a plurality of quantum dots each having discrete energy levels including an energy level of a ground state and an energy level of an excited state, the excited level being higher than the ground level even if energy due to an ambient temperature is provided on the quantum dots;

a barrier structure unit formed of a dielectric which surrounds the quantum dots;

an injection unit configured to inject an electron into a position of the ground level in each of the quantum dots via the barrier structure unit, utilizing a tunneling effect, or to prevent injection of an electron into the position, injecting the electron or preventing injection of the electron controlled by changing an energy level of the injection unit, the injection unit configured to include two transparent electrodes between which the barrier structure unit is interposed;

a voltage applying unit configured to apply a voltage to each of the transparent electrodes;

a first light source which emits, to the quantum dots, a first light beam having first energy for exciting electrons from the ground level to the excited level;

a second light source which emits, to the quantum dots, a second light beam having second energy different from the first energy; and

a controller configured to control the voltage, the first light beam, and the second light beam,

wherein the injection unit injects the electron into the position to form a new outermost orbital outside an existing outermost orbital.