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arXiv2013

Limits on Violations of Lorentz Symmetry and the Einstein Equivalence Principle using Radio-Frequency Spectroscopy of Atomic Dysprosium

We report a joint test of local Lorentz invariance and the Einstein equivalence principle for electrons, using long-term measurements of the transition frequency between two nearly degenerate states of atomic dysprosium. We present many-body calculations which demonstrate that the energy splitting of these states is particularly sensitive to violations of both special and general relativity. We limit Lorentz violation for electrons at the level of $10^{-17}$, matching or improving the best laboratory and astrophysical limits by up to a factor of 10, and improve bounds on gravitational redshift anomalies for electrons by 2 orders of magnitude, to $10^{-8}$. With some enhancements, our experiment may be sensitive to Lorentz violation at the level of $9\times 10^{-20}$.

hep-ph↗

arXiv2013

New limits on variation of the fine-structure constant using atomic dysprosium

We report on the spectroscopy of radio-frequency transitions between nearly-degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant, $α$, owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of $α$ competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in $^{164}$Dy and 235-MHz transition in $^{162}$Dy were measured over the span of two years. Linear variation of $α$ is found to be $\dotα/α= (-5.8\pm6.9)\times10^{-17}$ yr$^{-1}$, consistent with zero. The same data are used to constrain the dimensionless parameter $k_α$, characterizing a possible coupling of $α$ to a changing gravitational potential. We find that $k_α= (-5.5\pm5.2)\times10^{-7}$, essentially consistent with zero and the best constraint to date.

physics.atom-ph↗

arXiv2013

Coherent control at its most fundamental: CEP-dependent electron localization in photodissoziation of a H2+ molecular ion beam target

Measurements and calculations of the absolute carrier-envelope phase (CEP) effects in the photodissociation of the simplest molecule, H2+, with a 4.5-fs Ti:Sapphire laser pulse at intensities up to (4 +- 2)x10^14 Watt/cm^2 are presented. Localization of the electron with respect to the two nuclei (during the dissociation process) is controlled via the CEP of the ultra-short laser pulses. In contrast to previous CEP-dependent experiments with neutral molecules, the dissociation of the molecular ions is not preceded by a photoionization process, which strongly influences the CEP dependence. Kinematically complete data is obtained by time- and position-resolved coincidence detection. The phase dependence is determined by a single-shot phase measurement correlated to the detection of the dissoziation fragments. The experimental results show quantitative agreement with ab inito 3D-TDSE calculations that include nuclear vibration and rotation.

physics.chem-ph↗

arXiv2013

A Raman-induced Feshbach resonance in an effectively single-component Fermi gas

Ultracold gases of interacting spin-orbit coupled fermions are predicted to display exotic phenomena such as topological superfluidity and its associated Majorana fermions. Here, we experimentally demonstrate a route to strongly-interacting single-component atomic Fermi gases by combining an s-wave Feshbach resonance (giving strong interactions) and spin-orbit coupling (creating an effective p-wave channel). We identify the Feshbach resonance by its associated atomic loss feature and show that, in agreement with our single-channel scattering model, this feature is preserved and shifted as a function of the spin-orbit coupling parameters.

cond-mat.quant-gas↗

arXiv2013

A Laboratory Search for a Long-Range T-odd, P-odd Interaction from Axion-Like Particles using Dual Species Nuclear Magnetic Resonance with Polarized Xe-129 and Xe-131 Gas

We place new limits on potential T- and P- violating monopole-dipole interactions between unpolarized nucleons and neutrons using dual species magnetic resonance in polarzed Xe gas. Free-induction decay transients with relaxation times ~20 s allow high precision measurements of the NMR frequencies, whose ratios cancel magnetic fluctuations. The new limits on the product gsgp improve on previous laboratory work by 2 orders of magnitude.

physics.atom-ph↗

arXiv2013

Excitation of a single atom with exponentially rising light pulses

We investigate the interaction between a single atom and optical pulses in a coherent state with a controlled temporal envelope. In a comparison between a rising exponential and a square envelope, we show that the rising exponential envelope leads to a higher excitation probability for fixed low average photon numbers, in accordance to a time-reversed Weisskopf-Wigner model. We characterize the atomic transition dynamics for a wide range of the average photon numbers, and are able to saturate the optical transition of a single atom with ~50 photons in a pulse by a strong focusing technique. For photon numbers of ~1000 in a 15ns long pulse, we clearly observe Rabi oscillations.

