132 research outputs found
Quantum Parrondo's game with random strategies
We present a quantum implementation of Parrondo's game with randomly switched
strategies using 1) a quantum walk as a source of ``randomness'' and 2) a
completely positive (CP) map as a randomized evolution. The game exhibits the
same paradox as in the classical setting where a combination of two losing
strategies might result in a winning strategy. We show that the CP-map scheme
leads to significantly lower net gain than the quantum walk scheme
Employing online quantum random number generators for generating truly random quantum states in Mathematica
We present a new version of TRQS package for Mathematica computing system.
The package allows harnessing quantum random number generators (QRNG) for
investigating the statistical properties of quantum states. It implements a
number of functions for generating random states. The new version of the
package adds the ability to use the on-line quantum random number generator
service and implements new functions for retrieving lists of random numbers.
Thanks to the introduced improvements, the new version provides faster access
to high-quality sources of random numbers and can be used in simulations
requiring large amount of random data.Comment: New version of the package described in arXiv:1102.4598. Software
available at http://www.iitis.pl/~miszczak/trq
Models of quantum computation and quantum programming languages
The goal of the presented paper is to provide an introduction to the basic
computational models used in quantum information theory. We review various
models of quantum Turing machine, quantum circuits and quantum random access
machine (QRAM) along with their classical counterparts. We also provide an
introduction to quantum programming languages, which are developed using the
QRAM model. We review the syntax of several existing quantum programming
languages and discuss their features and limitations.Comment: 23 pages, 10 figures, 9 listing
Approximation of quantum control correction scheme using deep neural networks
We study the functional relationship between quantum control pulses in the
idealized case and the pulses in the presence of an unwanted drift. We show
that a class of artificial neural networks called LSTM is able to model this
functional relationship with high efficiency, and hence the correction scheme
required to counterbalance the effect of the drift. Our solution allows
studying the mapping from quantum control pulses to system dynamics and then
analysing the robustness of the latter against local variations in the control
profile.Comment: 6 pages, 3 figures, Python code available upon request. arXiv admin
note: text overlap with arXiv:1803.0516
Geometrical versus time-series representation of data in quantum control learning
Recently machine learning techniques have become popular for analysing
physical systems and solving problems occurring in quantum computing. In this
paper we focus on using such techniques for finding the sequence of physical
operations implementing the given quantum logical operation. In this context we
analyse the flexibility of the data representation and compare the
applicability of two machine learning approaches based on different
representations of data. We demonstrate that the utilization of the geometrical
structure of control pulses is sufficient for achieving high-fidelity of the
implemented evolution. We also demonstrate that artificial neural networks,
unlike geometrical methods, posses the generalization abilities enabling them
to generate control pulses for the systems with variable strength of the
disturbance. The presented results suggest that in some quantum control
scenarios, geometrical data representation and processing is competitive to
more complex methods.Comment: 12 pages, 14 figures, Python code available upon the reques
Lower and upper bounds on the fidelity susceptibility
We derive upper and lower bounds on the fidelity susceptibility in terms of
macroscopic thermodynamical quantities, like susceptibilities and thermal
average values. The quality of the bounds is checked by the exact expressions
for a single spin in an external magnetic field. Their usefulness is
illustrated by two examples of many-particle models which are exactly solved in
the thermodynamic limit: the Dicke superradiance model and the single impurity
Kondo model. It is shown that as far as divergent behavior is considered, the
fidelity susceptibility and the thermodynamic susceptibility are equivalent for
a large class of models exhibiting critical behavior.Comment: 19 page
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