Precision measurements of Schiff moments in heavy, deformed nuclei are sensitive probes of beyond standard model $T$, $P$ violation in the hadronic sector. While the most stringent limits on Schiff moments to date are set with diamagnetic atoms, polar polyatomic molecules can offer higher sensitivities with unique experimental advantages. In particular, symmetric top molecular ions possess $K$ doublets of opposite parity with especially small splittings, leading to full polarization at low fields, internal comagnetometer states useful for rejection of systematic effects, and the ability to perform sensitive searches for $T$, $P$ violation using a small number of trapped ions containing heavy exotic nuclei. We consider the symmetric top cation ${}^{225}\mathrm{Ra}{\mathrm{OCH}}_3^{+}$ as a prototypical and candidate platform for performing sensitive nuclear Schiff measurements and characterize in detail its internal structure using relativistic ab initio methods. The combination of enhancements from a deformed nucleus, large polarizability, and unique molecular structure make this molecule a promising platform to search for fundamental symmetry violation even with a single trapped ion.

Solid-state quantum dots are promising candidates for efficient light-matter interfaces connecting internal spin degrees of freedom to the states of emitted photons. However, selection rules prevent the combination of efficient spin control and optical cyclicity in this platform. By utilizing a photonic crystal waveguide we here experimentally demonstrate optical cyclicity up to $\approx 15$ through photonic state engineering while achieving high fidelity spin initialization and coherent optical spin control. These capabilities pave the way towards scalable multiphoton entanglement generation and on-chip spin-photon gates.

Quantum photon sources of high rate, brightness, and purity are increasingly desirable as quantum information systems are quickly scaled up and applied to many fields. Using a periodically poled lithium niobate microresonator on chip, we demonstrate photon-pair generation at high rates of 8.5 and 36.3 MHz using only 3.4 and $13.4\mu \mathrm{W}$ pump power, respectively, marking orders of magnitude improvement over the state of the art, across all material platforms. These results constitute the first direct measurement of the device’s giant single photon nonlinearity. The measured coincidence to accidental ratio is well above 100 at those high rates and reaches $14682\pm 4427$ at a lower pump power. The same chip enables heralded single-photon generation at tens of megahertz rates, each with low autocorrelation $g_H^{(2)}(0)=0.008$ and 0.097 for the microwatt pumps, which marks a new milestone. Such distinct performance, facilitated by the chip device’s noiseless and giant optical nonlinearity, will contribute to the forthcoming pervasive adoption of quantum optical information technologies.

Laser decoherence limits the stability of optical clocks by broadening the observable resonance linewidths and adding noise during the dead time between clock probes. Correlation spectroscopy avoids these limitations by measuring correlated atomic transitions between two ensembles, which provides a frequency difference measurement independent of laser noise. Here, we apply this technique to perform stability measurements between two independent clocks based on the ${{}^{1}S}_0\leftrightarrow {{}^{3}P}_0$ transition in ${}^{27}{\mathrm{Al}}^{+}$. By stabilizing the dominant sources of differential phase noise between the two clocks, we observe coherence between them during synchronous Ramsey interrogations as long as 8 s at a frequency of $1.12\times {10}^{15}\mathrm{Hz}$. The observed contrast in the correlation spectroscopy signal is consistent with the 20.6 s ${}^3{P}_0$ state lifetime and represents a measurement instability of $(1.8\pm 0.5)\times {10}^{-16}/\sqrt{\tau /\mathrm{s}}$ for averaging periods longer than the probe duration when dead time is negligible.

The neutral charge state plays an important role in quantum information and sensing applications based on nitrogen-vacancy centers. However, the orbital and spin dynamics remain unexplored. Here, we use resonant excitation of single centers to directly reveal the fine structure, enabling selective addressing of spin-orbit states. Through pump-probe experiments, we find the orbital relaxation time (430 ns at 4.7 K) and measure its temperature dependence up to 11.8 K. Finally, we reveal the spin relaxation time (1.5 s) and realize projective high-fidelity single-shot readout of the spin state ($\ge 98\%$).

