A quantum particle in a slowly changing potential well $V(x,t)=V(x-x_0\left(\epsilon t\right))$, periodically shaken in time at a slow frequency $\epsilon$, provides an important quantum mechanical system where the adiabatic theorem fails to predict the asymptotic dynamics over time scales longer than $\sim 1/\epsilon$. Specifically, we consider a double-well potential $V\left(x\right)$ sustaining two bound states spaced in frequency by ${\omega }_0$ and periodically shaken in a complex plane. Two different spatial displacements $x_0\left(t\right)$ are assumed: the real spatial displacement $x_0\left(\epsilon t\right)=Asin\left(\epsilon t\right)$, corresponding to ordinary Hermitian shaking, and the complex one $x_0\left(\epsilon t\right)=A-Aexp(-i\epsilon t)$, corresponding to non-Hermitian shaking. When the particle is initially prepared in the ground state of the potential well, breakdown of adiabatic evolution is found for both Hermitian and non-Hermitian shaking whenever the oscillation frequency $\epsilon$ is close to an odd resonance of ${\omega }_0$. However, a different physical mechanism underlying nonadiabatic transitions is found in the two cases. For the Hermitian shaking, an avoided crossing of quasienergies is observed at odd resonances and nonadiabatic transitions between the two bound states, resulting in Rabi flopping, can be explained as a multiphoton resonance process. For the complex oscillating potential well, breakdown of adiabaticity arises from the appearance of Floquet exceptional points at exact quasienergy crossing.

The time evolution of an initially prepared entangled state in the system of coupled quantum dots has been analyzed by means of two different theoretical approaches: equations of motion for all orders localized electron correlation functions, considering interference effects, and kinetic equations for the pseudoparticle occupation numbers with constraint on the possible physical states. Results obtained by means of different approaches were carefully analyzed and compared to each other. Revealing a direct link between concurrence (degree of entanglement) and quantum dots pair correlation functions allowed us to follow the changes of entanglement during the time evolution of the coupled quantum dots system. It was demonstrated that the degree of entanglement can be controllably tuned during the time evolution of quantum dots system.

Synchronously pumped optical parametric oscillators (SPOPOs) are optical cavities driven by mode-locked lasers, and containing a nonlinear crystal capable of down-converting a frequency comb to lower frequencies. SPOPOs have received a lot of attention lately because their intrinsic multimode nature makes them compact sources of quantum correlated light with promising applications in modern quantum information technologies. In this work we show that SPOPOs are also capable of accessing the challenging and interesting regime where spontaneous symmetry breaking confers strong nonclassical properties to the emitted light, which has eluded experimental observation so far. Apart from opening the possibility of studying experimentally this elusive regime of dissipative phase transitions, our predictions will have a practical impact, since we show that spontaneous symmetry breaking provides a specific spatiotemporal mode with large quadrature squeezing for any value of the system parameters, turning SPOPOs into robust sources of highly nonclassical light above threshold.

Here, it is shown that when two optical frequency combs with identical mode spacing but different offset frequencies copropagate through a nonlinear optical fiber, four-wave mixing between them generates new modes. Although the spacings between the new modes depend on the difference of the offset frequencies, they appear irregular because of the large number of possible four-wave-mixing processes. However, when the difference in the offset frequencies is an integer fraction of the mode spacing of the original combs, the cascaded four-wave mixing generates a new comb with a fixed mode spacing given by the difference in the offset frequencies. This process can be used to substantially increase the mode density of a frequency comb. The method can be used in conjunction with new sources of frequency combs, such as quantum cascade lasers and microresonators, which have large mode spacing of tens of GHz. Decreasing the mode spacing of such sources is likely to increase their applicability.

The localization of light in flat-band lattices has been recently proposed and experimentally demonstrated in several configurations, assuming a classical description of light. Here we study the problem of light localization in the quantum regime. We focus on quasi-one-dimensional and two-dimensional lattices which exhibit a perfect flat band inside their linear spectrum. Localized quantum states are constructed as eigenstates of the interaction Hamiltonian with a vanishing eigenvalue and a well defined total photon number. These are superpositions of Fock states with probability amplitudes given by positive as well as negative square roots of multinomial coefficients. The classical picture can be recovered by considering Poissonian superpositions of localized quantum states with different total photon number. We also study the separability properties of flat-band quantum states and apply them to the transmission of information via multicore fibers, where these states allow for the total passive suppression of photon crosstalk and exhibit robustness against photon losses. At the end, we propose an on-chip setup for the experimental preparation of localized quantum states of light for any number of photons.

We present a theoretical investigation of the Goos-Hänchen effect, i.e., the lateral shift of the light beam transmitted through one-dimensional biperiodic multilayered photonic systems consisting of equidistant magnetic layers separated by finite size dielectric photonic crystals. We show that the increase of the number of periods in the photonic-magnonic structure leads to increase of the Goos-Hänchen shift in the vicinity of the frequencies of defect modes located inside the photonic band gaps. Presence of the linear magnetoelectric coupling in the magnetic layers can result in a vanishing of the positive maxima of the cross-polarized contribution to the Goos-Hänchen shift.

