We propose a Raman quantum memory scheme that uses several atomic ensembles to store and retrieve the multimode highly entangled state of an optical quantum frequency comb, such as the one produced by parametric down-conversion of a pump frequency comb. We analyze the efficiency and the fidelity of such a quantum memory. Results show that our proposal may be helpful to multimode information processing using the different frequency bands of an optical frequency comb.

We present a horizontal gravity gradiometer atom interferometer for precision gravitational tests. The horizontal configuration is superior for maximizing the inertial signal in the atom interferometer from a nearby proof mass. In our device, we have suppressed spurious noise associated with the horizonal configuration to achieve a differential acceleration sensitivity of $4.2\times {10}^{-9}g/\sqrt{\mathrm{Hz}}$ over a 70-cm baseline or $3.0\times {10}^{-9}g/\sqrt{\mathrm{Hz}}$ inferred per accelerometer. Using the performance of this instrument, we characterize the results of possible future gravitational tests. We demonstrate a statistical uncertainty of $3\times {10}^{-4}$ for a proof-of-concept measurement of the gravitational constant that is competitive with the present limit of $1.2\times {10}^{-4}$ using other techniques. From this measurement, we provide a statistical constraint on a Yukawa-type fifth force at $8\times {10}^{-3}$ near the poorly known length scale of 10 cm. Limits approaching ${10}^{-5}$ appear feasible. We discuss improvements that can enable uncertainties falling well below ${10}^{-5}$ for both experiments.

Low-energy $(E_0=65\mathrm{eV})$ electron-impact single ionization of Ne $(2p)$ has been investigated to thoroughly test state-of-the-art theoretical approaches. The experimental data were measured using a reaction microscope, which can cover nearly the entire $4\pi$ solid angle for the secondary electron emission energies ranging from 2 to 8 eV, and projectile scattering angles ranging from $8.5^{\circ }$ to $20.0^{\circ }$. The experimental triple-differential cross sections are internormalized across all measured scattering angles and ejected energies. The experimental data are compared to predictions from a hybrid second-order distorted-wave Born plus $R$-matrix approach, the distorted-wave Born approximation with the inclusion of postcollision interaction (PCI), a three-body distorted-wave approach (3DW), and a $B$-spline $R$-matrix (BSR) with pseudostates approach. Excellent agreement is found between the experiment and predictions from the 3DW and BSR models, for both the angular dependence and the relative magnitude of the cross sections in the full three-dimensional parameter space. The importance of PCI effects is clearly visible in this low-energy electron-impact ionization process.

The cavity-optomechanical radiation pressure interaction provides the means to create entanglement between a mechanical oscillator and an electromagnetic field interacting with it. Here we show how we can utilize this entanglement within the framework of time-continuous quantum control, in order to engineer the quantum state of the mechanical system. Specifically, we analyze how to prepare a low-entropy mechanical state by (measurement-based) feedback cooling operated in the blue-detuned regime, the creation of bipartite mechanical entanglement via time-continuous entanglement swapping, and preparation of a squeezed mechanical state by time-continuous teleportation. The protocols presented here are feasible in optomechanical systems exhibiting a cooperativity larger than 1.

We present a momentum-resolved study of strong field multiple ionization of ionic targets. Using a deconvolution method we are able to reconstruct the electron momenta from the ion momentum distributions after multiple ionization up to four sequential ionization steps. This technique allows an accurate determination of the saturation intensity as well as of the electron release times during the laser pulse. The measured results are discussed in comparison to typically used models of over-the-barrier ionization and tunnel ionization.

A two-dimensional topologically ordered quantum memory is well protected against error if the energy gap is large compared to the temperature, but this protection does not improve as the system size increases. We review and critique some recent proposals for improving the memory time by introducing long-range interactions among anyons, noting that instability with respect to small local perturbations of the Hamiltonian is a generic problem for such proposals. We also discuss some broader issues regarding the prospects for scalable quantum memory in two-dimensional systems.

We study the quantum dynamics of interacting bosons in a three-dimensional disordered lattice. We show that the superfluid current induced by an adiabatic acceleration of the disordered lattice undergoes a dynamical instability signaling the onset of the Bose-glass phase. The dynamical superfluid–Bose-glass phase diagram is found in very good agreement with static superfluid fraction calculation. A different boundary is obtained when the disorder is suddenly quenched in a moving periodic lattice. In this case we do not observe a dynamical instability but rather a depletion of the superfluid density. Our analysis is based on a dynamical Gutzwiller approach which we show to reproduce the quantum Monte Carlo static phase diagram in the strong interaction limit.

