Nuclear magnetic resonance
In the Nuclear Magnetic Resonance (NMR) technique, electromagnetic waves are used to control and detect the spin of the nucleus of the atom. You must have heard about the NMR technique being used for spectroscopy and in chemistry as well. In chemistry, it is used to determine the structure of various molecules. In Figure 4.5 you can see the physical apparatus used to build an NMR quantum computer:
The NMR apparatus consists of a liquid sample containing either carbon, fluorine, nitrogen, or phosphorus, which can be regarded as an ensemble of n-bit quantum computers. The molecules of the liquid emit NMR signals of a frequency of 500 MHz when the magnetic field around them is 11.8 tesla and are commonly mixed in a solvent to prevent inter-molecular interactions. The bore of a large superconducting magnet holds the liquid sample, which is connected to the RF circuit containing amplifiers...