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NASA Tech Briefs

Dual-Ion-Trap Frequency Standards With Overlapping Cycles

G.J. Dick, John D. Prestage

Published Jul 1, 1992• 0 citations
OpenAlex

Abstract

Proposed scheme for enhancing performances of atomic frequency-standard apparatuses calls for two or more ion traps per apparatus interrogated in alternation by radio-frequency pulses. Provides nearly constant feedback gain, thereby providing nearly constant corrections for fluctuations in frequency of local oscillator. Degradation of performance by fluctuations in local oscillators reduced.

Related papers

Improved Linear-Ion-Trap Frequency Standard

John D. Prestage

Improved design concept for linear-ion-trap (LIT) frequency-standard apparatus proposed. Apparatus contains lengthened linear ion trap, and ions processed alternately in two regions: ions prepared in upper region of trap, then transported to lower region for exposure to microwave radiation, then returned to upper region for optical interrogation. Improved design intended to increase long-term frequency stability of apparatus while reducing size, mass, and cost.

NASA Tech Briefs•Mar 1, 1995•0 citations

Local oscillator induced degradation of medium-term stability in passive atomic frequency standards

G.J. Dick, John D. Prestage, C. A. Greenhall +1 more

As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fiuctuations in an ancillary local osciktor (L.O.). The efect is due to time variation in the gain of the feedback which compensates L.O. frequenq fluctuations. The high performance promised by new microwave and optical trapped ion standark may be severely compromised by this effect. We present un anabsk uf this performance limitatwn for the case of sequentially interrogated standards. The time dependence oJ the sensitivity of the interrogution process to L.O. frequenq fluctuations is evalu-ated for singde-pulse and double-puke "Ramvey " RF interrogation and also for amplitude moduluted pukes. The e$ect of these various time dependencies on performance of the standard is calculated for an L.O. with frequency fluctuations showing a typical 1 / f spectral density. A limiting 1 1 6 dependent deviation of fre-quencyjluctuutions k calculated as a function of pulse lengths, dead time, and pulse overlap. We also present conceptual und hardwure+riented solutions to this problem which achieve a much more nearly convtant sensitivity to L.O.fluctuatiofiv. Solutionr involve: we of double-puke interrogation; alternute interrogation of mulliple traps so that the "dead time " of one trap can be covered by operution of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RFpulves, the increasing sensitivity of one trup tends to compensate for the decreasing sensitivity of the otht: A solution making use of amplitude-modulated pulses is aLso presented which shows nominally zero time variation.

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A novel RF (Paul) ion trap apparatus, capable of providing extremely tight confinement is described. Strong localization of trapped ions reduces an important source of noise when using the ions as an optical frequency standard. Alternative cooling schemes, which provide stronger localization than conventional Doppler cooling are also discussed.>

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Experimental test of local oscillator-induced performance limitation for pulse-mode passive frequency standards

G.J. Dick, D. A. Stowers

An experimental test of Local-Oscillator (L.O.) degradation of time-sequential passive oscillator performance was accomplished using the TAG-controlled crystal oscillator described in an accompanying paper. For this quantitative demonstration, an electronic frequency-counter discriminator replaced the trapped ion physics package in a closed-loop experiment. With a 10 second cycle time and 5 second dead time, L.O. limited stability was demonstrated in excellent agreement with theoretical calculations. The results are also in agreement with computer simulations and confirm previous noise analysis for the case of a passive standard with short pulse "Ramsey" interrogation.

Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Nov 19, 2002•2 citations
Proposed scheme for enhancing performances of atomic frequency-standard apparatuses calls for two or more ion traps per apparatus interrogated in alternation by radio-frequency pulses. Provides nearly constant feedback gain, thereby providing nearly constant corrections for fluctuations in frequency of local oscillator. Degradation of performance by fluctuations in local oscillators reduced.
As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fiuctuations in an ancillary local osciktor (L.O.). The efect is due to time variation in the gain of the feedback which compensates L.O. frequenq fluctuations. The high performance promised by new microwave and optical trapped ion standark may be severely compromised by this effect. We present un anabsk uf this performance limitatwn for the case of sequentially interrogated standards. The time dependence oJ the sensitivity of the interrogution process to L.O. frequenq fluctuations is evalu-ated for singde-pulse and double-puke "Ramvey " RF interrogation and also for amplitude moduluted pukes. The e$ect of these various time dependencies on performance of the standard is calculated for an L.O. with frequency fluctuations showing a typical 1 / f spectral density. A limiting 1 1 6 dependent deviation of fre-quencyjluctuutions k calculated as a function of pulse lengths, dead time, and pulse overlap. We also present conceptual und hardwure+riented solutions to this problem which achieve a much more nearly convtant sensitivity to L.O.fluctuatiofiv. Solutionr involve: we of double-puke interrogation; alternute interrogation of mulliple traps so that the "dead time " of one trap can be covered by operution of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RFpulves, the increasing sensitivity of one trup tends to compensate for the decreasing sensitivity of the otht: A solution making use of amplitude-modulated pulses is aLso presented which shows nominally zero time variation.
An experimental test of Local-Oscillator (L.O.) degradation of time-sequential passive oscillator performance was accomplished using the TAG-controlled crystal oscillator described in an accompanying paper. For this quantitative demonstration, an electronic frequency-counter discriminator replaced the trapped ion physics package in a closed-loop experiment. With a 10 second cycle time and 5 second dead time, L.O. limited stability was demonstrated in excellent agreement with theoretical calculations. The results are also in agreement with computer simulations and confirm previous noise analysis for the case of a passive standard with short pulse "Ramsey" interrogation.