Field-effect transistor element and quantum computer device

A quantum dot device (100) for use as a qubit in a quantum computer is disclosed, comprising a channel region (106), a source region (108), a drain region (110), and at least two primary gate regions (120, 122, 124), wherein the at least two primary gate regions (120, 122, 124) are respectively provided with a main direction of extension (126, 128, 130) and disposed on a first surface of the channel region (106), and wherein the respective main directions of extension of the at least two primary gate regions are arranged substantially parallel to each other, at least one secondary gate region (118) having a main direction of extension (132) and disposed on a second opposite surface of the channel region (106), wherein the main direction of extension (132) of the at least one secondary gate region (118) is arranged substantially orthogonally to the respective main directions of extension (126, 128, 130) of the at least two primary gate regions (120, 122, 124). The device may also be formed in a non-planar semiconductor body, like a fin, see figure 6.