High-accuracy optical clock based on the octupole transition in 171Yb+

We experimentally investigate an optical frequency standard based on the 467 nm (642 THz) electric-octupole reference transition (2)S(1/2)(F=0)→(2)F(7/2)(F=3) in a single trapped (171)Yb(+) ion. The extraordinary features of this transition result from the long natural lifetime and from the 4f(13)6s(2) configuration of the upper state. The electric-quadrupole moment of the (2)F(7/2) state is measured as -0.041(5)ea(0)(2), where e is the elementary charge and a(0) the Bohr radius. We also obtain information on the differential scalar and tensorial components of the static polarizability and of the probe-light-induced ac Stark shift of the octupole transition. With a real-time extrapolation scheme that eliminates this shift, the unperturbed transition frequency is realized with a fractional uncertainty of 7.1×10(-17). The frequency is measured as 642 121 496 772 645.15(52) Hz.     

Observation and absolute frequency measurements of the 1S0-3P0 optical clock transition in neutral ytterbium

We report the direct excitation of the highly forbidden (6s2) 1S0 <--> (6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.     

Sub-Hertz optical frequency comparisons between two trapped 171Yb+ ions

We compare the frequencies of the 6s2S(1/2)(F = 0)-->5d2D(3/2)(F = 2) reference transition in 171Yb+ for two single ions stored in independent traps. The quadrupole moment of the 5d2D(3/2) state is measured to be 9.32(48) x 10(-40) C m2 and from the quadratic Stark shift the relevant scalar and tensor polarizabilities are determined to be alphaS(S(1/2)) - alphaS(D(3/2)) = -6.9(1.4) x 10(-40) J m2/V2 and alphaT(D(3/2)) = -13.6(2.2) x 10(-40) J m2/V2, respectively. In the absence of external perturbations we find a mean frequency difference between the two trapped ions of 0.26(42) Hz, corresponding to a relative difference of 3.8(6.1) x 10(-16). This is comparable to the agreement found in the most accurate comparisons between cesium fountain clocks.     

Realization of a SU(2)×SU(6) system of fermions in a cold atomic gas

We report the realization of a novel degenerate Fermi mixture with an SU(2)×SU(6) symmetry in a cold atomic gas. We successfully cool the mixture of the two fermionic isotopes of ytterbium 171Yb with the nuclear spin I=1/2 and 173Yb with I=5/2 below the Fermi temperature T_{F} as 0.46TF for 171Yb and 0.54TF for 173Yb. The same scattering lengths for different spin components make this mixture featured with the novel SU(2)×SU(6) symmetry. The nuclear spin components are separately imaged by exploiting an optical Stern-Gerlach effect. In addition, the mixture is loaded into a 3D optical lattice to implement the SU(2)×SU(6) Hubbard model. This mixture will open the door to the study of novel quantum phases such as a spinor Bardeen-Cooper-Schrieffer-like fermionic superfluid.     

Precision atomic spectroscopy for improved limits on variation of the fine structure constant and local position invariance

We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8x10(-6) per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |alpha/alpha|<1.3x10(-16) yr-1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards yield a coupled constraint of -1.5x10(-15)相似文献   

Limit on the present temporal variation of the fine structure constant

The comparison of different atomic transition frequencies over time can be used to determine the present value of the temporal derivative of the fine structure constant alpha in a model-independent way without assumptions on constancy or variability of other parameters, allowing tests of the consequences of unification theories. We have measured an optical transition frequency at 688 THz in 171Yb+ with a cesium atomic clock at 2 times separated by 2.8 yr and find a value for the fractional variation of the frequency ratio f(Yb)/f(Cs) of (-1.2+/-4.4)x10(-15) yr(-1), consistent with zero. Combined with recently published values for the constancy of other transition frequencies this measurement sets an upper limit on the present variability of alpha at the level of 2.0x10(-15) yr(-1) (1sigma), corresponding so far to the most stringent limit from laboratory experiments.     

