We present the full evaluation of a cold-atom gyroscope based on atom interferometry. We have performed extensive studies to determine the systematic errors, scale factor and sensitivity. We demonstrate that the acceleration noise can be efficiently removed from the rotation signal, allowing us to reach the fundamental limit of the quantum projection noise for short term measurements. The technical limits to the long term sensitivity and accuracy have been identified, clearing the way for the next generation of ultrasensitive atom gyroscopes.

We consider a partially spin-polarized atomic Fermi gas in a high-aspect-ratio trap, with a flux of predominantly spin-up atoms exiting the center of the trap. We argue that such a scenario can be produced by evaporative cooling, and we find that it can result in a substantially nonequilibrium polarization pattern for typical experimental parameters. We offer this as a possible explanation for the quantitative discrepancies in recent experiments on spin-imbalanced unitary Fermi gases.

We demonstrate a quadratic phase gate for one-way quantum computation in the continuous-variable regime. This canonical gate, together with phase-space displacements and Fourier rotations, completes the set of universal gates for realizing any single-mode Gaussian transformation such as arbitrary squeezing. As opposed to previous implementations of measurement-based squeezers, the current gate is fully controlled by the local oscillator phase of the homodyne detector. Verifying this controllability, we give an experimental demonstration of the principles of one-way quantum computation over continuous variables. Moreover, we can observe sub-shot-noise quadrature variances in the output states, confirming that nonclassical states are created through cluster computation.

Whether a spin-1/2 Fermi gas will become ferromagnetic as the strength of repulsive interaction increases is a long-standing controversial issue. Recently this problem has been studied experimentally by Jo et al. [Science 325, 1521 (2009)] in which the authors claim a ferromagnetic transition is observed. This work is to point out the results of this experiment cannot distinguish whether the system is in a ferromagnetic state or in a nonmagnetic but strongly short-range correlated state. A conclusive experimental demonstration of ferromagnetism relies on the observation of ferromagnetic domains.

In this paper, continuous variable stabilizer state is described by its generator matrix. Then the fact that any stabilizer state could be reduced to the corresponding weighed graph state under local unitary operation in the Clifford group is proved. A matrix equation, which is used to determine whether two stabilizer states are equivalent or not under local unitary operation in the Clifford group, is proposed. Then we apply the method to the five-mode unweighed graph states and demonstrate that our theory could be able to correctly and quickly find the equivalent classes of five-mode unweighed graph states.

We present simple mappings between classical lattice models and quantum circuits, which provide a systematic formalism to obtain quantum algorithms to approximate partition functions of lattice models in certain complex-parameter regimes. We, e.g., present an efficient quantum algorithm for the six-vertex model as well as a two-dimensional Ising-type model. We show that classically simulating these (complex-parameter) spin models is as hard as simulating universal quantum computation, i.e., BQP complete (BQP denotes bounded-error quantum polynomial time). Furthermore, our mappings provide a framework to obtain efficiently simulable quantum gate sets from exactly solvable classical models. We, e.g., show that the simulability of Valiant’s match gates can be recovered by using the solvability of the free-fermion eight-vertex model.

We derive several entanglement conditions employing non-Hermitian operators. We start with two conditions that were derived previously for field mode operators and use them to derive conditions that can be used to show the existence of field-atom entanglement and entanglement between groups of atoms. The original conditions can be strengthened by making them invariant under certain sets of local unitary transformations such as Gaussian operations. We then apply these conditions to several examples such as the Dicke model. We conclude with a short discussion of how local uncertainty relations with non-Hermitian operators can be used to derive entanglement conditions.

Within an adiabatic approximation to the three-body Coulomb system, we study the strength of the leading-order conformaly invariant attractive dipole interaction produced when a slow charged particle $q_3$ (with mass $m_3$) is captured by the first-excited state of a dimer [with individual masses and charges $\left(m_1,q_1\right)$ and $\left(m_2,q_2=-q_1\right)$]. The approach leads to a universal mass-charge critical condition for the existence of three-body level condensation, $\left(m_1^{-1}+m_2^{-1}\right)/\left[{\left(m_1+m_2\right)}^{-1}+m_3^{-1}\right]>\left|q_1/\left(24q_3\right)\right|$, as well as the ratio between the geometrically scaled energy levels. The resulting expressions can be relevant in the analysis of recent experimental setups with charged three-body systems, such as the interactions of excitons, or other matter-antimatter dimers, with a slow charged particle.

