  We propose a scheme to dynamically realize a quantum memory based on the
toric code. The code is generated from qubit systems with typical two-body
interactions (Ising, XY, Heisenberg) using periodic, NMR-like, pulse sequences.
It allows one to encode the logical qubits without measurements and to protect
them dynamically against the time evolution of the physical qubits. A weakly
coupled cavity mode mediates a long-range attractive interaction between the
stabilizer operators of the toric code, thereby suppressing the creation of
thermal anyons. This significantly increases the lifetime of the memory
compared to the code with noninteracting stabilizers. We investigate how the
fidelity, with which the toric code is realized, depends on the period length T
of the pulse sequence and the magnitude of possible pulse errors. We derive an
optimal period T_opt that maximizes the fidelity.
