The precise synchronization of distant clocks is a fundamental requirement for a wide range of applications. Here, we experimentally demonstrate an approach of quantum clock synchronization by distributing entangled and correlated photon pairs from a telecom-wavelength quantum dot over a metropolitan fiber network in the Stockholm area. By leveraging the tight time correlation between the emitted photons, we achieve a synchronization accuracy of tens of picoseconds. We show that our synchronization scheme is secure against spoofing attacks by performing a remote quantum state tomography to verify the origin of the entangled photons. We measured a distributed maximum entanglement fidelity of 0.817 +/- 0.040 to the |Phi+> Bell state and a concurrence of 0.660 +/- 0.086. These results highlight the potential of quantum dot-generated entangled pairs as a shared resource for secure time synchronization and quantum key distribution in real-world quantum networks. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Anderson localization (AL)—a fundamental wave phenomenon resulting from coherent interference in disordered potentials-has attracted substantial attention in quantum optics and ultracold atomic physics due to its universal nature and controllable experimental realizations. In this review, we survey recent advances in the study of localization physics, focusing primarily on AL, quasi-periodic modulation, and the emergence of mobility edges in optical and atomic systems. After briefly introducing the theoretical origins and historical context, we discuss the theoretical frameworks underlying localization phenomena, highlighting key models such as the Anderson tight-binding model and the Aubry–André quasiperiodic lattice. The core emphasis of this review lies in experimental developments: we comprehensively describe how ultracold atomic gases and optical platforms—including disordered waveguides and fiber loop systems—have enabled precise observation and characterization of localization transitions and mobility edges. Experimental methodologies, diagnostics, and challenges unique to each system are thoroughly addressed. Finally, we conclude by outlining promising future directions, such as many-body localization, non-Hermitian Anderson physics, and synthetic-dimension systems, emphasizing how the interplay between theory and experimental innovation continues to drive the field forward.

We explore the zero-phonon line of single photon emitters in helium-ion treated monolayer MoS2, which are currently understood in terms of single sulfur-site vacancies. By comparing the linewidths of the zero-phonon line as extracted directly from optical spectra with values inferred from the first-order autocorrelation function of the photoluminescence, we quantify bounds of the homogeneous broadening and of phonon-assisted contributions. The results are discussed in terms of both the independent boson model and ab-initio results as computed from GW and Bethe–Salpeter equation approximations.

Due to stringent thermal budgets in cryogenic technologies such as superconducting quantum computers and sensors, electronic building blocks that simultaneously offer low energy consumption, fast switching, low error rates, a small footprint, and simple fabrication are pivotal for large-scale devices. Here, we demonstrate a superconducting switch with attojoule switching energy, high speed (pico-second rise/fall times), and high integration density (on the order of 10^-2 μm² per switch). It consists of a superconducting nanochannel and a metal heater separated by an insulating silica layer. We experimentally demonstrate digital gate operations utilizing these nanostructures, such as NOT, NAND, NOR, AND, and OR gates, with a few femtojoules of energy consumption and ultralow bit error rates <10^-8. In addition, we build energy-efficient volatile memory elements with nanosecond operation speeds and a retention time over 10⁵ s. These superconducting switches open new possibilities for increasing the size and complexity of modern cryogenic technologies.

Color centers in silicon are leading qubits for scalable quantum information processing. We will discuss recent developments towards a technological platform including the formation of waveguide-integrated color centers, their spectral control, and on-chip single-photon detection.

Color centers in silicon are leading qubits for scalable quantum information processing. We will discuss recent developments towards a technological platform including the formation of waveguide-integrated color centers, their spectral control, and on-chip single-photon detection.

Superconducting nanowire single-photon detectors (SNSPDs), owing to their unique performance, are currently the standard detector in most demanding single-photon experiments. One important metric for any single-photon detector is the recovery time, which defines the minimum temporal separation between consecutive detection events. In SNSPDs, the recovery time is more subtle, as the detection efficiency does not abruptly drop to zero when the temporal separation between detection events gets smaller, instead, it increases gradually as the SNSPD current recovers. SNSPD's recovery time is dominated by its kinetic inductance, the readout impedance, and the degree of saturation of internal efficiency. Decreasing the kinetic inductance or increasing the readout impedance can accelerate the recovery process. Significant reduction of the SNSPD recovery time, by, for example, adding a series resistor in the readout circuitry, is possible but can lead to detector latching, which hinders further detector operation or enforces underbiasing and hence a reduction in detection efficiency. Previous research has demonstrated passive resistive networks for the reduction of recovery time that rely on trial and error to find the appropriate resistance values. Here, we show that, using a cryogenically compatible and tunable resistor technology, one can find the optimized impedance values, delivering fast SNSPD recovery time while maintaining maximum internal detection efficiency. Here, we show an increase of around twofold in both maximum achievable detection rates and the achievable detection efficiency at high photon fluxes, demonstrating detection rates close to 114 Mcps with no loss of internal detection efficiency.