We report the full internal state control of ultracold ${}^{23}\mathrm{Na}{}^{87}\mathrm{Rb}$ molecules, including vibrational, rotational, and hyperfine degrees of freedom. Starting from a sample of weakly bound Feshbach molecules, we realize the creation of molecules in single hyperfine levels of both the rovibrational ground and excited states with a high-efficiency and high-resolution stimulated Raman adiabatic passage. This capability brings broad possibilities for investigating ultracold polar molecules with different chemical reactivities and interactions with a single molecular species. Moreover, starting from the rovibrational and hyperfine ground state, we achieve rotational and hyperfine control with one- and two-photon microwave spectroscopy to reach levels not accessible by the stimulated Raman transfer. The combination of these two techniques results in complete control over the internal state of ultracold polar molecules, which paves the way to study state-dependent molecular collisions and state-controlled chemical reactions.

Recently, a measure has been put forward which allows for the quantification of the degree of reality of an observable for a given preparation [Bilobran and Angelo, Europhys. Lett. 112, 40005 (2015)]. Here we employ this quantifier to establish, on formal grounds, relations among the concepts of measurement, information, and physical reality. After introducing mathematical objects that unify weak and projective measurements, we study scenarios showing that an arbitrary-intensity unrevealed measurement of a given observable generally leads to an increase of its reality and also of its incompatible observables. We derive a complementarity relation connecting an amount of information associated with the apparatus with the degree of irreality of the monitored observable. Specifically for pure states, we show that the entanglement with the apparatus precisely determines the amount by which the reality of the monitored observable increases. We also point out some mechanisms whereby the irreality of an observable can be generated. Finally, using the aforementioned tools, we construct a consistent picture to address the measurement problem.

We study fingering instabilities and pattern formation at the interface of an oppositely polarized two-component Bose-Einstein condensate with strong dipole-dipole interactions in three dimensions. It is shown that the rotational symmetry is spontaneously broken by fingering instability when the dipole-dipole interactions are strengthened. Frog-shaped and mushroom-shaped patterns emerge during the dynamics due to the dipolar interactions. We also demonstrate the spontaneous density modulation and domain growth of a two-component dipolar BEC in the dynamics. Bogoliubov analyses in the two-dimensional approximation are performed, and the characteristic lengths of the domains are estimated analytically. Patterns resembling those in magnetic classical fluids are modulated when the number ratio of atoms, the trap ratio of the external potential, or tilted polarization with respect to the $z$ direction is varied.

We investigate anomalous ion-motional heating, a limitation to multiqubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation. Using a multizone surface-electrode trap in which ions can be held at five discrete distances from the metal electrodes, we measure power-law dependencies of the electric-field noise experienced by the ion on the ion-electrode distance $d$. We find a scaling of approximately $d^{-4}$ regardless of whether the electrodes are at room temperature or cryogenic temperature, despite the fact that the heating rates are approximately two orders of magnitude smaller in the latter case. Through auxiliary measurements using the application of noise to the electrodes, we rule out technical limitations to the measured heating rates and scalings. We also measure the frequency scaling of the inherent electric-field noise close to $1/f$ at both temperatures. These measurements eliminate from consideration anomalous-heating models which do not have a $d^{-4}$ distance dependence, including several microscopic models of current interest.

It is well known that a minimum error quantum measurement for arbitrary binary optical coherent states can be realized by a receiver that comprises interfering with a coherent reference light, photon counting, and feedback control. We show that, for ternary optical coherent states, a minimum error measurement cannot always be realized by such a receiver. The problem of finding an upper bound on the maximum success probability of such a receiver can be formulated as a convex programming problem. We derive its dual problem and numerically find the upper bound. At least for ternary phase-shift keyed coherent states, this bound does not reach the success probability of a minimum error measurement.

