  We present the solid-state quantum circuits that have been developed in order
to implement quantum bits suitable for a quantum processor. These qubits are
either based on the quantum state of a single particle (semiconductor qubits),
or on the quantum state of the global circuit (superconducting qubits). We
discuss more in detail the superconducting qubits, and present results on qubit
manipulation and readout. We explain the main strategies used to improve and
tio maintain quantum coherence.
