Atomic clocks for geodesy

Mehlstäubler, T. E.; Grosche, G.; Lisdat, Christian; Schmidt, Piet O.; Denker, Heiner

doi:10.1088/1361-6633/aab409

Cited by 211 publications

(118 citation statements)

References 357 publications

(582 reference statements)

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“…Optical clocks based on neutral atoms trapped in optical lattices and single trapped ions have reached estimated systematic uncertainties of a few parts in 10 −18 [1][2][3][4] or even below [5]. Taking advantage of these record uncertainties for applications ranging from relativistic geodesy [6][7][8][9] over fundamental physics [10][11][12] to frequency metrology [13][14][15][16][17] requires achieving statistical measurement uncertainties of the same level within practical averaging times τ (given in seconds). This has been achieved with single-ensemble optical lattice clocks in self-comparison experiments up to a level of 1.6 10 16 t - [18] and by implementing an effectively deadtime-free clock consisting of two independent clocks probed in an interleaved fashion [19,20], reaching a statistical uncertainty in the range of 5 10 17 t -.…”

Section: Introductionmentioning

confidence: 99%

Robust optical clock transitions in trapped ions using dynamical decoupling

et al. 2019

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We present a novel method for engineering an optical clock transition that is robust against external field fluctuations and is able to overcome limits resulting from field inhomogeneities. The technique is based on the application of continuous driving fields to form a pair of dressed states essentially free of all relevant shifts. Specifically, the clock transition is robust to magnetic field shifts, quadrupole and other tensor shifts, and amplitude fluctuations of the driving fields. The scheme is applicable to either a single ion or an ensemble of ions, and is relevant for several types of ions, such as Ca 40 + , Sr 88 + , Ba 138 + and Lu 176 + . Taking a spherically symmetric Coulomb crystal formed by 400 Ca 40 + ions as an example, we show through numerical simulations that the inhomogeneous linewidth of tens of Hertz in such a crystal together with linear Zeeman shifts of order 10MHz are reduced to form a linewidth of around 1Hz. We estimate a twoorder-of-magnitude reduction in averaging time compared to state-of-the art single ion frequency references, assuming a probe laser fractional instability of 10 15 -. Furthermore, a statistical uncertainty reaching 2.9×10 −16 in 1s is estimated for a cascaded clock scheme in which the dynamically decoupled Coulomb crystal clock stabilizes the interrogation laser for an Al 27 + clock.- [3,22,23]. The statistical uncertainty can be improved by probing for longer times, ultimately limited by the excited clock state lifetime or the laser coherence time [24,25]. Alternatively, the number of probed ions can be increased.Recently, multi-ion clock schemes have been proposed to address this issue [26][27][28][29]. However, several challenges have to be overcome to maintain and transfer the small and very well characterizable systematic shifts achievable with single trapped ions to larger ion crystals. The oscillating rf field in Paul traps results in ac Stark and second order Doppler shifts through micromotion [30][31][32]. Furthermore, electric field gradients from the trapping fields and the surrounding ions couple to atomic quadrupole moments, resulting in an electric quadrupole shift (QPS). The effects of micromotion can be avoided by trapping strings of ions in a precisionmachined linear Paul trap with negligible excess micromotion from trap imperfections [28,33]. The QPS in such Q 0 m J J J m , J j å = =-[67]. Such an average will also eliminate the linear Zeeman shift, assuming the field does not change between the frequency measurements contributing to the average. We propose a novel dynamical decoupling scheme in which robustness to this type of shifts is achieved by the application of a detuned driving field, mixing all m J states to form dressed states with effective Q 0 J m , j = . While the cancellation scheme is general and applies to tensor shifts of arbitrary electronic states, we consider in the following the Hamiltonian of the D 2 5 2 states of e.g.Ca + ions 2 1 , 1 0 J J 2

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Section: Introductionmentioning

confidence: 99%

Robust optical clock transitions in trapped ions using dynamical decoupling

et al. 2019

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“…proportional to Newtonian geopotential differences, and highprecision clocks are suitable tools for monitoring such effects, allowing to relate the gravitational potential and heights on Earth to an atomic reference. [20] According to general relativity, a clock at a lower altitude, thus operating in a stronger gravitational potential, will be slowed down relative to a clock at a higher altitude by a relative relativistic frequency shift f/f, which is related to the difference of the gravitational potential U through…”

Section: D Gravity Sensors For Chronometric Geodesymentioning

confidence: 99%

“…[12][13][14][15] Moreover, proposals were put forward to use this apparently unique nuclear transition to realize a γ -ray laser. [18][19][20] The thorium isomer has also been proposed as a tool to improve the precision of satellite based navigational systems. [18][19][20] The thorium isomer has also been proposed as a tool to improve the precision of satellite based navigational systems.…”

