4,613 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
Partitioned List Decoding of Polar Codes: Analysis and Improvement of Finite Length Performance
Polar codes represent one of the major recent breakthroughs in coding theory
and, because of their attractive features, they have been selected for the
incoming 5G standard. As such, a lot of attention has been devoted to the
development of decoding algorithms with good error performance and efficient
hardware implementation. One of the leading candidates in this regard is
represented by successive-cancellation list (SCL) decoding. However, its
hardware implementation requires a large amount of memory. Recently, a
partitioned SCL (PSCL) decoder has been proposed to significantly reduce the
memory consumption. In this paper, we examine the paradigm of PSCL decoding
from both theoretical and practical standpoints: (i) by changing the
construction of the code, we are able to improve the performance at no
additional computational, latency or memory cost, (ii) we present an optimal
scheme to allocate cyclic redundancy checks (CRCs), and (iii) we provide an
upper bound on the list size that allows MAP performance.Comment: 2017 IEEE Global Communications Conference (GLOBECOM
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
Age- and sex-related variations in the brain white matter fractal dimension throughout adulthood: an MRI study.
To observe age- and sex-related differences in the complexity of the global and hemispheric white matter (WM) throughout adulthood by means of fractal dimension (FD)
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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