127 research outputs found
Extraordinary exciton conductance induced by strong coupling
We demonstrate that exciton conductance in organic materials can be enhanced
by several orders of magnitude when the molecules are strongly coupled to an
electromagnetic mode. Using a 1D model system, we show how the formation of a
collective polaritonic mode allows excitons to bypass the disordered array of
molecules and jump directly from one end of the structure to the other. This
finding could have important implications in the fields of exciton transistors,
heat transport, photosynthesis, and biological systems in which exciton
transport plays a key role.Comment: Main text: 5 pages, 4 figures; Supplemental: 2 pages, 1 figure.
Version 2: Updated reference to related work arXiv:1409.2550. Version 3:
Updated to version accepted for publication in Physical Review Letter
Cavity-induced modifications of molecular structure in the strong coupling regime
In most theoretical descriptions of collective strong coupling of organic
molecules to a cavity mode, the molecules are modeled as simple two-level
systems. This picture fails to describe the rich structure provided by their
internal rovibrational (nuclear) degrees of freedom. We investigate a
first-principles model that fully takes into account both electronic and
nuclear degrees of freedom, allowing an exploration of the phenomenon of strong
coupling from an entirely new perspective. First, we demonstrate the
limitations of applicability of the Born-Oppenheimer approximation in strongly
coupled molecule-cavity structures. For the case of two molecules, we also show
how dark states, which within the two-level picture are effectively decoupled
from the cavity, are indeed affected by the formation of collective strong
coupling. Finally, we discuss ground-state modifications in the ultra-strong
coupling regime and show that some molecular observables are affected by the
collective coupling strength, while others only depend on the single-molecule
coupling constant.Comment: 12 pages, 8 figure
On the SN2 reactions modified in vibrational strong coupling experiments: Reaction mechanisms and vibrational mode assignments
Recent experiments have reported modified chemical reactivity under vibrational strong coupling (VSC) in microfluidic Fabry-Pérot cavities. In particular, the reaction rate of nucleophilic substitution reactions at silicon centers (SN2@Si) has been altered when a vibrational mode of the reactant was coupled to a confined light mode in the strong coupling regime. In this situation, hybrid light-matter states known as polaritons are formed and seem to be responsible for the modified chemical kinetics. These results are very encouraging for future applications of polaritonic chemistry to catalyze chemical reactions, with the ability to manipulate chemical phenomena without any external excitation of the system. Still, there is no theory capable of explaining the mechanism behind these results. In this work we address two points that are crucial for the interpretation of these experiments. Firstly, by means of electronic structure calculations we report the reaction mechanism in normal conditions of the two recently modified SN2@Si reactions, obtaining in both cases a triple-well PES where the rate-determining step is due to the Si-C and Si-O bond cleavage. Secondly, we characterize in detail the normal modes of vibration of the reactants. In the VSC experiments, reaction rates were modified only when specific vibrations of the reactants were coupled to a cavity mode. We find that these vibrations are highly mixed among the different fragments of the reactants leading to a completely new assignment of the IR peaks coupled to cavity modes in the original experimental works. Our results are fundamental for the interpretation of the VSC experiments given that in the absence of a theory explaining these results, the current phenomenological understanding relies on the assignment of the character of the vibrational IR peaksThis work was funded by the European Research Council
through Grant No. ERC-2016-StG-714870 and the Spanish
Ministry for Science, Innovation, and Universities-Agencia Estatal
de Investigacio´n through Grant No. RTI2018-099737-B-I00,
PCI2018-093145 (through the QuantERA program of the European
Commission), and MDM-2014-0377 (through the Marı´a
de Maeztu program for Units of Excellence in R&D
Quantum theory of collective strong coupling of molecular vibrations with a microcavity mode
We develop a quantum mechanical formalism to treat the strong coupling
between an electromagnetic mode and a vibrational excitation of an ensemble of
organic molecules. By employing a Bloch-Redfield-Wangsness approach, we show
that the influence of dephasing-type interactions, i.e., elastic collisions
