Engineering Quantum Entanglement

Researchers have developed a drastically smaller and more energy efficient method of creating coveted photon pairs that influence each other from any distance. The technology could transform computing, telecommunications, and sensing.

Physicists have spent more than a century measuring and making sense of the strange ways that photons, electrons, and other subatomic particles interact at extremely small scales. Engineers have spent decades figuring out how to take advantage of these phenomena to create new technologies.

In one such phenomenon, called quantum entanglement, pairs of photons become interconnected in such a way that the state of one photon instantly changes to match the state of its paired photon, no matter how far apart they are. 

Nearly 80 years ago, Albert Einstein referred to this phenomenon as "spooky action at a distance." Today, entanglement is the subject of research programs across the world — and it’s becoming a favored way to implement the most fundamental form of quantum information, the qubit. 

Currently, the most efficient way to create photon pairs requires sending lightwaves through a crystal large enough to see without a microscope. In a paper published today in Nature Photonics, a team led by Columbia Engineering researchers and collaborators, describe a new method for creating these photon pairs that achieves higher performance on a much smaller device using less energy. P. James Schuck, associate professor of mechanical engineering at Columbia Engineering, helped lead the research team.

These findings represent a significant step forward in the field of nonlinear optics, which is concerned with using technologies to change the properties of light for applications including lasers, telecommunications, and laboratory equipment. 

“This work represents the embodiment of the long-sought goal of bridging macroscopic and microscopic nonlinear and quantum optics,” says Schuck, who co-directs Columbia's MS in Quantum Science and Technology. “It provides the foundation for scalable, highly efficient on-chip integrable devices such as tunable microscopic entangled-photon-pair generators.” 

Peter Schuck (left) and Chiara Trovatello from the Schuck lab at Columbia Engineering

How it works

Measuring just 3.4 micrometers thick, the new device points to a future where this important component of many quantum systems can fit onto a silicon chip. This change would enable significant gains in the energy efficiency and overall technical capabilities of quantum devices.

To create the device, the researchers used thin crystals of a so-called van der Waals semiconducting transition metal called molybdenum disulfide. Then they layered six of these crystal pieces into a stack, with each piece rotated 180 degrees relative to the crystal slabs above and below. As light travels through this stack, a phenomenon called quasi-phase-matching manipulates properties of the light, enabling the creation of paired photons.

This paper represents the first time that quasi-phase-matching in any van der Waals material has been used to generate photon pairs at wavelengths that are useful for telecommunications. The technique is significantly more efficient than previous methods and far less prone to error. 

“We believe this breakthrough will establish van der Waals materials as the core of next-generation nonlinear and quantum photonic architectures, with them being ideal candidates for enabling all future on-chip technologies and replacing current bulk and periodically poled crystals,” Schuck says. 

“These innovations will have an immediate impact in diverse areas including satellite-based distribution and mobile phone quantum communication.” 

How it happened

Schuck and his team built on their previous work to develop the new device. In 2022, the group demonstrated that materials like molybdenum disulfide possess useful properties for nonlinear optics — but performance was limited by the tendency of light waves to interfere with one another while traveling through this material.

The team turned to a technique called periodic poling to counteract this problem, which is known as phase matching. By alternating the direction of the slabs in the stack, the device manipulates light in a way that enables photon pair generation at miniscule length scales. 

“Once we understood how amazing this material was, we knew we had to pursue the periodic poling, which could allow for the highly efficient generation of photon pairs.” - Peter Schuck
Written By:
Grant Currin
Columbia University
Image By:
Jane Nisselson/Columbia Engineering
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This work was supported by Programmable Quantum Materials, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under award DE-SC0019443. C.T. acknowledges the European Union’s Horizon Europe research and innovation programme under the Marie Skłodowska-Curie PIONEER HORIZON-MSCA-2021-PF-GF grant agreement no. 101066108. C.T. also acknowledges the Optica Foundation and Coherent Inc. for supporting this research through the Bernard J. Couillaud Prize 2022. G.C. acknowledges support by the Progetti di ricerca di Rilevante Interesse Nazionale (PRIN) of the Italian Ministry of Research 2022HL9PRP Overcoming the Classical limits of ultRafast spEctroSCopy with ENtangleD phOtons (CRESCENDO). C.T. and G.C. acknowledge funding from the European Union–NextGenerationEU under the National Quantum Science and Technology Institute (NQSTI) grant no. PE00000023-q-ANTHEM-CUP H43C22000870001. A.M. acknowledges funding from the European Union–NextGenerationEU under the Italian Ministry of University and Research (MUR) National Innovation Ecosystem grant no. ECS00000041-VITALITY-CUP E13C22001060006, and Progetti di ricerca di Rilevante Interesse Nazionale (PRIN) of the Italian Ministry of Research PHOTO (Photonic Terahertz devices based on topological materials) no. 316 2020RPEPNH. A.Y. acknowledges support from the Department of Defense (DoD) through the National Defense Science and Engineering Graduate (NDSEG) Fellowship Program. J.P. acknowledges funding from the Air Force Office of Scientific Research (FA9550-21-1-0323) and the Office of Naval Research (N000142212841). P.W. acknowledges support from the Air Force Office of Scientific Research under award number FA8655-20-1-7030 (PhoQuGraph) and FA8655-23-1-7063 (TIQI). This research was funded in whole or in part by the Austrian Science Fund (FWF) (10.55776/F71). The financial support by the Austrian Federal Ministry of Labour and Economy, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association is gratefully acknowledged. L.A.R. acknowledges support from the Erwin Schrödinger Center for Quantum Science and Technology (ESQ Discovery).