Magic wavelengths for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:msup><mml:mspace width="4pt" /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup><mml:mi>S</mml:mi><mml:mo>→</mml:mo><mml:mn>2</mml:mn><mml:msup><mml:mspace width="4pt" /><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msup><mml:mi>S</mml:mi></mml:mrow></mml:math>transition in helium

Notermans, Remy; Rengelink, R. J.; Leeuwen, K. A. H. van; Vassen, W.

doi:10.1103/physreva.90.052508

Cited by 24 publications

(60 citation statements)

References 48 publications

(69 reference statements)

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“…By comparing accurate atomic structure calculations [6] to highprecision isotope shift measurements, nuclear charge radii relative to the (accurately known [7]) 4 He nucleus can be 1 3 122 Page 2 of 8 the upper-and lower-state polarizability are exactly the same, canceling out the differential ac-Stark shift. In helium a high-precision calculation of the ac-polarizability of the 2 3 S level was recently reported [14], and we ourselves have made more approximate calculations on both the 2 3 S and 2 1 S levels [15]. Both works predict the polarizability of the 2 3 S level to vanish at around 413 nm (a so-called tune-out wavelength) which was later confirmed experimentally [16].…”

Section: Introductionmentioning

confidence: 79%

“…Based on the specifications of the seed lasers and amplifiers, the spectral linewidths of the infrared beams should be of the order of several tens of kHz. Because the nonlinear conversion steps do not significantly add to the fractional linewidth, the final UV output is expected to have a linewidth of ∼100 kHz, which is small compared to the scale at which the polarizability changes [15].…”

Section: Overviewmentioning

confidence: 99%

“…b Determination of the trap temperature based on minimum temperature (blue circles), and an extrapolation to zero hold time of the heating rate (red squares). From linear fits to these data, an upper (lower) bound is set on the temperature in the absence of heating of 0.62(2) µK W −1 (0.51(2) µK W −1 ) hybrid trap of comparable depth using our 1557 nm ODT for which off-resonant scattering is negligible [15]. Figure 7 shows the fitted temperature as a function of hold time in the hybrid trap.…”

Section: Hybrid Trapmentioning

confidence: 99%

“…Therefore, at a power (P) of 1 W and neglecting astigmatism, the beam has peak intensity Based on the polarizability (calculated in [15]), this translates to a trap depth of ∼6.0 µK W −1 for a single beam. The trap depth of our ODT is therefore far below the recoil temperature where k = 2π/ is the photon wavenumber and m is the atomic mass of helium.…”

Section: Trappingmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 79%

Section: Overviewmentioning

confidence: 99%

Section: Hybrid Trapmentioning

confidence: 99%

Section: Trappingmentioning

confidence: 99%

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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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“…This we will solve by working in a magic wavelength crossed dipole trap. At 319.8 nm the polarizabilities of the 2 3 S 1 and 2 1 S 0 states cancel [24]. We have generated 2 W narrowband radiation at this wavelength, more than enough to trap our atoms and have demonstrated trapping and Bose-Einstein condensation in a 319.8-nm dipole trap [25].…”

Section: Spectroscopymentioning

confidence: 99%

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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