In this paper, we investigate the counterintuitive dispersion effect associated with the poles and zeros of reflection and transmission functions in an Otto configuration when a surface plasmon resonance is excited. We show that the zeros and/or poles in the reflection and transmission functions may move into the upper-half complex-frequency plane (CFP), and these locations of the zeros and poles determine the dispersion properties of the whole structures (i.e., the frequency-dependent change of both reflected and transmitted phases). Meanwhile, we demonstrate various dispersion effects (both normal and abnormal) related to the changes of the poles and zeros in both reflection and transmission functions when considering the properties of metal substrates. For a realistic metal substrate in an Otto structure, there are the optimal thickness and incident angle, which correspond to the transitions of the zeros in the reflection function from the upper-half to lower-half CFP. These properties may be helpful to manipulate light propagation in optical devices.

The behavior of general nonclassical two-mode Gaussian states at a beam splitter is investigated. Single-mode nonclassicality as well as two-mode entanglement of both input and output states are analyzed suggesting their suitable quantifiers. These quantifiers are derived from local and global invariants of linear unitary two-mode transformations such that the sum of input (or output) local nonclassicality measures and entanglement measure gives a global invariant. This invariant quantifies the global nonclassicality resource. Mutual transformations of local nonclassicalities and entanglement induced by the beam splitter are analyzed considering incident noisy twin beams, single-mode noisy squeezed vacuum states, and states encompassing both squeezed states and twin beams. A rich tapestry of interesting nonclassical output states is predicted.

In this article, we present an application of optomechanical cavity for the absolute rotation detection. The optomechanical cavity is arranged in a Michelson interferometer in such a way that the classical centrifugal force due to rotation changes the length of the optomechanical cavity. The change in the cavity length induces a shift in the frequency of the cavity mode. The phase shift corresponding to the frequency shift in the cavity mode is measured at the interferometer output to estimate the angular velocity of absolute rotation. We derived an analytic expression to estimate the minimum detectable rotation rate in our scheme for a given optomechanical cavity. Temperature dependence of the rotation detection sensitivity is studied.

Arrays of coupled photonic cavities driven by external lasers represent a highly controllable setup to explore photonic transport. In this paper we address (quasi)-steady states of this system that exhibit photonic currents introduced by engineering driving and dissipation. We investigate two approaches: in the first one, photonic currents arise as a consequence of a phase difference of applied lasers and, in the second one, photons are injected locally and currents develop as they redistribute over the lattice. Effects of interactions are taken into account within a mean-field framework. In the first approach, we find that the current exhibits a resonant behavior with respect to the driving frequency. Weak interactions shift the resonant frequency toward higher values, while in the strongly interacting regime in our mean-field treatment the effect stems from multiphotonic resonances of a single driven cavity. For the second approach, we show that the overall lattice current can be controlled by incorporating few cavities with stronger dissipation rates into the system. These cavities serve as sinks for photonic currents and their effect is maximal at the onset of quantum Zeno dynamics.

Entanglement-assisted quantum communication employs preshared entanglement between sender and receiver as a resource. We apply the same framework to quantum metrology, introducing shared entanglement between the probe and the ancilla in the preparation stage and allowing entangling operations at the measurement stage, i.e., using some entangled ancillary system that does not interact with the system to be sampled. This is known to be useless in the noiseless case, but was recently shown to be useful in the presence of noise [R. Demkowicz-Dobrzanski and L. Maccone, Phys. Rev. Lett. 113, 250801 (2014); W. Dür, M. Skotiniotis, F. Fröwis, and B. Kraus, Phys. Rev. Lett. 112, 080801 (2014); E. M. Kessler, I. Lovchinsky, A. O. Sushkov, and M. D. Lukin, Phys. Rev. Lett. 112, 150802 (2014); R. Demkowicz-Dobrzański and J. Kolodynski, New J. Phys. 15, 073043 (2013)]. Here we detail how and when it can be of use. For example, surprisingly it is useful when two channels are randomly alternated, for both of which ancillas do not help (depolarizing). We show that it is useful for all levels of noise for many noise models and propose a simple optical experiment to test these results.

