Search

The comparison of optical oscillators is used both to determine their spectral characteristics and to perform fundamental research. To describe each individual laser system, it is necessary to compare at least three independent laser oscillators. Three ultrastable lasers with wavelengths of 1140, 1550, and 871 nm located in different laboratories at the Lebedev Physical Institute have been compared. A femtosecond frequency comb has been used to transfer stability between different spectral ranges. A fractional frequency instability has been obtained with the three-cornered hat method and phase noise of each laser has been analyzed. Using this method, it has been shown that the characteristics of the laser system at a wavelength of 871 nm are appropriate to control the quantum state of an optical qubit on a quadrupole transition in an ytterbium ion with a n-atural width of 3.1 Hz.

Ultracold ions provide one of the most promising platforms for quantum computing and make it possible to reach record coherence times, the fidelity of preparation and readout operations, and single- and two-qubit operations. Encoding quantum information in an optical qubit based on the $$^{2}{{S}_{{1/2}}}(F = 0,{{m}_{F}} = 0)$$ → $$^{2}{{D}_{{3/2}}}(F = 2,{{m}_{F}} = 0)$$ quadrupole transition in the 171Yb+ ion at a wavelength of 435.5 nm, which has potential advantages over similar systems in the scaling of the number of qubits and their sensitivity to fluctuations of the magnetic field, is proposed and experimentally studied. The proposed optical qubit in ytterbium is compared to other most widespread types of ion qubits. Experimental results on the implementation of the Pauli-X single-qubit operation are given. The fidelity of the operation is 96% after correction to the error of preparation and readout and is limited by the temperature of the ion.

A scheme is proposed for the third stage of laser cooling of thulium atoms at a wavelength of 506.2 nm, and a system for stabilising the laser radiation frequency is described, which provides the required characteristics. The transition at a wavelength of 506.2 nm is detected in a magneto-optical trap with the employment of the developed laser setup. The value of hyperfine splitting of the transition upper level is measured, and the single-dimension cooling at this wavelength is observed for the first time.

The so-called proton charge radius puzzle was one of the challenging problems in physics in the last decade. A significant (at the level of four standard deviations (4σ)) difference between the values of the root-mean-square proton charge radius measured in normal and muonic hydrogen has kindled lively discussions among both experimentalists and theoreticians specializing in quantum electrodynamics. The problem becomes even more glaring (up to 7σ) if data on the scattering of electrons on protons are taken into account. We review various methods that enable measurement of the proton charge radius, analyze the origin of the disagreement, and present results of recent experiments that aim at resolving this puzzle.

The design of a linear ion Paul trap for quantum-logical operations on ultracold ions with high reliability is developed. The general requirements for the trap are presented, its parameters are optimized, and electric fields are numerically simulated.

Ions in radio-frequency traps are widely used in various fields of applied and fundamental physics, such as metrology and quantum computing. One of the important tasks required for modern experiments is deep cooling of ion crystals. The results of simulations of an increase in the efficiency of deep cooling of linear ion crystals by the method of electromagnetically induced transparency (EIT cooling) by imposing an optical lattice on the radio-frequency trap have been reported. It has been shown that this method makes it possible to narrow the frequency range occupied by various vibrational modes of ions and to increase their axial frequencies of motion without violating the linear configuration of the crystal. Thus, for a crystal of eight ions in a Paul trap with secular frequencies ωz = 2π × 100 kHz and ωr = 2π × 650 kHz, the application of an optical lattice allows the reduction of the frequency range occupied by vibrational modes by a factor of 2. The dependence of the optimal power of the optical lattice for narrowing the vibrational spectrum on the number of particles in the trap and its parameters has been investigated.

Thermal noise of optical cavities limits the accuracy of many experiments on precision laser spectroscopy and interferometry. The study of the physical properties of this noise opens opportunities for the creation of more stable cavities, reduction of phase noise of optical radiation, and performance of accurate optical studies. The paper proposes a method of partial recording of TEM00 mode thermal noise of a Fabry-Perot cavity using two "probe" modes of higher order. The method allows partial compensation of noise in the fundamental mode. Mathematical modeling is performed, which confirms the efficiency of the method., Comment: 8 pages, 5 figures

We report the results of studying a compact laser system designed for manipulating a quantum state of the optical qubit based on the 2S1/2 → 2D3/2 quadrupole transition in the 171Yb+ ion at a wavelength of 435.5 nm. An emission power of the laser system reaches 500 μW at λ = 435.5 nm and the relative frequency instability of at most 3 × 10−15 is achieved at averaging intervals from 0.5 to 50 s with a subtracted linear frequency drift. The compactness of the developed system makes it possible to employ it in transportable systems including optical clocks.

