In an ideal test of the equivalence principle, the test masses fall in a common inertial frame. A real experiment is affected by gravity gradients, which introduce systematic errors by coupling to initial kinematic differences between the test masses. Here we demonstrate a method that reduces the sensitivity of a dual-species atom interferometer to initial kinematics by using a frequency shift of the mirror pulse to create an effective inertial frame for both atomic species. Using this method, we suppress the gravity-gradient-induced dependence of the differential phase on initial kinematic differences by 2 orders of magnitude and precisely measure these differences. We realize a relative precision of Δg/g≈6×10^{-11} per shot, which improves on the best previous result for a dual-species atom interferometer by more than 3 orders of magnitude. By reducing gravity gradient systematic errors to one part in 10^{13}, these results pave the way for an atomic test of the equivalence principle at an accuracy comparable with state-of-the-art classical tests.

Improvements in both theory and frequency metrology of fewelectron systems such as hydrogen and helium have enabled increasingly sensitive tests of quantum electrodynamics (QED), as well as ever more accurate determinations of fundamental constants and the size of the nucleus. At the same time advances in cooling and trapping of neutral atoms have revolutionized the development of increasingly accurate atomic clocks. Here, we combine these fields to reach the highest precision on an optical tranistion in the helium atom to date by employing a Bose-Einstein condensate confined in a magic wavelength optical dipole trap. The measured transition accurately connects the ortho-and parastates of helium and constitutes a stringent test of QED theory. In addition we test polarizability calculations and ultracold scattering properties of the helium atom. Finally, our measurement probes the size of the nucleus at a level exceeding the projected accuracy of muonic helium measurements currently being performed in the context of the proton radius puzzle. 1 2 R.J. RENGELINK ET AL.In the past decades, high-precision spectroscopy measurements in atomic physics scale systems have pushed precision tests of quantum electrodynamics (QED), one of the cornerstones of the standard model of physics, ever further [1, 2] and have led to accurate determinations of fundamental constants [3][4][5][6]. Recently however, measurements of transition frequencies in muonic hydrogen (µH) have revealed a discrepancy of six standard deviations [7, 8] with respect to the accepted CODATA value for the proton charge radius. This discrepancy, which has become known as the "proton radius puzzle", has stimulated strong interest in the field, as its confirmation implies the violation of lepton universality, one of the pillars of the standard model. New experiments in atomic hydrogen [9, 10], and muonic deuterium [11] have only deepened the puzzle, prompting research into other elements such as muonic helium (µ 3,4 He + ) [12]. From these measurements the charge radii of the alpha-particle and the helion (1.68 fm resp. 1.97 fm) are projected to be determined with sub-attometer accuracy, which should be compared to high-precision experiments in electronic helium atoms or ions.QED theory of the helium atom, with two electrons more complicated than hydrogen, has seen impressive improvements in recent years, with QED corrections up to order mα 6 now evaluated [2]. Recent experiments are in good agreement [13][14][15][16][17][18][19][20] and may allow a competitive value for the fine structure constant in the near future [21][22][23][24]. The anticipated evaluation of the next highest order corrections (mα 7 ) [2] would allow the determination of the 4 He nuclear charge radius with an accuracy better than 1%. At present nuclear charge radii can already be determined differentially, i.e. with respect to 4 He, due to cancellation of higher-order terms in the isotope shift. Using this approach the radii of the exotic halo nuclei 6 He and 8 He [25,26], as well as t...

We have calculated ac polarizabilities of the 2 3 S and 2 1 S states of both 4 He and 3 He in the range 318 nm to 2.5 μm and determined the magic wavelengths at which these polarizabilities are equal for either isotope. The calculations, only based on available ab initio tables of level energies and Einstein A coefficients, do not require advanced theoretical techniques. The polarizability contribution of the continuum is calculated using a simple extrapolation beyond the ionization limit, yet the results agree to better than 1% with such advanced techniques. Several promising magic wavelengths are identified around 320 nm with sufficient accuracy to design an appropriate laser system. The extension of the calculations to 3 He is complicated due to the additional hyperfine structure, but we show that the magic wavelength candidates around 320 nm are predominantly shifted by the isotope shift.

High-precision spectroscopy of the forbidden 2 3 S 1 → 2 1 P 1 transition in quantum degenerate metastable helium We have measured the forbidden 2 3 S1 → 2 1 P1 transition at 887 nm in a quantum degenerate gas of metastable 4 He atoms confined in an optical dipole trap. The determined transition frequency is 338 133 594.4 (0.5) MHz, from which we obtain an ionization energy of the 2 1 P1 state of 814 709 148.6 (0.5) MHz. This ionization energy is in disagreement by > 3σ with the most accurate quantum electrodynamics (QED) calculations available. Our measurements also provide a new determination of the lifetime of the 2 1 P1 state of 0.551 (0.004)stat ( +0.013 −0.000 )syst ns, which is the most accurate determination to date and in excellent agreement with theory.

