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Solid-state qubits with a photonic interface is very promising for quantum networks. Color centers in silicon carbide have shown excellent optical and spin coherence, even when integrated with membranes and nano-structures. Additionally, nuclear spins coupled with electron spins can serve as long-lived quantum memories. Pioneering work in previous has realized the initialization of a single nuclear spin and demonstrated its entanglement with an electron spin. In this paper, we report the first realization of single-shot readout for a nuclear spin in SiC. We obtain a deterministic readout fidelity of 98.2% with a measurement duration of 1.13 ms. With a dual-step readout scheme, we obtain a readout fidelity as high as 99.5% with a success efficiency of 89.8%. Our work complements the experimental toolbox of harnessing both electron and nuclear spins in SiC for future quantum networks., Comment: 5 pages, 4 figures

Towards realizing the future quantum internet, a pivotal milestone entails the transition from two-node proof-of-principle experiments conducted in laboratories to comprehensive, multi-node setups on large scales. Here, we report on the debut implementation of a multi-node entanglement-based quantum network over a metropolitan area. We equipped three quantum nodes with atomic quantum memories and their telecom interfaces, and combined them into a scalable phase-stabilized architecture through a server node. We demonstrated heralded entanglement generation between two quantum nodes situated 12.5 km apart, and the storage of entanglement exceeding the round-trip communication time. We also showed the concurrent entanglement generation on three links. Our work provides a metropolitan-scale testbed for the evaluation and exploration of multi-node quantum network protocols and starts a new stage of quantum internet research., Comment: 21 pages in total, 4 figures and 1 table in the main text, 5 figures and 8 tables in the supplementary material

Quantum internet gives the promise of getting all quantum resources connected, and it will enable applications far beyond a localized scenario. A prototype is a network of quantum memories that are entangled and well separated. Previous realizations are limited in the distance. In this paper, we report the establishment of remote entanglement between two atomic quantum memories physically separated by 12.5 km directly in a metropolitan area. We create atom-photon entanglement in one node and send the photon to a second node for storage. We harness low-loss transmission through a field-deployed fiber of 20.5 km by making use of frequency down-conversion and up-conversion. The final memory-memory entanglement is verified to have a fidelity of 90% via retrieving to photons. Our experiment paves the way to study quantum network applications in a practical scenario., Comment: 9 pages in total, 4 figures in the main text, and 5 figures in the supplementary material

Multiqubit entanglement is an indispensable resource for quantum information science. In particular, the entanglement of photons is of conceptual interest due to its implications in measurement-based quantum computing, communication, and metrology. The traditional way of spontaneous parametric down-conversion already demonstrates entanglement of up to a dozen photons but is hindered by its probabilistic nature. Here, we experimentally demonstrate an efficient approach for multi-photon generation with a Rydberg superatom, a mesoscopic atomic ensemble under Rydberg blockade. Using it as an efficient single-photon interface, we iterate the photon creation process that gives rise to a train of temporal photonic modes entangled in photon number degree. We detect the multiphoton entanglement via converting the photon number degree to a time-bin degree. Photon correlations verify entanglement up to 12 modes. The efficiency scaling factor for adding one photon is 0.27, surpassing previous results, and can be increased significantly without fundamental limitations., Comment: 11 pages, 9 figures

Hybrid matter-photon entanglement is the building block for quantum networks. It is very favorable if the entanglement can be prepared with a high probability. In this paper, we report the deterministic creation of entanglement between an atomic ensemble and a single photon by harnessing Rydberg blockade. We design a scheme that creates entanglement between a single photon's temporal modes and the Rydberg levels that host a collective excitation, using a process of cyclical retrieving and patching. The hybrid entanglement is tested via retrieving the atomic excitation as a second photon and performing correlation measurements, which suggest an entanglement fidelity of 87.8%. Our source of matter-photon entanglement will enable the entangling of remote quantum memories with much higher efficiency., Comment: 6 pages, 4 figures

With Rydberg dipole interactions, a mesoscopic atomic ensemble may behave like a two-level single atom, resulting in the so-called picture of superatom. It is in potential a strong candidate as a qubit in quantum information science, especially for efficient coupling with single photons via collective enhancement that is essential for building quantum internet to connect remote quantum computers. Previously, preliminary studies have been carried out in demonstrating basic concept of Rydberg superatom, a single-photon source, and entanglement with a single photon, etc. While a crucial element of single-shot qubit measurement is still missing. Here we realize the deterministic measurement of a superatom qubit via photon burst in a single shot. We make use of a low-finesse ring cavity to enhance the atom-photon interaction and obtain an in-fiber retrieval efficiency of 44%. Harnessing dipole interaction between two Rydberg levels, we may either create a sequence of multiple single photons or nothing, conditioned on the initial qubit state. We achieve a single-shot measurement fidelity of 93.2% in 4.8 us. Our work complements the experimental toolbox of harnessing Rydberg superatom for quantum information applications., Comment: 6 pages, 4 figures

