I'v read published books, articles and papers about Quantum-Computing. I found that all the materials I've seen are, instead of describing quantum gate from basic physics to abstraction, trying hard to avoid talking about the implementation details of quantum-gates.I firstly questioned myself: Am I searching in the wrong area where only formal mathematics are concerned?But I found those papers and books do have explained ion-traps, optical-switches and even laser-fibre in great detail.When it comes to quantum-gates they claimed to have used in their research, only matrices, equations, formulations and black-box components are shown.We all know about the unitaries and matrix computation. But if you print a quantum-gate matrix operator on an A4-paper, that ain't going to do anything when photons or electrons are thrown to it.So, does anyone know what is a quantum gate, concretely so that I can know: Is Quantum Gate a device using magnetic field to do element arithmetics?Is Quantum Gate a device using laser-beam?Is Quantum Gate a device using metal wire?When scientists happily multiply eigenstates by observables, do electrons collide in the gate when multiplied?Thanks in advance.
What does a tangible Quantum-Gate look like?
physics;quantum computing
You seem to have the idea that a quantum gate is a physical thing rather than just a conceptual thing. It doesn't  necessarily work that way. While CMOS  gates are usually actual physical devices, quantum gates may be just conceptual. Consider an ion trap. The ions represent qubits by using one electronic state as a $|0\rangle$ and another as a $|1 \rangle$. A quantum gate is performed by applying a $4 \times 4$ unitary matrix to two of these ions. This is done by shining a sequence of laser pulses on the ions. It's not a physical device into which two ions are input, in which they interact, and out of which the ions come with their states changed. Quantum gates are performed by shining laser pulses on the ions, but there's not necessarily one laser per quantum gatethe same lasers are used for many different quantum gates. Thus, you can't point to any specific piece of hardware and say this is the quantum gate.  And if you use flux qubits in superconductors for your quantum computer, the quantum gates don't use lasers at all, and they look completely different (and slightly more like CMOS devices). 