Coherent information

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

Tsallis entropy in phase-space quantum mechanics

Abstract: In this paper we define the quantum version of the Tsallis entropy in terms of quantum phase space distribution functions. The quantum Tsallis entropy is compared with Kenfack's nonclassicality indicator, for different systems, such as the Schr\"odinger cat state, the thermal state, a superposition of the ground and the first excited number states, and the harmonic oscillator state. These comparisons indicate that the Wigner representation gives us complete information about the state with the nonextensivity parameter $q=1$, while the Husimi representation hides some information with the nonextensivity parameter $ql1$.

A general formula for the classical capacity of a general quantum channel

Abstract: We derive a general formula of the channel capacity for any (classical-) quantum channel. It can be regarded as a quantum version of Verdu and Han's result (see IEEE Trans. Inform. Theory, vol.40, p.1147-57, 1994). Our results contain Holevo's (see IEEE Trans. Inform. Theory, vol.44, p.269-73, 1998) and Schumacher and Westmoreland's (see Phys. Rev. A, vol.56, p.131-8, 1997) results as the stationary and memoryless case.

Nature computes: information processing in quantum dynamical systems.

Abstract: Nature intrinsically computes. It has been suggested that the entire universe is a computer, in particular, a quantum computer. To corroborate this idea we require tools to quantify the information processing. Here we review a theoretical framework for quantifying information processing in a quantum dynamical system. So-called intrinsic quantum computation combines tools from dynamical systems theory, information theory, quantum mechanics, and computation theory. We will review how far the framework has been developed and what some of the main open questions are. On the basis of this framework we discuss upper and lower bounds for intrinsic information storage in a quantum dynamical system.

Accessible information and informational power of quantum 2-designs

Abstract: The accessible information and the informational power quantify the amount of information extractable from a quantum ensemble and by a quantum measurement, respectively. So-called spherical quantum 2-designs constitute a class of ensembles and measurements relevant in testing entropic uncertainty relations, quantum cryptography, and quantum tomography. We provide lower bounds on the entropy of 2-design ensembles and measurements, from which upper bounds on their accessible information and informational power follow, as a function of the dimension only. We show that the statistics generated by 2-designs, although optimal for the abovementioned protocols, never contains more than one bit of information. Finally, we specialize our results to the relevant cases of symmetric informationally complete (SIC) sets and maximal sets of mutually unbiased bases (MUBs), and we generalize them to the arbitrary-rank case.

Entangled states in the two-mode coherent fields interacting with a two-level atom

Abstract: We investigate the entanglement properties of the two-mode coherent fields interacting with a two-level atom via the two-photon transition. We discuss the quantum entanglement between the two-mode coherent fields and the two-level atom by using the quantum reduced entropy and that between the two-mode coherent fields by using the quantum relative entropy. We also examine the influences of the initial states of the atom and the two-mode coherent fields on the quantum entanglement of the system. Our results show that three types of entangled states can be prepared via the two-mode coherent fields interacting with a two-level atom and choosing appropriately the initial-state parameters of the system.