A transparent material exhibits ultrafast optical nonlinearity and is subject to optical pressure if irradiated by a laser beam. However, the effect of nonlinearity on optical pressure is often overlooked, even if a nonlinear optical pressure may be potentially employed in many applications, such as optical manipulation, biophysics, cavity optomechanics, quantum optics, and optical tractors, and is relevant in fundamental problems such as the Abraham-Minkoswky dilemma or the Casimir effect. Here, we show that an ultrafast nonlinear polarization gives indeed a contribution to the optical pressure that also is negative in certain spectral ranges; the theoretical analysis is confirmed by first-principles simulations. An order-of-magnitude estimate shows that the effect can be observable by measuring the deflection of a membrane made by graphene.

The superadiabatic quantum driving, producing a perfect adiabatic transfer on a given Hamiltonian by introducing an additional Hamiltonian, is theoretically analyzed for transfers within a three-level system. Our starting point is the stimulated Raman adiabatic passage, realized through different schemes of laser pulses. We determine the superadiabatic correction for each scheme. The fidelity, robustness, and transfer time of all the superadiabatic transfer schemes are discussed. We derive that all superadiabatic corrections are based on a $\pi$- (or near-$\pi$)-area pulse coupling between the initial and final states. The benefits in the protocol robustness overcome the difficulties associated to the actual implementation of the three-level superadiabatic transfer.

We present improved theoretical calculations of transition frequencies for the fundamental transitions $(L=0,v=1)\to (L^{\prime }=0,v^{\prime }=0)$ in the hydrogen molecular ions $H_2^{+}$ and HD${}^{+}$ with a relative uncertainty $4\times {10}^{-11}$ and for the two-photon transitions in the antiprotonic helium atom with a relative uncertainty ${10}^{-10}$. To do that, the one-loop self-energy correction of order $\alpha {\left(Z\alpha \right)}^6$ is derived in the two Coulomb center approximation, and numerically evaluated in the case of the aforementioned transitions. The final results also include a complete set of other spin-independent corrections of order $m{\alpha }^7$. The leading order corrections of ${\alpha }^2{ln}^3{\left(Z\alpha \right)}^{-2}{\left(Z\alpha \right)}^6$ are also considered that allows one to estimate a magnitude of yet uncalculated contributions.

Relativistic and QED corrections are calculated for the hyperfine splitting (hfs) in the $2S_{1/2}$ ground state of ${}^9\mathrm{Be}$${}^{+}$ ions with an exact account for electronic correlations. The achieved accuracy is sufficient to determine the finite nuclear size effects from the comparison to the experimental hfs value. The obtained results establish the ground to determine the neutron halo in ${}^{11}\mathrm{Be}$.

We address an open question about the existence of entangled continuous-variable (CV) Werner states with positive partial transpose (PPT). We prove that no such state exists by showing that all PPT CV Werner states are separable. The separability follows by observing that these CV Werner states can be approximated by truncating the states into a finite-dimensional convex mixture of product states. In addition, the constituents of the product states comprise a generalized non-Gaussian measurement which gives, rather surprisingly, a strictly tighter upper bound on quantum discord than photon counting. These results uncover the presence of only negative partial transpose entanglement and illustrate the complexity of more general nonclassical correlations in this paradigmatic class of genuine non-Gaussian quantum states.

We perform resolved optical sideband spectroscopy on a single ${}^{40}$Ca${}^{+}$ ion in a Penning trap. We probe the electric quadrupole allowed $S_{1/2}\leftrightarrow D_{5/2}$ transition at 729 nm and observe equally spaced sidebands for the three motional modes. The axial mode, parallel to the trap axis, is a one-dimensional harmonic oscillator, whereas the radial cyclotron and magnetron modes are circular motions perpendicular to the magnetic field. The total energy associated with the magnetron motion is negative, but here we probe only the (positive) kinetic energy. From the equivalent Doppler widths of the sideband spectra corresponding to the three motions we find effective temperatures of $1.1\pm 0.2$ mK, $7\pm 3$ mK, and $42\pm 8$ $\mu$K for the axial, modified cyclotron, and magnetron modes, respectively. These should be compared to the cooling limits, estimated using optimal laser parameters, of 0.38 mK, 0.8 mK, and $\sim$10 $\mu$K. In future work we aim to perform resolved-sideband cooling of the ion on the 729-nm transition.

When two chains of quantum systems are driven at their ends by a two-mode squeezed reservoir, they approach a steady state characterized by the formation of many entangled pairs. Each pair is made of one element of the first and one of the second chain. This effect has been already predicted under the assumption of broadband squeezing. Here we investigate the situation of finite-bandwidth reservoirs. This is done by modeling the driving bath as the output field of a nondegenerate parametric oscillator. The resulting non-Markovian dynamics is studied within the theoretical framework of cascade open quantum systems. It is shown that the formation of pair-entangled structures occurs as long as the normal-mode splitting of the arrays does not overcome the squeezing bandwidth of the reservoir.

The so-called remarkable formula [G. W. Ford, J. T. Lewis, and R. F. O'Connell, Phys. Rev. Lett. 55, 2273 (1985)] for the Helmholtz free energy is applied to the problem of determining the interaction potential to all orders in the coupling strength of a pair of oscillator dipoles interacting through the familiar dipole-dipole interaction of electrodynamics. Simple, straightforward calculations lead to expressions for (1) the London short-range potential, (2) the Casimir-Polder long-range potential, and (3) the potential at high temperature. Explicit results are shown for both the temperature dependence of the interaction potential and its deviation from the weak-coupling limit. It is stressed that the interaction potential is a change in free energy, not the energy; in particular, in the high temperature case, the change of energy is zero.