We report the single-cycle optical control of a freely propagating electron beam with an isolated cycle of midinfrared light. In particular, we produce and characterize a modulated electron current with peak-cycle-specific subfemtosecond structure in time. The direct effects of the carrier-envelope phase, amplitude, and dispersion of the optical waveform on the temporal composition, pulse durations, and chirp of the free-space electron wave function demonstrate the subcycle nature of our control. These results and concept may create novel opportunities in free-electron lasers, laser-driven particle accelerators, ultrafast electron microscopy, and wherever else high-energy electrons are needed with the temporal structure of single-cycle light.

We report on a multiparticle coincidence experiment performed at the European X-ray Free-Electron Laser at the Small Quantum Systems instrument using a COLTRIMS reaction microscope. By measuring two ions and two electrons in coincidence, we investigate double core-hole generation in ${\mathrm{O}}_2$ molecules in the gas phase. Single-site and two-site double core holes have been identified and their molecular-frame electron angular distributions have been obtained for a breakup of the oxygen molecule into two doubly charged ions. The measured distributions are compared to results of calculations performed within the frozen- and relaxed-core Hartree-Fock approximations.

Intensity squeezing—i.e., photon number fluctuations below the shot-noise limit—is a fundamental aspect of quantum optics and has wide applications in quantum metrology. It was predicted in 1979 that intensity squeezing could be observed in resonance fluorescence from a two-level quantum system. However, its experimental observation in solid states was hindered by inefficiencies in generating, collecting, and detecting resonance fluorescence. Here, we report the intensity squeezing in a single-mode fiber-coupled resonance fluorescence single-photon source based on a quantum dot–micropillar system. We detect pulsed single-photon streams with 22.6% system efficiency, which show sub-shot-noise intensity fluctuation with an intensity squeezing of 0.59 dB. We estimate a corrected squeezing of 3.29 dB at the first lens. The observed intensity squeezing provides the last piece of the fundamental picture of resonance fluorescence, which can be used as a new standard for optical radiation and in scalable quantum metrology with indistinguishable single photons.

Unconventional Weyl points (WPs), carrying topological charge 2 or higher, possess interesting properties different from ordinary charge-1 WPs, including multiple Fermi arcs that stretch over a large portion of the Brillouin zone. Thus far, such WPs have been observed in chiral materials and acoustic metamaterials, but there has been no clean demonstration in photonics in which the unconventional photonic WPs are separated from trivial bands. We experimentally realize an ideal symmetry-protected photonic charge-2 WP in a three-dimensional topological chiral microwave metamaterial. We use field mapping to directly observe the projected bulk dispersion, as well as the two long surface arcs that form a noncontractible loop wrapping around the surface Brillouin zone. The surface states span a record-wide frequency window of around 22.7% relative bandwidth. We demonstrate that the surface states exhibit a novel topological self-collimation property and are robust against disorder. This work provides an ideal photonic platform for exploring fundamental physics and applications of unconventional WPs.

Recent studies have revealed the counterintuitive possibility that increasing disorder can turn a topologically trivial insulator into a nontrivial insulator, called a topological Anderson insulator (TAI). Here, we propose and experimentally demonstrate a photonic TAI in a two-dimensional disordered gyromagnetic photonic crystal in the microwave regime. We directly observe the disorder-induced topological phase transition from a trivial insulator to a TAI with robust chiral edge states. We also demonstrate topological heterostructures that host edge states at interfaces between domains with different disorder parameters.

We measure isotope shifts for five ${\mathrm{Yb}}^{+}$ isotopes with zero nuclear spin on two narrow optical quadrupole transitions ${{}^{2}S}_{1/2}\to {{}^{2}D}_{3/2}$, ${{}^{2}S}_{1/2}\to {{}^{2}D}_{5/2}$ with an accuracy of $\sim 300\mathrm{Hz}$. The corresponding King plot shows a $3\times {10}^{-7}$ deviation from linearity at the $3\sigma$ uncertainty level. Such a nonlinearity can indicate physics beyond the Standard Model (SM) in the form of a new bosonic force carrier, or arise from higher-order nuclear effects within the SM. We identify the quadratic field shift as a possible nuclear contributor to the nonlinearity at the observed scale, and show how the nonlinearity pattern can be used in future, more accurate measurements to separate a new-boson signal from nuclear effects.

