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Project wiki for the Module QT5201U (Quantum control technology) - 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.

Deadline for the reports will be 30 April 23:59SGT!

Project proposals

Wavemeter based on interferometer

Basically, we are now trying to build a wavemeter based on Michelson interferometer. The goal is to measure laser with a wavelength from 1200nm to 1800nm which can be used for these lasers in our lab. This project consists of work about optics and electronic control. The control system is mainly implemented by using a Arduino UNO board and some basic circuits.

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 780.246 nm which corresponds to the transition $5S_{1/2},F=2\rightarrow 5P_{3/2},F=3$ of ⁸⁷Rb. 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.

Control over the atomic spins within certain molecules by NMR technique

NMR has been the workhorse for the experimental implementation of quantum protocols, allowing exquisite control of systems up to seven qubits in size. However, there exists some experimental limitations in terms of the cross-talk, coupled evolution, instrumental errors and so on. Thanks to the current advanced pulse techniques, we can reduce these influences and extend this technique to a new stage that the experimental limits can be neglected. In this experiment, we try to use composite pulses to compensate RF field strength variations and frequency offsets.

Optical control of TMDCs valley pseudospin 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.

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.

Microwave control of superconducting cavity and qubit

This project aims to perform a trial pre-experiment based on the cQED architecture including simulation, calibration, microwave control pulse programming, and so on. The 3D superconducting cavity sample is anchored to the MXC flange inside the Bluefors dilution refrigerator to reach a temperature of around 10mK. On the other hand, the generation of microwave control pulses and the acquisition of output signals are handled by a QM quantum control device, connecting the sample via the control lines and the output lines accordingly. Hence, we can realize several bosonic states via cavity driving and qubit control.

A Nanosecond Pulse Generator based on the Reconfigurable Phase-Locked Loop (PLL) Module in Field Programmable Gate Arrays (FPGAs)

Field Programmable Gate Arrays (FPGAs) are digital integrated circuits (ICs) that contain blocks of logic and interconnects which can be configured and reconfigured even after it is being deployed "in the field". This enables flexible tunability in the function of FPGA-based devices. We seek to realise the claims of Zhu & Wang (2015) to utilise the Phase-Locked Loop (PLL) module in FPGA to implement a nanosecond pulse generator with adjustable frequency and pulse width. Our circuit was designed with Quartus Prime.

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
15.2.2021	Homodyne detection techniques	Measurement of optical fields in many continuous variable scenarios require knowledge of optical homodyning and heterodyning techniques. These techniques, similar to their radiofrequency counterparts, rely on multiplying field amplitudes.
1.3.2021	Frequency control of laser systems, part 1	Many laser systems in quantum technologies require to have a well-defined frequency relationship with atomic transitions or solid state qubits. We cover typical techniques how laser systems can be controlled to a high enough accuracy, utilizing spectroscopy techniques and control systems.
2.3.2021	Frequency control of laser systems, part 2
8.3.2021	Interface to computers	High level interfacing between computers and electronic hardware: Standard device languages; some serial protocols, some aspects of microcontrollers and FPGAs
15.3.2021	Pulses in quantum control	Many quantum systems require short control pulses, either in form of optical pulses or radiofrequency pulses. This covers how they are used, and present a few techniques to generate such control pulses
22.3.2021	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.
12.4.2021	Control loops	Many experimental activities in controlling quantum systems require the control of classical systems, like the temperature stabilization of some device, or the frequency stabilization of a laser. This lecture gives a brief overview of some simple control concepts.
	Practical aspects of superconducting systems	We cover different materials, transition temperatures, temperature measurement techniques and thermal insulation / conduction techniques.

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