The nonlinear absorption process and associated phase shift in coupled optical cavities are studied experimentally by observing optical resonance properties. In the coupled cavity configuration, two optical cavities, one for a fundamental beam and the other for a second-harmonic (SH) beam, are coupled by a nonlinear crystal for the second-harmonic generation (SHG). The cavity for the SH beam effectively extends the nonlinear crystal length so that the frequency-conversion efficiency of the SHG, which is proportional to the square of the crystal length, is enhanced. In the observation, power reduction of the fundamental beam at resonance is observed as a small dip in the resonance curve. According to a model calculation, it is found that this power reduction is caused by blue-induced infrared absorption.

In traditional Hanbury Brown–Twiss (HBT) schemes, thermal intensity-intensity correlations (IICs) are phase insensitive. Here we propose a modified HBT scheme with phase conjugation to demonstrate phase-sensitive and nonfactorizable features of thermal IIC speckles. It shows that the novel phase-sensitive features originate from the correlation between the original and phase-conjugated thermal light. Our numerical simulation confirms the possibility of experimental realization, even for the cases of the imperfect phase conjugation. Unlike two-photon speckles, our scheme uses thermal light sources, not the entangled two-photon sources. Our result provides deeper insight into thermal correlations and may lead to significant applications in imaging and speckle technologies.

We propose a family of local $\mathcal{PT}$-symmetric photonic lattices with transverse refraction index gradient $\omega$, where the emergence of stable Bloch-Zener oscillations are controlled by the interplay of $\omega$ with the degree of non-Hermiticity $\gamma$ of the lattice. In the exact $\mathcal{PT}$-symmetric phase we identify a condition between $\omega$ and $\gamma$ for which a wave-packet self-imaging together with a cascade of splittings and giant recombinations occurs at various propagation distances. The giant wave-packet recombination is further enhanced by introducing local impurities.

We report the theoretical prediction and experimental observation of averaging of stochastic events with an equivalent result of calculating the arithmetic mean (or sum) of a rational number of realizations of the process under test, not necessarily limited to an integer record of realizations, as discrete statistical theory dictates. This concept is enabled by a passive amplification process, induced by self-imaging (Talbot) effects. In the specific implementation reported here, a combined spectral-temporal Talbot operation is shown to achieve undistorted, lossless repetition-rate division of a periodic train of noisy waveforms by a rational factor, leading to local amplification, and the associated averaging process, by the fractional rate-division factor.

We introduce a conceptually simple and experimentally feasible method to realize and detect photonic topological Chern insulators with a one-dimensional circuit quantum electrodynamics lattice. By periodically modulating the couplings in this lattice, we show that this one-dimensional model can be mapped into a two-dimensional Chern insulator model. In addition to allowing the study of photonic Chern insulators, this approach also provides a natural platform to realize experimentally Laughlin's pumping argument. Remarkably, based on the scattering theory of topological insulators and input-output formalism, we find that both the photonic edge state and topological invariant can be unambiguously probed with a simple dissipative few-resonator circuit-QED network.

We analyze the role of the dynamical Casimir effect as a resource for quantum technologies, such as quantum cryptography and quantum metrology. In particular, we consider the generation of Einstein-Podolsky-Rosen steering and Gaussian interferometric power, two useful forms of asymmetric quantum correlations, in superconducting waveguides modulated by superconducting quantum interferometric devices. We show that while a certain value of squeezing is required to overcome thermal noise and give rise to steering, any nonzero squeezing produces interferometric power which in fact increases with thermal noise.

We establish a direct connection of quantum Markovianity of an open system to its classical counterpart by generalizing the criterion based on the information flow. Here the flow is characterized by the time evolution of Helstrom matrices, given by the weighted difference of statistical operators, under the action of the quantum dynamical map. It turns out that the introduced criterion is equivalent to $P$ divisibility of a quantum process, namely, divisibility in terms of positive maps, which provides a direct connection to classical Markovian stochastic processes. Moreover, it is shown that mathematical representations similar to those found for the original trace-distance-based measure hold true for the associated generalized measure for quantum non-Markovianity. That is, we prove orthogonality of optimal states showing a maximal information backflow and establish a local and universal representation of the measure. We illustrate some properties of the generalized criterion by means of examples.

