Coherent information

About: Coherent information is a research topic. Over the lifetime, 1225 publications have been published within this topic receiving 46672 citations.

Five approaches to exact open-system dynamics: Complete positivity, divisibility and time-dependent observables

Abstract: To extend the classical concept of Markovianity to an open quantum system, different notions of the divisibility of its dynamics have been introduced. Here we analyze this issue by five complementary approaches: equations of motion, real-time diagrammatics, Kraus-operator sums, as well as time-local (TCL) and nonlocal (Nakajima-Zwanzig) quantum master equations. As a case study featuring several types of divisible dynamics, we examine in detail an exactly solvable noninteracting fermionic resonant level coupled arbitrarily strongly to a fermionic bath at arbitrary temperature in the wideband limit. In particular, the impact of divisibility on the time-dependence of the observable level occupation is investigated and compared with typical Markovian approximations. We find that the loss of semigroup-divisibility is accompanied by a prominent reentrant behavior: Counter to intuition, the level occupation may temporarily \emph{increase} significantly in order to reach a stationary state with \emph{smaller} occupation, implying a reversal of the measurable transport current. In contrast, the loss of the so-called completely-positive divisibility is more subtly signaled by the \emph{prohibition} of such current reversals in specific time-intervals. Experimentally, it can be detected in the family of transient currents obtained by varying the initial occupation. To quantify the nonzero footprint left by the system in its effective environment, we determine the exact time-dependent state of the latter as well as related information measures such as entropy, exchange entropy and coherent information.

Information theory density matrix for a simple quantum system

Abstract: The density matrix is derived that best describes, according to information theory, a one‐dimensional single particle quantum system, when the only information available is the values for the linear and quadratic position‐momentum moments. In addition, moment generating functions and the time development of the system under a simple interaction are considered.

Dynamic Polariton and Quantum State Swapping Between an Electromagnetic Field and Atomic Ensemble

Abstract: We analyse a dynamical swapping of the quantum state in coupled harmonic oscillators. The result can be applied to the interaction of a single-mode field with atomic ensemble in the weak field case. Similar to the case of electromagnetic induced transparency (EIT), a dynamic polariton is formed. Therefore, the quantum state of the field can be completely mapped on to the atomic medium, and vice versa. Using this dynamical swapping and the adiabatic transfer in the EIT between the field and atomic ensemble, we propose a scheme in which both the quantum and the coherent information can be transferred from one field to another.

Information theoretical analysis of the hydrogen atom

Abstract: This is an analysis of the statistical nature of the time-independent Schrodinger equation through the use of the information entropy concept. We first study the Schrodinger equation in a general way and then by actually computing entropies of various states of the hydrogen atom for a re-examination of the problem. It is found that there exists a variational procedure involving maximizing entropy for obtaining all solutions once one solution is known. Based on certain observations of the particular single system, some general conclusions can be deduced. First of all, we can safely say that the Schrodinger equation, among many other interpretations, is but the consequence of a principle of minimum potential energy expectation with certain proper constraints imposed. In addition, the ensemble concept in statistical thermodynamics is also useful in understanding microscopic quantum systems and many quantum mechanical concepts such as energy quantization and wave nodal properties can be discussed in the light of information theory and statistics in general.

Quantum Information Theory and Applications to Quantum Cryptography

Abstract: Classical and quantum information theory are simply explained. To be more specific it is clarified why Shannon entropy is used as measure of classical information and after a brief review of quantum mechanics it is possible to demonstrate why the density matrix is the main tool of quantum information theory. Then von Neumann entropy is introduced and with its help a great difference between classical and quantum information theory is presented: quantum entanglement. Moreover an information theoretic interpretation of quantum measurement is discussed. Data compression, error correction and noisy channel transmission are simply demonstrated for both classical and quantum cases. Finally using the above theory quantum cryptography is reviewed and the possibility of a commercial device realizing it is explored.