[chrjozefharibo]

For performing a quantum algorithm two sets of gates are needed, for instance single qubit rotations and a square root of swap gate. A hadamard gate is another example of a universal gate. Starting up your quantum computer, you will find it in its ground state, that is the state where all qubits are in their lowest energy state. From there you start to apply q gates to the qubits. These gates make the Hamiltonian of the system evolve in time. Depending on THE sequence of gate operations on qubits, you evolve from one state to the other, performing a certain algorithm. Read out of the final state depends on the implementation of the qubit. For atoms and diamond nv centers you can use a laser. For electron spins you can use a charge detector, for flux qubits you measure a magnetic field.