In this communication, we have demonstrated that SiO(2) nanoparticles can be generated by simply scratching the quartz or silicon wafer with a SiO(2) layer and confirmed it to be active for the growth of SWNTs for the first time. Furthermore, the SWNTs from SiO(2) has a much narrower size distribution. This may open a way to control the diameter of the SWNTs. More importantly, our work has found a series of oxides including Al(2)O(3), TiO(2), and rare earth oxides to be active for SWNT growth as well. These findings not only provide an alternative new type of catalysts for the growth of SWNTs but also give more insight into the role of the catalysts and a deeper understanding of the growth mechanism of SWNTs. The effective catalysts and catalytic activity for SWNT growth seem to be more size-dependent than the catalysts. Long oriented SWNTs generated from these catalysts enable us to rule out the relationship between the catalysts and the structures of the SWNTs. Thus controlled growth of SWNTs including the diameter and chirality is expected to be eventually realized.

We report an experimental realization of a narrow-band polarization-entangled photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous parametric down-conversion. This linewidth is comparable to the typical linewidth of atomic ensemble based quantum memories. Single-mode output is realized by setting a reasonable cavity length difference between different polarizations, using of temperature controlled etalons and actively stabilizing the cavity. The entangled property is characterized with quantum state tomography, giving a fidelity of 94% between our state and a maximally entangled state. The coherence length is directly measured to be 32 m through two-photon interference.PACS numbers: 03.67. Bg, 42.65.Lm The storage of photonic entanglement with quantum memories plays an essential role in linear optical quantum computation (LOQC) [1] to efficiently generate large cluster states [2], and in long-distance quantum communication (LDQC) to make efficient entanglement connections between different segments in a quantum repeater [3]. For the atomic ensemble based quantum memories [4,5,6], typical spectrum linewidth required for photons is on the order of several MHz. While spontaneous parametric down-conversion (SPDC) is the main method to generate entangled photons [7], the linewidth determined by the phase-matching condition is usually on the order of several THz which is about 10 6 times larger, making it unfeasible to be stored. Moreover, interference of independent broad-band SPDC sources requires a synchronization precision of several hundred fs [8]. While in LDQC, for the distance on the order of several hundred km, it becomes extremely challenging for the current synchronization technology [9,10]. But for a narrowband continuous-wave source at MHz level, due to the long coherence time, synchronization technique will be unnecessary, while coincidence measurements with time resolution of several ns with current commercial singlephoton detectors will be enough to interfere independent sources.Passive filtering with optical etalons is a direct way to get MHz level narrow-band entangled photons from the broad-band SPDC source, but it will inevitably result in a rather low count rate. In contrast, cavity-enhanced SPDC [11,12] provides a good solution for this problem. By putting the nonlinear crystal inside a cavity, the generation probability for the down-converted photons whose frequency matches the cavity mode will be enhanced greatly. The cavity acts as an active filter. The frequency of the generated photons lies within the cavity mode, which can be easily set to match the required atomic linewidth. Experimentally, Ou et al.[11] has realized a type-I source, in which the two photons generated have the same polarization, making it very difficult to generate entanglement. Wang et al.[13] made a further step by putting two type-I nonlinear crystals within a ring cavity to generate polarization entanglement, but unfortunately the output is multi-mode which does not fit the requirement of an...

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The low capacity and unsatisfactory rate capability of hard carbon still restricts its practical application for Li/K‐ion batteries. Herein, a low‐cost and large‐scale method is developed to fabricate phosphorus‐doped hard carbon (PHC‐700) by crosslinking phosphoric acid and epoxy resin and followed by annealing at 700 °C. H3PO4 acts not only as a crosslinker to solidify epoxy resin for promoting the degree of graphitization and lowering the specific surface area, but also as phosphorus source for forming PC and PO bonds, thus providing more active sites for Li/K storage. As a result, the PHC‐700 electrode delivers a highly reversible capacity of 1294.8 mA h g−1 at 0.1 A g−1 and a capacity of 214 mA h g−1 after 10 000 cycles at 10 A g−1. As for potassium‐ion batteries, PHC‐700 exhibits a reversible capacity of 381.9 mA h g−1 at 0.1 A g−1 and a capacity of 260 mA h g−1 after 1000 cycles at 0.2 A g−1. In situ Raman and in situ NMR measurements reveal that the P‐containing bonds can enhance the adsorption to alkali metal ions, and the PC bond can participate in electrochemical redox reaction by forming Lix PCy . Additionally, P‐doped hard carbon shows better structural/interfacial stability for improved long‐term cycling stability.

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A highly oriented mesoporous graphitic carbon nanospring (OGCS) with graphitic layers that are perpendicular to the axis is prepared by hydrothermal treatment of epoxy resin at 500 °C and annealing at 1400 °C. Water plays an important role in not only forming the graphitic carbon nanospring with a high [002] orientation and a large amount of active edge‐plane sites, but also in the generation of the mesoporous structure, which facilitate fast K‐ion adsorption and diffusion. In situ and ex situ measurements confirm that OGCS undergoes K‐adsorption in mesopores and then K‐intercalation in the graphite layer to form KC8 with a low discharge voltage. The spring‐like nanostructure can expand one‐dimensionally along the axial direction to accommodate the volume variation. The OGCS electrode thus shows a much better K‐storage performance than that of unoriented graphitic carbon.

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