Long-distance quantum communication and networking require quantum memory nodes with efficient optical interfaces and long memory times. We report the realization of an integrated two-qubit network node based on silicon-vacancy centers (SiVs) in diamond nanophotonic cavities. Our qubit register consists of the SiV electron spin acting as a communication qubit and the strongly coupled silicon-29 nuclear spin acting as a memory qubit with a quantum memory time exceeding 2 seconds. By using a highly strained SiV, we realize electron-photon entangling gates at temperatures up to 1.5 kelvin and nucleus-photon entangling gates up to 4.3 kelvin. We also demonstrate efficient error detection in nuclear spin–photon gates by using the electron spin as a flag qubit, making this platform a promising candidate for scalable quantum repeaters.

We study the collapse of an attractive atomic Bose-Einstein condensate prepared in the uniform potential of an optical-box trap. We characterize the critical point for collapse and the collapse dynamics, observing universal behavior in agreement with theoretical expectations. Most importantly, we observe a clear experimental signature of the counterintuitive weak collapse, namely, that making the system more unstable can result in a smaller particle loss. We experimentally determine the scaling laws that govern the weak-collapse atom loss, providing a benchmark for the general theories of nonlinear wave phenomena.

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An efficient, scalable source of shaped single photons that can be directly integrated with optical fiber networks and quantum memories is at the heart of many protocols in quantum information science. We demonstrate a deterministic source of arbitrarily temporally shaped single-photon pulses with high efficiency [detection efficiency ¼ 14.9%] and purity [g ð2Þ ð0Þ ¼ 0.0168] and streams of up to 11 consecutively detected single photons using a silicon-vacancy center in a highly directional fiberintegrated diamond nanophotonic cavity. Combined with previously demonstrated spin-photon entangling gates, this system enables on-demand generation of streams of correlated photons such as cluster states and could be used as a resource for robust transmission and processing of quantum information.

Millimeter-wave superconducting devices offer a platform for quantum experiments at temperatures above 1 K, and new avenues for studying light-matter interactions in the strong coupling regime. Using the intrinsic nonlinearity associated with kinetic inductance of thin film materials, we realize four-wave mixing at millimeter-wave frequencies, demonstrating a key component for superconducting quantum systems. We report on the performance of niobium nitride resonators around 100 GHz, patterned on thin (20-50 nm) films grown by atomic layer deposition, with sheet inductances up to 212 pH/ and critical temperatures up to 13.9 K. For films thicker than 20 nm, we measure quality factors from 1-6×10 4 , likely limited by two-level systems. Finally we measure degenerate parametric conversion for a 95 GHz device with a forward efficiency up to +16 dB, paving the way for the development of nonlinear quantum devices at millimeter-wave frequencies.For superconducting quantum circuits, the millimeterwave spectrum presents a fascinating frequency regime between microwaves and optics, giving access to a wider range of energy scales, and lower sensitivity to thermal background noise due to higher photon energies. Many advances have been made refining microwave quantum devices [1,2], typically relying on ultra-low temperatures in the millikelvin range to reduce sources of noise and quantum decoherence. Using millimeter-wave photons as building blocks for superconducting quantum devices offers transformative opportunities by allowing quantum experiments to be run at liquid Helium-4 temperatures, allowing higher device power dissipation and enabling large scale direct integration with semiconductor devices [2]. Millimeter-wave quantum devices could also provide new routes for studying strong-coupling light-matter interactions in this frequency regime [3][4][5][6][7], and present new opportunities for quantum-limited frequency conversion and detection [8,9].Recent interest in next-generation communication devices [10, 11] has led to important advances in sensitive millimeter-wave measurement technology around 100 GHz. Realizing quantum systems at these frequencies however requires both the demonstration of lowloss components -device materials with low absorption rates [12][13][14] and resonators with long photon lifetimes [15-20] -and most importantly, elements providing nonlinear interactions, which for circuit quantum optics can be realized with four-wave mixing Kerr terms in the Hamiltonian. One approach commonly used at microwave frequencies relies on aluminum Josephson junctions [2], which yield necessary four-wave mixing at low powers. However to avoid breaking Cooper pairs with high-frequency photons, devices at millimeter-wave frequencies are limited to materials with higher superconducting critical temperatures (T c ). Higher T c junctions have been implemented as high-frequency mixers for millimeter-wave detection [9,21,22], and ongoing efforts are improving losses for quantum applications [23,24].Kinetic inductance (KI)...