Estimating entanglement of unknown states

  title={Estimating entanglement of unknown states},
  author={Daniel Cavalcanti and Marcelo O. Terra Cunha},
  journal={Applied Physics Letters},
The experimental determination of entanglement is a major goal in the quantum information field. In general, the knowledge of the state is required in order to quantify its entanglement. Here we express a lower bound to the robustness of entanglement of a state based only on the measurement of the energy observable and on the calculation of a separability energy. This allows the estimation of entanglement dismissing the knowledge of the state in question. 
Entanglement detection
Single-experiment-detectable multipartite entanglement witness for ensemble quantum computing
Individual single-qubit measurements are performed simultaneously; hence complete detection of entanglement is performed in a single-run experiment, and the scheme is superior to the generally usedEntanglement witnesses that require a number of experiments and preparation of copies of quantum state for detection of Entanglement.
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.
Geometrically induced singular behavior of entanglement
We show that the geometry of the set of quantum states plays a crucial role in the behavior of entanglement in different physical systems. More specifically, it is shown that singular points at the
Quantifying necessary quantum resources for nonlocality
Nonlocality is one of the most important resources for quantum information protocols. The observation of nonlocal correlations in a Bell experiment is the result of appropriately chosen measurements
Entanglement detection and distillation for arbitrary bipartite systems
An inequality for detecting entanglement and distillability of arbitrary dimensional bipartite systems is presented and it is shown that this inequality provides a necessary and sufficient condition for distillable states.
Entanglement Theory and the Quantum Simulation of Many-Body Physics
In this thesis we present new results relevant to two important problems in quantum information science: the development of a theory of entanglement and the exploration of the use of controlled
Modeling the decay of entanglement for electron spin qubits in quantum dots
We investigate the time evolution of entanglement under various models of decoherence: a general heuristic model based on local relaxation and dephasing times, and two microscopic models describing
Automated machine learning can classify bound entangled states with tomograms
An Automated Machine Learning approach is presented to classify random states of two qutrits as separable or entangled using enough data to perform a quantum state tomography, without any direct measurement of its entanglement.
Machine-Learning-Assisted Many-Body Entanglement Measurement.
This work proposes a machine-learning-assisted scheme to measure the entanglement between arbitrary subsystems of size N A and N B, with O(N_{A}+N_{B}) measurements, and without any prior knowledge of the state.


Detection of entanglement with polarized photons: experimental realization of an entanglement witness.
The present demonstration has been performed with polarized photons in Werner states, a well-known family of mixed states that can be either separable or non separation, and is the first experimental realization of an entanglement witness.
Method for direct detection of quantum entanglement.
This work views this method as a new form of quantum computation, namely, as a decision problem with quantum data structure, which provides a sharp separability test and estimation of amount of entanglement for two qubits.
Distillation and bound entanglement
This review provides a systematic description of the main (qualitative) results concerning entanglement theory in the context of the so called boundEntanglement being a physical manifestation of basic limits for entanglements processing and quantum communication.
Detecting quantum entanglement
Witnessed Entanglement
We present a new measure of entanglement for mixed states. It can be approximately computable for every state and can be used to quantify all different types of multipartite entanglement. We show
Experimental detection of multipartite entanglement using witness operators.
A canonical way of constructing and decomposing witness operators so that they can be directly implemented with present technology is introduced and applied to three- and four-qubit entangled states of polarized photons, giving experimental evidence that the considered states contain true multipartite entanglement.
Experimental determination of entanglement with a single measurement
A linear optics experiment is reported in which a pure-state entanglement measure is directly observed, namely concurrence, which is measured with a single, local measurement on just one of the photons.
Experimental methods for detecting entanglement.
Here we present experimental realizations of two new entanglement detection methods: a three-measurement Bell inequality inequivalent to the Clauser-Horne-Shimony-Holt inequality and a nonlinear
Optimal teleportation with a mixed state of two qubits.
We consider a single copy of a mixed state of two qubits and derive the optimal trace-preserving local operations assisted by classical communication such as to maximize the fidelity of teleportation
Entanglement of formation and concurrence
The current understanding of entanglement of formation and the related concept of concurrence is reviewed, including discussions of additivity, the problem of finding explicit formulas, and connections between concurrence and other properties of bipartite states.