Apoorva Bisht
Author: Apoorva Bisht | Majors: Computer Science and Physics
I am currently in my third year of under graduation and majoring in physics and computer science. Being a computer science major gave me the opportunity to work on programming using FPGA.
I joined Dr. Nakamura’s lab in the Physics department in the second semester of my under graduation. The goal of the lab is to eventually identify reliable single photons sources. Single photons are promising candidates for qubits which are used for example in quantum computing. However, due to the inherent probabilistic nature of quantum optics, processes that generate single photons are highly non-deterministic i.e., we cannot determine when the next single photon would be arriving. This is not ideal for utilizing single photons for practical purposes. Thus, as a first step for any single photon application, we want a deterministic source of single photons. To convert the probabilistically generated single photons into a series of single photons at determined intervals, we decided to develop a photon routing system based on a flexible computer chip called Field Programmable Gate Array (FPGA).
The work done in fall 2021 is as follows.
Procedure
First couple of semesters of joining the lab were spent in developing a data acquisition system using a low-cost customizable field programmable gate array (FPGA). As a next step, I implemented a FPGA multi-channel pulse height analyzer application [1] to our experimental setup, which enabled me to perform correlation measurements on coherent (laser) light source and thermal light source. Using this setup, I was able to distinguish if the light source was random (laser) or bunched (thermal).
Regarding single photon generation, I separated the task in two steps: (A) probabilistic generation of single photons and (B) routing these probabilistically generated single photons to generate their regular sequence. So far, I made progress in (A) where a non-linear crystal BBO was used to generate the 360 nm light required for the SPDC process. This is shown in Figure 1. For this project, I first theoretically calculated the phase matching angle required for BBO crystal and ordered a custom crystal which is cut in that angle. The first BBO crystal, whose angle is precisely tuned with respect to the pump beam of 720 nm wavelength, successfully generated second harmonic light at 360 nm.
For step (B), I was able to implement a TDC (time-to-digital) application [2] that determines the time interval between two arriving pulses, which is an essential component to time tagging single photons.
Concluding Remarks
The progress during 2020-21 laid the foundation for the project that will be continued this year. We envision that our work could deliver a significant impact by demonstrating low-cost single photon generation system even suitable for undergraduate labs. Widespread use of deterministic single photons is expected to accelerate applications such as quantum communication, quantum computation, as well as quantum entanglement demonstration (Bell measurement).
Support for Research Project
Support from Honors College added to the motivation to work on the project. Writing the proposal and forming the timeline gave idea of what I want to accomplish over one academic year. Having documentation regarding the progress helped compare the work with the timeline and what adjustments should be made to the project. Funding from the grant provided support and allowed me to focus more on the project. I would like to sincerely thank the Honors College for supporting this project. In addition, these projects have helped greatly in laying the foundation for my future research endeavors.
Dr. Nakamura has provided constant support and guidance throughout the project, being available for discussions and explanations even during the holidays. I would like to sincerely thank Dr. Nakamura for his encouragement and guidance.
Conference Presentations
During the year 2021, the work done was presented at two conferences – INBRE at University of Arkansas and FiO LS Conference by Optica. These conferences gave me a chance to present my work and learn about projects being conducted by different research groups.
Future Plans
This year (Spring 2022 and Fall 2022), I plan to demonstrate the SPDC process and refine it, and develop the routing system. For the generation of SPDC light, we plan to optimize the alignment of the crystal further and aim to produce two identical photons that can be used for the routing system.
The development of routing system can be separated into following tasks:
A Generating probabilistic single photons second-harmonic generation (SHG) and spontaneous parametric down conversion (SPDC). (SHG part is completed last year)
B1 Time tagging photons using an FPGA application (developed last year)
B2 Developing the routing logic on FPGA (this year)
B3 Using switches to apply appropriate time delay in the routing system. (this year)
This year, I proceed with developing the routing system that uses time information about the single photons (B1) to apply an appropriate time delay and generate a regular sequence of single photons (B2 and B3)
References
- Potočnik. antonpotocnik.com/. (2017).
- Demin. pavel-demin.github.io/red-pitaya-notes/mcpha/.