We describe the first precision measurement of the electron’s electric dipole moment ($d_e$) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on ${}^{180}\mathrm{Hf}{}^{19}{\mathrm{F}}^{+}$ in its metastable ${{}^3\mathrm{\Delta }}_1$ electronic state, we obtain $d_e=(0.9\pm 7.7_{\mathrm{stat}}\pm 1.7_{\mathrm{syst}})\times {10}^{-29}e\mathrm{cm}$, resulting in an upper bound of $|d_e|<1.3\times {10}^{-28}e\mathrm{cm}$ (90% confidence). Our result provides independent confirmation of the current upper bound of $|d_e|<9.4\times {10}^{-29}e\mathrm{cm}$ [J. Baron et al., New J. Phys. 19, 073029 (2017)], and offers the potential to improve on this limit in the near future.

We create fermionic dipolar ${}^{23}\mathrm{Na}{}^6\mathrm{Li}$ molecules in their triplet ground state from an ultracold mixture of ${}^{23}\mathrm{Na}$ and ${}^6\mathrm{Li}$. Using magnetoassociation across a narrow Feshbach resonance followed by a two-photon stimulated Raman adiabatic passage to the triplet ground state, we produce $3\times 10^4$ ground state molecules in a spin-polarized state. We observe a lifetime of 4.6 s in an isolated molecular sample, approaching the $p$-wave universal rate limit. Electron spin resonance spectroscopy of the triplet state was used to determine the hyperfine structure of this previously unobserved molecular state.

The impact of a highly charged ion onto a solid gives rise to charge exchange between the ion and target atoms, so that a slow ion gets neutralized in the vicinity of the surface. Using highly charged Ar and Xe ions and the surface-only material graphene as a target, we show that the neutralization and deexcitation of the ions proceeds on a sub-10 fs time scale. We further demonstrate that a multiple Interatomic Coulombic Decay (ICD) model can describe the observed ultrafast deexcitation. Other deexcitation mechanisms involving nonradiative decay and quasimolecular orbital formation during the impact are not important, as follows from the comparison of our experimental data with the results of first-principles calculations. Our method also enables the estimation of ICD rates directly.

We demonstrate significantly improved magneto-optical trapping of molecules using a very slow cryogenic beam source and either rf modulated or dc magnetic fields. The rf magneto-optical trap (MOT) confines $1.0(3)\times {10}^5$ CaF molecules at a density of $7(3)\times {10}^6{\mathrm{cm}}^{-3}$, which is an order of magnitude greater than previous molecular MOTs. Near Doppler-limited temperatures of $340(20)\mu \mathrm{K}$ are attained. The achieved density enables future work to directly load optical tweezers and create optical arrays for quantum simulation.

We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of ${\mathrm{OH}}^{-}$ ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of $13.4\pm 0.2\mathrm{K}$ with $94.9\pm 0.3\%$ of the ions in the rotational ground state. This is consistent with the storage ring temperature of $13.5\pm 0.5\mathrm{K}$ as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an ${\mathrm{OH}}^{-}$ beam where $99.1\pm 0.1\%$ of approximately one million stored ions are in the $J=0$ rotational ground state. We measure the intrinsic lifetime of the $J=1$ rotational level to be $145\pm 28\mathrm{s}$.

The direct photodissociation of ${\mathrm{D}}_2$ at excitation energies above 14.76 eV occurs via two channels, $\mathrm{D}(2s)+\mathrm{D}(1s)$ and $\mathrm{D}(2p)+\mathrm{D}(1s)$. The branching ratios between the two have been measured from the dissociation threshold to $3200{\mathrm{cm}}^{-1}$ above it, and it is found that they show cosine oscillations as a function of the fragment wave vector magnitudes. The oscillation is due to an interference effect and can be simulated using the phase difference between the wave functions of the two channels, analogous to Young’s double-slit experiment. By fitting the measured branching ratios, we have determined the depths and widths of the effective spherical potential wells related to the two channels, which are in agreement with the effective depths and widths of the ab initio interaction potentials. The results of this Letter illustrate the importance of the relative phase between the fragments in controlling the branching ratios of the photodissociation channels.

