In current information and communication technology, pseudo random numbers generated by software are used for communication encryption.However, due to the vulnerability of pseudo-random numbers, encryption using true random numbers generated by a physically random phenomenon has been required.The unpolarized state of photons this time is one of the candidates.However, in the verification of randomness, in addition to the fact that all polarization states occur with equal probability (static randomness), there is no correlation between the polarizations of adjacent photons in time (dynamic randomness). It was necessary to confirm, and no evaluation method was established for dynamic randomness.

　Therefore, the research group realized a static and dynamic unpolarized state using the nitrogen-vacancy center, which is an impurity defect in diamond, and evaluated its characteristics.When the center of the nitrogen-vacancy is irradiated with a laser, the electrons are excited into one of two states called Ex and Ey, producing single horizontally and vertically polarized photons, respectively.However, at room temperature, the two electronic states are randomly mixed, so it is expected that photons in the unpolarized state will be generated.In addition, in order to observe the unpolarized state, the crystal plane of the sample was devised and observed from the axial direction of the nitrogen-vacancy center.Furthermore, a new evaluation method for dynamic non-polarization was developed and applied.As a result, we confirmed photons with almost completely randomly polarized light, both statically and dynamically.

　It is said that this achievement will advance the verification of basic problems of quantum mechanics and the technological development of quantum cryptography, and can also be applied to physical true random number generators.

Paper information: [Scientific Reports] Dynamically unpolarized single-photon source in diamond with intrinsic randomness