In this paper we report an experiment that verifies an atomic-ensemble quantum memory via a measurement-device-independent scheme. A single photon generated via Rydberg blockade in one atomic ensemble is stored in another atomic ensemble via electromagnetically induced transparency. After storage for a long duration, this photon is retrieved and interfered with a second photon to perform joint Bell-state measurement (BSM). Quantum state for each photon is chosen based on a quantum random number generator respectively in each run. By evaluating correlations between the random states and BSM results, we certify that our memory is genuinely entanglement-preserving., Comment: 10 pages, 8 figures

In an atomic ensemble, quantum information is typically carried as single collective excitations. It is very advantageous if the creation of single excitations is efficient and robust. Rydberg blockade enables deterministic creation of single excitations via collective Rabi oscillation by precisely controlling the pulse area, being sensitive to many experimental parameters. In this paper, we implement the adiabatic rapid passage technique to the Rydberg excitation process in a mesoscopic atomic ensemble. We make use of a two-photon excitation scheme with an intermediate state off-resonant and sweep the laser frequency of one excitation laser. We find the chirped scheme preserves internal phases of the collective Rydberg excitation and be more robust against variance of laser intensity and frequency detuning.

A cold atomic ensemble suits well for optical quantum memories, and its entanglement with a single photon forms the building block for quantum networks that give promise for many revolutionary applications. Efficiency and lifetime are among the most important figures of merit for a memory. In this paper, we report the realization of entanglement between an atomic ensemble and a single-photon with subsecond lifetime and high efficiency. We engineer dual control modes in a ring cavity to create entanglement and make use of 3-dimensional optical lattice to prolong memory lifetime. The memory efficiency is 38% for 0.1 second storage. We verify the atom-photon entanglement after 1 second storage by testing the Bell inequality with a result of $S=2.36\pm0.14$.

Silicon single-photon detectors (SPDs) are key devices for detecting single photons in the visible wavelength range. Photon detection efficiency (PDE) is one of the most important parameters of silicon SPDs, and increasing PDE is highly required for many applications. Here, we present a practical approach to increase PDE of silicon SPD with a monolithic integrated circuit of active quenching and active reset (AQAR). The AQAR integrated circuit is specifically designed for thick silicon single-photon avalanche diode (SPAD) with high breakdown voltage (250-450 V), and then fabricated via the process of high-voltage 0.35-$\mu$m bipolarCMOS-DMOS. The AQAR integrated circuit implements the maximum transition voltage of ~ 68 V with 30 ns quenching time and 10 ns reset time, which can easily boost PDE to the upper limit by regulating the excess bias up to a high enough level. By using the AQAR integrated circuit, we design and characterize two SPDs with the SPADs disassembled from commercial products of single-photon counting modules (SPCMs). Compared with the original SPCMs, the PDE values are increased from 68.3% to 73.7% and 69.5% to 75.1% at 785 nm, respectively, with moderate increases of dark count rate and afterpulse probability. Our approach can effectively improve the performance of the practical applications requiring silicon SPDs., Comment: 6 pages, 4 figures, accepted for publication in Review of Scientific Instruments

In this work, we systematically study the $\alpha$ decay preformation factors $P_{\alpha}$ and $\alpha$ decay half-lives of 152 nuclei around $Z$ = 82, $N$ = 126 closed shells based on a generalized liquid drop model while $P_{\alpha}$ is extracted from the ratio of the calculated $\alpha$ decay half-life to the experimental one. The results show that there is an obvious linear relationship between $P_{\alpha}$ and the product of valance protons (holes) $N_p$ and valance neutrons (holes) $N_n$. At the same time, we extract the $$P_{\alpha}$ values of even-even nuclei around $\emph{Z}$ = 82, $\emph{N}$ = 126 closed shells from the work of Sun \textit{et al.} [\href {https://doi.org/10.1088/1361-6471/aac981} {J. Phys. G: Nucl. Part. Phys. $\bm{45}$, 075106 (2018)}], in which the $P_{\alpha}$ can be calculated by two different microscopic formulas. We find that the $P_{\alpha}$ are also related to $N_pN_n$. Combining with our previous works [Sun \textit{et al.}, \href {https://doi.org/10.1103/PhysRevC.94.024338} {Phys. Rev. C $\bm{94}$, 024338 (2016)}; Deng \textit{et al.}, \href {https://doi.org/10.1103/ PhysRevC 96.024318} {ibid. $\bm{96}$, 024318 (2017)}; Deng \textit{et al.}, \href {https://doi.org/10.1103/PhysRevC.97.044322} {ibid. $\bm{97}$, 044322 (2018)}] and the work of Seif \textit{et al.} [\href {http://dx.doi.org/10.1103/PhysRevC.84.064608}{Phys. Rev. C $\bm{84}$, 064608 (2011)}], we suspect that this phenomenon of linear relationship for the nuclei around those closed shells is model independent. It may be caused by the effect of the valence protons (holes) and valence neutrons (holes) around the shell closures. Finally, using the formula obtained by fitting the $P_{\alpha}$ calculated by the generalized liquid drop model (GLDM), we calculate the $\alpha$ decay half-lives of these nuclei. The calculated results are agree with the experimental data well.

