Scalability of decoherence control in entangled systems

We investigate the scaling of decoherence rates and their dynamical suppression with the number N of qubits in various entangled states. Remarkably, for sufficiently large N, coherence time is always in the Zeno regime. This changes the scaling to the square root of the Markov-regime scaling. We find that a simple and effective control strategy is to locally modulate the individual qubits and thereby not only suppress the decoherence rate of each qubit, but also reduce the decoherence scaling of entangled states that are particularly fragile, from N2 to N, resulting in a dramatic reduction of the decoherence (by orders of magnitude). Surprisingly, the conditions for the effectiveness of such decoherence control are independent of N.