| 11. |
- Tyrberg, Barbro, et al.
(författare)
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Mot nya höjder : Make it taste (Make it move)
- 2017
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Annan publikation (populärvet., debatt m.m.)abstract
- Utmaningarna är en del av projektet Mot nya höjder. Projektets mål är att öka intresset för naturvetenskap, teknik och matematik bland skolelever.
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| 12. |
- Ogier, Robin, 1987, et al.
(författare)
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Near-Complete Photon Spin Selectivity in a Metasurface of Anisotropic Plasmonic Antennas
- 2015
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Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- Simple chiroptically active metamaterials are difficult to realize in practice but could pave the way for a range of important applications, such as sensitive optical biosensors, asymmetric catalysis, and novel polarization manipulation devices. We show that a metasurface based on a random arrangement of anisotropic but aligned gold nanoparticles can exhibit an almost perfect selectivity towards incident photon spin for evanescent excitation with visible to near-infrared light. The experimentally attained reflection contrast between left- and right-handed circularly polarized light peaks at similar to 90%, in excellent agreement with analytical theory. These results are important for the development of future photonic and plasmonic polarization-based technologies.
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| 13. |
- Eriksson, Karl-Erik, et al.
(författare)
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Bifurcation in Quantum Measurement
- 2017
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a generic model of (non-destructive) quantum measurement. It consists of two-level system μ interacting with a larger system A, in such a way that if μ is initially in one of the chosen basis states, it does not change but makes A change into a corresponding state (entanglement). The μA-interaction is described as a scattering process. Internal (unknown) variables of A may influence the transition amplitudes. It is assumed that the statistics of these variables is such that, in the mean, the μA-interaction is neutral with respect to the chosen basis states. It is then shown that, for a given initial state of μ, in the limit of a large system A, the statistics of the ensemble of available initial states leads to a bifurcation: those initial states of A that are efficient in leading to a final state, are divided into two separated subsets. For each of these subsets, μ ends up in one of the basis states. The probabilities in this branching confirm the Born rule.
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| 14. |
- Negi, Devendra Singh, et al.
(författare)
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Proposal for Measuring Magnetism with Patterned Apertures in a Transmission Electron Microscope
- 2019
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 122:3
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Tidskriftsartikel (refereegranskat)abstract
- We propose a magnetic measurement method utilizing a patterned post-sample aperture in a transmission electron microscope. While utilizing electron magnetic circular dichroism, the method circumvents previous needs to shape the electron probe to an electron vortex beam or astigmatic beam. The method can be implemented in standard scanning transmission electron microscopes by replacing the spectrometer entrance aperture with a specially shaped aperture, hereafter called ventilator aperture. The proposed setup is expected to work across the whole range of beam sizes -- from wide parallel beams down to atomic resolution magnetic spectrum imaging.
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| 15. |
- Zhang, Jiang, et al.
(författare)
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Fast non-Abelian geometric gates via transitionless quantum driving
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- A practical quantum computer must be capable of performing high fidelity quantum gates on a set of quantum bits (qubits). In the presence of noise, the realization of such gates poses daunting challenges. Geometric phases, which possess intrinsic noise-tolerant features, hold the promise for performing robust quantum computation. In particular, quantum holonomies, i.e., non-Abelian geometric phases, naturally lead to universal quantum computation due to their non-commutativity. Although quantum gates based on adiabatic holonomies have already been proposed, the slow evolution eventually compromises qubit coher- ence and computational power. Here, we propose a general approach to speed up an implementation of adiabatic holonomic gates by using transitionless driving techniques and show how such a universal set of fast geometric quantum gates in a superconducting circuit architecture can be obtained in an all geometric approach. Compared with standard non-adiabatic holonomic quantum computation, the holonomies ob- tained in our approach tends asymptotically to those of the adiabatic approach in the long run-time limit and thus might open up a new horizon for realizing a practical quantum computer.
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| 16. |
- Baggioli, Matteo, et al.
(författare)
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Holographic plasmon relaxation with and without broken translations
- 2019
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Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :9
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Tidskriftsartikel (refereegranskat)abstract
- We study the dynamics and the relaxation of bulk plasmons in strongly coupled and quantum critical systems using the holographic framework. We analyze the dispersion relation of the plasmonic modes in detail for an illustrative class of holographic bottom-up models. Comparing to a simple hydrodynamic formula, we entangle the complicated interplay between the three least damped modes and shed light on the underlying physical processes. Such as the dependence of the plasma frequency and the effective relaxation time in terms of the electromagnetic coupling, the charge and the temperature of the system. Introducing momentum dissipation, we then identify its additional contribution to the damping. Finally, we consider the spontaneous symmetry breaking (SSB) of translational invariance. Upon dialing the strength of the SSB, we observe an increase of the longitudinal sound speed controlled by the elastic moduli and a decrease in the plasma frequency of the gapped plasmon. We comment on the condensed matter interpretation of this mechanism.
