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===[[QKD receiver characterization (Polarization)]]===
=== [[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.
Calibrated polarization-state generator to characterize polarization analysis modules in QKD receivers 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).
'''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 <math>Z</math> and Pauli <math>X</math> 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.


<pre>
=== [[Control and measurement in the bosonic cQED system]] ===
                    ┌── PBS ── H ── det H    (Z / rectilinear arm)
Using control and measurement methods to characterize a dispersively coupled single superconducting cavity and single transmon qubit system, with a thorough review of the theories and experimental techniques behind it.
                    │      └── V ── det V
channel ── PC ── BS ┤
                    │      ┌── + ── det +    (X / diagonal arm)
                    └── HWP ┤
                    ~22.5° └── − ── det −
</pre>


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 (<math>H/V</math>) arm and a diagonal (<math>+/-</math>) arm. An HWP near <math>22.5^\circ</math> rotates the <math>X</math>-arm basis before its PBS. The four ports are monitored by detectors labelled <math>H,V,+,-</math>.
'''Team members:''' Grace Pang and Seungwon Jin


===[[Multi-tone RFSoC driver for an AOM]]===
A multi-tone RF synthesizer on an RFSoC board to drive an acousto-optic modulator(AOM).


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.
'''Team members:''' Mani Aarthy


===[[Placeholder for project title]]===
TBD.
'''Team members''' Wang Ziyan and Wu Jinbin


== Project plan ==
The project proceeds along the following steps:
# Assemble a free-space polarization-state generator (PSG: QWP + HWP after a fixed linear polarizer) able to span the full Bloch / Poincaré sphere.
# Assemble an analyzer to calibrate the QWP and HWP. Independently verify prepared states with a polarimeter.
# Validate preparation of <math>H,V,D,A,R,L</math>-polarized states and rigorously derive an uncertainty budget for the physically prepared states.
# Connect the calibrated PSG to
#* '''(4.1)''' a self-assembled PAM, and
#* '''(4.2)''' the PAM of a commercial QKD system.
#: Use a self-assembled fibre polarization controller, or the QKD receiver's own polarization controller, to rotate the reference frame (basis of the calibrated PSG) into the receiver frame (basis of the QKD receiver).
# Measure the input–output power ratio for all four PAM output ports, and from this derive an instrument matrix for the QKD receiver — or rather, an '''uncertainty region of instrument matrices''', due to non-zero preparation and measurement uncertainty.
# ''(Outside this course.)'' Calculate a conservative secure key rate for a worst-case PAM inside that uncertainty region. Maybe: Measure counts at APDs in instead of powermeter at PAM output ports for the characterization.


===[[Laser Phase Offset Lock]]===
We plan to implement an offset lock to phase stabilize a pair of External Cavity Diode Lasers (ECDL) at a fixed offset of 6.8 GHz, matching the Rb87 ground state hyperfine transition.


'''Team members:''' Bibhuti Thapa, Xu Zifang, Chan Jun Jie


== Required equipment (expected) ==
{| class="wikitable"
|-
! Item
! Use
! Notes / qty
|-
| Laser source at 1550 nm
| For preparation and power-ratio measurements
| Isolator needed?
|-
| Variable optical attenuator (VOA)
| Power control without changing laser drive
| Range covering both powermeter / polarimeter operation (+ maybe APD)
|-
| High-extinction linear polarizer <math>P_0</math> (Glan-type?)
| Defines generator <math>H</math> axis, fixed (not rotatable)
| 1
|-
| QWP and HWP
| PSG: span the Poincaré sphere
| 1 each for the generator (maybe one extra QWP if a validation analyzer is built instead of just using polarimeter)
|-
| Automated rotation mounts / stages
| Calibrated plate angles
| ≥2 (QWP, HWP); extra for analyzer plates
|-
| Analyzer PBS + two power meters
| Calibrate QWP/HWP (parallel and crossed ports, must be able to rotate PBS)
| Dual-channel preferred
|-
| Monitor pick-off (/Beamsplitter) + photodiode
| Normalize source drift during scans
| 1
|-
| Polarimeter
| Independent validation of prepared <math>H,V,D,A,R,L</math>
|
|-
| Fibre coupler, SMF patch leads
| Launch into fibre-coupled PAM / QKD Rx
|
|-
| Fibre polarization controller
| Align generator frame to receiver frame
| Freeze settings during calibrated acquisitions; may be possible to instead use the QKD Rx controller
|-
| Four-port power detection
| PAM input–output ratios on <math>H,V,+,-</math>
|
|-
| Self-assembled PAM
| First characterization target (step 4.1)
| (done / provided by colleague)
|-
| Commercial QKD receiver (PAM)
| Second characterization target (step 4.2)
| Already available, access to four PAM output ports
|-
| Breadboard / cage rods, mounts, irises
| Alignment
|
|-
| Temperature logger
| Waveplate / lab drift
| (optional for uncertainty budget)
|}


