Higher-order constraints on precision of the time-frequency metrology of atoms in optical lattices V. D. Ovsiannikov Physics Department, Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006, Russia V. G. Pal'chikov Institute of Metrology for Time and Space at National Research Institute for Physical--Technical and Radiotechnical Measurements, Mendeleevo, Moscow Region 141579, Russia FFK-14, Dubna, December 3, 2014 1 Contents 1. 2. a) b) c) d) e) f) g) h) 3. a) b) c) Principal goal: to determine irremovable clock-frequency shifts induced by multipole, nonlinear and anharmonic interaction of neutral Sr, Yb and Hg atoms with an optical lattice of a magic wavelength (MWL) . Attractive lattice of a Red-detuned MWL: Spatial distribution of atom-lattice interaction. Lattice potential wells. Lattice-induced clock-frequency shift. Numerical estimates of electromagnetic susceptibilities and clock-frequency shifts of neutral Sr, Yb and Hg atoms in a lattice of a red-detuned MWL. MWL for an atom in a traveling wave (TW). MWL for an atom in a standing wave (SW). MWL for equal dipole polarizabilities (EDP) in ground and excited clock states MWL precision. Elimination of nonlinear effects in a lattice of Sr blue-detuned MWL of λm=389.889 nm. Spatial distribution of interaction between atom and a repulsive lattice. Motion-insensitive standing-wave MWL (SW MWL). Numerical estimates of the blue-detuned-lattice-induced shifts FFK-14, Dubna, December 3, 2014 2 Typical structure of energy levels in alkaline-earth and alkaline-earth-like atoms (Mg, Ca, Sr, Zn, Cd, Yb, Hg) 1 P1 Radiation transitions between metastable and ground states, stimulated in odd 3 3 isotopes by the hyperfine interaction, is P2 This prohibition makes extremely narrow 3 1 the line of the clock transition, 0 0 which may be stimulated by an external D1 3 3 S1 P1 M2 3 «Clock» transition P0 strictly forbidden in even isotopes. PS magnetic field or by the circularly polarized lattice wave. This transition may be used as an oscillator with extremely high quality Q cl / 1017 2ω(M1+E1) E1 1 S0 The width (ΔS=1) of the oscillator depends on (and may be regulated by) the intensity of the lattice wave or a static magnetic field. FFK-14, Dubna, December 3, 2014 3 Natural isotope composition Even isotopes (J=0) abundance 24,26Mg: 90% 40→48Ca: 98.7% 84,86,88Sr: 93% 168→176Yb: 73% 196→204Hg: 69.8% 106→116Cd: 75% 64→70Zn: 95.9% Odd isotopes abundance (J≠0) 25Mg: 10% (J=5/2) 43Ca: 1.3% (J=7/2) 87Sr: 7% (J=9/2) 171,173Yb: 27% (J=1/2, 5/2) 199,201Hg: 30.2% (J=1/2,3/2) 111,113Cd: 25% (J=1/2) 67Zn: 4.1% (J=5/2) FFK-14, Dubna, December 3, 2014 4 2. Red-detuned MWL 2.a) Spatial distribution of atom-lattice interaction E( X , t ) 2E0 cos(kX )cos(t ), k c 2 Vˆ ( X , t ) Re Vˆ ( X ) exp(it ) Vˆ ( X ) VˆE1 cos(kX ) (VˆE 2 VˆM1 )sin(kX ) VˆE1 (r E0 ); 2 VˆE 2 r E0 n2 C2 ( , ) ; 6 FFK-14, Dubna, December 3, 2014 VˆM 1 [n E0 ] (Jˆ Sˆ ) 2 5 Eglatt(e) ( X ) Eg(2)(e) ( X ) Eg(4)(e) ( X ) ... E (2) g (e) † ˆ ˆ † ˆ ˆ ( X ) g (e) V ( X )G V ( X ) V ( X )G V ( X ) g (e) gE(1e ) ( ) cos 2 (kX ) gqm( e ) ( ) sin 2 ( kX ) I gqm( e ) ( ) gE(2e ) ( ) gM( e1) ( ); I is the laser intensity: 2 I is the mean intensity of a standing wave, 0 is the intensity of the node, 4 I is the intensity of antinode. Eg(4)(e) ( X ) g (e) ()cos4 (kX ) I 2 . FFK-14, Dubna, December 3, 2014 6 2b) Lattice potential wells. Clock-level shift is the Lattice-trap