  Quantum memory -- the capacity to store and faithfully recover unknown
quantum states -- is essential for quantum-enhanced technology. There is thus a
pressing need for operationally meaningful means to benchmark candidate
memories across diverse physical platforms. Here we introduce a universal
benchmark distinguished by its relevance across multiple key operational
settings, exactly quantifying (1) the memory's robustness to noise, (2) the
number of noiseless qubits needed for its synthesis, (3) its potential to speed
up statistical sampling tasks, and (4) performance advantage in non-local games
beyond classical limits. The measure is analytically computable for
low-dimensional systems and can be efficiently bounded in experiment without
tomography. We thus illustrate quantum memory as a meaningful resource, with
our benchmark reflecting both its cost of creation and what it can accomplish.
We demonstrate the benchmark on the five-qubit IBM Q hardware, and apply it to
witness efficacy of error-suppression techniques and quantify non-Markovian
noise. We thus present an experimentally accessible, practically meaningful,
and universally relevant quantifier of a memory's capability to preserve
quantum advantage.
