The interference between a sequence of Landau-Zener (LZ) transitions can produce Rabi oscillations (LZROs). This phenomenon is a kind of time-domain Landau-Zener-Stückelberg-Majorana (LZSM) interference. However, experimental demonstrations of this LZSM interference induced Rabi oscillation are extremely hard due to the short coherence time of the driven quantum system. Here, we study theoretically the time-domain LZSM interference between the clock transition in a one-dimensional ${}^{87}\mathrm{Sr}$ optical lattice clock (OLC) system. With the help of both the adiabatic-impulse model and Floquet numerical simulation method, the LZROs with special steplike structure are clearly found both in the fast- and slow-passage limit in the real experiment parameter regions. In addition, the dephasing effect caused by the system temperature can be suppressed with destructive interference in the slow-passage limit. Finally, we discuss the possible Bloch-Siegert shift while the pulse time is away from the half-integer and integer periods. Our work provides a clear road map to observe the LZROs on the OLC platform.

By means of a two-mode model, we show that transitions to different arrays of coexistent regimes in the phase space can be attained by rotating a double-well system, which consists of a toroidal condensate with two diametrically placed barriers. Such a configuration corresponds to the atomtronic counterpart of the well-known direct-current superconducting quantum interference device. Due to the phase gradient experimented by the on-site localized functions when the system is subject to rotation, a phase difference appears on each junction in order to satisfy the quantization of the velocity field around the torus. We demonstrate that such a phase can produce a significant change on the relative values of different types of hopping parameters. In particular, we show that within a determined rotation frequency interval a hopping parameter, usually disregarded in nonrotating systems, turns out to rule the dynamics. At the limits of such a frequency interval, bifurcations of the stationary points occur, which substantially change the phase-space portrait that describes the orbits of the macroscopic canonical conjugate variables. We analyze the emerging dynamics that combines the zero and $\pi$ Josephson modes, and evaluate the small-oscillation time periods of such orbits at the frequency range where each mode survives. All the findings predicted by the model are confirmed by Gross-Pitaevskii simulations.

We study the landscape of solutions of the coherent quantum states in a ring-shaped lattice potential in the context of ultracold atoms with an effective positive nonlinearity induced by interatomic interactions. The exact analytical solutions in the absence of lattice are used as a starting point, and the transformation of those solutions is mapped as the lattice is introduced and strengthened. This approach allows a simple classification of all the solutions into states with periods commensurate or incommensurate with the lattice period and those with or without nodes. Their origins are traced to the primary dispersion curve and the swallowtail branches of the lattice-free spectrum. The commensurate states tend to remain delocalized with increasing lattice depth, whereas the incommensurate ones may be localized. The symmetry and stability properties of the solutions are examined and correlated with branch energies. The crucial importance of rotation is highlighted by its utility in continuously transforming solutions and accessing in a finite ring with a few sites the full spectrum of nonlinear Bloch waves on an infinite lattice.

We investigate the use of programmable optical lattices for quantum simulation of Hubbard models, determining analytic expressions for the hopping and Hubbard $U$, finding that they are suitable for emulating strongly correlated systems with arbitrary structures, including those with a multiple site basis and impurities. Programmable potentials are highly flexible, with the ability to control the depth and shape of individual sites in the optical lattice dynamically. Quantum simulators of Hubbard models with (1) an arbitrary basis are required to represent many real materials of contemporary interest, (2) broken translational symmetry are needed to study impurity physics, and (3) dynamical lattices are needed to investigate strong correlations out of equilibrium. We derive analytic expressions for Hubbard Hamiltonians in programmable potential systems. We find experimental parameters for quantum simulation of Hubbard models with an arbitrary basis, concluding that programmable optical lattices are suitable for this purpose. Finally, we demonstrate how programmable optical lattices can be used for quantum simulation of ionic Hubbard models, and thus the onset of charge transfer insulating states, in parameter regimes that are currently inaccessible to experiment.

