Quantum Speed Limit In Structured Optical Fields

In this thesis,we consider atoms which interact with structured photic-field environments and study how three typical kinds of decoherence(amplitude-damping,phase-damping,general depolarizing)impact on quantum speed limit.We hope to provide some theoretical basis for the precise measurement of quantum states.We put forward a general quantum speed limit for open system dynamics on the basis of the trace distance.Our main research work may be divided into three parts as follows:Firstly,we take into account the atom-field model with amplitude damping in the case of Lorentzian spectrum density function.In general,there is a detune between the transition frequency of the atom and central frequency of the field.It is found out that the large detuning amount can induce the accelerating evolution in the weak-coupling regime while decrease the evolution speed in the strong-coupling case.The dynamics of a simple spin-boson model can be described by the phase-damping process.The increase of cutoff frequency of the Ohmic-like spectrum function or the condition of super-Ohmic reservoir can speed up quantum evolution.We demonstrate that physical mechanism of the potential capacity for quantum speed-up evolution is connected with energy or information flow.The result is attributed to the memory effect(non-markovian effect)of environment.Secondly,we obtain a general depolarizing decoherence under the circumstance of local external field and environmental temperature.There exists the dynamical transition from no speed-up to speed-up by adjusting the strength of external field.In the case of the Lorentzian spectral density function,the low temperature is beneficial for quantum evolution to accelerate but has tiny impact on ohimc-like dephasing model.It is shown that the experiments about quantum acceleration can be carried out in low-temperature environment.Finally,we study the decoherence process of multi-qubits with quantum entanglement in the three types of decoherence processes.The entanglement provides more energy for the system,which promotes quantum evolution speed in amplitude damping or depolarization damping process.However,the entanglement has no effects on the quantum speed limit in the phase damping process.It is shown that the quantum speed is accelerated with increasing the number of entangled qubits.