In this work we consider the dynamics of two tunnel-coupled chains after a quench in the tunneling strength is performed and the two systems are allowed to evolve independently. We describe the form of the initial state, comparing with previous results concerning the dynamics after the splitting of a one-dimensional gas of bosons into two phase-coherent systems. We compute different correlation functions, among which are those that are relevant for interference measurements, and discuss the emergence of effective temperatures also in connection with previous works.

We experimentally and theoretically study the peak fraction of a Bose-Einstein condensate loaded into a cubic optical lattice as the lattice potential depth and entropy per particle are varied. This system is well described by the superfluid regime of the Bose-Hubbard model, which allows for comparison with mean-field theories and exact quantum Monte Carlo (QMC) simulations. By correcting for systematic discrepancies between condensate and peak fraction, we find that the QMC simulations and measured peak fraction agree at low entropies per particle. At high entropy, however, we discover that the experiment consistently shows the presence of a condensate at temperatures higher than the critical temperature predicted by QMC simulations. This metastability suggests that turning on the lattice potential is nonadiabatic. To confirm this behavior, we compute the time scales for relaxation in this system, and find that equilibration times are comparable with the known heating rates. The similarity of these time scales implies that turning on the lattice potential adiabatically may be impossible. Our results point to the urgent need for a better theoretical and experimental understanding of the time scales for relaxation and adiabaticity in strongly interacting quantum gases, and the importance of model-independent probes of thermometry in optical lattices.

The collective interference of partially distinguishable bosons in multimode networks is studied via double-sided Feynman diagrams. The probability for many-body scattering events becomes a multidimensional tensor permanent, which interpolates between distinguishable particles and identical bosons and easily extends to mixed initial states. The permanent of the distinguishability matrix, composed of all mutual scalar products of the single-particle mode functions, emerges as a natural measure for the degree of interference: It yields a bound on the difference between event probabilities for partially distinguishable bosons and the idealized species and exactly quantifies the degree of bosonic bunching.

We explore the possible regimes of decaying two-dimensional quantum turbulence, and elucidate the nature of spectral energy transport by introducing a dissipative point-vortex model with phenomenological vortex-sound interactions. The model is valid for a large system with weak dissipation, and also for systems with strong dissipation, and allows us to extract a meaningful and unambiguous spectral energy flux associated with quantum vortex motion. For weak dissipation and large system size we find a regime of hydrodynamic vortex turbulence in which energy is transported to large spatial scales, resembling the phenomenology of the transient inverse cascade observed in decaying turbulence in classical incompressible fluids. For strong dissipation the vortex dynamics are dominated by dipole recombination and exhibit no appreciable spectral transport of energy.

Precise coherent control of the individual electronic spins associated with atomlike impurities in the solid state is essential for applications in quantum information processing and quantum metrology. We demonstrate all-optical initialization, fast coherent manipulation, and readout of the electronic spin of the negatively charged nitrogen-vacancy $\left({\text{NV}}^{-}\right)$ center in diamond at $T\sim \text{7}\text{K}$. We then present the observation of a novel double-dark resonance in the spectroscopy of an individual NV center. These techniques open the door for new applications ranging from robust manipulation of spin states using geometric quantum gates to quantum sensing and information processing.

We revisit the stabilization of ionization of atoms subjected to a superintense laser pulse using nonlinear dynamics. We provide an explanation for the lack of complete ionization at high intensity and for the decrease of the ionization probability as intensity is increased. We investigate the role of each part of the laser pulse (ramp-up, plateau, ramp-down) in this process. We emphasize the role of the choice for the ionization criterion, energy versus distance criterion.

We study a scheme for implementing a controlled-Z (cz) gate between two neutral-atom qubits based on the Rydberg blockade mechanism in a manner that is robust to errors caused by atomic motion. By employing adiabatic dressing of the ground electronic state, we can protect the gate from decoherence due to random phase errors that typically arise because of atomic thermal motion. In addition, the adiabatic protocol allows for a Doppler-free configuration that involves counterpropagating lasers in a ${\sigma }_{+}/{\sigma }_{-}$ orthogonal polarization geometry that further reduces motional errors due to Doppler shifts. The residual motional error is dominated by dipole-dipole forces acting on doubly excited Rydberg atoms when the blockade is imperfect. For reasonable parameters, with qubits encoded into the clock states of ${}^{133}\mathrm{Cs}$, we predict that our protocol could produce a cz gate in $<10$ $\mu \mathrm{s}$ with error probability on the order of ${10}^{-3}$.

