Search results for "kvanttifysiikka"
showing 10 items of 55 documents
Time-Linear Quantum Transport Simulations with Correlated Nonequilibrium Green’s Functions
2023
We present a time-linear scaling method to simulate open and correlated quantum systems out of equilibrium. The method inherits from many-body perturbation theory the possibility to choose selectively the most relevant scattering processes in the dynamics, thereby paving the way to the real-time characterization of correlated ultrafast phenomena in quantum transport. The open system dynamics is described in terms of an “embedding correlator” from which the time-dependent current can be calculated using the Meir-Wingreen formula. We show how to efficiently implement our approach through a simple grafting into recently proposed time-linear Green’s function methods for closed systems. Electron…
Developments in many-body theory of quantum transport and spectroscopy with non-equilibrium Green's functions and time-dependent density functional t…
2015
The problem of quantum dynamics in open systems has gained attention in recent decades and not the least due to the advances made in quantum transport in molecular systems. The main motivation behind quantum transport and molecular electronics is the futuristic goal to be able at some point to replace, or to complement, the silicon-based technology and to make the electronic devices faster. On a fundamental level, one has to deal with time-dependent processes where electron-electron or electron- phonon interactions are of great importance, and they can cause profound quantitative and qualitative changes on the physical and dynamical properties of electronic systems compared to the non-inter…
Mitä kirjoittaisit viestiin tulevaisuuden ihmiskunnalle?
2023
Kvanttitietokone voi laskea minuutissa laskun, jota tavallinen tietokone laskee vuosisadan
2023
Experimental study of quantum fluctuations in titanium nanowires in highly resistive environment
2009
One-loop corrections to light cone wave functions: the dipole picture DIS cross section
2018
We develop methods needed to perform loop calculations in light cone perturbation theory using a helicity basis, refining the method introduced in our earlier work. In particular this includes implementing a consistent way to contract the four-dimensional tensor structures from the helicity vectors with d-dimensional tensors arising from loop integrals, in a way that can be fully automatized. We demonstrate this explicitly by calculating the one-loop correction to the virtual photon to quark-antiquark dipole light cone wave function. This allows us to calculate the deep inelastic scattering cross section in the dipole formalism to next-to-leading order accuracy. Our results, obtained using …
Three-dimensional skyrmions in spin-2 Bose–Einstein condensates
2017
We introduce topologically stable three-dimensional skyrmions in the cyclic and biaxial nematic phases of a spin-2 Bose-Einstein condensate. These skyrmions exhibit exceptionally high mapping degrees resulting from the versatile symmetries of the corresponding order parameters. We show how these structures can be created in existing experimental setups and study their temporal evolution and lifetime by numerically solving the three-dimensional Gross-Pitaevskii equations for realistic parameter values. Although the biaxial nematic and cyclic phases are observed to be unstable against transition towards the ferromagnetic phase, their lifetimes are long enough for the skyrmions to be imprinted…
Polkuintegraaliperustilamenetelmä
2017
Tutustutaan lyhyesti polkuintegraaliperustilamenetelmään, joka on numeerinen satunnaislukumenetelmä kvanttimekaanisten monihiukkasjärjestelmien ominaisuuksien laskemiseen nollalämpötilassa. Ensiksi käydään läpi menetelmän syntyperä ja suhde muihin samankaltaisiin menetelmiin. Sitten tarkastellaan menetelmän taustalla vallitsevaa teoriaa lähtien kvanttimekaniikan ja tilastollisen fysiikan perustuksista. Teoriaosuuden pohjalta rakennetaan yksinkertainen mallitoteutus, jonka havainnollistamiseksi lasketaan kvanttiharmonisen oskillaattorin energia ja todennäköisyysjakauma sekä karkea arvio helium-4-nesteen parikorrelaatiofunktiolle. Lopuksi katsotaan vielä muutamia menetelmän olemassaolevia tai…
Topological polarization, dual invariants, and surface flat band in crystalline insulators
2020
We describe a three-dimensional crystalline topological insulator (TI) phase of matter that exhibits spontaneous polarization. This polarization results from the presence of (approximately) flat bands on the surface of such TIs. These flat bands are a consequence of the bulk-boundary correspondence of polarized topological media, and contrary to related nodal line semimetal phases also containing surface flat bands, they span the entire surface Brillouin zone. We also present an example Hamiltonian exhibiting a Lifshitz transition from the nodal line phase to the TI phase with polarization. Utilizing elasticity tetrads, we show a complete classification of 3D crystalline TI phases and invar…
Characterizing a dc-SQUID and a Mo/TiW/Cu -trilayer transition-edge sensor array
2017
Tutkielmassa määritettiin uuden suprajohtavan kvantti-interferenssilaitteen ja 256 pikseliä sisältävän sirun transitioreunailmaisimien ominaisuuksia. Komponentit vaativat erittäin matalia lämpötiloja ja suojauksen suurilta magneettikentiltä muuttuakseen suprajohtaviksi. Tärkeimmät mitatut ominaisuudet olivat suprajohtavan kvantti-interferenssilaitteen signaalin vahvistuskerroin sekä kohina ja transitioreunailmaisimen transitiolämpötila, normaalitilan vastus, virta-jännite-käyttäytyminen, sekä kohina. Motivaationa tutkimukselle oli etsiä käytetyn mittalaite kokonaisuuden herkkyyden rajat sekä pyrkiä sovittamaan teoreettista mallia transitioreunailmaisimen kohinan ymmärtämiseksi. Korkean taaj…