| 1. |
- San Sebastian, Eider, et al.
(författare)
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Enantiospecific Response in Cross-Polarization Solid-State Nuclear Magnetic Resonance of Optically Active Metal Organic Frameworks
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:42, s. 17989-17996
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Tidskriftsartikel (refereegranskat)abstract
- We report herein on a NMR-based enantiospecific response for a family of optically active metal-organic frameworks. Cross-polarization of the 1H-13C couple was performed, and the intensities of the 13C nuclei NMR signals were measured to be different for the two enantiomers. In a direct-pulse experiment, which prevents cross-polarization, the intensity difference of the 13C NMR signals of the two nanostructured enantiomers vanished. This result is due to changes of the nuclear spin relaxation times due to the electron spin spatial asymmetry induced by chemical bond polarization involving a chiral center. These experiments put forward on firm ground that the chiral-induced spin selectivity effect, which induces chemical bond polarization in the J-coupling, is the mechanism responsible for the enantiospecific response. The implications of this finding for the theory of this molecular electron spin polarization effect and the development of quantum biosensing and quantum storage devices are discussed.
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| 2. |
- Busto, David, et al.
(författare)
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Probing electronic decoherence with high-resolution attosecond photoelectron interferometry
- 2022
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 76:7
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).
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| 3. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Adiabatic elimination and subspace evolution of open quantum systems
- 2020
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Ingår i: Physical Review A. - 2469-9926. ; 101:4
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Tidskriftsartikel (refereegranskat)abstract
- Efficient descriptions of open quantum systems can be obtained by performing an adiabatic elimination of the fast degrees of freedom and formulating effective operators for the slow degrees of freedom in reduced dimensions. Here, we perform the construction of effective operators in frequency space, and using the final value theorem or alternatively the Keldysh theorem, we provide a correction for the trace of the density matrix which takes into account the non-trace-preserving character of the evolution. We illustrate our results with two different systems, one where the eliminated fast subspace is constituted by a continuous set of states and ones with discrete states. Furthermore, we show that the two models converge for very large dissipation and at coherent population trapping points. Our results also provide an intuitive picture of the correction to the trace of the density matrix as a detailed balance equation.
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| 4. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Classification of dark states in multilevel dissipative systems
- 2019
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Ingår i: Physical Review A. - 2469-9926. ; 99:5
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Tidskriftsartikel (refereegranskat)abstract
- Dark states are eigenstates or steady states of a system that are decoupled from the radiation. Their use, along with associated techniques such as stimulated Raman adiabatic passage, has extended from atomic physics, where it is an essential cooling mechanism, to more recent versions in the condensed phase where it can increase the coherence times of qubits. These states are often discussed in the context of unitary evolution and found with elegant methods exploiting symmetries, or via the Morris-Shore transformation. However, the link with dissipative systems is not always transparent, and distinctions between classes of coherent population trapping are not always clear. We present a detailed overview of the arguments to find stationary dark states in dissipative systems, and examine their dependence on the Hamiltonian parameters, their multiplicity, and purity. We evidence the class of dark states that depends not only on the detunings of the lasers but also on their relative intensities and phases. We illustrate the criteria with the more complex physical system of the hyperfine transitions of Rb87 and show how a knowledge of the dark-state manifold can guide the preparation of pure states.
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| 5. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Coherent two-dimensional spectroscopy of a Fano model
- 2016
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Ingår i: Physical Review B. - 1098-0121. ; 94:20
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Tidskriftsartikel (refereegranskat)abstract
- The Fano line shape arises from the interference of two excitation pathways to reach a continuum. Its generality has resulted in a tremendous success in explaining the line shapes of many one-dimensional spectroscopies - absorption, emission, scattering, conductance, photofragmentation - applied to very varied systems - atoms, molecules, semiconductors, and metals. Unraveling a spectroscopy into a second dimension reveals the relationship between states in addition to decongesting the spectra. Femtosecond-resolved two-dimensional electronic spectroscopy (2DES) is a four-wave mixing technique that measures the time evolution of the populations and coherences of excited states. It has been applied extensively to the dynamics of photosynthetic units, and more recently to materials with extended band structures. In this paper, we solve the full time-dependent third-order response, measured in 2DES, of a Fano model and give the system parameters that become accessible.
