Entanglement detection

  title={Entanglement detection},
  author={Otfried Guhne and G{\'e}za T{\'o}th},
What Criterion Can We Get From Precise Entanglement Witnesses?
A thorough study of a three-qubit Greenberger-Horne-Zeilinger (GHZ) state mixed with a W state and white noise finds a connection between Wootters formula and the matched entanglement witness.
Detecting entanglement of unknown quantum states with random measurements
This work investigates the use of random local measurements, from which entanglement witnesses are then constructed via semidefinite programming methods, and proposes a scheme of successively increasing the number of measurements until the presence ofEntanglement can be unambiguously concluded.
Quantitative entanglement witnesses of isotropic and Werner classes via local measurements
Quantitative entanglement witnesses allow one to bound the entanglement present in a system by acquiring a single expectation value. In this paper, we analyze a special class of such observables
Nonlinear improvement of qubit-qudit entanglement witnesses
The entanglement witness is an important and experimentally applicable tool for entanglement detection. In this paper, we provide a nonlinear improvement of any entanglement witness for $2\otimes d$
Measurement-device-independent entanglement witnesses for all entangled quantum states.
This work introduces the concept of measurement-device-independent entanglement witnesses (MDI-EWs), which allow one to demonstrateEntanglement of all entangled quantum states with untrusted measurement apparatuses, and shows how to systematically obtain such MDI-ews from standard entangler witnesses.
Geometry of Faithful Entanglement.
This work proves a structural result on the corresponding fidelity-based entanglement witnesses, resulting in a simple condition for faithfulness of a two-party state, and shows that faithful Entanglement is, in a certain sense, usefulEntanglement theory.
Device-Independent Entanglement Detection
Entanglement is one of the most intriguing feature of quantum physics. It allows several particles to be in a state which cannot be understood as a concatenation of the sate of each particle.
Device-Independent Entanglement Certification of All Entangled States.
We present a method to certify the entanglement of all entangled quantum states in a device-independent way. This is achieved by placing the state in a quantum network and constructing a correlation
Design and experimental performance of local entanglement witness operators
This work proposes and analyzes a class of entanglement witnesses that detect the presence ofEntanglement in subsystems of experimental multi-qubit stabilizer states and theoretically establishes the noise tolerance of the proposed witnesses and benchmark their practical performance by analyzing the local entangled structure of an experimental seven-qu bit quantum error correction code.
The structure of ultrafine entanglement witnesses
An entanglement witness is an observable with the property that a negative expectation value signals the presence of entanglement. The question arises how a witness can be improved if the expectation


Experimental detection of entanglement via witness operators and local measurements
Abstract In this paper we address the problem of detection of entanglement using only few local measurements when some knowledge about the state is given. The idea is based on an optimized
Characterizing Entanglement
Quantum entanglement is at the heart of many tasks in quantum information. Apart from simple cases (low dimensions, few particles, pure states), however, the mathematical structure of entanglement is
Quantitative entanglement witnesses
All these tests—based on the very same data—give rise to quantitative estimates in terms of entanglement measures, and if a test is strongly violated, one can also infer that the state was quantitatively very much entangled, in the bipartite and multipartite setting.
Characterizing entanglement with geometric entanglement witnesses
We show how to detect entangled, bound entangled and separable bipartite quantum states of arbitrary dimension and mixedness using geometric entanglement witnesses. These witnesses are constructed
Entanglement detection by local orthogonal observables.
A family of entanglement witnesses and corresponding positive maps that are not completely positive based on local orthogonal observables that can be physically realized by measuring a Hermitian correlation matrix of local orthosomatic observables.
Novel schemes for directly measuring entanglement of general states.
It is demonstrated that rank-1 local factorizable projective measurements, which are achievable with only one copy of an entangled state involved at a time in a sequential way, are sufficient to directly determine the concurrence of an arbitrary two-qubit entangled state.
Detecting quantum entanglement : entanglement witnesses and uncertainty relations
This thesis deals with methods of the detection of entanglement. After recalling some facts and definitions concerning entanglement and separability, we investigate two methods of the detection of
Entanglement witnesses and a loophole problem
We consider a possible detector-efficiency loophole in experiments that detect entanglement via the local measurement of witness operators. Here, only local properties of the detectors are known. We
Optimal entanglement criterion for mixed quantum states.
It is shown that Phi detects many entangled states with a positive partial transposition (PPT) and that it leads to a class of optimal entanglement witnesses which implies that there are no other witnesses which can detect more entangled PPT states.
Experimental Determination of Entanglement by a Projective Measurement
We describe a method in which the entanglement of any pure quantum state can be experimentally determined by a simple projective measurement, provided the state is available in a twofold copy. We