Quantum Decoherence

One of the most puzzling aspects of quantum mechanics is the measurement problem. Measurement problem is composed of three parts:

1- The problem of preferred basis.- what singles out preferred physical quantities such as position in nature?- e.g. why are physical systems usually observed to be in definite positions rather than the superpositions of positions.

2- The problem of non-observability of interference.- Why is it so difficult to observe quantum interference effects especially on macroscopic scales?

3- The problem of outcomes. - Why do measurements have outcomes at all, and what selects a particular outcome among the other possibilities described by the quantum probability distributions?

In standard quantum mechanics the measurement problem is supposed to be solved by adding the collapse of the wave packet through the interaction between the quantum system and the apparatus as a postulate. Nevertheless, one of the most relevant ways claiming to solve measurement problem, without necessity for collapse, is Decoherence. In the framework of decoherence the ubiquitous interaction between the quantum systems and their environment is responsible for non-observability of quantum effects in the classical realm. In other words, classicality is an emergent property which resulted from the interaction of open quantum systems with their environment.