arXiv subjects

N. Kolachevsky

Publications and source records attributed to N. Kolachevsky.

At least 19 recordsLinked to original sources

arXiv2024

Loading of the narrow line Tm MOT from a pulsed cold atomic beam

We report on building a pulsed source of cold Tm atoms and loading of the narrow-line magnito-optical trap (MOT) from the cold atomic beam. We achieve the loading rate of the first-stage MOT in the primary chamber up to $10^8$ atoms/s and obtain a cold atomic beam with the mean longitudinal velocity $\sim10$ m/s and angular spread of 18 mrad in a pulsed mode. We also introduce a novel method to enhance the capture velocity of the narrow-line MOT by incorporating additional axial cooling beam, and achieve loading efficiency $η= 10\%$ of the second-stage MOT in the science chamber. Our approach could be extended to other atomic species with similar properties, like Sr, Yb, Dy and Er, serving as a convenient alternative for the traditional 2D-MOT schemes. Providing rapid loading of the MOT in the science chamber, it would reduce preparation time of the atomic ensemble leading to a shorter dead time in spectroscopy experiments and higher repetition rate.

physics.atom-ph↗

arXiv2024

Synchronous Comparison of Two Thulium Optical Clocks

The experimental comparison of two thulium optical lattice clocks in a time interval of up to one hour has been carried out. The synchronous comparison of a clock transition in two independent atomic ensembles using a single ultrastable laser has allowed us to eliminate fluctuations of the laser frequency from the measured frequency difference and to reach a relative measurement error of $10^{-16}$ after 500-s averaging, which corresponds to a relative instability of $2\times10^{-15}/\sqrtτ$. The successful demonstration of the long-term operation of two systems using the synchronous comparison of clock transitions opens the possibility of studying systematic shifts in thulium optical clocks with an uncertainty of $10^{-17}$.

physics.atom-ph↗

arXiv2021

Efficient loading of thulium atoms in a compact MOT for a transportable optical clock

We report on building of a compact vacuum chamber for spectroscopy of ultracold thulium and trapping of up to 13 million atoms. Compactness is achieved by obviating a classical Zeeman slower section and placing an atomic oven close to a magneto-optical trap (MOT), specifically at the distance of 11 cm. In this configuration, we significantly gained in solid angle of an atomic beam, which is affected by MOT laser beams, and reached 1 million atoms loaded directly in the MOT. By exploiting Zeeman-like deceleration of atoms with an additional laser beam, we increased the number of trapped atoms to 6 million. Then we gained an extra factor of 2 by tailoring the MOT magnetic field gradient with an additional small magnetic coil. Demonstrated results show great perspective of the developed setup for realizing a compact high-performance optical atomic clock based on thulium atoms.

physics.atom-ph↗

arXiv2021

Extraordinary low systematic frequency shifts in bi-colour thulium optical clock

Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncertainty demonstrating incredible control over external perturbations of the clock transition frequency. At the same time there is an increasing demand for atomic and ionic transitions with minimal sensitivity to external fields, with practical operational wavelengths and robust readout protocols. One of the goals is to simplify clock's operation maintaining its relative uncertainty at low 10-18 level. It is especially important for transportable and envisioned space-based optical clocks. We proved earlier that the 1.14um inner-shell magnetic dipole transition in neutral thulium possesses very low blackbody radiation shift compared to other neutrals. Here we demonstrate operation of a bi-colour thulium optical clock with extraordinary low sensitivity to the Zeeman shift due to a simultaneous interrogation of two clock transitions and data processing. Our experiment shows suppression of the quadratic Zeeman shift by at least three orders of magnitude. The effect of tensor lattice Stark shift can be also reduced to below 10-18 in fractional frequency units. All these features make thulium optical clock almost free from hard-to-control systematic shifts. Together with convenient cooling and trapping laser wavelengths, it provides great perspectives for thulium lattice clock as a high-performance transportable system.

physics.atom-ph↗

arXiv2020

Simultaneous two initial clock states preparation for thulium optical clock

Due to the low sensitivity of the thulium optical clock to black-body radiation and good accuracy and stability estimations, it appears to be one of the most promising transportable optical clocks. One of the leading systematic effects for Tm clock transition, namely the second-order Zeeman effect, can be canceled by probing two clock transitions between different hyperfine levels of ground and metastable states during the clock operation. We prepare the atoms in $m_F=0$ state of both ground hyperfine levels simultaneously and excite alternately two clock transitions. Here we demonstrate efficient optical pumping into both target states via single-frequency radiation at 418.8 nm. The resulting population of $m_F=0$ states of ground hyperfine levels is 36% and 3.8% of the initial number of atoms with less than 4% and 0.4% on non-zero magnetic sublevels, correspondingly. We performed numerical simulations of the optical pumping process which is able to explain experimental results reasonably well.