Light beams carrying orbital-angular-momentum (OAM) play an important role in optical manipulation and communication owing to their unbounded state space. However, it is still challenging to efficiently discriminate different OAM modes and their superpositions. Here we demonstrate that neural networks can be trained to recognize OAM modes with different topological charges and unknown superpositions. Using intensity images of OAM modes generated in simulations and experiments as the input data, we illustrate that our neural network has the generalization power to recognize OAM modes beyond training areas with high accuracy, whose topological charges are up to $\pm 8$ and 104 for experimental and numerical data, respectively. Moreover, the trained neural network can correctly classify and predict arbitrary superpositions of two OAM modes with random topological charges. Our machine learning approach only requires a small portion of experimental samples and significantly reduces the cost in experiments.

We present a method to obtain the first-order temporal correlation function, $g^{\left(1\right)}\left(\tau \right)$, of the light scattered by an assembly of pointlike quantum scatterers, or equivalently its spectral power distribution. This method is based on the mirror-assisted backscattering interferometric setup. The contrast of its angular fringes was already linked to the convolution of $g^{\left(1\right)}\left(\tau \right)$ for different Rabi frequencies taking into account the incoming spatial intensity profile of the probe beam, but we show here that by simply adding a half wave plate to the interferometer in a specific configuration, the fringe contrast becomes $g^{\left(1\right)}\left(\tau \right)$ of the light scattered by atoms, which are now all subjected to the same laser intensity. This method has direct application to obtaining the saturated spectrum of quantum systems. We discuss some nontrivial aspects of this interferometric setup and propose an analogy with a double Mach-Zehnder interferometer.

Quantum fluctuations in the intensity of an optical probe is noise which limits measurement precision in absorption spectroscopy. Increased probe power can offer greater precision; however, this strategy is often constrained by sample saturation. Here, we analyze measurement precision for a generalized absorption model in which we account for saturation and explore its effect on both classical and quantum probe performance. We present a classical probe-sample optimization strategy to maximize precision and find that optimal probe powers always fall within the saturation regime. We apply our optimization strategy to two examples, high-precision Doppler broadened thermometry and an absorption spectroscopy measurement of chlorophyll a. We derive a limit on the maximum precision gained from using a nonclassical probe and find a strategy capable of saturating this bound. We evaluate amplitude-squeezed light as a viable experimental probe state and find it capable of providing precision that reaches to within $>85\%$ of the ultimate quantum limit with currently available technology.

We propose a mechanism to engineer an $n$-photon blockade in a nonlinear cavity with an $n$-photon parametric drive $\lambda ({\widehat{a}}^{†n}+{\widehat{a}}^n)$. When an $n$-photon-excitation resonance condition is satisfied, the presence of $n$ photons in the cavity suppresses the absorption of the subsequent photons. To confirm the validity of this proposal, we study the $n$-photon blockade in an atom-cavity system, a Kerr-nonlinear resonator, and two-coupled Kerr-nonlinear resonators. Our results demonstrate that $n$-photon bunching and $(n+1)$-photon antibunching can be simultaneously obtained in these systems. This effect is due both to the anharmonic energy ladder and to the nature of the $n$-photon drive. To show the importance of the drive, we compare the results of the $n$-photon drive with a coherent (one-photon) drive, proving the enhancement of antibunching in the parametric-drive case. This proposal is general and can be applied to realize the $n$-photon blockade in other nonlinear systems.

Nonlinear conversions within the plasmonic structures are important for ultrafast nanophotonics; however, the impact of higher-order dispersion on nonlinear polaritonic efficiency remains unexplored. In this work, we uncover the role of higher-order dispersion and self-steepening on nonlinear surface-plasmon polaritons (NSPPs) within a coherent plasmonic interface that comprises an atomic medium doped on top of a low-loss negative-index metamaterial (NIMM) layer. This dispersion in the atomic medium–NIMM interface yields nonlinear plasmonic phase match and resonant launching of Cherenkov SPPs. We establish time-reversal and $\mathcal{PT}$ symmetry breaking for propagated NSPPs that yield asymmetric plasmonic comb excitation and anomalous plasmonic phase singularities. Our work thereby suggests a fingerprint for nonlinear plasmonic field evolution through the appearance of a Cherenkov field and develops a framework for designing a frequency selector and nanoscopic pulse shaper, which opens prospects for nonlinear nanophotonic applications.

