Efficient nonlinear witnessing of non–absolutely separable states with lossy detectors

Patra, Ayan; Mal, Shiladitya; Sen, Aditi

doi:10.1103/physreva.104.032427

Cited by 5 publications

(1 citation statement)

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“…Other aspects concerning the set of AS states for bipartite systems have been discussed in the literature. To mention a few, it has been shown that AS states form a convex and compact set, and that one can construct operators to witness absolute separability [16] or lack thereof [17]. Recently, quantum maps that output absolutely separable states have been analysed in Ref.…”

Section: Introduction and Problem Statementmentioning

confidence: 99%

Maximum entanglement of mixed symmetric states under unitary transformations

Serrano-Ensástiga,

Martin

2023

SciPost Phys.

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We study the maximum entanglement that can be produced by a global unitary transformation for systems of two and three qubits constrained to the fully symmetric states. This restriction to the symmetric subspace appears naturally in the context of bosonic or collective spin systems. We also study the symmetric states that remain separable after any global unitary transformation, called symmetric absolutely separable (SAS) states, or absolutely classical for spin states. The results for the two-qubit system are deduced analytically. In particular, we determine the maximal radius of a ball of SAS states around the maximally mixed state in the symmetric sector, and the minimal radius of a ball that contains the set of SAS states. As an application of our results, we also analyse the temperature dependence of the maximum entanglement that can be obtained from the thermal state of a spin-1 system with a spin-squeezing Hamiltonian. For the symmetric three-qubit case, our results are mostly numerical, and we conjecture a 3-parameter family of states that achieves the maximum negativity in the unitary orbit of any mixed state. In addition, we derive upper bounds, apparently tight, on the radii of balls containing only/all SAS states.

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Section: Introduction and Problem Statementmentioning

confidence: 99%

Maximum entanglement of mixed symmetric states under unitary transformations

Serrano-Ensástiga,

Martin

2023

SciPost Phys.

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Measurement-device-independent nonlinear entanglement witnesses

Sen

Srivastava

Sen

2023

J. Phys. A: Math. Theor.

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Entanglement witnesses are one of the most effective methods to detect entanglement. It is known that nonlinear entanglement witnesses provide better entanglement detection than their linear counterparts, in that the former detect a strictly larger subset of entangled states than the latter. Whether linear or nonlinear, the method is measurement-device dependent, so that imperfect measurements may cause false certification of entanglement in a shared state. Measurement-device-independent entanglement witnesses provide an escape from such measurement dependence of the entanglement detection for linear entanglement witnesses. Here we present measurement-device-independent nonlinear entanglement witnesses for non-positive partial transpose entangled states as well as for bound entangled states with positive partial transpose. Although the witness considered herein does not detect a larger set of entangled states than other nonlinear entanglement witnesses, it is more efficient in that it never leads to a false detection corresponding to wrong measurements. The constructed measurement-device-independent nonlinear entanglement witnesses certify the entanglement of the same sets of entangled states as their device-dependent parents do, and therefore are better than the linear entanglement witnesses, device-independent or otherwise.

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