== Project plan ==
===[[Home-Built ECDL and Optical Sideband Generation]]===
The project proceeds along the following steps:
 
# Assemble a free-space polarization-state generator (PSG: QWP + HWP after a fixed linear polarizer) able to span the full Bloch / Poincaré sphere.
The project includes the construction and characterization of a Littrow ECDL, microwave-driven EOM sideband generation near 6.8 GHz, and optical beat-note techniques for relative frequency stabilization with an existing Rb87 trapping laser.
# Assemble an analyzer to calibrate the QWP and HWP.
 
# Validate preparation of <math>H,V,D,A,R,L</math>-polarized states and rigorously derive an uncertainty budget for the physically prepared states.
'''Team member:''' Liu Yiming
# Connect the calibrated PSG to
 
#* '''(4.1)''' a self-assembled PAM, and
 
#* '''(4.2)''' the PAM of a commercial QKD system.
===[[Thermal Drift Compensation via RF and DC Feedback for Thermal Device Control Applications]]===
#: Use a self-assembled fibre polarization controller, or the QKD receiver's own polarization controller, to rotate the reference frame (basis of the calibrated PSG) into the receiver frame (basis of the QKD receiver).
We plan to calibrate a thermally tunable microring resonator, compensate TEC-induced thermal drift using DC feedback, and evaluate gesture-image reconstruction through the AC channel.
# Measure the input–output power ratio for all four PAM output ports, and from this derive an instrument matrix for the QKD receiver — or rather, an '''uncertainty region''' of instrument matrices, due to non-zero preparation and measurement uncertainty.
 
# ''(Outside this course.)'' Calculate a conservative secure key rate for a worst-case PAM inside that uncertainty region. Maybe: Do measurements in attenuated form, click counts of QKD receiver's APDs instead of power meter.
'''Team members:''' Huang He, Ding Jiahao, Xu Anbang
 
===[[Measurement of Coherent States in Phase Space]]===
'''Team members:''' Lim Zi Way, Raghav Sah, Shawn Liew Hong Wei
 


== Required equipment (expected) ==
===[[Design and Construction of a Confocal Microscope for Photonic Material Characterization]]===
{| class="wikitable"
'''Team members:''' Kim Sihyung, Ankush Sharma, Liang Shuyi
|-
! Item
! Use
! Notes / qty
|-
| Laser source at 1550 nm
| For preparation and power-ratio measurements
| Isolator needed?
|-
| Variable optical attenuator (VOA)
| Power control without changing laser drive
| Range covering both powermeter / polarimeter operation (+ maybe APDs)
|-
| High-extinction linear polarizer <math>P_0</math> (Glan-type?)
| Defines generator <math>H</math> axis, fixed (not rotatable)
| 1
|-
| QWP and HWP
| PSG: span the Poincaré sphere
| 1 each for the generator (maybe one extra QWP if a validation analyzer is built instead of just using polarimeter)
|-
| Automated rotation mounts / stages
| Calibrated plate angles
| ≥2 (QWP, HWP); extra for analyzer plates
|-
| Analyzer PBS + two power meters
| Calibrate QWP/HWP (parallel and crossed ports, must be able to rotate PBS)
| Dual-channel preferred
|-
| Monitor pick-off (/Beamsplitter) + photodiode
| Normalize source drift during scans
| 1
|-
| Polarimeter
| Independent validation of prepared <math>H,V,D,A,R,L</math>
|
|-
| Fibre coupler, SMF patch leads
| Launch into fibre-coupled PAM / QKD Rx
|
|-
| Fibre polarization controller
| Align generator frame to receiver frame
| Freeze settings during calibrated acquisitions; may be possible to instead use the QKD Rx controller
|-
| Four-port power detection
| PAM input–output ratios on <math>H,V,+,-</math>
|
|-
| Self-assembled PAM
| First characterization target (step 4.1)
| (done / provided by colleague)
|-
| Commercial QKD receiver (PAM)
| Second characterization target (step 4.2)
| Already available, access to four PAM output ports
|-
| Breadboard / cage rods, mounts, irises
| Alignment
|
|-
| Temperature logger
| Waveplate / lab drift
| (optional for uncertainty budget)
|}


