What is the hardware for quantum gates?
I have lots of materials on the theory of quantum gates in terms of matrices, linear operators, and so forth. However, I would like to gain a basic understanding of how these matrices are achieved in practice. The difference is between knowing that a transistor acts as a switching or amplifying device, and knowing that this is achieved by making a PNP or NPN semiconductor sandwich etc. Web sites which explain it in non-specialist terms (I view hardware as a sort of necessary evil for the theory to be applicable) are welcome, as long as they do not send me to a site that requires paid access. All that I have been able to glean from the Internet is that crystals are often used. I don't need too much detail, but more detail than that.... Thanks in advance.