Photon is a vectorized query engine written in C++ that leverages data and instruction-level parallelism available in CPUs.

It’s 100% compatible with Apache Spark APIs which means you don’t have to rewrite your existing code ( SQL, Python, R, Scala) to benefit from its advantages. 

Photon is an ANSI compliant Engine, it was primarily focused on SQL but now the scope is much larger, with more ingestion sources, formats, APIs and methods since the launch.

for more information check the following article : https://msdatalab.net/introduction-to-databricks-photon/