Ramsey Spectroscopy with Displaced Frequency Jumps.

Sophisticated Ramsey-based interrogation protocols using composite laser pulse sequences have been recently proposed to provide next-generation high-precision atomic clocks with a near perfect elimination of frequency shifts induced during the atom-probing field interaction. We propose here a simple alternative approach to the autobalanced Ramsey interrogation protocol and demonstrate its application to a cold-atom microwave clock based on coherent population trapping (CPT). The main originality of the method, based on two consecutive Ramsey sequences with different dark periods, is to sample the central Ramsey fringes with frequency jumps finely adjusted by an additional frequency-displacement concomitant parameter, scaling as the inverse of the dark period. The advantage of this displaced frequency-jump Ramsey method is that the local oscillator (LO) frequency is used as a single physical variable to control both servo loops of the sequence, simplifying its implementation and avoiding noise associated with controlling the LO phase. When tested using a CPT cold-atom clock, the DFJR scheme reduces the sensitivity of the clock frequency to variations of the light shifts by more than an order of magnitude compared with the standard Ramsey interrogation. This simple method can be applied in a wide variety of Ramsey-spectroscopy based applications including frequency metrology with CPT-based and optical atomic clocks, mass spectrometry, and precision spectroscopy.

Dynamic regime of coherent population trapping and optimization of frequency modulation parameters in atomic clocks.

We theoretically investigate the dynamic regime of coherent population trapping (CPT) in the presence of frequency modulation (FM). We have formulated the criteria for quasi-stationary (adiabatic) and dynamic (non-adiabatic) responses of atomic system driven by this FM. Using the density matrix formalism for Λ system, the error signal is exactly calculated and optimized. It is shown that the optimal FM parameters correspond to the dynamic regime of atomic-field interaction, which significantly differs from conventional description of CPT resonances in the frame of quasi-stationary approach (under small modulation frequency). Obtained theoretical results are in good qualitative agreement with different experiments. Also we have found CPT-analogue of Pound-Driver-Hall regime of frequency stabilization.

Magnetic-dipole transitions in highly charged ions as a basis of ultraprecise optical clocks.

We evaluate the feasibility of using magnetic-dipole (M1) transitions in highly charged ions as a basis of an optical atomic clockwork of exceptional accuracy. We consider a range of possibilities, including M1 transitions between clock levels of the same fine-structure and hyperfine-structure manifolds. In highly charged ions these transitions lie in the optical part of the spectra and can be probed with lasers. The most direct advantage of our proposal comes from the low degeneracy of clock levels and the simplicity of atomic structure in combination with negligible quadrupolar shift. We demonstrate that such clocks can have projected fractional accuracies below the 10^{-20}-10^{-21} level for all common systematic effects, such as blackbody radiation, Zeeman, ac-Stark, and quadrupolar shifts.

Generalized Ramsey excitation scheme with suppressed light shift.

We experimentally investigate a recently proposed optical excitation scheme V. I. Yudin et al. [Phys. Rev. A 82, 011804(R) (2010)] that is a generalization of Ramsey's method of separated oscillatory fields and consists of a sequence of three excitation pulses. The pulse sequence is tailored to produce a resonance signal that is immune to the light shift and other shifts of the transition frequency that are correlated with the interaction with the probe field. We investigate the scheme using a single trapped ^{171}Yb^{+} ion and excite the highly forbidden (2)S(1/2) - (2)F(7/2) electric-octupole transition under conditions where the light shift is much larger than the excitation linewidth, which is in the hertz range. The experiments demonstrate a suppression of the light shift by four orders of magnitude and an immunity against its fluctuations.

Atomic clocks with suppressed blackbody radiation shift.

We develop a concept of atomic clocks where the blackbody radiation shift and its fluctuations can be suppressed by 1-3 orders of magnitude independent of the environmental temperature. The suppression is based on the fact that in a system with two accessible clock transitions (with frequencies ν1 and ν2) which are exposed to the same thermal environment, there exists a "synthetic" frequency ν(syn) ∝ (ν1 - ε12ν2) largely immune to the blackbody radiation shift. For example, in the case of 171Yb+ it is possible to create a synthetic-frequency-based clock in which the fractional blackbody radiation shift can be suppressed to the level of 10(-18) in a broad interval near room temperature (300±15 K). We also propose a realization of our method with the use of an optical frequency comb generator stabilized to both frequencies ν1 and ν2, where the frequency ν(syn) is generated as one of the components of the comb spectrum.

