N. Hinkley

An Atomic Clock with 10–18 Instability

Tick, Tick, Tick… Many aspects of everyday life from communication to navigation rely on the precise ticking of the microwave transitions of the atoms in atomic clocks. Optical transitions occur at much higher frequency and so offer the opportunity to reduce the scale of the ticks even more. Hinkley et al. (p. 1215, published online 22 August; see the Perspective by Margolis) compare the ticking of two optical clocks and report an instability near the 10−18 level. Such performance will improve tests of general relativity and pave the way for a redefinition of the second. An ytterbium-based optical clock exhibits a precision of nearly one part per quintillion. [Also see Perspective by Margolis] Atomic clocks have been instrumental in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Timekeeping precision at 1 part in 1018 enables new timing applications in relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests of physics beyond the standard model. Here, we describe the development and operation of two optical lattice clocks, both using spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of 1.6 × 10–18 after only 7 hours of averaging.

Ultrastable optical clock with two cold-atom ensembles

Optical clocks with a record low zero-dead-time instability of 6 × 10–17 at 1 second are demonstrated in two cold-ytterbium systems. The two systems are interrogated by a shared optical local oscillator to nearly eliminate the Dick effect. Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with the ‘dead’ time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise from the laser interrogating the atomic transition1,2. Despite recent advances in optical clock stability that have been achieved by improving laser coherence, the Dick effect has continually limited the performance of optical clocks. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock that is based on the interleaved interrogation of two cold-atom ensembles3. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability assessed to be for an averaging time τ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor of Q > 4 × 1015.

High-Accuracy Measurement of Atomic Polarizability in an Optical Lattice Clock

Presently, the Stark effect contributes the largest source of uncertainty in a ytterbium optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clocks sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels α(clock) = 36.2612(7)  kHz (kV/cm)(-2). The clocks uncertainty due to room temperature blackbody radiation is reduced by an order of magnitude to 3×10(-17).

Atomic clock with 1×10(-18) room-temperature blackbody Stark uncertainty.

The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5×10(-19). Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1×10(-18). Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

Determination of the 5d6s3D1 State Lifetime and Blackbody Radiation Clock Shift in Yb

Abstract : The Stark shift of the ytterbium optical clock transition due to room temperature blackbody radiation is dominated by a static Stark effect, which was recently measured to high accuracy [J. A. Sherman et al., Phys. Rev. Lett. 108, 153002 (2012)]. However, room temperature operation of the clock at 10{-18} inaccuracy requires a dynamic correction to this static approximation. This dynamic correction largely depends on a single electric dipole matrix element for which theoretically and experimentally derived values disagree significantly. We determine this important matrix element by two independent methods, which yield consistent values. Along with precise radiative lifetimes of 6s6p 3P1 and 5d6s 3D1, we report the clocks blackbody radiation shift to 0.05% precision.

Optical atomic clock measurements at the mHz level

Time (or its inverse, frequency) is the most precisely measured physical quantity and therefore is exploited in many fundamental investigations of nature. The advent of atomic clocks based on optical transitions has led to 10-100 times improvement in our timekeeping capabilities, with some measurements of optical frequencies reaching the mHz level [1,2]. Timekeeping precision at 1 part in 1018 enables new timing applications in relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests of physics beyond the standard model. Here, we describe the development of two optical lattice clocks, both using spin-polarized, ultracold atomic ytterbium, and we discuss their operation at 10-18 instability as well as measurements toward the goal of 10-18 uncertainty.

Atomic Clock with1×10−18Room-Temperature Blackbody Stark Uncertainty

The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5×10(-19). Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1×10(-18). Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

An atomic clock with

The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5×10(-19). Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1×10(-18). Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

1\times 10^{-18}

We report a high accuracy measurement of the differential static polarizability for the clock transition in a Yb lattice clock, a key parameter for determining the blackbody (BBR) shift of this transition. We further report efforts to determine the 〈6s5d³ D₁||D||6s6p³ P₀〉 reduced dipole matrix element, a critical ingredient in the non-static correction to the BBR shift. In all, we have reduced the largest uncertainty in the Yb lattice clock (that stemming from the BBR shift) by an order of magnitude.

room-temperature blackbody Stark uncertainty

Optical lattice clocks, which are based on highly-forbidden 1S0 ↔ 3P0 transitions of ultracold alkaline-earth atoms confined in standing-wave optical potentials [1], offer exquisite frequency stability and uncertainty. We leverage these advantages to determine the sensitivity of a ytterbium optical lattice clock to external electric fields at 20 part-per-million (ppm) accuracy [2]. We describe an electrode design compatible with various neutral optical atomic clocks and capable of absolute electric field generation at the ppm level. Importantly, the result bounds the uncertainty of the ytterbium clock frequency due to room-temperature blackbody radiation at the level of 3×10-17.