arXiv subjects

Tamar Seideman

Publications and source records attributed to Tamar Seideman.

At least 19 recordsLinked to original sources

arXiv2026

Macroscopic Spin-Orbit Interaction through Strong-Field Pumping of Inhomogeneously Aligned Molecular Ensemble

We study the strong-field interaction of a helical bi-chromatic pump with an anisotropic and inhomogeneous molecular system in the form of planar distribution of radially aligned molecular ensemble. This setting gives rise to macroscopic spin-orbit interaction where High Harmonic radiation is emitted while imbued with Orbital Angular Momentum (OAM) whose sign is directly dictated by the helicity of the pump field. We demonstrate this phenomenon in ensembles of $H_2^+$ and $N_2$ molecules with Time-Dependent Density Functional Theory (TDDFT) simulations.

physics.chem-ph↗

arXiv2020

Photoisomerization-coupled electron transfer

Photochromic molecular structures constitute a unique platform for constructing molecular switches, sensors and memory devices. One of their most promising applications is as light-switchable electron acceptor or donor units. Here, we investigate a previously unexplored process that we postulate may occur in such systems: an ultrafast electron transfer triggered by a simultaneous photoisomerization of the donor or the acceptor moiety. We propose a theoretical model for this phenomenon and, with the aid of DFT calculations, apply it to the case of a dihydropyrene-type photochromic molecular donor. By considering the wavepacket dynamics and the photoisomerization yield, we show that the two processes involved, electron transfer and photoisomerization, are in general inseparable and need to be treated in a unified manner. We finish by discussing how the efficiency of photoisomerization-coupled electron transfer can be controlled experimentally.

physics.chem-ph↗

arXiv2020

Beyond Marcus theory and the Landauer-Buttiker approach in molecular junctions. II. A self-consistent Born approach

Marcus and Landauer-Buttiker approaches to charge transport through molecular junctions describe two contrasting mechanisms of electronic conduction. In previous work, we have shown how these charge transport theories can be unified in the single-level case by incorporating lifetime broadening into the second-order quantum master equation. Here, we extend our previous treatment by incorporating lifetime broadening in the spirit of the self-consistent Born approximation. By comparing both theories to numerically converged hierarchical-equations-of-motion (HEOM) results, we demonstrate that our novel self-consistent approach rectifies shortcomings of our earlier framework which are present especially in the case of relatively strong electron-vibrational coupling. We also discuss circumstances under which the theory developed here simplifies to the generalised theory developed in our earlier work. Finally, by considering the high-temperature limit of our new self-consistent treatment, we show how lifetime broadening can also be self-consistently incorporated into Marcus theory. Overall, we demonstrate that the self-consistent approach constitutes a more accurate description of molecular conduction while retaining most of the conceptual simplicity of our earlier framework.

physics.chem-ph↗

arXiv2018

Friction as a consistent quantum-mechanical concept

A quantum analog of friction (understood as a completely positive, Markovian, translation-invariant and phenomenological model of dissipation) is known to be in odds with the detailed balance in the thermodynamic limit. We show that this is not the case for quantum systems with internal (e.g. spin) states non-adiabatically coupled to translational dynamics. For such systems, a quantum master equation is derived which phenomenologically accounts for the frictional effect of a uniform zero temperature environment. A simple analytical example is provided. Conjectures regarding the finite temperature case are also formulated. The results are important for efficient simulations of complex molecular dynamics and quantum reservoir engineering applications.

quant-ph↗

arXiv2018

Non-conservative Forces via Quantum Reservoir Engineering

A systematic approach is given for engineering dissipative environments that steer quantum wavepackets along desired trajectories. The methodology is demonstrated with several illustrative examples: environment-assisted tunneling, trapping, effective mass assignment, and pseudo-relativistic behavior. Non-conservative stochastic forces do not inevitably lead to decoherence - we show that purity can be well-preserved. These findings highlight the flexibility offered by non-equilibrium open quantum dynamics.

quant-ph↗

arXiv2018

Structure of optimal policies in quantum control

Using the Pontryagin maximum principle, the generic structure of optimal policies is deduced for typical quantum control tasks involving coherent lasers, magnetic fields and reservoir engineering. In addition, the periodic optimization is considered for the first time in view of prospective applications. We proved that nearly all optimal policies are actively constrained by technical bounds on control parameter but reduce to entirely bang-bang sequences only in special cases, such as the environmental control by random collisions. The results allow to arguably refute two generally accepted and concurring conjectures regarding the structure of optimal controls.

