Record ultra-broadband thanks to quantum entanglement

Engineers at the University of Rochester have achieved unprecedented bandwidth and brightness on chip-sized nanophotonic devices, thanks to so-called quantum entanglement - or what Albert Einstein once called "spectral action at a distance" - a phenomenon which occurs when two quantum particles are linked together, even when they are millions or billions of kilometers apart. Any observation of one particle affects the other as if they were communicating with each other. When this entanglement involves photons, interesting possibilities emerge, including the entanglement of photon frequencies, whose bandwidth can be controlled.

Researchers at the University of Rochester have taken advantage of this phenomenon to generate a Incredibly wide bandwidth using a thin-film nanophotonic device. The breakthrough could lead to higher dimensional encoding of information in quantum networks for information processing and communication. "This work represents a major leap forward in the production of ultra-wideband quantum entanglement on a nanophotonic chip," said Qiang Lin, professor of electrical and computer engineering. “And it demonstrates the power of nanotechnology for the development of future quantum devices for communication, computing and sensing.”

To date, most of the devices used to generate broadband entanglement of light resorted to dividing a mass 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 greater bandwidth.

The thin-film lithium niobate nanophotonic device created by Lin's laboratory instead uses a single waveguide with electrodes on both sides. While a mass device may be millimeter in diameter, the thin-film device is 600 nanometers thick, more than a million times smaller in its cross-sectional area than a bulk crystal, according to Usman Javid, PhD student and principal. author of the study. This makes the propagation of light extremely sensitive to the dimensions of the waveguide.

Indeed, even a variation of a few nanometers can cause significant changes to the phase and group velocity of the light propagating through it. . As a result, the researchers' thin-film device allows for precise control over the bandwidth where the torque generation process is matched to momentum. “We can then solve a parameter optimization problem to find the geometry that maximizes this bandwidth,” said Javid.