potential energy E latt g ( e) (X ) U latt g ( e) Dg ( e ) ( , , I ) ( X ) Dg (e) U E1 g (e) ( harm) g (e) X U 2 ( anh) g ( e) 4 X ; ( ) I g ( e ) ( , ) I , depth 2 Mat ( , , I ) U ( ) I 2 g ( e ) ( , ) I k , 2 4 k ( anh ) dqm 2 U g ( e ) ( , , I ) g ( e ) ( ) I 5 g ( e) ( , ) I 3 2 ( harm ) g (e) dqm g (e) 2 FFK-14, Dubna, December 3, 2014 2 7 X / L 5 4 3 2 1 n=0 U glatt(e) ( X ) / Dg (e) L / 2 Stark-trap potential and vibration-state energies of an atom in a standing wave of a lattice field FFK-14, Dubna, December 3, 2014 8 2 ˆ P at latt at Hˆ g ( e)(X )= U g ( e) ( X ), Pˆat i ; 2Mat X ˆ atg (e)(X)n(X)= Evib H g ( e) n(X) 1 1 anh 2 E (, , I , n) Dg (e) (, , I ) g (e) (, , I ) n -Eg (e) (, , I ) n n 2 2 anharmonic energy depth harmonic oscillations vib g (e) rec E anh Eg ( e ) ( , , I ) 2 rec t E 2 2Matc 2 3 g ( e ) ( , ) I 1 ; dqm g ( e ) ( ) is the recoil energy of a lattice photon FFK-14, Dubna, December 3, 2014 9 latt g (e) E E (0) g ( e) E vib g ( e) (, , I , n) The strict magic-wavelength condition should imply the equality vib Evib ( , , I , n ) E e mag g (mag , , I , n) To hold this condition, the equality should hold for the susceptibilities: E1 qm gdqm ( ) ( ) (e) g (e) g ( e ) ( ); qm g (e) ( ) E2 g (e) ( ) M1 g ( e) ( ); g ( e ) ( , ) glin( e ) ( ) 2 gc( e ) ( ) glin( e) ( ) ; | | 1. The most important of which is the E1 polarizability, so the primitive MWL condition implied (mag ) (mag ) E1 e E1 g FFK-14, Dubna, December 3, 2014 10 kHz nm Wavelength dependences of the linear in the lattice-laser intensity Stark shifts for Yb atoms in their upper 6s6p3P0 (e) and lower 6s2 1S0 (g) clock states at I 10kW/cm2. λmag =762.3 nm (theory) λmag =759.3537 nm (experiment) FFK-14, Dubna, December 3, 2014 11 ΔE/kHz nm Wavelength dependence of the linear in the lattice-laser intensity Stark shifts ΔE/kHz of clock states. I=25 kW/cm2 Hg atoms in their upper 6s6p3P0 (e) and lower 6s2 1S0 (g) λmag =364 nm (theory) λmag =362.53 nm (experiment) FFK-14, Dubna, December 3, 2014 12 kHz nm The wavelength dependence of Stark shifts ΔE/kHz of Mg clock levels. The shifts of the ground state 3s2 1S0 (red solid line) and the excited state 3s3p 3P0 (black dashed curve) in a lattice field of a laser intensity I=40 kW/cm^2 (chosen provisionally to provide the Stark trapping potential depth of about 40-50 photon recoil energies). The magic wavelength λmag≈453 nm is determined by the point of intersection of the lines. FFK-14, Dubna, December 3, 2014 13 kHz nm Stark shifts of magnesium clock levels in case of a right-handed circular polarization of lattice. Red solid line is for the ground state 3s2 1S0, all the rest for different magnetic sublevels of the excited 3s3p 3P1 state in a lattice field of a laser intensity I=40 kW/cm^2 (about 40-50 photon recoil energies). The magic wavelengths (MWL) are 419.5 nm for M=-1 and 448.1 nm for M=0 magnetic substates of the upper clock level 3s3p(3P1), correspondingly. There is no MWL for the state M=1 in a circularly polarized lattice. FFK-14, Dubna, December 3, 2014 14 kHz nm Stark shifts of magnesium clock levels in case of a linearly polarized lattice wave of the laser intensity I=40 kW/cm^2. The shifts of states 3s3p 3P1 (M=±1) are identical and completely equivalent to that of the state M=0 in a circularly polarized lattice beam with the MWL 448.1 nm, which is nearly equal to the MWL 453.5 nm for an averaged over M, independent of