Single-atom catalysts offering intriguing activity and selectivity are subject of intense investigation. Understanding the nature of single-atom active site and its dynamics under working state are crucial to improving their catalytic performances. Here, we identify at atomic level a general evolution of single atom into a near-free state under electrocatalytic hydrogen evolution condition, via operando synchrotron X-ray absorption spectroscopy. We uncover that the single Pt atom tends to dynamically release from the nitrogen-carbon substrate, with the geometric structure less coordinated to support and electronic property closer to zero valence, during the reaction. Theoretical simulations support that the Pt sites with weakened Pt-support interaction and more 5d density are the real active centers. The single-atom Pt catalyst exhibits very high hydrogen evolution activity with only 19 mV overpotential in 0.5 M H 2 SO 4 and 46 mV in 1.0 M NaOH at 10 mA cm −2 , and long-term durability in wide-pH electrolytes.

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An active and stable photocatalyst to directly split water is desirable for solar‐energy conversion. However, it is difficult to accomplish overall water splitting without sacrificial electron donors. Herein, we demonstrate a strategy via constructing a single site to simultaneously promote charge separation and catalytic activity for robust overall water splitting. A single Co1‐P4 site confined on g‐C3N4 nanosheets was prepared by a facile phosphidation method, and identified by electron microscopy and X‐ray absorption spectroscopy. This coordinatively unsaturated Co site can effectively suppress charge recombination and prolong carrier lifetime by about 20 times relative to pristine g‐C3N4, and boost water molecular adsorption and activation for oxygen evolution. This single‐site photocatalyst exhibits steady and high water splitting activity with H2 evolution rate up to 410.3 μmol h−1 g−1, and quantum efficiency as high as 2.2 % at 500 nm.

Quantum teleportation [1] faithfully transfers a quantum state between distant nodes in a network, enabling revolutionary information processing applications [2][3][4]. Here we report teleporting quantum states over a 30 km optical fibre network with the input single photon state and the EPR state prepared independently. By buffering photons in 10 km coiled optical fibre, 1

Proposed electrocatalytic proton reduction intermediates of hydrogenase mimics were synthesized, observed, and studied computationally. A new mechanism for H(2) generation appears to involve Fe(2)(CO)(6)(1,2-S(2)C(6)H(4)) (3), the dianions {[1,2-S(2)C(6)H(4)][Fe(CO)(3)(μ-CO)Fe(CO)(2)](2-) (3(2-)), the bridging hydride {[1,2-S(2)C(6)H(4)][Fe(CO)(3)(μ-CO)(μ-H)Fe(CO)(2)]}(-), 3H(-)(bridging), and the terminal hydride 3H(-)(term-stag), {[1,2-S(2)C(6)H(4)][HFe(CO)(3)Fe(CO)(3)]}(-), as intermediates. The dimeric sodium derivative of 3(2-), {[Na(2)(THF)(OEt(2))(3)][3(2-)]}(2) (4) was isolated from reaction of Fe(2)(CO)(6)(1,2-S(2)C(6)H(4)) (3) with excess sodium and was characterized by X-ray crystallography. It possesses a bridging CO and an unsymmetrically bridging dithiolate ligand. Complex 4 reacts with 4 equiv. of triflic or benzoic acid (2 equiv. per Fe center) to generate H(2) and 3 in 75% and 60% yields, respectively. Reaction of 4 with 2 equiv. of benzoic acid generated two hydrides in a 1.7 : 1 ratio (by (1)H NMR spectroscopy). Chemical shift calculations on geometry optimized structures of possible hydride isomers strongly suggest that the main product, 3H(-)(bridging), possesses a bridging hydride ligand, while the minor product is a terminal hydride, 3H(-)(term-stag). Computational studies support a catalytic proton reduction mechanism involving a two-electron reduction of 3 that severs an Fe-S bond to generate a dangling thiolate and an electron rich Fe center. The latter iron center is the initial site of protonation, and this event is followed by protonation at the dangling thiolate to give the thiol thiolate [Fe(2)H(CO)(6)(1,2-SHSC(6)H(4))]. This species then undergoes an intramolecular acid-base reaction to form a dihydrogen complex that loses H(2) and regenerates 3.

