Qubit-resonator system as an application to quantum computation.

摘要

The recent development of quantum computation has inspired lots of interesting ideas in a variety of fields. It is surprising, and yet not surprising, to see that even systems with very distinct forms can resemble each other in many ways. In our study of a solid state mesoscopic system, we found that it bears many features similar to those being seen in cavity quantum electrodynamics in quantum optics. Here the role of the atom is played by a Cooper pair box (CPB), and the cavity is replaced by a transmission line resonator. This combined qubit-resonator system, though its size is much larger than a real atom, still gives us several revelations about fundamental quantum physics.; Due to the interaction between the Cooper pair box and the resonator photon field, their properties both change to reflect each other's character. Like an atom, the CPB aquires a Lamb shift to its own energy splitting, and the resonator changes its frequency based on the state of the CPB. The latter is especially important, because by taking advantage of this feature we can devise readout schemes that do not perturb the CPB. Since the CPB is practically hidden inside the resonator, the shielding could potentially lead to an enhancement of the qubit lifetime.; Quantum computation requires at least stages of control, operation, and readout. We show that even though the qubit is hidden inside the resonator, we can still control it with standard NMR techniques using microwaves. Furthermore, the resonator itself may also serve as a medium for communicating among multiple qubits and facilitating quantum operations. Therefore, this system, if realized in the experiments, could be a promising candidate for the basic structure of a quantum computer in the future.