Quantum mechanics: new experiments, new applications, new formulations

Some of the quantum mechanical conceptual problems, their current status, and related theoretical developments are reviewed. The characteristics of the entangled quantum states are analyzed, and new experiments on and quantum information applications of such states are discussed. The well-known paradox of the Schroedinger cat (the impossibility of observing superpositions of macroscopically distinct states that are predicted by quantum mechanics) is discussed. It is shown that decoherence prevents distinguishing between a superposition and the corresponding mixture. This overcomes the difficulties associated with the paradoxical nature of quantum measurement within the framework of the theory of open systems. The suggestion of Wigner and others that the observer's consciousness be included in the theory of quantum measurement is discussed in this context. A hypothesis is put forward which might enable the functioning of consciousness to be describe in quantum measurement terms