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We study the coherence preservation of quantum bit in photonic crystal using input–output trace distance. The input–output trace distance can be extremely short and the information hardly dissipates when the quantum bit frequency lies deep inside the photonic band gap. Different from the behavior in cavities, the undissipated information of the quantum bit can be held in the photonic band gap due to the effective interaction between the quantum bit and photonic crystal. A factor called coherence radius is defined in this paper for evaluating the quantum coherence preservation in photonic crystal, which is straightly linked to the visibility of input–output trace distance and the coherence of quantum states. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate that low refractive-index three-dimensional photonics crystals with a planar defect, fabricated with the direct laser writing method, can be used to effectively enhance the spontaneous emission (SE) of semiconductor quantum dots (QDs). To achieve this, we develop a controllable and reliable method to integrate quantum dots into the defect-embedded photonic crystals (PCs). Although the overlapping of different direction stop gaps in low refractive-index defect-free three-dimensional photonic crystals imposes a challenge to realize spontaneous emission enhancement at the band edge wavelength, we achieve a 15% enhancement of the spontaneous emission by introducing a tailored planar defect. [ABSTRACT FROM AUTHOR]