The physics involved in the fundamental conservation equations of the spin and orbital angular momenta leads to new laws and phenomena that are disclosed here. To this end, we analyze the scattering of an electromagnetic wave field by the canonical system constituted by a small particle, which is assumed to be dipolar in the wide sense. Specifically, under quite general conditions these laws lead to understanding the contribution and weight of each of those angular momenta to the electromagnetic torque exerted by the field on the object, which is shown to consist of an extinction and a scattering, or recoil, part. This leads to an interpretation of its effect different than that taken up until now by many theoretical and experimental works, and implies that a part of the recoil torque cancels the usually called intrinsic torque, which was often considered to be responsible for the particle spinning. In addition, we obtain the contribution of the spatial structure of the wave to this torque, unknown to this date, showing its effect in the orbiting of the object, and demonstrating that it often leads to a negative torque on a single particle, i.e., opposite to the incident helicity, producing an orbital motion contrary to its spinning. Furthermore, we establish a decomposition of the electromagnetic torque into conservative and nonconservative components in which the helicity and the spin angular momentum play a role analogous to the energy and its flux for electromagnetic forces. These phenomena are illustrated with examples of beams, also showing the difficulties of some paraxial formulations whose fields do not hold the transversality condition.

Open Fabry-Perot microcavities represent a promising route for achieving a quantum electrodynamics (cavity-QED) platform with diamond-based emitters. In particular, they offer the opportunity to introduce high-purity, minimally fabricated material into a tunable, high quality factor optical resonator. Here, we demonstrate a fiber-based microcavity incorporating a thick ($>10\mu \text{m}$) diamond membrane with a finesse of 17 000, corresponding to a quality factor $Q\sim {10}^6$. Such minimally fabricated thick samples can contain optically stable emitters similar to those found in bulk diamond. We observe modified microcavity spectra in the presence of the membrane, and we develop analytic and numerical models to describe the effect of the membrane on cavity modes, including loss and coupling to higher-order transverse modes. We estimate that a Purcell enhancement of approximately 20 should be possible for emitters within the diamond in this device, and we provide evidence that better diamond surface treatments and mirror coatings could increase this value to 200 in a realistic system.

We study the problem of quantum state transfer from the optical cavity field to the microwave resonator in cavity electro-optic modulators. We give the analytical expression of the transfer fidelities of Gaussian states and some non-Gaussian states. We discuss the influences of the electro-optic coupling strength and the temperature of the environment on the fidelity of the state transfer. We show that it is possible to achieve high transfer fidelity for Gaussian states and some non-Gaussian states. We find that the transfer fidelity of the non-Gaussian state produced by performing the photon-addition operation, the photon-subtraction operation, or the photon-subtraction-then-addition operation on a Gaussian state is lower than that of the corresponding Gaussian state.

We show that in the protocol proposed in Phys. Rev. A 91, 042306 (2015), a dishonest sender can always ensure with certainty that the receiver fails to get the secret message. Thus the security requirement of oblivious transfer is not met. This security problem also makes the protocol unsuitable for serving as a building block for 1-out-of-2 oblivious transfer.

In the Comment the author states that the proposed all-or-nothing oblivious transfer (OT) protocol in our paper is insecure against a dishonest Alice and, as a corollary, derives an attack to Crépeau's construction of 1-out-of-2 OT. The security criterion used in the Comment is indeed stronger than the one used in our paper. However, we argue that the criterion used in our paper is in the spirit of the original idea of the OT protocol proposed by Rabin. Moreover, a protocol that satisfies the criterion in our paper can be used to construct useful multiparty protocols. Finally, the protocol in our paper can be used, together with a secure bit commitment scheme, to construct a 1-out-of-2 OT secure against malicious Alice, achieving the security requirement considered in the Comment.

By combining a parameterized Hermitian matrix, the realignment matrix of the bipartite density matrix, and the vectorization of its reduced density matrices, we present a family of separability criteria which are stronger than the computable cross-norm or realignment (CCNR) criterion. With linear contraction methods, the proposed criteria can be used to detect the multipartite entangled states that are biseparable under any bipartite partitions. Moreover, we show by examples that the presented multipartite separability criteria can be more efficient than the corresponding multipartite realignment criterion based on CCNR, multipartite correlation tensor criterion, and multipartite covariance matrix criterion.

