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We observe a weakly allowed optical transition of atomic ytterbium from the ground state to the metastable state $4f^{13}5d6s^2 \: (J=2)$ for all five bosonic and two fermionic isotopes with resolved Zeeman and hyperfine structures. This inner-shell orbital transition has been proposed as a new frequency standard as well as a quantum sensor for new physics. We find magic wavelengths through the measurement of the scalar and tensor polarizabilities and reveal that the measured trap lifetime in a three-dimensional optical lattice is 1.9(1) s, which is crucial for precision measurements. We also determine the $g$ factor by an interleaved measurement, consistent with our relativistic atomic calculation. This work opens the possibility of an optical lattice clock with improved stability and accuracy as well as novel approaches for physics beyond the standard model., 12 pages, 8 figures

We report the first experimental determination of the collision-energy dependence of the muon transfer rate from the ground state of muonic hydrogen to oxygen at near-thermal energies. A sharp increase by nearly an order of magnitude in the energy range 0 - 70 meV was found that is not observed in other gases. The results set a reliable reference for quantum-mechanical calculations of low-energy processes with exotic atoms, and provide firm ground for the measurement of the hyperfine splitting in muonic hydrogen and the determination of the Zemach radius of the proton by the FAMU collaboration., 30 pages, 10 figures

Electrical detection of nitrogen-vacancy (N-V) centers in diamond is advantageous for developing and integrating quantum information processing devices and quantum sensors and has the potential to achieve a higher collection efficiency than that of optical techniques. However, the mechanism for the electrical detection of N-V spins is not fully understood. In this study, we observe positive contrast in photocurrent detected magnetic resonance (PDMR). Note that negative PDMR contrast is usually observed. To discuss the sign of the PDMR contrast, we numerically analyze the dynamics of photocarrier generation by N-V centers using a seven-level rate model. It is found that the sign of the PDMR contrast depends on the difference in the photocurrent generated from the excited states and the metastable state of N-V centers. Furthermore, we demonstrate ac magnetic field sensing using spin coherence with the PDMR technique. ac magnetic field measurement with the PDMR technique is still challenging because the noise from a fluctuating magnetic environment is greater than the measured signal. Here, we introduce noise suppression using a phase-cycling-based noise-canceling technique. We demonstrate electrically detected ac magnetic field sensing with a sensitivity of 29 nT Hz[−1/2]. Finally, we discuss sensitivity enhancement based on the proposed model.

We report on the experimental realization of a bosonic quantum degenerate mixture of highly magnetic ¹⁶⁸Er and nonmagnetic ¹⁷⁴Yb. Quantum degeneracy is reached by forced evaporation in an all-optical trap. Formation of the two Bose-Einstein condensates is confirmed by analysis of the cloud shape and the observed inversions of the aspect ratios. The results open a path for possible new experiments on magnetic and nonmagnetic impurity physics as well as on the quantum chaotic behavior of Feshbach resonances and their dependencies on minor variations of the reduced masses.

We demonstrate the universal properties of dissipative Tomonaga-Luttinger (TL) liquids by calculating correlation functions and performing finite-size scaling analysis of a non-Hermitian XXZ spin chain as a prototypical model in one-dimensional open quantum many-body systems. Our analytic calculation is based on effective field theory with bosonization, finite-size scaling approach in conformal field theory, and the Bethe-ansatz solution. Our numerical analysis is based on the density-matrix renormalization group generalized to non-Hermitian systems (NH-DMRG). We uncover that the model in the massless regime with weak dissipation belongs to the universality class characterized by the complex-valued TL parameter, which is related to the complex generalization of the $c=1$ conformal field theory. As the dissipation strength increases, the values of the TL parameter obtained by the NH-DMRG begin to deviate from those obtained by the Bethe-ansatz analysis, indicating that the model becomes massive for strong dissipation. Our results can be tested with the two-component Bose-Hubbard system of ultracold atoms subject to two-body loss., 23 pages, 7 figures, to appear in Phys. Rev. B

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g. vanadium, emit in one of the telecom bands, but the large ground state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long-time coherent storage of quantum states. The proposed nuclear-spin preparation protocol thus marks the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC., 12 Pages, 5 figures

