Transverse Breathing Mode of an Elongated Bose-Einstein Condensate

We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because of the scaling invariance of the nonlinear Schrödinger (Gross-Pitaevskii) equation, the oscillation is monochromatic and sinusoidal at short times, even under strong excitation. For ultralow temperatures, the quality factor $Q={\omega }_0/{\gamma }_0$ can exceed 2000, where ${\omega }_0$ and ${\gamma }_0$ are the mode angular frequency and damping rate. This value is much larger than any previously reported for other eigenmodes of a condensate. We also present the temperature variation of ${\omega }_0$ and ${\gamma }_0$.