Masayuki Nakano (Caltech) -- LIGO detectors status and upgrades

The O4 observation run will conclude in the latter half of 2025, after which LIGO will undergo a two-year period of commissioning and upgrades in preparation for the next observation run, O5. In this talk, I will briefly introduce the upgrades implemented during O4, with a particular focus on frequency-dependent squeezing. Following that, I will present the upgrade plans for O5, which include:

• Test mass upgrade

• Larger beam splitter and suspension

• Jitter noise reduction (Jitter attenuation cavity)

• Quantum noise reduction (further squeezing and Balanced-Homodyne detection)