Sub-dekahertz ultraviolet spectroscopy of 199Hg+

Using a laser that is frequency locked to a Fabry-Perot etalon of high finesse and stability, we probe the 5d(10)6s (2)S(1/2)(F = 0)<-->5d(9)6s(2) (2)D(5/2)(F = 2) Deltam(F) = 0 electric-quadrupole transition of a single laser-cooled 199Hg+ ion stored in a cryogenic radio-frequency ion trap. We observe Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm ( 1.06x10(15) Hz), yielding a line Q approximately 1.6x10(14). We perform a preliminary measurement of the 5d(9)6s(2) (2)D(5/2) electric-quadrupole shift due to interaction with the static fields of the trap, and discuss the implications for future trapped-ion optical frequency standards.     

Laser diode partially end-pumped electro-optically Q-switched Yb:YAG slab laser

A laser diode partially end-pumped, electro-optically Q-switched, Yb:Y_3Al_5O_(12)(Yb:YAG) slab laser was reported. We obtained output energy of 14.6 mJ/pulse with a pulse width of 30 ns at a repetition frequency of 2 k Hz, and the corresponding peak power was 480 kW. The beam quality factors M~2 in the unstable direction and the stable direction was 1.32 and 1.25, respectively.     

Observation of the 1S0-3P0 transition in atomic ytterbium for optical clocks and qubit arrays

We report an observation of the weak 6 1S0-6 3P0 transition in (171,173)Yb as an important step to establishing Yb as a primary candidate for future optical frequency standards, and to open up a new approach for qubits using the 1S0 and 3P0 states of Yb atoms in an optical lattice.     

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).     

High-Resolution Laser Spectroscopy of YbCl: The B(2)Sigma(+)-X(2)Sigma(+) Transition

High-resolution laser excitation spectra have been obtained for the 0-0, 1-1, and 0-1 bands of the B(2)Sigma(+)-X(2)Sigma(+) transition of YbCl and a rotational analysis has been performed on the (174)Yb(35)Cl and (172)Yb(35)Cl isotopomers. Comparison of the spin-rotation constant, gamma, for the B(2)Sigma(+) state with the lambda-doubling constant of the A(2)Pi(1/2) state (1) shows that the two excited states form a unique perturber pair arising from the 6psigma and 6ppi orbitals centered on the Yb(+) ion. The principal results for the B(2)Sigma(+) state are B(e)=0.097552(5) cm(-1), R(e)=2.43623(6) ?, gamma(e)=-2.1655(6)x10(-4) cm(-1), and DeltaG(1/2)=313.111(2) cm(-1). Copyright 2001 Academic Press.     

Doppelresonanzexperimente zur Untersuchung der Hyperfeinstruktur des 6s6p 3 P 1-Zustandes von171Yb und173Yb

For the odd Yb isotopes¹⁷¹Yb and¹⁷³Yb the hyperfine splitting of the 6s6p ³ P ₁ state has been measured by optical double resonance in zero magnetic field. Taking into account second order corrections due to the influence of the 6¹ P ₁ and 6³ P _0,2 states, the following results for the magnetic splitting constantA and the electric quadrupole interaction constantB have been derived: A(¹⁷¹Yb)=3958.228 (60) Mc/s, A(¹⁷³Yb)=?1094.318 (35) Mc/s, S(¹⁷³Yb)=?825.904 (85) Mc/s. The hyperfine structure anomaly of the isotopes¹⁷¹Yb and^{171 173}Yb was determined to be Δ=?0.352 (10)%.     

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.     

