Increasing the Coherence Time of Josephson Junction Phase Qubit

This research aims at building highly coherent Josephson Junction Phase Qubits which can be initialized, controlled, coupled and measured to build a quantum computer. Our qubit is a superconducting electrical circuit which behaves like an artificial atom due to the quantum mechanical properties of the incorporated Josephson junction. We use its two lowest energy levels to represent the two logical states |0> and |1>. During the operation of the qubit we found fluctuations of the energy level splitting which lead to shorter coherence time and limited performance of the device. Two important candidates causing this decoherence were critical current noise and magnetic flux noise. These could be distinguished by operating the Qubit with two opposite senses of flux bias. While critical current noise has the same effect on the splitting for both senses of flux bias, magnetic flux noise has an opposite effect on the splitting. Since we found the noise at the two operating points to be anti-correlated, it was concluded that the primary source of this decoherence was magnetic flux noise. The next step is to find the source of this noise and reduced it to improve the performance of our qubit.