The temporal purity of single photons is crucial to the indistinguishability of independent photon sources for the fundamental study of the quantum nature of light and the development of photonic technologies. Currently, the technique for single photons heralded from time-frequency entangled biphotons created in nonlinear crystals does not guarantee the temporal-quantum purity, except using spectral filtering. Nevertheless, an entirely different situation is anticipated for narrow-band biphotons with a coherence time far longer than the time resolution of a single-photon detector. Here we demonstrate temporally pure single photons with a coherence time of 100 ns, directly heralded from the time-frequency entangled biphotons generated by spontaneous four-wave mixing in cold atomic ensembles, without any supplemented filters or cavities. A near-perfect purity and indistinguishability are both verified through Hong-Ou-Mandel quantum interference using single photons from two independent cold atomic ensembles. The time-frequency entanglement provides a route to manipulate the pure temporal state of the single-photon source. DOI: 10.1103/PhysRevLett.117.013602 The purity of the quantum state of a single photon is a prerequisite of its indistinguishability with single photons from other independent sources, and the latter is an essential basis for the realization of a scalable quantum network with distant and independent nodes [1][2][3][4][5]. Furthermore, the temporal purity of a single photon is crucial to the development of photonic technologies for quantum information science [6,7]. The traditional method to produce indistinguishable single photons is heralding time-frequency entangled biphotons generated from spontaneous parametric down-conversion (SPDC) in a nonlinear crystal which is pumped by ultrashort pulses [4,5,8]. In recent decades many new physical systems have been developed [9-13] to obtain pure single photons without time-frequency entanglement built in.In the community of quantum communication, SPDC in χ ð2Þ nonlinear media is still the preferable way to produce entangled biphotons because of its simplicity in the operation and the potential for on-chip integration and scaling up [14][15][16]. However, the intrinsic feasible phase matching condition of SPDC crystal allows an extremely broad range of temporal modes. Therefore, the typical temporal coherence time of the photon source is of femtosecond scale. Compared to the time response of most commercial single-photon detectors, which is about 1 ns, this temporal coherence time is so short that the trigger photon of the heralded single photon is measured with a large time uncertainty. This time uncertainty damages the temporal quantum purity of the single-photon source. To circumvent the time uncertainty problem due to the slowness of the detectors, a common practice is to use external spectral filtering including passive filtering with narrowband filters [4,5,17] and active filtering with an optical cavity [18]. In this case, the temporal state o...

The electrochemical behavior of iron-doped nickel hydroxide is remarkably consistent across the diverse fabrication protocols employed throughout the literature, which contrasts with variations reported in composition-dependent changes in structure and...

The beam-splitter (BS) is one of the most common and important components in modern optics, and lossless BS which features unitary transformation induces Hermitian evolution of light. However, the practical BS based on the conversion between different degree of freedoms are naturally non-Hermitian, as a result of essentially open quantum dynamics. In this work, we experimentally demonstrate a non-Hermitian BS for the interference between traveling photonic and localized magnonic modes. The non-Hermitian magnon-photon BS is achieved by the coherent and incoherent interaction mediated by the excited levels of atoms, which is reconfigurable by adjusting the detuning of excitation. Unconventional correlated interference pattern is observed at the photon and magnon output ports. Our work is potential for extending to single-quantum level to realize interference between a single photon and magnon, which provides an efficient and simple platform for future tests of non-Hermitian quantum physics.

Numerous fabrication protocols are known to yield transition metal oxides with structures related to layered double hydroxides, but the effect of fabrication protocol on the uniformity of mixed-metal compositions remain largely unexplored. We have analysed the apparent solubility limits and the structural implications of iron ions in nickel hydroxide lattices for materials prepared by four different fabrication protocols. Opposing shifts in the (100) and (001) reflection in powder X-ray diffraction results revealed a contraction of the nickel lattice upon successful incorporation of iron, with Ni-M distances exhibiting an apparently linear decrease with respect to iron content. This feature revealed the amount of iron incorporated into nickel-based materials to be dependent on fabrication protocol, varying from apparently negligible concentrations to over fifty atomic percent. The dependency of structure on fabrication protocols provides a handle to improve fundamental understanding of catalytically relevant coordination environments.

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