Postdoc in Digital Signal Processing for Quantum Cryptography in Telecom Networks

DTU Physics
Friday 27 Oct 17

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Are you an expert in digital signal processing for telecommunication systems and looking for a new opportunity? We are offering a research position for the development of highly efficient receivers for new quantum communication systems with a prime focus on Continuous-Variable Quantum Communication and Cryptography.

Quantum cryptography, or more specifically quantum key distribution, solves the task of distributing a key between two parties whose security and secrecy is information theoretically proven – in contrast to classical algorithms like Diffie-Hellman which are only computationally secure.

To achieve this goal continuous variable quantum key distribution systems use Gaussian distributed quadrature amplitude modulated coherent states and optical heterodyne detection with a free-running local oscillator, a setup similar to classical telecommunication systems with the difference that the coherent states have to overlap and classical noise sources are detrimental. Digital signal processing is used for pairing the transmitter and the receiver. The aim of the project is to develop suitable algorithms that can work with the low signal-to-noise ratio (in the order of 0.5).

The project will be hosted by the section for Quantum Physics and Information Technology (QPIT) at the Department of Physics, Technical University of Denmark (DTU) headed by Prof. Ulrik L. Andersen. It will be carried out in close collaboration with Assoc. Prof Darko Zibar from the High-Speed Optical Communications group at the Department of Photonics Engineering.   

The overarching vision of the project is to establish a secure quantum communication network in the city of Copenhagen based on continuous variable quantum key distribution. Within the project we will have a special focus on developing rugged, robust, high-efficiency and high rate systems compatible with field implementations. We are working towards the construction of device independent systems that are resilient against any potential device attacks. It is an interdisciplinary and innovative project that involves experts within cryptography, classical post processing, hardware development, fabrication and security analysis.

The project is part of the Quantum Innovation Center – Qubiz (, which is a joint Danish national center including DTU, Copenhagen University and Aarhus University with the mission to harness the very strong Danish research positions within quantum technology for creating new quantum technology businesses. The project is also part of the Center for Quantum Technologies – QuantumDTU ( 

QPIT conducts widely recognized research within a range of diverse topics such as continuous-variable quantum information processing, quantum enhanced sensing, and engineering of solid state quantum systems. We have extensive experience in continuous variable quantum key distribution and quantum information (1-3).   

High-speed optical communication group has extensive experience in the field of coherent optical communication. The group has made significant contributions to the field in terms of novel receiver architectures. The work has been published in the top journal and conferences within the field.

(1) Pirandola et al., “High-rate measurement-device-independent quantum cryptography”, Nature Photonics 9, 397 (2015). - Selected in the top-five Danish research of the year 2015 by Ingeniøren.
(2) Madsen et al., “Continuous variable quantum key distribution with modulated entangled states”, Nature Communications 3, 1083 (2012)
(3) Marshall et al., “Continuous-variable quantum computing on encrypted data”, Nature Communications 7, 13764 (2016)

Responsibilities and tasks
We are looking for a highly motivated candidate that will be in charge of developing, optimizing, implementing and testing digital signal processing algorithms for quantum key distribution receivers. The special challenge is the requirement for very low signal-to-noise ratios in quadrature amplitude modulated coherent signals.

Some of the tasks you are involved in are: 

  • Development of algorithms for equalization, carrier and clock recovery in the very low SNR regime of quantum key distribution
  • Implementation of the algorithms in matlab or python
  • Optical link implementation for testing the algorithms in close collaboration with the other team members
  • Engaging in a close collaboration between DTU Physics and DTU Fotonik
  • Supervision of students

Candidates should have a PhD degree or equivalent.

You are expected to have experience with optical communication and digital signal processing and are familiar with the standard approaches for pairing transmitters and receivers including carrier and clock recovery with and without pilot tones.   


  • You have experience with matlab or python
  • Experience with hardware implementations of algorithms is considered a plus
  • You have the ability to work independently, to plan and carry out complicated tasks
  • You are highly motivated and dedicated to carry out research and innovation at the highest standards.
  • You thrive on collaboration and teamwork

We offer
DTU is a leading technical university globally recognized for the excellence of its research, education, innovation and scientific advice. We offer a rewarding and challenging job in an international environment. We strive for academic excellence in an environment characterized by collegial respect and an academic freedom tempered by responsibility.

Salary and terms of employment
The appointment will be based on the collective agreement with the Danish Confederation of Professional Associations. The allowance will be agreed with the relevant union. The period of employment is 2 years.

The work will take place at the DTU campus in Lyngby. 

You can read more about career paths at DTU here.  

Further information
Informal inquiries can be made to Assoc. Prof. Darko Zibar,, Assist. Prof. Tobias Gehring, or Prof. Ulrik L. Andersen,  

Application procedure
Please submit your online application no later than 24 November 2017 (Local time). Applications must be submitted as one PDF file containing all materials to be given consideration. To apply, please open the link "Apply online", fill in the online application form, and attach all your materials in English in one PDF file. The file must include: 

  • Application (cover letter)
  • CV
  • Diploma (MSc/PhD)
  • List of publications
Applications and enclosures received after the deadline will not be considered.

All interested candidates irrespective of age, gender, disability, race, religion or ethnic background are encouraged to apply.

QPIT's vision is to understand, engineer and control complex quantum systems of light and matter, and to exploit these systems for quantum information processing and quantum metrology. We are a large, highly international research group of students and staff with diverse backgrounds. We have a friendly and dynamic research environment with close, daily interaction among all group members and strong collaborations with many academic and industrial partners. Technical support is excellent with electronics and process engineers embedded in the section and a large capacity, skilled mechanical workshop at the Department. We are situated just north of Copenhagen at the Lyngby campus of DTU, one of the leading technical universities of Northern Europe, where we enjoy newly renovated office and lab space.

DTU is a technical university providing internationally leading research, education, innovation and scientific advice. Our staff of 5,800 advance science and technology to create innovative solutions that meet the demands of society; and our 11,000 students are being educated to address the technological challenges of the future. DTU is an independent academic university collaborating globally with business, industry, government, and public agencies.