Study paves the way for advanced quantum networks – 12/03/2023 – Science

Transmitting information coherently, in the band of the electromagnetic spectrum between microwaves and infrared light, is fundamental for the development of advanced quantum networks used in computing and communication.

A study carried out by researchers from the State University of Campinas (Unicamp), in collaboration with colleagues from ETH Zürich, in Switzerland, and TU Delft, in the Netherlands, focused on the use of nanometric optomechanical cavities for this purpose.

These nanometer-scale resonators promote the interaction of high-frequency mechanical vibrations with infrared light, at wavelengths used by the telecommunications industry.

The article on this subject was published by the group in the journal Nature Communications.

“Nanomechanical resonators act as bridges between superconducting circuits and optical fibers. Superconducting circuits are, today, one of the most promising technologies for quantum computing, while optical fibers are already established as transmitters of information over long distances, with little noise and without loss of signal”, says Thiago Alegre, professor at the Gleb Wataghin Institute of Physics (IFGW-Unicamp) and coordinator of the study.

The researcher reports that one of the central innovations of the study is the introduction of dissipative optomechanics. Traditional optomechanical devices rely on purely dispersive interactions. In these, only the photons confined in the cavity are efficiently dispersed. In the dissipative approach, photons can be scattered directly from the waveguide to the resonator. “This enables greater control of the optoacoustic interaction,” explains Alegre.

Until the present study, dissipative optomechanical interaction had only been demonstrated at low mechanical frequencies, precluding important applications such as quantum state transfer between photonic (optical) and phononic (mechanical) domains.

The study showed the first dissipative optomechanical system operating in a regime in which the mechanical frequency exceeds the optical dissipation rate.

“We managed to increase the mechanical frequency by two orders of magnitude and increase the optomechanical coupling rate by ten times. This offers very promising prospects for the development of even more effective devices”, highlights the researcher.

Quantum networks

The devices, manufactured in collaboration with TU Delft, employ well-established technologies in the semiconductor industry in their design. Nanometric silicon beams suspended and free to vibrate allow the confinement of infrared light and mechanical vibrations simultaneously. Next to it, a waveguide, positioned to allow the coupling of the optical fiber to the cavity, gives rise to dissipative coupling, a fundamental ingredient for the results presented by the researchers.

The study offers new possibilities for building quantum networks. And, beyond this immediate horizon of application, it also establishes a basis for future fundamental research. “Our expectation is to be able to individually manipulate mechanical modes and mitigate optical nonlinearities in optomechanical devices”, concludes the Unicamp professor.

In addition to Alegre, the study had the participation of André Garcia Primo, Pedro Vinícius Pinho and Gustavo Silva Wiederhecker, from Unicamp; by Rodrigo da Silva Benevides, from ETH Zürich; and Simon Gröblacher from TU Delft. The work received funding from FAPESP through seven projects.