physics.atom-ph↗

arXiv2019

Pressure Shifts in High-Precision Hydrogen Spectroscopy: I. Long-Range Atom-Atom and Atom-Molecule Interactions

We study the theoretical foundations for the pressure shifts in high-precision atomic beam spectrosopy of hydrogen, with a particular emphasis on transitions involving higher excited P states. In particular, the long-range interaction of an excited hydrogen atom in a 4P state with a ground-state and metastable hydrogen atom is studied, with a full resolution of the hyperfine structure. It is found that the full inclusion of the 4P_1/2 and 4P_3/2 manifolds becomes necessary in order to obtain reliable theoretical predictions, because the 1S ground state hyperfine frequency is commensurate with the 4P fine-structure splitting. An even more complex problem is encountered in the case of the 4P-2S interaction, where the inclusion of quasi-degenerate 4S-2P_1/2 state becomes necessary in view of the dipole couplings induced by the van der Waals Hamiltonian. Matrices of dimension up to 40 have to be treated despite all efforts to reduce the problem to irreducible submanifolds within the quasi-degenerate basis. We focus on the phenomenologically important second-order van der Waals shifts, proportional to 1/R^6 where R is the interatomic distance, and obtain results with full resolution of the hyperfine structure. The magnitude of van der Waals coefficients for hydrogen atom-atom collisions involving excited P states is drastically enhanced due to energetic quasi-degeneracy; we find no such enhancement for atom-molecule collisions involving atomic nP states, even if the complex molecular spectrum involving ro-vibrational levels requires a deeper analysis.

physics.atom-ph↗

arXiv2019

Pressure Shifts in High-Precision Hydrogen Spectroscopy: II. Impact Approximation and Monte-Carlo Simulations

We investigate collisional shifts of spectral lines involving excited hydrogenic states, where van der Waals coefficients have recently been shown to have large numerical values when expressed in atomic units. Particular emphasis is laid on the recent hydrogen 2S-4P experiment (and an ongoing 2S-6P experiment) in Garching, but numerical input data are provided for other transitions (e.g., involving S states), as well. We show that the frequency shifts can be described, to sufficient accuracy, in the impact approximation. The pressure related effects were separated into two parts, (i) related to collisions of atoms inside of the beam, and (ii) related to collisions of the atoms in the atomic beam with the residual background gas. The latter contains both atomic as well as molecular hydrogen. The dominant effect of intra-beam collisions is evaluated by a Monte-Carlo simulation, taking the geometry of the experimental apparatus into account. While, in the Garching experiment, the collisional shift is on the order of 10 Hz, and thus negligible, it can decisively depend on the experimental conditions. We present input data which can be used in order to describe the effect for other transitions of current and planned experimental interest.

physics.atom-ph↗

arXiv2018

Inner-shell clock transition in atomic thulium with small BBR shift

With direct polarizability measurements we demonstrated extremely low sensitivity of the inner-shell clock transition at $1.14\,μ$m in Tm atoms to external dc electric fields and black-body radiation (BBR). We measured differential polarizabilities of clock levels in Tm at wavelengths of 810--860\,nm and at 1064\,nm and inferred the static scalar differential polarizability of the inner-shell clock transition of $-0.047(18)$ atomic units corresponding to only $2\times10^{-18}$ fractional frequency shift from BBR at the room temperature. This is a few orders of magnitude smaller compared to the BBR shift of the clock transitions in the neutral atoms (Sr, Yb, Hg) and competes with the least sensitive ion species (e.g. Al$^+$ or Lu$^+$). For the $1.14\,μ$m clock transition, we experimentally determined the "magic" wavelength of $813.320(6)$\,nm, recorded the transition spectral linewidth of $10$\,Hz, and measured its absolute frequency of $262\,954\,938\,269\,213(30)$\,Hz.

physics.atom-ph↗

arXiv2017

Optical trapping of anti-hydrogen towards an atomic anti-clock

The Anti-Matter Factory at CERN is gearing up, commissioning of the Extra Low ENergy Antiprotons (ELENA) ring is ongoing and the first anti-protons are foreseen to circulate in the decelerator very soon. The unprecedented flux of low energy antiprotons delivered by ELENA will open a new era for precision tests with antimatter including laser and microwave spectroscopy and tests of its gravitational behaviour. Here we propose a scheme to load the ultra cold anti-hydrogen atoms that will be produced by the GBAR experiment in an optical lattice tuned at the magic wavelength of the 1S-2S transition in order to measure this interval at a level comparable or even better than its matter counter part. This will provide the most sensitive test of CPT symmetry parametrised in the framework of the Standard Model Extension.

