Main Page

Wiki page for course QT5201U (Quantum control technology) - AY2026/27S1

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.

Next class: Mon 17 Aug 2026 in the seminar room S15 level 5.

Project pages

Example project title

One sentence, describing what this project is is about.

Team members: A, B, C

QKD receiver characterization (Polarization)

Calibrated polarization-state generator to characterize polarization analysis modules in QKD receiver and rigorously quantify the impact on secure key rates.

Team members: Elias X. Huber, various AI agents (open to join forces with other humans as well, you can reach me at elias.x.huber[at typical nus sufix]; please note though that I will likely do the experiment at UTown (CREATE Tower), my schedule tends to be a bit inflexible for team-work, and I am a theorist with no lab experience).

QKD receivers are subject to imperfections which, if not adequately considered in security proofs, may compromise the security of generated secret keys. This project considers receivers that measure polarization in the Pauli $Z$ and Pauli $X$ bases (a passive-basis-choice "BB84 measurement"). Such a receiver consists of a polarization analysis module (PAM) followed by single-photon detectors. A simple schematic is given below.

                    ┌── PBS ── H ── det H     (Z / rectilinear arm)
                    │       └── V ── det V
channel ── PC ── BS ┤
                    │       ┌── + ── det +    (X / diagonal arm)
                    └── HWP ┤
                     ~22.5° └── − ── det −

Light from the quantum channel (single-mode fibre, optionally after a polarization controller PC) is split by a non-polarizing beam splitter (BS) into a rectilinear ($H/V$) arm and a diagonal ($+/-$) arm. An HWP near $22.5^{\circ }$ rotates the $X$-arm basis before its PBS. The four ports are monitored by detectors labelled $H,V,+,-$.

Imperfections such as arm-dependent loss, biased beam-splitting ratios, or a low PBS extinction ratio may leak (partial) key information to an adversary or enable active attacks that bias detectors. As part of my work/PhD, I have been working on (theoretical) methods to integrate PAM characterization data into a QKD security proof. This project aims to build calibrated polarization preparation and characterize first a self-assembled PAM and subsequently the PAM of a real QKD receiver.

Resources

Some hopefully useful references should go here.

Recommended literature

• Bahaa E. A. Saleh, Malvin Carl Teich: Fundamentals of Photonics, Wiley; available as e-book in NUS. Excellent reference book for many optics topics.

Recorded classes

Date	Topic	Description	Reference
17.8.2026	Paraxial ray optics	A recap of how to deal with classical ray optics through ABCD matrices	Saleh, Teich: Fundamentals of Photonics
18.8.2026	Paraxial wave optics	Working towards Gaussian beams found with lasers...	same as above
24.8.2026	Optical cavities 1	Fabry-Perot, simple 1D dimensional
25.8.2026	Optical cavities 2	Transverse mode structure, optical coating basics

Complete playlist: https://www.youtube.com/playlist?list=PLN-Fk1m9cTD4

Previous version of this course wiki

• AY2012S2: https://ay2021s2.qt5201.org

Getting started

Consult the User's Guide for information on using the wiki software.

• MediaWiki FAQ
• Math can be entered in LaTeX style: <math>r^2=\sqrt{x^2+y^2}</math> renders as $r^2=\sqrt{x^2+y^2}$
• Should you miss any module or functionality of this wiki, please contact me (Christian Kurtsiefer).