A quantum bit computation method includes operating a two-quantum-bit gate on quantum bits of a first physical system and a second physical system, second energy states of second physical systems except for the first physical system and the second physical system do not change, three energy states being represented by |0>, |1> and |3>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1> and |3>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits, flipping quantum bits of first physical systems after operating the two-quantum-bit gate, executing no operations by a time equal to a time for operating the two-quantum-bit gate, after flipping the quantum bits, and again flipping the quantum bits of the first physical systems after executing no operations.