Frequency shifts in an optical lattice clock due to magnetic-dipole and electric-quadrupole transitions.

We report a hitherto undiscovered frequency shift for forbidden J = 0-->J = 0 clock transitions excited in atoms confined to an optical lattice. These shifts result from magnetic-dipole and electric-quadrupole transitions, which have a spatial dependence in an optical lattice that differs from that of the stronger electric-dipole transitions. In combination with the residual translational motion of atoms in an optical lattice, this spatial mismatch leads to a frequency shift via differential energy level spacing in the lattice wells for ground state and excited state atoms. We estimate that this effect could lead to fractional frequency shifts as large as 10(-16), which might prevent lattice-based optical clocks from reaching their predicted performance levels. Moreover, these effects could shift the magic wavelength in lattice clocks in three dimensions by as much as 100 MHz, depending on the lattice configuration.

Optical lattice induced light shifts in an yb atomic clock.

We present an experimental study of the lattice-induced light shifts on the (1)S(0) --> (3)P(0) optical clock transition (nu(clock) approximately 518 THz) in neutral ytterbium. The "magic" frequency nu(magic) for the 174Yb isotope was determined to be 394 799 475(35) MHz, which leads to a first order light shift uncertainty of 0.38 Hz. We also investigated the hyperpolarizability shifts due to the nearby 6s6p(3)P(0) --> 6s8p(3)P(0), 6s8p(3)P(2), and 6s5f(3)F(2) two-photon resonances at 759.708, 754.23, and 764.95 nm, respectively. By measuring the corresponding clock transition shifts near these two-photon resonances, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 microK deep, lattice at the magic wavelength. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10(-17).

Optical lattice polarization effects on hyperpolarizability of atomic clock transitions.

The light-induced frequency shift due to hyperpolarizability (i.e., terms of second-order in intensity) is studied for a forbidden optical transition, J = 0 --> J = 0. A simple universal dependence on the field ellipticity is obtained. This result allows minimization of the second-order light shift with respect to the field polarization for optical lattices operating at a magic wavelength (at which the first-order shift vanishes). We show the possibility for the existence of a magic elliptical polarization, for which the second-order frequency shift vanishes. The optimal polarization of the lattice field can be either linear, circular, or magic elliptical. The obtained results could improve the accuracy of lattice-based atomic clocks.

Experimental preparation of pure superposition states of atoms via elliptically polarized bichromatic radiation.

We propose a simple and effective way of creating pure dark superposition states. The generation of pure states is carried out by using bichromatic radiation with controllable polarization ellipticity. We experimentally confirm analytic formulas for polarization ellipticity to obtain m-m pure dark states in the system of Zeeman sublevels of alkali atoms. For 87Rb we experimentally accumulated 60% of the atoms in the 0-0 dark state and 50% into the (+/-1) - (+/-1) dark states.

Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice.

We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

Coherent population trapping resonances in thermal (85)Rb vapor: D(1) versus D(2) line excitation.

We have compared coherent population trapping (CPT) resonances, both experimentally and theoretically, for excitation of the D(1) and D(2) transitions of thermal (85)Rb vapor. Excitation of the D(1) line results in greater resonance contrast than excitation of the D(2) line and in a reduction in the resonance width, in agreement with theoretical expectations. These results translate into a nearly tenfold improvement in performance for the application of CPT resonances to a frequency standard or a sensitive magnetometer when the D(1) line, rather than the D(2) line, is used.

Coherent population trapping resonances in thermal (85)Rb vapor: D(1) versus D(2) line excitation: errata.

In our recent Letter,(1) Ref. 12 was printed incorrectly. The correct reference is M. Zhu, Coherent population trapping-based frequency standard and method for generating a frequency standard incorporating a quantum absorber that genrates the CPT state with high frequency, U.S. patent 6,359,916 (March 19, 2002).

