Research

Inverse-designed silicon nitride nanophotonics

Toby Bi, Shuangyou Zhang, Egemen Bostan, Danxian Liu, Aditya Paul, Olga Ohletz, …, Kiyoul Yang, and Pascal Dell’Haye

Published in Nature Communications

Silicon nitride photonics has enabled integration of a variety of components for applications in linear and nonlinear optics, including telecommunications, optical clocks, astrocombs, bio-sensing, and LiDAR. With the advent of inverse design – where desired device performance is specified and closely achieved through iterative, gradient-based optimisation – and the increasing availability of silicon nitride photonics via foundries, it is now feasible to expand the photonic design library beyond the limits of traditional approaches and unlock new functionalities. In this work, we present inverse-designed photonics on a silicon nitride platform and demonstrate both the design capabilities and experimental verification by realising precisely tailored wavelength-division multiplexers, mode-division multiplexers, and high-Q resonators with controllable wavelength range and dispersion. This demonstrates inverse-designed enhanced manipulation of orthogonal bases of light. Furthermore, we use these inverse-designed structures to form optical cavities that hold promise for on-chip nonlinear and quantum optics experiments.

Ion-chain sympathetic cooling and gate dynamics

Aditya Paul and Crystal Noel

Featured as Editors’ Suggestion in Physical Review Applied

Entangling gates like Mølmer-Sorensen gates utilize the motional degree of freedom of these ions, while misalignment can lead to local gradients in Rabi frequency, underscoring the importance of reducing ion motion. However, because cooling is a decoherent process, ion chains are cooled sympathetically; i.e., particular ions are designated as coolants and are used for laser cooling, reducing the motion of the qubit ions through the Coulomb interaction. However, best practices for sympathetic cooling have not been found yet. This study aims to use computational simulation and analysis techniques in order to shed some light on best practices for sympathetic cooling, such as coolant placement, cooling duty cycle, and number of gates per cooling cycle.

A scaled local gate controller for optically-addressable qubits

Bichen Zhang, Pai Peng, Aditya Paul, and Jeff D. Thompson

Featured as cover article for Feb. 2024 issue of Optica

Optical tweezer arrays are powerful tools for quantum information science, especially when trapping neutral Rydberg atom qubits. These arrays are generally generated by two \(n-\) and \(m-\)tone acousto-optical deflectors, allowing for tight, replicable optical foci. However, these systems lack individual control over sites, and suffer from limited geometries. In this project, I designed a tweezer array generator using a spatial light modulator and digital micromirror device. Phase estimation was done with a modified version of the Gerchberg-Saxton algorithm, and computer vision methods were employed to process, calibrate, and control these tweezer grids at high speed. Tests showed that this system was highly scalable, able to generate up to 104 tweezer sites, switch 4900 sites, and image 1419 sites at once. The system also achieved switching speeds of ~50 kHz, with contrast ratios of above 104, giving a Rabi frequency ratio bound of \(<10^{-2}\). Future work includes camera-based phase estimation, improvements in SLM Gaussian beam generation, and large-scale XZZX surface code addressing.