## Concurrence as a function of damping probability *p*

**Figure 3.** Concurrence as a function of damping probability *p*. (a) α = 0.7, β = 0.35, γ = 0.4, δ = 0.48. (b) α = 0.10, β = 0.55, γ = −0.60, δ = 0.57. The dashed lines correspond to the concurrence after amplitude damping, and the solid line is the recovered concurrence of the scheme in section 3. The other three curves with symbols are the concurrences of the extended scheme in section 6 with *x* = 0.8, *x* = 0.5 and *x* = 0.1.

**Abstract**

Quantum entanglement is a critical resource for quantum information and quantum computation. However, entanglement of a quantum system is subjected to change due to the interaction with the environment. One typical result of the interaction is the amplitude damping that usually results in the reduction of the entanglement. Here we propose a protocol to protect quantum entanglement from the amplitude damping by applying Hadamard and CNOT gates. As opposed to some recently studied methods, the scheme presented here does not require weak measurement in the reversal process, leading to a faster recovery of entanglement. We propose a possible experimental implementation based on linear optical system.