Universität Wien
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260041 SE Quantum non-locality (2020S)

5.00 ECTS (2.00 SWS), SPL 26 - Physik
Continuous assessment of course work
Moodle

Registration/Deregistration

Note: The time of your registration within the registration period has no effect on the allocation of places (no first come, first served).

Details

max. 15 participants
Language: English

Lecturers

Classes

Mi 14:00-15:30 Uhr, IQOQI, Seminar room
Begin: 11.03.2020

Information

Aims, contents and method of the course

As shown by Bell, the correlations established by two separate observers conducting measurements over a joint quantum system do not admit, in general, a classical explanation (namely, they are non-local). Hence a single quantum experiment is enough to rule out all classical theories. Following Bell’s spirit, in this course we will learn what makes correlations physical (classical, quantum or otherwise) and how different assumptions on the underlying experimental setups translate at the level of correlations. Our starting point will be the mathematical structure of the set of quantum correlations. We will argue that correlations in any future theory superseding quantum physics cannot be very different from those of the quantum set (although there is room for discrepancy). We will also show that strong enough quantum correlations can severely restrict the parameters of the quantum formalism used to describe the experiment. In fact, in some situations, correlations alone can fully determine the structure of the underlying state and measurement operators involved in a Bell-type experiment.

Assessment and permitted materials

Each student is assigned a recent research article on quantum nonlocality. Through a series of one-to-one communications between the teacher and each student, the teacher makes sure that the student has correctly understood the contents of the paper (this part will not be evaluated). Next, the student must present, one by one and in the dates agreed with the teacher, three essays on popular science where the student explains the article to: a) a seven-year-old kid; b) an adult with no scientific background; c) another physicist. After each essay is delivered, the student receives feedback from the teacher for the next essay (this might involve further rounds of communication), as well as a numerical grade. The grade is decided on the basis of how well the main message of the paper was summarized and adapted to the knowledge of the intended reader. The final grade will be the rounded arithmetic average of the grades of each essay.

Minimum requirements and assessment criteria

Linear algebra and quantum physics.

Examination topics

1. Classical black boxes

a) Bell’s theorem. Characterization of Bell nonlocality.

b) Hidden variable models with secret communication.

c) Boxes in large symmetric systems

2. Quantum black boxes

a) The limits of quantum correlations: Tsirelson’s bound. XOR games.

b) Finite dimensions are not enough: non-closure of the set of quantum boxes.

c) Characterization of quantum boxes

3. Classifying general physical theories by their correlations

a) Physical sets of correlations. Closure under wirings: definition, properties, examples. Monotones under wirings.

b) Do we expect correlations to be very different from quantum? Five device-independent physical principles to constrain physical correlations: no-trivial communication complexity, no-advantage for nonlocal computation, information causality, macroscopic locality and local orthogonality.

c) The limitations of black box physics: the almost-quantum set of correlations

3. Applications of quantum non-locality

a) Lower bounding the Hilbert space dimension with correlations

b) Self-testing: quantum systems which verify themselves

Reading list

Nicolas Brunner, Daniel Cavalcanti, Stefano Pironio, Valerio Scarani, Stephanie Wehner, Bell nonlocality, Rev. Mod. Phys. 86, 419 (2014).

Nicolas Brunner, Stefano Pironio, Antonio Acin, Nicolas Gisin, Andre Allan Methot, Valerio Scarani, Testing the Hilbert space dimension, Phys. Rev. Lett. 100, 210503 (2008).

Ben Lang, Tamas Vertesi, Miguel Navascues, Closed sets of correlations: answers from the zoo, Journal of Physics A 47, 424029 (2014).

Miguel Navascues, Tamas Vertesi, Bounding the set of finite dimensional quantum correlations, Phys. Rev. Lett. 115, 020501 (2015).

Jean-Daniel Bancal, Stefano Pironio, Antonio Acin, Yeong-Cherng Liang, Valerio Scarani, Nicolas Gisin, Quantum nonlocality based on finite-speed causal influences leads to superluminal signaling, Nature Physics 8, 867 (2012).

Jordi Tura, Gemma De las Cuevas, Remigiusz Augusiak, Maciej Lewenstein, Antonio Acín, J. Ignacio Cirac, Energy as a detector of nonlocality of many-body spin systems, Phys. Rev. X 7, 021005 (2017).

Miguel Navascués, Yelena Guryanova, Matty J. Hoban, Antonio Acín, Almost quantum correlations, Nature Communications 6, 6288 (2015).

G. Brassard, H. Buhrman, N. Linden, A. A. Methot, A. Tapp and F. Unger, F., Limit on Nonlocality in Any World in Which Communication Complexity Is Not Trivial, Phys. Rev.
Lett., 96 250401, (2006).

N. Linden, S. Popescu, A. J. Short, and A. Winter, Quantum Nonlocality and Beyond: Limits from Nonlocal Computation, Phys. Rev. Lett. 99, 180502 (2007).

M. Pawlowski, T. Paterek, D. Kaszlikowski, V. Scarani, A. Winter, and M. Zukowski, Information Causality as a physical principle, Nature 461, 1101 (2009).

M. Navascués and H. Wunderlich, A glance beyond the quantum model, Proc. Royal Soc. A 466:881-890 (2009).

T. Fritz, A. B. Sainz, R. Augusiak, J. B. Brask, R. Chaves, A. Leverrier and A. Acín, Local orthogonality as a multipartite principle for quantum correlations, Nature Communications 4, 2263 (2013).

Association in the course directory

M-VAF A 2, M-VAF B, MaV 5, MaG 18

Last modified: Mo 23.03.2020 09:08