Method for universal detection of two-photon polarization entanglement

Abstract

Detecting and quantifying quantum entanglement of a given unknown state poses problems that are fundamentally important for quantum information processing. Surprisingly, no direct (i.e., without quantum tomography) universal experimental implementation of a necessary and sufficient test of entanglement has been designed even for a general two-qubit state. Here we propose an experimental method for detecting a collective universal witness, which is a necessary and sufficient test of two-photon polarization entanglement. It allows us to detect entanglement for any two-qubit mixed state and to establish tight upper and lower bounds on its amount. A different element of this method is the sequential character of its main components, which allows us to obtain relatively complicated information about quantum correlations with the help of simple linear-optical elements. As such, this proposal realizes a universal two-qubit entanglement test within the present state of the art of quantum optics. We show the optimality of our setup with respect to the minimal number of measured quantities.

7 pages, 5 figures

References in corpus (8)

• Entanglement detection
• Taming multiparticle entanglement
• Estimating entanglement measures in experiments
• Measuring Multipartite Concurrence with a Single Factorizable Observable
• Estimating entanglement monotones with a generalization of the Wootters formula
• Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix
• Construction of optimal witness for unknown two-qubit entanglement
• Collectibility for Mixed Quantum States

Cited by in corpus (6)

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• Comparative study of nonclassicality, entanglement, and dimensionality of multimode noisy twin beams
• Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix
• Direct method for measuring and witnessing quantum entanglement of arbitrary two-qubit states through Hong-Ou-Mandel interference
• Experimental hierarchy of two-qubit quantum correlations without state tomography
• Two methods for measuring Bell nonlocality via local unitary invariants of two-qubit systems in Hong-Ou-Mandel interferometers