# Quantum information processing with photons

### Tuesday, 14 Jan. 2014, 17:30 - 18:30

**Presenter:** Stefanie Barz; Universität Wien, Quantenoptik, Quantennanophysik und Quanteninformation

**Where:** Lise-Meitner-Hörsaal, Universität Wien, Fakultät für Physik 1090 Wien, Strudlhofgasse 4/Boltzmanngasse 5, 1. Stock

Vortrag im Rahmen der Verleihung des Loschmidt-Preises 2013 der Chemisch-Physikalischen Gesellschaft.

*Abstract:* 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. In a second experiment, a new concept in quantum computing called blind quantum computing is implemented [2, 3]. Blind quantum computing shows an additional fundamental advantage of quantum over classical computation: a computation can be made private. Thus, 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. This demonstrates a significant progress towards the realization of unconditionally secure quantum cloud computing and may become a key ingredient in real-life applications. Finally, the concept of blind quantum computing is applied to the field of complexity theory, and in particular 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]. This verification procedure is a first step towards answering the open question of whether it is possible to verify that a quantum computation is correct without having access to quantum resources.

[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)