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Project wiki for the Module QT5201U - AY20/21S2

Welcome to the wiki project page. This will be the place for documenting projects. To be able to write something to this wiki, we need to create a user login manually. If you have not yet created an account, do let me know - Christian.

Project proposals

Here, links/short descriptions to projects should be listed.

Example project

This is just a dummy project.

Wavemeter based on interferometer

Basically we are now trying to build a wavemeter which can measure wavelength from 1200nm to 1800nm because the measurement tool for these lasers is not available now in our lab. It is based on Michelson interferometer.

Coincidence Time Measurement of Pulsed Lasers & "Useful" Applications

Proof-of-concept experiment to show how one may use commonly-available materials to measure difference in laser path lengths to sub-millimeter precision with a copper target (TBC). This experiment is done using a 355nm, 120 MHz, 10ps pulsed laser. Upon showing that such a measurement is possible, we shall go on to explore some for-fun applications of this "technology" and see how far and precise we can get.

Saturated Absorption Spectroscopy + Frequency Modulation Locking on the D2 line of Rubidium 87

With a combination of the Saturation Spectroscopy and Frequency Modulation techniques, we aim at stabilizing the wavelength of a Diode Laser at approximately 780.241 nm which corresponds to the transition $5S_{1/2}\to 5P_{3/2}$ (also known as D2 line) of Rubidium 87. Additionally we will implement in the experiment a Red Pitaya, which is a minicomputer capable of replacing things like an Oscilloscope, Function Generator and PID controller. Therefore reducing the space needed for the experiment.

Optical Control of Semiconductor Qubits

Quantum dots or single electron transistors, allow for individual control of single charge or spin. In addition, some semiconductor monolayers possess a sizeable direct bandgap of ≈1.5–2 eV in the optical range allowing electrostatic confinement and optical manipulation of carriers. Therefore, we try to adopt the method of this theoretical paper, and see if we can control single qubit or couple 2 qubits optically.

• Paper link (PDF): 📑
• Paper link (Original): 📑, local copy here

A temperature-tunable etalon for optical telecommunication wavelength

This project aims to build a Fabry-perot interferometer (also called Etalon) that works at the optical telecommunication wavelengths (1260nm-1625nm). This depicted etalon is made out of a single piece of polished silicon wafer with a thickness of about 100μm. The free spectral range (FSR) of the etalon can be adjusted by changing its thickness through temperature tuning. We will also explore the possibility of applying highly reflective (HR) coatings to the silicon wafer to achieve a high cavity finesse and a narrow transmission line-width.

Laminar Air Flow-Based Acusto-Optical Modulator

Not an active project! Just a random idea, might be fun to try. As discussed during the AOM lecture, a media with a slow speed of sound is preferred for construction of AOMs. The most common material through which the speed of sound is very very slow would be air. Unfortunately, atmospheric air by itself is very chaotic and is not optimal for use in the context of an AOM. Given these considerations, is it possible for a small chamber of a laminar flow of air, modulated by some acoustic frequency, act as an effective AOM?

Material requests

Please add stuff we should organize one way or the other here:

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Stuff to be covered in the lecture slots on Mondays (sometimes Tuesdays as well)

Feel free to add topics or aspects to this list. At the moment, this is just a copy of the tentative syllabus:

Date	Topic	Description
18.1. 2021	Paraxial optics, part 1	Optical systems often work with Gaussian beams. We cover practical design techniques like the ABCD matrix formalism for simple optical systems.
19.1. 2021	Paraxial optics, part 2 (only first part of lecture)
25.1. 2021	Optical cavities, part 1	Many optical techniques require to work with optical cavities. We cover how to design them, and how to couple light into very basic devices. This lecture covered some theory basics.
26.1. 2021	Optical cavities, part 2	Some more aspects of optical cavities, and dielectric coatings for mirrors and such
1.2.2021	Optical fiber technology	Some properties of optical fibers as the most common optical waveguide are covered, including optical mode spectrum, dispersion and transmission properties.
8.2.2021	Optical modulators, part 1	Many optical modulation techniques require rely on devices or materials where optical properties can be changed electrically; we cover accousto-optical and electro-optical devices, as well as liquid crystal systems.
9.2.2021	Optical modulators, part 2
	Practical aspects of superconducting systems	We cover different materials, transition temperatures, temperature measurement techniques and thermal insulation / conduction techniques.
	Frequency control of laser systems	Many laser systems in quantum technologies require to have a well-defined frequency relationship with atomic transitions of solid state qubits. We cover typical techniques how laser systems can be controlled to a high enough accuracy, utilizing spectroscopy techniques and control systems.
	Homodyne detection techniques	Measurement of optical fields in many continuous variable scenarios require knowledge of optical homodyning and heterodyning techniques.
	Generating pulse sequences	Many quantum systems require short control pulses, either in form of optical pulses or radiofrequency pulses. We present a few techniques to generate such control pulses
	Interface to computers	High level interfacing between computers and electronic hardware: Simple python scripting, standard device languages
	High voltage techniques	Working with high voltages requires a spectrum of techniques that is differing from more conventional electronics. A few aspects (field emission, dielectric strength, specific components) are covered.

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