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.

There exist oscillating current distributions that cannot generate radiation; these configurations are known as anapoles. Our goal is to theoretically demonstrate that an oscillating electric dipole, located in the vicinity of a subwavelength sphere and polarized tangentially, can yield an anapole. This paper complements our recent study [J. R. Zurita-Sánchez, Phys. Rev. Research 1, 033064 (2019)], devoted to an anapole arising from an electric dipole with radial polarization. Our methodology relies on the multipolar expansion of the excitation and scattered electromagnetic fields with respect to the center of the spherical particle. We found that an anapole arises when the effective electric and magnetic dipoles, induced by the dipolar source, vanish. The aforementioned anapole condition considers that the lowest multipolar order contribution is responsible for the radiative response of the emitter. However, high-order multipoles yield an unavoidable residual radiated power which is much smaller still than the radiated power of the dipole in the absence of the scatterer. Particularly, for a nonabsorbing sphere, the geometrical and dielectromagnetic parameters that lead to an anapole state are determined. As a practical scenario, we exploit the anapole excitation for controlling the spontaneous emission decay rate of an excited atom (or a molecule). In comparison to the decay rate of an excited atom without the scatterer, the radiative decay in the presence of the particle can be inhibited by a factor of about three orders of magnitude; this factor is quite large for an open system like ours. Furthermore, we show that by varying the orientation of the atomic transition dipole moment from a tangential direction, where the anapole condition is satisfied, to a radial direction, the atom can change from a state in which the spontaneous emission rate is inhibited to one in which this rate is enhanced. Hence, the anapole setup enables the versatile control of the radiative properties of an atom, and it provides the possibility for implementing applications related to the sensing and localization of atoms.

The realization of multimode optomechanical interactions in the single-photon strong-coupling regime is a desired task in cavity optomechanics, but it remains a big challenge in realistic physical systems. In this work we propose a reliable scheme to simulate a three-mode optomechanical system working in the single-photon strong-coupling regime based on the Fredkin-type interaction. This is achieved by utilizing two strong drivings to the two exchange-coupled modes in the Fredkin-type coupling involving one optical mode and two mechanical-like modes. As an application of this enhanced three-mode nonlinear optomechanical coupling, we show how to generate entangled cat states of the mechanical-like modes using the conditional displacement mechanism. The quantum coherence effects in the generated states are investigated by calculating the two-mode joint Wigner function and quantum entanglement. The influence of the system dissipation on the state generation is also considered. This work will open up a different route to the study of multimode optomechanical interactions at the single-photon level.

Quantum integer factorization is a potential quantum computing solution that may revolutionize cryptography. Nevertheless, a scalable and efficient quantum algorithm for noisy intermediate-scale quantum computers looks far-fetched. We propose an alternative factorization method, within the digitized-adiabatic quantum computing paradigm, by digitizing an adiabatic quantum factorization algorithm enhanced by shortcuts to adiabaticity techniques. We find that this fast factorization algorithm is suitable for available gate-based quantum computers. We test our quantum algorithm in an IBM quantum computer with up to six qubits, surpassing the performance of the more commonly used factorization algorithms on the long way towards quantum advantage.

The non-Markovian nature of open quantum dynamics lies in the structure of multitime correlations, which are accessible by means of interventions. Here, by examining multitime correlations, we show that it is possible to engineer non-Markovian systems with only long-term memory but seemingly no short-term memory, so that their non-Markovianity is completely nondetectable by any interventions up to an arbitrarily large time. Our results raise the question about the assessability of non-Markovianity: in principle, non-Markovian effects that are perfectly elusive to interventions may emerge at much later times.

We study the Bayesian approach to thermometry with no prior knowledge about the expected temperature scale, through the example of energy measurements on fully or partially thermalized qubit probes. We show that the most common Bayesian estimators, namely the mean and the median, lead to high-temperature divergences when used for uninformed thermometry. To circumvent this and achieve better overall accuracy, we propose two new estimators based on an optimization of relative deviations. Their global temperature-averaged behavior matches a modified van Trees bound, which complements the Cramér-Rao bound for smaller probe numbers and unrestricted temperature ranges. Furthermore, we show that, using partially thermalized probes, one can increase the range of temperatures to which the thermometer is sensitive at the cost of the local accuracy.

Standard theoretical descriptions of the dynamics of open quantum systems rely on the assumption that the correlations with the environment can be neglected at some reference (initial) time. While being reasonable in specific instances, such as when the coupling between the system and the environment is weak or when the interaction starts at a distinguished time, the use of initially uncorrelated states is questionable if one wants to deal with general models, taking into account the mutual influence that the open-system and environmental evolutions perform on each other. Here we introduce a perturbative method that can be applied to any microscopic modeling of the system-environment interaction, including fully general initial correlations. Extending the standard technique based on projection operators that single out the relevant part of the global dynamics, we define a family of projections adapted to a convenient decomposition of the initial state, which involves a convex mixture of product operators with proper environmental states. This leads us to characterize the open-system dynamics via an uncoupled system of differential equations, which are homogeneous and whose number is limited by the dimensionality of the open system, for any kind of initial correlations. Our method is further illustrated by means of two case studies, for which it reproduces the expected dynamical behavior in the long-time regime more consistently than the standard projection technique.