We observe a dramatic difference in optical line shapes of a 4 He Bose-Einstein condensate and a 3 He degenerate Fermi gas by measuring the 1557-nm 2 3 S − 2 1 S magnetic dipole transition (8 Hz natural linewidth) in an optical dipole trap. The 15 kHz FWHM condensate line shape is only broadened by mean field interactions, whereas the degenerate Fermi gas line shape is broadened to 75 kHz FWHM due to the effect of Pauli exclusion on the spatial and momentum distributions. The asymmetric optical line shapes are observed in excellent agreement with line shape models for the quantum degenerate gases. For 4 He a triplet-singlet s-wave scattering length a = +50(10)stat(43)syst a0 is extracted. The high spectral resolution reveals a doublet in the absorption spectrum of the BEC, and this effect is understood by the presence of a weak optical lattice in which a degeneracy of the lattice recoil and the spectroscopy photon recoil leads to Bragg-like scattering.The bosonic or fermionic nature of a particle is a fundamental property, and trapped quantum degenerate gases display dramatic different behaviour depending on the quantum statistical nature of the gas. At low temperatures identical bosons accumulate in the lowest state in the trap, leading to Bose-Einstein condensation. In contrast, identical fermions cannot occupy the same state due to the Pauli exclusion principle, and will 'fill' all states in the trap from the bottom up until no more atoms -or states -are available. A drastic difference in line shape of a narrow optical transition is expected when measured in a Bose-Einstein condensate (BEC) and a degenerate Fermi gas (DFG). In this Letter we show a direct comparison of this difference between a BEC of metastable 4 He and a DFG of metastable 3 He trapped in an optical dipole trap (ODT).We do this work in the framework of high-precision frequency metrology in helium, aimed at testing quantum electrodynamics (QED). Comparison of accurate transition frequencies is used to determine fundamental physical parameters that are difficult to measure otherwise, such as the nuclear charge radius of an atom. Recently high-precision frequency metrology in (muonic) hydrogen and deuterium resulted in a remarkable discrepancy in the determination of the proton and deuteron charge radius [1,2]. This discrepancy, also known as the 'proton radius puzzle', is currently under scrutiny by many groups all over the world and similar work is ongoing for helium [3]. To determine the 3 He-4 He nuclear charge radius difference, we recently measured the doubly forbidden 2 3 S − 2 1 S transition at 1557 nm (natural linewidth 8 Hz) in both quantum degenerate 4 He and 3 He with 1.8 kHz and 1.5 kHz accuracy, respectively [4]. The measured isotope shift, combined with QED calculations, allowed a determination of a squared nuclear charge radius difference of 1.028(11) fm 2 [5]. To compare this determination to measurements in muonic helium ions [3] we aim to measure the 2 3 S − 2 1 S transition frequency with ≪ 1 kHz accuracy. Using a narrow lin...

Photo-ionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in Focus Ion Beam (FIB) instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with a brightness of 2.1 × 10 7 A/(m 2 sr eV) at a current of 1 nA can be created using a compact 5 cm long 2D magneto-optical compressor which is more than an order of magnitude better than the current state of the art Liquid Metal Ion Source.

The generation of a register of highly coherent, but independent, qubits is a prerequisite to performing universal quantum computation. Here we introduce a qubit encoded in two nuclear spin states of a single 87Sr atom and demonstrate coherence approaching the minute-scale within an assembled register of individually-controlled qubits. While other systems have shown impressive coherence times through some combination of shielding, careful trapping, global operations, and dynamical decoupling, we achieve comparable coherence times while individually driving multiple qubits in parallel. We highlight that even with simultaneous manipulation of multiple qubits within the register, we observe coherence in excess of 105 times the current length of the operations, with $${T}_{2}^{{{{{\mathrm{echo}}}}}}=\left(40\pm 7\right)$$ T 2 echo = 40 ± 7 seconds. We anticipate that nuclear spin qubits will combine readily with the technical advances that have led to larger arrays of individually trapped neutral atoms and high-fidelity entangling operations, thus accelerating the realization of intermediate-scale quantum information processors.

We present a new interferometer technique whereby multiple extreme ultraviolet light pulses are generated at different positions within a single laser focus (i.e., from successive sources) with a highly controllable time delay. The interferometer technique is tested with two generating media to create two extreme ultraviolet light pulses with a time delay between them. The delay is found to be a consequence of the Gouy phase shift. Ultimately the apparatus is capable of accessing unprecedented time scales by allowing stable and repeatable delays as small as 100 zs.