Microwave leakage-induced frequency shifts in the primary frequency Standards NIST-F1 and IEN-CSF1

Shirley, J.H.; Levi, Filippo; Heavner, Thomas P.; Calonico, Davide; Yu, Dai-Hyuk; Jefferts, Steven R.

doi:10.1109/tuffc.2006.186

Cited by 34 publications

(29 citation statements)

References 15 publications

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“…Heavner et al considered that the amplitude dependence of "any microwave lensing shift scales just like the microwave leakage shift," which is proportional to δν/ν= A n sin(n π/2) = A' φ sin(φ) (dashed curve in Fig. 1a and, in [1], Fig 6), reporting measurements with Rabi pulse areas of φ=n π/2 for n=1,3,5, … [1,7,14,16]. Previously, we have shown that the microwave lensing shift scales as δν/ν ∝ φ 1 /sin(φ 1 ) [2][3][4], where φ 1 (2) is the Rabi pulse area in the first (second) Ramsey interaction.…”

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confidence: 99%

Comment on ‘First accuracy evaluation of NIST-F2’

Gibble¹

2015

Metrologia

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We discuss the treatment of the systematic frequency shifts due to microwave lensing and distributed cavity phase in "First accuracy evaluation of NIST-F2" 2014 Metrologia 51 174-182. We explain that the microwave lensing frequency shift is generally non-zero and finite in the limit of no applied microwave field. This systematic error was incorrectly treated and we find that it contributes a significant frequency offset. Accounting for this shift implies that the measured microwave amplitude dependence (e.g due to microwave leakage) is comparable to the total reported inaccuracy. We also discuss the importance of vertically aligning the fountain perpendicular to the axis of the cavity feeds, when the cavity has only two independent feeds. Finally, we note that background gas collisions have a different behavior for cold clock atoms than for clock atoms at room-temperature, and therefore room temperature measurements do not directly apply to lasercooled clocks.We comment on several aspects of the recent accuracy evaluation of NIST-F2 [1], which reported a total systematic uncertainty of 1.1×10 −16 . Our most significant remark regards the evaluation of the microwave lensing frequency shift [2-6], which was briefly described in [1] and more fully presented in a recent preprint [7]. They calculated a frequency offset of 0.2×10 −16 that goes to zero in the limit of zero microwave amplitude. We show that this frequency shift of NIST-F2 is larger, of order 0.9×10 −16 , and comparable to other evaluations, which range from 0.6×10 −16 to 0.9×10 −16 [4][5][6]. In [1] Heavner et al. included microwave lensing with other systematic errors that depend on microwave amplitude, such as microwave leakage. When the shift that we calculate is removed from their measured amplitude dependence, the clock's frequency has a significant amplitude dependence with an offset at optimal amplitude from other amplitude dependent shifts (e.g. microwave leakage) that is comparable to the total systematic

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confidence: 99%

Comment on ‘First accuracy evaluation of NIST-F2’

Gibble¹

2015

Metrologia

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“…Similarly the frequency shift at n=5 is 5 times that at n=1, and the shift at n=7 is -7 times that at n=1 etc. Thus, for data taken at odd integer multiples of the pattern of frequency shifts is identical to that from microwave leakage below the Ramsey cavity [6].…”

Section: Model and Resultsmentioning

confidence: 78%

“…The microwave synthesizer which generates the microwaves for state-selection is attenuated and strongly detuned when the atoms are outside the state-selection area and therefore cannot induce a frequency bias. Microwave-leakage induced frequency-biases resulting from leakage above the Ramsey interaction cavity is precluded in our fountains by the design of the drift region and has a different behaviour vs. microwave amplitude in any case [5][6][7][8]. This leaves microwave leakage after the second Ramsey interaction as the only possible source of leakage induced frequency bias.…”

Section: Model and Resultsmentioning

confidence: 99%

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Measurement of the Microwave Lensing shift in NIST-F1 and NIST-F2

Jefferts

Heavner

Barlow

et al. 2016

J. Phys.: Conf. Ser.

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Abstract. With several Primary Frequency Standards (PFS) across the world demonstrating systematic fractional frequency uncertainties on order of 1 x 10 -16 , it is crucial to accurately measure or model even small frequency shifts that could affect the ultimate PFS uncertainty, and thus ultimately impact the rate of Coordinated Universal Time (UTC) which relies on precision PFS measurements. Recently there has been controversy about the physical causes and size of PFS frequency shifts due to microwave lensing effects. We present here the first measurements of microwave lensing frequency shifts in the PFS NIST-F1 and NIST-F2. The measured frequency shifts agree well with the recent theory of Ashby et al [1].

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“…Before the full uncertainty evaluation can be made, the uncertainty in the microwave power dependence shift will be evaluated by measuring the frequency as a function of the microwave power [40] or using an interference switch to suppress the influence of the microwave leakage on the atoms in the interrogation region [41]. Next, other type B uncertainties will be reduced by further experiments, such as the measurement of the long-term variation in the magnetic field in the interrogation region, and by monitoring the temperature of the vacuum chamber.…”

Section: Discussionmentioning

confidence: 99%

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

Takamizawa

Yanagimachi

Tanabe

et al. 2015

IEEE Trans. Instrum. Meas.

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We describe the preliminary evaluation of the frequency corrections and their uncertainty in the cesium fountain primary frequency standard (PFS) NMIJ-F2 under development at National Metrology Institute of Japan (NMIJ). In NMIJ-F2, cold atoms generated from a vapor-loaded optical molasses in the (001) configuration are optically pumped to the Zeeman sublevels of m F = 0 to increase the number of atoms involved in the Ramsey interrogation. Moreover, a cryocooled sapphire oscillator with ultralow phase noise is employed as the local oscillator to avoid degradation of the frequency stability due to the Dick effect. As a result, we have obtained a very high fractional frequency stability of 9.7 × 10 −14 τ −1/2 . As for systematic frequency shifts, the fractional correction for the second-order Zeeman shift is experimentally estimated to be (−165.5 ± 0.5) × 10 −15 from the first-order Zeeman shift of atoms in m F = +1 launched to various heights. The fractional frequency correction for cold-atom collisions is estimated to be (+3.3 ± 0.4) × 10 −15 by extrapolating the frequency to zero density from the frequencies measured for various nonzero atom numbers. We will soon be able to make a comparison with other atomic fountain PFSs at the 1 × 10 −15 level.Index Terms-Atomic fountain clock, primary frequency standard (PFS), uncertainty evaluation.

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Microwave leakage-induced frequency shifts in the primary frequency Standards NIST-F1 and IEN-CSF1

Cited by 34 publications

References 15 publications

Comment on ‘First accuracy evaluation of NIST-F2’

Comment on ‘First accuracy evaluation of NIST-F2’

Measurement of the Microwave Lensing shift in NIST-F1 and NIST-F2

Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

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