physics.atom-ph↗

arXiv2017

Two-temperature momentum distribution in a Thulium magneto-optical trap

Second-stage laser cooling of thulium atoms at the 530.7 nm transition with a natural linewidth of 350 kHz offers an interesting possibility to study different regimes of a magneto-optical trap (MOT). The intermediate value of the spectral linewidth of the cooling transition allows the observation of three distinct regimes depending on intensity and detuning of the cooling beams. Namely, the "bowl-shaped" regime when light pressure force competes with gravity, the "double structure" regime with interplay between Doppler and polarization-gradient (sub-Doppler) cooling, and the "symmetric" regime when Doppler cooling dominates over sub-Doppler cooling and gravity. The polarization-gradient cooling manifests itself by a two-temperature momentum distribution of atoms resulting in a double-structure of the spatial MOT profile consisting of a cold central fraction surrounded by a hot halo. We studied the "double structure" regime at different saturation parameters and compared observations with calculations based on semiclassical and quantum approaches. The quantum treatment adequately reproduces experimental results if the MOT magnetic field is properly taken into account.

physics.atom-ph↗

arXiv2017

Long-range interactions of hydrogen atoms in excited states. I. 2S-1S interactions and Dirac-delta perturbations

The theory of the long-range interaction of metastable excited atomic states with ground-state atoms is analyzed. We show that the long-range interaction is essentially modified when quasi-degenerate states are available for virtual transitions. A discrepancy in the literature regarding the van der Waals coefficient C_6(2S;1S) describing the interaction of metastable atomic hydrogen (2S state) with a ground-state hydrogen atom is resolved. In the the van der Waals range a_0 << R << a_0/alpha, where a_0= hbar/(alpha m c) is the Bohr radius and alpha is the fine structure constant, one finds the symmetry-dependent result E_{2S;1S}(R) ~ (-176.75 +/- 27.98) E_h (a_0/R)^6 (E_h denotes the Hartree energy). In the Casimir-Polder range a_0/alpha << R << hbar c/L, where L = E(2S_{1/2})-E(2P_{1/2}) is the Lamb shift energy, one finds E_{2S;1S}(R) ~ (-121.50 +/- 46.61) E_h (a_0/R)^6. In the the Lamb shift range R >> hbar c/L, we find an oscillatory tail with a negligible interaction energy below 10^(-36) Hz. Dirac-delta perturbations to the interaction are also evaluated and results are given for all asymptotic distance ranges; these effects describe the hyperfine modification of the interaction, or, expressed differently, the shift of the hydrogen 2S hyperfine frequency due to interactions with neighboring 1S atoms. The 2S hyperfine frequency has recently been measured very accurately in atomic beam experiments.

physics.atom-ph↗

arXiv2017

Long-range interactions of hydrogen atoms in excited states. II. Hyperfine-resolved 2S-2S system

The interaction of two excited hydrogen atoms in metastable states constitutes a theoretically interesting problem because of the quasi-degenerate 2P_{1/2} levels which are removed from the 2S states only by the Lamb shift. The total Hamiltonian of the system is composed of the van der Waals Hamiltonian, the Lamb shift and the hyperfine effects. The van der Waals shift becomes commensurate with the 2S-2P_{3/2} fine-structure splitting only for close approach (R < 100 a_0, where a_0 is the Bohr radius) and one may thus restrict the discussion to the levels with n=2 and J=1/2 to good approximation. Because each S or P state splits into an F=1 triplet and an F=0 hyperfine singlet (eight states for each atom), the Hamiltonian matrix {\em a priori} is of dimension 64. A careful analysis of symmetries the problem allows one to reduce the dimensionality of the most involved irreducible submatrix to 12. We determine the Hamiltonian matrices and the leading-order van der Waals shifts for states which are degenerate under the action of the unperturbed Hamiltonian (Lamb shift plus hyperfine structure). The leading first- and second-order van der Waals shifts lead to interaction energies proportional to 1/R^3 and 1/R^6 and are evaluated within the hyperfine manifolds. When both atoms are metastable 2S states, we find an interaction energy of order E_h chi (a_0/R)^6, where E_h and L are the Hartree and Lamb shift energies, respectively, and chi = E_h/L ~ 6.22 \times 10^6 is their ratio.

physics.atom-ph↗

arXiv2016

Inner-shell magnetic dipole transition in Tm atom as a candidate for optical lattice clocks