quant-ph↗

arXiv2017

Emergence of Landauer Transport from Quantum Dynamics: A Model Hamiltonian Approach

The Landauer expression for computing current-voltage characteristics in nanoscale devices is efficient and widely applicable but not suited to transient phenomena and time dependent currents because it assumes that the charge carrier population attains a time independent dynamic equilibrium as soon as the external voltage is turned on. In this article, we construct a very general expression for a time dependent current in an electrode-molecule-electrode arrangement. Utilizing a model Hamiltonian, we propagate the Schrodinger wave function equation to numerically compute the time dependent population in the individual sub-systems. The current in each electrode (defined in terms of the rate of change of the corresponding population) has two components, one due to the charges originating from the same electrode and the other due to the charges initially residing at the other electrode. We derive an analytical expression for the first component and illustrate that it agrees reasonably with the numerical counterpart at early times. The structural form reveals that the initial occupancy can be factored out of the time dependent segment of the expression. We take this cue to construct a Landauer style formula and demonstrate that the current obtained from this simplified formula overlaps with our most general numerical current only after the charge flow settles into a steady state. Thus, we illustrate the emergence of Landauer transport from a true first-principles quantum dynamics calculation without any prior assumptions. Subsequently, we investigate the ingredients in our model that regulate the onset time scale of this Landauer regime. We compare the performance of our general current expression with the Landauer current for time dependent electronic coupling. Finally, we comment on the applicability of the Landauer formulas to compute hot-electron current arising upon plasmon decoherence.

cond-mat.mes-hall↗

arXiv2017

No thermalization without correlations

The proof of the long-standing conjecture is presented that Markovian quantum master equations are at odds with quantum thermodynamics under conventional assumptions of fluctuation-dissipation theorems (implying a translation invariant dissipation). Specifically, except for identified systems, persistent system-bath correlations of at least one kind, spatial or temporal, are obligatory for thermalization. A systematic procedure is proposed to construct translation invariant bath models producing steady states that well-approximate thermal states. A quantum optical scheme for the laboratory assessment of the developed procedure is outlined.

quant-ph↗

arXiv2017

A systematic four-dimensional approach to strong field control of molecular torsions

We introduce a four-dimensional quantum model for describing the torsional control of $\rm G_{16}$-type molecules in the electronic ground state, based on the symmetry-adapted variational method. We define conditions for which lower-dimensional models, commonly used to simulate the strong-field control of molecular torsions, are reliable approximations to a four-dimensional treatment. In particular, we study the role of different types of rotational-torsional couplings---the field-free coupling and the field-induced coupling---and show that the conclusions recently drawn on the role of rotational-torsional couplings in the process of torsional alignment are not correct. Furthermore, we demonstrate how important an adequate description of the molecular polarizability is for reliably predicting the torsional alignment.

physics.chem-ph↗

arXiv2016

Quantum friction: environment engineering perspectives

We prove a generalization of the Lindblad's fundamental no-go result: A quantum system cannot be completely frozen and, in some cases, even thermalized via translationally invariant dissipation -- the quantum friction. Nevertheless, a practical methodology is proposed for engineering nearly perfect quantum analogs of classical friction within the Doppler cooling framework. These findings pave the way for hallmark dissipative engineering (e.g. nonreciprocal couplings) with atoms and molecules.

quant-ph↗

arXiv2015

A direct basis approach to nonorthogonality in second quantization. Theory and application

We present a direct basis formalism for using nonorthogonal basis sets in the second quantization framework. As an alternative to the dual basis formalism, a direct basis retains the Hermiticity relation between the creation and annihilation operators, with which the form of quantum operators -- e.g. the number operator and the Hamiltonian -- can be readily interpreted and manipulated. To tackle the difficulty of formulating quantum operators in the direct basis, we introduce the coefficient matrix and the generalized creation and annihilation operators, with which an arbitrary N-particle operator can be generated by simple matrix manipulations with the metric tensor of a general basis set. We illustrate the application of the direct basis formalism with the Hubbard Hamiltonian and a dynamical study with the Heisenberg equations of motion

physics.chem-ph↗

arXiv2015

Quantum optimal environment engineering for efficient photoinduced charge separation

