Current Research Interests

Quantum Key Distribution

  • Unstructured QKD
    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.Recent Publications:

  • Side-Channel
  • Network QKD
  • Development of Optical Protocols

Quantum Repeater

  • Analysis of Quantum Repeater Architectures
    What architectures should Quantum Repeaters eventually have to avoid conceptional bottlenecks in their development? We work closely with the groups of Liang Jiang (Yale) and Jungsang Kim (Duke) on this question.Recent Publications:

    • S. Muralidharan, J. Kim, N. Lütkenhaus, M. D. Lukin, L. Jiang, Ultrafast and fault-tolerant quantum communication across long distances
      Phys. Rev. Letters, Vol. 112, 250501 (2014)
    • S. Muralidharan, L. Li, J. Kim, N. Lütkenhaus, M.D. Lukin, L. Jiang, Efficient long distance quantum communication, Nature Scientific Reports 6, 20463, (2016)
    • R. Namiki, L. Jiang, J. Kim, N. Lütkenhaus; “Role of syndrome information on a one-way quantum repeater using teleportation-based error correction”, Phys. Rev. A 94, 052304 (2016){DARPA,IndustryCanada,NSERC Discovery}[RP]
  • Beating the repeaterless bounds for lossy bosonic channels
    The repeaterless bounds (TGW14PLOB15) 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 repeaterless bounds 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.Recent Publications:

      • Could Gaussian regenerative stations act as quantum repeaters?
        R. Namiki, O. Gittsovich, S. Guha, N. LütkenhausPhys Rev. A 90, 062316 (2014)
      • Overcoming lossy channel bounds using a single quantum repeater node
        David Luong, Liang Jiang, Jungsang Kim, Norbert Lütkenhaus
        Appl. Phys. B, 122:96 (2016)

    Quantum Communication & Information Complexity

    •  Optical Implementations of Protocols with Quantum Advantage
      We are working on protocols that show a quantitative quantum advantage over classical protocols and can be implemented with simple optical tools such as laser pulses and threshold detectors.Recent Publications:

      • J.M. Arrazola, N. Lütkenhaus, Quantum fingerprinting with coherent states and a constant mean number of photons, Phys. Rev. A, 89, 062305 (2014)
      • J. M. Arrazola, N. Lütkenhaus, Quantum Communication with Coherent States and Linear Optics, Phys. Rev. A, 90, 042335 (2014)
      • Feihu Xu,Juan Miguel Arrazola, Kejin Wei, Wenyuan Wang, Pablo Palacios-Avila, Chen Feng, Shihan Sajeed, Norbert Lütkenhaus, Hoi-Kwong Lo; Experimental quantum fingerprinting with weak coherent states,
        Nature Communications 6, 8735, (2015)
      • J.M. Arrazola, M Karasamanis, N. Lütkenhaus, Practical quantum retrieval games, Phys Rev A 93 062311 (2016)
      • J. M. Arrazola, D. Touchette, Quantum Advantage on Information Leakage for Equality, arXiv:1607.07516
    • Network Applications