Narrowing the Parameter Space of Collapse Models with Ultracold Layered Force Sensors

Abstract

Despite the unquestionable empirical success of quantum theory, witnessed by the recent uprising of quantum technologies, the debate on how to reconcile the theory with the macroscopic classical world is still open. Spontaneous collapse models, based on stochastic and nonlinear modifications of the Schrödinger equation, are the only experimentally testable solution so far proposed. Here, we describe a new experiment based on monitoring a high quality factor microcantilever loaded by a layered test mass, specifically designed to test the Continuous Spontaneous Localization (CSL) model. The measurements are in good agreement with pure thermal motion for temperatures down to 100 mK. From the absence of excess noise we infer a new bound on the collapse rate at the characteristic length rc = 10 −7 m, which improves over previous mechanical experiments by more than one order of magnitude. Our results are explicitly challenging a well-motivated region of the CSL parameter space proposed by Adler.

Gravitational Forces Between Nonclassical Mechanical Oscillators

“…It is encouraging that a simple gluing of a mass to an oscillator still allows for a Q value in the one million range, as also observed in Ref. [110].…”

Testing the foundation of quantum physics in space via Interferometric and non-interferometric experiments with mesoscopic nanoparticles

“…For comparison, the blue dot-dashed line shows the upper bound that could be achieved with a ground-based interferometric experiment with m = 10 7 amu and times t 1 = t 2 = 9.95 s-free-falling times which are clearly beyond current reach for ground-based experiments-as discussed in a recent study of four of the authors 26 . Finally, the dashed gray line represents the upper bounds given by current non-interferometric tests 41,53,70,72 , the black dotted lines on the top of the figure are the current upper bounds coming from interferometric tests 16,40,127,129 , and the gray area at the bottom of the plot represents the theoretical lower-bound 130 .…”

“…(1) is conducive to an investigation on potential deviations from standard quantum theory due, for instance, to collapse models. Due to its interesting phenomenology, theoretical interest, and current strong experimental effort in testing it 23,[37][38][39][40][41] , in the following, we will focus on the Continuous Spontaneous Localization (CSL) model. The CSL model describes, through a stochastic and non-linear modification of the Schrödinger equation, the collapse of the wave function as a spontaneous process whose strength increases with the mass of the system 42 .…”

“…And X-ray measurements-which exploit the fact that the collapse mechanism makes charged particles emit radiation [68][69][70] -have already provided strong limits on the Diósi-Penrose model 71 . In this context, also optomechanical experiments are of particular relevance 41,53,54,[72][73][74][75][76] . They are typically used to characterize noise [77][78][79] , and thus possibly discriminate between standard and non-standard noise sources 41 .…”

“…The dashed red line indicates the upper bound that could be obtained by decreasing the pressure to P = 3 × 10 −14 Pa so that the main limitation would be represented by the statistical error. These bounds are compared to the strongest bonds and corresponding excluded parameter regions present in literature: X-rays emission (blue region) 70 , LISA Pathfinder (green region) 53,55 , multilayer cantilever (brown region) 41 . The gray region is the theoretical lower bound, which is estimated by requiring the collapse to become effective at the mesoscopic scale where the quantum-to-classical transition is expected 127 .…”