Design, Fabrication and Characterization of a Microwave Resonator ...

1 Motivation and OutlineQuantum Information Processing is a field with a huge variety of aims, purposes and applications.It includes, among others, the large field of quantum computing, a subject of interestin many research areas.There are some realizations even with superconducting devices (e.g. the charge qubit)or, to stay in the field of solid state physics, quantum dots, realized with semiconductorsand also in the field of atomic physics where individual atoms play the role of quantumtwo-level systems. In liquid nuclear magnetic resonance (NMR) the factorization of 15 wasrealized with seven spin-1/2 nuclei in a molecule used as quantum bits [20]. The calculationwas done with the Shor algorithm which is well known in quantum information theory [17].Beyond the experiments done at different institutes also companies are interested in the fieldof building a quantum computer. Recently D-Wave Systems, Inc., Canada presented theirproposal of a quantum computer in public [1].Although many different qubits have been realized, one central problem in quantum computingis the coupling of qubits, in order to make operations and generate entangled quantumstates. The multidisciplinary field of quantum computing yielded a simple scheme. In quantumoptics quantum computing is realized with atoms placed in a 3d cavity, which has theadvantage of providing a readout scheme for the qubit. Using cavities with wavelengths inthe millimeter regime it is possible to copy this scheme directly to the world of solid statequbits. This idea was realized with quantum dots [15] and proposed for superconductingcharge qubits by Blais et al. [2]. In this work the regimes of zero and large detuning betweenthe artificial atom and the cavity were discussed. In the large detuning regime thelifetime of a qubit will be enhanced and a dispersive quantum non-demolition readout of thequbit will be possible. Also control and entanglement of qubits by using the cavity modes asa ”bus” system is possible. The resonator with a charge qubit inside was realized by Frunzioet al. [6], Wallraff et al. [21] experimentally verified the strong coupling of a qubit and acavity in the resonant and the detuned regime for the first time. The Rabi splitting of theinteraction of the cavity and the qubit was observed. Yang et al. [23] investigated the implementationof entanglement of two Cooper pair boxes within a microwave cavity in detail.They found that the information transfer from one qubit to another can be realized with highfidelity. The cavity has the advantage of working like a magnetic filter, therefore, decoherencecaused by the external environment is strongly suppressed. With frequency matchingit is possible to selectively couple microwave pulses and any particular qubit in the cavity.While these experiments deal with charge qubits a new approach will be done with fluxqubits. This work is a small step into this new field of flux qubits in a cavity. Our aim is toproduce and understand high Q cavities. Later on these will be used for placing a flux qubitinside, in order to compare this type of realization with the one with a charge qubit and toanalyze decoherence and noise effects (e.g. charge noise). A single qubit will be placed in1