Improving the sensitivity grating-echo atom interferometers for measurements of gravity
Bibliographic record
Abstract
Precision measurements of gravitational acceleration g have far reaching applications in navigation and sensing as well as for tests of general relativity. Grating-echo atom interferometers (AIs) utilize simple setups and distinctive excitation schemes that involve a single excitation laser, and do not require velocity selection. They have demonstrated measurements of gravity precise to 75 parts per billion (ppb) by dropping laser-cooled atomic samples through ~ 1 cm. Here we describe progress toward realizing a cold atom gravimeter using an echo AI designed for drop heights of ~30 cm. The experimental technique involves illuminating the falling sample of laser-cooled rubidium atoms with two standing wave (sw) pulses separated by time t = T. The sw pulses are composed of two traveling-wave components, each having a wave vector of magnitude k = 2π/λ. Momentum state interference produces one-dimensional density gratings with a period λ/2 immediately after each excitation pulse. These gratings dephase due to the velocity distribution of the sample along the sw axis. The AI uses an echo technique to cancel the effect of velocity dephasing and observe a rephased density grating in the vicinity of the echo time τ = 2Τ. The grating contrast and phase are measured by coherently backscattering a traveling wave readout pulse from the sample. The grating phase, measured with respect to a vibrationally stabilized inertial reference frame, scales as 2kgΤ2. A drawback of echo AIs is the signal-to-noise ratio, which is limited by the contrast of the grating and systematic effects due the refractive index of the sample. Here, we review improvements to the experimental design and investigate methods of improving the signal-to-noise ratio by optimizing the atom-field coupling. We describe progress toward realizing our goals of increasing the grating contrast and the backscattered signal. The improved contrast is expected to allow the experiment to be carried out at a lower density to reduce corrections due to the refractive index. We discuss a variety of excitation schemes for achieving a target precision of a few ppb.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".