We quantify the consequences of a private key leakage and private randomness generated during quantum key distribution. We provide simple lower bounds on the one-way distillable key after the leakage has been detected. We also show that the distributed private randomness does not drop by more than twice the number of qubits of the traced-out system. We further focus on irreducible private states, showing that their two-way distillable key is nonlockable. We then strengthen this result by referring to the idea of recovery maps. We further consider the action of a special case of side channels on some of the private states. Finally, we connect the topic of (non-)Markovian dynamics with that of hacking. In particular, we show that an invertible map is non-CP-divisible if and only if there exists a state whose the key witnessed by a particular privacy witness increases in time. This complements the recent result of J. Kołodyński et al. [Phys. Rev. A 101, 020303(R) (2020)] where the log-negativity was connected with the (non-)Markovianity of the dynamics.

Quantum communications capacity using direct transmission over length-$L$ optical fiber scales as $R\sim e^{-\alpha L}$, where $\alpha$ is the fiber's loss coefficient. The rate achieved using a linear chain of quantum repeaters equipped with quantum memories, probabilistic Bell state measurements (BSMs), and switches used for spatial multiplexing, but no quantum error correction, was shown to surpass the direct-transmission capacity. However, this rate still decays exponentially with the end-to-end distance, viz., $R\sim e^{-s\alpha L}$, with $s<1$. We show that the introduction of temporal multiplexing—i.e., the ability to perform BSMs among qubits at a repeater node that were successfully entangled with qubits at distinct neighboring nodes at different time steps—leads to a subexponential rate-vs-distance scaling, i.e., $R\sim e^{-t\sqrt{\alpha L}}$, which is not attainable with just spatial or spectral multiplexing. We evaluate analytical upper and lower bounds to this rate and obtain the exact rate by numerically optimizing the time-multiplexing block length and the number of repeater nodes. We further demonstrate that incorporating losses in the optical switches used to implement time multiplexing degrades the rate-vs-distance performance, eventually falling back to exponential scaling for very lossy switches. We also examine models for quantum memory decoherence and describe optimal regimes of operation to preserve the desired boost from temporal multiplexing. Quantum memory decoherence is seen to be more detrimental to the repeater's performance over switching losses.

Ionization potentials, excitation energies, transition properties, and hyperfine structure constants of the low-lying $3p^{6}3d^9{}^2{D}_{5/2}, 3p^{6}3d^9{}^2{D}_{3/2}, 3p^{5}3d^{10}{}^2{P}_{3/2}$, and $3p^{5}3d^{10}{}^2{P}_{1/2}$ atomic states of the Co-like highly charged ions such as $\mathrm{Y}^{12+}, \mathrm{Zr}^{13+}, \mathrm{Nb}^{14+}, \mathrm{Mo}^{15+}, \mathrm{Tc}^{16+}, \mathrm{Ru}^{17+}, \mathrm{Rh}^{18+}, \mathrm{Pd}^{19+}, \mathrm{Ag}^{20+}$, and $\mathrm{Cd}^{21+}$ are investigated. The singles and doubles approximated relativistic coupled-cluster theory in the framework of one electron removal Fock-space formalism is employed over the Dirac-Hartree-Fock calculations to account for the electron correlation effects for determining the aforementioned properties. Higher-order relativistic corrections due to the Breit interaction and quantum electrodynamics effects in the evaluation of energies are also quantified explicitly. Our estimated values are compared with the other available theoretical calculations and experimental results, which are found to be in good agreement with each other.