The dissociation of ${\mathrm{N}}_2$ and ${{\mathrm{N}}_2}^{+}$ has been studied by using the ab initio density-matrix renormalization-group (DMRG) method. Accurate potential energy surfaces (PESs) have been obtained for the electronic ground states of ${\mathrm{N}}_2$ ($X^1{\mathrm{\Sigma }}_g^{+}$) and ${\mathrm{N}}_2{}^{+}$ ($X^2{\mathrm{\Sigma }}_g^{+}$) as well as for the ${\mathrm{N}}_2{}^{+}$ excited state $B^2{\mathrm{\Sigma }}_u^{+}$. Inherent to the DMRG approach, the eigenvalues of the reduced density matrix ($\rho$) and their correlation functions are at hand. Thus we can apply quantum information theory directly and investigate how the wave function changes along the PES and depict differences between the different states. Moreover, by characterizing quantum entanglement between different pairs of orbitals and analyzing the reduced density matrix, we achieved a better understanding of the multireference character featured by these systems.

We study a dispersion-compensated high-finesse optical Fabry-Perot microcavity under high-intensity cw pumping. The Kerr nonlinearity in the optical coatings causes a spontaneous four-wave mixing process, which leads to the emission of time-correlated photon pairs. The photon frequencies are shifted by $\pm 1$ free spectral range relative to the pump frequency. This setup allows for constructing a photon-pair source with precisely adjustable frequency difference between the emitted photons, which may have applications in quantum communication.

Recently we have demonstrated scalable, nondestructive, and high-fidelity detection of the internal state of ${}^{87}\mathrm{Rb}$ neutral atoms in optical dipole traps using state-dependent fluorescence imaging [M. Martinez-Dorantes, W. Alt, J. Gallego, S. Ghosh, L. Ratschbacher, Y. Völzke, and D. Meschede, Phys. Rev. Lett. 119, 180503 (2017)]. In this paper we provide experimental procedures and interpretations to overcome the detrimental effects of heating-induced trap losses and state leakage. We present models for the dynamics of optically trapped atoms during state-dependent fluorescence imaging and verify our results by comparing Monte Carlo simulations with experimental data. Our systematic study of dipole force fluctuations heating in optical traps during near-resonant illumination shows that off-resonant light is preferable for state detection in tightly confining optical potentials.

It is well known that correlations predicted by quantum mechanics cannot be explained by any classical (local-realistic) theory. The relative strength of quantum and classical correlations is usually studied in the context of Bell inequalities, but this tells us little about the geometry of the quantum set of correlations. In other words, we do not have a good intuition about what the quantum set actually looks like. In this paper we study the geometry of the quantum set using standard tools from convex geometry. We find explicit examples of rather counterintuitive features in the simplest nontrivial Bell scenario (two parties, two inputs, and two outputs) and illustrate them using two-dimensional slice plots. We also show that even more complex features appear in Bell scenarios with more inputs or more parties. Finally, we discuss the limitations that the geometry of the quantum set imposes on the task of self-testing.

We use quantum information measures to study the local quantum phase transition that occurs for trapped spinless fermions in one-dimensional lattices. We focus on the case of a harmonic confinement. The transition occurs upon increasing the characteristic density and results in the formation of a band-insulating domain in the center of the trap. We show that the ground-state bipartite entanglement entropy can be used as an order parameter to characterize this local quantum phase transition. We also study excited eigenstates by calculating the average von Neumann and second Renyi eigenstate entanglement entropies, and compare the results with the thermodynamic entropy and the mutual information of thermal states at the same energy density. While at low temperatures we observe a linear increase of the thermodynamic entropy with temperature at all characteristic densities, the average eigenstate entanglement entropies exhibit a strikingly different behavior as functions of temperature below and above the transition. They are linear in temperature below the transition but exhibit activated behavior above it. Hence, at nonvanishing energy densities above the ground state, the average eigenstate entanglement entropies carry fingerprints of the local quantum phase transition.

