Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTheory of atmospheric quantum channels based on the law of total probability
98
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The atmospheric turbulence is the main factor that influences quantum properties of propagating optical signals and may sufficiently degrade the performance of quantum communication protocols. The probability distribution of transmittance (PDT) for free-space channels is the main characteristics of the atmospheric links. Applying the law of total probability, we derive the PDT by separating the contributions from turbulence-induced beam wandering and beam-spot distortions. As a result, the obtained PDT varies from log-negative Weibull to truncated log-normal distributions depending on the channel characteristics. Moreover, we show that the method allows one to consistently describe beam tracking, a procedure which is typically used in practical long-distance free-space quantum communication. We analyze the security of decoy-state quantum key exchange through the turbulent atmosphere and show that beam tracking does not always improves quantum communication.
rate research
Read More
Many fundamental and applied experiments in quantum optics require transferring nonclassical states of light through large distances. In this context the free-space channels are a very promising alternative to optical fibers as they are mobile and enable to establish communications with moving objects, using satellites for global quantum links. For such channels the atmospheric turbulence is the main disturbing factor. The statistical properties of the fluctuating transmittance through the turbulent atmosphere are given by the probability distribution of transmittance (PDT). We derive the consistent PDTs for the atmospheric quantum channels by step-by-step inclusion of various atmospheric effects such as beam wandering, beam broadening and deformation of the beam into elliptic form, beam deformations into arbitrary forms. We discuss the applicability of PDT models for different propagation distances and optical turbulence strengths in the case when the receiver module has an annular aperture. We analyze the optimal detection and correction strategies which can improve the channel transmission characteristics. The obtained results are important for the design of optical experiments including postselection and adaptive strategies and for the security analysis of quantum communication protocols in free-space.
Active control of quantum systems enables diverse applications ranging from quantum computation to manipulation of molecular processes. Maximum speeds and related bounds have been identified from uncertainty principles and related inequalities, but such bounds utilize only coarse system information, and loosen significantly in the presence of constraints and complex interaction dynamics. We show that an integral-equation-based formulation of conservation laws in quantum dynamics leads to a systematic framework for identifying fundamental limits to any quantum control scenario. We demonstrate the utility of our bounds in three scenarios -- three-level driving, decoherence suppression, and maximum-fidelity gate implementations -- and show that in each case our bounds are tight or nearly so. Global bounds complement local-optimization-based designs, illuminating performance levels that may be possible as well as those that cannot be surpassed.
Free-space quantum links have clear practical advantages which are unaccessible with fiber-based optical channels --- establishing satellite-mediated quantum links, communications through hardly accessible regions, and communications with moving objects. We consider the effect of the atmospheric turbulence on properties such as quadrature squeezing, entanglement, Bell nonlocality, and nonclassical statistics of photocounts, which are resources for quantum communications. Depending on the characteristics of the given channels, we study the efficiency of different techniques, which enable to preserve these quantum features---post-, pre-selection, and adaptive methods. Furthermore, we show that copropagation of nonclassically-correlated modes, which is used in some communication scenarios, has clear advantages in free-space links.
We study the Kimble-Braunstein continuous-variable quantum teleportation with the quantum channel physically realized in the turbulent atmosphere. In this context, we examine the applicability of different strategies preserving the Gaussian entanglement [Bohmann et al., Phys. Rev. A 94, 010302(R) (2016)] for improving the fidelity of the coherent-state teleportation. First, we demonstrate that increasing the squeezing parameter characterizing the entangled state is restricted by its optimal value, which we derive for realistic experimentally-verified examples. Further, we consider the technique of adaptive correlations of losses and show its performance for channels with large squeezing parameters. Finally, we investigate the efficiencies of postselection strategies in dependence on the stochastic properties of the channel transmittance.
We discuss the problem of separating the total correlations in a given quantum joint probability distribution into nonlocality, contextuality and classical correlations. Bell discord and Mermin discord which qunatify nonlocality and contextuality of quantum correlations are interpreted as distance measures in the nonsignaling polytope. A measure of total correlations is introduced to divide the total amount of correlations into a purely nonclassical part and a classical part. We show that quantum correlations satisfy additivity relations among these three measures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