Die Hyperfeinstruktur des 6s 6p 3 P 1-Zustandes von171Yb und173Yb

The hyperfine structure of the 6s 6p ³ P ₁ state of¹⁷¹Yb and¹⁷³Yb has been investigated by the level crossing technique and by optical double resonance. The following results for the magnetic hfs splitting constantA and for the electric quadrupole interaction constantB have been obtained:A(¹⁷¹Yb)=3959.1(14)Mc/sec;A(¹⁷³Yb)=?1094.7(6) Mc/sec;B(¹⁷³Yb)=?826.9(9) Mc/sec. The hyperfine structure anomaly of the isotopes¹⁷¹Yb and¹⁷³Yb was determined to beΔ=?0.36(3)%.     

Search for B0s-->micro+micro- and B0d-->micro+micro- decays in pp collisions at square root s = 1.96 TeV

We report on a search for B(0)(s)-->micro(+)micro(-) and B(0)(d)-->micro(+)micro(-) decays in pp collisions at square root of s=1.96 TeV using 171 pb(-1) of data collected by the CDF II experiment at the Fermilab Tevatron Collider. The decay rates of these rare processes are sensitive to contributions from physics beyond the standard model. One event survives all our selection requirements, consistent with the background expectation. We derive branching ratio limits of B(B(0)(s)-->micro(+)micro(-))<5.8x10(-7) and B(B(0)(d)-->micro(+)micro(-))<1.5x10(-7) at 90% confidence level.     

Determination of the absolute microwave frequency of laser-cooled ^{171}\hbox {Yb}^+

\(^{171}\hbox {Yb}^+\) ions confined within a linear quadrupole trap were laser cooled to below 1 K. The microwave frequency of the hyperfine splitting of the ground state was continuously measured over 6 h. Frequency was corrected by evaluating the systematic shifts in each clock measurement. The absolute microwave frequency was determined as 12 642 812 118.468 2(4) Hz, in strong agreement with previously reported measurements.     

Measurement of the B(e2) of (7)(lambda)Li and shrinkage of the hypernuclear size

We report on the first measurement of a hypernuclear gamma-transition probability. gamma rays emitted in the E2(5/2(+)-->1/2(+)) transition of (7)(Lambda)Li were detected by a large-acceptance germanium detector array (Hyperball), and the lifetime of the parent state ( 5/2(+)) was determined by the Doppler shift attenuation method. The obtained result, 5.8(+0.9)(-0.7)+/-0.7 ps, was then converted into the reduced transition probability [ B(E2)] to be B(E2;5/2(+)-->1/2(+)) = 3.6+/-0.5(+0.5)(-0.4) e(2) fm(4). Compared with the B(E2) of the corresponding E2(3(+)-->1(+)) transition in the 6Li nucleus, our result gives evidence that the size of the 6Li core in (7)(Lambda)Li is smaller than the 6Li nucleus in the free space.     

New limits on coupling of fundamental constants to gravity using 87Sr optical lattice clocks

The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu.     

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.     

Observation of B+-->a1+(1260)K0 and B0-->a1-(1260)K+

We present branching fraction measurements of the decays B(+)-->a(1)(+)(1260)K(0) and B(0)-->a(1)(-)(1260)K(+) with a(1)(+/-)(1260)-->pi(-/+)pi(+/-)pi(+/-). The data sample corresponds to 383 x 10(6) BB pairs produced in e(+)e(-) annihilation through the Upsilon(4S) resonance. We measure the products of the branching fractions B(B(+)-->a(1)(+)(1260)K(0)B(a(1)(+)(1260)-->pi(-)pi(+)pi(+))=(17.4+/-2.5+/-2.2) x 10(-6) and B(B(0)-->a(1)(-)(1260)K(+)B(a(1)(-)(1260)-->pi(+)pi(-)pi(-)) = (8.2+/-1.5+/-1.2) x 10(-6). We also measure the charge asymmetries A(ch)(B(+)-->a(1)(+)(1260)K(0) = 0.12+/-0.11+/-0.02 and A(ch)(B(0)-->a(1)(-)(1260)K+) = -0.16+/-0.12+/-0.01. The first uncertainty quoted is statistical and the second is systematic.