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Notermans, Remy; Vassen, W.

doi:10.1103/physrevlett.112.253002

Cited by 40 publications

(41 citation statements)

References 41 publications

(56 reference statements)

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“…for fundamental tests of two-electron quantum electrodynamic theory [11][12][13]. So far, 4 He * BECs have been obtained in Ioffe-Pritchard or cloverleaf type of magnetic traps [14][15][16][17][18][19][20], which has been subsequently transferred to a single-beam [21,22] or crossed-beam ODT [11] (see Ref.…”

Section: Introductionmentioning

confidence: 99%

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

et al. 2015

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Alternatively, one loads the atoms first in a magnetic trap and performs evaporative cooling and afterward transfers a dense and compact atomic cloud into an ODT, which now requires a much lower ODT power, at the expense of experimental complexity. Within this last category, a very elegant approach is the hybrid trap (HT), introduced in Ref.[1], consisting of a simple quadrupole magnetic trap (QMT) and a single-beam ODT. Efficient evaporation and BoseEinstein condensation (BEC) have been demonstrated (see, e.g., [1][2][3]), using ODT powers of only a few Watts. By switching off the QMT completely, the atoms are transferred from the HT to a pure ODT.The hybrid trap has been mostly applied to 87 Rb, but is assumed to be generally applicable to other magnetically trappable atomic species [1]. However, the application of HT strongly depends on the mass of atom. Most importantly, the rates of Majorana loss and heating, which determine the temperature that can be reached by evaporative cooling in a QMT, scale inversely with mass [4,5]. This limits the transfer efficiency for light atoms, or puts constraints on the trap volume and trap depth, and therefore the power, of the ODT. Furthermore, for light atoms evaporative cooling in the HT is limited as the additional axial confinement provided by the QMT is small because of the small levitation gradient, below which the QMT has to operate in the HT. Finally, the small levitation gradient puts experimental limits on the control of the displacement of the QMT with respect to the ODT, which further limits the axial confinement.Here we report on the production of a metastable triplet helium ( 4 He * ) BEC using a single-beam HT with a moderate power of less than 3 W, demonstrating the application of HT for a light atom. Our work provides a novel and simple method for obtaining a 4 He * BEC, which can be used for atom optics experiments [6][7][8][9][10] or precision spectroscopy Abstract We demonstrate a simple scheme to reach Bose-Einstein condensation (BEC) of metastable triplet helium atoms using a single-beam optical dipole trap with moderate power of less than 3 W. Our scheme is based on RF-induced evaporative cooling in a quadrupole magnetic trap and transfer to a single-beam optical dipole trap that is located below the magnetic trap center. We transfer 1 × 10 6 atoms into the optical dipole trap, with an initial temperature of 14 µK, and observe efficient forced evaporative cooling both in a hybrid trap, in which the quadrupole magnetic trap operates just below the levitation gradient, and in the pure optical dipole trap, reaching the onset of BEC with 2 × 10 5 atoms and a pure BEC of 5 × 10 4 atoms. Our work shows that a single-beam hybrid trap can be applied for a light atom, for which evaporative cooling in the quadrupole magnetic trap is strongly limited by Majorana spin-flips, and the very small levitation gradient limits the axial confinement in the hybrid trap.

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Section: Introductionmentioning

confidence: 99%

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

et al. 2015

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“…The possibility to accurately calculate level energies and wavefunctions has allowed confrontation with several other experimental results. Radiative lifetimes of the 2 3 S 1 and 2 1 P 1 states have been measured in cold clouds of helium atoms initially prepared in the metastable 2 3 S 1 state of 4 He [10,11], showing good agreement with theory. Also molecular potentials for two metastable helium atoms can be calculated very accurately in some cases.…”

