Bit Quantum Gates on Single Atoms

6 Quantum Computers First Steps Towards a Realization 

This is not yet sufficient to performing any arbitrary possible 1-bit quantum gate. What we need in addition to the rotations (6.10) are phase shifts conditional to the state of the atom  

According to this transformation a relative phase change 0 between the two states 1 ) and e) takes place. This kind of transformation can be accomplished by applying a laser to the atom which is not resonant with the transition ) — e). This means that no periodic exchange of excitation can take place due to energy conservation reasons. However, the time evolution will induce a conditional phase shift according to (6.11). 

With resonant and non-resonant laser interaction we can in principle perform any arbitrary 1-bit quantum gate on atoms. Atomic qubits are technologically feasible and have already been realized experimentally for example in the context of single trapped ions (Bollinger et al. 1991). The basics of this technology will be discussed in Section 6.4.5. 

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