Quantum communication between remote superconducting systems is being studied intensively to increase the number of integrated superconducting qubits and to realize a distributed quantum computer. Since optical photons must be used for communication outside a dilution refrigerator, the direct conversion of microwave photons to optical photons has been widely investigated. However, the direct conversion approach suffers from added photon noise, heating due to a strong optical pump, and the requirement for large cooperativity. Instead, for quantum communication between superconducting qubits, we propose an entanglement distribution scheme using a solid-state spin quantum memory that works as an interface for both microwave and optical photons. The quantum memory enables quantum communication without significant heating inside the refrigerator, in contrast to schemes using high-power optical pumps. Moreover, introducing the quantum memory naturally makes it possible to herald entanglement and parallelization using multiple memories., Comment: 17 pages, 11 figures

We investigate an attractive force caused by light induced dipole-dipole interactions in freely expanding ultracold 87Rb atoms. This collective, light-triggered effect results in a self-confining potential with interesting features: it exhibits nonlocal properties, is attractive for both red and blue-detuned light fields and induces a remarkably strong force that depends on the gradient of the atomic density. The experimental data are discussed in the framework of a theoretical model based on a local-field approach for the light scattered by the atomic cloud., Comment: 13 pages, 9 figures

Non-Gaussian quantum states have been deterministically prepared and autonomously stabilized in single- and two-mode circuit quantum electrodynamics architectures via engineered dissipation. However, it is currently unknown how to scale up this technique to multi-mode non-Gaussian systems. Here, we upgrade dissipation engineering to collective (normal) modes of nonlinear resonator arrays and show how to stabilize multi-mode Schrodinger cat states. These states are multi-photon and multi-mode quantum superpositions of coherent states in a single normal mode delocalized over an arbitrary number of cavities. We consider tailored dissipative coupling between resonators that are parametrically driven and feature an on-site nonlinearity, which is either a Kerr-type nonlinearity or an engineered two-photon loss. For both types of nonlinearity, we find the same exact closed-form solutions for the two-dimensional steady-state manifold spanned by superpositions of multi-mode Schrodinger cat states. We further show that, in the Zeno limit of strong dissipative coupling, the even parity multi-mode cat state can be deterministically prepared from the vacuum. Remarkably, engineered two-photon loss gives rise to a fast relaxation towards the steady state, protecting the state preparation against decoherence due to intrinsic single-photon losses and imperfections in tailored dissipative coupling, which sets in at longer times. The relaxation time is independent of system size making the state preparation scalable. Multi-mode cat states are naturally endowed with a noise bias that increases exponentially with system size and can thus be exploited for enhanced robust encoding of quantum information., 20 pages, 8 figures; Section 8 and Appendices C, G, and H added in v2; Section 1 and Figure 1 revised in v2

Quantum phase slips are a dual process of particle tunneling in coherent networks. Besides being of central interest to condensed matter physics, quantum phase slips are resources that are sought to be manipulated in quantum circuits. Here, we devise a specific matter-wave circuit enlightening quantum phase slips. Specifically, we investigate the quantum many-body dynamics of two side-by-side ring-shaped neutral bosonic systems coupled through a weak link. By imparting a suitable magnetic flux, persistent currents flow in each ring with given winding numbers. We demonstrate that coherent phase slips occur as winding number transfer among the two rings, with the populations in each ring remaining nearly constant. Such a phenomenon occurs as a result of a specific entanglement of circulating states, that, as such, cannot be captured by a mean-field treatment of the system. Our work can be relevant for the observation of quantum phase slips in cold-atom experiments and their manipulation in matter-wave circuits. To make contact with the field, we show that the phenomenon has clear signatures in the momentum distribution of the system providing the time-of-flight image of the condensate. We thank G. Catelani and W. Jordan Chetcuti for discussion. A.P.-O. acknowledges financial support from Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya cofunded by the European Union Regional Development Fund within the ERDF Operational Program of Catalunya (project QuantumCat, Ref. No. 001-P-001644).

