Researchers Use Quantum Effects to Achieve Ultrabroadband Bandwidth

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Researchers at the University of Rochester have used a thin-film nanophotonic device and the phenomenon of quantum entanglement to generate very large bandwidth — a record for ultrabroadband, the researchers said. The researchers entangled photons and, specifically, their frequencies in the work.

The breakthrough could lead to enhanced sensitivity and resolution for experiments in metrology and sensing, including in spectroscopy, nonlinear microscopy, and quantum OCT.

Quantum entanglement occurs when two quantum particles are connected, even when they are apart. Any observation of one particle affects the other as if the particles were in communication. When this entanglement behavior involves photons, entangling the photons’ frequencies — the bandwidth of which can be controlled — is a possibility.

To date, most devices used to generate broadband entanglement of light divide a bulk crystal into small sections, each with slightly varying optical properties, and each generating different frequencies of the photon pairs. The frequencies are then added together to give a larger bandwidth.

The process is inefficient, however, and reduces brightness and the purity of the photons, said Usman Javid, a Ph.D. student in the lab of Qiang Lin, a professor of electrical and computer engineering who led the research. In these devices, there will always be a trade-off between the bandwidth and the brightness of the generated photon pairs.

“We have completely circumvented this trade-off with out dispersion engineering technique to get both: a record-high bandwidth at a record-high brightness,” Javid said.

Researchers in the lab of Qiang Lin at the University of Rochester have generated record ‘ultrabroadband’ bandwidth of entangled photons using the thin-film nanophotonic device illustrated here. At top left, a laser beam enters a periodically poled thin-film lithium niobate waveguide (banded green and gray). Entangled photons (purple and red dots) are generated with a bandwidth exceeding 800 nanometers. (Illustration by Usman Javid and Michael Osadciw). Courtesy of University of Rochester.
Researchers in the lab of Qiang Lin at the University of Rochester have generated record ‘ultrabroadband’ bandwidth of entangled photons using the thin-film nanophotonic device illustrated here. At top left, a laser beam enters a periodically poled thin-film lithium niobate waveguide (banded green and gray). Entangled photons (purple and red dots) are generated with a bandwidth exceeding 800 nm. Illustration by Usman Javid and Michael Osadciw, courtesy of University of Rochester.
The nanophotonic device consists of a thin film of lithium niobate. It uses a single waveguide with electrodes on both sides. Whereas a bulk device can be millimeters across, the Rochester team’s device has a thickness of 600 nm. This makes it more than a million times smaller in its cross-sectional area than a bulk crystal, and, as a result, the propagation of light extremely sensitive to the dimensions of the waveguide.

Even a variation of a few nanometers can change the phase and group velocity of the light through which it is propagating. As a result, the device allows precise control over the bandwidth in which the pair generation process is momentum matched.

“We can then solve a parameter optimization problem to find the geometry that maximizes this bandwidth,” Javid said.

The device could additionally lead to the higher-dimensional encoding of information in quantum networks for information processing and communications. However, the device is ready only to be deployed in experiments in a laboratory setting, according to Javid. For it to be used commercially, a more efficient and cost-effective fabrication process is needed. Lithium niobate fabrication will take some time to mature enough to make financial sense, he said.

“This work represents a major leap forward in producing ultrabroadband quantum entanglement on a nanophotonic chip,” Qiang Lin said.

The research was published in Physical Review Letters (

Published: November 2021
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
quantum entanglement
Quantum entanglement is a phenomenon in quantum mechanics where two or more particles become correlated to such an extent that the state of one particle instantly influences the state of the other(s), regardless of the distance separating them. This means that the properties of each particle, such as position, momentum, spin, or polarization, are interdependent in a way that classical physics cannot explain. When particles become entangled, their individual quantum states become inseparable,...
Metrology is the science and practice of measurement. It encompasses the theoretical and practical aspects of measurement, including the development of measurement standards, techniques, and instruments, as well as the application of measurement principles in various fields. The primary objectives of metrology are to ensure accuracy, reliability, and consistency in measurements and to establish traceability to recognized standards. Metrology plays a crucial role in science, industry,...
quantum sensing
Quantum sensing refers to a class of sensing technologies that leverage principles from quantum mechanics to enhance the precision and sensitivity of measurements. Traditional sensors operate based on classical physics, but quantum sensing exploits quantum properties, such as superposition and entanglement, to achieve improved performance in terms of accuracy, resolution, and sensitivity. Key concepts and characteristics of quantum sensing include: Superposition: Quantum sensors can...
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
thin film
A thin layer of a substance deposited on an insulating base in a vacuum by a microelectronic process. Thin films are most commonly used for antireflection, achromatic beamsplitters, color filters, narrow passband filters, semitransparent mirrors, heat control filters, high reflectivity mirrors, polarizers and reflection filters.
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