How useful can machine learning be in a quantum laboratory? Here we raise the question of the potential of intelligent machines in the context of scientific research. A major motivation for the present work is the unknown reachability of various entanglement classes in quantum experiments. We investigate this question by using the projective simulation model, a physics-oriented approach to artificial intelligence. In our approach, the projective simulation system is challenged to design complex photonic quantum experiments that produce high-dimensional entangled multiphoton states, which are of high interest in modern quantum experiments. The artificial intelligence system learns to create a variety of entangled states, and improves the efficiency of their realization. In the process, the system autonomously (re)discovers experimental techniques which are only now becoming standard in modern quantum optical experiments -a trait which was not explicitly demanded from the system but emerged through the process of learning. Such features highlight the possibility that machines could have a significantly more creative role in future research.
Quantum information technology 1 largely relies on a precious and fragile resource, quantum entanglement, a highly nontrivial manifestation of the coherent superposition of states of composite quantum systems. However, our knowledge of the time evolution of this resource under realistic conditions-that is, when corrupted by environment-induced decoherence-is so far limited, and general statements on entanglement dynamics in open systems are scarce 2-11 . Here we prove a simple and general factorization law for quantum systems shared by two parties, which describes the time evolution of entanglement on passage of either component through an arbitrary noisy channel. The robustness of entanglement-based quantum information processing protocols is thus easily and fully characterized by a single quantity.Whenever we contemplate the potential technological applications of quantum information theory 1 , from secure quantum communication to quantum teleportation 12 , to quantum computation 13 , we need to worry about the unavoidable and detrimental coupling of any such quantum device to uncontrolled degrees of freedom-typically lumped together under the label 'environment' . Coupling to the environment induces decoherence [14][15][16] ; that is, it gradually destroys the phase relationship between quantum states, and thus their ability to interfere. In composite quantum systems, these phase relationships (or 'coherences') are at the origin of strong quantum correlations between measurements on distinct system constituents-which then are entangled. The promises of quantum information technology rely on exploring precisely these nonclassical correlations.Yet, entanglement is not equivalent to many-particle coherences: it is an even stronger property, and hard to quantifyall commonly accepted entanglement measures 17 are nonlinear functions of the density matrix, which describes the state of the composite quantum system, and in particular the coherences. Although an elaborate theory on the time evolution of quantum states under environment coupling is to hand, virtually no general results on entanglement dynamics have been stated. Hitherto, the time evolution of entanglement always needed to be deduced from the time evolution of the state 2-10 . In the present letter, a direct relationship between the initial and final entanglements
Identical particles exhibit correlations even in the absence of inter-particle interaction, due to the exchange (anti)symmetry of the manyparticle wavefunction. Two fermions obey the Pauli principle and anti-bunch, whereas two bosons favor bunched, doubly occupied states. Here, we show that the collective interference of three or more particles leads to much more diverse behavior than expected from the boson-fermion dichotomy known from quantum statistical mechanics. The emerging complexity of many-particle interference is tamed by a simple law for the strict suppression of events in the Bell multiport beam splitter. The law shows that counting events are governed by widely species-independent interference, such that bosons and fermions can even exhibit identical interference signatures, while their statistical character remains subordinate. Recent progress in the preparation of tailored many-particle
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