We measure isotope shifts for neutral Yb isotopes on an ultranarrow optical clock transition $^{1}\text{S}_{0}-^{3}\text{P}_{0}$ with an accuracy of a few Hz. The part-per-billion precise measurement was possible by loading the ultracold atoms into a three-dimensional magic-wavelength optical lattice and alternately interrogating the isotope pairs, thus minimizing the effects due to the optical lattice light-shift and inter-atomic interaction as well as the drifts of a clock laser frequency and a magnetic field. The determined isotope shifts, combined with one of the recently reported isotope-shift measurements of Yb$^+$ on two optical transitions, allow us to construct the King plots. Extremely large nonlinearity with the corresponding $\chi^2$ on the order of $10^4$ is revealed, and is not explained by a quadratic field shift. We further carry out the generalized King plot for three optical transitions so that we can eliminate the contribution arising from a higher-order effect within the Standard Model which might explain the observed nonlinearity of King plots for two transitions. Our analysis of the generalized King plot shows a deviation from linearity at the 3$\sigma$ level, indicating that there exist at least two higher order contributions in the measured isotope shifts. Then, under the reasonable assumption to attribute them to higher-order field shifts within the Standard Model, we obtain the upper bound of the product of the couplings for a new boson mediating a force between electrons, and neutrons $|y_ey_n|/(\hbar c)< 1\times10^{-10}$ for the mass less than 1 keV with the 95% confidence level is derived, providing an important step towards probing new physics via isotope-shift spectroscopy., Comment: 15 pages, 8 figures

A dynamic mean-field theory for spin ensembles (spinDMFT) at infinite temperatures on arbitrary lattices is established. The approach is introduced for an isotropic Heisenberg model with $S = \tfrac12$ and external field. For large coordination numbers, it is shown that the effect of the environment of each spin is captured by a classical time-dependent random mean-field which is normally distributed. Expectation values are calculated by averaging over these mean-fields, i.e., by a path integral over the normal distributions. A self-consistency condition is derived by linking the moments defining the normal distributions to spin autocorrelations. In this framework, we explicitly show how the rotating wave approximation becomes a valid description for increasing magnetic field. We also demonstrate that the approach can easily be extended. Exemplarily, we employ it to reach a quantitative understanding of a dense ensemble of spins with dipolar interaction which are distributed randomly on a plane including static Gaussian noise as well., Comment: 33 pages, 37 figures

Recent years have enjoyed an overwhelming interest in quantum thermodynamics, a field of research aimed at understanding thermodynamic tasks performed in the quantum regime. Further progress, however, seems to be obstructed by the lack of experimental implementations of thermal machines in which quantum effects play a decisive role. In this work, we introduce a blueprint of quantum field machines, which - once experimentally realized - would fill this gap. Even though the concept of the QFM presented here is very general and can be implemented in any many body quantum system that can be described by a quantum field theory. We provide here a detailed proposal how to realize a quantum machine in one-dimensional ultra-cold atomic gases, which consists of a set of modular operations giving rise to a piston. These can then be coupled sequentially to thermal baths, with the innovation that a quantum field takes up the role of the working fluid. In particular, we propose models for compression on the system to use it as a piston, and coupling to a bath that gives rise to a valve controlling heat flow. These models are derived within Bogoliubov theory, which allows us to study the operational primitives numerically in an efficient way. By composing the numerically modelled operational primitives we design complete quantum thermodynamic cycles that are shown to enable cooling and hence giving rise to a quantum field refrigerator. The active cooling achieved in this way can operate in regimes where existing cooling methods become ineffective. We describe the consequences of operating the machine at the quantum level and give an outlook of how this work serves as a road map to explore open questions in quantum information, quantum thermodynamic and the study of non-Markovian quantum dynamics., Comment: 48 pages, 18 figures, replaced by published version

We report on the cancellation of quantum backaction noise in an optomechanical cavity. We perform measurements of the displacement of the microresonator, one in reflection of the cavity and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light transmitted by the optomechanical cavity allows us to cancel the backaction noise between 2 and 50 kHz as a consequence of the strong optical spring present in the detuned cavity. This cancellation yields a more sensitive measurement of the microresonator’s position with a 2 dB increase in sensitivity. To confirm that the backaction is eliminated, we measure the noise in the transmission signal as a function of circulating power and use a correlation technique between two photodetectors to remove shot noise. Remaining backaction noise would be observable as a power-dependent noise floor, which is not observed. Eliminating the effects of backaction in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of backaction in interferometric gravitational wave detectors such as Advanced LIGO, VIRGO, and KAGRA.

