34 research outputs found
Computation of the asymptotic states of modulated open quantum systems with a numerically exact realization of the quantum trajectory method
Quantum systems out of equilibrium are presently a subject of active
research, both in theoretical and experimental domains. In this work we
consider time-periodically modulated quantum systems which are in contact with
a stationary environment. Within the framework of a quantum master equation,
the asymptotic states of such systems are described by time-periodic density
operators. Resolution of these operators constitutes a non-trivial
computational task. To go beyond the current size limits, we use the quantum
trajectory method which unravels master equation for the density operator into
a set of stochastic processes for wave functions. The asymptotic density matrix
is calculated by performing a statistical sampling over the ensemble of quantum
trajectories, preceded by a long transient propagation. We follow the ideology
of event-driven programming and construct a new algorithmic realization of the
method. The algorithm is computationally efficient, allowing for long 'leaps'
forward in time, and is numerically exact in the sense that, being given the
list of uniformly distributed (on the unit interval) random numbers, , one could propagate a quantum trajectory (with 's
as norm thresholds) in a numerically exact way. %Since the quantum trajectory
method falls into the class of standard sampling problems, performance of the
algorithm %can be substantially improved by implementing it on a computer
cluster. By using a scalable -particle quantum model, we demonstrate that
the algorithm allows us to resolve the asymptotic density operator of the model
system with states on a regular-size computer cluster, thus reaching
the scale on which numerical studies of modulated Hamiltonian systems are
currently performed
Unfolding quantum master equation into a system of real-valued equations: computationally effective expansion over the basis of generators
Dynamics of an open -state quantum system is typically modeled with a
Markovian master equation describing the evolution of the system's density
operator. By using generators of group as a basis, the density operator
can be transformed into a real-valued 'Bloch vector'. The Lindbladian, a
super-operator which serves a generator of the evolution, %in the master
equation, can be expanded over the same basis and recast in the form of a real
matrix. Together, these expansions result is a non-homogeneous system of
real-valued linear differential equations for the Bloch vector. Now one
can, e.g., implement a high-performance parallel simplex algorithm to find a
solution of this system which guarantees exact preservation of the norm and
Hermiticity of the density matrix. However, when performed in a straightforward
way, the expansion turns to be an operation of the time complexity
. The complexity can be reduced when the number of
dissipative operators is independent of , which is often the case for
physically meaningful models. Here we present an algorithm to transform quantum
master equation into a system of real-valued differential equations and
propagate it forward in time. By using a scalable model, we evaluate
computational efficiency of the algorithm and demonstrate that it is possible
to handle the model system with states on a single node of a
computer cluster
Extreme plasma states in laser-governed vacuum breakdown
Triggering vacuum breakdown at the upcoming laser facilities can provide
rapid electron-positron pair production for studies in laboratory astrophysics
and fundamental physics. However, the density of the emerging plasma should
seemingly stop rising at the relativistic critical density, when the plasma
becomes opaque. Here we identify the opportunity of breaking this limit using
optimal beam configuration of petawatt-class lasers. Tightly focused laser
fields allow plasma generation in a small focal volume much less than
, and creating extreme plasma states in terms of density and
produced currents. These states can be regarded as a new object of nonlinear
plasma physics. Using 3D QED-PIC simulations we demonstrate the possibility of
reaching densities of more than cm, which is an order of
magnitude higher than previously expected. Controlling the process via the
initial target parameters gives the opportunity to reach the discovered plasma
states at the upcoming laser facilities
Variations in the Intragene Methylation Profiles Hallmark Induced Pluripotency
We demonstrate the potential of differentiating embryonic and induced pluripotent stem cells by the regularized linear and decision tree machine learning classification algorithms, based on a number of intragene methylation measures. The resulting average accuracy of classification has been proven to be above 95%, which overcomes the earlier achievements. We propose a constructive and transparent method of feature selection based on classifier accuracy. Enrichment analysis reveals statistically meaningful presence of stemness group and cancer discriminating genes among the selected best classifying features. These findings stimulate the further research on the functional consequences of these differences in methylation patterns. The presented approach can be broadly used to discriminate the cells of different phenotype or in different state by their methylation profiles, identify groups of genes constituting multifeature classifiers, and assess enrichment of these groups by the sets of genes with a functionality of interest
Ultrabright GeV photon source via controlled electromagnetic cascades in laser-dipole waves
One aim of upcoming high-intensity laser facilities is to provide new high-flux gamma-ray sources. Electromagnetic cascades may serve for this, but are known to limit both field strengths and particle energies, restricting efficient production of photons to sub-GeV energies. Here we show how to create a directed GeV photon source, enabled by a controlled interplay between the cascade and anomalous radiative trapping. Using advanced 3D QED particle-in-cell (PIC) simulations and analytic estimates, we show that the concept is feasible for planned peak powers of 10 PW level. A higher peak power of 40 PW can provide photons with GeV energies in a well-collimated 3 fs beam, achieving peak brilliance ph smradmm/0.1BW. Such a source would be a powerful tool for studying fundamental electromagnetic and nuclear processes