33 research outputs found
Coherent control of multipartite entanglement
Quantum entanglement between an arbitrary number of remote qubits is examined
analytically. We show that there is a non-probabilistic way to address in one
context the management of entanglement of an arbitrary number of mixed-state
qubits by engaging quantitative measures of entanglement and a specific
external control mechanism. Both all-party entanglement and weak inseparability
are considered. We show that for , the death of all-party entanglement
is permanent after an initial collapse. In contrast, weak inseparability can be
deterministically managed for an arbitrarily large number of qubits almost
indefinitely. Our result suggests a picture of the path that the system
traverses in the Hilbert space
Bounding the entanglement of N qubits with only four measurements
We introduce a new measure for the genuinely N-partite (all-party)
entanglement of N-qubit states using the trace distance metric, and find an
algebraic formula for the GHZ-diagonal states. We then use this formula to show
how the all-party entanglement of experimentally produced GHZ states of an
arbitrary number of qubits may be bounded with only four measurements
Violating Bell inequality using weak coherent states
We present an experimental investigation of two-photon interference using a
continuous-wave laser. We demonstrate the violation of the CHSH inequality
using the phase randomized weak coherent states from a continuous wave laser.
Our implementation serves as an approach to reveal the quantum nature of a
source that is considered to be a classical source.Comment: 6 pages, 2 figure
Genuinely Multipartite Concurrence of N-qubit X-matrices
We find an algebraic formula for the N-partite concurrence of N qubits in an
X-matrix. X- matricies are density matrices whose only non-zero elements are
diagonal or anti-diagonal when written in an orthonormal basis. We use our
formula to study the dynamics of the N-partite entanglement of N remote qubits
in generalized N-party Greenberger-Horne-Zeilinger (GHZ) states. We study the
case when each qubit interacts with a partner harmonic oscillator. It is shown
that only one type of GHZ state is prone to entanglement sudden death; for the
rest, N-partite entanglement dies out momentarily. Algebraic formulas for the
entanglement dynamics are given in both cases
Hanbury Brown and Twiss Interferometry with Twisted Light
The rich physics exhibited by random optical wave fields permitted Hanbury
Brown and Twiss to unveil fundamental aspects of light. Furthermore, it has
been recognized that optical vortices are ubiquitous in random light and that
the phase distribution around these optical singularities inprints a spectrum
of orbital angular momentum onto a light field. We demonstrate that random
fluctuations of light give rise to the formation of correlations in the orbital
angular momentum components and angular positions of pseudothermal light. The
presence of these correlations is manisfested through distinct interference
structures in the orbital angular momentum-mode distribution of random light.
These novel forms of interference correspond to the azimuthal analog of the
Hanbury Brown and Twiss effect. This family of effects can be of fundamental
importance in applications where entanglement is not required and where
correlations in angular position and orbital angular momentum suffice. We also
suggest that the azimuthal Hanbury Brown and Twiss effect can be useful in the
exploration of novel phenomena in other branches of physics and astrophysics.Comment: Science Advance
Tavis-Cummings model beyond the rotating wave approximation: Quasi-degenerate qubits
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.Comment: 12 Pages, 8 Figures. Comparison to the rotating wave approximation
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