We report the first measurement of ground-state diamagnetism of isolated neutral atoms in an atomic beam. We realize this measurement using magnetic deflection of fringes in a long-baseline matter-wave interferometer. The observed diamagnetic susceptibilities of −5.8±0.2±0.4×10^{−9} m^{3}/kg for barium and −7.0±0.3±0.7×10^{−9} m^{3}/kg for strontium are in good agreement with the theoretical values and correspond to a measured force on the order of 10^{−26} N. The high force sensitivity also allows us to observe the isotope dependence of the interference visibility due to the nuclear permanent magnetic moment, thereby demonstrating a new method for neutral isotope selection. The universality of the technique allows the magnetism of a wide range of atoms and molecules to be studied in the gas phase.

We study the properties of Bose polarons in two dimensions using quantum Monte Carlo techniques. Results for the binding energy, the effective mass, and the quasiparticle residue are reported for a typical strength of interactions in the gas and for a wide range of impurity-gas coupling strengths. A lower and an upper branch of the quasiparticle exist. The lower branch corresponds to an attractive polaron and spans from the regime of weak coupling where the impurity acts as a small density perturbation of the surrounding medium to deep bound states which involve many particles from the bath and extend as far as the healing length. The upper branch corresponds to an excited state where due to repulsion a low-density bubble forms around the impurity but might be unstable against decay into many-body bound states. Interaction effects strongly affect the quasiparticle properties of the polaron. In particular, in the strongly correlated regime, the impurity features a vanishing quasiparticle residue, signaling the transition from an almost free quasiparticle to a bound state involving many atoms from the bath., 8 pages, 5 figures

We study airplane boarding in the limit of large number of passengers using geometric optics in a Lorentzian metric. The airplane boarding problem is naturally embedded in a 1+1 dimensional space-time with a flat Lorentzian metric. The duration of the boarding process can be calculated based on a representation of the one-dimensional queue of passengers attempting to reach their seats, into a two-dimensional space-time diagram. The ability of a passenger to delay other passengers depends on their queue positions and row designations. This is equivalent to the causal relationship between two events in space-time, whereas two passengers are time-like separated if one is blocking the other, and space-like if both can be seated simultaneously. Geodesics in this geometry can be utilized to compute the asymptotic boarding time, since space-time geometry is the many-particle (passengers) limit of airplane boarding. Our approach naturally leads to a novel definition of an effective refractive index. The introduction of an effective refractive index enables, for the first time, an analytical calculation of the average boarding time for groups of passengers with different aisle-clearing time distribution. In the past, airline companies attempted to shorten the boarding times by trying boarding policies that either allow slow or fast passengers to board first. Our analytical calculations, backed by discrete-event simulations, support the counter-intuitive result that the total boarding time is shorter with the slow passengers boarding before the fast passengers. This is a universal result, valid for any combination of the parameters that characterize the problem --- percentage of slow passengers, ratio between aisle-clearing times between the fast and the slow groups, and the density of passengers along the aisle. We find an improvement of up to 28% compared with the Fast-First boarding policy., 34 pages, 13 figures

Electron-impact single-ionization cross sections for the W5+ ion have been studied experimentally and theoretically. Measurements of a detailed ionization spectrum and of absolute cross sections were performed employing the crossed-beams method in the energy range from the ionization onset up to 1000 eV. The experimental data show a prominent contribution of W5+ ions in metastable states. The theoretical analysis includes level-to-level calculations from the 4f145s25p65d ground configuration and long-lived levels of the 6s, 5p55d2, 4f135d2, and 4f135d6s configurations. Direct-ionization and excitation-autoionization contributions to the total single-ionization cross sections were calculated employing a distorted-wave approximation. Radiative damping was taken into account. It is shown that correlation effects play an important role and lead to substantial reduction of cross sections. Theory and experiment are in quite good agreement when, within a statistical model, a (85±9)% fraction of parent ions in the ground configuration is assumed. The strongest contributions of metastable parent ions arise from the 5p55d2 and 4f135d2 configurations. The experimental part of this study was supported by the Deutsche Forschungsgemeinschaft under Project No. Mu 1068/20. M.F.G. acknowledges the Deutsche Forschungsgemeinschaft for supporting his research stays at the Gießen Institut für Atom-und Molekülphysik through Grants No. Mu-1068/19 and No. Mu-1068/21. A.B. is supported by the German Federal Ministry of Education and Research (BMBF) through Grant No. 05P19RGFA1. Part of the computations were performed using resources of the High Performance Computing Center “HPC Sauletekis” in Vilnius University Faculty of Physics. We thank K. Spruck, A. Becker, J. Hellhund, and J. Rausch for their help in the present experimental program. Scopus