Nonclassical multi-photon and number states are attractive because of their wide applicability, and experimental generation of these states is a longstanding aim. We prepare photon triplets using a spontaneous Raman scattering process in a hot atomic ensemble cascaded by a spontaneous parametric downconversion process in a periodically poled nonlinear waveguide; strong temporal correlations are observed between the photons. This represents the first combination of nonlinear processes of different orders with different physical systems, and demonstrates the scheme's feasibility. The triplets exist in the telecommunications band, which is promising for testing of quantum mechanical laws for multi-photon entanglement over large distances.Multipartite entanglement and correlations have numerous potential applications in the fundamental quantum mechanics and quantum information fields [1], and many physical systems have therefore been used to generate triplets or eight-photon states [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Significant progress has been made with successful demonstrations of quantum communication complexity reduction [2,10], topological error correction [11], and fundamental testing of nonlocality [3,12]. Also, approximately 10,000 entangled modes in the continuous variables field have been prepared [17].Many techniques and physical systems have been proposed for direct generation of photon triplets. The methods include triexcitations in quantum dots [18], combinations of second-order nonlinear processes [19], and high-energy electron-position collisions [20]. More recently, a technique that uses cascaded photon pair sources prepared in a nonlinear spontaneous parametric downconversion (SPDC) process in a nonlinear crystal has been used to prepare genuine tripartite photons [14,15]. Also, a predicted two-photon photonic polarized entangled state has been realized without post-selection [16] using this method. Another way to generate tripartite photons is through the use of two SPDC processes cascaded by a sum-frequency process [21][22][23], where single photon nonlinear interaction is demonstrated. However, we have noted that all protocols used to prepare triplets use the same physical systems (e.g., two pp crystals in [14][15][16], and three pp crystals in [23]) and the same order of nonlinear process (e.g., the second order in [14][15][16]23,24], and the third order in [25]). In the future, quantum networks will have to include many physical systems and interaction processes; generation of a photon triplet using combinations of physical systems is therefore interesting and merits investigation.In this Letter, we realize hybrid-cascaded preparation of tripartite photons for the first time, to the best of our knowledge, when using a combination of two physical systems: a hot atomic ensemble and a nonlinear waveguide. In our work, the spontaneous Raman scattering (SRS) process in a hot Rb atomic cell in a collinear configuration is initially used to prepare the nonclassical photon pair ...

Entanglement is a vital resource for realizing many tasks such as teleportation, secure key distribution, metrology, and quantum computations. To effectively build entanglement between different quantum systems and share information between them, a frequency transducer to convert between quantum states of different wavelengths while retaining its quantum features is indispensable. Information encoded in the photon's orbital angular momentum (OAM) degrees of freedom is preferred in harnessing the information-carrying capacity of a single photon because of its unlimited dimensions. A quantum transducer, which operates at wavelengths from 1558.3 to 525 nm for OAM qubits, OAM-polarization hybrid-entangled states, and OAM-entangled states, is reported for the first time. Nonclassical properties and entanglements are demonstrated following the conversion process by performing quantum tomography, interference, and Bell inequality measurements. Our results demonstrate the capability to create an entanglement link between different quantum systems operating in a photon's OAM degrees of freedom, which will be of great importance in building a high-capacity OAM quantum network.

A better understanding of how interfacial structure affects charge carrier recombination would benefit the development of highly efficient organic photovoltaic (OPV) devices. In this paper, transient photovoltage (TPV) and charge extraction (CE) measurements are used in combination with synchrotron radiation photoemission spectroscopy (SRPES) to gain insight into the correlation between interfacial properties and device performance. OPV devices based on PCDTBT/PC71BM with a Ca interlayer were studied as a reference system to investigate the interfacial effects on device performance. Devices with a Ca interlayer exhibit a lower recombination than devices with only an Al cathode at a given charge carrier density (n). In addition, the interfacial band structures indicate that the strong dipole moment produced by the Ca interlayer can facilitate the extraction of electrons and drive holes away from the cathode/polymer interface, resulting in beneficial reduction in interfacial recombination losses. These results help explain the higher efficiencies of devices made with Ca interlayers compared to that without the Ca interlayer.