polarization (scalar) shift; the MWL for the M=0 state is 527 nm. The shifts of upper clock states experience the resonance enhancement on the 3s4s(3S1)-state at 517 nm, except for the state M=0 in the case of linearly polarized lattice and M=1 (M=-1) state in the right-handed (left-handed) case of circular polarization FFK-14, Dubna, December 3, 2014 15 2c) Lattice-induced clock-frequency shift. latt cl (0) cl ; latt cl latt cl (0) cl E E ; (0) e (0) g latt cl E E ; vib e vib g 1 1 anh 2 D n E n n ; 2 2 D eE1 ( ) gE1 ( ) I e ( ) g ( ) I 2 ; e g 2 Erec I edqm () 2e () I gdqm () 2 g () I ; E anh 3 rec e ( , ) g ( , ) E dqm dqm I 2 e ( ) g ( ) FFK-14, Dubna, December 3, 2014 16 (n, , I ) c1/2 (n) I latt cl If 1/2 c1 (n, ) I c3/2 (n, ) I c2 ( ) I 3/2 2 sign l ( , mag ) sign c ( , mag ) , then mag 1/ 1 / c l (mag , mag ) 0 FFK-14, Dubna, December 3, 2014 17 2.d) Numerical estimates of electromagnetic susceptibilities and clock-frequency uncertainties Table 1 mag Atom Sr /nm kHz mE1 kW/cm mqm 2 mHz 2 kW/cm Hz Re ml kW/cm2 2 Hz Im ml kW/cm 2 2 Hz Re mc kW/cm2 2 Hz Im mc kW/cm2 2 kHz m I 2 kW/cm 10 9 mE1 E rec kW/cm kHz 2 1 Yb Hg 813.42727 389.889 759.35374 362.53 45.2 – 92.7 40.5 5.70 1.38 – 13.6 -8.06 8.25 –200.0 1150 – 366.3 – 2.50 0 2.48 0 4.34 – 311.0 1550 240.2 2.53 0 2.37 0 6.37 25.05 74.8 18.03 13.1 10.3 0.720 0.134 15.1 2.00 7.57 0.254 3.47 FFK-14, Dubna, December 3, 2014 18 μHz/(kW/cm2)2 nm 3P 2 3P 0 3F 2 The wavelength (in nanometers) dependence of the hyperpolarizability (in μHz/(kW/cm2)2) of clock transition in Yb atoms for the linear (red dashed curve) and circular (black solid curve) polarization of the lattice-laser wave. The vertical lines indicate positions of two-photon resonances on 6s8p(3P2) state at 754.226 nm, 6s8p(3P0) state at 759.71 nm (this resonance appears only for linear polarization) and 6s5f(3F2) state at 764.953 nm FFK-14, Dubna, December 3, 2014 19 μHz/(kW/cm2)2 nm 3P 2 3P 0 3F 2 The wavelength (in nanometers) dependence of the hyperpolarizability (in μHz/(kW/cm2)2) of clock transition in Sr atoms for the linear (red dashed curve) and circular (black solid curve) polarization of the lattice-laser wave. The vertical lines indicate positions of two-photon resonances on 5s7p(3P2) state at 795.5 nm, 5s7p(3P0) state at 797 nm (this resonance does not appear for circular polarization) and 5s4f(3F2) state at 818.6 nm FFK-14, Dubna, December 3, 2014 20 2.e) MWL for an atom in a traveling wave Due to homogeneous spatial distribution of intensity in a traveling wave, the second-order shift of clock levels is determined by the sum of E1, E2 and M1 polarizabilities g(e) () gE(1e) () gqm(e) () So, the MWL is determined from the equality 2 c / t m t m ( ) ( ) . g t m e FFK-14, Dubna, December 3, 2014 t m t 21 At this condition, Dt tqm I t I 2 Dt(0) tqm t I / t , where Dt(0) t I ; tqm eqm (mt ) gqm (mt ); t e ( ) g ( ); t m t m clt (n, , I ) and coefficients for the intensity dependence of the shift are t c1/2 (n) tqm Etrec t c 3/2 ( , n) t ( ) t 2n 1 ; Etrec t c1t ( , n) tqm 3Etrec 1 2 t ( ) n n ; 2 t 2 2n 1 ; c 2t ( ) t ( ), FFK-14, Dubna, December 3, 2014 22 mHz (a) Sr TW MWL (n=0) mHz kW/cm2 (b) Yb TW MWL (n=0) kW/cm2 Intensity I/(kW/cm2) dependence of the lattice-induced clock-frequency shift (Δν/mHz) for (a) Sr and (b) Yb atoms in a linearly (red solid), elliptically (green dotted) and circularly (black dashed) polarized lattice of a