Section: Introductionmentioning

confidence: 99%

“…[16,17] Synchronized networks of highly precise nuclear clocks have been proposed to serve as detectors for dark matter in the form of topological defects or as 3D gravity sensors for precise geodesy and to locally characterize the gravitational potential and its perturbances (e.g., by volcanic or seismic activities). [18][19][20] The thorium isomer has also been proposed as a tool to improve the precision of satellite based navigational systems. Any improvement in satellite-based navigation accuracy would turn out largely beneficial to speeding up the era of autonomous driving or improving industrial applications like component or freight tracking.…”

Section: Introductionmentioning

confidence: 99%

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Improving Our Knowledge on the ^229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants

Thirolf

Wense

2019

Annalen der Physik

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For more than four decades, the lowest excitation in the whole landscape of atomic nuclei, the low-lying, isomeric state of 229 Th, the so-called thorium isomer, has challenged physicists of various disciplines. Being a solitaire with its uniquely low excitation energy of <10 eV, its predicted lifetime of a few hours results in an extremely sharp relative linewidth E/E as low as 10 -20 . While until recently the indication of its existence was based only on indirect evidence, its unique properties inspired a multitude of potential applications, like the use of the thorium isomer as a nuclear frequency standard, potentially able to outperform even the best atomic clocks and a sensitivity-enhanced access to potential temporal variations of fundamental constants. The various proposals to exploit the unique properties of 229m Th are presented herein, in particular focusing on its ability to serve as a test bench for time variations of fundamental constants like the fine structure constant.

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“…Atomic clocks based on high-precision spectroscopy of isolated quantum systems are currently the most precise scientific instruments, with fractional frequency instabilities and accuracies at the 10 −18 level [1][2][3][4][5]. Frequency measurements at this level enable improved tests of fundamental physics, as well as new applications like chronometric geodesy [6,7].…”

Section: Introductionmentioning

confidence: 99%

Combined error signal in Ramsey spectroscopy of clock transitions

et al. 2018

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We have developed a universal method to form the reference signal for the stabilization of arbitrary atomic clocks based on Ramsey spectroscopy. Our approach uses an interrogation scheme of the atomic system with two different Ramsey periods and a specially constructed combined error signal (CES) computed by subtracting two error signals with the appropriate calibration factor. CES spectroscopy allows for perfect elimination of probe-induced light shifts and does not suffer from the effects of relaxation, time-dependent pulse fluctuations and phase-jump modulation errors and other imperfections of the interrogation procedure. The method is simpler than recently developed autobalanced Ramsey spectroscopy techniques (Sanner et al 2018 Phys. Rev. Lett. 120 053602; Yudin et al 2018 Phys. Rev. Appl. 9 054034), because it uses a single error signal that feeds back on the clock frequency. The use of CES is a general technique that can be applied to many applications of precision spectroscopy.clocks were theoretically described in [27], which proposed the use of pulses of differing durations ( 1 2 t t ¹ ) and the use of composite pulses instead of the standard Ramsey sequence with two equal π/2 pulses. This 'hyper-Ramsey' scheme has been successfully realised in an ion clock based on an octupole transition in Yb + [5,28], where a suppression of the light shift by four orders of magnitude and an immunity against its fluctuations were demonstrated. Further developments in Ramsey spectroscopy resulted in additional suppression of probe-fieldinduced frequency shifts. For example, the hyper-Ramsey approach uses new phase variants to construct error signals [29][30][31][32] to significantly suppress the probe-field-induced shifts in atomic clocks. However, as was shown in [33], all previous hyper-Ramsey methods [5, 27-29, 31, 34] are sensitive to decoherence and spontaneous relaxation, which can prevent the achievement of state-of-the-art performance in some systems. To overcome the effect of decoherence, a more complicated construction of the error signal was recently proposed in [35], which requires four measurements for each frequency point (instead of two) combined with the use of the generalized hyper-Ramsey sequences presented in [31]. Nevertheless the method in [35] is not free from other disadvantages related to technical issues such as time-dependent pulse area fluctuations and/or phase-jump modulation errors during the measurements.The above approaches [5, 27-29, 31, 34, 35] are all one-loop methods, since they use one feedback loop and one error signal. However, frequency stabilization can also be realized with two feedback loops combined with Ramsey sequences with different dark periods T 1 and T 2 [33,36,37]. For example, the synthetic frequency protocol [33] in combination with the original hyper-Ramsey sequence [27] allows for substantial reduction in the sensitivity to decoherence and imperfections of the interrogation procedure. Auto-balanced Ramsey spectroscopy (ABRS) is another effective approach that was ...

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Atomic clocks for geodesy

Cited by 211 publications

References 357 publications

Robust optical clock transitions in trapped ions using dynamical decoupling

Robust optical clock transitions in trapped ions using dynamical decoupling

Improving Our Knowledge on the ^229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants

Combined error signal in Ramsey spectroscopy of clock transitions

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Atomic clocks for geodesy

Cited by 211 publications

References 357 publications

Robust optical clock transitions in trapped ions using dynamical decoupling

Robust optical clock transitions in trapped ions using dynamical decoupling

Improving Our Knowledge on the 229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants

Combined error signal in Ramsey spectroscopy of clock transitions

Contact Info

Product

Resources

About

Improving Our Knowledge on the ^229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants