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**From**: StatFizSzeminar <statfiz AT glu.elte.hu>**To**: fizinfo AT lists.kfki.hu**Subject**: [Fizinfo] Stat Fiz Szeminarium**Date**: Wed, 06 Feb 2019 16:48:45 +0100

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ELTE TTK Fizikai Intézet

STATISZTIKUS FIZIKAI SZEMINÁRIUM

2019. február 13.

szerda

11.00

János Asbóth

Wigner SZFI

"Kitaev's Toric Code Model: Topological Quantum

Excitations and how they hide Quantum Information"

I will give an elementary introduction to Kitaev's Toric

Code model [1], which forms the basis of the "surface

code" version of topological quantum computing [2] that

IBM, Google, and Rigetti are trying to implement. The

Toric Code is an exactly solvable Hamiltonian for

spin-1/2's living on edges of a planar graph, with

n-body-interactions between spins that share a plaquette

or a vertex. The interaction terms all commute, and so

can be interpreted as counting the number (mod 2) of

elementary excitations on each plaquette and at each vertex.

These excitations can be created, moved, and fused, by

acting on the state of the system with unitary operators.

The excitations are topological similarly to vortices in

superfluids: they can be created and destroyed only pairwise

in the bulk, but can be "brought in" or "pushed out" at

suitable boundaries of the planar graph. In this sense,

boundaries of holes can store topological excitations at

no energy cost, which ensures topological degeneracy of

the ground state, and can be used to hide and - to a

certain extent - manipulate quantum bits.

[1]: Alexei Kitaev, Chris Laumann: Topological

phases and quantum computation, Les Houches lecture notes,

arXiv:0904.2771

[2]: Fowler et al: Surface codes: Towards practical large-

scale quantum computation, Phys. Rev. A 86, 032324 (2012)

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KÖZÖS RÉSZECSKE ÉS

STATISZTIKUS FIZIKAI SZEMINÁRIUM

2019. február 13.

szerda

14.15

András László

Wigner RMI

"General Relativity experiment with spin polarized

particle beams"

In experimental proposals published in the last two

decades, a so called frozen spin storage ring concept

emerged, for setting upper experimental bounds to

electric dipole moment (EDM) of charged elementary

particles with spin. In a recent paper of ours

(Class.Quant.Grav.35(2018)175003), a fully covariant

general relativistic (GR) calculation was presented

on the Earth's gravitational modification effect on

the spin transport inside such a frozen spin storage

ring. It turns out that in certain configurations,

Earth's gravity is expected to produce a similar order

of magnitude effect as the aimed EDM sensitivity, and

thus it becomes kind of realistic to experimentally

see this GR effect. If such an experiment could be

conducted, it could provide a novel test of GR: with

microscopic particles, at relativistic speeds, along

non-geodesic (forced) trajectories, and the tensorial

nature of GR would be at test, not merely the

gravitational drag. In more technical terms: the GR

correction to the so called Thomas precession could be

tested in lab. For details on the experimental idea,

we refer to: arXiv:1901.06217 (Proceedings of

Spin2018 Conference).

1117, Budapest, Pázmány P. sétány 1/A, Északi tömb 2.54

honlap: http://glu.elte.hu/~statfiz

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**[Fizinfo] Stat Fiz Szeminarium**,*StatFizSzeminar, 02/06/2019*- <Possible follow-up(s)>
**[Fizinfo] Stat Fiz Szeminarium**,*StatFizSzeminar, 02/13/2019***[Fizinfo] Stat Fiz Szeminarium**,*StatFizSzeminar, 02/20/2019***[Fizinfo] Stat Fiz Szeminarium**,*StatFizSzeminar, 02/28/2019*

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