traveling-wave MWL FFK-14, Dubna, December 3, 2014 23 mHz Hg TW MWL (n=0) ( , n, I ) kW/cm2 ( , n, I ) Intensity _I_/(kW/cm2)) dependence of the lattice-induced clock-frequency shift (Δν/mHz) in Hg atoms in a linearly (red solid), elliptically (green dotted) and circularly (black dashed) polarized lattice of a traveling-wave MWL. The imaginary part – clockfrequency broadening ( , n, I ) Im ( , n, I ) for linear (black solid) and circular (red dashed) polarizations are negative values (thin curves at the plot bottom). FFK-14, Dubna, December 3, 2014 24 2.f) MWL for an atom in a standing wave of an optical lattice (motion-insensitive MWL) gdqm (ms ) edqm (ms ) sdqm. At this condition, с1/s 2 ( , n) 0; с ( , n) s 1 qm s rec s dqm s 1 2 t s ( ) n n с1 ( , n), 2 rec s dqm s 2n 1 , 3E 2 E с ( , n) s ( ) s 3/ 2 FFK-14, Dubna, December 3, 2014 с ( ) s ( ). s 2 25 mHz (a) Sr SW MWL (n=0) mHz kW/cm2 (b) Yb SW MWL (n=0) kW/cm2 Intensity _I_/(kW/cm2)) dependence of the lattice-induced clock-frequency shift (Δν/mHz) for (a) Sr and (b) Yb atoms in a linearly (red solid) elliptically (green dotted) and circularly (black dashed) polarized lattice of a standing-wave MWL FFK-14, Dubna, December 3, 2014 26 Hg SW MWL (n=0) kW/cm2 ( , n, I ) ( , n, I ) mHz Intensity _I_/(kW/cm2)) dependence of the lattice-induced clock-frequency shift (Δν/mHz) in Hg atoms in a linearly (red solid), elliptically (green dotted) and circularly (blue dashed) polarized lattice of a standing-wave MWL. The imaginary part – clockfrequency broadening ( , n, I ) Im ( , n, I ) for linear (red solid) and circular (black dashed) polarizations are negative values (thin curves at the plot top). FFK-14, Dubna, December 3, 2014 27 2.g) MWL for equal dipole polarizabilities in ground and excited clock states E1 gE1 (mE1 ) eE1 (mE1 ) mag . At this condition, c1/E12 (n) mqm rec EErec 3 E 1 1 E1 2 1 E1 n , c1 ( , n) E1 E1 ( ) n n , E1 m 2 2 m 2 rec E c3/E12 ( , n) EE11 E1 ( ) 2n 1 , c2E1 ( ) E1 ( ). m FFK-14, Dubna, December 3, 2014 28 (a) Sr EDP MWL (b) Yb (n=0) mHz EDP MWL (n=0) mHz kW/cm2 kW/cm2 Intensity I/(kW/cm2)) dependence of the lattice-induced clock-frequency shift (Δν/mHz) for: (a) Sr and (b) Yb atoms in a linearly (red solid), elliptically (green dotted) and circularly (black dashed) polarized lattice of an “equal dipole polarizabilities” MWL. FFK-14, Dubna, December 3, 2014 29 Hg EDP MWL (n=0) ( 0, n, I ) kW/cm2 (mag , n, I ) ( 0, n, I ) (| | 1, n, I ) (| | 1, n, I ) mHz Intensity _I_/(kW/cm2)) dependence of the lattice-induced clock-frequency shift, Re(Δν/mHz) in Hg atoms in a linearly (red solid), elliptically (green dotted) and circularly (blue dashed) polarized lattice of an “equal dipole polarizabilities” MWL. The imaginary part – clock-frequency broadening ( , n, I ) Im ( , n, I ) for linear (red solid) and circular (black dashed) polarizations are negative values. FFK-14, Dubna, December 3, 2014 30 Dependence of the lattice-induced clock-frequency shift on the lattice intensity I, circular polarization degree ξ and on the vibration quantum number n in Yb 1. For the TW MWL ( g (mt ) e (mt ) t ): clTW 1.79(2n 1) I 1/ 2 [8.06 (0.0136 0.0225 2 )(2n2 2n 1)]I (0.0814 0.1348 2 )(2n 1) I 3/ 2 (0.366 0.606 2 ) I 2 ; 2. For the SW MWL ( gdqm (ms ) edqm (ms ) sdqm ): clSW [8.06 (0.0136 0.0225 2 )(2n2 2n 1)]I (0.0814 0.1348 2 )(2n 1) I 3/ 2 (0.366 0.606 2 ) I 2 ; 3. For the ED MWL ( g (m ) e (m ) m ): E1 