We study optomechanically induced transparency (OMIT) in a compound system consisting of an optical cavity and an acoustic molecule, which features not only double OMIT peaks but also light advance. We find that by selectively driving one of the acoustic modes, OMIT peaks can be amplified either symmetrically or asymmetrically, accompanied by either significantly enhanced advance or a transition from advance to delay of the signal light. The sensitive impacts of the mechanical driving fields on the optical properties, including the signal transmission and its higher-order sidebands, are also revealed. Our results confirm that selective acoustic control of OMIT devices provides a versatile route to achieve multiband optical modulations, weak-signal sensing, and coherent communications of light.

In one-out-of-$m$ spacetime-constrained oblivious transfer (SCOT), Alice and Bob agree on $m$ pairwise spacelike separated output spacetime regions $R_0,R_1,...,R_{m-1}$ in an agreed reference frame in a spacetime that is Minkowski, or close to Minkowski; Alice inputs a message ${\mathbf{x}}_i$ in the causal past of a spacetime point $Q_i$ of $R_i$, for $i\in \{0,1,...,m-1\}$; Bob inputs $b\in \{0,1,...,m-1\}$ in the intersection of the causal pasts of $Q_0,Q_1,...,Q_{m-1}$ and outputs ${\mathbf{x}}_b$ in $R_b$; Alice remains oblivious to $b$ anywhere in spacetime; and Bob is unable to obtain ${\mathbf{x}}_i$ in $R_i$ and ${\mathbf{x}}_j$ in $R_j$ for any pair of different numbers $i,j\in \{0,1,...,m-1\}$. We introduce unconditionally secure one-out-of-$m$ SCOT protocols extending the one-out-of-two SCOT protocols of Pitalúa-García [Phys. Rev. A 93, 062346 (2016)] and Pitalúa-García and Kerenidis [Phys. Rev. A 98, 032327 (2018)], for arbitrary integers $m\ge 2$. We define the task of one-out-of-$m$ distributed quantum access with classical memory (DQACM), which works as a subroutine to implement a class ${\mathcal{P}}_{\text{CC}}$ of one-out-of-$m$ SCOT protocols where distant agents only need to communicate classically. We present unconditionally secure one-out-of-$m$ DQACM protocols and one-out-of-$m$ SCOT protocols of the class ${\mathcal{P}}_{\text{CC}}$, for arbitrary integers $m\ge 2$. We discuss various generalizations of SCOT. In particular, we introduce a straightforward extension of SCOT to a $k$-out-of-$m$ setting, and suggest protocols where distant agents only need to communicate classically, while we leave the investigation of their security as an open problem.

Polarized nuclei are a powerful tool in nuclear-spin studies and in the search for physics beyond the standard model. Systems which compare two nuclear species have thus far been limited by anomalous yet reproducible frequency variations of unknown origin. We studied the self-interactions in a ${}^3\mathrm{He}-{}^{129}\mathrm{Xe}$ system by independently addressing, controlling, and measuring the influence of each component of the nuclear-spin polarization. Our results directly rule out prior explanations of the shifts and demonstrate experimentally that they can be explained by species-dependent self-interactions. We also report a gas-phase frequency shift induced by ${}^{129}\mathrm{Xe}$ on ${}^3\mathrm{He}$.

We present a detailed description of experimental studies of the parity violation effect in an isotopic chain of atomic ytterbium (Yb), whose results were reported in a recent paper [Antypas et al., Nat. Phys. 15, 120 (2019)]. We discuss the principle of these measurements, made on the Yb $6s^2 {}^1{S}_0\to 5d6s {}^{3}D_1$ optical transition at 408 nm, describe the experimental apparatus, and give a detailed account of our studies of systematic effects in the experiment. Our results offer a direct observation of the isotopic variation in the atomic parity violation effect, a variation which is in agreement with the prediction of the standard model. These measurements are used to constrain electron-proton and electron-neutron interactions, mediated by a light $Z^{\prime }$ boson.

