Minimum output entropy of a non-Gaussian quantum channel

We introduce a model of non-Gaussian quantum channel that stems from the combination of two physically relevant processes occurring in open quantum systems, namely amplitude damping and dephasing. For it we find input states approaching zero output entropy, while respecting the input energy constraint. These states fully exploit the infinite dimensionality of the Hilbert space. Upon truncation of the latter, the minimum output entropy remains finite and optimal input states for such a case are conjectured thanks to numerical evidences

Entanglement dynamics for qubits dissipating into a common environment

We provide an analytical investigation of the entanglement dynamics for a system composed of an arbitrary number of qubits dissipating into a common environment. Specifically we consider initial states whose evolution remains confined on low dimensional subspaces of the operators space. We then find for which pairs of qubits entanglement can be generated and can persist at steady state. Finally, we determine the stationary distribution of entanglement as well as its scaling versus the total number of qubits in the system

Entanglement from dissipative dynamics into overlapping environments

We consider two ensembles of qubit dissipating into two overlapping environments, that is with a certain number of qubit in common that dissipate into both environments. We then study the dynamics of bipartite entanglement between the two ensembles by excluding the common qubit. To get analytical solutions for an arbitrary number of qubit we consider initial states with a single excitation and show that the largest amount of entanglement can be created when excitations are initially located among side (non common) qubit. Moreover, the stationary entanglement exhibits a monotonic (resp. non-monotonic) scaling versus the number of common (resp. side) qubit

Quantum information transmission through a qubit chain with quasi-local dissipation

We study quantum information transmission in a Heisenberg-XY chain where qubits are affected by quasi-local environment action and compare it with the case of local action of the environment. We find that for open boundary conditions the former situation always improves quantum state transfer process, especially for short chains. In contrast, for closed boundary conditions quasi-local environment results advantageous in the strong noise regime. When the noise strength is comparable with the XY interaction strength, the state transfer fidelity through chain of odd/even number of qubits in presence of quasi-local environment results smaller/greater than that in presence of local environment

Group-covariant extreme and quasi-extreme channels

Constructing all extreme instances of the set of completely positive trace-preserving (CPTP) maps, i.e., quantum channels, is a challenging valuable open problem in quantum information theory. Here we introduce a systematic approach that enables us to construct exactly those extreme channels that are covariant with respect to a finite discrete group or a compact connected Lie group. Innovative labeling of quantum channels by group representations enables us to identify the subset of group-covariant channels whose elements are group-covariant generalized-extreme channels. Furthermore, we exploit essentials of group representation theory to introduce equivalence classes for the labels and also partition the set of group-covariant channels. As a result we show that it is enough to construct one representative of each partition. We construct Kraus operators for group-covariant generalized-extreme channels by solving systems of linear and quadratic equations for all candidates satisfying the necessary condition for being group-covariant generalized-extreme channels. Deciding whether these constructed instances are extreme or quasi-extreme is accomplished by solving system of linear equations. We formalize the problem of constructing and classifying group-covariant generalized extreme channels, thereby yielding an algorithmic approach to solving, which we express as pseudocode. To illustrate the application and value of our method, we solve for explicit examples of group-covariant extreme channels. With unbounded computational resources to execute our algorithm, our method always delivers a description of an extreme channel for any finite-dimensional Hilbert-space and furthermore guarantees a description of a group-covariant extreme channel for any dimension and for any finite-discrete or compact connected Lie group if such an extreme channel exists