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| 6. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Non-Hermitian Hamiltonians for linear and nonlinear optical response : A model for plexcitons
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:10
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Tidskriftsartikel (refereegranskat)abstract
- In polaritons, the properties of matter are modified by mixing the molecular transitions with light modes inside a cavity. Resultant hybrid light-matter states exhibit energy level shifts, are delocalized over many molecular units, and have a different excited-state potential energy landscape, which leads to modified exciton dynamics. Previously, non-Hermitian Hamiltonians have been derived to describe the excited states of molecules coupled to surface plasmons (i.e., plexcitons), and these operators have been successfully used in the description of linear and third order optical response. In this article, we rigorously derive non-Hermitian Hamiltonians in the response function formalism of nonlinear spectroscopy by means of Feshbach operators and apply them to explore spectroscopic signatures of plexcitons. In particular, we analyze the optical response below and above the exceptional point that arises for matching transition energies for plasmon and molecular components and study their decomposition using double-sided Feynman diagrams. We find a clear distinction between interference and Rabi splitting in linear spectroscopy and a qualitative change in the symmetry of the line shape of the nonlinear signal when crossing the exceptional point. This change corresponds to one in the symmetry of the eigenvalues of the Hamiltonian. Our work presents an approach for simulating the optical response of sublevels within an electronic system and opens new applications of nonlinear spectroscopy to examine the different regimes of the spectrum of non-Hermitian Hamiltonians.
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| 7. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Two-dimensional Fano lineshapes : Excited-state absorption contributions
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:18
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Tidskriftsartikel (refereegranskat)abstract
- Fano interferences in nanostructures are influenced by dissipation effects as well as many-body interactions. Two-dimensional coherent spectroscopies have just begun to be applied to these systems where the spectroscopic signatures of a discrete-continuum structure are not known. In this article, we calculate the excited-state absorption contribution for different models of higher lying excited states. We find that the characteristic asymmetry of one-dimensional spectroscopies is recovered from the many-body contributions and that the higher lying excited manifolds have distorted lineshapes that are not anticipated from discrete-level Hamiltonians. We show that the Stimulated Emission cannot have contributions from a flat continuum of states. This work completes the Ground-State Bleach and Stimulated Emission signals that were calculated previously [D. Finkelstein-Shapiro et al., Phys. Rev. B 94, 205137 (2016)]. The model reproduces the observations reported for molecules on surfaces probed by 2DIR.
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| 8. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Understanding radiative transitions and relaxation pathways in plexcitons
- 2021
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Ingår i: Chem. - : Elsevier BV. - 2451-9308 .- 2451-9294. ; 7:4, s. 1092-1107
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Tidskriftsartikel (refereegranskat)abstract
- Molecular aggregates on plasmonic nanoparticles have emerged as attractive systems for the studies of polaritonic light-matter states, called plexcitons. Such systems are tunable, scalable, easy to synthesize, and offer sub-wavelength confinement, all while giving access to the ultrastrong light-matter coupling regime, promising a plethora of applications. However, the complexity of these materials prevented the understanding of their excitation and relaxation phenomena. Here, we follow the relaxation pathways in plexcitons and conclude that while the metal destroys the optical coherence, the molecular aggregate coupled to surface processes significantly contributes to the energy dissipation. We use two-dimensional electronic spectroscopy with theoretical modeling to assign the different relaxation processes to either molecules or metal nanoparticle. We show that the dynamics beyond a few femtoseconds has to be considered in the language of hot electron distributions instead of the accepted lower and upper polariton branches and establish the framework for further understanding.
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| 9. |
- Lai, Kwan To, et al.
(författare)
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Fano resonance between Stokes and anti-Stokes Brillouin scattering
- 2021
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Ingår i: Physical Review Research. - 2643-1564. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, the manipulation of Fano resonances in the time domain has unlocked deep insights into a broad spectrum of systems' coherent dynamics. Here, inelastic scattering of light with coherent acoustic phonons is harnessed to achieve complex Fano resonances. The sudden change of phonon momentum during reflection leads to a transition from anti-Stokes to Stokes light scattering, producing two different resonances that interfere in the measurement process. We highlight the conditions necessary to achieve such interference, revealing an underlying symmetry between photons and phonons, and verify the theory experimentally. Then, we demonstrate the possibility to characterize energy and coherence losses at rough interfaces, thus providing a mechanism for nondestructive testing of interface quality. Our results describe numerous unexplained observations in ultrafast acoustics and can be generalized to the scattering of light with any waves.
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| 10. |
- Lai, Kwan To, et al.
(författare)
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Ultrafast strain waves reconstruction from coherent acoustic phonons reflection
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:9, s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- Picosecond ultrasonics, which studies laser-induced high-frequency strain waves, is a reliable and versatile method for nondestructive materials' characterization. Strain waves are generated through a light interaction with charges and their subsequent relaxation, and these waves conceal a wealth of information on the material. However, strain waves are detected through their convolution with a sensitivity function, which blurs much of this information. Here, we show that the reflection of strain waves at a free surface leads to the appearance of a Fano resonance in the reflectivity spectrum, accompanied by a drastic increase in the detection bandwidth. We take advantage of this feature to provide a method for the reconstruction of strain waves. We apply it to unambiguously highlight the exact origin of the generation of coherent acoustic phonons in Stranski-Krastanov grown quantum dots, revealing that both the wetting layer and quantum dots are responsible for the generation. Our results will offer the possibility to understand better the interaction of light with charges and their interactions with the lattice.
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