The possibility to induce predetermined coherent quantum dynamics by controlling only the dissipative environmental parameters (such as temperature and pressure) is studied using the combined optimal control and environment engineering frameworks. As an example, we consider the problem of transforming an optically excited donor state into free charge carriers via intermediate higher-lying bridge state(s), with a view to solar energy conversion. In this context, vibrational bath engineering allows to promote fast, directional charge transfer and to suppress recombinative losses.

quant-ph↗

arXiv2015

Role of control constraints in quantum optimal control

The problems of optimizing the value of an arbitrary observable of the two-level system at both a fixed time and the shortest possible time is theoretically explored. Complete identification and classification along with comprehensive analysis of globally optimal control policies and traps (i.e. policies which are locally but not globally optimal) is presented. The central question addressed is whether the control landscape remains trap-free if control constraints of the inequality type are imposed. The answer is astonishingly controversial, namely, although formally it is always negative, in practice it is positive provided that the control time is fixed and chosen long enough.

quant-ph↗

arXiv2015

Wigner representation of the rotational dynamics of rigid tops

We propose a methodology to design Wigner representations in phase spaces with nontrivial topology having evolution equations with desired mathematical properties. As an illustration, two representations of molecular rotations are developed to facilitate the analysis of molecular alignment in moderately intense laser fields, reaction dynamics, scattering phenomena and dissipative processes.

quant-ph↗

arXiv2014

Coherent Phase Control of Internal Conversion in Pyrazine

Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the $S_2$ and $S_1$ states. Very different, non-classical behavior was observed when a genetic algorithm (GA) was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T$<1.5$ ps) and late (T$>1.5$ ps) target times. In the former case, the ion signal was largely suppressed for $t 1.5$ ps the ion growth curve followed the classical rate equations for $t<T$, while for $t \gg T$ the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the $S_2$ potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for $S_0 \rightarrow S_2$ followed by incoherent decay of the excited molecules.

physics.atom-ph↗

arXiv2014

A real-space method for highly parallelizable electronic transport calculations

We present a real-space method for first-principles nano-scale electronic transport calculations. We use the non-equilibrium Green's function method with density functional theory and implement absorbing boundary conditions (ABCs, also known as complex absorbing potentials, or CAPs) to represent the effects of the semi-infinite leads. In real space, the Kohn-Sham Hamiltonian matrix is highly sparse. As a result, the transport problem parallelizes naturally and can scale favorably with system size, enabling the computation of conductance in relatively large molecular junction models. Our use of ABCs circumvents the demanding task of explicitly calculating the leads' self-energies from surface Green's functions, and is expected to be more accurate than the use of the jellium approximation. In addition, we take advantage of the sparsity in real space to solve efficiently for the Green's function over the entire energy range relevant to low-bias transport. We illustrate the advantages of our method with calculations on several challenging test systems and find good agreement with reference calculation results.

cond-mat.mes-hall↗

arXiv2013

Ultrafast Energy Transfer Between Molecular Assemblies and Surface Plasmons in the Strong Coupling Regime

The nonlinear optical dynamics of nano-materials comprised of plasmons interacting with quantum emitters is investigated by a self-consistent model based on the coupled Maxwell-Liouville-von Neumann equations. It is shown that ultra-short resonant laser pulses significantly modify the optical properties of such hybrid systems. It is further demonstrated that the energy transfer between interacting molecules and plasmons occurs on a femtosecond time scale and can be controlled with both material and laser parameters.

cond-mat.mes-hall↗

arXiv2013

Orientational decomposition of molecular high harmonic emission in three dimensions

An important goal in molecular physics and chemistry today is to obtain structure-dependent information about molecular function to obtain a deeper understanding into chemical reactions. However, until now, asymmetric tops, which comprise the widest and most general class of molecules, remain principally unexplored. This gap is particularly evident in high harmonic generation (HHG). HHG has successfully obtained structural information about electron hole pairs or orbitals for simple linear molecules. Unfortunately, for more complicated molecules, the emission from different molecular directions interfere, concealing individual angular signatures. Here we introduce a method to extract orientation-dependent information from asymmetric tops and apply it to the sulfur dioxide (SO2) molecule. We use the rotational revival structure to decompose the angular contributions of HHG emission. This method also extends HHG-based tomographic imaging into three dimensions and makes it applicable to a much wider class of systems than previously envisioned. Our results suggest that HHG is a powerful tool to probe electron orbital structure and dynamics of complex molecules.

physics.atom-ph↗