The nuclear-spin optical rotation (NSOR) effect, which has potential applications in correlated nuclear-spin-resonance optical spectroscopy, has previously been explored experimentally and theoretically in liquid Xe. Calculations of the Xe NSOR constant are very challenging because the result is sensitive to correlations, relativistic effects, and the choice of basis, with strong cancellation between contributions from lowest and remaining states. The relativistic configuration-interaction many-body-theory approach, presented here, is promising because this approach has been successful in predicting various properties of noble-gas atoms, such as energies, oscillator strengths (OSs), Verdet constants, and photoionization cross sections. However, correlations become stronger along the sequence of noble-gas atoms and the theoretical accuracy in Xe is not as high as, for example, in neon and argon. To improve the accuracy of the Xe Verdet and NSOR constants, which are calculated as explicit sums over the excited states, theoretical values for the several lowest levels are replaced with empirical values of energies, OSs, and hyperfine structure constants. We found that the Xe Verdet constant is in excellent agreement with accurate measurements. To take into account liquid effects, empirical data for energy shifts were also used to correct the NSOR constant. The resulting Xe NSOR constant is in a good agreement with experiment, although the liquid-state effect is treated quite approximately.

We calculate interspecies Rydberg-Rydberg interaction strengths for the heavy alkali metals Rb and Cs. The presence of strong Förster resonances makes interspecies coupling a promising approach for long-range entanglement generation. We also provide an overview of the strongest Förster resonances for Rb-Rb and Cs-Cs using different principal quantum numbers for the two atoms. We show how interspecies coupling can be used for high fidelity quantum nondemolition state measurements with low cross-talk in qubit arrays.

We investigate the applicability of norm-conserving pseudopotentials to intense laser-matter interactions by performing time-dependent density functional theory simulations with an all-electron potential and with norm-conserving pseudopotentials. We find pseudopotentials to be reliable for the simulation of above-threshold ionization over a broad range of laser intensities both for the total ionization probability and the photoelectron energy spectrum. For the simulation of high-order-harmonic generation, pseudopotentials are shown to be applicable for lower-order harmonics in the spectral range in which the one-photon recombination dipole-matrix element can be recovered by the pseudopotential calculation.

We investigate the finite-temperature properties of the one-dimensional two-component Bose gas (2CBG) with repulsive contact interaction in a harmonic trap. Making use of a lattice embedding for the 2CBG and the quantum transfer matrix, we derive a system of two nonlinear integral equations characterizing the thermodynamics of the uniform system for all values of the relevant parameters: temperature, strength of the interaction, chemical potential, and magnetic field. This system allows for an easy numerical implementation in stark contrast with the infinite number of equations obtained by employing the thermodynamic Bethe ansatz. We use this exact solution coupled with the local density approximation to compute the density profiles and local density correlation function of the inhomogeneous gas for a wide range of coupling strengths and temperatures. Our results show that the polarization in the center of the trap influences heavily the local correlator especially in the experimentally accessible Tonks-Girardeau regime.

The recent analysis, based on the mean-field approximation (MFA), has predicted that the critical quantum collapse of the bosonic wave function, pulled to the center by the inverse-square potential in the three-dimensional space, is suppressed by the repulsive cubic nonlinearity in the bosonic gas, the collapsing ground state being replaced by a regular one. We demonstrate that a similar stabilization acts in a quantum many-body system, beyond the MFA. While the collapse remains possible, repulsive two-particle interactions give rise to a metastable gaseous state, which is separated by a potential barrier from the collapsing regime. The stability of this state improves with the increase of the number of particles. The results are produced by calculations of the variational energy, with the help of the Monte Carlo method.

It is shown that sufficiently large periodic modulations in the coefficients of a nonlinear Schrödinger equation can drastically impact the spatial shape of the Peregrine soliton solutions: they can develop multiple compression points of the same amplitude, rather than only a single one, as in the spatially homogeneous focusing nonlinear Schrödinger equation. The additional compression points are generated in pairs forming a comblike structure. The number of additional pairs depends on the amplitude of the modulation but not on its wavelength, which controls their separation distance. The dynamics and characteristics of these generalized Peregrine solitons are analytically described in the case of a completely integrable modulation. A numerical investigation shows that their main properties persist in nonintegrable situations, where no exact analytical expression of the generalized Peregrine soliton is available. Our predictions are in good agreement with numerical findings for an interesting specific case of an experimentally realizable periodically dispersion modulated photonic crystal fiber. Our results therefore pave the way for the experimental control and manipulation of the formation of generalized Peregrine rogue waves in the wide class of physical systems modeled by the nonlinear Schrödinger equation.

