Abstract

Condensed matter physics needs quantum mechanics to explain properties of large numbers of phonons, electrons or spins. Now a new field is emerging where macroscopic solid state objects are designed and fabricated to act as individual quantum two-level systems that can be manipulated with external signals, similar to artificial atoms and molecules. Superconducting circuits have a natural advantage. The picture shows our first flux quantum bit, as fabricated by Caspar van der Wal . It exhibits quantum superpositions of clockwise and anti-clockwise persistent currents of 0.5 microampere. These flux qubits can be driven with microwaves, they are coherent up to microseconds. Two qubits can be coupled inductively and be entangled. We have realized a non-destuctive readout procedure with ideal quantum projection. We anticipate that larger quantum circuits can be made for quantum information processing and for direct simulation of periodic quantum systems with many degrees of freedom.