Using the test-particle method, we solve numerically the Boltzmann equation for an ultracold gas of trapped fermions with realistic particle number and trap geometry in the normal phase. We include a mean-field potential and in-medium modifications of the cross section obtained within a T-matrix formalism. After some tests showing the reliability of our procedure, we apply the method to realistic cases of practical interest, namely the anisotropic expansion of the cloud and the radial quadrupole mode oscillation. Our results are in good agreement with experimental data. Although the in-medium effects significantly increase the collision rate, we find that they have only a moderate effect on the anisotropic expansion and on frequency and damping rate of the quadrupole mode.

We experimentally demonstrate an atom number detector capable of simultaneous detection of two mesoscopic ensembles with single-atom resolution. Such a sensitivity is a prerequisite for quantum metrology at a precision approaching the Heisenberg limit. Our system is based on fluorescence detection of atoms in a hybrid trap in which a dipole barrier divides a magneto-optical trap into two separated wells. We introduce a noise model describing the various sources contributing to the measurement error and report a limit of up to 500 atoms for single-atom resolution in the atom number difference.

We investigate the interaction of metastable $2S$ hydrogen atoms with a perfectly conducting wall, including parity-breaking $S-P$ mixing terms (with full account of retardation). The neighboring $2P_{1/2}$ and $2P_{3/2}$ levels are found to have a profound effect on the transition from the short-range, nonrelativistic regime, to the retarded form of the Casimir-Polder interaction. The corresponding $P$ state admixtures to the metastable $2S$ state are calculated. We find the long-range asymptotics of the retarded Casimir-Polder potentials and mixing amplitudes for general excited states, including a fully quantum electrodynamic treatment of the dipole-quadrupole mixing term. The decay width of the metastable $2S$ state is roughly doubled even at a comparatively large distance of 918 a.u. (Bohr radii) from the perfect conductor. The magnitude of the calculated effects is compared to the unexplained Sokolov effect.

Using the inherent timing stability of pulses from a mode-locked laser, we measure the cesium $6P_{3/2}$ excited-state lifetime. An initial pump pulse excites cesium atoms in two counterpropagating atomic beams to the $6P_{3/2}$ level. A subsequent synchronized probe pulse ionizes atoms that remain in the excited state and the photoions are collected and counted. By selecting pump pulses that vary in time with respect to the probe pulses, we obtain a sampling of the excited-state population in time, resulting in a lifetime value of 30.462(46) ns. The measurement uncertainty (0.15%) is slightly larger than our previous report of 0.12% [J. F. Sell et al., Phys. Rev. A 84, 010501(R) (2011)] due to the inclusion of additional data and systematic errors. In this follow-up paper we present details of the primary systematic errors encountered in the measurement, which include atomic motion within the intensity profiles of the laser beams, quantum beating in the photoion signal, and radiation trapping. Improvements to further reduce the experimental uncertainty are also discussed.

We demonstrate a method for preparing and detecting all eigenstates of a three-level microwave dressed system with a single trapped ion. The method significantly reduces the experimental complexity of gate operations with dressed-state qubits, as well as allowing all three of the dressed states to be prepared and detected, thereby providing access to a qutrit that is well protected from magnetic field noise. In addition, we demonstrate individual addressing of the clock transitions in two ions using a strong static magnetic field gradient, showing that our method can be used to prepare and detect microwave dressed states in a string of ions when performing multi-ion quantum operations with microwave and radio frequency fields. The individual addressability of clock transitions could also allow for the control of pairwise interaction strengths between arbitrary ions in a string using lasers.

We analyze the conditions under which local operations and classical communication enable entanglement transformations between bipartite pure Gaussian states. A set of necessary and sufficient conditions had been found [G. Giedke et al., Quant. Inf. Comput. 3, 211 (2003)] for the interconversion between such states that is restricted to Gaussian local operations and classical communication. Here, we exploit majorization theory in order to derive more general (sufficient) conditions for the interconversion between bipartite pure Gaussian states that goes beyond Gaussian local operations. While our technique is applicable to an arbitrary number of modes for each party, it allows us to exhibit surprisingly simple examples of $2\times 2$ Gaussian states that necessarily require non-Gaussian local operations to be transformed into each other.