Direct Experimental Evidence for Strong Admixture of Different Parity States in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi/></mml:mrow><mml:mrow><mml:mn>11</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Li</mml:mi></mml:math>

Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus ${}^{11}\mathrm{Li}$ incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the ${}^{10}\mathrm{Li}$ fragments gives access to the momentum distribution of the removed neutron in ${}^{11}\mathrm{Li}$. From the shape of the distribution, the $({1s}_{1/2}{)}^{2}$ contribution to the mixture of $({1s}_{1/2}{)}^{2}$ and $({0p}_{1/2}{)}^{2}$ components in the ground-state wave function was determined to be $(45\ifmmode\pm\else\textpm\fi{}10)%$. The angular correlation between the knocked out neutron and the one from the decay of ${}^{10}\mathrm{Li}$ shows a skew distribution signaling interference of these two different parity states.