We investigate the possible effect of cascade transitions from the $\left(4s5p\right){}^3{P}_{0,1,2}$ states to the $\left(4s5s\right){}^3{S}_1$ state of Zn. The polarization of the light emitted in the subsequent decay to the $\left(4s4p\right){}^3{P}_{0,1,2}$ states has been the subject of recent controversy, with significant disagreement between the experimental data reported by Pravica et al. [Phys. Rev. A 83, 040701 (2011)] and by Clayburn and Gay [Phys. Rev. Lett. 119, 093401 (2017)] in the cascade-free region below $\approx 7.6$ eV incident energy and relatively good agreement above. The cross sections for excitation of the $\left(4s5p\right){}^3{P}_{0,1,2}$ states, as well as higher-lying triplet states, and the linear polarization of the cascade radiation seem too small to produce a significant alignment of the $\left(4s5s\right){}^3{S}_1$ state, thereby raising additional questions regarding the origin of the relatively large linear polarizations measured above the cascade threshold.

It was recently discovered that molecular ionization at high x-ray intensity is enhanced, in comparison with that of isolated atoms, through a phenomenon called CREXIM (charge-rearrangement-enhanced x-ray ionization of molecules). X-ray absorption selectively ionizes heavy atoms within molecules, triggering electron transfer from neighboring atoms to the heavy-atom sites and enabling further ionization there. The present theoretical study demonstrates that the CREXIM effect increases with the size of the molecule, as a consequence of increased intramolecular electron transfer from the larger molecular constituents attached to the heavy atoms. We compare x-ray multiphoton ionization dynamics of xenon, iodomethane, and iodobenzene after interacting with an intense x-ray pulse. Although their photoionization cross sections are similar, iodomethane and iodobenzene molecules are more ionized than xenon atoms. Moreover, we predict that the average total charge of iodobenzene is much larger than that of iodomethane, because of the large number of electrons in the benzene ring. The positive charges transferred from the iodine site to the benzene ring are redistributed such that the higher carbon charges are formed at the far end from the iodine site. Our first-principles calculations provide fundamental insights into the interaction of molecules with x-ray free-electron laser (XFEL) pulses. These insights need to be taken into account for interpreting and designing future XFEL experiments.

We develop a theory for cavity cooling of the center-of-mass motion of a levitated nanoparticle through coherent scattering into an optical cavity. We analytically determine the full coupled Hamiltonian for the nanoparticle, cavity, and free electromagnetic field. By tracing out the latter, we obtain a master equation for the cavity and the center-of-mass motion, where the decoherence rates ascribed to recoil heating, gas pressure, and trap displacement noise are calculated explicitly. Then we benchmark our model by reproducing published experimental results for three-dimensional cooling. Finally, we use our model to demonstrate the possibility of ground-state cooling along each of the three motional axes. Our work illustrates the potential of cavity-assisted coherent scattering to reach the quantum regime of levitated nanomechanics.

Traditionally, optical spatial dispersion (OSD) is defined as the dependence $\widehat{\varepsilon }\left(\vec{k}\right)$ of the dielectric permittivity tensor $\widehat{\varepsilon }$ on the light wave vector $\vec{k}$, similarly to the frequency ($\omega$) dispersion of the dielectric tensor $\varepsilon \left(\omega \right)$. We have developed an approach for the description of the OSD phenomena in the framework of Jones calculus. In Jones calculus the differential Jones matrix (DJM) $N$ is the generalization of the light wave-vector $\vec{k}$ in the same sense that $\vec{k}$ is the generalization of the light wave number $k$. The latter inspires us to expect that there must exist a way to describe the OSD phenomena in terms of the DJM. We show that such a relation between the OSD phenomena and Jones calculus indeed exists. To prove the latter we derive a general relation between the DJM and components of the dielectric permittivity tensor $\widehat{\varepsilon }$. We establish the relation of the DJM approach, proposed in this paper, to the traditional OSD approach of the gyration pseudotensor as well as to that developed by Mauguin for light propagation in cholesteric liquid crystals [M. C. Mauguin, Bull. Soc. Fr. Mineral. Crystallogr. N3, 71 (1911)]. We demonstrate that both the gyration pseudotensor and Mauguin's approach can be derived as particular cases of the proposed DJM approach. In our approach the integral Jones matrix (IJM) of the medium taking into account OSD is the product of the IJM without taking into account OSD by the correction IJM, which accounts for the OSD effects. In a general case, when all components of the OSD DJM $N^D$ are nonzero, the secular equation for the refractive indices of the eigenwaves is a quartic equation. The coefficient $a_3$ at the cubic term in the secular equation is nonzero only for nonzero OSD corrections to the average refractive index. For transparent crystals at nonzero OSD correction to the average refractive index and zero to all other correction parameters in $N^D$, the secular equation has two distinct real and two complex-conjugate roots. We assign the complex-conjugate roots to the forward and backward light scattering. Therefore, taking into account the OSD effect on the refractive index, the Jones calculus becomes capable of describing light scattering. The proposed Jones calculus approach is a general tool for taking into account OSD in optically inhomogeneous media, in which several or all OSD correction parameters are simultaneously nonzero, for example, in liquid-crystal cells with a spatially nonuniform director field, including those containing defects.

