1,911 research outputs found
Dynamic regimes of fluids simulated by multiparticle-collision dynamics
We investigate the hydrodynamic properties of a fluid simulated with a
mesoscopic solvent model. Two distinct regimes are identified, the `particle
regime' in which the dynamics is gas-like, and the `collective regime' where
the dynamics is fluid-like. This behavior can be characterized by the Schmidt
number, which measures the ratio between viscous and diffusive transport.
Analytical expressions for the tracer diffusion coefficient, which have been
derived on the basis of a molecular-chaos assumption, are found to describe the
simulation data very well in the particle regime, but important deviations are
found in the collective regime. These deviations are due to hydrodynamic
correlations. The model is then extended in order to investigate self-diffusion
in colloidal dispersions. We study first the transport properties of heavy
point-like particles in the mesoscopic solvent, as a function of their mass and
number density. Second, we introduce excluded-volume interactions among the
colloidal particles and determine the dependence of the diffusion coefficient
on the colloidal volume fraction for different solvent mean-free paths. In the
collective regime, the results are found to be in good agreement with previous
theoretical predictions based on Stokes hydrodynamics and the Smoluchowski
equation.Comment: 15 pages, 15 figure
Efficient algorithm for multi-qudit twirling for ensemble quantum computation
We present an efficient algorithm for twirling a multi-qudit quantum state.
The algorithm can be used for approximating the twirling operation in an
ensemble of physical systems in which the systems cannot be individually
accessed. It can also be used for computing the twirled density matrix on a
classical computer. The method is based on a simple non-unitary operation
involving a random unitary. When applying this basic building block
iteratively, the mean squared error of the approximation decays exponentially.
In contrast, when averaging over random unitary matrices the error decreases
only algebraically. We present evidence that the unitaries in our algorithm can
come from a very imperfect random source or can even be chosen
deterministically from a set of cyclically alternating matrices. Based on these
ideas we present a quantum circuit realizing twirling efficiently.Comment: 11 pages including 6 figures, revtex4; v2: presentation improved,
sections VI and VII added; v3: small changes before publicatio
Quantum Emulation of Molecular Force Fields: A Blueprint for a Superconducting Architecture
In this work, we propose a flexible architecture of microwave resonators with
tunable couplings to perform quantum simulations of problems from the field of
molecular chemistry. The architecture builds on the experience of the D-Wave
design, working with nearly harmonic circuits instead of qubits. This
architecture, or modifications of it, can be used to emulate molecular
processes such as vibronic transitions. Furthermore, we discuss several aspects
of these emulations, such as dynamical ranges of the physical parameters,
quenching times necessary for diabaticity, and, finally, the possibility of
implementing anharmonic corrections to the force fields by exploiting certain
nonlinear features of superconducting devices.Comment: 14 pages, 4 figure
Deep Strong Coupling Regime of the Jaynes-Cummings model
We study the quantum dynamics of a two-level system interacting with a
quantized harmonic oscillator in the deep strong coupling regime (DSC) of the
Jaynes-Cummings model, that is, when the coupling strength g is comparable or
larger than the oscillator frequency w (g/w > 1). In this case, the
rotating-wave approximation cannot be applied or treated perturbatively in
general. We propose an intuitive and predictive physical frame to describe the
DSC regime where photon number wavepackets bounce back and forth along parity
chains of the Hilbert space, while producing collapse and revivals of the
initial population. We exemplify our physical frame with numerical and
analytical considerations in the qubit population, photon statistics, and
Wigner phase space.Comment: Published version, note change of title: DSC regime of the JC mode
Microwave Photon Detector in Circuit QED
Quantum optical photodetection has occupied a central role in understanding
radiation-matter interactions. It has also contributed to the development of
atomic physics and quantum optics, including applications to metrology,
spectroscopy, and quantum information processing. The quantum microwave regime,
originally explored using cavities and atoms, is seeing a novel boost with the
generation of nonclassical propagating fields in circuit quantum
electrodynamics (QED). This promising field, involving potential developments
in quantum information with microwave photons, suffers from the absence of
photodetectors. Here, we design a metamaterial composed of discrete
superconducting elements that implements a high-efficiency microwave photon
detector. Our design consists of a microwave guide coupled to an array of
metastable quantum circuits, whose internal states are irreversibly changed due
to the absorption of photons. This proposal can be widely applied to different
physical systems and can be generalized to implement a microwave photon
counter.Comment: accepted in Phys. Rev. Let
Quantum Simulation with a Boson Sampling Circuit
In this work we study a system that consists of matter qubits that
interact through a boson sampling circuit, i.e., an -port interferometer,
embedded in two different architectures. We prove that, under the conditions
required to derive a master equation, the qubits evolve according to effective
bipartite XY spin Hamiltonians, with or without local and collective
dissipation terms. This opens the door to the simulation of any bipartite spin
or hard-core boson models and exploring dissipative phase transitions as the
competition between coherent and incoherent exchange of excitations. We also
show that in the purely dissipative regime this model has a large number of
exact and approximate dark states, whose structure and decay rates can be
estimated analytically. We finally argue that this system may be used for the
adiabatic preparation of boson sampling states encoded in the matter qubits.Comment: 9 pages, 3 figure
Trains, tails and loops of partially adsorbed semi-flexible filaments
Polymer adsorption is a fundamental problem in statistical mechanics that has
direct relevance to diverse disciplines ranging from biological lubrication to
stability of colloidal suspensions. We combine experiments with computer
simulations to investigate depletion induced adsorption of semi-flexible
polymers onto a hard-wall. Three dimensional filament configurations of
partially adsorbed F-actin polymers are visualized with total internal
reflection fluorescence microscopy. This information is used to determine the
location of the adsorption/desorption transition and extract the statistics of
trains, tails and loops of partially adsorbed filament configurations. In
contrast to long flexible filaments which primarily desorb by the formation of
loops, the desorption of stiff, finite-sized filaments is largely driven by
fluctuating filament tails. Simulations quantitatively reproduce our
experimental data and allow us to extract universal laws that explain scaling
of the adsorption-desorption transition with relevant microscopic parameters.
Our results demonstrate how the adhesion strength, filament stiffness, length,
as well as the configurational space accessible to the desorbed filament can be
used to design the characteristics of filament adsorption and thus engineer
properties of composite biopolymeric materials
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