= Cold-atom collapse and revival after a lattice quench
A concrete <quantum quench> experiment loaded a <Bose-Einstein condensate> of $^{87}\mathrm{Rb}$ <chemical atoms> from a <magnetic field> trap into an <optical lattice>: three orthogonal $838\,\mathrm{nm}$ <laser> <standing waves>, with approximately $125\,\mathrm{\mu m}$ <beam waists>. An $80\,\mathrm{ms}$ loading ramp preceded a $50\,\mathrm{\mu s}$ increase in lattice depth. This suppressed <quantum tunnelling> while retaining each well's vibrational <ground state>. The switch preserved atom-number populations rather than freezing every motional degree of freedom.<Collapse and revival of the matter wave field of a Bose-Einstein condensate by Markus Greiner and others>[Greiner and others, manuscript pp. 3–4: preparation and switching; p. 7, Methods: wavelength, beam waists and lattice geometry]{ref}
After variable hold times, releasing the traps and taking <photon absorption> images after $16\,\mathrm{ms}$ of flight revealed disappearance and return of <interference> peaks. Background-subtracted peak counts supplied a coherent fraction. Varying final depth tested the predicted revival period $h/U$; varying initial depth tested the collapse's sensitivity to atom-number statistics. Peak broadening outside counting windows and spatial variation of $U$ limited later signals.<Collapse and revival of the matter wave field of a Bose-Einstein condensate by Markus Greiner and others>[Manuscript p. 4 and figure 2 caption on p. 11: flight and image extraction; figure 3 caption on p. 12: readout limitations; figures 4–5 captions on pp. 13–14: final-depth and initial-depth comparisons]{ref}
Here $U$ is the on-site interaction <energy>. The approximate isolated-well <Hamiltonian operator> $H=U\hat n(\hat n-1)/2$, with <number operator> $\hat n$, gives different <quantum phases> to its <number states>, which later rephase. This is a many-level realization of the distinction between fixed populations and changing <quantum phases>.<Collapse and revival of the matter wave field of a Bose-Einstein condensate by Markus Greiner and others>[Manuscript pp. 2–3, equations (1)–(2): isolated-well Hamiltonian and number-state phase evolution]{ref}
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