Quantum information processing with photons
Dr. Stefanie Barz (Vienna Center for Quantum Science and Technology, University of Vienna)

Quantum physics has revolutionized our understanding of information processing and enables computational speed-ups that are unattainable using classical computers. In this talk I will present a series of experiments in the field of photonic quantum computing.
The first experiment is in the field of photonic state engineering and realizes the generation of heralded polarization-entangled photon pairs [1]. It overcomes the limited applicability of photon-based schemes for quantum information processing tasks, which arises from the probabilistic nature of photon generation.
The second experiment uses polarization-entangled photonic qubits to implement blind quantum computing, a new concept in quantum computing [2, 3]. Blind quantum computing enables a nearly-classical client to access the resources of a more computationally-powerful quantum server without divulging the content of the requested computation.
A third experiment shows how the concept of blind quantum computing can be applied to the field of verification. A new method is developed and experimentally demonstrated to verify the correctness and the entangling capabilities of a quantum computer [4].
Finally, I will present an experiment realizing a measured universal two-qubit photonic quantum processor by applying two consecutive CNOT gates to the same pair of polarization-encoded qubits. To demonstrate the flexibility of our system, we implement various instances of the quantum algorithm for the solving of systems of linear equations [5].

[1] S. Barz, G. Cronenberg, A. Zeilinger, and P. Walther, Nature Photonics 4, 553 (2010)
[2] A. Broadbent, J. Fitzsimons and E. Kashefi, in Proceedings of the 50th Annual Symposium on Foundations of Computer Science, 517 (2009)
[3] S. Barz, E. Kashefi, A. Broadbent, J. Fitzsimons, A. Zeilinger, and P. Walther, Science 335, 303 (2012)
[4] S. Barz, J. Fitzsimons, E. Kashefi, and P. Walther, Nature Physics 9, 727 (2013)
[5] S. Barz, I. Kassal, M. Ringbauer, Y. O. Lipp, B. Dakic, A. Aspuru-Guzik, P. Walther, arXiv:1302.1210