Two ultrastable laser systems for the clock transition spectroscopy in the strontium frequency standard are developed. The high stability of laser radiation frequency is provided by the active loop for frequency referencing to the Fabry–Perot reference cavity. The used cavities are made of glass with ultra-low thermal expansion coefficient and are 48 cm long which provides an extremely low thermal noise limit of 7 × 10–17. The relative frequency drift velocity of laser systems is 216 mHz/s which allows the implementation of high-accuracy spectroscopy of the clock transition in strontium.

Fluctuations of residual amplitude modulation in a scheme of laser frequency stabilisation by a Fabry – Perot cavity reduce the frequency stability of the laser systems intended for interrogating clock transitions of atoms and ions. The dependences of the residual amplitude modulation on a temperature of the waveguide-based electro-optical modulator used for modulating the radiation phase and on polarisation of the radiation are measured. The parameters are found, at which the influence of the residual amplitude modulation on the frequency stability is minimal. A system for active compensation is created, which reduces the contribution of fluctuations of residual amplitude modulation to the instability down to 2.1 × 10−16, which makes it possible to reach the thermal noise limit of a silicon cryogenic cavity.

An optical frequency transfer at a wavelength of 1542 nm via an ultra-stable 5-m free-space link with active compensation of the phase noise caused by atmospheric fluctuations is demonstrated. The link-induced phase noise and its contribution to the frequency transfer instability are investigated. It is shown that, with the phase compensation system switched on, the link contribution to the relative transfer instability in terms of Allan deviation reaches 1.7 × 10−19 for a 5000-s averaging time.

We characterize a 1.14 μm ultrastable semiconductor laser system for precision spectroscopy of Tm inner-shell clock transition using a frequency comb. We stabilize both the repetition and the carrierenvelope offset frequencies of a commercial Ti : sapphire femtosecond laser to a passive hydrogen maser using a home-built f-2f interferometer. By measuring the absolute frequency of the 1.14 μm laser stabilized to a high-finesse ULE cavity, we determine the zero-expansion temperature point of the cavity and the rate of linear drift of the the cavity resonance frequency due to “aging” of the ULE glass. We achieve less than 10 Hz frequency instability of the laser within 1,000 s after the linear drift compensation. We also measured the absolute frequency of the 1.14 μm transition in Tm to be 262 954 938 269 213(30) Hz.

The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidths. We present two ultrastable laser systems based on 48-cm-long Fabry–Perot cavities made of ultralow expansion glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between the two lasers reaches 1.6 × 10 − 15 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, and sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration was easier to manufacture and transport, it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physical Institute to the All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology (VNIIFTRI), where they serve as local oscillators for spectroscopy of the clock transition in the recently developed strontium 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 (ionic) transitions and new interrogation and readout protocols providing minimal sensitivity to external fields and possessing practical operational wavelengths. One of the goals is to simplify the clock operation while maintaining the relative uncertainty at a low 10−18 level achieved at the shortest averaging time. This is especially important for transportable and envisioned space-based optical clocks. Here, we demonstrate implementation of a synthetic frequency approach for a thulium optical clock with simultaneous optical interrogation of two clock transitions. Our experiment shows suppression of the quadratic Zeeman shift by at least three orders of magnitude. The effect of the tensor lattice Stark shift in thulium can also be reduced to below 10−18 in fractional frequency units. This makes the thulium optical clock almost free from hard-to-control systematic shifts. The “simultaneous” protocol demonstrates very low sensitivity to the cross-talks between individual clock transitions during interrogation and readout., There are continuous efforts in improving the stability and systematic shifts of optical clocks. Here the authors demonstrate thulium optical clock utilizing bicolor scheme involving interrogation of both hyperfine levels and they are able to cancel the quadratic Zeeman shift.

The 17 m open-air link for coherent transfer of ultrastable optical frequency signal have been demonstrated. The fractional frequency instability caused by air turbulence is suppressed by more than 3 orders of magnitude with the help of active noise compensation system and reaches 1.7∙10-19 after averaging time of 1000 s. The link contribution to uncertainty is decreased by more than 400 times and is equal to 5∙10-20.

