Laser-driven recollision physics is typically accessible only at field intensities high enough for tunnel ionization. Using an extreme ultraviolet pulse for ionization and a near-infrared (NIR) pulse for driving of the electron wave packet lifts this limitation. This allows us to study recollisions for a broad range of NIR intensities with transient absorption spectroscopy, making use of the reconstruction of the time-dependent dipole moment. Comparing recollision dynamics with linear vs circular NIR polarization, we find a parameter space, where the latter favors recollisions, providing evidence for the so far only theoretically predicted recolliding periodic orbits.

Spin-orbit interactions in evanescent fields have recently attracted significant interest. In particular, the transfer of the Belinfante spin momentum perpendicular to the propagation direction generates polarization-dependent lateral forces on particles. However, it is still elusive as to how the polarization-dependent resonances of large particles synergize with the incident light’s helicity and resultant lateral forces. Here, we investigate these polarization-dependent phenomena in a microfiber-microcavity system where whispering-gallery-mode resonances exist. This system allows for an intuitive understanding and unification of the polarization-dependent forces. Contrary to previous studies, the induced lateral forces at resonance are not proportional to the helicity of incident light. Instead, polarization-dependent coupling phases and resonance phases generate extra helicity contributions. We propose a generalized law for optical lateral forces and find the existence of optical lateral forces even when the helicity of incident light is zero. Our work provides new insights into these polarization-dependent phenomena and an opportunity to engineer polarization-controlled resonant optomechanical systems.

We demonstrate that x-ray fluorescence emission, which cannot maintain a stationary interference pattern, can be used to obtain images of structures by recording photon-photon correlations in the manner of the stellar intensity interferometry of Hanbury Brown and Twiss. This is achieved utilizing femtosecond-duration pulses of a hard x-ray free-electron laser to generate the emission in exposures comparable to the coherence time of the fluorescence. Iterative phasing of the photon correlation map generated a model-free real-space image of the structure of the emitters. Since fluorescence can dominate coherent scattering, this may enable imaging uncrystallised macromolecules.

The single-exciton strong coupling with the localized plasmon mode (LPM) at room temperature is highly desirable for exploiting quantum technology. However, its realization has been a very low probability event due to the harsh critical conditions, severely compromising its application. Here, we present a highly efficient approach for achieving such a strong coupling by reducing the critical interaction strength at the exceptional point based upon the damping inhibition and matching of the coupled system, instead of enhancing the coupling strength to overcome the system’s large damping. Experimentally, we compress the LPM’s damping linewidth from about 45 nm to about 14 nm using a leaky Fabry–Perot cavity, a good match to the excitonic linewidth of about 10 nm. This method dramatically relaxes the harsh requirement in mode volume by more than an order of magnitude and allows a maximum direction angle of the exciton dipole relative to the mode field of up to around 71.9°, significantly improving the success rate of achieving the single-exciton strong coupling with LPMs from about 1% to about 80%.

The fluctuations of the electromagnetic field are at the origin of the near-field radiative heat transfer between nanostructures, as well as the Casimir forces and torques that they exert on each other. Here, working within the formalism of fluctuational electrodynamics, we investigate the simultaneous transfer of energy and angular momentum in a pair of rotating nanostructures. We demonstrate that, due to the rotation of the nanostructures, the radiative heat transfer between them can be increased, decreased, or even reversed with respect to the transfer that occurs in the absence of rotation, which is solely determined by the difference in the temperature of the nanostructures. This work unravels the unintuitive phenomena arising from the simultaneous transfer of energy and angular momentum in pairs of rotating nanostructures.

Recently, solid-state mechanical resonators have become a platform for demonstrating nonclassical behavior of systems involving a truly macroscopic number of particles. Here, we perform the most macroscopic quantum test in a mechanical resonator to date, which probes the validity of quantum mechanics by ruling out a classical description at the microgram mass scale. This is done by a direct measurement of the Wigner function of a high-overtone bulk acoustic wave resonator mode, monitoring the gradual decay of negativities over tens of microseconds. While the obtained macroscopicity of $\mu =11.3$ is on par with state-of-the-art atom interferometers, future improvements of mode geometry and coherence times could test the quantum superposition principle at unprecedented scales and also place more stringent bounds on spontaneous collapse models.

We analyze an unusual class of bosonic dynamical instabilities that arise from dissipative (or non-Hermitian) pairing interactions. We show that, surprisingly, a completely stable dissipative pairing interaction can be combined with simple hopping or beam-splitter interactions (also stable) to generate instabilities. Further, we find that the dissipative steady state in such a situation remains completely pure up until the instability threshold (in clear distinction from standard parametric instabilities). These pairing-induced instabilities also exhibit an extremely pronounced sensitivity to wave function localization. This provides a simple yet powerful method for selectively populating and entangling edge modes of photonic (or more general bosonic) lattices having a topological band structure. The underlying dissipative pairing interaction is experimentally resource friendly, requiring the addition of a single additional localized interaction to an existing lattice, and is compatible with a number of existing platforms, including superconducting circuits.