Whereas in standard quantum-state tomography one estimates an unknown state by performing various measurements with known devices, and whereas in detector tomography one estimates the positive-operator-valued-measurement elements of a measurement device by subjecting to it various known states, we consider here the case of SPAM (state preparation and measurement) tomography where neither the states nor the measurement device are assumed known. For $d$-dimensional systems measured by $d$-outcome detectors, we find there are at most $d^2(d^2-1)$ “gauge” parameters that can never be determined by any such experiment, irrespective of the number of unknown states and unknown devices. For the case $d=2$ we find gauge-invariant quantities that can be accessed directly experimentally and that can be used to detect and describe SPAM errors. In particular, we identify conditions whose violations detect the presence of correlations between SPAM errors. From the perspective of SPAM tomography, standard quantum-state tomography and detector tomography are protocols that fix the gauge parameters through the assumption that some set of fiducial measurements is known or that some set of fiducial states is known, respectively.

A discrete time quantum walk on the star network is considered, on which the walker has a waiting probability at any time step and for any of the $N$ nodes. This contrasts with a previous continuous time analysis, in which the walker in any of the $N-1$ leaf nodes is forced to jump back to the central hub. The model amounts to considering two coin operators, one for the hub (with $N$ possible states) and another one for all leaf nodes (with two possible states). The solution depends on $N$ and $\theta$, an angle gauging the action of the coin operator on the leaf nodes. Periodic solutions are identified, which can be represented as superposition of large-period branches, sharing a relative small number of shapes and displaced by a regular interval. It is shown that the large period is very sensitive to the choice of $N$ and $\theta$. The possibility of experimental applications of this property is briefly mentioned.

The logic Bell-state which encodes many physical qubits in a logic qubit has great application potential in the future quantum communication field, for it is robust to the decoherence in a noisy environment. In this paper, we propose a complete logic Bell-state analysis (LBSA) with the help of the auxiliary single atoms trapped in the low-quality cavity. We construct the parity-check measurement gate based on the photonic Faraday rotation effect and complete the task combined with the Hadamard operation and single-qubit measurement. The number of physical qubits encoded in each logic qubit does not affect the analysis. We also discuss the application of this LBSA in the fields of quantum teleportation and logic-qubit entanglement swapping. Our LBSA protocol may have practical application in future long-distance quantum communication.

Participator resonant Auger decay spectra populating the $X, A, B$, and $C$ states of ${\mathrm{CO}}_2{}^{+}$ are recorded with angular and vibrational resolution for selected photon energies in the vicinity of the C $1s\to {\pi }^{*}$ resonance of ${\mathrm{CO}}_2$ using a narrow photon bandwidth and a high-resolution electron spectrometer. The measured electron spectra and the corresponding angular distribution parameters exhibit significant changes as functions of the photon energy across the resonance and with respect to the vibrational sublevels of a final ionic state. The measured spectra are interpreted by ab initio electronic structure and nuclear dynamics calculations which attribute observed variations to the effects of lifetime vibrational interference and of electronic state interference between the direct ionization amplitude and the resonant amplitudes for the excitation and decay of two overlapping resonant states of different symmetry. The present results provide deeper insight into the femtosecond relaxation dynamics of the core-excited ${\mathrm{CO}}_2$, which is not achievable with lower resolution, angle-averaged measurements.

The magic wavelength for an optical lattice for hydrogen atoms that cancels the lowest order ac Stark shift of the $1S\text{−}2S$ transition is calculated to be 513 nm. The magnitudes of the ac Stark shift $\mathrm{\Delta }E=-119$ $\text{Hz}/(\text{kW}/{\mathrm{cm}}^2)$ and the slope $d\mathrm{\Delta }E/d\nu =-2.77$ $\text{Hz}/(\text{GHz} \text{kW}/{\mathrm{cm}}^2)$ at the magic wavelength suggest that a stable and narrow-line-width trapping laser is necessary to achieve a deep enough optical lattice to confine hydrogen atoms in a way that gives a small enough light shift for the precision spectroscopy of the $1S\text{−}2S$ transition.

We calculated the spectra of the first six members of the Mg-like isoelectronic sequence using different approximations. The most accurate results were obtained with the configuration-interaction+all-order method (CI+AO), which provided relative accuracy for transition energies on the level of 0.1% or better. On this level of accuracy, the Breit and QED corrections become important for systems with a nuclear charge of $Z\gtrsim 20$. The retardation part of the Breit interaction and QED corrections for the partial waves with $l\ne 0$ are still too small to be significant.

Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet et al., Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by $28.9\mathrm{MeV}{\mathrm{u}}^{-1}\mathrm{P}{\mathrm{b}}^{56+}$ ions, and laser-generated carbon ion beams of 0.045 to $0.5\mathrm{MeV}{\mathrm{u}}^{-1}$, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the “next-generation” accelerators or laser facilities.