We report on the local control of the transition frequency of a spin $1/2$ encoded in two Rydberg levels of an individual atom by applying a state-selective light shift using an addressing beam. With this tool, we first study the spectrum of an elementary system of two spins, tuning it from a nonresonant to a resonant regime, where “bright” (super-radiant) and “dark” (subradiant) states emerge. We observe the collective enhancement of the microwave coupling to the bright state. We then show that after preparing an initial single spin excitation and letting it hop due to the spin-exchange interaction, we can freeze the dynamics at will with the addressing laser, while preserving the coherence of the system. In the context of quantum simulation, this scheme opens exciting prospects for engineering inhomogeneous $XY$ spin Hamiltonians or preparing spin-imbalanced initial states.

We demonstrate a new technique for detecting the amplitude of arbitrarily chosen components of radio-frequency waveforms based on stroboscopic backaction evading measurements. We combine quantum nondemolition measurements and stroboscopic probing to detect waveform components with magnetic sensitivity beyond the standard quantum limit. Using an ensemble of $1.5\times 10^6$ cold rubidium atoms, we demonstrate entanglement-enhanced sensing of sinusoidal and linearly chirped waveforms, with 1.0(2) and 0.8(3) dB metrologically relevant noise reduction, respectively. We achieve volume-adjusted sensitivity of $\delta B\sqrt{V}\approx 3.96\mathrm{fT}\sqrt{{\mathrm{cm}}^3/\mathrm{Hz}}$, comparable to the best rf magnetometers.

We report attosecond-scale probing of the laser-induced dynamics in molecules. We apply the method of high-harmonic spectroscopy, where laser-driven recolliding electrons on various trajectories record the motion of their parent ion. Based on the transient phase-matching mechanism of high-order harmonic generation, short and long trajectories contributing to the same harmonic order are distinguishable in both the spatial and frequency domains, giving rise to a one-to-one map between time and photon energy for each trajectory. The short and long trajectories in ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ are used simultaneously to retrieve the nuclear dynamics on the attosecond and ångström scale. Compared to using only short trajectories, this extends the temporal range of the measurement to one optical cycle. The experiment is also applied to methane and ammonia molecules.

We report on the precise measurement of the atomic mass of a single proton with a purpose-built Penning-trap system. With a precision of 32 parts per trillion our result not only improves on the current CODATA literature value by a factor of 3, but also disagrees with it at a level of about 3 standard deviations.

Photodetachment thermometry on a beam of ${\mathrm{OH}}^{-}$ in a cryogenic storage ring cooled to below 10 K is carried out using two-dimensional frequency- and time-dependent photodetachment spectroscopy over 20 min of ion storage. In equilibrium with the low-level blackbody field, we find an effective radiative temperature near 15 K with about 90% of all ions in the rotational ground state. We measure the $J=1$ natural lifetime (about 193 s) and determine the ${\mathrm{OH}}^{-}$ rotational transition dipole moment with 1.5% uncertainty. We also measure rotationally dependent relative near-threshold photodetachment cross sections for photodetachment thermometry.

We demonstrate that two-dimensional atomic emitter arrays with subwavelength spacing constitute topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with nontrivial Chern numbers and topologically protected, long-lived edge states. Due to the inherent nonlinearity of constituent emitters, such systems provide a platform for exploring quantum optical analogs of interacting topological systems.

We report on the experimental investigation of individual Cs atoms impinging on a dilute cloud of ultracold Rb atoms with variable density. We study the relaxation of the initial nonthermal state and detect the effect of single collisions which has so far eluded observation. We show that, after few collisions, the measured spatial distribution of the tracer atoms is correctly described by a Langevin equation with a velocity-dependent friction coefficient, over a large range of Knudsen numbers. Our results extend the simple and effective Langevin treatment to the realm of light particles in dilute gases. The experimental technique developed opens up the microscopic exploration of a novel regime of diffusion at the level of individual collisions.

We present a technique to measure the amplitude of a center-of-mass (c.m.) motion of a two-dimensional ion crystal of $\sim 100$ ions. By sensing motion at frequencies far from the c.m. resonance frequency, we experimentally determine the technique’s measurement imprecision. We resolve amplitudes as small as 50 pm, 40 times smaller than the c.m. mode zero-point fluctuations. The technique employs a spin-dependent, optical-dipole force to couple the mechanical oscillation to the electron spins of the trapped ions, enabling a measurement of one quadrature of the c.m. motion through a readout of the spin state. We demonstrate sensitivity limits set by spin projection noise and spin decoherence due to off-resonant light scattering. When performed on resonance with the c.m. mode frequency, the technique demonstrated here can enable the detection of extremely weak forces ($<1\mathrm{yN}$) and electric fields ($<1\mathrm{nV}/\mathrm{m}$), providing an opportunity to probe quantum sensing limits and search for physics beyond the standard model.

