(Untitled)
agenda-interim-2021-qirg-02-qirg-01-00

** Abstract **

We consider entanglement-based quantum networks, where pre-shared multipartite
entangled states serve as a resource to fulfill general network requests on
demand [1,2]. Such a top-down approach is unique to quantum networks, and
offers new possibilities and features such as speeding up network requests, and
network optimization independent of the underlying physical structure. The main
challenge here is to identify suitable resource states shared between network
devices that can be modified by local means such that the desired output state
(and hence the desired network functionality) can be guaranteed. This minimizes
generation times for target states, and allows for network structures that are
independent of physical links, as the resources states can be generated prior
to requests and then stored until they are needed.

We present a modular and flexible architecture to achieve this aim [1]. We also
provide a stack model for such entanglement-based networks [2], and introduce
network protocols at different layers to achieve the desired network
configuration and fulfill network requests.  Such entanglement-based networks
are independent of the topology of the underlying physical network, which can
be utilized to design optimized networks [3] tailored to the desired
functionality by choosing appropriate multipartite entangled states to store.
This allows one to minimize memory requirements and entanglement, and we
present clustering and merging algorithms for such an optimization.

Finally, we show how to make quantum networks, both standard and
entanglement-based, genuine quantum by providing them with the possibility of
handling superposed tasks and superposed addressing [4]. This extension of
their functionality relies on a quantum control register, which specifies not
only the task of the network, but also the corresponding weights in a
coherently superposed fashion. This allows one e.g. to prepare superposition of
different target states, or to send information among a superposition of
different paths. Such an approach can also be utilized in randomized
benchmarking of circuits or networks [5], where we develop protocols with
increased efficiency and functionality.  A brief overview over other relevant
network protocols, such as improved entanglement purification methods [6],
transmission of big quantum data in bipartite and multipartite scenarios [7],
and delocalized storage of information in quantum networks [8] is also provided.

References:
[1] A. Pirker, J. Wallnöfer and W. Dür, New J. Phys. 20, 053054 (2018).
[2] A. Pirker and W. Dür, New J. Phys. 21, 033003 (2019).
[3] J. Miguel-Ramiro, A. Pirker and W. Dür, Optimized quantum networks, in
preparation (2021) [4] J. Miguel-Ramiro, A. Pirker and W. Dür, E-print:
arXiv:2005.00020 . [5] Jorge Miguel-Ramiro, Alexander Pirker and Wolfgang Dür,
Phys. Rev. Research 3, 033038 (2021). [6] F. Riera-Sabat, P. Sekatski, A.
Pirker and W. Dür, E-print:arXiv:2011.07078 (to appear in PRL). [7] M. Zwerger,
A. Pirker, V. Dunjko, H.J. Briegel and W. Dür, Phys. Rev. Lett. 120, 030503
(2018); J. Wallnöfer, A. Pirker, M. Zwerger and W. Dür, Scientific Reports 9,
314 (2019); [8] Jorge Miguel-Ramiro and W. Dür, New J. Phys. 22, 043011 (2020).

** Speaker bio **

Wolfgang Dür is an Associate Prof. at the University of Innsbruck. He is
interested in all aspects of quantum information theory, where he has
contributed to various topics, including quantum networks, quantum metrology,
measurement-based quantum computation, decoherence and large-scale
entanglement, quantum information theory and multipartite entanglement. He is
also involved in teacher education, and working on didactic of physics – in
particular how to teach the mysteries of quantum mechanics at high-school level.

During his master thesis he has co-invented the quantum repeater, and worked on
various aspects of long-distance quantum communication and quantum networks in
the last 20 years, including protocols for entanglement purification and error
correction, repeater schemes for bipartite and multipartite systems and network
architectures. He is also one of the pioneers of research on multipartite
entanglement, with the W-state associated with him, but also with many
contributions in the context of graph states and measurement-based quantum
information processing, highlighting the improved robustness of such an
approach in the context of quantum computation and communication. He is also
interested in fundamental aspects of quantum mechanics, including Bell
inequalities and the treatment of macroscopic quantum systems, in particular
w.r.t. to limitations to prepare, maintain, measure and use such systems. In
addition he has contributed to quantum metrology showing how to utilize methods
from quantum error correction and quantum control to overcome or reduce the
influence of noise and imperfections on sensing of local and non-local
quantities.

Research overview:

Publications in refereed journals: >130 (>35 in Phys.Rev.Lett., Nature, Nature
Physics) Citations: >6000 (ISI citation index), h-Index 34; >17600 (Google
scholar), h-Index 55

Talks at conferences/workshops: >20

Selected works:
H.-J. Briegel, W. Dür, J. I. Cirac, and P. Zoller,  Phys. Rev. Lett. 81, 5932
(1998). ``Quantum repeaters: The role of imperfect local operations in quantum
communication'' W. Dür , G. Vidal and J. I. Cirac, Phys. Rev. A 62, 062314
(2000). ``Three qubits can be entangled in two inequivalent ways'' –  selected
as 50th anniversary milestone paper, https://journals.aps.org/pra/50th H. J.
Briegel, D.E. Browne, W. Dür, R. Raussendorf and M. Van den Nest, Nature
Physics 5, Vol. 1, 19-26 (2009). `` Measurement-based quantum computation’’ W.
Dür, M. Skotiniotis, F. Fröwis and B. Kraus, Phys. Rev. Lett. 112, 080801
(2014). `` Improved quantum metrology using quantum error-correction’’ P.
Sekatski, M. Skotiniotis, J. Kolodynski and W. Dür, Quantum 1, 27 (2017);
``Quantum metrology with full and fast quantum control‘‘ M. Zwerger, A. Pirker,
V. Dunjko, H.J. Briegel and W. Dür, Phys. Rev. Lett. 120, 030503 (2018). ``
Long-range big quantum-data transmission ‘‘ F. Fröwis, P. Sekatski, W. Dür,
N.Gisin and N. Sangouard,  Rev. Mod. Phys. 90, 025004 (2018), ``Macroscopic
quantum states: measures, fragility and implementations‘‘ A. Pirker and W. Dür,
New J. Phys. 21, 033003 (2019), ``A quantum network stack and protocols for
reliable entanglement-based networks ‘‘ Andrea López-Incera and Wolfgang Dür.
Entangle me!, A game to demonstrate the principles of quantum mechanics, Am. J.
Phys. 87, 95 (2019) (Editor's pick).