We introduce a set of electric-field based inequalities capable of detecting multilevel entanglement from a system of N quantum emitters. We determine that the polarization channel as well as the direction of detection can enhance entanglement detection, a feature specific to multilevel systems. We demonstrate the efficiency of the witnesses to detect genuine multipartite entanglement by applying it to families of paradigmatic quantum states, such as Dicke states, singlet states and W-like states. The detection is not only robust to noise, but also applies to mixed entangled states. Our findings open up possibilities for the detection of entanglement without local measurements in systems of multilevel emitters such as superconducting qubits, Rydberg atoms or quantum dots.
We demonstrate that nonlinear entanglement witnesses can be made particularly useful for entanglement detection in hyperentangled or multilevel states. We test this idea experimentally on the platform of linear optics using a hyperentangled state of two photons. Instead of several simultaneous copies of two-photon entangled states, one can directly measure the witness on a single copy of a hyperentangled state. Our results indicate that hyperentanglement can be used for quick entanglement detection and it provides a practical test bed for experiments with nonlinear entanglement witnesses.
The paper presents a scheme to detect entanglement arising from the quantum nature of gravity between a spin qubit and photons, using Stokes parameters. One of the crucial tests of the general theory of relativity is the bending of light due to the curvature. Recently, a quantum counterpart of this experiment to test the quantum nature of the gravitational interaction has been proposed, in which the spin-2, massless graviton yields entanglement between matter and a photon sector. Hence, it provides one of the most crucial experimental signatures for testing the quantum nature of gravity in a lab, since only spin-2-induced entanglement can yield the correct deflection of light due to matter. Here, we propose a positive partial-transpose (PPT) witness criterion for witnessing such an entanglement. We scan the entangled states in this context by studying the overlap of the final state, which is proportional to the entanglement phase. We exploit the Stokes observables to measure the photon state and the spins in the matter sector, thereby constructing a witness for the quantum nature of gravity in this setup. To quantify this entanglement, we will couple the photon to a local oscillator, whose phase need to be controlled to probe the orthogonal components of the macroscopic interference in the laser beam. We have shown that for a non-maximally entangled state mediated by the quantum nature of gravity, the witness attains a maximal negativity of
−0.052. Our findings indicate that this witness effectively detects entanglement within the range
0.71≤∣γ∣<1, where
γ is the overlap between the two coherent states of the photon, providing a clear signature of quantum correlations.
The generation and the characterization of multipartite entangled light is an important and challenging task in quantum optics. In this paper the entanglement properties of the light emitted from a planar semiconductor microcavity are studied. The intracavity scattering dynamics leads to the emission of light that is described by a four-partite
W state. Its multipartite correlations are identified by using the method of entanglement witnesses. Entanglement conditions are derived, which are based on a general witness constructed from
W states. The results can be used to detect entanglement of light that propagates through lossy and even turbulent media.