While a continuous Brownian description of noise from heat and pressure is adequate to model measurements with relatively long integration times, these forces are ultimately generated by quantized degrees of freedom like phonons and gas particles. Fundamentally, the ultimate limit of this sensing problem is to resolve all of the individual system-sensor collisions. Here we propose the use of nanomechanical devices operated with impulse readout sensitivity around the standard quantum limit to sense ultralow gas pressures by directly counting the individual collisions of gas particles on a sensor. We illustrate this in two paradigmatic model systems: an optically levitated nanobead and a tethered membrane system in a phononic band-gap shield.

Scattering resonances are relatively rare in positron scattering, with the only observed instances to date being vibrational Feschbach resonances, observed through their effect on the annihilation cross section. In this study, we present observations of resonances in vibrational excitation by positron impact on ethane, ethylene, and acetylene, and explore the dynamics of positron resonance formation and decay. There are far fewer resonances observed in the excitation spectra than in the annihilation channel. Due to the difficulties inherent in measuring relevant scattering processes at the low energies required to observe the resonances, the formation and decay modes of these resonances are still not well understood. Theory suggests that intramolecular vibrational energy redistribution plays a key role in resonance formation and decay, which should lead to enhancement of the vibrational excitation cross sections in the region of the resonance energies. These results demonstrate that further work is required to fully understand these systems.

In this study, we perform a set of benchmark variational calculations for the ground state and for the 18 lowest bound excited ${}^{2}S$ and ${}^{2}P$ states of the boron atom. The nonrelativistic wave function of each state is generated in an independent calculation by expanding its wave function in terms of a large number ($10000–16000$) of all-electron explicitly correlated Gaussian functions (ECG). The Hamiltonian used in the calculations explicitly depends on the mass of the boron nucleus. The nonlinear parameters of the ECGs are extensively optimized with a procedure that employs the analytic energy gradient determined with respect to these parameters. These highly accurate nonrelativistic wave functions are used to compute the transition dipole moments and the corresponding oscillator strengths for all allowed transitions between the considered states. These quantities are reported for the transitions of the ${}^{10}\mathrm{B}$ and ${}^{11}\mathrm{B}$ isotopes, as well as for the boron atom with an infinite nuclear mass, ${}^{\infty }\mathrm{B}$, and used to evaluate the isotopic shifts of the oscillator strengths. The results generated in this work are considerably more accurate than the data obtained in the previous theoretical calculations.

We study three-body recombination in the helium-helium-silver system at cold collision energies. The three-body Schrödinger equation is solved combining the slow variable discretization and adiabatic approaches with the $R$-matrix propagation method, in order to calculate the product-state-selective total and partial recombination rates in the ${}^4\mathrm{He}+{}^4\mathrm{He} +$ Ag system. Recombination at collision energies less than 10 mK is found to take place dominantly to the product molecule ${}^4\mathrm{He}\mathrm{Ag}$ in its least bound state, while the three atoms recombine mainly to the ${}^4\mathrm{He}_2$ molecule in its ground state at higher collision energies.

We perform a detailed semianalytical study of the characteristics of strong-field processes induced by an ultrashort linearly polarized pulse with two carrier frequencies. We show that the photoelectron spectra depend to a great extent on the absolute phases of the field components and on the duration of the pulse. By using the saddle-point method, we show that this dependence can be exploited to control the electron dynamics in the laser field. Besides the photoelectron spectra, we also investigate the spectra of high-order harmonics. Again, we find a strong dependence on the absolute phases and the duration of the pulse. We present the spectra using a false color scale in the absolute phase-harmonic energy plane, and show that particular regions in this plane can be assessed using the simple man's model founded on the classical solution of the Newton equation of motion. Finally, we investigate the symmetry properties of the photoelectron and high-order harmonic spectra with respect to the transformation which includes the change of the absolute phase, and compare them with those valid for a long driving pulse with a flat envelope.

The temporal sidelobes of few-cycle pulses seriously restrict their applications in ultrafast science. We propose a unique mechanism that enables the generation of sub-two-cycle pulses with a high temporal quality. A robust spatiotemporal soliton could be formed from pulse self-compression by modulating the dispersion of the air-plasma channel via the adjusted plasma density. The self-cleaning of the spatiotemporal soliton leads to the elimination of sidelobes in the temporal profile of the sub-two-cycle pulse. The required density of the preformed plasma for an arbitrary central wavelength from the near-infrared to midinfrared regime is predicted theoretically and confirmed by ($3\mathrm{D}+1$) simulations.