Fraunhofer light diffraction across a thin two-dimensional lattice of cold atoms subject to transverse hybrid modulations of two standing-wave crossed pump fields is seen to yield lopsided patterns of various degrees of symmetry. We show that one can fully restrain the diffraction of a weak incident probe to two diagonal or adjacent quadrants or even just to a single quadrant, depending on the phases of two standing-wave pumps and on the probe detuning. Different diffraction symmetries with respect to the axes or diagonals of the diffraction plane quadrants are interpreted here in terms of different out-of-phase interplay of absorption and dispersion periodic distributions, resulting from different combinations of Hermitian, $\mathcal{PT}$-symmetric, and non-Hermitian modulations.

© 2018 American Physical Society. We investigate the role of quantum interference phenomena on the characteristics of the fields radiated by an array of quantum emitters. In analogy to, but distinct from, classical outcomes, we demonstrate that the array geometry empowers control over direction-dependent photon statistics of arbitrary order. Our formulation enables the recognition of configurations providing spatial correlations with no classical counterpart. For example, we identify a system in which the angular distribution of the average number of photons is independent of the number and position of the emitters, while its higher-order photon statistics exhibit a directional behavior. These results extend our understanding of the fields generated by ensembles of quantum emitters, with potential applications to nonclassical light sources.

We develop energy efficient, continuous microwave schemes to couple electron and nuclear spins, using phase or amplitude modulation to bridge their frequency difference. These controls have promising applications in biological systems, where microwave power should be limited, as well as in situations with high Larmor frequencies due to large magnetic fields and nuclear magnetic moments. These include nanoscale NMR where high magnetic fields achieves enhanced thermal nuclear polarization and larger chemical shifts. Our controls are also suitable for quantum information processors and nuclear polarization schemes., E. S. and J. C. acknowledge financial support from Spanish MINECO/FEDER FIS2015-69983-P, Basque Government IT986-16, as well as from QMiCS (820505) and OpenSuperQ (820363) of the EU Flagship on Quantum Technologies. J. C. acknowledges support by the Juan de la Cierva Grant No. IJCI-2016-29681. E. T. and J. J. G. R. acknowledge support from Spanish MINECO/FEDER Project No. FIS2015-70856-P, No. FIS2016-81891-REDT and CAMPRICYT ProjectQUITEMAD þ CMNo. S2013- ICE2801. M. B. P. acknowledges support by the ERC Synergy grant BioQ (Grant No. 319130), the EU project HYPERDIAMOND, the QuantERA project NanoSpin, the BMBF project DiaPol, the state of Baden-Württemberg through bwHPC, and the German Research Foundation (DFG) through Grant No. INST 40/467-1 FUGG. This material is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Advance Scientific Computing Research (ASCR), Quantum Algorithms Teams project under field work proposal ERKJ335.

Helium atom is the simplest many-body electronic system provided by nature. The exact solution to the Schr\"odinger equation is known for helium ground and excited states, and represents a workbench for any many-body methodology. Here, we check the ab initio many-body GW approximation and Bethe-Salpeter equation (BSE) against the exact solution for helium. Starting from Hartree-Fock, we show that GW and BSE yield impressively accurate results on excitation energies and oscillator strength, systematically improving time-dependent Hartree-Fock. These findings suggest that the accuracy of BSE and GW approximations is not significantly limited by self-interaction and self-screening problems even in this few electron limit. We further discuss our results in comparison to those obtained by time-dependent density-functional theory., Comment: 6 pages, 2 figures, 3 tables