ITP-quantumseminare

itp-quantumseminare@lists.phys.ethz.ch

July 2020

1 participants
2 discussions

tomorrow's group meeting @ 1500
by Joe Renes 13 Jul '20

13 Jul '20

Hi all, Tomorrow Giulia Mazzola will tell us about her master thesis at IBM, on "Simulating Yang-Mills Lattice Gauge Theories on Digital Quantum Computers". See below for the abstract. Here's the link: https://ethz.zoom.us/j/362994444. Best, -joe Abstract: Gauge theories represent the most successful description of elementary particles and their fundamental interactions. In computing the real-time dynamics in lattice gauge theories however, standard classical numerical methods suffer from an exponential scaling of the required resources with growing system size and thus, display severe limitations for the simulation of real-time phenomena. Quantum computers might provide a potential framework to tackle this problem as lattice gauge theories can be efficiently represented using resources which are polynomial in the system size. Here, we review different encoding schemes for non-abelian Yang-Mills lattice gauge theories with dynamical fermionic matter such as quantum chromodynamics in arbitrary dimensions on digital circuit-based quantum computers. On the other hand, we apply promising variational quantum algorithms for near-term quantum computation to study the groundstate properties of small abelian lattice gauge theory systems like quantum electrodynamics in (1+1)- and (2+1)-spacetime dimensions. Specifically, we investigate the performance of physically motivated variational forms that preserve the gauge symmetry of the theory, thereby allowing for an efficient sampling in the physical Hilbert space of states. Therewith, we demonstrate the phenomenon of flux-string breaking in form of a phase diagram and further present the results of simulations on real superconducting quantum hardware as a proof-of-principle. By generalizing this scheme to non-abelian Yang-Mills theories, such gauge invariant variational forms might be included in variational real-time evolution algorithms, providing a potential path towards simulating real-time dynamics of lattice gauge theories on near-term quantum devices.

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tomorrow's group meeting at 3pm
by Joe Renes 06 Jul '20

06 Jul '20

Hi all, Tomorrow Anne-Catherine de la Hamette will tell us about her master thesis with Thomas Galley at Perimeter Institute, entitled "Quantum reference frames: a relational approach to quantum theory". See the abstract below for more details. Zoom link: https://ethz.zoom.us/j/362994444. Best, -joe Abstract Reference frames are essential in the description of physical phenomena. Often used implicitly, they appear as idealized classical systems. Following a more fundamental approach and considering them as physical systems subject to the laws of quantum mechanics, they become quantum reference frames (QRFs). A rigorous treatment of QRFs is indispensable both in the construction of a relational theory of quantum mechanics and of quantum gravity. Not only do the properties of QRFs give rise to numerous applications in quantum information; they are also expected to improve our understanding of observer-dependent settings such as the Wigner's friend experiment. In this talk, we present a relational formalism based on the group and representation theoretic nature of reference frames. By identifying coordinate systems with elements of a symmetry group G, we define a general operator for reversibly transforming between QRFs associated to the group G. We explore the properties of this operator in different cases and show how it gives rise to transformations between coordinate systems which are `in a superposition' relative to other coordinate systems. Finally, we apply the relational formalism and the change of reference system developed in this work to the Wigner's friend thought experiment.

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