The main steps in the development of the ideas on decoherence are briefly reviewed, together with their present achievements.Unsolved problems are also pointed out. I. EARLY LANDMARKS
Since the 1980s, researchers have taken giant steps in understanding how to use quantum mechanics for solving real problems—for example, making a computer that works according to the laws of quantum mechanics. In recent decades, researchers have tried to develop a platform for quantum information and computation that can be integrated into digital and telecom technologies without the need of a cryogenic environment. The current status of research in the field of quantum integrated photonics will be reviewed. A review of the most common integrated photonic platforms will be given, together with the main achievements and results in the last decade.
In this article, I shall focus on two of the main problems raising interpre-tational issues in quantum mechanics, namely the notorious measurement problem (discussed together with the theory of measurement in section 4) and the equally important but not quite as widely discussed problem of the classical regime (discussed together with decoherence in section 3). The two problems are distinct, but they are both intimately related to some of the is-sues arising from entanglement and density operators, which are thus briefly reviewed in section 2. A few fundamentals are rehearsed in section 1. The article will aim to be fairly non-technical in language, but modern in out-look and covering the chosen topics in more depth than most introductory treatments. The philosophy and foundations of quantum mechanics offer many more examples of live research issues, and much progress has been achieved re-cently in such traditional approaches as collapse theories, pilot-wave the-ories and Everett interpretations, and in the (time-honoured but recently revived) area of axiomatic reconstructions of the theory. Recent years have
The destruction of quantum-mechanical phase coherence by a fluctuating quantum bath has been investigated mostly for a single particle. However, for electronic transport through disordered samples and mesoscopic interference setups, we have to treat a many-fermion system subject to a quantum bath. Here, we review a novel technique for treating this situation in the case of ballistic interferometers, and discuss its application to the electronic Mach-Zehnder setup. We use the results to bring out the main features of decoherence in a many-fermion system and briefly discuss the same ideas in the context of weak localization.