  A nonperturbative theory is presented for the creation by an oscillating
potential of spin-entangled electron-hole pairs in the Fermi sea. In the weak
potential limit, considered earlier by Samuelsson and Buttiker, the
entanglement production is much less than one bit per cycle. We demonstrate
that a strong potential oscillation can produce an average of one Bell pair per
two cycles, making it an efficient source of entangled flying qubits.
