3,382 research outputs found
Entanglement criterion via general symmetric informationally complete measurements
We study the quantum separability problem by using general symmetric
informationally complete measurements and present a separability criterion for
arbitrary dimensional bipartite systems. We show by detailed examples that our
criterion is more powerful than the existing ones in entanglement detection.Comment: 8 pages, 5 figure
Connections of geometric measure of entanglement of pure symmetric states to quantum state estimation
We study the geometric measure of entanglement (GM) of pure symmetric states
related to rank-one positive-operator-valued measures (POVMs) and establish a
general connection with quantum state estimation theory, especially the maximum
likelihood principle. Based on this connection, we provide a method for
computing the GM of these states and demonstrate its additivity property under
certain conditions. In particular, we prove the additivity of the GM of pure
symmetric multiqubit states whose Majorana points under Majorana representation
are distributed within a half sphere, including all pure symmetric three-qubit
states. We then introduce a family of symmetric states that are generated from
mutually unbiased bases (MUBs), and derive an analytical formula for their GM.
These states include Dicke states as special cases, which have already been
realized in experiments. We also derive the GM of symmetric states generated
from symmetric informationally complete POVMs (SIC~POVMs) and use it to
characterize all inequivalent SIC~POVMs in three-dimensional Hilbert space that
are covariant with respect to the Heisenberg--Weyl group. Finally, we describe
an experimental scheme for creating the symmetric multiqubit states studied in
this article and a possible scheme for measuring the permanent of the related
Gram matrix.Comment: 11 pages, 1 figure, published versio
Isolated spin qubits in SiC with a high-fidelity infrared spin-to-photon interface
The divacancies in SiC are a family of paramagnetic defects that show promise
for quantum communication technologies due to their long-lived electron spin
coherence and their optical addressability at near-telecom wavelengths.
Nonetheless, a mechanism for high-fidelity spin-to-photon conversion, which is
a crucial prerequisite for such technologies, has not yet been demonstrated.
Here we demonstrate a high-fidelity spin-to-photon interface in isolated
divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that
divacancies in 4H-SiC have minimal undesirable spin-mixing, and that the
optical linewidths in our current sample are already similar to those of recent
remote entanglement demonstrations in other systems. Moreover, we find that
3C-SiC divacancies have millisecond Hahn-echo spin coherence time, which is
among the longest measured in a naturally isotopic solid. The presence of
defects with these properties in a commercial semiconductor that can be
heteroepitaxially grown as a thin film on shows promise for future quantum
networks based on SiC defects.Comment: 26 pages, 4 figure
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