Nikesh S. Dattani

A general approach to quantum dynamics using a variational master equation: Application to phonon-damped Rabi rotations in quantum dots

We develop a versatile master equation approach to describe the nonequilibrium dynamics of a two-level system in contact with a bosonic environment, which allows for the exploration of a wide range of parameter regimes within a single formalism. As an experimentally relevant example, we apply this technique to the study of excitonic Rabi rotations in a driven quantum dot, and compare its predictions to the numerical Feynman integral approach. We find excellent agreement between the two methods across a generally difficult range of parameters. In particular, the variational master equation technique captures effects usually considered to be nonperturbative, such as multiphonon processes and bath-induced driving renormalization, and can give reliable results even in regimes in which previous master equation approaches fail.

Why Quantum Coherence Is Not Important in the Fenna–Matthews–Olsen Complex

We develop and present an improvement to the conventional technique for solving the Hierarchical Equations of Motion (HEOM), which can reduce the memory cost by up to 75% while retaining the same (or even better) convergence rate and accuracy. This allows for a full calculation of the population dynamics of the 24-site FMO trimer for long time scales with very little effort, and we present the first fully converged, exact results for the 7-site subsystem of the monomer, and for the full 24-site trimer. We then show where our exact 7-site results deviate from the approximation of Ishizaki and Fleming [A. Ishizaki and G. R. Fleming, Proc. Natl. Acad. Sci. U.S.A., 2009, 106, 17255]. Our exact results are then compared to calculations using the incoherent Förster theory, and it is found that the time scale of energy transfer is roughly the same, regardless of whether or not coherence is considered. This means that coherence is not likely to improve the efficiency of the transfer. In fact, the incoherent theory often tends to overpredict the rates of energy transfer, suggesting that, in some cases, quantum coherence may actually slow the photosynthetic process.

A DPF analysis yields accurate analytic potentials for Li

A combined-isotopologue direct-potential-fit (DPF) analysis of optical and photoassociation spectroscopy data for the

_2(a\,^3\Sigma^+_u)

a\,^{3}\Sigma_u^+

and Li

and

_2(1\,^3 \Sigma^+_g)

1\,^3\Sigma_g^+

that incorporate 3-state mixing near the

states of Li

1\,^3 \Sigma^+_g

_2

-state asymptote

has yielded accurate analytic potential energy functions for both states. The recommended M3LR

FeynDyn: A MATLAB program for fast numerical Feynman integral calculations for open quantum system dynamics on GPUs

_{5,3}^{8.0}(3)