ED E1 ED E1 clED 0.895(2n 1) I 1/ 2 (0.0136 0.0225 2 )(2n2 2n 1) I (0.0814 0.1348 2 )(2n 1) I 3/ 2 (0.366 0.606 2 ) I 2 . FFK-14, Dubna, December 3, 2014 31 2.h) MWL precision Uncertainties of the clock frequency are directly proportional to the uncertainties of the MWL: cl cl m m The principal contribution to the derivative comes from the E1 polarizability in the lattice well depth and in the frequency of harmonic vibrations: cl ( ) m 1 I n m m m 2 E1 m FFK-14, Dubna, December 3, 2014 32 A 15% precision estimate of frequency derivatives for polarizabilities in Sr atoms gives: cl m E1 1 1 1 mag I n res res m 2 2 e g (0) (0) res E E g 5 s 5 p ( 1P ) 5 s 2 ( 1S 1 0 ; m 281.95 THz, ) (0) eres E5(0) E m 72.778 THz; s 6 s ( 3S ) 5s5 p ( 3P ) 1 0 cl 1 10 10 6.57 I 1.52 I n . m 2 For I=10 kW/cm2 the departure from the magic frequency Δωm < 100 kHz provides the fractional uncertainty of the clock frequency at the level | cl | / cl 1018 FFK-14, Dubna, December 3, 2014 33 Conclusions 1 (Red-detuned MWL) 1. At least 3 different methods may be used for determining MWL for the redt s detuned optical lattice, providing MWL, m , m and their mean value mE1 (mt ms ) / 2 (in Sr, ms mt 20.5 MHz ). These MWLs provide different lattice-induced shifts and uncertainties on the clock frequency, with different dependencies on the lattice laser intensity. 2. The polarizabilities contribute only to the lattice potential depth and harmonic oscillation frequencies and never contribute to the anharmonic terms, where the contributions come from hyperpolarizabilities only. 3. The hyperpolarizability provides quadratic, power 3/2 and linear contributions to the lattice-potential depth, frequency of vibrations and anharmonic interaction, correspondingly. At I>10 kW/cm2 the hyperpolarizability contribution to the lattice-induced shift in Sr and Yb atoms becomes comparable or exceeding that of polarizability. In Hg atoms the hyperpolarizability terms do not exceed 10% of polarizability terms at I<100 kW/cm2. FFK-14, Dubna, December 3, 2014 34 3. Elimination of nonlinear effects in a lattice of Sr blue-detuned MWL of λm=389.889 nm 3.1. Spatial distribution of interaction between atom and a repulsive lattice. Trapped atoms locate near nodes of the lattice field: E( X , t ) 2E0 sin(kX )sin(t ), Atom-lattice interaction: Vˆ ( X ) VˆE1 sin(kX ) (VˆE 2 VˆM 1 )cos(kX ) FFK-14, Dubna, December 3, 2014 35 The second-order term is linear in the laser intensity I and is determined by the E1 and multipole polarizabilities ( E2, M1…) : Eg(2)( e ) ( X ) g (e) Vˆ † ( X )GVˆ ( X ) Vˆ ( X )G Vˆ † ( X ) g (e) 2 qm gdqm ( ) sin ( kX ) (e) g ( e ) ( ) I where the dipole polarizability is gE(1e) ( ) 0; E1 ( ) qm ( ) 0; gdqm ( ) (e) g (e) g (e) gE(1e ) ( ) >> gqm( e ) ( ) ; gqm(e) ( ) gM(e1) ( ) gE(2e ) ( ). The fourth-order term is quadratic in the laser intensity I and is determined by the dipole hyperpolarizability: (4) g (e) E ( X ) g (e) ()sin (kX )I . 