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We investigate the entanglement dynamics of two qubits interacting with a graphene nanodisk using the macroscopic quantum electrodynamics method. By modifying the free-space decay rate of each qubit, we study the coupling strength between the nanoparticle and the qubits. We find that as the free-space decay rate increases, the decaying Rabi oscillations featured in the qubit population dynamics change to complex non-Markovian dynamical population evolution. This is also reflected on the concurrence, which at weak or moderate light–matter coupling conditions, attains values up to 0.5, while as the coupling conditions become stronger, larger values are also transiently observed. Our findings indicate that graphene nanostructures can provide a platform for the realization of high degree of entanglement in the strong coupling regime at the nanoscale, essential for quantum technology applications. [ABSTRACT FROM AUTHOR]

In this paper, we model the three-dimensional escape dynamics of single submicron-sized aerosol droplets in optical multiple Bessel beam traps. Trapping in counter-propagating Bessel beams (CPBBs) is compared with a newly proposed quadruple Bessel beam (QBB) trap, which consists of two perpendicularly arranged CPBB traps. Calculations are performed for perfectly and imperfectly aligned traps. Mie-theory and finite-difference time-domain methods are used to calculate the optical forces. The droplet escape kinetics are obtained from the solution of the Langevin equation using a Verlet algorithm. Provided the traps are perfectly aligned, the calculations indicate very long lifetimes for droplets trapped either in the CPBB or in the QBB trap. However, minor misalignments that are hard to control experimentally already severely diminish the stability of the CPBB trap. By contrast, such minor misalignments hardly affect the extended droplet lifetimes in a QBB trap. The QBB trap is found to be a stable, robust optical trap, which should enable the experimental investigation of submicron droplets with radii down to 100 nm. Optical binding between two droplets and its potential role in preventing coagulation when loading a CPBB trap is briefly addressed. [ABSTRACT FROM AUTHOR]

We consider the control of internal conversion between the S2(1B2u) excited electronic state of pyrazine and the S1(1B3u) state. The study is performed both during and after the femtosecond excitation of the ground electronic state S0(1Ag) to form the S2 state. The dynamics is examined using the newly developed 'effective modes' technique which enables the full computation of quantum dynamics in multi-dimensional spaces. Using this technique, we also investigate the coherent control of population transfer from S0 to the S2 and S1 electronic states. We find that the use of shaped laser pulses enables a significant delay of the internal conversion. For example, after 60 fs, the S2 population amounts to ∼60% of the initial S0 population, and remains at ∼20% after 100 fs, in contrast to the S0 electronic state which is completely depopulated within 75 fs. [ABSTRACT FROM AUTHOR]

We investigate the intramolecular energy transfer dynamics of the S2 excited electronic state of pyrazine due to radiationless transitions to energetically lower-lying singlet electronic states using a new time-dependent method. The femtosecond decay of S2 to the S1 excited state and the picosecond decay of S2 to the ground electronic state S0 are studied within an efficient methodology for computing the intramolecular dynamics in multidimensional configurational spaces. Our method is based on partitioning the full configuration space into the (small) subspace of interest Q and the rest, the subspace P. The exact equations of motion for the states in Q, under the influence of P, are derived in the time domain in form of a system of integrodifferential equations. Their numerical solution is readily obtained when the Q space consists of just a few states. Otherwise, the integrodifferential equations for the states in Q are transformed into a (larger) system of ordinary differential equations, which can be solved by a single diagonalization of a general complex matrix. The former approach is applied to study the pyrazine picosecond S2→S0 dynamics and the latter is applied to the study of the ultrafast pyrazine S2→S1 decay dynamics. [ABSTRACT FROM AUTHOR]

We show that the quantum dynamics of a system comprised of a subspace Q coupled to a larger subspace P can be recast as a reduced set of “coarse grained” ordinary differential equations with constant coefficients. These equations can be solved by a single diagonalization of a general complex matrix. The method makes no assumptions about the strength of the couplings between the Q and the P subspaces, nor is there any limitation on the initial population in P. The utility of the method is demonstrated via computations in three following areas: molecular compounds, photonic materials, and condensed phases. [ABSTRACT FROM AUTHOR]

We present a nonperturbative time-dependent quantum mechanical theory of the laser catalysis and control of a bifurcating A+BC↔hω0ABC*(v)↔hω0AB+C reaction, with ABC*(v) denoting an intermediate, electronically excited, complex of ABC in the vth vibrational state. We apply this theory to the low collision energy fermion-boson light-induced exchange reaction, 6Li(2S)+7Li2(3Σu+)↔hω0(6Li7Li7Li)*↔hω06Li7Li(3Σ+)+7Li(2S). We show that at very low collision energies and energetically narrow (∼0.01 cm-1) initial reactant wave packets, it is possible to tune the yield of the exchange reaction from 0 to near-unity (yield >=99%) values. Controllability is somewhat reduced at collisions involving energetically wider (∼1 cm-1) initial reactant wave packets. At these energetic bandwidths, the radiative reactive control, although still impressive, is limited to the 0%–76% reactive-probabilities range. [ABSTRACT FROM AUTHOR]