The paper is devoted to the Lamb shift and fine structure in a hydrogenlike muonic atom with a spinless nucleus up to the order ${\alpha }^{5}m$ with all the recoil corrections included. Enhanced contributions of a higher order are also considered. We present the results on the pure QED contribution and on the finite-nuclear-size contribution, proportional to $R_N^2$, with the higher-order corrections included. We also consider the consistency of the pure QED theory and the evaluation of the nuclear-structure effects. Most of the QED theory is the same as the theory for the case of the nuclear spin 1/2. Additional nuclear-spin-dependent terms are considered in detail. The issue of the difference for the theories with a spinor nucleus and a scalar one is discussed for the recoil contributions in the order ${\left(Z\alpha \right)}^{4}m,\alpha {\left(Z\alpha \right)}^{4}m$, and ${\left(Z\alpha \right)}^{5}m$. The numerical results are presented for the muonic atoms with two lightest scalar nuclei, helium-4 and beryllium-10. We compare the theory of those muonic atoms with theory for the muonic hydrogen. Some higher-order finite-nuclear-size corrections for the Lamb shift in muonic hydrogen are revisited.

Two different master-equation approaches are formally derived to address the dynamics of open quantum systems interacting with a thermal environment (such as sunlight). They lead to two physical results: nonsecular equations, which show noise-induced (Fano) coherences; and secular equations, which do not. An experimental test for the appearance of nonsecular terms is proposed using Ca atoms in magnetic fields excited with broadband incoherent radiation. Significantly different patterns of fluorescence are predicted, allowing for a clear test of the validity of the secular and nonsecular approach and for the observation of Fano coherences.

A shortcut to adiabaticity (STA) guides the nonadiabatic dynamics of a quantum system towards an equilibrium state without the requirement of slow driving. We report a demonstration of a STA in a strongly coupled system, i.e., a three-dimensional anisotropic Fermi gas at unitarity. Exploiting the emergent conformal symmetry, the time dependence of the trap frequencies is engineered so that the final state in a nonadiabatic expansion or compression is stationary and free from residual excitations. The universal scaling dynamics is verified both in the noninteracting limit and at unitarity.

Parity-time ($\mathcal{PT}$)-symmetric wave devices, which exploit balanced interactions between material gain and loss, exhibit extraordinary properties, including lasing and flux-conserving scattering processes. In a seemingly different research field, periodically driven systems, also known as time-Floquet systems, have been widely studied as a relevant platform for reconfigurable active wave control and manipulation. In this article, we explore the connection between $\mathcal{PT}$-symmetry and parametric time-Floquet systems. Instead of relying on material gain, we use parametric amplification by considering a time-periodic modulation of the refractive index at a frequency equal to twice the incident signal frequency. We show that the scattering from a simple parametric slab, whose dynamics follows the Mathieu equation, can be described by a $\mathcal{PT}$-symmetric scattering matrix, whose $\mathcal{PT}$-breaking threshold corresponds to the Mathieu instability threshold. By combining different parametric slabs modulated out of phase, we create $\mathcal{PT}$-symmetric time-Floquet systems that feature exceptional scattering properties, such as coherent perfect absorption (CPA)-laser operation and bidirectional invisibility. These bidirectional properties, rare for regular $\mathcal{PT}$-symmetric systems, are related to a compensation of parametric amplification due to multiple scattering between two parametric systems modulated with a phase difference.

We study the efficiency of adaptive optics (AO) correction for the free-space propagation of entangled photonic orbital-angular-momentum (OAM) qubit states to reverse moderate atmospheric turbulence distortions. We show that AO can significantly reduce crosstalk to modes within and outside the encoding subspace and thereby stabilize entanglement against turbulence. This method establishes a reliable quantum channel for OAM photons in turbulence, and it enhances the threshold turbulence strength for secure quantum communication by at least a factor 2.

Single, double, and triple ionization of the ${\mathrm{C}}^{+}$ ion by a single photon have been investigated in the energy range 286 to 326 eV around the $K$-shell single-ionization threshold at an unprecedented level of detail. At energy resolutions as low as 12 meV, corresponding to a resolving power of 24 000, natural linewidths of the most prominent resonances could be determined. From the measurement of absolute cross sections, oscillator strengths, Einstein coefficients, multielectron Auger decay rates, and other transition parameters of the main $K$-shell excitation and decay processes are derived. The cross sections are compared to results of previous theoretical calculations. Mixed levels of agreement are found despite the relatively simple atomic structure of the ${\mathrm{C}}^{+}$ ion with only five electrons. This paper is a followup to a previous Letter [A. Müller et al., Phys. Rev. Lett. 114, 013002 (2015)].