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| 17. |
- Chico, Jonathan, et al.
(författare)
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First-principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys
- 2016
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 93:21
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Tidskriftsartikel (refereegranskat)abstract
- Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co(2)MnZ, Co(2)FeZ, and Mn(2)VZ with Z = (Al, Si, Ga, Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2FeSi and the ferrimagnetic Mn2VAl. Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.
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| 18. |
- Nicolai, L., et al.
(författare)
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Bi ultra-thin crystalline films on InAs(111)A and B substrates: a combined core-level and valence-band angle-resolved and dichroic photoemission study
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Bi on both the In-terminated (A) face and the As-terminated (B) face of InAs(111) has been investigated by low-energy electron diffraction, scanning tunnelling microscopy, and photoelectron spectroscopy using synchrotron radiation. The changes upon Bi deposition of the In 4d and Bi 5d(5/2) photoelectron signals allow to get a comprehensive picture of the Bi/InAs(111) interface. From the early stage the Bi growth on the A face is epitaxial, contrary to that on the B face that proceeds via the formation of islands. Angle-resolved photoelectron spectra show that the electronic structure of a Bi deposit of approximate to 10 bi-layers on the A face is identical to that of bulk Bi, while more than approximate to 30 bi-layers are needed for the B face. Both bulk and surface electronic states observed are well accounted for by fully relativistic ab initio calculations performed using the one-step model of photoemission. These calculations are used to analyse the dichroic photoemission data recorded in the vicinity of the Fermi level around the (Gamma) over bar point of the Brillouin zone.
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| 19. |
- Shi, Juanzi, et al.
(författare)
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Photo-Oxidation Reveals H-Aggregates Hidden in Spin-Cast-Conjugated Polymer Films as Observed by Two-Dimensional Polarization Imaging
- 2019
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 31:21, s. 8927-8936
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-cast intermolecular interactions in conjugated polymer films lead to the formation of excited states delocalized over a few oriented and tightly packed conjugated segments. The optoelectronic properties of conjugated polymers are strongly dependent on the presence of such oriented domains at a nanoscale level. We observe oriented domains as large as several micrometers in size spontaneously formed in spin-cast PBDT-TPD films. Two-dimensional polarization imaging of fresh and photodegraded films showed a much higher visibility of the oriented domains in the degraded samples. We propose that the film is a mixture of two phases with different degrees of chain alignment. The photoluminescence of the more anisotropic phase is more stable against photodegradation in comparison with the less anisotropic phase. Photodegradation predominately quenches photoluminescence of the less anisotropic phase making the oriented domains more visible in the polarization contrasts. Spectral and energy transfer properties of the more oriented phase allowed us to assign it to weakly coupled H-aggregates with the suppressed 0-0 vibronic transition. Stable photoluminescence of H-aggregates in comparison with that of nonaggregated (less oriented) chains may help to understand degradation mechanisms of polymer devices and shows the role of energy transfer in this process. Selective degradation-induced quenching can reveal hidden inhomogeneity of conjugated polymer films.
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| 20. |
- Campanini, Donato, et al.
(författare)
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Raising the superconducting T-c of gallium : In situ characterization of the transformation of alpha-Ga into beta-Ga
- 2018
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:18
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Tidskriftsartikel (refereegranskat)abstract
- Gallium (Ga) displays several metastable phases. Superconductivity is strongly enhanced in the metastable beta-Ga with a critical temperature T-c = 6.04(5) K, while stable alpha-Ga has a much lower T-c < 1.2 K. Here we use a membrane-based nanocalorimeter to initiate the transition from alpha-Ga to beta-Ga on demand, as well as study the specific heat of the two phases on one and the same sample. The in situ transformation is initiated by bringing the temperature to about 10 K above the melting temperature of alpha-Ga. After such treatment, the liquid supercools down to 232 K, where beta-Ga solidifies. We find that beta-Ga is a strong-coupling type-I superconductor with Delta(0)/k(B)T(c) = 2.00(5) and a Sommerfeld coefficient gamma(n) = 1.53(4) mJ/molK(2), 2.55 times higher than that in the alpha phase. The results allow a detailed comparison of fundamental thermodynamic properties between the two phases.
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