The technical difficulties are numerous and seem almost
insurmountable. However, much progress has been made during
the last two decades. Solving the problems of the environment-
induced decoherence and scalability are the ultimate challenges.
0
0.2
0.4
0.6
0.8
1
Probability
|⇓↓>
|⇑↓>
|⇓↑>
|⇑↑>
|0↓>
|0↑>
|⇓↓>
|⇑↓>
|⇓↑>
|⇑↑>
|0↓>
|0↑>
Input
|⇓↓>
|⇑↓>
|⇓↑>
|⇑↑>
|0↓>
|0↑>
|⇓↓>
Output
|⇑↓> |⇓↑> |⇑↑> |0↓> |0↑>
1 0
0 1
0 1
1 0
1
1
0
0
0
0
0 0
0 0
Input
Output
Fig. 5. Truth table of the CNOT gate and its graphical representation. For a given input state, the output is a superposition of three states (see Eqs. (4) and (8)). The numerical
values given in the table are the probabilities of measuring the spin system in a state jmS ms 〉. The effective table consists of the first four lines.
M. Hebbache / Solid State Communications 194 (2014) 20–24 23
An important step in this direction seems to have been made
by a quantum computing company using superconducting flux
qubits [38].
We investigated the possibility to implement a two-qubit
quantum CNOT gate that uses the electron spins carried by the
vacancy-nitrogen defect of diamond and a nearby nitrogen atom in
substitutional position. This is a new approach. It is the hyperfine
interaction which is usually considered. The manipulation of spins
is realized by irradiation of the spin system with a two-pulse
sequence. The free parameters involved in Eqs. (4)–(8) offer other
possibilities that can be explored.