We develop a theoretical predictive model for an all-pass ring resonator that enables the most complete description of linear coupling regimes. The model is based on eigenmode decomposition of Maxwell's equations with a full account of the confined and leaky modes, as opposed to the existing phenomenological methods restricted to the confined modes only. This model enables a quantitative description of all-pass ring resonators and provides insights into the physics underlying microring-waveguide coupling. We experimentally validate the model using transmission measurements in the linear regime of aluminum nitride resonators. The developed model is then used to explore the field enhancement in microrings crucial for nonlinear photonic applications.

In the Advanced $\mathrm{Virgo}+$ interferometric gravitational-wave detector, the length control of the Fabry-Pérot cavities in the arms and of the detuned filter cavity, used for generating frequency-dependent squeezing, uses an auxiliary green beam at half of the operation laser wavelength (1064 nm). While operating the filter cavity with such a bichromatic control scheme for tens of hours, we observed that the mirror reflection phase shift of the fields at the two wavelengths responds differently to temperature changes in the mirrors, causing a change in the relative resonance condition of the two beams. In this paper we show that this thermal detuning effect can be explained by considering the thermomechanical properties of the mirror coating. Our experimental measurements are in good agreement with the theoretical predictions and allow us to drive requirements on the bicolor coating design and mirror temperature stability for long-term stable cavity control.

We study many-body entanglements and spectra of the extended bosonic Hatano-Nelson model in the hard-core limit. We show that the system undergoes a phase transition from a gapless phase to a charge-density-wave phase accompanied by a parity-time transition in the first-excited state. The phase transition is characterized by the crossing of the ground-state biorthogonal-order parameter and the sudden change of the first-excited-state entanglement entropy. The gapless phase is verified by the logarithmic scaling of the ground-state entanglement entropy with the central charge $c=1$. Furthermore, we show that all energy spectral clusters would form ellipses in strong nearest-neighbor interactions, for which we establish a universal scaling law. The lengths of the major and minor axes are shown to obey power laws with respect to the nearest-neighbor interaction. The exact expressions are derived for the numbers of energy levels on the outermost elliptic ring of each clusters.

Transduction of quantum signals between the microwave and the optical ranges will unlock powerful hybrid quantum systems enabling information processing with superconducting qubits and low-noise quantum networking through optical photons. Most microwave-to-optical quantum transducers suffer from thermal noise due to pump absorption. We analyze the coupled thermal and wave dynamics in electro-optic transducers that use a two-step scheme based on an intermediate frequency state in the THz range. Our analysis, supported by numerical simulations, shows that the two-step scheme operating with a continuous pump offers near-unity external efficiency with a multiorder noise suppression compared to single-step transduction. As a result, two-step electro-optic transducers may enable quantum-noise-limited interfacing of superconducting quantum processors with optical channels at MHz-scale bit rates.

One of the simplest possible quantum circuits, consisting of a cnot gate, a Hadamard gate, and a measurement on one of the outputs is known to lead to chaotic dynamics when applied iteratively on an ensemble of equally prepared qubits. The evolution of pure initial quantum states is characterized by a fractal (in the space of states), formed by the border of different convergence regions. We examine how the ideal evolution is distorted in the presence of both coherent error and incoherent initial noise, which are typical imperfections in current implementations of quantum computers. It is known that under the influence of initial noise only, the fractal is preserved, moreover, its dimension remains constant below a critical noise level. We systematically analyze the effect of coherent Hadamard gate errors by determining fixed points and cycles of the evolution. We combine analytic and numerical methods to explore to what extent the dynamics is altered by coherent errors in the presence of preparation noise as well. We show that the main features of the dynamics, and especially the fractal borders, are robust against the discussed noise, they will only be slightly distorted. We identify a range of error parameters, for which the characteristic properties of the dynamics are not significantly altered. Hence, our results allow to identify reliable regimes of operation of iterative protocols.

The nuclear-polarization corrections to the energy levels of highly charged ions are systematically investigated to leading order in the fine-structure constant. To this end, the notion of effective photon propagators with nuclear-polarization insertions is employed, where the nuclear excitation spectrum is calculated by means of the Hartree-Fock-based random-phase approximation. The effective Skyrme force is used to describe the interaction between nucleons, and the model dependence is analyzed. To leading order, the formalism predicts two contributions given by the effective vacuum-polarization and self-energy diagrams. The existing ambiguity around the vacuum-polarization term is resolved by demonstrating that it is effectively absorbed in the standard finite-nuclear-size correction. The self-energy part is evaluated with the full electromagnetic electron-nucleus interaction taken into account, where the importance of the effects of the nuclear three-currents is emphasized.

