ELFT HÍRADÓ

[StatFizSzeminar <statfiz AT glu.elte.hu>]

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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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