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Seminários de Óptica e Informação Quântica

Data: Sexta-Feira 09/10/2015, Sala A5-01, 11 am.

Palestrante: Ivan Berbert Coulamy (UFF)

Título: Scaling of the local quantum uncertainty at quantum phase transitions

Resumo: We investigate the behavior of the local quantum uncertainty (LQU) between a block of $L$ qubits and one single qubit in a composite system of $n$ qubits driven through a quantum phase transition (QPT). In this scenario, we provide an analysis of the scaling of the LQU at a first-order and a second-order QPT. For a first-order QPT, we consider a Hamiltonian implementation of the quantum search through a space of $N=2^n$ elements. By analytical evaluation, we show that the LQU exponentially saturates to a constant value at the critical point as we increase the block length $L$, with the saturation enhanced by the system size $n$. On the other hand, at non-critical points, the LQU tends to vanish for large $n$. In the case of second-order QPTs, we consider the transverse-field Ising model with open boundary conditions. By implementing a numerical analysis via density matrix renormalization group (DMRG), we show that the concavity of the LQU as a function of the block size $L$ characterizes the QPT.  For both first-order and second-order QPTs, we also consider the LQU as a function of the coupling parameter, showing that the LQU exhibits a pronounced behavior at the quantum critical point for fixed block sizes of $L$ qubits.