Based on the Bethe-Salpeter equation eigenstates, we present a first-principles many-body formalism for calculating the two-photon absorption (TPA) coefficient of semiconductors. We apply this formalism to calculate the TPA spectra of MoS2 and WS2 monolayers. The all-electron full-potential linearised augmented-plane wave based functions are used for solving the Bethe-Salpeter equation. The calculated spectra are in good agreement with the available experimental ones for WS2 monolayer. The calculated TPA spectra exhibit significant excitonic effects when compared to those based on the independent particle approximation. The physical origin of TPA excitonic transitions of MoS2 and WS2 monolayers are revealed by tracing the sum-over-states process. We show that the spin-orbit coupling effect leads to characteristic double peaks with an interval of half spin-orbit splitting energy. These double peaks mainly originate from the transitions at the vicinity of K point., Comment: 16 pages, 5 figures, 3 tables

Quantum internet will enable a number of revolutionary applications. It relies on entanglement of remote quantum memories over long distances. Despite enormous progresses so far, the maximal physical separation achieved between two nodes is 1.3 km, and challenges for long distance remain. Here we make a significant step forward by entangling two atomic ensembles in one lab via photon transmission through metropolitan-scale fibers. We use cavity enhancement to create bright atom-photon entanglement, and harness quantum frequency conversion to shift the atomic wavelength to telecom. We realize entanglement over 22 km field-deployed fibers via two-photon interference, and entanglement over 50 km coiled fibers via single-photon interference. Our experiment can be extended to physically separated nodes with similar distance as a functional segment for atomic quantum networks, thus paving the way towards establishing atomic entanglement over many nodes and over much longer distance.

Entanglement between a single photon and a matter qubit is an indispensable resource for quantum repeater and quantum networks. With atomic ensembles, the entanglement creation probability is typically very low to inhibit high-order events. In this paper, we propose and experimentally realize a scheme which creates atom-photon entanglement with an intrinsic efficiency of 50%. We make use of Rydberg blockade to generate two collective excitations, lying in separate internal states. By introducing the momentum degree of freedom for the excitations, and interfering them via Raman coupling, we entangle the two excitations. Via retrieving one excitation, we create the entanglement between the polarization of a single photon and the momentum of the remaining atomic excitation, with a measured fidelity of 0.901(8). The retrieved optical field is verified to be genuine single photons. The realized entanglement may be employed to create entanglement between two distant nodes in a fully heralded way and with a much higher efficiency., Comment: 8 pages, 7 figures

Quantum network has significant applications both practically and fundamentally. A hybrid architecture with photons and stationary nodes is highly promising. So far, experimental realizations are limited to two nodes with two photons. Going beyond state of the art by entangling many photons with many quantum nodes is highly appreciated. Here, we report an experiment realizing hybrid entanglement between three photons and three atomic-ensemble quantum memories. We make use of three similar setups, in each of which one pair of photon-memory entanglement with high overall efficiency is created via cavity enhancement. Through three-photon interference, the three quantum memories get entangled with the three photons. Via measuring the photons and applying feedforward, we heraldedly entangle the three memories. Our work demonstrates the largest size of hybrid memory-photon entanglement, which may be employed as a build block to construct larger and complex quantum network., Comment: 8 pages, 6 figures

Interference of multiple photons via a linear-optical network has profound applications for quantum foundation, quantum metrology and quantum computation. Particularly, a boson sampling experiment with a moderate number of photons becomes intractable even for the most powerful classical computers, and will lead to "quantum supremacy". Scaling up from small-scale experiments requires highly indistinguishable single photons, which may be prohibited for many physical systems. Here we experimentally demonstrate a time-resolved version of boson sampling by using photons not overlapping in their frequency spectra from three atomic-ensemble quantum memories. Time-resolved measurement enables us to observe nonclassical multiphoton correlation landscapes. An average fidelity over several interferometer configurations is measured to be 0.936(13), which is mainly limited by high-order events. Symmetries in the landscapes are identified to reflect symmetries of the optical network. Our work thus provides a route towards quantum supremacy with distinguishable photons., Comment: 5 pages, 3 figures, 1 table