1. A quantum bit computation method comprising: preparing an optical resonator with a resonance frequency; preparing a plurality of first physical systems contained in the optical resonator and including four energy states and two energy states, the four energy states being represented by |0>, |1>, |3> and |5>, the two energy states being represented by |2> and |4>, energies of |2> and |4> being higher than energies of |0>, |1>, |3> and |5>, a transition frequency between |3> and |2> being equal to the resonance frequency, |0> and |1> representing quantum bits; shifting |0> of each of a first physical system and a second physical system, included in the first physical systems, to |3> by emitting thereto light pulses resonating with |0>-|4> transitions of the first physical system and the second physical system and |3>-|4> transitions of the first physical system and the second physical system; shifting |1> of the first physical system and the second physical system to |5> by emitting thereto light pulses resonating with |1>-|4> transitions of the first physical system and the second physical system and |5>-|4> transitions of the first physical system and the second physical system; emitting, to the optical resonator, a single-photon pulse with the resonance frequency; flipping quantum bits of second physical systems except for the first physical system and the second physical system, the second physical systems being included in the first physical systems; flipping |3> and |5> of each of the first physical system and the second physical system; executing no operations by a time equal to a time for emitting the single-photon pulse to the optical resonator; returning |3> of each of the first physical system and the second physical system to |0> by emitting thereto light pulses resonating with the |0>-|4> transitions and the |3>-|4> transitions; returning |5> of the first physical system and the second physical system to |1> by light pulses resonating with the |1>-|4> transitions and the |5>-|4> transitions; and flipping quantum bits of the first physical systems.