As a potential candidate for quantum computation and metrology, the nitrogen vacancy (NV)center in diamond presented both challenges and opportunities resulted from charge state conversion. By utilizing different lasers for the photon-induced charge
state conversion, we achieved the sub-diffraction charge state manipulation. The charge state depletion (CSD) microscopy resolution was improved to 4.1 nm by optimizing the laser pulse sequences. Subsequently, the electron spin state dynamics of adjacent NV centers were selectively detected via the CSD. The experimental results demonstrated that the CSD can improve the spatial resolution of the measurement of NV centers for nanoscale sensing and quantum information.
The indistinguishability of independent single photons is presented by decomposing the single photon pulse into the mixed state of different transform limited pulses. The entanglement between single photons and outer environment or other photons indu
ces the distribution of the center frequencies of those transform limited pulses and makes photons distinguishable. Only the single photons with the same transform limited form are indistinguishable. In details, the indistinguishability of single photons from the solid-state quantum emitter and spontaneous parametric down conversion is examined with two-photon Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the indistinguishability are discussed, where the usage of spectral filter is highlighted.
We describe and examine entanglement between different degrees of freedom in multiphoton states based on the permutation properties. From the state description, the entanglement comes from the permutation asymmetry. According to the different permuta
tion properties, the multiphoton states can be divided into several parts. It will help to deal with the multiphoton interference, which can be used as the measurement of the entanglement.