Formal expressions and their corresponding expansions in terms of Kohn-Sham (KS) orbitals are deduced for the exchange potential $v_x\left(\mathbf{r}\right)$. After an alternative derivation of the basic optimized effective potential integrodifferential equations is given through a Hartree-Fock adiabatic connection perturbation theory, we present an exact infinite expansion for $v_x\left(\mathbf{r}\right)$ that is particularly simple in structure. It contains the very same occupied-virtual quantities that appear in the well-known optimized effective potential integral equation, but in this new expression $v_x\left(\mathbf{r}\right)$ is isolated on one side of the equation. An orbital-energy modified Slater potential is its leading term which gives encouraging numerical results. Along different lines, while the earlier Krieger-Li-Iafrate approximation truncates completely the necessary first-order perturbation orbitals, we observe that the improved localized Hartree-Fock (LHF) potential, or common energy denominator potential (CEDA), or effective local potential (ELP), incorporates the part of each first-order orbital that consists of the occupied KS orbitals. With this in mind, the exact correction to the LHF, CEDA, or ELP potential (they are all equivalent) is deduced and displayed in terms of the virtual portions of the first-order orbitals. We close by observing that the newly derived exact formal expressions and corresponding expansions apply as well for obtaining the correlation potential from an orbital-dependent correlation energy functional.

Two-photon decay of hydrogenlike ions is studied within the framework of second-order perturbation theory, based on the relativistic Dirac’s equation. Special attention is paid to the effects arising from the summation over the negative-energy (intermediate virtual) states that occur in such a framework. In order to investigate the role of these states, detailed calculations have been carried out for the $2s_{1/2}\to 1s_{1/2}$ and $2p_{1/2}\to 1s_{1/2}$ transitions in neutral hydrogen H as well as for hydrogenlike xenon ${\text{Xe}}^{53+}$ and uranium ${\text{U}}^{91+}$ ions. We found that for a correct evaluation of the total and energy-differential decay rates, summation over the negative-energy part of Dirac’s spectrum should be properly taken into account both for high-$Z$ and low-$Z$ atomic systems.

Two-photon above-threshold ionization processes in the x-ray regime are studied using atomic hydrogen as a model system. Within the minimal-coupling formalism of nonrelativistic quantum electrodynamics, two distinct interactions—$\hat{\mathbf{A}}\cdot \hat{\mathbf{p}}$ in second order and ${\hat{\mathbf{A}}}^2$ in first order—contribute to the two-photon absorption amplitude. The relative importance of these two interactions is assessed. It is found that above a photon energy of 6.8 keV, the contribution from ${\hat{\mathbf{A}}}^2$ to the total two-photon absorption cross section dominates. In this high-energy regime, above-threshold ionization is a nonsequential purely nondipole process. Rate equations are employed to calculate the probabilities of ionization by Compton scattering, one-photon absorption, and two-photon absorption.

In this work, we apply approximate expansions of Gaussian-type geminals of $r_{12}$ to replace the integer and half-integer powers of $r_{12}$ in Hylleraas-Gaussian basis, and use a full configuration-interaction method to calculate the energies of ${{}^{1}0}^{+}$, ${{}^1\left(-1\right)}^{+}$, and ${{}^1\left(-2\right)}^{+}$ states for helium atom in magnetic fields between 0 and 100 a.u. Compared to the configuration-interaction method with Gaussian basis, at least $1\times {10}^{-4}$ improvement in the precision of energies has been made when calculated mean value of $r_{12}$ is less than 5.67 a.u. and more than $5\times {10}^{-4}$ improvement in precision of results has been achieved when calculated mean value of $r_{12}$ is less than 2.41 a.u. The ground-state energy of helium atom in our calculation is $-2.9037155$ in the absence of magnetic field. This work presents a general method which can attain high precise ground and low-lying states energies in the whole field regime and is hopeful to be extended to more complex atomic and molecular systems (lithium, beryllium, and ${\text{H}}_2$, etc.).

A two-component four-fermion system with equal masses, interspecies $s$-wave scattering length $a_s$, and vanishing intraspecies interactions under external spherically symmetric harmonic confinement is considered. Using a correlated Gaussian basis set expansion approach, we determine the energies and various structural properties of the energetically lowest-lying gaslike state throughout the crossover for various ranges of the underlying two-body potential. Extrapolating to the zero-range limit, our numerical results show explicitly that the total energy, the trap energy, as well as certain aspects of the pair distribution function and of the momentum distribution are related through the so-called integrated contact intensity $I\left(a_s\right)$. Furthermore, it is shown explicitly that the total energy and the trap energy are related through a generalized virial theorem that accounts for a nonzero range.

We show that it is possible to achieve laser oscillation and two-mode entanglement by using dressed-state phase-dependent electromagnetically induced transparency (EIT) in a double $\Lambda$ system. Under certain conditions, two beams of bichromatic fields induce the depopulation of a coherent superposition state of the two excited states and the quantum beat of a pair of cavity fields. While one of two beams of bichromatic fields dresses the atoms, the other and the pair of cavity fields are in phase-controlled EIT interaction with the dressed atoms. On the basis of this, the pair of cavity fields not only operates well above threshold and exhibit subshot noise but also is in an entangled state. This mechanism suggests an efficient way to achieve bright entangled source of light.

