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Foto (Matthias Groppe): Holographie-Apparatur von Herrn Dr. Andreas Redler

Foto: Foto (Matthias Groppe): Holographie-Apparatur von Herrn Dr. Andreas Redler

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Multi-walker Quantum Walk

Quantum walks describe the coherent propagation of a quantum particle on a prescribed network. Its dynamics are governed by a coin operation which acts on the internal degree of freedom of the walker and a subsequent step operation which shifts the walker to the left or to the right, the positional external degree of freedom, depending on the internal degree of freedom.

Similar versatile as its classical counterpart, the random walk, quantum walks exhibit a proven framework for developing different quantum algorithms, e.g. in quantum computing, quantum search or quantum state transfer, and for the understanding of quantum transport and localization phenomena, e.g. in photosynthesis.

In the group we have already successfully established several photonic quantum walk implementations. They are based on fiber or free-space loop architectures using time-multiplexing techniques. With these setups we have already demonstrated quantum walks in one and two dimensions, quantum-to-classical transitions, Anderson localization, graph percolation and recurrence. You can find all our publications in the corresponding section of our group homepage.

The next step will be to combine such a quantum walk loop architecture with an efficient single photon waveguide source, based on periodically poled KTP, to study multi-particle effects. In the group we have already a long-time experience in building single photon sources. The content of the PhD thesis therefore is to build a quantum walk experiment for a wavelength of 1550nm and setup a compatible single photon source. The goal is to minimize the network losses and to increase the source efficiency such that high step numbers for several (>= 3) walkers can be achieved.

With fast electro-optical modulators we can directly address the internal degree of freedom position- and time-dependently, which will allow us to investigate the time evolution of the walkers facing a noisy environment. For weak noise the quantum interferences will not wash out immediately, but surprising branching patterns occur in the intensity distribution which are already found in completely different contexts, e.g. ocean and tsunami waves, electron waves in semiconductors with defects or microwave flow in cavities in presence of disorder. Their impact on the multi-walker entanglement in the quantum walk evolution needs to be investigated.

You will work within the quantum walk project together with other PhD students and Post-Docs, so you can benefit from our knowledge and expertise. But you will have also the freedom to work independently on your own setup.

The thesis will contain:

·        Rebuilding of a time-multiplexing quantum walk adapted to the source characteristics

·        Setting up a compatible single photon source

·        Experimental work with fast switching electro-optical modulators

·        Numerical simulations of noise and decoherence effects in many-particle systems

·        Collaborations within a large network of national and international scientists of different fields

·        Presentation of your results at workshops and conferences

Interested? Please get in touch with


Dr. Sonja Barkhofen

Phone 05251 60 5878

Mail: sonja.barkhofen@upb.de


Prof. Dr. Christine Silberhorn

Phone: 05251 60 5884
Mail: christine.silberhorn@upb.de 

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