The Josephson junction is an ideal solid-state system for building “electrical atoms” that can function as quantum bits for a quantum computer. Recent advances in the materials and design of phase quibits have dramatically improved their coherence so that high-fidelity quantum logic operations can be performed. Combined with advances in microwave electronics, full characterization of single and coupled qubit logic gates are now possible using quantum tomography techniques. I will report on several recent experiments of our group demonstrating tomographic state measurement of single and coupled qubit logic gates that provides direct proof of entanglement.
We believe this experimental approach has unique advantages because our qubit has 50 ohm impedance, which enables the use of simple qubit coupling over long distance. With only modest improvements we can begin scaling up the number of qubits to start testing more complex quantum algorithms.