Multimode Ultrastrong Coupling with FW-BICs in THz Metasurface

Various physical systems, that show the phenomena of ultra strong coupling (USC), have applications in nonlinear harmonic generation, low loss on-chip communication, and will be critical for quantum computing architectures including the growing sector of quantum information technology. USC can be achieved by placing an emitter inside an optical cavity with distinct resonances. The interaction between the two resonances is exhibited through a spectral line splitting such as that in any two coupled resonators and the resonant coupling leads to light–matter hybridization into two normal modes with an energy separation known as the vacuum Rabi splitting in which the USC regime is reached. For quantum computing platforms, the stronger the coupling the more efficient qubit-photon coupling can become which provides shorter operation times. The USC regime also allows the possibility of replacing quantum gates just by their very nature due to the natural evolution of a USC system. In quantum information technology, particularly quantum computation, the core idea is to use multiple interconnected quantum systems to perform calculations, enabling the use of numerous qubits. The strength of the coupling between qubits determines the speed at which a quantum computer can process information. To achieve ultra-fast quantum computing, extremely strong couplings between qubits are essential. Exploring this phenomenon in the terahertz (THz) region is crucial, as it provides a greater communications bandwidth compared to microwave frequencies. A unit cell of the metasurface consisting of a 200 nm thick Al thin film that consists of the cavity-dipole system on a 150 µm thick quartz substrate. The cavity-dipole system consists of a cavity that is 280 µm x 30 µm and a ribbon that is 10 µm wide with its length parametrically varied from 50 to 270 µm. The ribbon displays a dipole resonance. As the ribbon varies parametrically, the dipole resonance changes as well. The dipole resonance sweeps the frequency range that overlaps with the first, second and third cavity modes. This effect causes three anti-crossings to occur in our metasurface. Numerical calculations were performed using the ANSYS HFSS to predict the spectral response of the structure which was illuminated at normal incidence under a TE polarized wave. Periodic boundary conditions are applied to mimic the periodic unit cell. The contour plot shows anti-crossing at zero-detuning with a rabi splitting (ΩR) of 0.186 for the first cavity mode. The second cavity mode has an anti-crossing with a rabi splitting (ΩR) of 0.158. Showing that this structure produces results in multimode USC. The rabbi splitting was used in the two-band Hamiltonian to predict the FW-BIC locations. Coupled mode theory (CMT) was used to approximate the upper and lower polaritons. Since this is multimode coupling, it is more complex, and a fuller semi-classical theory is needed to describe the complex light-matter interactions. Experimental results via THz-TDS spectroscopy have also been conducted that have confirmed the results shown numerically.

Author dc:creator

• Tenyu Aikawa (17130834)

• Physics
• Optics

Statement dc:rights

• In Copyright
• Open Access after 2028-01-01

DOI dc:identifier

https://doi.org/10.25417/uic.31451830.v1

OAI identifier oai:identifier

oai:figshare.com:article/31451830