We perform high-resolution spectroscopy of the $3d{{}^2\mathrm{D}}_{3/2}-3d{{}^2\mathrm{D}}_{5/2}$ interval in all stable even isotopes of ${{}^A\mathrm{Ca}}^{+}$ ($A=40$, 42, 44, 46, and 48) with an accuracy of $\sim 20\mathrm{Hz}$ using direct frequency-comb Raman spectroscopy. Combining these data with isotope shift measurements of the $4s{{}^2\mathrm{S}}_{1/2}\leftrightarrow 3d{{}^2\mathrm{D}}_{5/2}$ transition, we carry out a King plot analysis with unprecedented sensitivity to coupling between electrons and neutrons by bosons beyond the standard model. Furthermore, we estimate the sensitivity to such bosons from equivalent spectroscopy in ${\mathrm{Ba}}^{+}$ and ${\mathrm{Yb}}^{+}$. Finally, the data yield isotope shifts of the $4s{{}^2\mathrm{S}}_{1/2}\leftrightarrow 3d{{}^2\mathrm{D}}_{3/2}$ transition at 10 parts per billion through combination with recent data of Knollmann, Patel, and Doret [Phys. Rev. A 100, 022514 (2019)].

Extinction of light by material particles stems from losses incurred by absorption or scattering. The extinction cross section is usually treated as an additive quantity, leading to the exponential laws that govern the macroscopic attenuation of light. In this Letter, we demonstrate that the extinction cross section of a large gold nanoparticle can be substantially reduced—i.e., the particle becomes more transparent—if a single molecule is placed in its near field. This partial cloaking effect results from a coherent plasmonic interaction between the molecule and the nanoparticle, whereby each of them acts as a nanoantenna to modify the radiative properties of the other.

We report a new measurement of the positronium (Ps) $2{{}^{3}S}_1\to 2{{}^{3}P}_0$ interval. Slow Ps atoms, optically excited to the radiatively metastable $2{{}^{3}S}_1$ level, flew through a microwave radiation field tuned to drive the transition to the short-lived $2{{}^{3}P}_0$ level, which was detected via the time spectrum of subsequent ground state Ps annihilation radiation. After accounting for Zeeman shifts we obtain a transition frequency ${\nu }_0=18501.02\pm 0.61\mathrm{MHz}$, which is not in agreement with the theoretical value of ${\nu }_0=18498.25\pm 0.08\mathrm{MHz}$.

Free-electron lasers provide a source of x-ray pulses short enough and intense enough to drive nonlinearities in molecular systems. Impulsive interactions driven by these x-ray pulses provide a way to create and probe valence electron motions with high temporal and spatial resolution. Observing these electronic motions is crucial to understand the role of electronic coherence in chemical processes. A simple nonlinear technique for probing electronic motion, impulsive stimulated x-ray Raman scattering (ISXRS), involves a single impulsive interaction to produce a coherent superposition of electronic states. We demonstrate electronic population transfer via ISXRS using broad bandwidth (5.5 eV full width at half maximum) attosecond x-ray pulses produced by the Linac Coherent Light Source. The impulsive excitation is resonantly enhanced by the oxygen $1s\to 2{\pi }^{*}$ resonance of nitric oxide (NO), and excited state neutral molecules are probed with a time-delayed UV laser pulse.