We investigate theoretically the many-emitter phonon laser based on optically driven semiconductor quantum dots within an acoustic nanocavity. We map the phonon laser Hamiltonian to a Tavis-Cummings-type interaction with an unexpected additional many-emitter energy shift. This many-emitter interaction with the cavity mode results in a variety of resonances dependent on the number of participating emitters. We show that the many-emitter phonon laser also includes the single-emitter resonance besides these collective phenomena. However, we obtain a high quantum yield addressing these collective resonances. We clearly demonstrate the best setup for maximal enhancement and show that the output can be increased even more via lasing at the two-phonon resonance.

A damping term in the theoretical model of our paper [Phys. Rev. A 83, 013827 (2011)] was questioned by the author of the Comment. The author argued this damping term cannot exactly describe the spontaneous decay or quantum jump process and, thus, concluded that our results are prone to be incorrect. However, the physics of electromagnetically induced transparency (EIT) is mainly determined by the ground-state coherence and the optical coherence of the probe transition. We show here that the damping term in our paper described the relaxation process of optical coherence in the EIT system, but not the spontaneous decay process of the population. The case of spontaneous decay used in the argument of the Comment is not an issue in typical EIT studies, in which the probe field is weak and treated as the perturbation. Furthermore, the experimental data in the paper were taken under the condition of a weak probe field. Our theoretical model in the weak-probe condition actually deals with the two coherences of EIT physics, and is suitable for analysis of the data. We believe the results of the study, focusing on the dynamics of slow light and light storage in Doppler-broadened EIT media, are correct.

Starting from the de Gennes theory of director fluctuations in nematics, we report on a model of the spatial fluctuations in nematicon propagation. We demonstrate that, when the long-range correlation that characterizes nematic liquid crystals is taken into account in the thermal noise, it is possible to account for the spatial oscillations and propagation losses experienced by nematicons. Increasing the power of the nematicon, the oscillation amplitudes increase and the propagation losses decrease. The nematicon is then more strongly confined and deviates more, but is less scattered by the thermally induced perturbations of the refractive index. All the results are in good agreement with the experimental observations.

We investigate the effect of counter-rotating-wave terms on the non-Markovianity in quantum open systems by employing the hierarchical equations of motion in the framework of the non-Markovian quantum state diffusion approach. As illustrative examples, the non-Markovian memory effect of a qubit embedded in a bosonic or a fermionic environment with a detuned Lorentz spectrum at zero temperature is analyzed. It is found that the counter-rotating-wave terms are able to enhance the observed non-Markovianity whether the environment is composed of bosons or fermions. This result suggests that the rotating-wave approximation may reduce the non-Markovianity in quantum open systems. Moreover, we find that the modification of the non-Markovianity due to the different statistical properties of environmental modes becomes larger with the increase of the system-environment coupling strength.

We propose an efficient scheme for a coherent quantum interface between microwave and optical photons using nitrogen-vacancy (NV) centers in diamond. In this setup, an NV center ensemble is simultaneously coupled to an optical and a microwave cavity. We show that, by using the collective spin excitation modes as an intermediary, quantum states can be transferred between the microwave cavity and the optical cavity through either a double-swap scheme or a dark-state protocol. This hybrid quantum interface may provide interesting applications in single microwave photon detections or quantum information processing.

Quantum interference plays an important role in various intense-laser-driven atomic phenomena, e.g., above-threshold ionization and high-order-harmonic generation, and provides a useful tool in ultrafast imaging of atomic and molecular structure and dynamics. However, it has eluded observation in nonsequential double ionization (NSDI), which serves as an ideal prototype to study electron-electron correlation. Thus far, NSDI usually could be well understood from a semiclassical perspective, where all quantum aspects have been ignored after the first electron has tunneled. Here we perform coincidence measurements for NSDI of xenon subject to laser pulses at 2400 nm. It is found that the intensity dependence of the asymmetry parameter between the yields in the second and fourth quadrants and those in the first and third quadrants of the electron-momentum-correlation distributions exhibits a peculiar fast oscillatory structure, which is beyond the scope of the semiclassical picture. Our theoretical analysis indicates that this oscillation can be attributed to interference between the contributions of different excited states in the recollision-excitation-with-subsequent-ionization channel. Our work demonstrates the significant role of quantum interference in NSDI and may create an additional pathway towards manipulation and imaging of the ultrafast atomic and molecular dynamics in intense laser fields.

Long-lived rovibrational states of the metastable ${{\mathrm{D}}_2}^{-}$ molecular anion, with lifetimes of the order of microseconds, were studied by recording the time-of-flight difference between D and ${\mathrm{D}}^{-}$ fragments produced by spontaneous dissociation of the ${{\mathrm{D}}_2}^{-}$ complex. The simulated time-of-flight spectrum was adjusted to the experimental results, allowing us to extract the resonance energy relative to the dissociation threshold. A single value was found, $22.8\pm 0.3$ meV, which is somewhat larger than resonance energies predicted by theory for long-lived ${{\mathrm{D}}_2}^{-}$ rovibrational states with $(J,v)$ quantum numbers (37,0), (37,1), and (38,0) [Phys. Rev. A 75, 012507 (2007)]. This discrepancy seems due to the extreme sensitivity of these metastable states to minute features of the potential energy curve. The spectral feature is explained by the competition between autodetachment and spontaneous dissociation decay channels.

