Large scale simulations of light-matter interaction in natural photosynthetic antenna complexes containing more than one hundred thousands chlorophyll molecules, comparable with natural size, have ...been performed. Photosynthetic antenna complexes present in Green sulfur bacteria and Purple bacteria have been analyzed using a radiative non-Hermitian Hamiltonian, well known in the field of quantum optics, instead of the widely used dipole-dipole Frenkel Hamiltonian. This approach allows to study ensembles of emitters beyond the small volume limit (system size much smaller than the absorbed wavelength), where the Frenkel Hamiltonian fails. When analyzed on a large scale, such structures display superradiant states much brighter then their single components. An analysis of the robustness to static disorder and dynamical (thermal) noise, shows that exciton coherence in the whole photosynthetic complex is larger than the coherence found in its parts. This provides evidence that the photosynthetic complex as a whole has a predominant role in sustaining coherences in the system even at room temperature. Our results allow a better understanding of natural photosynthetic antennae and could drive experiments to verify how the response to the electromagnetic radiation depends on the size of the photosynthetic antenna.
As recently manifested , the quench dynamics of isolated quantum systems consisting of a finite number of particles, is characterized by an exponential spreading of wave packets in the many-body ...Hilbert space. This happens when the inter-particle interaction is strong enough, thus resulting in a chaotic structure of the many-body eigenstates considered in an unperturbed basis. The semi-analytical approach used here, allows one to estimate the rate of the exponential growth as well as the relaxation time, after which the equilibration (thermalization) emerges. The key ingredient parameter in the description of this process is the width \(\Gamma\) of the Local Density of States (LDoS) defined by the initially excited state, the number of particles and the interaction strength. In this paper we show that apart from the meaning of \(\Gamma\) as the decay rate of survival probability, the width of the LDoS is directly related to the diagonal entropy and the latter can be linked to the thermodynamic entropy of a system equilibrium state emerging after the complete relaxation. The analytical expression relating the two entropies is derived phenomenologically and numerically confirmed in a model of bosons with random two-body interaction, as well as in a deterministic model which becomes completely integrable in the continuous limit.
We address the question of the relevance of thermalization to the increase of correlations in the quench dynamics of an isolated system with a finite number of interacting bosons. Specifically, we ...study how, in the process of thermalization, the correlations between occupation numbers increase in time resulting in the emergence of the Bose-Einstein distribution. We show, both analytically and numerically, that before saturation the two-point correlation function increases quadratically in time. This time dependence is at variance with the exponential increase of the number of principal components of the wave function, recently discovered and explained in Ref.\cite{BIS18}. We also demonstrate that the out-of-time-order correlator (OTOC) increases algebraically in time but not exponentially as predicted in many publications. Our results, that can be confirmed experimentally in traps with interacting bosons, may be also relevant to the problem of black hole scrambling.
Localized Thermal States Borgonovi, Fausto; Izrailev, Felix M
arXiv.org,
09/2017
Paper, Journal Article
Open access
It is believed that thermalization in closed systems of interacting particles can occur only when the eigenstates are fully delocalized and chaotic in the preferential (unperturbed) basis of the ...total Hamiltonian. Here we demonstrate that at variance with this common belief the typical situation in the systems with two-body inter-particle interaction is much more complicated and allows to treat as thermal even eigenstates that are not fully delocalized. Using a semi-analytical approach we establish the conditions for the emergence of such thermal states in a model of randomly interacting bosons. Our numerical data show an excellent correspondence with the predicted properties of {\it localized thermal eigenstates}.
Magnetic resonance force microscopy (MRFM) is a rapidly evolving field which originated in 1990s and matured recently with the first detection of a single electron spin below the surface of a ...non-transparent solid. Further development of MRFM techniques will have a great impact on many areas of science and technology including physics, chemistry, biology, and even medicine. Scientists, engineers, and students from various backgrounds will all be interested in this promising field.The objective of this "multi-level" book is to describe the basic principles, applications, and the advanced theory of MRFM. Focusing on the experimental oscillating cantilever-driven adiabatic reversals (OSCAR) detection technique for single electron spin, this book contains valuable research data for scientists working in the field of quantum physics or magnetic resonance. Readers unfamiliar with quantum mechanics and magnetic resonance will be able to obtain an understanding and appreciation of the basic principles of MRFM.
Efficient devices for light harvesting and photon sensing are fundamental building blocks of basic energy science and many essential technologies. Recent efforts have turned to biomimicry to design ...the next generation of light-capturing devices, partially fueled by an appreciation of the fantastic efficiency of the initial stages of natural photosynthetic systems at capturing photons. In such systems extended excitonic states are thought to play a fundamental functional role, inducing cooperative coherent effects, such as superabsorption of light and supertransfer of photoexcitations. Inspired by this observation, we design an artificial light-harvesting and photodetection device that maximally harnesses cooperative effects to enhance efficiency. The design relies on separating absorption and transfer processes (energetically and spatially) in order to overcome the fundamental obstacle to exploiting cooperative effects to enhance light capture: the enhanced emission processes that accompany superabsorption. This engineered separation of processes greatly improves the efficiency and the scalability of the system.
We study quench dynamics in the many-body Hilbert space using two isolated systems with a finite number of interacting particles: a paradigmatic model of randomly interacting bosons and a dynamical ...(clean) model of interacting spins-\(1/2\). For both systems in the region of strong quantum chaos, the number of components of the evolving wave function, defined through the number of principal components \(N_{pc}\) (or participation ratio), was recently found to increase exponentially fast in time Phys. Rev. E 99, 010101R (2019). Here, we ask whether the out-of-time ordered correlator (OTOC), which is nowadays widely used to quantify instability in quantum systems, can manifest analogous time-dependence. We show that \(N_{pc}\) can be formally expressed as the inverse of the sum of all OTOC's for projection operators. While none of the individual projection-OTOC's shows an exponential behavior, their sum decreases exponentially fast in time. The comparison between the behavior of the OTOC with that of the \(N_{pc}\) helps us better understand wave packet dynamics in the many-body Hilbert space, in close connection with the problems of thermalization and information scrambling.
The onset of thermalization in a closed finite system of randomly interacting bosons, at the level of a single eigenstate, is discussed. The main interest is in the emergence of the Bose-Einstein ...distribution of single-particle occupation numbers, establishing a global and local criterion for thermalization. We show how to define the temperature of a given eigenstate, provided that it has a chaotic structure in the basis defined by single-particle states. The analytical expression for the eigenstate temperature as a function of the inter-particle interaction and energy is complemented by numerical data.
Phys. Rev. E 99, 010101 (2019) We demonstrate analytically and numerically that in isolated quantum systems
of many interacting particles, the number of many-body states participating in
the ...evolution after a quench increases exponentially in time, provided the
eigenstates are delocalized in the energy shell. The rate of the exponential
growth is defined by the width $\Gamma$ of the local density of states (LDOS)
and is associated with the Kolmogorov-Sinai entropy for systems with a well
defined classical limit. In a finite system, the exponential growth eventually
saturates due to the finite volume of the energy shell. We estimate the time
scale for the saturation and show that it is much larger than $\hbar/\Gamma$.
Numerical data obtained for a two-body random interaction model of bosons and
for a dynamical model of interacting spin-1/2 particles show excellent
agreement with the analytical predictions.
