# Physical implementation of gates on IBM Q

There is a lot of quantum gates in IBM Q Composer, however, only few are implemented physically while others can be composed of them.

When one looks at description of a quantum processor in IBM Q interface, there is a list of basis gates. For example those are id, u1, u2, u3, cx for Melbourne processor. However, gates $$I$$, $$U1$$ and $$U2$$ are special cases of $$U3$$. If one removes statement include "qelib1.inc"; from QASM code, only $$CNOT$$ and $$U3$$ gates are left. So, it seems that all single qubit gates are implemented with $$U3$$ and there is of course two qubits $$CNOT$$.

According to IBM Q manual, $$U3$$ gate is implemented by three frame changes and two $$X_{\pi/2}$$ pulses.

My questions are these:

1. Which gates are implemented physically on IBM Q? I would expect $$CNOT$$ and some single qubit gates but which ones?
2. What are frame changes and $$X_{\pi/2}$$ pulses used for gate implementation?