Inducing and controlling the ultrafast molecular rotational dynamics using shaped laser fields is essential in numerous applications. Several approaches exist that allow following the coherent molecular motion in real time, including Coulomb explosion-based techniques and recovering molecular orientation from the angular distribution of high harmonics. We theoretically consider a nonintrusive optical scheme for visualizing the rotational dynamics in an anisotropic molecular gas. The proposed method allows determining the instantaneous orientation of the principal optical axes of the gas. The method is based on probing the sample using ultrashort circularly polarized laser pulses and recording the transmission image through a vortex wave plate. We consider two example excitations: molecular alignment induced by an intense linearly polarized laser pulse and unidirectional molecular rotation induced by a polarization-shaped pulse. The proposed optical method is promising for visualizing the dynamics of complex symmetric- and asymmetric-top molecules.

We demonstrate the generation of a trapped ion oscillator with a scale of $10\mu \mathrm{m}$ via fast trap center displacement. Applying an offset voltage to the ion trap electrode helps achieve a displacement of the trap center within the timescale of 5 ns. The fluorescence dynamics of the ion is analyzed after the displacement to estimate the oscillation amplitude. The realized trap displacement is seven times larger than that achieved in previous work. Thus, this result is an important step toward the realization of a gyroscope using a single trapped ion.

It was recently argued that one-dimensional systems of several strongly interacting fermions of different mass undergo critical transitions between different spatial orderings when the external confinement adiabatically changes its shape. In this work, we explore their dynamical properties when finite-time drivings are considered. By detailed analysis of many-body spectra, we show that the dynamics is typically guided only by the lowest eigenstates and may be well understood in the language of the generalized Landau-Zener mechanism. In this way, we can precisely capture the dynamical response of the system to the external driving. As a consequence, we show that by appropriate tailoring of the parameters of the driving, one can target the desired many-body state in a noninfinite time. Our theoretical predictions can be straightforwardly utilized in upcoming state-of-the-art experiments with ultracold atoms.

The acclaimed Maxwell-Bloch (or Arecchi-Bonifacio) equations are a valid dynamical model, effectively describing wave propagation in nonlinear optical media: from the amplification in input-output devices to multimode instabilities arising in laser systems. However, the inherent spatial variability of the physical observables represents an obstacle to fast simulations and analysis, especially whenever networks of active elements have to be considered. In this paper, we propose an approach which, stripping the spatial dependence of its role as a generator of dynamical richness, allows for a compelling simple portrait. It leads to (a few) ordinary differential equations in input-output configurations, complemented by a time-delayed feedback in closed-loop setups. Such a scheme reproduces accurately the dynamics, paving the way to a plain treatment of the wealth of phenomena described by the Maxwell-Bloch equations.

Quantum emitters interacting with photonic band-gap materials lead to the appearance of qubit-photon bound states that mediate decoherence-free, tunable emitter-emitter interactions. Recently, it has been shown that when these band gaps have a topological origin, like in the photonic Su-Schrieffer-Heeger (SSH) model, these qubit-photon bound states feature chiral shapes and certain robustness to disorder. In this paper, we consider a more general situation where the emitters interact with an extended SSH photonic model with longer-range hoppings that displays a richer phase diagram than its nearest-neighbor counterpart, e.g., phases with larger winding numbers. In particular, we first study the features of the qubit-photon bound states when the emitters couple to the bulk modes in the different phases, discern their connection with the topological invariant, and show how to further tune their shape through the use of giant atoms, i.e., nonlocal couplings. Then, we consider the coupling of emitters to the edge modes appearing in the different topological phases. Here, we show that giant-atom dynamics can distinguish between all different topological phases, in contrast to the case with local couplings. Finally, we provide a possible experimental implementation of the model based on periodic modulations of circuit QED systems. Our paper enriches the understanding of the interplay between topological photonics and quantum optics.

We describe a technique to measure the position of a dipolar scatterer based on self-homodyne detection of the scattered light. The method can theoretically reach the Heisenberg limit, at which information gained about the position is constrained only by the back action of the scattered light. The technique has applications in the fields of levitated optomechanics and trapped ions and is generally applicable to the position determination of confined light scatterers.