We report experimental observation of slow or fast light in configuration of counterpropagating saturating and probe waves in erbium-doped fibers with saturable absorption. The delayed or accelerated probe light propagation is shown to be associated with two-wave mixing (TWM) between these two waves via dynamic population grating. As compared with recording at 1526 nm from the central region of ${\text{Er}}^{3+}$ fundamental absorption spectrum, at 1485 nm, the population grating has significant admixture of the refractive index component. This results in a significant asymmetry of the TWM-induced transmittance of the probe wave as a function of the frequency offset $\Delta \Omega$ between the waves and shifts position of the maximum group delay from zero $\Delta \Omega$. The same reason ensures appearance of a significant group advancement for the frequency offset of the opposite sign.

We report the anisotropic collision-induced scattering (CIS) spectrum of two neon atoms at room temperature. The covered spectral range hitherto restricted to $170{\text{cm}}^{-1}$ is here tripled. Both our measurements and quantum-mechanical calculations obtained on the basis of large-scale ab initio anisotropy representations reveal a well-defined saddle-shaped wing. This peculiar structure is experimental evidence of a binary CIS line shape with an aspect other than a smooth wing in a logarithmic plot. Equally interesting is the fact that this feature has been predicted (though only qualitatively) by the simple semiempirical model long ago reported by Meinander, Tabisz, and Zoppi [J. Chem. Phys. 84, 3005 (1986)], but no emphasis had at that time been placed on the aspect of the wing of the model spectrum probably due to the lack of high-frequency experimental data.

An efficient method to generate an isolated short attosecond pulse is presented theoretically. We show that, by adding a 0.5 fs, 62.3 nm extreme ultraviolet (xuv) attosecond pulse to a synthesized two-color field at a proper time, the harmonic intensity is effectively enhanced by 1–3 orders of magnitude compared with the two-color case and the harmonic spectrum higher than 260th order reveals an ultrabroad xuv supercontinuum. In addition, the short quantum path is selected to effectively contribute to the high order harmonics, and an isolated 40 as pulse is obtained. Our calculated results also show that, by adding a 0.5 fs, 29.6 nm xuv attosecond pulse to the synthesized two-color field at a proper time, the enhancement of the high-order harmonics and an ultrabroad xuv supercontinuum is observed, and the selection of the long quantum path can be achieved, then an isolated attosecond pulse as short as 39 as is generated.

Isolated nuclear spins provide a promising building block for quantum information science, motivating development of techniques to characterize, control, and detect them in suitable systems. Working with the nitrogen-vacancy center in diamond, we demonstrate robust initialization, manipulation, and readout of individual ${}^{13}\text{C}$, ${}^{15}\text{N}$, and ${}^{14}\text{N}$ nuclear spins and identify a mechanism to extend our results to arbitrary magnetic field environments. These techniques enable precise characterization of nuclear-spin hyperfine parameters and coherence properties and may pave the way for nuclear-spin-based quantum information architectures in diamond.

We propose to implement a sub-shot-noise matter-wave interferometer via the stimulated dissociation of a molecular Bose-Einstein condensate and study the collisional loss of atom-molecule coherence during its phase-acquisition time. The obtained $n$-atom states are two-atom [SU(1,1)] coherent states with number variance $\Delta n\propto n$ compared to $\Delta n\propto \sqrt{n}$ for the spin [SU(2)] coherent states formed by coherent splitting of an atomic condensate. Consequently, the Lorentzian atom-molecule phase diffusion is faster than the Gaussian phase diffusion between separated atomic condensates by a $\sqrt{n}$ factor.

The class of $d$-setting, $d$-outcome Bell inequalities proposed by Ji and co-workers [Phys. Rev. A 78, 052103 (2008)] are reexamined. For every positive integer $d>2$, we show that the corresponding nontrivial Bell inequality for probabilities provides the maximum classical winning probability of the Clauser-Horne-Shimony-Holt-like game with $d$ inputs and $d$ outputs. We also demonstrate that the general classical upper bounds given by Ji et al. are underestimated, which invalidates many of the corresponding correlation inequalities presented thereof. We remedy this problem, partially, by providing the actual classical upper bound for $d\le 13$ (including nonprime values of $d$). We further determine that for prime value $d$ in this range, most of these probability and correlation inequalities are tight, i.e., facet-inducing for the respective classical correlation polytope. Stronger lower and upper bounds on the quantum violation of these inequalities are obtained. In particular, we prove that once the probability inequalities are given, their correlation counterparts given by Ji and co-workers are no longer relevant in terms of detecting the entanglement of a quantum state.