This question already has an answer here:
Quantum gates seem to be like black boxes. Although we know what kind of operation they will perform, we don't know if it's actually possible to implement in reality (or, do we?). In classical computers, we use AND, NOT, OR, XOR, NAND, NOR, etc which are mostly implemented using semiconductor devices like diodes and transistors. Are there similar experimental implementations of quantum gates? Is there any "universal gate" in quantum computing (like the NAND gate is universal in classical computing)?