We studied the generation and dynamics of solitonic pulses, platicons, in microresonators at normal group velocity dispersion due to the pump amplitude modulation. We proposed that, if the required frequency of amplitude modulation is too large for available modulators, it is possible to use subharmonic phase modulation for platicon generation. It was also demonstrated that it is possible to control the repetition rate of platicons by tuning the modulation frequency. The tuning range for platicons was found to be much wider than for bright solitons. We also studied the influence of high-order dispersion on platicon properties. It was shown that both third-order dispersion and pump modulation govern platicon dynamics, making it quite different from the dynamics of dissipative Kerr solitons. Third-order dispersion was also shown to significantly affect the optimal conditions for the platicon generation and repetition rate tuning range.

We apply reverse engineering to find electromagnetic pulses that allow for the control of populations in quantum systems under dephasing and thermal noises. In particular, we discuss two-level systems given their importance in the description of several molecular systems as well as quantum computing. Such an investigation naturally finds applications in a multitude of physical situations involving the control of quantum systems. We present an analytical description of the pulse which solves a constrained dynamics where the initial and final populations are fixed a priori. This constrained dynamics is sometimes impossible, and we precisely spot the conditions for that. One of our results is the presentation of analytical conditions for the establishment of steady states for finite coherence in the presence of noise. This might naturally find applications in quantum memories.

Momentum distributions of electron-positron pairs created from the vacuum by an oscillating in time electric field are calculated in the framework of quantum field theory. A pronounced enhancement of those distributions is observed as the frequency of the electric field passes across the one-photon threshold. Below that threshold the pairs preferentially carry a longitudinal momentum, while above the threshold they tend to carry a transverse momentum. Such momentum sharing has an impact on the number of produced pairs: It grows fast with increasing the field frequency below the threshold but it saturates at a roughly constant value above it. On the other hand, at the fixed frequency above the one-photon threshold, the number of pairs scales quadratically with the field strength. This typically perturbative scaling holds even for large electric fields. Thus, the validity of the perturbation theory is extended here to processes which result in creation of particles with substantial transverse momenta.

We present absolute-frequency measurements in ultracold ${}^{39}\mathrm{K}$ samples of the transitions from the $4s_{1/2}$ ground state to $n{p}_{1/2}$ and $n{p}_{3/2}$ Rydberg states. A global nonlinear regression of the $n{p}_{1/2}$ and $n{p}_{3/2}$ term values yields an improved wave number of 35009.8139710(22)${}_{\mathrm{sys}}{\left(3\right)}_{\mathrm{stat}}{\mathrm{cm}}^{-1}$ for the first ionization threshold of ${}^{39}\mathrm{K}$ and the quantum defects of the $n{p}_{1/2}$ and $n{p}_{3/2}$ series. In addition, we report the frequencies of selected one-photon transitions $n^{\prime }{s}_{1/2}\leftarrow n{p}_{3/2}, n^{\prime }{d}_j\leftarrow n{p}_{3/2}, n^{\prime }{f}_{j^{\prime }}\leftarrow n{d}_j$, and $n^{\prime }{g}_{j^{\prime }}\leftarrow n{f}_j$ and two-photon transitions $n{f}_{j^{\prime }}\leftarrow n{p}_j$ determined by millimeter-wave spectroscopy, where $j$ is the total angular-momentum quantum number. By combining the results from the laser and millimeter-wave spectroscopic experiments, we obtain improved values for the quantum defects of the $s_{1/2}, d_{3/2}, d_{5/2}, f_j$, and $g_j$ states. For the $d_j$ series, the inverted fine structure was confirmed for $n\ge 32$. The fine-structure splitting of the $f$ series is less than 100 kHz at $n=31$, significantly smaller than the hydrogenic splitting, and the fine structure of the $g$ series is regular for $n\ge 30$, with a fine-structure splitting compatible with the hydrogenic prediction. From the measured quantum defects of the $f$ and $g$ series we derive an estimate for the static dipole ${\alpha }_{\mathrm{d}}$ and quadrupole ${\alpha }_{\mathrm{q}}$ polarizabilities of the ${\mathrm{K}}^{+}$ ion core. Additionally, the hyperfine splitting of the $4s_{1/2}$ ground state of ${}^{39}\mathrm{K}$ was determined to be 461.719700(5) MHz using radio-frequency spectroscopy and Ramsey-type interferometry.

