Sharing and receiving information plays a pivotal role in science and technology. Quantum communication relies on the principles of quantum mechanics to transmit information in a nonclassical manner. Existing quantum communication protocols are commonly based on shared entangled states between sender and receiver, while the transmitting medium is classical. We here demonstrate that information transfer may be enhanced in a quantum correlated medium without entanglement distribution. We concretely show that nonclassical correlations, with nonzero discord, between the first two spins of a spin chain that acts as a quantum wire can increase the information flow and reduce the propagation time. We relate this effect to the breaking of the spatial symmetry of the out-of-time-order correlator that characterizes the spread of information through the medium.
Sharing and receiving information plays a pivotal role in science and technology. Quantum communication relies on the principles of quantum mechanics to transmit information in a nonclassical manner. Existing quantum communication protocols are commonly based on shared entangled states between sender and receiver, while the transmitting medium is classical. We here demonstrate that information transfer may be enhanced in a quantum correlated medium without entanglement distribution. We concretely show that nonclassical correlations, with nonzero discord, between the first two spins of a spin chain that acts as a quantum wire can increase the information flow and reduce the propagation time. We relate this effect to the breaking of the spatial symmetry of the out-of-time-order correlator that characterizes the spread of information through the medium.
We study the transport of quantum correlations across a chain of interacting spin-1/2 particles. As a quantitative figure of merit, we choose a symmetric version of quantum discord and compare it with the transported entanglement, addressing various operating regimes of the spin medium. Discord turns out to be better transported for a wide range of working points and initial conditions of the system. We relate this behavior to the efficiency of propagation of a single excitation across the spin chain. Moreover, we point out the role played by a magnetic field in the dynamics of discord in the effective channel embodied by the chain. Our analysis can be interestingly extended to transport processes in more complex networks and the study of nonclassical correlations under general quantum channels.
Introduction.The field of quantum communication represents a fundamental shift in the way information is transmitted and secured.Classical communication systems, relying on classical bits, are vulnerable to eavesdropping due to their deterministic nature.Quantum communication, based on the principles of quantum mechanics, employs qubits and entanglement to provide a novel approach to secure information transfer.This paper explores the foundational concepts, recent developments, and future prospects of quantum communication. Quantum Key Distribution.A pivotal utility within the realm of quantum communication is Quantum Key Distribution (QKD), a concept initially formulated by Bennett and Brassard in 1984 [1].QKD capitalizes on the unique attributes of quantum states to establish a secure key shared between two communicating parties.This cryptographic key serves the dual purpose of encoding and decoding messages, rendering any surreptitious interception unmistakably conspicuous.Entanglement in Quantum Communication.Entanglement, a phenomenon that gained fame through the exposition by Einstein, Podolsky, and Rosen in their 1935 publication [2], assumes a pivotal role in the domain of quantum communication.Entangled qubits exhibit an intricate correlation, where any measurement performed on one qubit instantaneously influences its entangled counterpart, irrespective of the spatial separation between them.This distinctive property is skillfully employed to identify any covert surveillance in Quantum Key Distribution (QKD) systems, thus fortifying the security of the communication channel. Recent Advancements, Challenges and Future Directions.In recent times, quantum communication has experienced substantial progress.Remarkable breakthroughs encompass the deployment of satellite-based quantum communication systems to ensure global, secure information exchange [3], alongside the creation of pragmatic Quantum Key Distribution (QKD) devices tailored for real-world use [4].These strides serve to propel quantum communication further toward its practical and extensive realization.While quantum communication has made notable headway, it is not without its lingering hurdles.These encompass the necessity for innovating quantum repeater technologies, which are instrumental in augmenting the reach of quantum communication.Additionally, the mitigation of environmental interference in quantum channels remains a formidable challenge.Moreover, there exists a pressing demand for standardization and the enhancement of interoperability within quantum protocols.Continuous research endeavors persist in tackling these issues and propelling the field forward [5]. Conclusion.Quantum communication represents a paradigm shift in secure information transfer, with quantum entanglement at its core.Recent advancements
Transmitting quantum states and entanglement through quantum channels is one of the key requirements for the development of quantum computation. Quantum discord has received much attention in quantum computation. We transfer quantum discord through two parallel XXZ spin chains with phase shift. The maximum discord can be enhanced by the phase shift. It will take more time to obtain an enhanced maximum discord in some cases, but for other cases, both the maximum and speed are enhanced by the phase shift. In the thermodynamic limit, the effect of the phase shift disappears and the maximum discord exponentially decays with increasing of the receiving position. Our results on spin chains are generalized to a family of linear Hamiltonians.
While for single-mode bosonic fields, one talks about nonclassicality of quantum states, which plays an important role in various quantum information processing tasks, for composite systems, one talks about quantum correlations such as quantum entanglement and quantum discord, which are crucial and indispensable for implementation of quantum communication and computation. Both nonclassicality and quantum correlations are quantum features of physical systems and fundamental resources which can be exploited to bring supremacy over classical systems. A natural question arises on the relation and interconversion between these two resources. In this work, we investigate the conversion of single-mode nonclassicality into quantum correlations via beamsplitters. Our work is based on the idea of Asbó et al . ( Phys. Rev. Lett. , 94 (2005) 173602) of converting nonclassicality into quantum entanglement via a balanced beamsplitter. Through a paradigmatic setup with Gaussian states fed into the beamsplitters, we demonstrate that quantum correlations between the output states, as exhibited by either entanglement or quantum discord, increase monotonically with nonclassicality of the input Gaussian states, as quantified by an information-theoretic measure in terms of the Wigner-Yanase skew information.
Networks of quantum devices with coherent control over their configuration offer promising advantages in quantum information processing, including quantum communication, computation, and sensing. So far, the investigation of these advantages assumed that the control system was initially uncorrelated with the data processed by the network. Here, we explore the power of quantum correlations between data and control, showing two communication tasks that can be accomplished with information-erasing channels if and only if the sender shares prior entanglement with a third party (the ``controller'') controlling the network configuration. The first task is to transmit classical messages without leaking information to the controller. The second task is to establish bipartite entanglement with a receiver, or, more generally, to establish multipartite entanglement with a number of spatially separated receivers.
The ability to distribute quantum entanglement is a prerequisite for many fundamental tests of quantum theory and numerous quantum information protocols. Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in a carrier that is sent from one party to the other. Intriguingly, entanglement can be increased even when the exchanged carrier is not entangled with the parties. However, in light of the defining property of entanglement stating that it cannot increase under classical communication, the carrier must be quantum. Here we show that, in general, the increase of relative entropy of entanglement between two remote parties is bounded by the amount of nonclassical correlations of the carrier with the parties as quantified by the relative entropy of discord. We study implications of this bound, provide new examples of entanglement distribution via unentangled states, and put further limits on this phenomenon.