Information capacities description of spin chains correlations

Saikat Sur, V. Subrahmanyam

Vittorio Giovannetti, Rosario Fazio

Information capacities achievable in the multi-parallel-use scenarios are employed to characterize the quantum correlations in unmodulated spin chains. By studying the qubit amplitude damping channel, we calculate the quantum capacity $Q$, the entanglement assisted capacity ${C}_{E}$, and the classical capacity ${C}_{1}$ of a spin chain with ferromagnetic Heisenberg interactions.

Beni Yoshida

Vittorio Giovannetti, Rosario Fazio

Information capacities are used to characterize the quantum correlations in unmodulated spin chains. By studying the qubit amplitude damping channel, we calculate the quantum capacity Q, the entanglement assisted capacity C_E, and the classical capacity C_1 of a spin chain with ferromagnetic Heisenberg interactions.

Marco Radaelli, Gabriel Teixeira Landi, Kavan Kishore Modi +1 more

Abstract Many real-world tasks include some kind of parameter estimation, i.e. the determination of a parameter encoded in a probability distribution. Often, such probability distributions arise from stochastic processes. For a stationary stochastic process with temporal correlations, the random variables that constitute it are identically distributed but not independent. This is the case, for instance, for quantum continuous measurements. In this article, we derive the asymptotic Fisher information rate for a stationary process with finite Markov order. We give a precise expression for this rate which is determined by the process’ conditional distribution up to its Markov order. Second, we demonstrate with suitable examples that correlations may both enhance or hamper the metrological precision. Indeed, unlike for entropic information quantities, in general nothing can be said about the sub- or super-additivity of the joint Fisher information in the presence of correlations. To illustrate our results, we apply them to thermometry on an Ising spin chain, considering nearest-neighbour and next-to-nearest neighbour coupling. In this case, the asymptotic Fisher information rate is directly connected to the specific heat capacity of the spin chain. We observe that the presence of correlations strongly enhances the estimation precision in an anti-ferromagnetic chain, while in a ferromagnetic chain this is not the case.