We analyze the Stern-Gerlach experiment in phase space with the help of the matrix Wigner function, which includes the spin degree of freedom. Such analysis allows for an intuitive visualization of the quantum dynamics of the device. We include the interaction with the environment, as described by the Caldeira-Leggett model. The diagonal terms of the matrix provide us with information about the two components of the state that arise from interaction with the magnetic field gradient. In particular, from the marginals of these components, we obtain an analytical formula for the position and momentum probability distributions in the presence of decoherence that shows a diffusive behavior for large values of the decoherence parameter. These features limit the dynamics of the present model. We also observe the decay of the nondiagonal terms with time and use this fact to quantify the amount of decoherence from the norm of those terms in phase space. From here, we can define a decoherence time scale, which differs from previous results that make use of the same model. We analyze a typical experiment and show that, for that setup, the decoherence time is much smaller than the characteristic time scale for the separation of the two beams, implying that they can be described as an incoherent mixture of atoms traveling in the up and down directions with opposite values of the spin projection. Therefore, entanglement is quickly destroyed in the setup we analyzed.

An optical procedure in the context of continuous variables to verify bipartite entanglement without destroying both systems and their entanglement is proposed. To perform the nondestructive verification of entanglement, the method relies on beam-splitter and quantum nondemolition (QND) interactions of the signal modes with two ancillary probe modes. The probe modes are measured by homodyne detections, and the obtained information is used to feed forward modulation of signal modes, concluding the procedure. Characterizing the method by figures of merit used in QND processes, we can establish the conditions for an effectively quantum scheme. Based on such conditions, it is shown that the classical information acquired from the homodyne detections of probe modes is sufficient to verify the entanglement of the output signal modes. The processing impact due to added noise on the output entanglement is assessed in the case of Gaussian modes.

We study the generation of transient entanglement induced by a single-photon Gaussian wave packet in multiatom bidirectional-waveguide QED. In particular, we investigate the effect of increasing the number of atoms on the average pairwise entanglement. We demonstrate, by selecting smaller decay rates and in chiral-waveguide settings, that both entanglement survival times and maximum generated entanglement can be increased by at least a factor of $\sim 3/2$, independent of the number of atoms. In addition, we analyze the influence of detuning and delays on the robustness of the generated entanglement. There are potential applications of our results in entanglement-based multiqubit quantum networks.

Laser-field-free three-dimensional orientation, corresponding to the complete control of spatial directions of asymmetric top molecules, is achieved with combined weak electrostatic and elliptically polarized laser fields with an 8-ns turnon and a 150-fs turnoff, which is shaped by a plasma shutter. Rotationally cold 3,4-dibromothiophene molecules are used as a sample, and their lower-lying rotational states are selected by a molecular deflector to increase the degrees of orientation. After the rapid turnoff of the pump pulse, higher degrees of orientation are maintained for 5–10 ps, which is long enough for various applications including electronic stereodynamics in molecules with femtosecond pulses.

A study of the $\lambda$ and $N$ atomic configurations under dipolar interaction with two modes of electromagnetic radiation is presented. The corresponding quantum phase diagrams are obtained by means of a variational procedure. Both configurations exhibit normal and collective (super-radiant) regimes. While the latter in the $\lambda$ configuration divides itself into two subregions, corresponding to each of the modes, that in the $N$ configuration may be divided into two or three subregions depending on whether the field modes divide the atomic system into two separate subsystems or not. Our variational procedure compares well with the exact quantum solution. The properties of the relevant field and matter observables are obtained.

We propose a set of subradiant states which can be prepared and detected in a one-dimensional optical lattice. We find that the decay rates are highly dependent on the spatial phases imprinted on the atomic chain, which allows systematic investigations of the subradiance in fluorescence experiments. The time evolution of these states can have a long decay time where up to 100 ms of lifetime is predicted for 100 atoms. They can also show decayed Rabi-like oscillations with a beating frequency determined by the difference of the cooperative Lamb shift in the subspace. Experimental requirements are also discussed for practical implementation of the subradiant states. Our proposal provides a scheme for quantum storage of photons in arrays of two-level atoms through the preparation and detection of subradiant states, which offers opportunities for quantum many-body state preparation and quantum information processing in optical lattices.

We consider a non-Hermitian generalization of the Kitaev model and study the existence of stable Majorana zero energy modes. We show that they exist in the limit of zero chemical potential even if balanced gain and loss are randomly distributed along the lattice. We show that Majorana zero modes also appear if the chemical potential is different from zero provided that not the full Hamiltonian but the non-Hermitian part of the Hamiltonian is $\mathcal{PT}$ symmetric.