Section: Introductionmentioning

confidence: 72%

Ultracold metastable helium: Ramsey fringes and atom interferometry

et al. 2016

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equation cannot be solved exactly. Level energies are therefore more difficult to calculate than for atomic hydrogen showing a more stringent test of atomic physics theory. Calculations of level energies and transition frequencies have pushed our understanding of atomic physics since the twenties of last century. A major breakthrough occurred in the nineties with the advent of variational calculations in a double basis set in correlated form for the electrons, adding relativistic and quantum electrodynamics (QED) terms in orders of the fine structure constant α and the reduced electron to helium mass ratio µ/M He [1, 2]. As nonrelativistic calculations can now be performed to virtually arbitrary precision, measurements of level energies nowadays are sensitive to QED and nuclear size effects. As these effects are strongest for S-states and small principle quantum number n, the n 1,3 S states are theoretically the most promising to test QED. In particular the n = 2 states are important for high-resolution spectroscopy as these also show long lifetimes, 7800 s for the 2 3 S 1 state and 20 ms for the 2 1 S 0 state (natural linewidth 8 Hz), while the 2 3 P state has, for an allowed electric dipole transition, a relatively long lifetime of 98 ns (natural linewidth 1.6 MHz). A helium level scheme is shown in Fig. 1.Transition frequencies in helium can nowadays be measured more accurately than calculated, where the theoretical limitation is in the calculation of high-order QED terms. This hampers extraction of the charge radius of the helium nucleus (the alpha-particle for 4 He and the helion for 3 He ) from transition frequencies with an accuracy that can compete with other experiments. However, in calculating transition isotope shifts between 4 He and 3 He, QED terms cancel to a large extent, allowing very accurate extraction of the difference in the (squared) nuclear charge radii of the alpha-particle and the helion. This is particularly interesting in relation to the proton size puzzle [3][4][5]. To help solving Abstract We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a 1.5 µm optical dipole trap. Applying a single π/2 rf pulse we demonstrate that 50% of the atoms initially in the m = +1 state can be transferred to the magnetic field insensitive m = 0 state. Two π/2 pulses with varying time delay allow a Ramsey-type measurement of the Zeeman shift for a high precision measurement of the 2 3 S 1 -2 1 S 0 transition frequency. We show that this method also allows strong suppression of mean-field effects on the measurement of the Zeeman shift, which is necessary to reach the accuracy goal of 0.1 kHz on the absolute transition frequencies. Theoretically the feasibility of using metastable triplet helium atoms in the m = 0 state for atom interferometry is studied demonstrating favorable conditions, compared to the alkali atoms that are used traditionally, for a non-QED determination of the fine structure constant.

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“…Now that we are able to produce sufficient power at 319.8 nm, we implement the laser system into our existing setup [5,10] to demonstrate trapping and to characterize the trap lifetime. We prepare the beam for trapping by enlarging it with a 1:2 telescope and focus it inside the vacuum chamber with an f = 400 mm lens to a waist of w (1) 0 × w (2) 0 = 64.3(1.0) × 55.6(7) µm 2 .…”

Section: Trappingmentioning

confidence: 99%

“…Frequency metrology has been employed as a sensitive test of QED calculations, both from the ground state [1,2] and from the long-lived (lifetime ~8000 s) metastable 2 3 S state (He * ) [3][4][5]. Another interesting target for spectroscopy is to probe the influence on level energies of the finite size of the nucleus.…”

Section: Introductionmentioning

confidence: 99%

A simple 2 W continuous-wave laser system for trapping ultracold metastable helium atoms at the 319.8 nm magic wavelength

2016

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extracted. This method was employed to determine charge radii of the halo nuclei 6 He and 8 He [8] but also to measure the 4 He − 3 He differential nuclear charge radius [9,10]. These measurements are relevant to current investigations into the so-called proton radius puzzle which arose when a similar measurement of the proton radius in µH found a 7σ discrepancy with the 2010 CODATA value [11]. Current efforts investigating the nuclear charge radii of µ 3 He + and µ 4 He + are projected to reach an experimental uncertainty at the sub-attometer (am) level [12]. Determinations of the 4 He − 3 He differential nuclear charge radius with comparable accuracy in electronic systems provide a valuable cross-check for these measurements.Currently, the two most accurate measurements of the 4 He − 3 He differential nuclear charge radius have achieved accuracies of 3 [9] and 11 am 2 [10], roughly an order of magnitude less precise than the projection of the µHe experiment, but disagree by 4σ. The former experiment resolved the 2 3 S → 2 3 P transition to within one thousandth of the 1.6-MHz natural linewidth and is not expected to be improved upon in the near future. The latter experiment was performed on the doubly forbidden 2 3 S → 2 1 S transition whose 8 Hz natural linewidth is not a limiting factor but has a very low excitation rate and thus requires a long interaction time. To achieve this He * atoms were cooled to quantum degeneracy (a BoseEinstein condensate (BEC) of 4 He * , and in a degenerate Fermi gas of 3 He * ) and trapped in an optical dipole trap (ODT). The accuracy of this experiment was limited by experimental effects, mainly the ac-Stark shift induced by the ODT.This problem is also encountered in optical lattice clocks where it is solved by employing so-called magic wavelength traps [13]. In a magic wavelength trap, the wavelength of the trapping laser is chosen such that AbstractHigh-precision spectroscopy on the 2 3 S → 2 1 S transition is possible in ultracold optically trapped helium, but the accuracy is limited by the ac-Stark shift induced by the optical dipole trap. To overcome this problem, we have built a trapping laser system at the predicted magic wavelength of 319.8 nm. Our system is based on frequency conversion using commercially available components and produces over 2 W of power at this wavelength. With this system, we show trapping of ultracold atoms, both thermal (~0.2 μk) and in a Bose-Einstein condensate, with a trap lifetime of several seconds, mainly limited by off-resonant scattering .

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High-Precision Spectroscopy of the Forbidden2 S13→2

Cited by 40 publications

References 41 publications

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

Ultracold metastable helium: Ramsey fringes and atom interferometry

A simple 2 W continuous-wave laser system for trapping ultracold metastable helium atoms at the 319.8 nm magic wavelength

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