We develop a method to improve the population transfer and final-channel control of multichannel photodissociation reactions. The method is applied to the photodissociation of methyl iodide, CH3(v)+I*(2P1/2)←CH3I→CH3(v)+I(2P3/2). Our method is based on simultaneously exciting many two-photon pathways that lead to the same final outcome, each proceeding via a different intermediate bound state. The selectivity of the final product state(s) is a result of coherently controlled interference between the quantum pathways. The improvement in the population transfer yield from the ground state to the selected dissociative channel(s) is made possible by executing the process in an adiabatic fashion. [ABSTRACT FROM AUTHOR]

An application of a recently proposed [P. Král et al., Phys. Rev. Lett. 90, 033001 (2003)] two step optical control scenario to the purification of a racemic mixture of 1,3 dimethylallene is presented. Both steps combine adiabatic and diabatic passage phenomena. In the first step, three laser pulses of mutually perpendicular linear polarizations, applied in a “cyclic adiabatic passage” scheme, are shown to be able to distinguish between the L and D enantiomers due to their difference in matter-radiation phase. In the second step, which immediately follows the first, a sequence of pulses is used to convert one enantiomer to its mirror-imaged form. This scenario, which only negligibly populates the first excited electronic state, proves extremely useful for systems such as dimethylallene, which can suffer losses from dissociation and internal conversion upon electronic excitation. We computationally observe conversion of a racemic mixture of dimethylallene to a sample containing ≈95% of the enantiomer of choice. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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The time dependent quantum dynamics of the large amplitude motion of the NH stretching chromophore in NHD[sub 2] is investigated during and after coherent multiphoton excitation by calculation of the wave packet evolution using global analytical potential energy and electric dipole hypersurfaces of ammonia derived from ab initio calculations. Intramolecular vibrational redistribution between the NH stretching and bending motion and coupling to the radiation field induces a diffusion of probability density into the NH chromophore space, which includes the inversion coordinate. However, inversion remains essentially dominated by a tunneling process, even at average energies well above the inversion barrier. [ABSTRACT FROM AUTHOR]

We suggest that a very significant reduction in the group velocity of light occurs in a laser induced barrier-hopping process, known as "Laser Catalysis." In this process a system is made to hop over a potential barrier via a virtual transition to an excited bound state. As in electromagnetically induced transparency (EIT), the light absorption is predicted to dip to zero at a certain frequency, thereby also changing the refractive index, inducing in turn the slowing down of the group velocity of the light. In contrast to EIT, a single pulse is predicted to induce its own transparency and in contrast to self-induced transparency the process is predicted to be insensitive to the pulse area (as long as the pulse is intense enough to meet the adiabaticity criterion). Thus, the medium becomes transparent to the light, as the laser induced barrier-hopping process brings about a fundamental change in the medium. [ABSTRACT FROM AUTHOR]

We present a nonperturbative time-dependent quantum mechanical theory of the laser catalysis and control of a bifurcating A+BC<-->(variant Planck's over 2pi omega(0))ABC*(v)<-->(variant Planck's over 2pi omega(0) )AB+C reaction, with ABC*(v) denoting an intermediate, electronically excited, complex of ABC in the vth vibrational state. We apply this theory to the low collision energy fermion-boson light-induced exchange reaction, (6)Li((2)S)+(7)Li(2)((3)Sigma(u)(+))<-->(variant Planck's over 2pi omega(0))((6)Li(7)Li(7)Li)*<-->(variant Planck's over 2pi omega(0))(6)Li(7)Li((3)Sigma(+))+(7)Li((2)S). We show that at very low collision energies and energetically narrow (approximately 0.01 cm(-1)) initial reactant wave packets, it is possible to tune the yield of the exchange reaction from 0 to near-unity (yield >or=99%) values. Controllability is somewhat reduced at collisions involving energetically wider (approximately 1 cm(-1)) initial reactant wave packets. At these energetic bandwidths, the radiative reactive control, although still impressive, is limited to the 0%-76% reactive-probabilities range.

We develop a method to improve the population transfer and final-channel control of multichannel photodissociation reactions. The method is applied to the photodissociation of methyl iodide, CH3(v)+I*(2P1/2)<--CH3I-->CH3(v)+I(2P3/2). Our method is based on simultaneously exciting many two-photon pathways that lead to the same final outcome, each proceeding via a different intermediate bound state. The selectivity of the final product state(s) is a result of coherently controlled interference between the quantum pathways. The improvement in the population transfer yield from the ground state to the selected dissociative channel(s) is made possible by executing the process in an adiabatic fashion.