Certain aspects of some unitary quantum systems are well described by evolution via a non-Hermitian effective Hamiltonian, as in the Wigner-Weisskopf theory for spontaneous decay. Conversely, any non-Hermitian Hamiltonian evolution can be accommodated in a corresponding unitary system $+$ environment model via a generalization of Wigner-Weisskopf theory. This demonstrates the physical relevance of novel features such as exceptional points in quantum dynamics, and opens up avenues for studying many-body systems in the complex plane of coupling constants. In the case of lattice field theory, sparsity lends these channels the promise of efficient simulation on standardized quantum hardware. We thus consider quantum operations that correspond to Suzuki-Lie-Trotter approximation of lattice field theories undergoing nonunitary time evolution, with potential applicability to studies of spin or gauge models at finite chemical potential, with topological terms, to quantum phase transitions—a range of models with sign problems. We develop non-Hermitian quantum circuits and explore their promise on a benchmark, the quantum one-dimensional Ising model with complex longitudinal magnetic field, showing that observables can probe the Lee-Yang edge singularity. The development of attractors past critical points in the space of complex couplings indicates a potential for study on near-term noisy hardware.

We propose a protocol to realize fast high-fidelity quantum state transfer between distant optomechanical interfaces connected by a continuum waveguide. The scheme consists of three steps: two accelerating adiabatic processes joined by a population conversion process. In comparison to the traditional adiabatic technique, our method reaches a higher transfer fidelity with a shorter time. Numerical results show that the fidelity of this transfer scheme in the dissipative system mainly depends on the protocol speed and the coupling strength of the waveguide and cavities. Assisted by inverting the pulse sequence, bidirectional transfer can be implemented, indicating the potential to build a quantum network.

We present results on the digital quantum simulations of beam-splitter and squeezing interactions. The bosonic Hamiltonians are mapped to qubits and then digitalized in order to implement them in the IBM quantum devices. We use error mitigation and postselection to achieve high-fidelity digital quantum simulations of single-mode and two-mode interactions, as evinced—where possible—by full tomography of the resulting states. We achieve fidelities above 90% in the case of single-mode squeezing with low squeezing values and ranging from 60% to 90% for large squeezing and in the more complex two-mode interactions.

We demonstrate the use of a single trapped ion as a sensor to probe electric-field noise from interchangeable test surfaces. As proof of principle, we measure the magnitude and distance dependence of electric-field noise from two ion-trap-like samples with patterned Au electrodes. This trapped-ion sensor could be combined with other surface characterization tools to help elucidate the mechanisms that give rise to electric-field noise from ion-trap surfaces. Such noise presents a significant hurdle for performing large-scale trapped-ion quantum computations.

Energy levels, magnetic dipole, and electric quadrupole hyperfine structure of the superheavy element rutherfordium $(\mathrm{Rf},Z=104)$ and its first three ions are calculated using a combination of the configuration interaction, linearized coupled-cluster single-doubles, and many-body perturbation theory techniques. The results are to be used in future interpretations of the measurements in terms of nuclear magnetic dipole and electric quadrupole moments. To have a guide on the accuracy of the study, we perform similar calculations for hafnium $(\mathrm{Hf}Z=72)$ and its ions. Hf is a lighter analog of Rf with a similar electronic structure. Good agreement with the experiment for Hf and with available previous calculations of the energy levels of Rf is demonstrated.

Employing a semiclassical quantum-trajectory Monte Carlo model, we comprehensively study the formerly overlooked strong-field photoelectron holographic pattern, “the spiral,” originating from the interference of the forward and backward rescattering trajectories. We include the multipass rescattering trajectories, which were left out before, and find that only the ones revisiting the parent ion for the same even number of times (including zero) before the recollision from adjacent half cycles can lead to the spiral. By using a rescattering sphere to differentiate trajectories, we revealed that after the recollision only the backward rescattering trajectories with the turning point outside the sphere can interfere with the forward ones and result in the spiral eventually. The relationship between the fringe width of the spiral and the ionization time is identified. This study gives a deeper understanding of how to use the spiral as a holographic tool.

We develop two approximate theories to describe the miscible and immiscible droplets that can occur in a binary mixture of highly magnetic bosonic atoms. In addition to allowing simpler calculations, the approximate theories provide insight into the role of quantum fluctuations in the two regimes. Results are validated by comparison to those from the extended Gross-Pitaevskii equation. As an application, we solve for the ground-state droplets crossing the miscible-immiscible transition as a function of the short-ranged interspecies interaction parameter. We consider regimes where the transition occurs suddenly or as a smooth cross-over. Using dynamical calculations, we show that the character of the transition is revealed in the number of domains produced when ramping the droplet into the immiscible regime.