First Measurements of High Frequency Cross-Spectra from a Pair of Large Michelson Interferometers

Abstract

Measurements are reported of the cross-correlation of spectra of differential position signals from the Fermilab Holometer, a pair of colocated 39 m long, high power Michelson interferometers with flat broadband frequency response in the MHz range. The instrument obtains sensitivity to high frequency correlated signals far exceeding any previous measurement in a broad frequency band extending beyond the 3.8 MHz inverse light-crossing time of the apparatus. The dominant but uncorrelated shot noise is averaged down over 2 × 10 8 independent spectral measurements with 381 Hz frequency resolution to obtain 2.1 × 10 −20 m= ffiffiffiffiffiffi Hz p sensitivity to stationary signals. For signal bandwidths Δf > 11 kHz, the sensitivity to strain h or shear power spectral density of classical or exotic origin surpasses a milestone PSD δh < t p where t p ¼ 5.39 × 10 −44 =Hz is the Planck time.

Statistical model of exotic rotational correlations in emergent space-time

“…With Planck length normalization, the predicted signal is detectable. Assuming sensitivity similar to that already achieved with the Fermilab Holometer [8,15], a highly significant detection is expected after several hours of integration. With several hundred hours of data, the program should be able to probe an order of magnitude lower.…”

“…As in previous estimates of holographic geometrical fluctuations with similar displacement magnitude [9][10][11][12][13][14], directions in this model on scale R fluctuate on timescale ≈ R/c, with a variance of about ∆θ 2 R ≈ l P /R, which leads to a signal with a power spectral density of fractional displacement noise about equal to a Planck time [8]. However, purely rotational fluctuations would a E-mail: o.kwon@kaist.ac.kr arXiv:1607.03048v4 [gr-qc] 8 Jun 2017 2 not have been detected in current experiments that constrain holographic fluctuations with this sensitivity [15], due to their purely radial light paths. As shown below, a definitive signature of rotational correlations can be measured using modified experimental configurations.…”

Exotic rotational correlations in quantum geometry

“…As seen above, the component of light that propagates in a transverse direction accumulates an exotic phase displacement that grows like a Planck random walk. The predicted amplitude of the effect is large enough to detect with the sensitivity already achieved by a correlated, superluminally sampled dual interferometer system [10,11].…”

Statistical measures of Planck scale signal correlations in interferometers

“…This maintains the same form of straightforward linearity used in the previous section, just with longer functional support. In particular, the maximum normalization of this model, corresponding to Ξ(τ = 0)/L = 2 P ≡ ct P / √ π, was used as a "baseline model" to estimate experimental sensitivity for design purposes and tested during the initial run of the Holometer [35,36]. Figure 5 shows the full range of models reflecting a generalized understanding of linearity in this framework of overlapping causal diamonds (and consistent with the constraints outlined in Section II B).…”