In this work we discuss interrogation scheme required for the use of synthetic frequency in thulium optical lattice clock and underlying specifics of servo signal generation. In order to achieve insensitivity of the synthetic frequency to periodic oscillations of the magnetic field, simultaneous interrogation of two clock transitions is beneficial, which complicates optimization of digital lock parameters and may result in crosstalk. We used numerical simulations to test the performance of digital locks and verify absence of systematic frequency shifts related to the interrogation scheme.

The 1.14 µm inner-shell magnetic dipole transition in neutral thulium possesses very low blackbody radiation shift in comparison to other neutrals. Together with other features of Tm electronic structure it opens new perspectives for compact optical clocks almost free from hard-to-control systematic shifts.

Trapped ions nowadays play an important role in both fundamental science and technical applications. Due to its convenient energy structure, singly charged ytterbium ion is widely used in microwave and optical frequency standards, tests of fundamental theories, and quantum information science. In this paper, we present the results of wavelengths measurements in the 2S1/2→2P1/2 and 2D3/2→3[3/2]1/2 transitions in 170Yb+, 171Yb+, 172Yb+, 174Yb+, and 176Yb+ ions with uncertainties of 50 and 20 MHz, respectively. We reach a factor of three-times improvement in the accuracy with respect to the previously published data, which significantly simplifies the process of initial ion trapping and cooling, in a laser system and an ion trap designed for the YBIS Project aimed for developing a compact and transportable optical clock based on a single 171Yb+ ion.

A contribution of a temperature drift near the silicon thermal expansion coefficient zero point to the fractional frequency instability of a silicon cavity is analysed. The thermal expansion coefficient of silicon is measured by an optical method near the zero point T 0 = 123 K. It is shown that the frequency instability due to cavity temperature drifts observed in an experiment does not exceed a thermal noise limit at averaging intervals of up to 20 s.

One of the key systematic effects limiting the performance of state-of-the-art optical clocks is the blackbody radiation (BBR) shift. Here, we demonstrate unusually low sensitivity of a 1.14 μm inner-shell clock transition in neutral Tm atoms to BBR. By direct polarizability measurements, we infer a differential polarizability of the clock levels of −0.063(30) atomic units corresponding to a fractional frequency BBR shift of only 2.3(1.1) × 10−18 at room temperature. This amount is several orders of magnitude smaller than that of the best optical clocks using neutral atoms (Sr, Yb, Hg) and is competitive with that of ion optical clocks (Al+, Lu+). Our results allow the development of lanthanide-based optical clocks with a relative uncertainty at the 10−17 level., Precise and stable optical clocks are important for fundamental science and applications. Here the authors demonstrate a clock transitions in thulium (Tm), which has a small black body radiation frequency shift and is suitable for transportable atomic clocks.

The schematic diagram of the compact transportable optical frequency standard based on the quadrupole transition in a single 171Yb+ ion with a relative instability at the levelx of 5 · 10−16, less than 1m3 in volume and less than 300 kg in weight is presented. The ionic trap and laser systems are described. Trapping and laser cooling of the 174Yb+ ion are experimentally demonstrated.

We propose a method for EIT ground state cooling of 171Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).

We eliminate the largest systematic shift in thulium optical clock — the second-order Zeeman shift — using average frequency of two clock transitions. This reduces the total systematic shift down to mHz level.

Remarkable advancements in the ability to create, manipulate, and measure quantum systems are paving the way to build next generations of devices based on quantum physics. Quantum technologies in Russia are on the list of strategically important cross-cutting directions in the framework of the National Technology Initiative programs and the Digital Economy National Program. The broad focus includes quantum computing and simulation, quantum communications, quantum metrology and sensing. This paper reviews existing research on quantum science and technologies in Russia and summarizes the main goals for the next few years that form the basis of an upcoming major national initiative.

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., Comment: 7 pages, 2 Figures

We calculate uncertainty budget of a developing thulium optical lattice clock. We estimate necessary level of control over various experimental parameters to achieve total systematic uncertainty of better than 10−17 in fractional units. We show, that clock transition frequency is insensitive to an ambient temperature, as well as quadratic Zeeman shift when interrogating two transition between different hyperfine levels. The optical lattice shift of the clock transition frequency is below 1 mHz for the lattice laser frequency stability of better than 3 MHz around the magic wavelength and relative fluctuation of the lattice polarization and a bias magnetic field of less than 1 mrad.