quant-ph↗

arXiv2013

Enhanced atom interferometer readout through the application of phase shear

We present a method for determining the phase and contrast of a single shot of an atom interferometer. The application of a phase shear across the atom ensemble yields a spatially varying fringe pattern at each output port, which can be imaged directly. This method is broadly relevant to atom interferometric precision measurement, as we demonstrate in a 10 m Rb-87 atomic fountain by implementing an atom interferometric gyrocompass with 10 millidegree precision.

physics.atom-ph↗

arXiv2013

Stability of a unitary Bose gas

We study the stability of a thermal $^{39}$K Bose gas across a broad Feshbach resonance, focusing on the unitary regime, where the scattering length $a$ exceeds the thermal wavelength $λ$. We measure the general scaling laws relating the particle-loss and heating rates to the temperature, scattering length, and atom number. Both at unitarity and for positive $a \ll λ$ we find agreement with three-body theory. However, for $a<0$ and away from unitarity, we observe significant four-body decay. At unitarity, the three-body loss coefficient, $L_3 \propto λ^4$, is three times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes $^{39}$K particularly promising for studies of many-body physics in a unitary Bose gas.

cond-mat.quant-gas↗

arXiv2013

High resolution probe of coherence in low-energy charge exchange collisions with oriented targets

The trapping lasers of a magneto-optical trap (MOT) are used to bring Rb atoms into well defined oriented states. Coupled to recoil-ion momentum spectroscopy (RIMS), this yields a unique MOTRIMS setup which is able to probe scattering dynamics, including their coherence features, with unprecedented resolution. This technique is applied to the low-energy charge exchange processes Na$^+$+Rb($5p_{\pm 1}$) $\rightarrow$ Na($3p,4s$)+Rb$^+$. The measurements reveal detailed features of the collisional interaction which are employed to improve the theoretical description. All of this enables to gauge the reliability of intuitive pictures predicting the most likely capture transitions.

physics.atom-ph↗

arXiv2013

Quantum metrology with a scanning probe atom interferometer

We use a small atomic Bose-Einstein condensate as an interferometric scanning probe to map out a microwave field near a chip surface with a few micrometers resolution. Using entanglement between the atoms we overcome the standard quantum limit of interferometry by 4 dB and maintain enhanced performance for interrogation times up to 20 ms. This demonstrates the usefulness of quantum metrology with entangled states when the particle number is limited due to the small probe size. Extending atom interferometry to micrometer spatial resolution enables new applications in electromagnetic field sensing, surface science, and the search for fundamental short-range interactions.

quant-ph↗

arXiv2013

Nuclear polarization corrections in the mu-4He+ Lamb shift

Stimulated by the proton radius conundrum, measurements of the Lamb shift in various light muonic atoms are planned at PSI. The aim is to extract the rms charge radius with high precision, limited by the uncertainty in the nuclear polarization corrections. We present an ab-initio calculation of the nuclear polarization for mu-4He+ leading to an energy correction in the 2S-2P transitions of $δ_{pol}=-2.47$ meV $\pm$ 6%. We use two different state-of-the-art nuclear Hamiltonians and utilize the Lorentz integral transform with hyperspherical harmonics expansion as few-body methods. We take into account the leading multipole contributions, plus Coulomb, relativistic and finite-nucleon-size corrections. Our main source of uncertainty is the nuclear Hamiltonian, which currently limits the attainable accuracy. Our predictions considerably reduce the uncertainty with respect to previous estimates and should timely serve the mu-4He+ experiment planned for 2013.

nucl-th↗

arXiv2013

Quasiparticle lifetime in ultracold fermionic mixtures with density and mass imbalance

We show that atomic Fermi mixtures with density and mass imbalance exhibit a rich diversity of scaling laws for the quasiparticle decay rate beyond the quadratic energy and temperature dependence of conventional Fermi liquids. For certain densities and mass ratios, the decay rate is linear whereas in other cases it exhibits a plateau. Remarkably, this plateau extends from the deeply degenerate to the high temperature classical regime of the light species. Many of these scaling laws are analogous to what is found in very different systems including dirty metals, liquid metals, and high temperature plasmas. The Fermi mixtures can in this sense span a whole range of seemingly diverse and separate physical systems. Our results are derived in the weakly interacting limit making them quantitatively reliable. The different regimes can be detected with radio-frequency spectroscopy.

