36 research outputs found
Negativity vs Entropy in Entanglement Witnessing
In this work, we prove that while all measures of mixedness can be used to
witness entanglement, no measure of mixedness is more sensitive than the
negativity of the partial transpose. However, computing either the negativity
or differences between von Neumann entropies to witness entanglement requires
complete knowledge of the joint density matrix (and is therefore not practical
at high dimension). In light of this, we examine joint vs marginal purities as
a witness of entanglement, (which can be obtained directly through interference
measurements) and find that comparing purities is actually more sensitive at
witnessing entanglement than using von Neumann entropies while also providing
tight upper and lower bounds to it in the high-entanglement limit.Comment: 4 pages, 1 figur
Unconditional remote entanglement using second-harmonic generation and twin two-mode squeezed vacuum states
We propose a photonics-based, continuous-variable (CV) form of remote
entanglement utilizing strictly second-order nonlinear optical interactions
that does not require the implementation of a state-projective measurement
(i.e. remote entanglement without conditioning). This scheme makes use of two
separate down-converters, wherein the corresponding nonlinear crystals are
driven by strong classical fields as prescribed by the parametric
approximation, as well as a fully quantum mechanical model of nondegenerate
second harmonic generation (SHG) whose evolution is described by the trilinear
Hamiltonian of the form . By driving the SHG process
with the signal modes of the two down-converters, we show entanglement
formation between the generated second-harmonic mode (SH-mode) and the
non-interacting joint-idler subsystem without the need for any state-reductive
measurements on the interacting modes
Quantifying Tri-partite Entanglement with Entropic Correlations
We show how to quantify tri-partite entanglement using entropies derived from
experimental correlations. We use a multi-partite generalization of the
entanglement of formation that is greater than zero if and only if the state is
genuinely multi-partite entangled. We develop an entropic witness for
tripartite entanglement, and show that the degree of violation of this witness
places a lower limit on the tripartite entanglement of formation. We test our
results in the three-qubit regime using the GHZ-Werner state and the W-Werner
state, and in the high-dimensional pure-state regime using the triple-Gaussian
wavefunction describing the spatial and energy-time entanglement in photon
triplets generated in third-order spontaneous parametric down-conversion. In
addition, we discuss the challenges in quantifying the entanglement for
progressively larger numbers of parties, and give both entropic and
target-state-based witnesses of multi-partite entanglement that circumvent this
issue.Comment: 14 pages, 6 figures (removed inequality (formerly appendix B4) due to
typo
Quantifying Entanglement in a 68-billion Dimensional Quantum State Space
Entanglement is the powerful and enigmatic resource central to quantum information processing, which promises capabilities in computing, simulation, secure communication, and metrology beyond what is possible for classical devices. Exactly quantifying the entanglement of an unknown system requires completely determining its quantum state, a task which demands an intractable number of measurements even for modestly-sized systems. Here we demonstrate a method for rigorously quantifying high-dimensional entanglement from extremely limited data. We improve an entropic, quantitative entanglement witness to operate directly on compressed experimental data acquired via an adaptive, multilevel sampling procedure. Only 6,456 measurements are needed to certify an entanglement-of-formation of 7.11 ± .04 ebits shared by two spatially-entangled photons. With a Hilbert space exceeding 68 billion dimensions, we need 20-million-times fewer measurements than the uncompressed approach and 1018-times fewer measurements than tomography. Our technique offers a universal method for quantifying entanglement in any large quantum system shared by two parties
Nonlinear Photon Pair Generation in a Highly Dispersive Medium
Photon pair generation in silicon photonic integrated circuits relies on four wave mixing via the third order nonlinearity. Due to phase matching requirements and group velocity dispersion, this method has typically required TE polarized light. Here, we demonstrate TM polarized photon pair production in linearly uncoupled silicon resonators with more than an order of magnitude more dispersion than previous work. We achieve measured rates above 2.8 kHz and a heralded second order correlation of . This method enables phase matching in dispersive media and paves the way for novel entanglement generation in silicon photonic device