Nonsequential double ionization (NSDI) of atoms driven by parallel-polarized two-color (PPTC) fields composed of two equal-intensity multiple-cycle laser pulses is investigated using a three-dimensional classical ensemble model. The ion momentum distribution shows pronounced asymmetry and strongly depends on the relative phase of the two pulses. The ion momentum distributions exhibit a double- or not yet observed triple-hump structure, depending on the relative phase of the two pulses. More interestingly, the three peaks of the ion momentum distribution correspond to the first-returning recollision, the odd-returning recollision (without the first returning recollision), and the even-returning recollision. This means that the number of electron returnings is mapped onto the ion momentum distribution. The information about the number of electron returnings can be directly retrieved from the observed ion momentum distribution in the PPTC field with equal intensities. Moreover, the proportions of the three types of trajectories in NSDI, the returning energy of the ionized electron, and the ionization mechanism can be well manipulated by changing the relative phase of the two pulses.

We experimentally demonstrate that well-designed driven lattices are versatile tools to simultaneously tune multiple key parameters (spin-dependent interactions, spinor phase, and quadratic Zeeman energy) for manipulating phase diagrams of spinor gases with negligible heating and atom losses. This opens avenues for studying engineered Hamiltonians and dynamical phase transitions. Modulation-induced harmonics generate progressively narrower separatrices at driving-frequency-determined higher magnetic-field strengths. This technique enables exploration of multiple, previously inaccessible parameter regimes of spinor dynamics (notably high magnetic-field strengths, tunable spinor phase, and individually tunable spin-preserving and spin-changing collisions) and widens the range of cold-atom applications, e.g., in quantum sensing and studies of nonequilibrium dynamics.

Microphotonic quantum memory presents a promising avenue for miniaturizing and scaling up memories for quantum network applications. While conventional microphotonic cavities can provide enhanced light-matter-interaction to improve the memory efficiency, they are constrained by inherent limitations when utilizing the quantum memory protocol of the revival of silenced echo (ROSE). These limitations primarily arise from the high sensitivity to cavity fabrication imperfections, which scatter stored optical modes into alternate modes and cause a subsequent reduction in efficiency. In this study, we propose that the incorporation of robust edge states and defect states in topological photonic crystals offers a solution to overcome this inherent limitation. The spatial-phase-mismatching effect that underlies ROSE is topologically protected, effectively mitigating the distortion of stored optical states caused by imperfection scattering and improves the memory efficiency.

Cavity magnomechanics has shown great potential in studying macroscopic quantum effects, especially for quantum entanglement, which is a key resource for quantum information science. Here we propose to realize magnon mediated nonreciprocal photon-phonon entanglement, which exhibits asymmetry when opposite magnetic or driving fields are respectively applied to the magnons with the Kerr effect or the photons with the Sagnac effect. We find that the mean magnon number can selectively exhibit nonreciprocal linear or nonlinear (bistable) behavior with the strength of the strong driving field on the cavity. Assisted by this driving field, the magnon-phonon coupling is greatly enhanced, leading to the nonreciprocal photon-phonon entanglement via the swapping interaction between the magnons and photons. This nonreciprocal entanglement can be significantly enhanced with the magnon Kerr and Sagnac effects. Given the available parameters, the nonreciprocal photon-phonon entanglement can be preserved at $\approx 3$ K, showing remarkable resilience against the bath temperature. The result reveals that our paper holds promise in developing various nonreciprocal devices with both the magnon Kerr and Sagnac effects in cavity magnomechanics.

We present a scheme to generate distant bipartite and tripartite entanglement between an atomic ensemble and an yttrium iron garnet (YIG) sphere in coupled microwave cavities. We consider an atomic ensemble in a single-mode microwave cavity which is coupled with a second single-mode cavity having a YIG sphere. Our system, therefore, has five excitation modes, namely, cavity-1 photons, an atomic ensemble, cavity-2 photons, a magnon and a phonon mode in the YIG sphere. We show that significant bipartite entanglement exists between indirectly coupled subsystems in the cavities which is robust against temperature. Moreover, we present suitable parameters for a significant tripartite entanglement of the ensemble, magnon, and phonon modes. We also demonstrate the existence of tripartite entanglement between the magnon and phonon modes of the YIG sphere with indirectly coupled cavity photons. Interestingly, this distant tripartite entanglement is of the same order as that previously found for a single-cavity system. We show that cavity-cavity coupling strength affects both the degree and transfer of quantum entanglement between various subsystems. Therefore, an appropriate cavity-cavity coupling optimizes the distant entanglement by increasing the entanglement strength and its robustness against temperature.