  One of the major obstacles faced by quantum-enabled technology is the
environmental noise that causes decoherence in the quantum system, thereby
destroying much of its quantum aspects and introducing errors while the system
undergoes quantum operations and processing. A number of techniques have been
invented to mitigate the environmental effects, and many of these techniques
are specific to the environment and the quantum tasks at hand. Here, we propose
a protocol that makes arbitrary environments effectively noise-free or
transparent using an ancilla, which, in particular, is well suited to protect
information stored in atoms. The ancilla, which is the photons, is allowed to
undergo restricted but a wide class of noisy operations. The protocol transfers
the information of the system onto the decoherence-free subspace and later
retrieves it back to the system. Consequently, it enables full protection of
quantum information and entanglement in the atomic system from decoherence. We
propose experimental schemes to implement this protocol on atomic systems in an
optical cavity.
