In the area of quantum semiconductor physics, interesting research has been progressing based on semiconductor hetero- and nano-structures with the concept of carrier interaction. It has been found that two-dimensional systems show fruitful quantum Hall properties depending on orbital, spin and valley degrees of freedom. Superfluidity-like phenomena may appear in bilayer systems. We are also studying semiconductor nanostructures, such as quantum wires, quantum point contacts and quantum dots. Carrier interactions in these nanostructures enable us to manipulate single electrons (spins) in semiconductors. Recently, it has been found that nuclear spins play an important role under certain quantum Hall conditions. Coherent control of nuclear spins was demonstrated in a semiconductor nanodevice and nuclear spin relaxation was used as a sensitive detector to study electron spin features in semiconductor structures. Interaction between photons and nuclear spins via electron spins will be realized by using a combination of optical and electrical methods. NMR and MRI have been widely used in chemistry and medical science, and their extension to solid-state physics may open a way to novel spintronics including nuclear spins. Our studies of semiconductor quantum systems have resulted in the coherent control of carriers, spins, and nuclear spins, and represent fundamental advances toward quantum computers. These studies will be carried out in collaboration with NTT Basic Research Laboratories where world-class knowledge and technologies have been accumulated for crystal growth, nano-processing and semiconductor physics.