RESUMEN

The radioisotope thorium-229 (229Th) is renowned for its extraordinarily low-energy, long-lived nuclear first-excited state. This isomeric state can be excited by vacuum ultraviolet (VUV) lasers and 229Th has been proposed as a reference transition for ultra-precise nuclear clocks. To assess the feasibility and performance of the nuclear clock concept, time-controlled excitation and depopulation of the 229Th isomer are imperative. Here we report the population of the 229Th isomeric state through resonant X-ray pumping and detection of the radiative decay in a VUV transparent 229Th-doped CaF2 crystal. The decay half-life is measured to 447(25) s, with a transition wavelength of 148.18(42) nm and a radiative decay fraction consistent with unity. Furthermore, we report a new "X-ray quenching" effect which allows to de-populate the isomer on demand and effectively reduce the half-life. Such controlled quenching can be used to significantly speed up the interrogation cycle in future nuclear clock schemes.

RESUMEN

This paper presents an absolute X-ray photon energy measurement method that uses a Bond diffractometer. The proposed system enables the prompt and rapid in situ measurement of photon energies over a wide energy range. The diffractometer uses a reference silicon single-crystal plate and a highly accurate angle encoder called SelfA. The performance of the system is evaluated by repeatedly measuring the energy of the first excited state of the potassium-40 nuclide. The excitation energy is determined as 29829.39 (6) eV, and this is one order of magnitude more accurate than the previous measurement. The estimated uncertainty of the photon energy measurement was 0.7 p.p.m. as a standard deviation and the maximum observed deviation was 2 p.p.m.

RESUMEN

The metastable first excited state of thorium-229, 229mTh, is just a few electronvolts above the nuclear ground state1-4 and is accessible by vacuum ultraviolet lasers. The ability to manipulate the 229Th nuclear states with the precision of atomic laser spectroscopy5 opens up several prospects6, from studies of fundamental interactions in physics7,8 to applications such as a compact and robust nuclear clock5,9,10. However, direct optical excitation of the isomer and its radiative decay to the ground state have not yet been observed, and several key nuclear structure parameters-such as the exact energies and half-lives of the low-lying nuclear levels of 229Th-remain unknown11. Here we present active optical pumping into 229mTh, achieved using narrow-band 29-kiloelectronvolt synchrotron radiation to resonantly excite the second excited state of 229Th, which then decays predominantly into the isomer. We determine the resonance energy with an accuracy of 0.07 electronvolts, measure a half-life of 82.2 picoseconds and an excitation linewidth of 1.70 nanoelectronvolts, and extract the branching ratio of the second excited state into the ground and isomeric state. These measurements allow us to constrain the 229mTh isomer energy by combining them with γ-spectroscopy data collected over the past 40 years.

RESUMEN

We report the observation of two-photon emission from a coherently excited vibrational state of solid parahydrogen, which is also a known quantum solid. Coherence between the ground and the excited states is prepared by stimulated Raman scattering using two visible laser pulses. The two-photon emission is triggered by another mid-infrared laser pulse. It was observed that the two-photon emission persists even when the trigger pulse is injected long after the excitation. This is due to the long decoherence time of the vibrational states of solid parahydrogen. It is found that the emission intensity increases even after the excitation pulses pass through the target completely. This coherence development is highly suppressed at high target temperatures and high residual orthohydrogen concentrations. Effects of target annealing and laser-induced damage on the target are also observed.

RESUMEN

The coherence decay of the v = 2 vibrational state (vibrons) of solid parahydrogen was measured via time-resolved coherent anti-Stokes Raman spectroscopy. We found that the decay curve has a non-exponential time profile in the time scale of 200 ns at a low temperature below 5 K and a low orthohydrogen impurity concentration (~0.01%). This behavior, as also observed in the case of the v = 1 vibrons, represents a signature of band structure of the v = 2 state in the solid phase. The maximum coherence decay time of 50 ns in an exponential part was achieved, which shows excellence of the v = 2 state for coherent processes. We also found that finite temperatures, orthohydrogen impurities, and other structural inhomogeneity accelerate the decay, hiding the non-exponential feature of the vibron band.

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