Van der Waals materials are known for their unique ability to form stacks of thin atomic layers, each with its own distinct properties. In this case, the researchers layered six thin pieces of molybdenum disulfide, each rotated 180 degrees relative to its neighboring layers. This specific stacking orientation induces a phenomenon called quasi-phase matching, which manipulates the light traveling through the material. This manipulation enables the creation of paired photons, a crucial step in quantum information processing.
The device developed by the team is the first to use quasi-phase matching in a van der Waals material to generate photon pairs at wavelengths suitable for telecommunications. The results show that this new technique is not only far more efficient than previous methods but also significantly less prone to error. These advancements could pave the way for more reliable and efficient quantum devices, contributing to faster and more secure communication systems.
Schuck expressed optimism about the potential impact of this work. “We believe this breakthrough will establish van der Waals materials as the core of next-generation nonlinear and quantum photonic architectures,” he said. “They are ideal candidates for enabling future on-chip technologies, potentially replacing current bulk materials and periodically poled crystals used in photon-pair generation.”
How the Team Made it Happen
The breakthrough described in Nature Photonics builds on previous work by Schuck and his collaborators. In 2022, the team demonstrated that molybdenum disulfide—a material previously known for its potential in nonlinear optics—had useful properties for creating entangled photon pairs. However, performance was limited by interference between light waves traveling through the material, a phenomenon that complicated the generation of photon pairs.
To overcome this challenge, the team turned to a technique known as periodic poling, which is used to align the crystal structure in a way that mitigates the interference. By alternating the direction of the atomic layers in the stack, they were able to manipulate the light passing through the material, allowing for more efficient photon pair generation. This technique effectively enhanced the material’s performance, enabling the creation of photon pairs at extremely small length scales.
“We understood that molybdenum disulfide had the potential to perform exceptionally well in photon-pair generation,” Schuck said. “Once we realized the material’s full capabilities, we knew that periodic poling would be the key to making it work efficiently.”
The result is a device that is not only more efficient than previous methods but also far more compact. Its small size and scalability mean that it could be integrated into the next generation of quantum communication systems, including those based on satellite networks and mobile devices.
A New Era for Quantum Devices
This breakthrough has the potential to revolutionize many aspects of quantum technology, from communication to computing. Photon pairs are fundamental to many quantum protocols, including quantum key distribution (QKD) for secure communication and quantum teleportation for information transfer. The ability to generate these photon pairs on a much smaller, more energy-efficient scale opens up new possibilities for quantum systems that can be embedded in everyday devices.
Quantum communication systems, for example, rely on the secure transmission of information using entangled photons. These systems promise to be virtually tamper-proof, offering unparalleled security for sensitive data. With the new device developed by Schuck’s team, it becomes possible to generate the necessary entangled photon pairs more efficiently and on a smaller scale, making quantum communication more practical and scalable.
In addition to quantum communication, the new technology could also play a significant role in quantum computing. Quantum computers use qubits, which rely on the superposition and entanglement of quantum states. By improving the efficiency and scalability of entangled photon-pair generation, Schuck and his team are making an important contribution to the realization of large-scale quantum computing.
Looking Ahead
The team’s work represents just the beginning of what could be a transformative shift in quantum technology. As researchers continue to refine and expand upon these findings, it is likely that even more advanced techniques will emerge, bringing quantum technologies closer to mainstream use. The integration of van der Waals materials into on-chip quantum devices could provide the foundation for future technologies that are not only more efficient but also more accessible and adaptable.
Schuck and his team are already looking ahead to further improvements. They envision a future where these tiny, highly efficient photon-pair generators are integrated into portable devices, enabling real-time, secure quantum communication. As quantum systems continue to evolve, breakthroughs like this one will play a key role in making these systems a ubiquitous part of our technological landscape.
Reference: Chiara Trovatello et al, Quasi-phase-matched up- and down-conversion in periodically poled layered semiconductors, Nature Photonics (2025). DOI: 10.1038/s41566-024-01602-z