By photoionizing hyperfine (HF) levels of the Cs state $6{}^2{P}_{3/2}$ in a slow and cold atom beam, we find how their population depends on the excitation laser power. The long time (around $180\mu \mathrm{s})$ spent by the slow atoms inside the resonant laser beam is large enough to enable exploration of a unique atom-light interaction regime heavily affected by time-dependent optical pumping. We demonstrate that, under such conditions, the onset of nonlinear effects in the population dynamics and optical pumping occurs at excitation laser intensities much smaller than the conventional respective saturation values. The evolution of population within the HF structure is calculated by numerical integration of the multilevel optical Bloch equations. The agreement between numerical results and experiment outcomes is excellent. All main features in the experimental findings are explained by the occurrence of “dark” and “bright” resonances leading to power-dependent branching coefficients.

We study the sensitive detection of a weak static magnetic field via Faraday rotation induced by an ensemble of spins in a bimodal degenerate microwave cavity. We determine the limit of the resolution for the sensitivity of the magnetometry achieved using either single-photon or multiphoton inputs. For the case of a microwave cavity containing an ensemble of nitrogen-vacancy defects in diamond, we obtain a magnetometry sensitivity exceeding $5.2\mathrm{n}\mathrm{T}/\sqrt{\mathrm{Hz}}$ utilizing a single-photon probe field, while for a multiphoton input we achieve a subfemtotesla sensitivity using a coherent-probe microwave field with power of $P_{\text{in}}=1\mathrm{n}\mathrm{W}$.

We investigate the fast transport of an atom or a packet of atoms by different kinds of nonharmonic traps including power-law traps. The study is based on the reverse-engineering method. Exact results are obtained and applied to design robust transport protocols. The optimization of the transport trajectory is performed with classical trajectories and remains valid for the transport of a wave packet.

Using a three-dimensional semiclassical model that incorporates tunneling and Coulomb field effect, we investigate photoelectron angular distributions from single ionization of atoms in intense elliptically polarized laser fields. We have studied the photoelectron angular distributions of the first and second recollisions by tracing the respective tunnel-ionized electron trajectories. Through studying the instant of ionization and recollision with respect to the laser phase, the relative contributions of the first recollision and second recollision on two-dimensional photoelectron angular distributions have been analyzed, respectively. We find that the relative contribution of the later recollision increases with the ellipticity. The electron recollision favors the later recollision trajectory at larger field ellipticity and the later recollision trajectory contributes dominantly to the yield of the high-energy photoelectrons. We have analyzed the dependence of high-energy photoelectrons on the initial momentum and the ionization phase with respect to the laser field.

Because of the inherent coupling, the influence from the phonon bath on the coherent energy exchange between a quantum-dot (QD) two-state system (TSS) and a resonant optical mode is a twofold action. One action is the influence on the construction of the coherence, and the other is on the constructed coherence. The latter has been extensively studied by the master-equation approach, whereas the former has been ignored so far. In the present paper, the influence from the phonon bath on the construction of the coherence is studied by using the small-polaron theory. It is found that in the presence of phonon coupling, the construction of the coherence depends on the state evolution of the phonon bath during the energy exchange. The coherence construction probability is calculated and found to be a decreasing function of both temperature and coupling strength. The spectrum including the twofold decoherence effect is calculated and the obtained result can help one to understand some peculiar observations in the photoluminescence spectrum of a QD TSS system, including the additional cavity line in the strong-coupling regime and the additional coherent scattering in the case of the Mollow triplet.

The outstanding progress in nanostructure fabrication and cooling technologies allows what was unthinkable a few decades ago: bringing single-mode mechanical vibrations to the quantum regime. The coupling between photon and phonon excitations is a natural source of nonclassical states of light and mechanical vibrations, and its study within the field of cavity optomechanics is developing lightning fast. Photonic crystal cavities are highly integrable architectures that have demonstrated the strongest optomechanical coupling to date and should therefore play a central role for such hybrid quantum-state engineering. In this context, we propose a realistic heralding protocol for the on-chip preparation of remotely entangled mechanical states, relying on the state-of-the-art optomechanical parameters of a silicon-based nanobeam structure. Pulsed sideband excitation of a Stokes process, combined with single-photon detection, allows the writing of a delocalized mechanical Bell state in the system, signatures of which can then be read out in the optical field. A measure of entanglement in this protocol is provided by the visibility of a characteristic quantum interference pattern in the emitted light.