with a background bath of phonons, critically depends on the nature of the bath
modes. In particular, for long-range phonons corresponding to a common bath,
the dynamics of the "bright state" (the collective superposition of molecular
vibrations coupling to the cavity mode) is effectively decoupled from other
system eigenstates. For the case of independent baths (or short-range phonons),
incoherent energy transfer occurs between the bright state and the uncoupled
dark states. However, these processes are suppressed when the Rabi splitting is
larger than the frequency range of the bath modes, as achieved in a recent
experiment [Shalabney et al., Nat. Commun. 6, 5981 (2015)]. In both cases, the
dynamics can thus be described through a single collective oscillator coupled
to a photonic mode, making this system an ideal candidate to explore cavity
optomechanics at room temperature.Comment: 13 pages, 4 figure
Molecular photodissociation enabled by ultrafast plasmon decay
We propose a strategy for enabling photodissociation of a normally photostable molecule through coupling to a nanoparticle plasmon. The large possible coupling on the single-molecule level combined with the highly lossy nature of plasmonic modes, with lifetimes on the order of femtoseconds, opens an ultrafast decay channel for the molecule. For plasmon mode frequencies below the vertical photoexcitation energy of the molecule, the difference between the excitation and emission energies is converted into vibrational energy on the molecular ground state in a Raman-like process. Under the correct conditions, this energy can be high enough to enable efficient photodissociation on the electronic ground state. We demonstrate the concept using numerical simulations of the Lindblad master equation for the hydrogen molecule in the vicinity of an aluminum nanoparticle and explore the photodissociation efficiency as a function of various system parametersThis work was funded by the European Research Council through Grant No. ERC-2016-StG-714870 and by the Spanish Ministry for Science, Innovation, and Universities–Agencia Estatal de Investigación through Grant Nos. RTI2018-099737-B-I00, PCI2018-093145 (through the QuantERA program of the European Commission), and CEX2018-000805-M (through the Maria de Maeztu program for Units of Excellence in R&D
Accurate truncations of chain mapping models for open quantum systems
The dynamics of open quantum systems are of great interest in many research fields, such as for the interaction of a quantum emitter with the electromagnetic modes of a nanophotonic structure. A powerful approach for treating such setups in the non-Markovian limit is given by the chain mapping where an arbitrary environment can be transformed to a chain of modes with only nearest-neighbor coupling. However, when long propagation times are desired, the required long chain lengths limit the utility of this approach. We study various approaches for truncating the chains at manageable lengths while still preserving an accurate description of the dynamics. We achieve this by introducing losses to the chain modes in such a way that the effective environment acting on the system remains unchanged, using a number of different strategies. Furthermore, we demonstrate that extending the chain mapping to allow next-nearest neighbor coupling permits the reproduction of an arbitrary environment, and adding longer-range interactions does not further increase the effective number of degrees of freedom in the environmentThis work has been funded by the European Research Council through grant ERC-2016- StG-714870 and by the Spanish Ministry for Science, Innovation, and Universities—Agencia Estatal de Investigación through grants RTI2018-099737-B-I00, PCI2018-093145 (through the QuantERA program of the European Commission), and CEX2018-000805-M (through the María de Maeztu program for Units of Excellence in R&D
Nanoplasmonic near-field synthesis
The temporal response of resonances in nanoplasmonic structures typically
converts an incoming few-cycle field into a much longer near-field at the spot
where non-linear physical phenomena including electron emission, recollision
and high-harmonic generation can take place. We show that for practically
useful structures pulse shaping of the incoming pulse can be used to synthesize
the plasmon-enhanced field and enable single-cycle driven nonlinear physical
phenomena. Our method is demonstrated for the generation of an isolated
attosecond pulse by plasmon-enhanced high harmonic generation. We furthermore
show that optimal control techniques can be used even if the response of the
plasmonic structure is not known a priori.Comment: 6 page
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