My name is Andrew Files, and I am majoring in Mechanical Engineering and Physics. I am apart of the College of Engineering, Fulbright College of Arts and Sciences and the Honors College. I am conducting research under Dr. Hiro Nakamura in the Department of Physics. This semester I worked under Dr. Nakamura in the Quantum Photonics lab on the project
‘Developing Titanium Oxide Platform for Quantum Photonics.’ This project spans multiple semesters, and I will continue to work on this project in the Spring Semester.

I was approached by my TA in my University Physics I lab about doing research under Dr. Nakamura in the Spring of 2023. I met with him, and we talked about what types of projects the Quantum Photonics lab works on and where I might fit into all of it. He decided that for the Fall
Semester of 2023, it would be best if I continued the work on a previous project where another student had left off. I began developing and optimizing a system to view the generation of the
Spontaneous Parametric Down-Converted (SPDC) photons in a non-linear barium borate (BBO)
crystal. The original focus of this project was to develop the system and test the versatility of
titanium oxide crystals in quantum photonic applications. However, the project shifted to focus
more deeply on making the system more robust and reliable.

The goal with the system is to be able to put any material in front of the laser and test it for
SPDC capabilities. This requires complex opto-mechanical components as well as some
complicated calibration and alignment processes. BBO is a stable source of SPDC photons and
was thus an ideal candidate for calibrating the set up. We used it as a benchmark to ensure the
system was capable of the precise and high resolution imaging necessary for this
measurement.

Our main issues were with alignment and polarization effects present in our optical set up.
SPDC of bulk (thickness larger than about 0.5 mm) crystals requires a very precise angular
relationship between the surface of the crystal and the beam of the laser. This presents a
significant issue when trying to calibrate the set up because we don’t know whether our
measurement is bad or the stem is misaligned. Eventually, we were able to get a signal and
move on to attenuating and sharpening the image. The other issue, polarization, is relevant
because the SPDC phenomenon produces two signals that have orthogonal polarizations. So, if
any of our components introduced a polarization dependence, we will lose at least one of the
signals. We were able to remove all of these effects and get the proper signal after several
months of tuning.

I presented my methodology and preliminary data at the Honors Undergraduate Research
Symposium this semester under the title ‘Developing a Single-Photon Image system based on a
Scanning Avalanche Photo-Diode’. I also presented the final set up and results at the Arkansas
IDeA Network of Biomedical Research Excellence (INBRE) Conference at the University of
Arkansas under the title ‘Developing a Single Photon Detection System Using SPDC in BBO’.
My future plans are to move on to testing 2D Van der Waals layered materials, starting with
niobium oxide diiodide (NbOI₂), for SPDC capabilities.