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Jean-Pierre Likforman

Publications and source records attributed to Jean-Pierre Likforman.

7 recordsLinked to original sources
arXiv2025

Incoherent repumping scheme in the $^{88}$Sr$^{+}$ five-level manifold

Laser-cooled trapped ions are at the heart of modern quantum technologies and their cooling dynamics often deviate from the simplified two-level atom model. Doppler cooling of the $^{88}$Sr$^{+}$ ion involves several electronic levels and repumping channels that strongly influence fluorescence. In this work, we study a repumping scheme for the $^{88}$Sr$^{+}$ ion by combining precision single-ion spectroscopy with comprehensive numerical modeling based on optical Bloch equations including 18 Zeeman sublevels. We show that, although the observed fluorescence spectra retain a Lorentzian lineshape, their width and amplitude cannot be explained by a two-level atom description. Moreover, we find the optimal repumping conditions for maximizing the photon scattering rate.

physics.atom-ph↗
arXiv2018

Absolute Single Ion Thermometry

We describe and experimentally implement a single-ion local thermometry technique with absolute sensitivity adaptable to all laser-cooled atomic ion species. The technique is based on the velocity-dependent spectral shape of a quasi-dark resonance tailored in a J $\rightarrow$ J transition such that the two driving fields can be derived from the same laser source leading to a negligible relative phase shift. We validated the method and tested its performances in an experiment on a single 88 Sr + ion cooled in a surface radio-frequency trap. We first applied the technique to characterise the heating-rate of the surface trap. We then measured the stationary temperature of the ion as a function of cooling laser detuning in the Doppler regime. The results agree with theoretical calculations, with an absolute error smaller than 100 $μ$K at 500 $μ$K, in a temperature range between 0.5 and 3 mK and in the absence of adjustable parameters. This simple-to-implement and reliable method opens the way to fast absolute measurements of single-ion temperatures in future experiments dealing with heat transport in ion chains or thermodynamics at the single-ion level.

physics.atom-ph↗
arXiv2015

Precision measurement of the branching fractions of the 5p 2 P 1/2 state in 88 Sr + with a single ion in a micro fabricated surface trap

We measured the branching fractions for the decay of the 5p 2 P 1/2 state of 88 Sr + by applying a recently demonstrated photon-counting sequential method (M. Ramm et al., Phys. Rev. Lett. 111, 023004) to a single ion laser-cooled in a micro fabricated surface trap. The branching fraction for the decay into the 5s 2 S 1/2 ground level was found to be p = 0.9453 +0.0007 --0.0005. This result is in good agreement with recent theoretical calculations but disagrees with previous experimental measurements, however affected by a one order of magnitude larger uncertainty. This experiment also demonstrates the reliability and the performances of ion micro trap technology in the domain of precision measurements and spectroscopy. PACS numbers: 32.70.Cs, 06.30.Ft, 37.10.Ty

quant-ph↗
arXiv2014

Isotope shifts of natural Sr+ measured by laser fluorescence in a sympathetically cooled Coulomb crystal

We measured by laser spectroscopy the isotope shifts between naturally-occurring even-isotopes of strontium ions for both the $5s\,\,^2S_{1/2}\to 5p\,\,^2P_{1/2}$ (violet) and the $4d\,\,^2D_{3/2}\to 5p\,\,^2P_{1/2}$ (infrared) dipole-allowed optical transitions. Fluorescence spectra were taken by simultaneous measurements on a two-component Coulomb crystal in a linear Paul trap containing $10^3$--$10^4$ laser-cooled Sr$^+$ ions. The isotope shifts are extracted from the experimental spectra by fitting the data with the analytical solution of the optical Bloch equations describing a three-level atom in interaction with two laser beams. This technique allowed us to increase the precision with respect to previously reported data obtained by optogalvanic spectroscopy or fast atomic-beam techniques. The results for the $5s\,\,^2S_{1/2}\to 5p\,\,^2P_{1/2}$ transition are $ν_{88}-ν_{84}=+378(4)$ MHz and $ν_{88}-ν_{86}=+170(3)$ MHz, in agreement with previously reported measurements. In the case of the previously unexplored $4d\,\,^2D_{3/2}\to 5p\,\,^2P_{1/2}$ transition we find $ν_{88}-ν_{84}=-828(4)$ MHz and $ν_{88}-ν_{86}=-402(2)$ MHz. These results provide more data for stringent tests of theoretical calculations of the isotope shifts of alkali-metal-like atoms. Moreover, they simplify the identification and the addressing of Sr$^+$ isotopes for ion frequency standards or quantum-information-processing applications in the case of multi-isotope ion strings.

physics.atom-ph↗
arXiv2011

Quantum correlations by four-wave mixing in an atomic vapor in a non-amplifying regime: a quantum beam splitter for photons

We study the generation of intensity quantum correlations using four-wave mixing in a rubidium vapor. The absence of cavity in these experiments allows to deal with several spatial modes simultaneously. In the standard, amplifying, configuration, we measure relative intensity squeezing up to 9.2 dB below the standard quantum limit. We also theoretically identify and experimentally demonstrate an original regime where, despite no overall amplification, quantum correlations are generated. In this regime a four-wave mixing set-up can therefore play the role of a photonic beam splitter with non--classical properties, i.e. a device that splits a coherent state input into two quantum correlated beams.

quant-ph↗
arXiv2008

Photoionisation loading of large Sr+ ion clouds with ultrafast pulses

This paper reports on photoionisation loading based on ultrafast pulses of singly-ionised strontium ions in a linear Paul trap. We take advantage of an autoionising resonance of Sr neutral atoms to form Sr+ by two-photon absorption of femtosecond pulses at a wavelength of 431nm. We compare this technique to electron-bombardment ionisation and observe several advantages of photoionisation. It actually allows the loading of a pure Sr+ ion cloud in a low radio-frequency voltage amplitude regime. In these conditions up to 4x10^4 laser-cooled Sr+ ions were trapped.

quant-ph↗