The disorder-induced localization of few bosons interacting via a contact potential is investigated through the analysis of the level-spacing statistics familiar from random matrix theory. The model we consider is defined in a continuum and describes one-dimensional bosonic atoms exposed to the spatially correlated disorder due to an optical speckle field. First, we identify the speckle-field intensity required to observe, in the single-particle case, the Poisson level-spacing statistics, which is characteristic of localized quantum systems, in a computationally and experimentally feasible system size. Then, we analyze the two-body and the three-body systems, exploring a broad interaction range, from the noninteracting limit up to moderately strong interactions. Our main result is that the contact potential does not induce a shift towards the Wigner-Dyson level-spacing statistics, which would indicate the emergence of an ergodic chaotic state, indicating that localization can occur also in interacting few-body systems in a continuum. We also analyze how the ground-state energy evolves as a function of the interaction strength.

We demonstrate, both experimentally and theoretically, a method that allows us to modify the spatial properties of photon pairs produced by the process of spontaneous parametric down-conversion (SPDC) with an apertured, zeroth-order Bessel-Gauss beam. Concentrating on the use of a half-plane aperture, we show that the phase-matching conditions for non-paraxial pump beams can be controlled by simply changing the aperture orientation. Partially blocking the pump beam, leads to a selection of either one of two individual cones that form a dual-cone SPDC angular spectrum, or a portion of both of them. We can likewise determine the shape and orientation of the conditional angular spectrum. This control of the SPDC spatial properties could be useful for quantum information processing protocols.

We can generate the conditions for observing flat bands on initially trivial lattices by, for example, exciting a given system simultaneously with different orthogonal states. In this work, we demonstrate that a one-dimensional binary lattice supports always a trivial flat band, which is formed by isolated single-site vertical dipolar states. These flat-band modes correspond to the highest localized modes for any discrete system, without the need of any additional mechanism like, e.g., disorder or nonlinearity. By fulfilling a specific relation between lattice parameters, an extra flat band can be excited as well, with modes composed by fundamental and dipolar states that occupy only three lattice sites. Additionally, by inspecting the lattice edges, we are able to construct analytical Shockley surface modes, which can be compact or present staggered or unstaggered tails. We believe that our proposed model could be a good candidate for observing transport and localization phenomena on a simple one-dimensional linear photonic lattice.

In order to study the temporal coherence of a single-mode dye-cavity photon condensate, a model is developed for the dynamics which treats the condensate mode on a quantum-mechanical level. The effects of driving-dissipation and Kerr interactions on the number fluctuations are studied analytically and numerically, including the finding of a long-$\tau$ antibunching effect. Depending on the interaction strength, we quantitatively observe an exponential Schawlow-Townes-like decay or Gaussian Henry-like decay of phase correlations. The adequacy of a heuristic phasor model originating from laser physics in describing the number and phase dynamics is validated within the experimentally relevant parameter regime. The ratio of the first- and second-order coherence times is shown to be inversely proportional to the number fluctuations, with a prefactor that varies smoothly throughout the crossover between canonical and grand-canonical statistics.

Quantum Darwinism attempts to explain the emergence of objective reality of the state of a quantum system in terms of redundant information about the system acquired by independent noninteracting fragments of the environment. The consideration of interacting environmental elements gives rise to a rich phenomenology, including the occurrence of non-Markovian features, whose effects on objectification in the manner of quantum Darwinism needs to be fully understood. We study a model of local interaction between a simple quantum system and a multimode environment that allows for a clear investigation of the interplay between information trapping and propagation in the environment and the emergence of quantum Darwinism. We provide strong evidence of the correlation between non-Markovianity and quantum Darwinism in such a model, thus providing strong evidence of a potential link between such fundamental phenomena.