A method for performing a precision measurement of the Rydberg constant $R_{\infty }$ using cold circular Rydberg atoms is proposed. These states have long lifetimes as well as negligible quantum electrodynamics and no nuclear-overlap corrections. Due to these advantages, the measurement can help solve the proton radius puzzle [J. C. Bernauer and R. Pohl, Sci. Am. 310, 32 (2014)]. The atoms are trapped using a Rydberg-atom optical lattice and transitions are driven using a recently demonstrated lattice-modulation technique to perform Doppler-free spectroscopy. The circular-state transition frequency yields $R_{\infty }$. Laser wavelengths and beam geometries are selected such that the lattice-induced transition shift is minimized. The selected transitions have no first-order Zeeman and Stark corrections, leaving only manageable second-order Zeeman and Stark shifts. For Rb, the projected relative uncertainty of $R_{\infty }$ in a measurement under the presence of the earth's gravity is ${10}^{-11}$, with the main contribution coming from the residual lattice shift. This could be reduced in a future microgravity implementation. The next-important systematic uncertainty arises from the ${\mathrm{Rb}}^{+}$ polarizability (relative-uncertainty contribution of $\approx 3\times {10}^{-12}$).

Second-stage laser cooling of thulium atoms at the 530.7 nm transition with a natural linewidth of 350 kHz offers an interesting possibility to study different regimes of a magneto-optical trap (MOT). The intermediate value of the spectral linewidth of the cooling transition allows the observation of three distinct regimes depending on the intensity and detuning of the cooling beams, namely, the “bowl-shaped” regime when light pressure force competes with gravity, the “double structure” regime with interplay between the Doppler and polarization-gradient (sub-Doppler) cooling, and the “symmetric” regime when Doppler cooling dominates over sub-Doppler cooling and gravity. The polarization-gradient cooling manifests itself by a two-temperature momentum distribution of atoms resulting in a double-structure of the spatial MOT profile consisting of a cold central fraction surrounded by a hot halo. We studied the double structure regime at different saturation parameters and compared observations with calculations based on semiclassical and quantum approaches. The quantum treatment adequately reproduces experimental results if the MOT magnetic field is properly taken into account.

The rotational wave-packet dynamics in electronically excited pyrimidine induced by a femtosecond laser pulse at 321.5 nm has been studied by time-resolved mass spectroscopy and photoelectron velocity-map imaging. The rotational revival features at 81.3 ps, which are the direct manifestation of field-free nonadiabatic alignment, are clearly observed in both the time-dependent ion yields and photoelectron angular distributions. In particular, the out-of-phase recurrences in the parent-ion and fragment-ions transients indicate the different directions of the ionization transition-dipole moments for the generation of the parent ion and fragment ions. By tuning the polarization of the probe light parallel or perpendicular to that of the pump light, we demonstrate the potential application of nonadiabatic alignment to manipulate the branching ratio of photoionization products.

We demonstrate a two-dimensional (2D) grating magneto-optical trap (GMOT) with a single input cooling laser beam and a planar diffraction grating using ${}^{87}\mathrm{Rb}$. This configuration increases experimental access when compared with a traditional 2D magneto-optical trap (MOT). As described in the paper, the output flux is several hundred million rubidium atoms/s at a mean velocity of 16.5(9) m/s and a velocity distribution of 4(3) m/s standard deviation. We use the atomic beam from the 2D GMOT to demonstrate loading of a three-dimensional (3D) GMOT with $2.46\left(7\right)\times {10}^8$ atoms. Methods to improve output flux are discussed.

We study the superfluid behavior motion of interacting particles in a periodic potential subject to an external ac force. We observe a dynamical stabilization of the superfluid motion in the presence of ac forces around the boundary of the Brillouin zone. We analyze relevant nonlinear Floquet-Bloch states within the mean field approximation that display loops in the energy spectrum. In particular, we investigate with some detail the transport properties of these states at the edge of the Brillouin zone, showing the existence of a nonvanishing motion of particles. These findings are corroborated by a nonlinear generalization of the Hellmann-Feynman expression for the group velocity. Our results shed new light on the observation of stable persistent motion of particles in periodic potentials.

We study optical forces acting upon semiconductor quantum dots and the force-driven motion of the dots in a colloid. In the spectral range of exciton transitions in quantum dots, when the photon energy is close to the exciton energy, the polarizability of the dots is drastically increased. It leads to a resonant increase of both the gradient and the scattering contributions to the optical force, which enables the efficient manipulation with the dots. We reveal that the optical grating of the colloid leads to the formation of a fluid photonic crystal with spatially periodic circulating fluxes and density of the dots. Pronounced resonant dielectric response of semiconductor quantum dots enables a separation of the quantum dots with different exciton frequencies.