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Author:Kreula, Juha
Title:Spin-asymmetric Josephson effect in optical superlattices
Spin-asymmetrinen Josephsonin ilmiö optisissa superhiloissa
Publication type:Master's thesis
Publication year:2013
Pages:[6] + 79      Language:   eng
Department/School:Teknillisen fysiikan laitos
Main subject:Fysiikka (laskennallinen fysiikka)   (Tfy-105)
Supervisor:Törmä, Päivi
Instructor:Massel, Francesco ; Heikkinen, Miikka
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Location:P1 Ark Aalto  155   | Archive
Keywords:ultracold Fermi gases
Josephson effect
optical lattice
Hubbard model
time-evolving block decimation
ultrakylmät Fermi-kaasut
Josephsonin ilmiö
optinen hila
Hubbardin ilmiö
time-evolving block decimation -algoritmi
Abstract (eng): This work considers the theory of ultracold Fermi gases.
We study the spin-asymmetric Josephson effect where the spin components of a Cooper pair feel spin-dependent potentials during the tunneling process and as a result oscillate at the same Josephson frequency but with different amplitudes.
This contrasts the conventional interpretation of the Josephson effect in which the Cooper-paired spins 'tunnel together'.

Here, we propose a new experimental arrangement to detect the yet-unobserved spin-asymmetric Josephson effect.
We investigate two-component fermions in a one-dimensional spin-dependent optical superlattice described by a Fermi-Hubbard Hamiltonian and simulate the dynamics of the set-up with the essentially exact time-evolving block decimation (TEBD) numerical method.

We demonstrate that the characteristics of the spin-asymmetric Josephson effect, frequency-synchronized particle number oscillations with spin-asymmetric critical currents, are present in the system.
We show that the Josephson frequency depends only on the sum of the spin-dependent potential offsets between two adjacent sites in the super-lattice.
We further exhibit that significant asymmetries of over 10% in the critical currents of the spin components are feasible.
We also evince that the properties of the particle currents in the super-lattice system agree with the analytical results given by a Hubbard dimer model consisting of only one unit cell of the super-lattice in the strongly interacting limit.
Abstract (fin): Tämä työ käsittelee ultrakylmien Fermi-kaasujen teoriaa.
Työssä tutkitaan spinasymmetristä Josephsonin ilmiötä, jossa Cooperin parin spin-komponentteihin kohdistuu tunneloinnissa spinistä riippuva potentiaali.
Tämän seurauksena spinkomponentit oskilloivat samalla Josephsonin taajuudella mutta eri amplitudeilla.

Työssä tutkitaan uudenlaista koejärjestelyä toistaiseksi vielä havaitsemattoman spinasymmetrisen Josephsonin ilmiön löytämiseksi.
Ehdotettu koeasetelma koostuu fermioneista yksiulotteisessa optisessa superhilassa, jota kuvataan Fermi-Hubbardin mallilla ja jonka aikakehitystä mallinnetaan time-evolving block decimation (TEBD) -algoritmilla.

Työssä osoitetaan, että spin-asymmetriselle Josephsonin ilmiölle tyypilliset ominaisuudet eli saman taajuiset mutta amplitudiltaan erisuuruiset hiukkasvirrat löytyvät tutkitusta systeemistä.
Työssä näytetään myös, että Josephsonin taajuus riippuu vain kahden vierekkäisten hilapaikan potentiaalierojen summasta ja että systeemillä on mahdollista saavuttaa yli 10 prosentin epäsymmetria Josephson-virran amplitudeissa.
Lisäksi osoitetaan, että superhilan hiukkasvirtojen ominaisuudet voidaan selittää kahdesta hilapaikasta koostuvalla Hubbardin mallilla voimakkaan vuorovaikutuksen rajalla.
ED:2013-06-05
INSSI record number: 46834
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