We study numerically the expansion dynamics of an initially confined quantum wave packet in the presence of a disordered potential and a uniform bias force. For white-noise disorder, we find that the wave packet develops asymmetric algebraic tails for any ratio of the force to the disorder strength. The exponent of the algebraic tails decays smoothly with that ratio and no evidence of a critical behavior on the wave density profile is found. Algebraic localization features a series of critical values of the force-to-disorder strength where the $m\mathrm{th}$ position moment of the wave packet diverges. Below the critical value for the $m\mathrm{th}$ moment, we find fair agreement between the asymptotic long-time value of the $m\mathrm{th}$ moment and the predictions of diagrammatic calculations. Above it, we find that the $m\mathrm{th}$ moment grows algebraically in time. For correlated disorder, we find evidence of systematic delocalization, irrespective to the model of disorder. More precisely, we find a two-step dynamics, where both the center-of-mass position and the width of the wave packet show transient localization, similar to the white-noise case, at short time and delocalization at sufficiently long time. This correlation-induced delocalization is interpreted as due to the decrease of the effective de Broglie wavelength, which lowers the effective strength of the disorder in the presence of finite-range correlations.

In this work we model and realize stimulated Raman adiabatic passage (STIRAP) in the diatomic ${}^{23}{\mathrm{Na}}^{40}\mathrm{K}$ molecule from weakly bound Feshbach molecules to the rovibronic ground state via the $\left|v_d=5,J=\mathrm{\Omega }=1\right.〉$ excited state in the $d^3\mathrm{\Pi }$ electronic potential. We demonstrate how to set up a quantitative model for polar molecule production by taking into account the rich internal structure of the molecules and the coupling laser phase noise. We find excellent agreement between the model predictions and the experiment, demonstrating the applicability of the model in the search for an ideal STIRAP transfer path. In total we produce 5000 fermionic ground-state molecules. The typical phase-space density of the sample is 0.03 and induced dipole moments of up to 0.54 D can be observed.

From generation of backscatter-free transmission lines, to optical isolators, to chiral Hamiltonian dynamics, breaking time-reversal symmetry is a key tool for development of next-generation photonic devices and materials. Of particular importance is the development of time-reversal-broken devices in the low-loss regime, where they can be harnessed for quantum materials and information processors. In this work, we experimentally demonstrate the isolation of a single, time-reversal-broken running-wave mode of a moderate-finesse optical resonator. Nonplanarity of the optical path produces a round-trip geometrical (Pancharatnam) polarization rotation, breaking the inversion symmetry of the photonic modes. The residual time-reversal symmetry between forward-${\sigma }^{+}$–backward-${\sigma }^{-}$ modes is broken through an atomic Faraday rotation induced by an optically pumped ensemble of ${}^{87}\mathrm{Rb}$ atoms residing in the resonator. We observe a splitting of 6.3 linewidths between time-reversal partners and a corresponding optical isolation of ∼20.1(4) dB, with 83(1)% relative forward cavity transmission. Finally, we explore the impact of twisted resonators on T-breaking of intracavity Rydberg polaritons, a crucial ingredient of photonic materials and, specifically, topological optical matter. As a highly coherent approach to time-reversal breaking, this work will find immediate application in the creation of photonic materials and also in switchable narrow-band optical isolators.

By measuring the cyclotron frequency ratio of ${}^3\mathrm{He}^{+}$ to ${\mathrm{HD}}^{+}$ directly, with confirmation from measurements using ${\mathrm{H}}_3{}^{+}$ as an intermediary, we obtain $M\left[{}^3\mathrm{He}^{+}\right]/M\left[{\mathrm{HD}}^{+}\right]=0.998048085122\left(23\right)$ and hence the mass difference $m_p+m_d-m_h=0.00589743219\left(7\right)$ u. This result disagrees by more than four standard deviations with the value inferred from current precise literature values for the atomic masses of the proton, deuteron, and nucleus of ${}^3\mathrm{He}$.