We propose novel quantum antennas and metamaterials with a strong magnetic response at optical frequencies. Our design is based on the arrangement of natural quantum emitters with only electric dipole transition moments at distances smaller than a wavelength of light but much larger than their physical size. In particular, we show that an atomic dimer can serve as a magnetic antenna at its antisymmetric mode to enhance the decay rate of a magnetic transition in its vicinity by several orders of magnitude. Furthermore, we study metasurfaces composed of atomic bilayers with and without cavities and show that they can fully reflect the electric and magnetic fields of light, thus, forming nearly perfect electric or magnetic mirrors. The proposed metamaterials will embody the intrinsic quantum functionalities of natural emitters such as atoms, ions, color center, or molecules and can be fabricated with available state-of-the-art technologies, promising several applications both in classical optics and quantum engineering.

We demonstrate microwave dressing on ultracold, fermionic ${}^{23}\mathrm{Na}{}^{40}\mathrm{K}$ ground-state molecules and observe resonant dipolar collisions with cross sections exceeding 3 times the $s$-wave unitarity limit. The origin of these interactions is the resonant alignment of the approaching molecules’ dipoles along the intermolecular axis, which leads to strong attraction. We explain our observations with a conceptually simple two-state picture based on the Condon approximation. Furthermore, we perform coupled-channel calculations that agree well with the experimentally observed collision rates. The resonant microwave-induced collisions found here enable controlled, strong interactions between molecules, of immediate use for experiments in optical lattices.

A fine manipulation of population transfer among molecular quantum levels is a key technology for control of molecular processes. When a light field intensity is increased to the TW-PW ${\mathrm{cm}}^{-2}$ level, it becomes possible to transfer a population to specific excited levels through nonlinear light-molecule interaction, but it has been a challenge to control the extent of the population transfer. We deplete the population in the ${\mathrm{X}}^2{\mathrm{\Sigma }}_g^{+}(v=0)$ state of ${\mathrm{N}}_2^{+}$ almost completely by focusing a dual-color (800 nm and $1.6\mu \mathrm{m}$) intense femtosecond laser pulse in a nitrogen gas, and make the intensity of ${\mathrm{N}}_2^{+}$ lasing at 391 nm enhanced by 5–6 orders of magnitude. By solving a time-dependent Schrödinger equation describing the population transfer among the three lowest electronic states of ${\mathrm{N}}_2^{+}$, we reveal that the ${\mathrm{X}}^2{\mathrm{\Sigma }}_g^{+}(v=0)$ population is depleted by the vibrational Raman excitation followed by the electronic excitation ${\mathrm{A}}^2{\mathrm{\Pi }}_u(v=2,3,4)\leftarrow {\mathrm{X}}^2{\mathrm{\Sigma }}_g^{+}(v=1)\leftarrow {\mathrm{X}}^2{\mathrm{\Sigma }}_g^{+}(v=0)$, resulting in the excessive population inversion between the ${\mathrm{B}}^2{\mathrm{\Sigma }}_u^{+}(v=0)$ and ${\mathrm{X}}^2{\mathrm{\Sigma }}_g^{+}(v=0)$ states. Our results offer a promising route to efficient population transfer among vibrational and electronic levels of molecules by a precisely designed intense laser field.

A quantity known as the contact is a fundamental thermodynamic property of quantum many-body systems with short-range interactions. Determination of the temperature dependence of the contact for the unitary Fermi gas of infinite scattering length has been a major challenge, with different calculations yielding qualitatively different results. Here we use finite-temperature auxiliary-field quantum Monte Carlo (AFMC) methods on the lattice within the canonical ensemble to calculate the temperature dependence of the contact for the homogeneous spin-balanced unitary Fermi gas. We extrapolate to the continuum limit for 40, 66, and 114 particles, eliminating systematic errors due to finite-range effects. We observe a dramatic decrease in the contact as the superfluid critical temperature is approached from below, followed by a gradual weak decrease as the temperature increases in the normal phase. Our theoretical results are in excellent agreement with the most recent precision ultracold atomic gas experiments. We also present results for the energy as a function of temperature in the continuum limit.

We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between ${}^2\mathrm{\Sigma }$ CaF molecules in the absolute ground state $|X,v=0,N=0,F=0⟩$, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of $1.4(8)\times {10}^{-10}{\mathrm{cm}}^3/\mathrm{s}$, which is below, but close to, the predicted universal loss rate.