  Preserving entanglement is a crucial dynamical process for entanglement-based
quantum computation and quantum-information processes, such as one-way quantum
computing and quantum key distribution. However, the problem of quantifying the
ability of an experimental process to preserve two-qubit entanglement in
experimentally feasible ways is not well understood. Accordingly, herein, we
consider the use of two measures, namely composition and robustness, for
quantitatively characterizing the ability of a process to preserve
entanglement, referred to henceforth as entanglement preservability. A fidelity
benchmark is additionally derived to identify the ability of a process to
preserve entanglement. We show that the measures and introduced benchmark are
experimentally feasible and require only local measurements on single qubits
and preparations of separable states. Moreover, they are applicable to all
physical processes that can be described using the general theory of quantum
operations, e.g., qubit dynamics in photonic and superconducting systems. Our
method extends the existing tools for analyzing channels, e.g., channel
resource theory, to quantify entanglement preservability for
non-trace-preserving quantum processes. The results are of significant interest
for applications in quantum-information processing in which entanglement
preservation is required.
