arXiv subjects

N. Awasthi

Publications and source records attributed to N. Awasthi.

3 recordsLinked to original sources

arXiv2019

Quantum speed limit time for correlated quantum channel

Memory effects play a fundamental role in the dynamics of open quantum systems. There exist two different views on memory for quantum noises. In the first view, the quantum channel has memory when there exist correlations between successive uses of the channels on a sequence of quantum systems. These types of channels are also known as correlated quantum channels. In the second view, memory effects result from correlations which are created during the quantum evolution. In this work we will consider the first view and study the quantum speed limit time for a correlated quantum channel. Quantum speed limit time is the bound on the minimal time which is needed for a quantum system to evolve from an initial state to desired states. The quantum evolution is fast if the quantum speed limit time is short. In this work, we will study the quantum speed limit time for some correlated unital and correlated non-unital channels. As an example for unital channels we choose correlated dephasing colored noise. We also consider the correlated amplitude damping and correlated squeezed generalized amplitude damping channels as the examples for non-unital channels. It will be shown that the quantum speed limit time for correlated pure dephasing colored noise is increased by increasing correlation strength, while for correlated amplitude damping and correlated squeezed generalized amplitude damping channels quantum speed limit time is decreased by increasing correlation strength.

quant-ph↗

arXiv2019

Investigate the effects of the existence of correlation between two consecutive use of the quantum channel on quantum speed limit time

Memory effects play an important role in the theory of open quantum systems. There are two completely independent insights about memory for quantum channels. In quantum information theory, the memory of the quantum channel is depicted by the correlations between consecutive uses of the channel on a set of quantum systems. In the theory of open quantum systems memory effects result from correlations which are created during the quantum evolution. Here, we study the quantum speed limit time for correlated quantum channel i.e. when there exist correlation between consecutive uses of quantum channel . Quantum speed limit time is the bound on the minimal time evolution between initial and target states. It is apply for quantifying the maximum speed of quantum evolution. In this work, we will consider correlated pure dephasing colored noise as an example of unital quantum channels and correlated squeezed generalized amplitude damping channel as an example of non-unital quantum channels. We evaluate the quantum speed limit time for these two channel. We find that regardless of whether the channel is unital or not, the quantum speed limit time is increased by increasing correlation between two consecutive uses of the channel.

quant-ph↗

arXiv2008

Reduced carbon solubility in Fe nano-clusters and implications for the growth of single-walled carbon nanotubes

Various diameters of alumina-supported Fe catalysts are used to grow single-walled carbon nanotubes (SWCNTs) with chemical vapor decomposition. We find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nano-clusters at low temperature. We show that, as a function particles size, there are three scenarios compatible with steady state-, limited- and no-growth of SWCNTs, corresponding to unaffected, reduced and no solubility of C in the particles. The result raises previously unknown concerns about the growth feasibility of small and very-long SWCNTs within the current Fe CVD technology, and suggests new strategies in the search of better catalysts.

cond-mat.mtrl-sci↗