The effects of quantum-mechanical interference with a far-off-resonant transition on saturated-absorption measurements of atomic fine-structure intervals are found to be substantially larger than measurement uncertainty, and it is shown how properly taking them into account brings several previous measurements into agreement.
Spectroscopic measurements of transition frequencies in various atomic systems are a significant part of modern physics. They enable the testing of fundamental interactions, the determination of physical constants, and the study of fundamental symmetries that occur in nature with unprecedented accuracy. Studies based on two-photon spectroscopy of simple atoms represent some of the most accurate experiments to date. The verification of precision experimental results is largely supported by theoretical analysis, which is most rigorous for light, nonrelativistic atoms and ions. In the last decade, much attention in the literature has been paid to the study of the quantum interference effect (QIE) in hydrogen and hydrogenlike atomic systems. This has made it possible to significantly reduce the experimental error in determining the appropriate transition frequency. The theoretical description of the QIE corresponds to the consideration of similar pathways arising for close-lying resonant states into which the transition frequency is measured. In the present work, the influence of the emission process on the absorption profile formation is investigated. The results of the studies carried out in this work show the need to take into account the effect of quantum interference in cascade radiation for the precise determination of the absorption transition frequency to highly excited states in two-photon spectroscopic experiments.
We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a $$1.5 \,\upmu {\mathrm{m}}$$ 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 23S1 – 21S0 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.
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 $$ 1.5\kern0.166667em \upmu \mathrm{m} $$ 1.5 μ m optical dipole trap. Applying a single π/2 π / 2 rf pulse we demonstrate that 50% of the atoms initially in the m=+1 m = + 1 state can be transferred to the magnetic field insensitive m=0 m = 0 state. Two π/2 π / 2 pulses with varying time delay allow a Ramsey-type measurement of the Zeeman shift for a high precision measurement of the 23S1 2 3 S 1 – 21S0 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 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.
Modern resonance spectroscopic experiments on the measurement of transition frequencies in atoms have reached a level where a meticulous description of all aspects of the studied processes has become obligatory. The precision achieved has led to the fact that the determination of the transition frequency on the basis of measured data is substantially refined by theoretical treatment of the observed spectral line profile. Thus, a large impact of effects arising beyond the resonance approximation, in particular due to the effect of quantum interference, is found experimentally. We show that the picture becomes even more complicated when the observed spectral line profile is ``identified'' with one of the processes---emission or absorption. An accurate determination of the transition frequency requires a description of the absorption line profile inseparable from the emission process, and vice versa. The theoretical aspects discussed in this paper create prerequisites for more accurate experiments.
Precision spectroscopy of simple atomic systems has refined our understanding of the fundamental laws of quantum physics. In particular, helium spectroscopy has played a crucial role in describing two-electron interactions, determining the fine-structure constant and extracting the size of the helium nucleus. Here we present a measurement of the doubly forbidden 1557-nanometer transition connecting the two metastable states of helium (the lowest energy triplet state 2 (3)S(1) and first excited singlet state 2 (1)S(0)), for which quantum electrodynamic and nuclear size effects are very strong. This transition is weaker by 14 orders of magnitude than the most predominantly measured transition in helium. Ultracold, submicrokelvin, fermionic (3)He and bosonic (4)He atoms are used to obtain a precision of 8 × 10(-12), providing a stringent test of two-electron quantum electrodynamic theory and of nuclear few-body theory.