We demonstrate an observation of zero to $\pi$ continuously controllable cross-phase-modulation based on an $N$-type electromagnetically-induced-transparency scheme in a room-temperature ${}^{87}\mathrm{Rb}$ vapor. We theoretically and experimentally show that the signal field acquires a $\pi$ phase shift compared with the reference light in the presence of the phase-control field. Using the method of the optical Mach-Zehnder interferometer, we demonstrate that a zero to $\pi$ continuously controllable phase gate can be built by modulating the phase-control field. In addition, our theoretical calculation agrees well with the experimental observation, and the results presented in this work hold potential applications for the orthogonal polarization or vector gate in quantum information processing.

In this paper we develop an analytical method for spatial shaping of diffraction- and attenuation-resistant beams carrying finite power in absorbing media. This can be achieved through suitable discrete superposition of Bessel-Gauss beams, where the approach can be seen as an extension of the frozen wave method, without the inconvenience of infinite power flux and spatial periodicity of the resulting beams.

We study relaxation oscillations in a semiconductor quantum-dot laser using the electron-hole asymmetry model [M. Abusaa et al., Phys. Rev. A 87, 063827 (2013)]. Two relaxation oscillations are found at simultaneous lasing in the ground and excited states in a wide range of quantum-dot laser parameters. One of these two relaxation oscillations is close to in-phase oscillation and the other may be antiphase oscillation at certain parameters.

In this article, we theoretically study the quantum statistical properties of the light transmitted through or reflected from an optical cavity, filled by an atomic medium with strong optical nonlinearity induced by Rydberg-Rydberg van der Waals interactions. Atoms are driven on a two-photon transition from their ground state to a Rydberg level via an intermediate state by the combination of a weak signal field and a strong control beam. By using a perturbative approach, we get analytic results which remain valid in the regime of weak feeding fields, even when the intermediate state becomes resonant thus generalizing our previous results. We can thus investigate quantitatively new features associated with the resonant behavior of the system. We also propose an effective nonlinear three-boson model of the system which, in addition to leading to the same analytic results as the original problem, sheds light on the physical processes at work in the system.

We consider the dynamics of intracavity electromagnetically induced transparency (EIT) in an ensemble of strongly interacting Rydberg atoms. By combining the advantage of variable cavity lifetimes with intracavity EIT and strongly interacting Rydberg dark-state polaritons, we show that such an intracavity EIT system could exhibit a very strong photon blockade effect.

The Wigner function is a useful tool for exploring the transition between quantum and classical dynamics, as well as the behavior of quantum chaotic systems. Evolving the Wigner function for open systems has proved challenging, however; a variety of methods have been devised but suffer from being cumbersome and resource intensive. Here we present an efficient fast-Fourier method for evolving the Wigner function that has a complexity of $O(NlogN)$ where $N$ is the size of the array storing the Wigner function. The efficiency, stability, and simplicity of this method allows us to simulate open-system dynamics previously thought to be prohibitively expensive. As a demonstration we simulate the dynamics of both one-particle and two-particle systems under various environmental interactions. For a single particle we also compare the resulting evolution with that of the classical Fokker–Planck and Koopman–von Neumann equations and show that the environmental interactions induce the quantum-to-classical transition as expected. In the case of two interacting particles we show that an environment interacting with one of the particles leads to the loss of coherence of the other.

The Kapitza-Dirac effect, which refers to electron scattering at standing light waves, is studied in the Bragg regime with counterpropagating elliptically polarized electromagnetic waves with the same intensity, wavelength, and degree of polarization for two different setups. In the first setup, where the electric-field components of the counterpropagating waves have the same sense of rotation, we find distinct spin effects. The spins of the scattered electrons and of the nonscattered electrons, respectively, precess with a frequency that is of the order of the Bragg-reflection Rabi frequency. When the electric-field components of the counterpropagating waves have an opposite sense of rotation, which is the second considered setup, the standing wave has linear polarization, and no spin effects can be observed. Our results are based on numerical solutions of the time-dependent Dirac equation and the analytical solution of a relativistic Pauli equation, which accounts for the leading relativistic effects.