Light forces can be harnessed to levitate mesoscopic objects and cool them down toward their motional quantum ground state. Roadblocks on the way to scale up levitation from a single to multiple particles in close proximity are the requirements to constantly monitor the particles’ positions as well as to engineer light fields that react fast and appropriately to their movements. Here, we present an approach that solves both problems at once. By exploiting the information stored in a time-dependent scattering matrix, we introduce a formalism enabling the identification of spatially modulated wavefronts, which simultaneously cool down multiple objects of arbitrary shapes. An experimental implementation is suggested based on stroboscopic scattering-matrix measurements and time-adaptive injections of modulated light fields.

Strong-field ionization of molecules releases electrons which can be accelerated and driven back to recombine with their parent ion, emitting high-order harmonics. This ionization also initiates attosecond electronic and vibrational dynamics in the ion, evolving during the electron travel in the continuum. Revealing this subcycle dynamics from the emitted radiation usually requires advanced theoretical modeling. We show that this can be avoided by resolving the emission from two families of electronic quantum paths in the generation process. The corresponding electrons have the same kinetic energy, and thus the same structural sensitivity, but differ by the travel time between ionization and recombination—the pump-probe delay in this attosecond self-probing scheme. We measure the harmonic amplitude and phase in aligned ${\mathrm{CO}}_2$ and ${\mathrm{N}}_2$ molecules and observe a strong influence of laser-induced dynamics on two characteristic spectroscopic features: a shape resonance and multichannel interference. This quantum-path-resolved spectroscopy thus opens wide prospects for the investigation of ultrafast ionic dynamics, such as charge migration.

An electronic wave packet has significant spatial evolution besides its temporal evolution, due to the delocalized nature of composing electronic states. The spatial evolution was not previously accessible to experimental investigations at the attosecond timescale. A phase-resolved two-electron-angular-streaking method is developed to image the shape of the hole density of an ultrafast spin-orbit wave packet in the krypton cation. Furthermore, the motion of an even faster wave packet in the xenon cation is captured for the first time: An electronic hole is refilled 1.2 fs after it is produced, and the hole filling is observed on the opposite side where the hole is born.

When light scatters off a sphere, it produces a rich Mie spectrum full of overlapping resonances. Single resonances can be explained with a quantum analogy and result in Fano profiles. However, the full spectrum is so complex that recognizable patterns have not been found, and is only understood by comparing to numerical simulations. Here we show the directional Mie spectrum of evaporating water droplets arranged in consecutive Fano Combs. We then fully explain it by expanding the quantum analogy. This turns the droplet into an “optical atom" with angular momentum, tunneling, and excited states.

Optomechanics is a prime example of light matter interaction, where photons directly couple to phonons, allowing the precise control and measurement of the state of a mechanical object. This makes it a very appealing platform for testing fundamental physics or for sensing applications. Usually, such mechanical oscillators are in highly excited thermal states and require cooling to the mechanical ground state for quantum applications, which is often accomplished by using optomechanical backaction. However, while massive mechanical oscillators are desirable for many tasks, their frequency usually decreases below the cavity linewidth, significantly limiting the methods that can be used to efficiently cool. Here, we demonstrate a novel approach relying on an intrinsically nonlinear cavity to backaction-cool a low frequency mechanical oscillator. We experimentally demonstrate outperforming an identical, but linear, system by more than 1 order of magnitude. Furthermore, our theory predicts that with this approach we can also surpass the standard cooling limit of a linear system. By exploiting a nonlinear cavity, our approach enables efficient cooling of a wider range of optomechanical systems, opening new opportunities for fundamental tests and sensing.

A gas of interacting fermions confined in a quasi one-dimensional geometry shows a BEC to BCS crossover upon slowly driving its coupling constant through a confinement-induced resonance. On one side of the crossover the fermions form tightly bound bosonic molecules behaving as a repulsive Bose gas, while on the other they form Cooper pairs, whose size is much larger than the average interparticle distance. Here we consider the situation arising when the coupling constant is varied suddenly from the BEC to the BCS value. Namely, we study a BEC-to-BCS quench. By exploiting a suitable continuum limit of recently discovered solvable quenches in the Hubbard model, we show that the local stationary state reached at large times after the quench can be determined exactly by means of the quench action approach. We provide an experimentally accessible characterization of the stationary state by computing local pair correlation function as well as the quasiparticle distribution functions. We find that the steady state is increasingly dominated by two-particle spin singlet bound states for stronger interaction strength, but that bound state formation is inhibited at larger BEC density. The bound state rapidity distribution displays quartic power-law decay suggesting a violation of Tan’s contact relations.

Vibrational dynamics in conventional molecules usually takes place on a timescale of picoseconds or shorter. A striking exception are ultralong-range Rydberg molecules, for which dynamics is dramatically slowed down as a consequence of the huge bond length of up to several micrometers. Here, we report on the direct observation of vibrational dynamics of a recently observed Rydberg-atom-ion molecule. By applying a weak external electric field of a few millivolts per centimeter, we are able to control the orientation of the photoassociated ultralong-range Rydberg molecules and induce vibrational dynamics by quenching the electric field. A high resolution ion microscope allows us to detect the molecule’s orientation and its temporal vibrational dynamics in real space. Our study opens the door to the control of molecular dynamics in Rydberg molecules.

