  Photonic Random-Access Memories (P-RAM) are an essential component for the
on-chip non-von Neumann photonic computing by eliminating optoelectronic
conversion losses in data links. Emerging Phase Change Materials (PCMs) have
been showed multilevel memory capability, but demonstrations still yield
relatively high optical loss and require cumbersome WRITE-ERASE approaches
increasing power consumption and system package challenges. Here we demonstrate
a multi-state electrically-programmed low-loss non-volatile photonic memory
based on a broadband transparent phase change material (Ge2Sb2Se5, GSSe) with
ultra-low absorption in the amorphous state. A zero-static-power and
electrically-programmed multi-bit P-RAM is demonstrated on a
silicon-on-insulator platform, featuring efficient amplitude modulation up to
0.2 dB/{\mu}m and an ultra-low insertion loss of total 0.12 dB for a 4-bit
memory showing a 100x improved signal to loss ratio compared to other
phase-change-materials based photonic memories. We further optimize the
positioning of dual micro-heaters validating performance tradeoffs.
Experimentally we demonstrate a half-a million cyclability test showcasing the
robust approach of this material and device. Low-loss photonic
retention-of-state adds a key feature for photonic functional and programmable
circuits impacting many applications including neural networks, LiDAR, and
sensors for example.
