Ratchet effect in dc SQUIDs

We analyzed voltage rectification for de SQUIDs biased with ac current with zero mean value. We demonstrate that the reflection symmetry in the 2-dime nsional SQUID potential is broken by an applied flux and with appropriate a symmetries in the de SQUID. Depending on the type of asymmetry, we obtain a rocking or a simultaneously rocking and flashing ratchet. the latter showi ng multiple sign reversals in the mean voltage with increasing amplitude of the ac current. Our experimental results are in agreement with numerical s olutions of the Langevin equations for the asymmetric de SQUID.