Accelerated state expansion of a nanoparticle in a dark inverted potential

While the wave packet of a massive particle grows linearly under free dynamics, it grows exponentially in an inverted harmonic potential, offering a pathway to rapidly increase quantum fluctuations to macroscopic dimensions. In this work, we experimentally demonstrate this principle by expanding the center-of-mass thermal state of a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>125</a:mn> <a:mspace width="0.16em"/> <a:mi mathvariant="normal">n</a:mi> <a:mi mathvariant="normal">m</a:mi> </a:mrow> </a:math> silica nanoparticle to a position uncertainty of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mn>43.4</e:mn> <e:mspace width="0.16em"/> <e:mi mathvariant="normal">n</e:mi> <e:mi mathvariant="normal">m</e:mi> </e:mrow> </e:math> within <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mn>260</i:mn> <i:mspace width="0.16em"/> <i:mi>µ</i:mi> <i:mi mathvariant="normal">s</i:mi> </i:mrow> </i:math> . This expansion, achieved using an inverted dark potential to minimize decoherence from photon recoil, represents a 952-fold increase, reaching a scale comparable to the nanoparticle's physical size. This work represents a key advancement toward preparing macroscopic quantum superpositions at unprecedented mass and length scales.