Properties of a High-T$_c$ Intrinsic Phase Qubit

We discuss the properties of high-T$_c$ intrinsic phase qubits. An intrinsic phase qubit is a superconducting ring made of a Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystal, intercepted by two intrinsic Josephson junction stacks. As a stack consists of many intrinsic Josephson junctions, an intrinsic phase qubit can be regarded as a multi-junction system, i.e. a system of many degrees of freedom in phase space. However, I-V characteristics and switching current distributions of our samples show that an intrinsic phase qubit behaves like a system with only two degrees of freedom, independent of the number of junctions in the stacks, as long as the two stacks are uniform. Due to the large self-inductance, the potential of an intrinsic phase qubit has several minima. In order to perform quantum operations from a single well, a technique using low-frequency microwaves is presented.