# SciPost Thesis Link

Title: | Quantum Mechanics & The Big World -- order, broken symmetry and coherence in quantum many-body systems | |

Author: | Jasper van Wezel | |

As Contributor: | Jasper van Wezel | |

Type: | Ph.D. | |

Discipline: | Physics | |

Subject area: | Condensed Matter Physics - Theory | |

Approach: | Theoretical | |

URL: | http://hdl.handle.net/1887/11468 | |

Degree granting institution: | Leiden | |

Supervisor(s): | Jeroen van den Brink and Jan Zaanen | |

Defense date: | 2007-04-04 |

### Abstract:

Quantum Mechanics is one of the most successful physical theories of the last century. It explains physical phenomena from the smallest to the largest lengthscales. Despite this triumph, quantum mechanics is often perceived as a mysterious theory, involving superposition states that are alien to our everyday Big World. The construction of a future quantum computer relies on our ability to manipulate quantum superposition states in qubits. In this thesis it is shown that these qubits can be subtly influenced by the physics associated with spontaneous symmetry breaking. This process destroys the quantum nature of the qubit and renders it useless for quantum computation. An even more fundamental problem with quantum superpositions is that they cannot be reconciled with the theory of general relativity. In the end of this thesis a model is proposed which describes the effective, deteriorating, influence of gravity on quantum states, thus suggesting a path toward the demise of quantum mechanics in the big world.