Mechanical degrees of freedom, which have often been overlooked in various quantum systems, have been studied for applications ranging from quantum information processing to sensing. Here, we develop a hybrid platform consisting of a magnomechanical cavity and an optomechanical cavity, which are coherently coupled by the straightway physical contact. The phonons in the system can be manipulated either with the magnetostrictive interaction or optically through the radiation pressure. Together with mechanical state preparation and sensitive readout, we demonstrate the microwave-to-optical conversion with an ultrawide tuning range up to 3 GHz. In addition, we observe a mechanical motion interference effect, in which the optically driven mechanical motion is canceled by the microwave-driven coherent motion. Manipulating mechanical oscillators with equal facility through both magnonic and photonic channels enables new architectures for signal transduction between the optical, microwave, mechanical, and magnetic fields.

We report the realization of a Bose-Einstein condensate of europium atoms, which is a strongly dipolar species with unique properties, a highly symmetric $[\mathrm{Xe}]4f^{7}6s^2{}^8{S}_{7/2}$ electronic ground state and a hyperfine structure. By means of evaporative cooling in a crossed optical dipole trap, we produce a condensate of ${}^{151}\mathrm{Eu}$ containing up to $5\times {10}^4$ atoms. We estimate the scattering length of ${}^{151}\mathrm{Eu}$ to be $a_s=110(4){\mathrm{a}}_{\mathrm{B}}$ after comparing the velocities of expansion of condensates to different orientations of the atomic magnetic moments, where ${\mathrm{a}}_{\mathrm{B}}$ is the Bohr radius. We observe deformation of the condensate in the vicinity of the Feshbach resonance at 1.32 G with a width of 10 mG.

In quantum logic spectroscopy (QLS), one species of trapped ion is used as a sensor to detect the state of an otherwise inaccessible ion species. This extends precision measurements to a broader class of atomic and molecular systems for applications like atomic clocks and tests of fundamental physics. Here, we develop a new technique based on a Schrödinger cat interferometer to address the problem of scaling QLS to larger ion numbers. We demonstrate the basic features of this method using various combinations of ${}^{25}{\mathrm{Mg}}^{+}$ logic ions and ${}^{27}{\mathrm{Al}}^{+}$ spectroscopy ions. We observe higher detection efficiency by increasing the number of ${}^{25}{\mathrm{Mg}}^{+}$ ions. Applied to multiple ${}^{27}{\mathrm{Al}}^{+}$, this method will improve the stability of high-accuracy optical clocks and could enable Heisenberg-limited QLS.

Floquet engineering offers a compelling approach for designing the time evolution of periodically driven systems. We implement a periodic atom-light coupling to realize Floquet atom optics on the strontium ${{}^{1}S}_0-{}^3{P}_1$ transition. These atom optics reach pulse efficiencies above 99.4% over a wide range of frequency offsets between light and atomic resonance, even under strong driving where this detuning is on the order of the Rabi frequency. Moreover, we use Floquet atom optics to compensate for differential Doppler shifts in large momentum transfer atom interferometers and achieve state-of-the-art momentum separation in excess of $400\hslash k$. This technique can be applied to any two-level system at arbitrary coupling strength, with broad application in coherent quantum control.

We demonstrate a light-pulse atom interferometer based on the diffraction of free-falling atoms by a picosecond frequency-comb laser. More specifically, we coherently split and recombine wave packets of cold ${}^{87}\mathrm{Rb}$ atoms by driving stimulated Raman transitions between the $|5s{}^2{S}_{1/2},F=1⟩$ and $|5s{}^2{S}_{1/2},F=2⟩$ hyperfine states, using two trains of picosecond pulses in a counterpropagating geometry. We study the impact of the pulses’ length as well as the interrogation time onto the contrast of the atom interferometer. Our experimental data are well reproduced by a numerical simulation based on an effective coupling that depends on the overlap between the pulses and the atomic cloud. These results pave the way for extending light-pulse interferometry to transitions in other spectral regions and therefore to other species, for new possibilities in metrology, sensing of gravito-inertial effects, and tests of fundamental physics.

Tin-vacancy centers in diamond are promising spin-photon interfaces owing to their high quantum efficiency, large Debye-Waller factor, and compatibility with photonic nanostructuring. Benchmarking their single-photon indistinguishability is a key challenge for future applications. Here, we report the generation of single photons with ${99.7}_{-2.5}^{+0.3}\%$ purity and 63(9)% indistinguishability from a resonantly excited tin-vacancy center in a single-mode waveguide. We obtain quantum control of the optical transition with 1.71(1)-ns-long $\pi$ pulses of 77.1(8)% fidelity and show it is spectrally stable over 100 ms. A modest Purcell enhancement factor of 12 would enhance the indistinguishability to 95%.