Testing a Quantum Inequality with a Meta-analysis of Data from Squeezed Light

TL;DR

This study tests a quantum inequality related to negative energy density using a meta-analysis of experimental data from squeezed light, revealing violations that challenge the theoretical basis of QIs.

Contribution

It provides the first experimental test of a quantum inequality for squeezed light through a comprehensive meta-analysis of decades of data.

Findings

Quantum inequality is violated by most measured data.

Different time sampling functions do not reconcile the violations.

Results question the validity of the current quantum inequalities.

Abstract

In quantum field theory, coherent states can be created that have negative energy density, meaning it is below that of empty space, the free quantum vacuum. If no restrictions existed regarding the concentration and permanence of negative energy regions, it might, for example, be possible to produce exotic phenomena such as Lorentzian transversable wormholes, warp drives, time machines, violations of the second law of thermodynamics, and naked singularities. Quantum Inequalities (QIs) have been proposed that restrict the size and duration of the regions of negative quantum vacuum energy that can be accessed by observers. However, QIs generally are derived for situations in cosmology and are very difficult to test. Direct measurement of vacuum energy is difficult and to date no QI has been tested experimentally. We test a proposed QI for squeezed light by a meta-analysis of published data obtained from experiments with optical parametric amplifiers (OPA) and balanced homodyne detection. Over that last three decades, researchers in quantum optics have been trying to maximize the squeezing of light and the quantum vacuum and have succeeded in reducing the variance in the quantum vacuum fluctuations to -15 dB. To apply the QI, a time sampling function is required. In our meta-analysis different time sampling functions for the QI were examined, but in all physically reasonable cases the QI is violated by much or all of the measured data. This brings into question the basis for QI. Possible explanations are given for this surprising result.