616 research outputs found
Operator fidelity susceptibility: an indicator of quantum criticality
We introduce the operator fidelity and propose to use its susceptibility for
characterizing the sensitivity of quantum systems to perturbations. Two typical
models are addressed: one is the transverse Ising model exhibiting a quantum
phase transition, and the other is the one dimensional Heisenberg spin chain
with next-nearest-neighbor interactions, which has the degeneracy. It is
revealed that the operator fidelity susceptibility is a good indicator of
quantum criticality regardless of the system degeneracy.Comment: Four pages, two figure
Photon-assisted Landau-Zener transition: Role of coherent superposition states
We investigate a Landau-Zener (LZ) transition process modeled by a quantum
two-level system (TLS) coupled to a photon mode when the bias energy is varied
linearly in time. The initial state of the photon field is assumed to be a
superposition of coherent states, leading to a more intricate LZ transition.
Applying the rotating-wave approximation (RWA), analytical results are obtained
revealing the enhancement of the LZ probability by increasing the average
photon number. We also consider the creation of entanglement and the change of
photon statistics during the LZ process. Without the RWA, we find some
qualitative differences of the LZ dynamics from the RWA results, e.g., the
average photon number no longer monotonically enhances the LZ probability. The
ramifications and implications of these results are explored.Comment: 9 pages, 7 figure
Adiabatic Creation of Atomic Squeezing in Dark States vs. Decoherences
We study the multipartite correlations of the multi-atom dark states, which
are characterized by the atomic squeezing beyond the pairwise entanglement. It
is shown that, in the photon storage process with atomic ensemble via
electromagnetically induced transparency (EIT) mechanism, the atomic squeezing
and the pairwise entanglement can be created by adiabatically manipulating the
Rabi frequency of the classical light field on the atomic ensemble. We also
consider the sudden death for the atomic squeezing and the pairwise
entanglement under various decoherence channels. An optimal time for generating
the greatest atomic squeezing and pairwise entanglement is obtained by studying
in details the competition between the adiabatic creation of quantum
correlation in the atomic ensemble and the decoherence that we describe with
three typical decoherence channels.Comment: 11 pages, 13 figure
Disentanglement in a quantum critical environment
We study the dynamical process of disentanglement of two qubits and two
qutrits coupled to an Ising spin chain in a transverse field, which exhibits a
quantum phase transition. We use the concurrence and negativity to quantify
entanglement of two qubits and two qutrits, respectively. Explicit connections
between the concurrence (negativity) and the decoherence factors are given for
two initial states, the pure maximally entangled state and the mixed Werner
state. We find that the concurrence and negativity decay exponentially with
fourth power of time in the vicinity of critical point of the environmental
system.Comment: 8 pages, 6 figure
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