  The surging interest in quantum computing, space electronics, and
superconducting circuits has led to new developments in cryogenic data storage
technology. Quantum computers promise to far extend our processing capabilities
and may allow solving currently intractable computational challenges. Even with
the advent of the quantum computing era, ultra-fast and energy-efficient
classical computing systems are still in high demand. One of the classical
platforms that can achieve this dream combination is superconducting single
flux quantum (SFQ) electronics. A major roadblock towards implementing scalable
quantum computers and practical SFQ circuits is the lack of suitable and
compatible cryogenic memory that can operate at 4 Kelvin (or lower)
temperature. Cryogenic memory is also critically important in space-based
applications. A multitude of device technologies have already been explored to
find suitable candidates for cryogenic data storage. Here, we review the
existing and emerging variants of cryogenic memory technologies. To ensure an
organized discussion, we categorize the family of cryogenic memory platforms
into three types: superconducting, non-superconducting, and hybrid. We
scrutinize the challenges associated with these technologies and discuss their
future prospects.
