Publications (6)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: Beyond the simplest case of bipartite qubits, the composite Hilbert space of
multipartite systems is largely unexplored. In order to explore such systems,
it is important to derive analytic expressions for parameters which
characterize the system's state space. Two such parameters are the degree of
genuine multipartite entanglement and the degree of mixedness of the system's
state. We explore these two parameters for an N-qubit system whose density
matrix has an X form. We derive the class of states that has the maximum amount
of genuine multipartite entanglement for a given amount of mixedness. We
compare our results with the existing results for the N=2 case. The critical
amount of mixedness above which no N-qubit X-state possesses genuine
multipartite entanglement is derived. It is found that as N increases, states
with higher mixedness can still be entangled.
10/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a new witness operation for the non-classical character of a
harmonic oscillator state. The method does not require state reconstruction.
For all harmonic oscillator states that are classical, a bound is established
for the evolution of a qubit which is coupled to the oscillator. Any violation
of the bound can be rigorously attributed to the non-classical character of the
initial oscillator state.
07/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: By focusing on the X-matrix part of a density matrix of two qubits we provide
an algebraic lower bound for the concurrence. The lower bound is generalized
for cases beyond two qubits and can serve as a sufficient condition for
non-separability for bipartite density matrices of arbitrary dimension.
Experimentally, our lower bound can be used to confirm non-separability without
performing a complete state tomography.
04/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The Tavis-Cummings model for more than one qubit interacting with a common
oscillator mode is extended beyond the rotating wave approximation (RWA). We
explore the parameter regime in which the frequencies of the qubits are much
smaller than the oscillator frequency and the coupling strength is allowed to
be ultra-strong. The application of the adiabatic approximation, introduced by
Irish, et al. (Phys. Rev. B \textbf{72}, 195410 (2005)), for a single qubit
system is extended to the multi-qubit case. For a two-qubit system, we identify
three-state manifolds of close-lying dressed energy levels and obtain results
for the dynamics of intra-manifold transitions that are incompatible with
results from the familiar regime of the RWA. We exhibit features of two-qubit
dynamics that are different from the single qubit case, including calculations
of qubit-qubit entanglement. Both number state and coherent state preparations
are considered, and we derive analytical formulas that simplify the
interpretation of numerical calculations. Expressions for individual collapse
and revival signals of both population and entanglement are derived.
01/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We study the dynamics of two qubits interacting with a single mode of a
harmonic oscillator beyond the rotating wave approximation in the ideally
degenerate regime. Exact analytic expressions are obtained for state properties
of interest, including qubit entanglement for a certain class of initial states
of the oscillator and the qubits. Qualitative differences and similarities in
the evolution of the qubits in the degenerate regime when the oscillator is
treated quantum mechanically and classically are discussed.
05/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The entanglement dynamics of two remote qubits is examined analytically. The
qubits interact arbitrarily strongly with separate harmonic oscillators in the
idealized degenerate limit of the Jaynes-Cummings Hamiltonian. In contrast to
well known non-degenerate RWA results, it is shown that ideally degenerate
qubits cannot induce bipartite entanglement between their partner oscillators.
05/2011;