[The monitoring of immunological indices in odontogenic abscesses and phlegmons and their differential diagnostic meaning]. / Monitoring immunologicheskikh pokazatelei pri odontogennykh abstsessakh i flegmonakh i ikh differentsial'no-diagnosticheskaia znachimost.

The immune homeostasis parameters have been monitored in 31 patients with odontogenic abscesses and phlegmons. Immunological values possessing differential diagnostic significance have been detected. Activation of phagocytosis, spontaneous and stimulated activity of phagocytes in parallel with a moderate decrease in the cellular functional reserve, increased immunoregulatory index, and moderate shifts in the concentrations of IgG and IgM are characteristic of odontogenic abscesses, while odontogenic phlegmons are characterized by deep depression of the phagocyte function and failure of cellular and humoral immunity. The disorders in the immune functions of patients with odontogenic phlegmons normalized 2 weeks later than in those with odontogenic abscesses. Both diseases run a wave-like course and are characterized by phasic changes in immunological parameters, which is significant for determining pathogenesis and choosing appropriate immunocorrective therapy.

[The time characteristics of the exacerbation of chronic periodontitis and of odontogenic perimaxillary abscesses]. / Vremennye kharakteristiki obostreniia khronicheskogo periodontita i odontogennykh okolocheliustnykh abstsessov.

Time course of some laboratory values and clinical manifestations of inflammatory process is studied in 52 patients with exacerbations of chronic periodontitis and 284 patients with odontogenic perimaxillary abscesses. Routine laboratory studies (clinical and biochemical analyses of the blood and urine) were carried out. Acute odontogenic inflammations are characterized by an intermittent course with periodicity of about a week. The end of the first week from the disease onset coincided with recovery in exacerbation of chronic periodontitis and with the beginning of stabilization of inflammatory process in abscess. Recovery after abscess was observed 2 weeks after disease onset. These regularities may be useful for specifying the pathogenesis, terms of check-ups, and duration of treatment.

[A computerized expert system for the diagnosis and prognosis of the course of acute odontogenic inflammatory diseases (DIAPRO)]. / Komp'iuternaia ékspertnaia sistema diagnostiki i prognozirovaniia techeniia ostrykh odontogennykh vospalitel'nykh zabolevanii (DIAPRO).

A computer-aided expert system for diagnosis and prediction of the course of acute odontogenic inflammatory diseases DIAPRO is created. Based on commonly used laboratory and clinical parameters, it permits a long-distance diagnosis of acute maxillofacial inflammations and their complications and provides data for 13 signs of patient's status.

[The prediction of the outcomes of severe odontogenic inflammatory diseases of the maxillofacial area taking into account biorhythms]. / Prognozirovanie iskhodov tiazhelykh odontogennykh vospalitel'nykh zabolevanii cheliustno-litsevoi oblasti s uchetom bioritmov.

Time course of laboratory parameters is assessed in 31 patients with severe maxillofacial inflammations, hospitalized in intensive care wards. The patients were followed up for 4 to 42 days. Routine blood and urine analyses were monitored. Wave-like fluctuations in all laboratory parameters with periodicity of about a week (biorhythms) were detected. In lethal outcomes, the rhythms were disordered (desynchronized) and counterphases were detected. A grave course of inflammation is for the first time graphically represented critical periods of the diseases are determined; this will help planning the rational terms for monitoring the homeostasis, predict the disease outcome, and improve the treatment of such patients.

[The clinico-biophysical parallels of mixed saliva in odontogenic inflammatory diseases]. / Kliniko-biofizicheskie paralleli smeshannoi sliuny pri odontogennykh vospalitel'nykh zabolevaniiakh.

Mixed salivary pools of 102 patients suffering from odontogenic inflammations were examined in microwave field over the period of 3 to 42 days from the disease onset. Immunoglobulins of the three main classes were measured in these salivary pools starting from the fourth through the 28th day of the disease. Graphs reflecting the time course of the coefficient of biophysical parameters and immunoglobulin levels in patients' mixed saliva were plotted and a mathematical model of an odontogenic inflammation described for the first time, and the markers of the phases of these inflammations defined.