25 research outputs found
State-space distribution and dynamical flow for closed and open quantum systems
We present a general formalism for studying the effects of dynamical
heterogeneity in open quantum systems. We develop this formalism in the state
space of density operators, on which ensembles of quantum states can be
conveniently represented by probability distributions. We describe how this
representation reduces ambiguity in the definition of quantum ensembles by
providing the ability to explicitly separate classical and quantum sources of
probabilistic uncertainty. We then derive explicit equations of motion for
state space distributions of both open and closed quantum systems and
demonstrate that resulting dynamics take a fluid mechanical form analogous to a
classical probability fluid on Hamiltonian phase space, thus enabling a
straightforward quantum generalization of Liouville's theorem. We illustrate
the utility of our formalism by analyzing the dynamics of an open two-level
system using the state-space formalism that are shown to be consistent with the
derived analytical results
Symmetrized Drude Oscillator Force Fields Improve Numerical Performance of Polarizable Molecular Dynamics
Drude oscillator potentials are a popular and computationally efficient class
of polarizable models that represent each polarizable atom as a positively
charged Drude core harmonically bound to a negatively charged Drude shell. We
show that existing force fields that place all non-Coulomb forces on the Drude
core and none on the shell inadvertently couple the dipole to non-Coulombic
forces. This introduces errors where interactions with neutral particles can
erroneously induce atomic polarization, leading to spurious polarizations in
the absence of an electric field and exacerbating violations of equipartition
in the employed Carr-Parinello scheme. A suitable symmetrization of the
interaction potential that correctly splits the force between the Drude core
and shell can correct this shortcoming, improving the stability and numerical
performance of Drude oscillator based simulations. The symmetrization procedure
is straightforward and only requires the rescaling of a few force field
parameters
Excitation of Molecular Systems by Incoherent Light
The excitation of molecular systems by incoherent light is studied primarily using a V-system model in the Partial Secular Bloch-Redfield formalism.
First, the dynamical regimes are characterized for a system irradiated by suddenly turned on light and the relevant timescales are defined in terms of system parameters.
Then excitation by slowly turned-on light is studied, showing a decay in the magnitude of noise-induced coherences with increasing turn-on times, leading to their disapearance in the very slow turn-on limit relevant to many natural systems.M.Sc
Nonequilibrium Work Relations and Response Theories in Ensemble Quantum Systems
We develop a nonequilibrium response theory for macroscopic quantum systems that separates the contributions of ensemble heterogeneity and intrinsic quantum uncertainty. To accomplish this, we describe systems with a quantum P-ensemble, which goes beyond the standard density matrix description by explicitly specifying the classical heterogeneity between individual quantum systems in an ensemble. We use the P-ensemble formalism to present quantum generalizations of linear response theory and the Jarzynski nonequilibrium work relation. We derive these generalizations from a Bochkov-Kuzovlev generating functional for quantum P-ensembles, which can be further utilized to derive all orders of response theory that apply to ensemble quantum systems. We contrast these developments with their ρ-ensemble analogs, and we discuss how these P-ensemble theories provide a guide for an effective application of single molecule experiments
On the Design of Molecular Excitonic Circuits for Quantum Computing: The Universal Quantum Gates
This manuscript presents a theoretical strategy for encoding elementary quantum computing operations into the design of molecular excitonic circuits. Specifically, we show how the action of a unitary transformation of coupled two-level systems can be equivalently represented by the evolution of an exciton in a coupled network of dye molecules. We apply this strategy to identify the geometric parameters for circuits that perform universal quantum logic gate operations. We quantify the design space for these circuits and how their performance is affected by environmental noise
On the design of molecular excitonic circuits for quantum computing: the universal quantum gates
This manuscript presents a strategy for controlling the transformation of excitonic states through the design of circuits made up of coupled organic dye molecules. Specifically, we show how unitary transformation matrices can be mapped to the Hamiltonians of physical systems of dye molecules with specified geometric and chemical properties. The evolution of these systems over specific time scales encodes the action of the unitary transformation. We identify bounds on the complexity of the transformations that can be represented by these circuits and on the optoelectronic properties of the dye molecules that comprise them. We formalize this strategy and apply it to determine the excitonic circuits of the four universal quantum logic gates: NOT, Hadamard, π/8 and CNOT. We discuss the properties of these circuits and how their performance is expected to be influenced by the presence of environmental noise.National Science Foundation (Grant CHE-1839155)United States. Department of Energy (Award DE-SC0019998