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 2 0 , where e is the elementary charge and a0 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 The basis of all precise atomic clocks is a transition frequency that represents an unperturbed quantum property of the chosen atomic system. The most impressive progress in clocks of high accuracy has recently been made with optical transitions between states with vanishing electronic angular momentum (J = 0) in Al + and Sr [1,2]. The frequency of this type of transition is in general only weakly affected by external electric and magnetic fields. Here we present a precision study of a reference transition of a very different type, an electric-octupole transition (∆J = 3) connecting the 2 S 1/2 ground state with the 2 F 7/2 first excited state in 171 Yb + , and show that it has a very low sensitivity to field-induced frequency shifts, making it a promising basis for an optical clock of the highest accuracy.At variance with other ion frequency standards, 171 Yb + offers the advantage of two optical reference transitions with high quality factor which have rather different physical characteristics. A frequency standard based on the electric-quadrupole 2 S 1/2 → 2 D 3/2 transition [3,4] is established as one of the secondary representations of the SI second. The electric-octupole 2 S 1/2 → 2 F 7/2 transition investigated in this Letter was first studied at the National Physical Laboratory (UK) [5]. The extraordinary features of this transition result from the long natural lifetime of the 2 F 7/2 state in the range of several years [5,6] and from its electronic configuration (4f 13 6s 2 ) consisting of a hole in the 4f shell surrounded by a spherically symmetric 6s shell. Since the octupole transition can be resolved with a linewidth that is virtually unaffected by spontaneous decay and determined only by the available laser stability, a quantum projection noise limited single-ion frequency standard with very low instability can be realized. The electric-quadrupole moment of the 2 F 7/2 state is predicted to be much smaller than that of the 2 D 3/2 state [7] so that the transition frequency is only weakly affected by the quadrupole shift from electric field gradients. Furthermore, there are no strong dipole transitions from the 2 F 7/2 state with excitation en...

The isotope Th is the only nucleus known to possess an excited stateTh in the energy range of a few electronvolts-a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than typical nuclear excitation energies. Of the many applications that have been proposed for this nuclear system, which is accessible by optical methods, the most promising is a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of the doubly charged Th ion and the determination of the fundamental nuclear properties of the isomer, namely, its magnetic dipole and electric quadrupole moments, as well as its nuclear charge radius. Following the recent direct detection of this long-sought isomer, we provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.

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.PACS numbers: 42.62. Fi,32.70.Jz,32.60.+i,06.30.Ft Ramsey's method of separated oscillatory fields was crucial for the progress in precision spectroscopy and the development of atomic clocks [1] and is an important tool in quantum information processing [2]. In the Ramsey scheme, two levels of a quantum system are brought into a coherent superposition by a first excitation pulse followed by a free evolution period. After a second excitation pulse the population in one of the levels is detected, which shows the effect of the interference of the second pulse with the time-evolved superposition state. In the original experiments with atomic and molecular beams, this permitted the recording of a resonance line shape with a width that is mainly determined by the total interaction time, without shifts and broadening through inhomogeneous excitation conditions. Ramsey's method is employed mainly to excite states with a natural lifetime exceeding the interaction time, so that primarily transitions forbidden by electric dipole selection rules are investigated. Especially in the case of optical spectroscopy the high probe light intensities required to drive these transitions will unavoidably lead to level shifts through the dynamical Stark effect. This so-called light shift appears through the nonresonant coupling to other energy levels by the probe light and is usually proportional to its intensity. Several methods were investigated to compensate this shift, for example, linear extrapolation to zero intensity or the use of an additional inversely shifting field [3]. Nevertheless, a wide range of precise frequency measurements presently suffer from significant uncertainties due to light shift. Here, two-photon [4][5][6][7], higher order multipole [8,9], and magnetic-field induced transitions [10][11][12][13] are good examples.In this Letter we present the first experimental realization of a generalized Ramsey excitation scheme, the so-called "hyper-Ramsey" spectroscopy (HRS) recently Here νL is the probe laser frequency and ν0 the unperturbed transition frequency. The laser step frequency ∆S is assumed to be equal to the light shift ∆L and the intensity I0 is chosen to obtain a pulse a...

A test of Lorentz invariance for electromagnetic waves was performed by comparing the resonance frequencies of two optical resonators as a function of orientation in space. In terms of the Robertson-Mansouri-Sexl theory, we obtain ␤ − ␦ −1/2=͑+0.5± 3 ± 0.7͒ ϫ 10 −10 , a tenfold improvement compared to the previous best results. We also set a first upper limit for a parameter of the standard model extension test theory, ͉͑ e− ͒ ZZ ͉ Ͻ 2 ϫ 10 −14 .

We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in 229 Th. We review the status of the experiments that aim at a direct optical observation of this transition and outline the plans for high-resolution laser spectroscopy experiments.