The impulsive alignment of the noble-gas dimers ${\mathrm{Ne}}_2$, ${\mathrm{Ar}}_2$, ${\mathrm{Kr}}_2$, and ${\mathrm{Xe}}_2$ is experimentally investigated by determining the alignment through Coulomb explosion imaging after their double ionization. This approach yields a favorably detailed insight into the temporal evolution of the alignment succeeding the aligning laser pulse. Particular emphasis is put on analyzing higher order coherences induced in the density matrix as these coherences determine the details of the temporal evolution of the aligned molecular ensemble. The recorded data enable an extraction of polarizability anisotropies for the dimers and of their rotational constants in the vibrational ground state. At the elevated level of rotational excitation obtained, centrifugal distortion starts influencing the temporal evolution of the alignment.

We compare direct state measurement (DSM, or weak state tomography) to conventional state reconstruction (tomography) through accurate Monte Carlo simulations. We find that DSM is much less precise than tomography, but it is surprisingly robust to its inherent bias, which introduces an unavoidable error in the reconstruction. In addition to studying DSM and proposing a method to estimate such bias from the experimental data, we show that the number of DSM measurements can be optimized and that the dimensionality of the DSM pointer is irrelevant: Both finite- and infinite-dimensional pointers provide comparable reconstructions.

I use a time-dependent Lagrangian formalism and a variational trial function to study the dynamics of a two-component vortex in a spin-orbit-coupled Bose-Einstein condensate (BEC). For a single-component BEC, various experiments have validated this theoretical approach, for example a thermal quench that yields a quantized vortex in roughly 25% of trials [Freilich et al., Science 329, 1182 (2010)]. To be definite, I assume the specific spin-orbit form used by Lin and coworkers [Nature (London) 462, 628 (2009); Nature (London) 471, 83 (2011)] in recent NIST experiments, which introduces a spatial asymmetry because of the external Raman laser beams. I here generalize this formalism to include a two-component order parameter that has quantized circulation in each component but not necessarily with the same circulation. For example, a singly quantized vortex in just one component yields a BEC analog of the half-quantized vortex familiar in ${}^3$He-A and in $p$-wave chiral superconductors. This and other unusual two-component vortices have both periodic trajectories and unbounded trajectories that leave the condensate, depending on the initial conditions. The optimized phase of the order parameter induces a term in the particle current that cancels the contribution from the vector potential, leaving pure circulating current around the vortex.

We propose a scheme to obtain stable nonlinear optical pulses and realize their storage and retrieval in an ultracold ladder-type three-level atomic gas via electromagnetically induced transparency. Based on Maxwell-Bloch equations we derive a nonlinear equation governing the evolution of the probe-field envelope and show that optical solitons with an ultraslow propagating velocity and extremely low generation power can be created in the system. Furthermore, we demonstrate that such ultraslow optical solitons can be stored and retrieved by switching a control field off and on. Due to the balance between dispersion and nonlinearity, the ultraslow optical solitons are robust during propagation, and hence their storage and retrieval are more desirable than those of linear optical pulses. This raises the possibility of realizing the storage and retrieval of light and quantum information by using solitonic pulses.

We propose and analyze the performance of a technique to generate mode and polarization hyperentangled photons in monolithic semiconductor waveguides using two concurrent type-II spontaneous parametric down-conversion (SPDC) processes. These two SPDC processes are achieved by waveguide engineering which allows for simultaneous modal phase matching with the pump beam in a higher-order mode. Paired photons generated in each process are cross polarized and guided by different guiding mechanisms, which produces entanglement in both polarization and spatial mode. Theoretical analysis shows that the output quantum state has a high quality of hyperentanglement by spectral filtering with a bandwidth of a few nanometers, while off-chip compensation is not needed. This technique offers a path to realize an electrically pumped hyperentangled photon source.

It has long been known that a free electron in an intense plane-wave field has a mass shell that differs from the usual free-electron mass shell, with a form that implies that an intensity-dependent increase in mass occurs. It has been an attractive but elusive goal to observe this mass shift. Many schemes have been proposed by which a definitive measurement might be made, and some claims of success exist, but these tests are not conclusive. It is shown here that the intense-field mass shell is not the result of a change in mass. Rather, it is a consequence of the potential energy that a charged particle must possess in the presence of a plane-wave field. When the effects of this potential are incorporated in a properly covariant form, the mass shift no longer appears and kinematic relations are conventional. If the plane-wave pulse is sufficiently long to allow the electron to exit the field adiabatically, then there is no alteration at all of the mass shell expression. Other aspects of the role played by a ponderomotive 4-potential are examined. It is also shown that the putative “relativistic mass” of the electron is illusory when confronted with covariance requirements. Both “mass increases” of the free electron are thereby nullified by fundamental principles.

We propose and experimentally investigate a scheme for narrow-line cooling of KRb molecules in the rovibrational ground state. We show that the spin-forbidden $X{}^1{\Sigma }^{+}\to b{}^3{\Pi }_{0^{+}}$ transition of KRb is well suited for realizing narrow-line laser cooling of molecules because it has highly diagonal Franck-Condon factors and a narrow line width. To confirm the prediction, we performed optical and microwave spectroscopy of ultracold ${}^{41}$K${}^{87}$Rb molecules, and determined the line width [$2\pi \times$ 4.9(4) kHz] and Franck-Condon factors for the $X{}^1{\Sigma }^{+}(v^{\prime \prime }=0)\to b{}^3{\Pi }_{0^{+}}(v^{\prime }=0)$ transition [0.9474(1)]. This result opens the door towards all-optical production of polar molecules at sub-microkelvin temperatures.