Curator's Take
This article proposes a reversible‑pointer interferometer that amplifies which‑branch information into a mesoscopic nanoparticle’s motion before recombining it, offering a direct visibility‑loss test of Continuous Spontaneous Localization (CSL). By using a 10⁻¹⁸ kg particle at sub‑kelvin temperatures, the scheme could improve existing matter‑wave CSL bounds by four to five orders of magnitude with only ~10⁵ experimental shots. It therefore provides a realistic, scalable pathway to probe collapse models that complements recent optomechanical and non‑interferometric efforts, even though it still sits above the strongest indirect exclusion limits.
— Mark Eatherly
Summary
We propose a measurement-like interferometric test of Continuous Spontaneous Localization (CSL), in which a trapped nanoparticle acts as a reversible mesoscopic pointer rather than as the initially prepared microscopic superposition. A microscopic two-branch system applies opposite weak forces to the nanoparticle, temporarily amplifying which-branch information into branch-conditioned pointer displacements. After one weak-trap period the pointer positions and momenta recombine, so ordinary quantum mechanics predicts recovery of the microscopic coherence, whereas CSL predicts an irreversible visibility loss accumulated while the pointer mass distributions were separated. For a $10^{-18},{\rm kg}$ nanoparticle driven by a $10^{-21},{\rm N}$ differential force at $T=0.4,{\rm K}$, including thermal breathing and an ordinary loss budget $Λ_{\rm loss}\lesssim 0.1$, we find $λ_{\min}\simeq 1.4\times 10^{-10},{\rm s}^{-1}$ at $r_c=100,{\rm nm}$ with $10^5$ shots. A more aggressive lower-frequency point reaches $λ_{\min}\simeq 8.7\times 10^{-12},{\rm s}^{-1}$. These sensitivities would improve over digitized direct matter-wave CSL bounds by about $7\times 10^3$ and $10^5$, respectively, while remaining above the strongest non-interferometric bounds. The proposal is therefore aimed at a substantially stronger direct visibility-loss test of CSL, and at a reversible measurement-like realization of collapse sensitivity, rather than at the strongest overall exclusion curve.