4 FFK-14, Dubna, December 3, 2014 2 36 The Stark-effect energy determines the trap potential energy for excited and ground-state atom: Eglatt( e ) ( X ) Eg(2)( e ) ( X ) Eg(4)( e ) ( X ) U glatt( e ) ( X ) 2 gqm( e ) ( ) I gdqm ( ) I ( kX ) (e) 4 dqm g (e) (kX ) ( ) I 3 g ( e ) ( ) I ; 3 2 The difference between top (X=λ/4) and bottom (X=0) of the trap potential latt g (e) D U latt g (e) latt dqm 2 X U (0) ( ) I ( ) I g (e) g (e) g (e ) 4 is the depth of the lattice well, quite similar to the red-detuned lattice, but the positionindependent energy shift involves only the E2-M1 polarizability gqm , in contrast ( e ) ( ) to the red-detuned MWL, where both E1 polarizability and hyperpolarizability were involved. FFK-14, Dubna, December 3, 2014 37 3 k2 rec For D E E k BT , E , 2 2M atom is trapped into an eigenstate of the vibrational Hamiltonian latt g (e) rec therm with the energy vib g (e) E ( I , , n) U (0) g (e) bottom 1 anh 1 2 g ( e ) n -Eg (e ) ( , I ) n n 2 2 harmonic oscillations anharmonic energy Ug(0)(e) Uglatt(e) (0) gqm(e) ()I rec latt g ( e ) 2 -Erec gdqm ( ) I 2 E Dg ( e ) (e) anh g (e) E 3 rec 3 g ( e ) ( , ) I ( , I ) E 1 ; dqm 2 g ( e ) ( ) FFK-14, Dubna, December 3, 2014 38 Lattice-induced clock-frequency shift is vib 1/ 2 cllatt (m , I , n) Evib E c ( n ) I c1 ( , n)I e g 1/ 2 where c1/ 2 (n) Erec edqm (m ) gdqm (m ) (2n 1); rec 3 E c1 ( , n) eqm (m ) 2 e ( , m ) g ( , m ) 2 1 dqm dqm n n ; 2 e (m ) g (m ) FFK-14, Dubna, December 3, 2014 39 3.2. Motion-insensitive standing-wave MWL (SW MWL) is determined by the equality edqm (m ) gdqm (m ), the lattice-induced clock-frequency shift is latt cl m 1 ( , I , , n) c ( , n)I , rec 3 E Re c1 ( , n) eqm (m ) 2 Dmlatt 3E rec Im c1 ( , n) 2 Dmlatt 1 2 n n Re m ( ) I ; 2 1 2 n n Im m ( ) I , 2 Dmlatt is the depth of the lattice well at the MWL frequency The hyperpolarizability effects in the shift and broadening (caused by two-photon rec latt ionization) are strongly reduced by the factor E / Dm 1 (as follows from the data of table 1 for the blue MWL, b 389.889 nm, Erec / Dlatt 1/(6I ), where m m intensity is in kW/cm2). FFK-14, Dubna, December 3, 2014 40 3.3. Numerical estimates of the blue-detuned-latticeinduced shifts From the data of table 1 for the Sr blue-detuned MWL we have Re c1 ( , n 0) (13.74 0.05 2 ) mHz/(kW/cm 2 ), Im c1 ( , n) (0.606 0.026 2 )( n 2 n 1/ 2) Hz/(kW/cm 2 ) In the blue-detuned lattice of Sr atoms the shift of the clock frequency is directly proportional to the lattice-laser intensity and is mainly determined by the difference of E2-M1 polarizabilities of the clock levels. The influence of hyperpolarizability appears only in the third digit number. The broadening (imaginary part of the shift) is more than 4 orders smaller than the shift. For I=10 kW/cm2 the lattice-induced shift is about 137 mHz, the latticeinduced width is about 6 μHz. The hyperpolarizability effects in the shift and broadening (caused by two-photon ionization) rec latt are strongly reduced by the factor E / Dm 1 (as follows from the data of table 1 for b the blue MWL, m 389.889 nm, Erec / Dlatt 1/(6I ),where intensity is in kW/cm 2). m FFK-14, Dubna, December 3, 2014 41 Conclusions 2 1. The motion-insensitive blue-detuned MWL depends on only the polarizabilities and is not influenced by hyperpolarizability effects. 2. The hyperpolarizability effects on the clock levels appear only in anharmonic interaction of atom with lattice. 2 3. The intensity of the lattice laser I 4 kW/cm is sufficient to trap atoms cooled to 1 μK at the lowest vibrational state. 4. To achieve the clock frequency precision at the 18th decimal place, the irremovable multipole-interaction-induced shift by the field of optical lattice should be taken into account with uncertainty below 1.0%. FFK-14, Dubna, December 3, 2014 42 Thank you for attention! FFK-14, Dubna, December 3, 2014 43