==Resources==
==Resources==
Line 202: Line 63:
===Recommended literature===
===Recommended literature===
* Bahaa E. A. Saleh, Malvin Carl Teich: Fundamentals of Photonics, Wiley; available as [https://libproxy1.nus.edu.sg/login?url=https://search.ebscohost.com/login.aspx?direct=true&db=nlebk&AN=26193&site=ehost-live&ebv=EB&ppid=pp_Cover  e-book in NUS]. Excellent reference book for many optics topics.
* Bahaa E. A. Saleh, Malvin Carl Teich: Fundamentals of Photonics, Wiley; available as [https://libproxy1.nus.edu.sg/login?url=https://search.ebscohost.com/login.aspx?direct=true&db=nlebk&AN=26193&site=ehost-live&ebv=EB&ppid=pp_Cover  e-book in NUS]. Excellent reference book for many optics topics.
* Mark Fox: Quantum Optics: An Introduction, Oxford University Press; available as [https://libproxy1.nus.edu.sg/login?url=https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=208564 e-book in NUS]. Nice book on traditional quantum optics topics.
* Christopher C. Davis: Lasers and electro-optics, Cambridge; available as [https://libproxy1.nus.edu.sg/login?url=https://dx.doi.org/10.1017/CBO9781139016629 e-book in NUS]. Good overall book on optics-related aspects useful for controlling quantum systems.
===Recorded classes===
===Recorded classes===


Line 230: Line 94:
| Transverse mode structure, optical coating basics
| Transverse mode structure, optical coating basics
|  
|  
|-
| 14.9.2026
| [https://youtu.be/Lwt6eJe12h0 Homo- and heterodyning basics]
| Radiofrequency origins of mixers, optical version
| any quantum optics text (e.g. Mark Fox, see above)
|-
| 15.9.2026
| [https://youtu.be/2nhP60FKstQ Optical Modularors 1]
| Mostly Electro-optical modulators, some LCD as well
| e.g. Davis: Laser and Electro-optics
|-


|}
|}

Latest revision as of 14:19, 24 September 2026

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 receivers 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).


Control and measurement in the bosonic cQED system

Using control and measurement methods to characterize a dispersively coupled single superconducting cavity and single transmon qubit system, with a thorough review of the theories and experimental techniques behind it.

Team members: Grace Pang and Seungwon Jin

Multi-tone RFSoC driver for an AOM

A multi-tone RF synthesizer on an RFSoC board to drive an acousto-optic modulator(AOM).

Team members: Mani Aarthy

Placeholder for project title

TBD. Team members Wang Ziyan and Wu Jinbin


Laser Phase Offset Lock

We plan to implement an offset lock to phase stabilize a pair of External Cavity Diode Lasers (ECDL) at a fixed offset of 6.8 GHz, matching the Rb87 ground state hyperfine transition.

Team members: Bibhuti Thapa, Xu Zifang, Chan Jun Jie


Home-Built ECDL and Optical Sideband Generation

The project includes the construction and characterization of a Littrow ECDL, microwave-driven EOM sideband generation near 6.8 GHz, and optical beat-note techniques for relative frequency stabilization with an existing Rb87 trapping laser.

Team member: Liu Yiming


Thermal Drift Compensation via RF and DC Feedback for Thermal Device Control Applications

We plan to calibrate a thermally tunable microring resonator, compensate TEC-induced thermal drift using DC feedback, and evaluate gesture-image reconstruction through the AC channel.

Team members: Huang He, Ding Jiahao, Xu Anbang

Measurement of Coherent States in Phase Space

Team members: Lim Zi Way, Raghav Sah, Shawn Liew Hong Wei


Design and Construction of a Confocal Microscope for Photonic Material Characterization

Team members: Kim Sihyung, Ankush Sharma, Liang Shuyi

Resources

Some hopefully useful references should go here.

  • Bahaa E. A. Saleh, Malvin Carl Teich: Fundamentals of Photonics, Wiley; available as e-book in NUS. Excellent reference book for many optics topics.
  • Mark Fox: Quantum Optics: An Introduction, Oxford University Press; available as e-book in NUS. Nice book on traditional quantum optics topics.
  • Christopher C. Davis: Lasers and electro-optics, Cambridge; available as e-book in NUS. Good overall book on optics-related aspects useful for controlling quantum systems.

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
14.9.2026 Homo- and heterodyning basics Radiofrequency origins of mixers, optical version any quantum optics text (e.g. Mark Fox, see above)
15.9.2026 Optical Modularors 1 Mostly Electro-optical modulators, some LCD as well e.g. Davis: Laser and Electro-optics

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

Previous version of this course wiki

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 r2=x2+y2
  • Should you miss any module or functionality of this wiki, please contact me (Christian Kurtsiefer).
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