Unraveling Quantum Bonds: Mastering Nanoscale Entanglement Engineering

In one of these phenomena, termed quantum entanglement, pairs of photons become linked in such a manner that the condition of one photon instantaneously alters to align with the condition of its paired photon, irrespective of their distance apart.

Almost 80 years ago, Albert Einstein dubbed this phenomenon as “spooky action at a distance.” Presently, entanglement is under investigation across various research initiatives globally – and it is increasingly being favored as a method to realize the most basic unit of quantum information, the qubit.

At present, the most effective method to generate photon pairs necessitates directing light waves through a crystal sizable enough to be seen without a microscope. In a study published today in Nature Photonics, a group led by Columbia Engineering scientists and collaborators introduces a novel approach for producing these photon pairs that achieves superior performance using a significantly smaller apparatus with reduced energy consumption. P. James Schuck, associate professor of mechanical engineering at Columbia Engineering, played a pivotal role in leading the research team.

These discoveries mark a considerable advancement in the realm of nonlinear optics, which focuses on utilizing technologies to alter the properties of light for various applications, including lasers, telecommunications, and scientific apparatus.

“This research symbolizes the realization of the long-desired objective of connecting macroscopic and microscopic nonlinear and quantum optics,” states Schuck, who co-directs Columbia’s MS in Quantum Science and Technology. “It lays the groundwork for scalable, highly efficient on-chip integrable devices such as tunable microscopic entangled-photon-pair generators.”

How it operates

Measuring only 3.4 micrometers in thickness, the new apparatus suggests a future where this vital component of numerous quantum systems can be integrated onto a silicon chip. This transformation could lead to significant improvements in energy efficiency and overall technical capabilities of quantum devices.

To construct the device, the researchers utilized thin crystals of a so-called van der Waals semiconductor known as molybdenum disulfide. They then stacked six of these crystal segments, with each piece rotated 180 degrees relative to the slabs above and below it. As light traverses this stack, a phenomenon called quasi-phase-matching alters the characteristics of the light, enabling the production of paired photons.

This publication signifies the first instance that quasi-phase-matching in any van der Waals material has been employed to produce photon pairs at wavelengths suitable for telecommunications. The method is notably more efficient than earlier approaches and significantly less likely to produce errors.

“We are confident that this breakthrough will position van der Waals materials as the foundation for next-generation nonlinear and quantum photonic architectures, positioning them as ideal candidates for facilitating all future on-chip technologies and substituting current bulk and periodically poled crystals,” Schuck remarks.

“These advancements will have an immediate influence across various fields, including satellite-based distribution and mobile quantum communication.”

How it transpired

Schuck and his team built upon their previous research to develop the new device. In 2022, the team showcased that materials like molybdenum disulfide possessed valuable properties for nonlinear optics – yet performance was hindered by the interference tendencies of light waves while passing through the material.

The group turned to a procedure known as periodic poling to mitigate this issue, recognized as phase matching. By alternating the orientation of the slabs within the stack, the device regulates light in a manner that enables photon pair generation at minuscule length scales.

“Once we comprehended the remarkable nature of this material, we were determined to pursue the periodic poling, which could facilitate the highly efficient generation of photon pairs,” Schuck explains.

This research took place within Programmable Quantum Materials, a Department of Energy energy frontier research center (EFRC) at Columbia, as part of a broader effort to investigate and utilize quantum materials. This work was made possible through contributions from the Baso, Delor, and Dean laboratories. Postdoctoral researcher Chiara Trovatello spearheaded the initiative.