# Norbert Lutkenhaus

Professor, Executive Director, Institute for Quantum Computing

Location: QNC 4129

Phone: 519-888-4567 x32870

## Biography

Professor Lütkenhaus' research group explores the interface between quantum communication theory and quantum optical implementations. They translate between abstract protocols (described by qubits) and physical implementations (described for example by laser pulses); they benchmark implementations to properly characterize quantum advantage and exploit quantum mechanical structures for use in quantum communication.

## Research Interests

- Quantum communication and its quantum optical implementations
- The theory of practical quantum key distribution systems
- Methods and tools for entanglement verification
- Linear optic quantum logic operation and measurement implementation
- Quantum state detection and estimation theory
- Quantum Science
- Quantum Communication
- Quantum Information Processing

## Scholarly Research

Professor Lütkenhaus runs the Optical Quantum Communication Theory Group in which they research:
1. Quantum Key Distribution,
2. Quantum Repeater,
3. Quantum Communication Complexity
Most QKD protocols that we analyze today have a high symmetry in signals and measurements. Key rate calculations are basically multi-parameter optimization with a non-linear objective function. The symmetry of QKD protocols allows us often to perform this optimization analytically. However, imperfections in experimental realizations often break the symmetry: Think for example at beam-splitters that do not have exact 50/50 splitting ratios, detectors that differ in their detection efficiency. Many protocols also have too many parameters, even if some symmetry persists. This often includes protocol implementations with side-channels (see below).Our group develops methods that allow to calculate canonically secret key rates for arbitrary QKD protocols. This method is based on the theory of convex optimization and allows for efficient numerical evaluations.
The TGW bound gives an upper bound on how much secret key per mode we can get by using lossy bosonic channels (free-space links, optical fiber). The goal of a quantum repeater is to design set-ups that use lossy bosonic channels, but augments them by intermediate repeater stations and classical communication channels between the stations. The goal is to do better than to send signals directly through the lossy bosonic channels without the repeater stations. Our particular interest is to find out what is the simplest set-up to beat this bound, no matter what the distance is. Note that we are not particularly interested whether the resulting secret key rate scales polynomially or exponentially, as long as it is better than what the TGW bound offers. Our research approaches this question from both sides: no-go theorems to identify what does not work, and specific protocols that tell us what works.

## Education

- 2003 Habilitation, University Erlangen-Nürnberg, Nürnberg, Bavaria, Germany
- 1996 PhD Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom
- 1993 MSc Physics, University Ludwig-Maximilians-Universität München, Munich, Germany
- 1990 BSc Physics, University RWTH, Aachen, Germany

## Awards

- 2015, Outstanding Referee Award, American Physical Society
- 2009, Outstanding Performance Award, University of Waterloo

## Professional Associations

- 2015 - present United Kingdom Quantum Communications Hub, Member, Advisory Board
- 2015-present QCrypt, Member of Steering Committee
- 2014 - present ETSI QKD-ISG, Vice-Chair

## Affiliations and Volunteer Work

- Faculty, Institute for Quantum Computing
- Cross Appointed faculty, Department of Applied Mathematics
- Affiliate Member, The Perimeter Institute for Theoretical Physics
- Affiliate Member, Centre for Applied Cryptographic Research

## Teaching*

- PHYS 115 - Mechanics
- Taught in 2019, 2020

- PHYS 768 - Special Topics in Quantum Information Processing
- Taught in 2020, 2022, 2024

- QIC 890 - Topics in Quantum Information
- Taught in 2020, 2022, 2024

* Only courses taught in the past 5 years are displayed.

## Selected/Recent Publications

- R. Namiki; “Schmidt-number benchmarks for continuous-variable quantum devices”,Phys. Rev. A 93, 052336 (2016)
- C. Pfizer, N. Lütkenhaus, S. Wehner, P. J. Coles, ; “Sifting attacks in finite-size quantum key distribution”, New Journal of Physics, 18, 053001, (2016)
- S. Muralidharan, L. Li, J. Kim, N. Lütkenhaus, M.D. Lukin, L. Jiang, “Efficient long distance quantum communication”,Nature Scientific Reports 6, 20463, (2016)
- W.P. Schleich, K. S. Ranade, C. Anton, M. Arndt, M. Aspelmeyer, M Bayer, G. Berg, T. Calarco, H. Fuchs, E. Giacobino, M. Grassl, P. Hänggi, W. M. Heckl, I.. Hertel, S.Huelga, F. Jelezko, B. Keimer, J.P. Kotthaus, G. Leuchs, N. Lütkenhaus, U.Maurer, T. Pfau, M. B. Plenio, E. M. Rasel, O. Renn, C. Silberhorn, J. Schiedmayer, D. Schmitt-Landsiedel, K. Schönhammer, A.Ustinov, P.Walther, H. Weinfurter, E. Welzl, R. Wiesendanger, S. Wolf, A. Zeilinger, P. Zoller, “Quantum Technology: From research to application”, Applied Physics B,122,130, (2016)
- D.Luong , L. Jiang, J. Kim, N. Lütkenhaus, “Overcoming lossy channel bounds using a single quantum repeater node”, Applied Physics B, 122, 96 , (2016)
- J.M. Arrazola, P. Wallden, E. Andersson; “Multiparty quantum signature schemes”;Quantum Information and Computation, 16, 435-464 (2016)

## Patents

- Lütkenhaus, N., Ma, X.F., 2016. System and method for quantum key distribution. [US Patent Office] Patent number 9,294,272, filed September 12, 2012 (issued, 2013). [WIPO Patent] Patent number WO/2013/037062, filed September 12, 2012 (issued, 2013).
- Lütkenhaus, N., 2011. Polarization to Phase Converter. [US Patent Office] Patent number 8,068,741, filed April 10, 2002 (issued, 2004).
- Lütkenhaus, N., Cohen, Jayson L., Lo, Hoi-Kwong., 2007. Efficient Use of Detectors for Random Number Generation. [US Patent Office] Patent number 7,197,523, filed May 3, 2002 (issued, 2003).