measured by the photodetectors 603 and 604 as a result of the measurement an h polarized light beam was observed in the case of the ion in the cavity 1301 and a v polarized light beam was observed in the case of the ion in the cavity 1302 from this it was confirmed that the states of the ions in the cavities 1301 and 1302 were 1 gt and 0 gt respectively similarly if the initial states of the ions are 1 gt and 0 gt 0 gt and 1 gt and 0 gt and 0 gt they have to be changed after the above operation is performed thereon to 1 gt and 1 gt 0 gt and 1 gt and 0 gt and 0 gt respectively it was confirmed that these changes occurred the results of the measurements indicate that cz gate operations were realized between the two atoms ions referring then to fig1 a description will be given of example 4 in which an etalon is used as a switching mirror example 4 differs from example 3 shown in fig1 only in that in the former etalons with a finesse of about 100 is used instead of the ring cavities the other structures are similar to those of example 3 in example 4 an incident light beam enters each etalon at an incident angle of about 5 degrees after cz gate operations were performed on atoms.