The degree of non-Markovianity of quantum processes has been characterized in several different ways in the recent literature. However, the relationship between the non-Markovian behavior and the flow of information between the system and the environment through an entropic measure has not been yet established. We propose an entanglement-based measure of non-Markovianity by employing the concept of assisted knowledge, where the environment E, acquires information about a system S, by means of its measurement apparatus A. The assisted knowledge, based on the accessible information in terms of von Neumann entropy, monotonically increases in time for all Markovian quantum processes. We demonstrate that the signatures of non-Markovianity can be captured by the nonmonotonic behavior of the assisted knowledge. We explore this scenario for a two-level system undergoing a relaxation process, through an experimental implementation using an optical approach that allows full access to the state of the environment. The inevitable interaction between a system and its environment typically results in the loss of quantum features, such as coherence [1,2]. One important aspect in the study of these so-called open quantum systems is the concept of non-Markovianity, which arises due to memory effects of the environment. Non-Markovian features might enable the system to recover part of the lost coherence and information back from the environment [1][2][3][4]. Although these memory effects have been investigated in the past, only recently an increase in the understanding of nonMarkovianity from a quantum information perspective has emerged [5][6][7][8][9][10][11].The non-Markovian nature of a dynamical quantum map can be characterized through a number of distinct methods [5][6][7][8][9][10]. To date, the measure defined by Breuer, Laine, and Piilo [6] based on trace distance, is the most significant quantifier of the degree of non-Markovianity, due to its interpretation: non-Markovianity manifests itself as a reverse flow of information from the environment back to the system. An alternative method to measure the degree of non-Markovianity relies on the fact that local, completely positive trace-preserving (CPTP) maps cannot increase the entanglement between an open quantum system and an isolated ancillary system [12]. Exploiting this property, Rivas, Huelga, and Plenio (RHP) have defined another measure for the degree of non-Markovianity [7]. According to the RHP measure, a dynamical process is said to be nonMarkovian if the entanglement between the open system and the isolated ancilla temporarily increases throughout the dynamics. Although the RHP measure provides a connection between the non-Markovian behavior of dynamical maps and entanglement, a meaning in terms of information flow is still lacking in this approach.Here, we propose an entanglement-based measure of non-Markovianity having a direct information based interpretation. Our method is based on the decoherence program [13], where a system S is coupled to a measurement ...

We study the dynamics of quantum correlations of two coupled double quantum dots containing two excess electrons. The dissipation is included through the contact with an oscillator bath. We solve the Redfield master equation in order to determine the dynamics of the quantum discord and the entanglement of formation. Based on our results, we find that the quantum discord is more resistant to dissipation than the entanglement of formation for such a system. We observe that this characteristic is related to whether the oscillator bath is common to both qubits or not and to the form of the interaction Hamiltonian. Moreover, our results show that the quantum discord might be finite even for higher temperatures in the asymptotic limit.

Quantum discord (QD) measures the fraction of the pairwise mutual information that is locally inaccessible in a multipartite system. Fundamental aspects related to two important measures in quantum information theory, namely the entanglement of formation (EOF) and the conditional entropy, can be understood in terms of the distribution of this form of local inaccessible information (LII). As such, the EOF for an arbitrarily mixed bipartite system AB can be related to the gain or loss of LII due to the extra knowledge that a purifying ancillary system E has on the pair AB. Similarly, a clear meaning of the negativity of the conditional entropy for AB is given. We employ these relations to elucidate important and yet not well-understood quantum features, such as the bipartite entanglement sudden death and the distinction between EOF and QD for quantifying quantum correlation. For that we introduce the concept of LII flow that quantifies the LII shared in a multipartite system when sequential local measurements are carried out.

We study the non-Markovianity of the dynamics of open quantum systems, focusing on the cases of independent and common environmental interactions. We investigate the degree of non-Markovianity quantified by two distinct measures proposed by Luo, Fu, and Song and Breuer, Laine, and Pillo. We show that the amount of non-Markovianity, for a single qubit and a pair of qubits, depends on the quantum process, the proposed measure, and whether the environmental interaction is collective or independent. In particular, we demonstrate that while the degree of non-Markovianity generally increases with the number of qubits in the system for independent environments, the same behavior is not always observed for common environments. In the latter case, our analysis suggests that the amount of non-Markovianity could increase or decrease depending on the properties of the considered quantum process.

Photocurrent spectroscopy of intersubband transitions in GaInAsN/(Al)GaAs asymmetric quantum well infrared photodetectors