Since the seminal paper published by Albert Einstein, Boris Podolski and Nathan Rosen in 1935, and the famous series of papers published by Erwin Schrödinger in the years 1935 and 1936, entanglement has occupied a central position in quantum physics. This peculiar phenomenon has posed formidable challenges to several generations of physicists. In fact, it took about 30 years since the 1935 papers for the first mathematical consequence of this property to be demonstrated by John S. Bell and about 30 years more for entanglement to be recognized as a possible resource for quantum communication and quantum computation.
Evolving from a daunting concept to a useful resource, entanglement is at the heart of many suggested applications, involving the efficient transmission of information through dense coding or teleportation, the security of transmitted data through quantum cryptography, the efficient solution of the factorization problem, a speedier data search protocol, efficient measurement of parameters in quantum metrology, and quantum simulations of problems with exponential demand of resources in classical computers.
Motivated by these suggested applications and also by the fundamental role played by entanglement in quantum mechanics, important experimental results have been obtained in the last few years, concerning the generation and analysis of multiparty entangled states, the transfer of entanglement between two systems, macroscopic signatures of entanglement, and the dynamics of entangled states under the action of the environment.
And yet many fundamental problems remain unsolved. Among them, the characterization of entanglement for multiparticle systems, the role of entanglement in quantum metrology under decoherence, the dynamics of entanglement for a system in contact with its environment. This last problem is directly related to a practical question: the assessment of the robustness of the applications mentioned above. It also concerns a fundamental problem in physics: the subtle relation between the classical and the quantum world.