Integrated photonics beam delivery via tilted Bragg gratings for quantum technology

Abstract

The use of free space optics hinders the current trapped-ion quantum computer on the scalability front as the number of free space optics elements required scales with the number of the ions, potentially millions of them. This project investigates a possible solution of replacing free-space optics by fully integrating photonics with UV-written tilted Bragg grating. The foundation for this solution is established by confirming the method for generating an arbitrary beam in free space above the chip from an integrated planar waveguide with possible polarisation control. This method will infer that even the readout devices, such as a big lens, can be replaced by integrating tilted Bragg gratings, offering one step closer to the realisation of a monolithic trapped-ion quantum computer.

Theoretical investigation into the tilted Bragg grating approach was started with an analytical solution derived from a beam tracing approach. Considering thin slices parallel to the face of the grating slices and integrating over the grating length allowed us to solve for the scattering rate of the output beam resulting from tilted Bragg gratings. This scattering rate depends on the polarisation of the input mode and is crucial for reverse engineering the required index distribution of grating design that can generate an arbitrary beam.

Methods for generating an arbitrary beam in 2D and 3D were discussed and the validity of these methods were tested. For the 2D model, the comparison was made with numerical finite element method (FEM) simulations of the grating designs and for the 3D model, the verification is done by comparing the derived grating struc- ture against the hologram resulting from the interference pattern formed from the pump and the desired output beam. The comparison results have shown excellent agreements. Furthermore, theoretical models were used to compare the experimental data generated from 213 nm dual interferometry written grating to confirm the possible realisation of the complex tilted Bragg grating design with full control of polarisation.

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Identifiers

ORCID for Dong-Woo Ko: orcid.org/0000-0001-6552-8824

ORCID for Peter Horak: orcid.org/0000-0002-8710-8764

ORCID for James Gates: orcid.org/0000-0001-8671-5987

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