Coherent Electromagnetic Manipulations Of Single Quantum Systems

In the past few decades, quantum coherent control has attracted much attention, and has made many significant results. Especially, quantum coherent control is an important approach to achieve quantum computing, quantum cryptography communication. The crucial idea of quantum coherent control is to steer a quantum system form the initial state to the target state by changing the external conditions, such as electric or magnetic fields. In general, there are two methods to achieve quantum coherent control; one is Rabi oscillation method, which is sensitive to the pulse durations, and the other is the population passages technique, such as stimulated Raman adiabatic passage, which is insensitive to the pulse durations. In this paper, by using the basic method of quantum coherent control, we investigate how to implement the coherent manipulations of quantum states in various physical systems, e.g., moving quantum dots, surface-state electrons on liquid helium, superconducting electronic, and cavity QED systems, etc.. for the foundamental quantum logic operations and the generations of photonic Fock states.In chapter 2, the dynamics of a single electron transported by a surface acoustic wave along a quasi-one-dimensional electronic waveguide is investigated. If the wavelength of the surface acoustic wave is approximately equal to the length of the channel, then the potential of the electron trap driven by the acoustic wave can be regarded as a moving quantum dot. Here, the flying qubit introduced is encoded by the two lowest levels of the electron in the moving quantum dot, and the Rabi oscillation between these two levels could be implemented by applying properly selected microwave pulses. By using the Coulomb interaction between the electrons in different MQDs, we show that a desirable two-qubit operation, i.e., i-swap gate, could be realized. Readouts of the present flying qubits are also feasible with the current single-electron detected technique.In chapter 3, the electrons trapped on the surface of liquid helium are investiged. We use the technique of Stark-chired rapid adiabatic passage to achive the cohenrent control of electronic states. Different from the previous proposal by using the precisely-designed durations (such as the p-pulses) of the Rabi oscillations and the tunable interbit couplings, here we show that the desired coherent population transfers between the logic states can be deterministically realized, and thus quantum computation could be implemented, both adiabatically and non-adiabatically, by performing the duration-insensitive quantum manipulations.In chaper 4, we investigate Stark-chirped rapid adiabatic passage (SCRAP) with dissipation. We discuss how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with weak noises.In chaper 5, a single-photon Fock state produced by the technique of shortcut to adiabatic passage is invesitgated. Differing from the usual method to obtain single-photon radiations by the spontaneous emissions of the excited atoms, here we propose an approach to produce optical Fock states on demand in the usual atom-cavity system via utilizing the technique of shortcuts to adiabatic passages. It is shown that, by applying auxiliary pulse(s) (besides the usual pumps to excite atom in the cavity), the desirable transitionless quantum drivings for Fock state productions (FSPs) could be implemented deterministically. Compared with the previous method based on stimulated Raman adiabatic passages for the FSPs, the present proposal suppress effectively the unwanted but practically unavoidable nonadiabatic transitions during the drivings. As a consquence, the efficiency of FSPs by the present technique should be significantly high, even in the presence of various atomic and cavity dissipations.