We report on preliminary results of frequency instability of two laser systems stabilized by perspective cryogenic monocrystalline silicon cavities. The obtained value of 5×10−15 exceeds the thermal noise floor by more than an order of magnitude. The most likely reason is residual amplitude modulation fluctuations in the electro-optical scheme.

The paper studies the excitation of the $^{229}\mathrm{Th}$ nucleus to the anomalously low-lying isomeric state $3/{2}^{+}(8.28\ifmmode\pm\else\textpm\fi{}0.17$ eV) in the electron bridge process via the continuum of the electron spectrum. Resonant excitation of the nucleus was found to be always possible in the scheme, no matter where the electron levels of an atom or ion were located. Formulas for the excitation cross section by narrow and wide laser lines are obtained. In the resonance, where the process under consideration turns into laser photoionization followed by nuclear excitation in electron capture, the cross section of the process was shown to be comparable in magnitude with that of the photoionization of the thorium atom. Experimental schemes for testing the effect were proposed, which would allow measuring the frequency of the nuclear isomeric transition $3/{2}^{+}\ensuremath{\rightarrow}5/{2}^{+}$ to a high precision, which is the first-priority (and still unresolved) task for creating a nuclear clock.

The development of the optical frequency comb technique has enabled a wide use of atomic optical clocks by allowing frequency conversion from the optical to the radio frequency range. Today, the fractional instability of such clocks has reached the record eighteen-digit level, two orders of magnitude better than for cesium fountains representing the primary frequency standard. This is paralleled by the development of techniques for transferring accurate time and optical frequency signals, including fiber links. With this technology, the fractional instability of transferred frequency can be lowered to below 10−18 with an averaging time of 1000 s for a 1000 km optical link. At a distance of 500 km, a time signal uncertainty of 250 ps has been achieved. Optical links allow comparing optical clocks and creating a synchronized time and frequency standard network at a new level of precision. Prospects for solving new problems arise, including the determination of the gravitational potential, the measurement of the continental Sagnac effect, and precise tests of fundamental theories.

We discuss extension of a recently proposed method based on continuous spectroscopy of 88Sr atoms trapped into a moving optical lattice [Appl. Phys. Express,14(7),072006(2021)] to operation of bicolor thulium optical clocks. Simultaneous interrogation of two clock transitions at 1.14μm and building up a synthetic frequency provides a straightforward way to significantly suppress the first-order Doppler shift and cancel out the second-order Zeeman shift, the latter being one of the major uncertainty sources in the originally proposed 88Sr setup. In our configuration, the total systematic frequency shift is 4×10−16 and instability at or lower than 10−18 after 1 hour of integration.

We have developed a compact vacuum system for laser cooling and spectroscopy of neutral thulium 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 with only 15 mW of MOT cooling beams net power. By exploiting Zeeman-like deceleration of atoms with an additional laser beam and tailoring the MOT magnetic field gradient with a small magnetic coil, we demonstrated trapping of up to 13 million atoms. These results show great perspective of the developed setup for realizing a compact high-performance optical atomic clock based on thulium atoms.

How big is the proton? The discrepancy between the size of the proton extracted from the spectroscopy of muonic hydrogen and the value obtained by averaging previous results for “regular” hydrogen has puzzled physicists for the past 7 years. Now, Beyer et al. shed light on this puzzle (see the Perspective by Vassen). The authors obtained the size of the proton using very accurate spectroscopic measurements of regular hydrogen. Unexpectedly, this value was inconsistent with the average value of previous measurements of the same type. Also unexpectedly, it was consistent with the size extracted from the muonic hydrogen experiments. Resolving the puzzle must now include trying to understand how the old results relate to the new, as well as reexamining the sources of systematic errors in all experiments. Science , this issue p. 79 ; see also p. 39

A 5-m-long fibre link with a phase noise compensation system for optical frequency signal transmission at a wavelength of 1.14 μm is demonstrated. The stability of the noise compensation system in the presence of harmonic mechanical perturbations is assessed and the relative transmitted signal frequency instability is shown to be 3.8 × 10−15 at an averaging time of 1 s and 3.5 × 10−20 over 850 s.