Theoretical Physics(DTP)
Physique théorique (DPT)
Philip STAMP
University of British Columbia
Mechanisms of Decoherence and dynamics of Decoherence in networks of Qubits
The major problem confronting the construction of quantum information processing networks of any kid is decoherence, caused either by the interactions of the network with the surrounding environment, or from the time-dependent changes in the network parameters as computations or processing are carried out. To quantify decoherence we need (i) realistic physical models of what causes it, and (ii) means of calculating network dynamics. The main decoherence in solid-state qubit networks at low T comes from localized excitations in the environment (the ‘spin bath’). How this works is discussed quantitatively for superconducting and magnetic qubit networks, and compared with experiment. In optical systems the decoherence comes from unwanted photon modes. The problem of network dynamics raises a second fundamental question- how do decoherence rates increase with the number of entangled qubits? This question can be answered in detail with models incorporating spin and oscillator baths acting on ‘quantum memory’ networks. If there is time I will also discuss decoherence for topological quantum computer designs.