cond-mat.quant-gas↗

arXiv2013

Equivalence Principle and Bound Kinetic Energy

We consider the role of the internal kinetic energy of bound systems of matter in tests of the Einstein equivalence principle. Using the gravitational sector of the standard model extension, we show that stringent limits on equivalence principle violations in antimatter can be indirectly obtained from tests using bound systems of normal matter. We estimate the bound kinetic energy of nucleons in a range of light atomic species using Green's function Monte Carlo calculations, and for heavier species using a Woods-Saxon model. We survey the sensitivities of existing and planned experimental tests of the equivalence principle, and report new constraints at the level of between a few parts in $10^{6}$ and parts in $10^{8}$ on violations of the equivalence principle for matter and antimatter.

gr-qc↗

arXiv2013

Dynamic core polarization in strong-field ionization of CO molecules

The orientation-dependent strong-field ionization of CO molecules is investigated using the fully propagated three-dimensional time-dependent Hartree-Fock theory. The full ionization results are in good agreement with recent experiments. The comparisons between the full method and single active orbital (SAO) method show that although the core electrons are generally more tightly bounded and contribute little to the total ionization yields, their dynamics cannot be ignored, which effectively modify the behaviors of electrons in the highest occupied molecular orbital. By incorporating it into the SAO method, we identify that the dynamic core polarization plays an important role in the strong-field tunneling ionization of CO molecules, which is helpful for future development of tunneling ionization theory of molecules beyond single active electron approximation.

physics.atom-ph↗

arXiv2013

Experimental recovery of a qubit from partial collapse

We describe and implement a method to restore the state of a single qubit, in principle perfectly, after it has partially collapsed. The method resembles the classical Hahn spin-echo, but works on a wider class of relaxation processes, in which the quantum state partially leaves the computational Hilbert space. It is not guaranteed to work every time, but successful outcomes are heralded. We demonstrate using a single trapped ion better performance from this recovery method than can be obtained employing projection and post-selection alone. The demonstration features a novel qubit implementation that permits both partial collapse and coherent manipulations with high fidelity.

quant-ph↗

arXiv2013

Realizing the Harper Hamiltonian with Laser-Assisted Tunneling in Optical Lattices

We experimentally implement the Harper Hamiltonian for neutral particles in optical lattices using laser-assisted tunneling and a potential energy gradient provided by gravity or magnetic field gradients. This Hamiltonian describes the motion of charged particles in strong magnetic fields. Laser-assisted tunneling processes are characterized by studying the expansion of the atoms in the lattice. The band structure of this Hamiltonian should display Hofstadter's butterfly. For fermions, this scheme should realize the quantum Hall effect and chiral edge states.

cond-mat.quant-gas↗

arXiv2013

Time delay in the recoiling valence-photoemission of Ar endohedrally confined in C$_{60}$

Effects of confinement and electron correlations on the relative time delay between the 3s and 3p photoemissions of Ar confined endohedrally in C$_{60}$ are investigated using the time dependent local density approximation - a method that is also found to mostly agree with recent time delay measurements between the 3s and 3p subshells in atomic Ar. At energies in the neighborhood of 3p Cooper minimum, correlations with C$_{60}$ electrons are found to induce opposite temporal effects in the emission of Ar 3p hybridized symmetrically versus that of Ar 3p hybridized antisymmetrically with C$_{60}$. A recoil-type interaction model mediated by the confinement is found to best describe the phenomenon.

physics.atom-ph↗

arXiv2013

Vibrationally Resolved Decay Width of Interatomic Coulombic Decay in HeNe

We investigate the ionization of HeNe from below the He 1s3p excitation to the He ionization threshold. We observe HeNe$^+$ ions with an enhancement by more than a factor of 60 when the He side couples resonantly to the radiation field. These ions are an experimental proof of a two-center resonant photoionization mechanism predicted by Najjari et al. [Phys. Rev. Lett. 105, 153002 (2010)]. Furthermore, our data provide electronic and vibrational state resolved decay widths of interatomic Coulombic decay (ICD) in HeNe dimers. We find that the ICD lifetime strongly increases with increasing vibrational state.

physics.atm-clus↗