  Gain and loss modulation are ubiquitous in nature. An exceptional point
arises when both the eigenvectors and eigenvalues coalesce, which in a physical
system can be achieved by engineering the gain and loss coefficients, leading
to a wide variety of counter-intuitive phenomena. In this work we demonstrate
the existence of an exceptional point in an exciton polariton condensate in a
double-well potential. Remarkably, near the exceptional point, the polariton
condensate localized in one potential well can be switched off by an additional
optical excitation in the other well with very low (far below threshold) laser
power which surprisingly induces additional loss into the system. Increasing
the power of the additional laser leads to a situation in which gain dominates
in both wells again, such that the polaritons re-condense with almost the same
density in the two potential wells. Our results offer a simple way to optically
manipulate the polariton lasing process in a double-well potential structure.
Extending such configuration to complex potential well lattices offers exciting
prospects to explore high-order exceptional points and non-Hermitian
topological photonics in a non-equilibrium many-body system.