Which quantum states minimize the unavoidable uncertainty arising from the noncommutativity of two observables? The immediate answer to such a question is: it depends. Due to the plethora of uncertainty measures there are many answers. Here, instead of restricting our study to a particular measure, we present plausible axioms for the set $\mathcal{F}$ of bona fide information-theoretic uncertainty functions. Then, we discuss the existence of states minimizing uncertainty with respect to all members of $\mathcal{F}$, i.e., universal minimum uncertainty states (MUSs). We prove that such states do not exist within the full state space and study the effect of classical noise on the structure of minimum uncertainty states. We present an explicit example of a qubit universal MUS that arises when purity is constrained by introducing a threshold amount of noise. For higher dimensional systems we derive several no-go results limiting the existence of noisy universal MUSs. However, we conjecture that universality may emerge in an approximate sense. We conclude by discussing connections with thermodynamics, and highlight the privileged role that nonequilibrium free energy $F_2$ plays close to equilibrium.

We present the implementation of a programmable atom-photon quantum interface, employing a single trapped ${}^{40}\mathrm{Ca}^{+}$ ion and single photons. Depending on its mode of operation, the interface serves as a bidirectional atom-photon quantum-state converter, as a source of entangled atom-photon states, or as a quantum frequency converter of single photons. The interface lends itself particularly to interfacing ions with spontaneous parametric down-conversion–based single-photon or entangled-photon-pair sources.

Accurate calculations of the nuclear recoil effect on the Lamb shift of hydrogenlike atoms are presented. Numerical results are reported for the $ns$ states with $n\le 5$ and for the $2p_{1/2}$ and $2p_{3/2}$ states. The calculations are performed to the first order in the electron-nucleus mass ratio and to all orders in the nuclear binding strength parameter $Z\alpha$ (where $Z$ is the nuclear charge number and $\alpha$ is the fine structure constant). The obtained results provide accurate predictions for the higher-order remainder beyond the known $Z\alpha$-expansion terms. In the case of hydrogen, the remainder was found to be much larger than anticipated. This result resolves the previously reported disagreement between the numerical all-order and the analytical $Z\alpha$-expansion approaches for the nuclear recoil effect on the hydrogen Lamb shift.

The virial expansion for cold two-component Fermi and Bose atomic gases is considered in the presence of a waveguide and in the vicinity of a Feshbach resonance. The interaction between atoms and the coupling with the Feshbach molecules is modeled using a quantitative separable two-channel model. The scattering phase shift in an atomic waveguide is defined. This permits us to extend the Beth-Uhlenbeck formula for the second-order virial coefficient to this inhomogeneous case.

We study the dynamics of fermions loaded in an optical lattice with a superimposed parabolic trap potential. In the recent Hamburg experiments [J. Heinze et al., Phys. Rev. Lett. 110, 085302 (2013)] on quantum simulation of photoconductivity, a modulation pulse on the optical lattice transferred part of the population of the lowest band to an excited band, leaving a hole in the particle distribution of the lowest band. The subsequent intricate dynamics of both excited particles and holes can be explained by a semiclassical approach based on the evolution of the Wigner function. Here we provide a more detailed analysis of the dynamics, taking into account the dimensionality of the system and finite-temperature effects, aiming at reproducing experimental results on longer time scales. A semiclassical wave packet is constructed more accurately than in the previous theory. As a result, semiclassical dynamics indeed reproduces experimental data and full quantum numerical calculations with a much better accuracy. In particular, the fascinating phenomenon of collapse and revival of holes is investigated in more detail. We presume that the experimental setup can be used for deeper exploration of nonlinear waves in fermionic gases.

We observe and characterize intrinsic optical bistability in a dilute Rydberg vapor. The bistability is characterized by sharp jumps between states of low and high Rydberg occupancy with jump-up and -down positions displaying hysteresis depending on the direction in which the control parameter is changed. We find that the shift in frequency of the jump point scales with the fourth power of the principal quantum number. Also, the width of the hysteresis window increases with increasing principal quantum number, before reaching a peak and then closing again. The experimental results are consistent with predictions from a simple theoretical model based on semiclassical Maxwell–Bloch equations including the effects of interaction-induced broadening and level shifts. These results provide insight into the dynamics of driven dissipative systems.