We consider a narrow magneto-dipole transition in the $^{169}$Tm atom at the wavelength of $1.14\,μ$m as a candidate for a 2D optical lattice clock. Calculating dynamic polarizabilities of the two clock levels $[\text{Xe}]4f^{13}6s^2 (J=7/2)$ and $[\text{Xe}]4f^{13}6s^2 (J=5/2)$ in the spectral range from $250\,$nm to $1200\,$nm, we suggest the "magic" wavelength for the optical lattice at $807\,$nm. Frequency shifts due to black-body radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction and other effects which can perturb the transition frequency are calculated. The transition at $1.14\,μ$m demonstrates low sensitivity to the BBR shift corresponding to $8\times10^{-17}$ in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than $5 \times 10^{-18}$ in fractional units. By direct excitation of the $1.14\,μ$m transition in Tm atoms loaded into an optical dipole trap, we set the lower limit for the lifetime of the upper clock level $[\text{Xe}]4f^{13}6s^2 (J=5/2)$ of $112\,$ms which corresponds to a natural spectral linewidth narrower than $1.4\,$Hz. The polarizability of the Tm ground state was measured by the excitation of parametric resonances in the optical dipole trap at $532\,$nm.

quant-ph↗

arXiv2013

Measurement of the 5D Level Polarizabilty in Laser Cooled Rb atoms

We report on accurate measurements of the scalar and tensor polarizabilities of the 5D fine structure levels 5D3/2 and 5D5/2 in Rb. The measured values show reasonable correspondence to previously published theoretical predictions, but are more accurate. We implemented laser excitation of the 5D level in a laser cooled cloud of optically polarized Rb-87 atoms placed in a constant electric field.

quant-ph↗

arXiv2011

Low phase noise diode laser oscillator for 1S-2S spectroscopy in atomic hydrogen

We report on a low-noise diode laser oscillator at 972 nm actively stabilized to an ultra-stable vibrationally- and thermally compensated reference cavity. To increase the fraction of laser power in the carrier we designed a 20 cm long external cavity diode laser with an intra-cavity electro-optical modulator. The fractional power in the carrier reaches 99.9% which corresponds to a rms phase noise of $ϕ^2_\textrm{rms}=1\,\textrm{mrad}^2$ in 10\,MHz bandwidth. Using this oscillator we recorded 1S-2S spectra in atomic hydrogen and have not observed any significant loss of the excitation efficiency due to phase noise multiplication in the three consecutive 2-photon processes.

quant-ph↗

arXiv2010

Sub-Doppler Laser Cooling of Thulium Atoms in a Magneto-optical Trap

We have experimentally studied sub-Doppler laser cooling in a magneto-optical trap for thulium atoms working at the wavelength of 410.6\,nm. Without any dedicated molasses period of sub-Doppler cooling, the cloud of $3\times 10^6$ atoms at the temperature of 25(5)\,$μ$K was observed. The measured temperature is significantly lower than the Doppler limit of 240$μ$K for the cooling transition at 410.6\,nm. High efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé-$g$ factors of the lower $4f^{13}6s^{2}\, (J\,=\,{7}/{2})$ and the upper $4f^{12}5d_{3/2}6s^{2}\, (J\,=\,{9}/{2})$ cooling levels.}

quant-ph↗

arXiv2010

Magneto-Optical Trap for Thulium Atoms

Thulium atoms are trapped in a magneto-optical trap using a strong transition at 410 nm with a small branching ratio. We trap up to $7\times10^{4}$ atoms at a temperature of 0.8(2) mK after deceleration in a 40 cm long Zeeman slower. Optical leaks from the cooling cycle influence the lifetime of atoms in the MOT which varies between 0.3 -1.5 s in our experiments. The lower limit for the leaking rate from the upper cooling level is measured to be 22(6) s$^{-1}$. The repumping laser transferring the atomic population out of the F=3 hyperfine ground-state sublevel gives a 30% increase for the lifetime and the number of atoms in the trap.

physics.atom-ph↗

arXiv2009

New Measurement of the 2S Hyperfine Interval in Atomic Hydrogen

An optical measurement of the 2S hyperfine interval in atomic hydrogen using two-photon spectroscopy of the 1S-2S transition gives a value of 177 556 834.3(6.7) Hz. The uncertainty is 2.4 times smaller than achieved by our group in 2003 and more than 4 times smaller than for any independent radio-frequency measurement. The specific combination of the 2S and 1S hyperfine intervals predicted by QED theory $D_{21}=8 f_{\rm HFS}({2S}) - f_{\rm HFS}({1S})=48 953(3)$ Hz is in good agreement with the value of 48 923(54) Hz obtained from this experiment.

physics.atom-ph↗