In this Letter we realize a narrow spectroscopic feature using a technique that we refer to as magnetically induced optical transparency. A cold ensemble of ${}^{88}\mathrm{Sr}$ atoms interacts with a single mode of a high-finesse optical cavity via the 7.5 kHz linewidth, spin forbidden ${}^1{S}_0$ to ${}^3{P}_1$ transition. By applying a magnetic field that shifts two excited state Zeeman levels, we open a transmission window through the cavity where the collective vacuum Rabi splitting due to a single level would create destructive interference for probe transmission. The spectroscopic feature approaches the atomic transition linewidth, which is much narrower than the cavity linewidth, and is highly immune to the reference cavity length fluctuations that limit current state-of-the-art laser frequency stability.

Strong laser-induced magnetization of oxygen gas at room temperature and atmospheric pressure is achieved experimentally on the subnanosecond time scale. The method is based on controlling the electronic spin of paramagnetic molecules by means of manipulating their rotation with an optical centrifuge. Spin-rotational coupling results in a high degree of spin polarization on the order of one Bohr magneton per centrifuged molecule. Owing to the nonresonant interaction with the laser pulses, the demonstrated technique is applicable to a broad class of paramagnetic rotors. Executed in a high-density gas, it may offer an efficient way of generating macroscopic magnetic fields remotely (as shown in this work) and producing a large amount of spin-polarized electrons.

We report simultaneous conjugate Ramsey-Bordé interferometers with a sample of low-mass (lithium-7) atoms at 50 times the recoil temperature. We optically pump the atoms to a magnetically insensitive state using the $2S_{1/2}-2P_{1/2}$ line. Fast stimulated Raman beam splitters address a broad velocity class and unavoidably drive two conjugate interferometers that overlap spatially. We show that detecting the summed interference signals of both interferometers, using state labeling, allows recoil measurements and suppression of phase noise from vibrations. The use of “warm” atoms allows for simple, efficient, and high-flux atom sources and broadens the applicability of recoil-sensitive interferometry to particles that remain difficult to trap and cool.

We demonstrate a quantum nanophotonics platform based on germanium-vacancy (GeV) color centers in fiber-coupled diamond nanophotonic waveguides. We show that GeV optical transitions have a high quantum efficiency and are nearly lifetime broadened in such nanophotonic structures. These properties yield an efficient interface between waveguide photons and a single GeV center without the use of a cavity or slow-light waveguide. As a result, a single GeV center reduces waveguide transmission by $18\pm 1\%$ on resonance in a single pass. We use a nanophotonic interferometer to perform homodyne detection of GeV resonance fluorescence. By probing the photon statistics of the output field, we demonstrate that the GeV–waveguide system is nonlinear at the single-photon level.

Organic microcavities are photonic nanostructures that strongly confine the electromagnetic field, allowing exotic quantum regimes of light-matter interaction with disordered organic semiconductors. The unambiguous interpretation of the spectra of organic microcavities has been a long-standing challenge due to several competing effects involving electrons, vibrations, and cavity photons. Here we present a theoretical framework that is able to describe the main spectroscopic features of organic microcavities consistently. We introduce a class of light-matter excitations called dark vibronic polaritons, which strongly emit but only weakly absorb light in the same frequency region of the bare electronic transition. A successful comparison with experimental data demonstrates the applicability of our theory. The proposed microscopic understanding of organic microcavities paves the way for the development of optoelectronic devices enhanced by quantum optics.

We propose a photonic crystal nanocavity design with self-similar electromagnetic boundary conditions, achieving ultrasmall mode volume ($V_{\text{eff}}$). The electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions. We illustrate the design concept with a silicon-air one-dimensional photon crystal cavity that reaches an ultrasmall mode volume of $V_{\text{eff}}\sim 7.01\times {10}^{-5}{\lambda }^3$ at $\lambda \sim 1550\mathrm{nm}$. We show that the extreme light concentration in our design can enable ultrastrong Kerr nonlinearities, even at the single-photon level. These features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics.