Chiral Prethermalization in Split Condensates

Anchor paper: K. Agarwal, E.G. Dalla Torre, B. Rauer, T. Langen, J. Schmiedmayer, E. Demler, "Chiral prethermalization in supersonically split condensates," Phys. Rev. Lett. 113, 190401 (2014). [arXiv:1402.6716]

Background

In 1D quasicondensates, splitting a condensate into two coherently coupled halves and letting them dephase produces a well-studied "prethermal" state, with phase correlations settling into an effective-temperature description (confirmed in Schmiedmayer-group atom-chip experiments). This picture assumed a gentle split, creating left- and right-moving phonon-like excitations symmetrically, equilibrating to one common effective temperature. Open question: what happens when the splitting perturbation itself moves supersonically — faster than the speed of sound — as in realistic finite-time chip-based splitting, potentially outrunning and asymmetrically imprinting the two counter-propagating phonon branches?

New results

A supersonic "unzipping" of a 1D condensate produces a qualitatively new, chiral prethermal state: right- and left-moving Bogoliubov excitations acquire different, Doppler-shifted effective temperatures rather than relaxing to one shared value, following a Lorentz-boost-like relation set by the splitting and release velocities. This chirality is readable via fringe contrast at a supersonically-moving release point, and an accelerating release point was predicted to reveal a spacelike analog of the Unruh effect. The authors draw a direct analogy to the CMB dipole anisotropy, where relative motion through an isotropic thermal bath produces an apparent directional temperature difference via Doppler shifting — framing chiral prethermalization as a table-top realization of that same relativistic-kinematic effect.

Schematic of the protocol: a 1D condensate is coherently split at supersonic velocity v_s, evolves freely, then is released at supersonic velocity v_r, with resulting fringe contrast revealing the chiral, Doppler-shifted prethermal temperatures.

Related work in this direction

• K. Agarwal, E.G. Dalla Torre, J. Schmiedmayer, E. Demler, "Quantum heat waves in a one-dimensional condensate," PRB 95, 195157 (2017) — extends this framework by studying how the asymmetric phonon populations manifest as propagating heat-wave signatures and thermal transport.