  Spin noise (SN) spectroscopy measurements on delicate semiconductor spin
systems, like single InGaAs quantum dots, are currently not limited by optical
shot noise but rather by the electronic noise of the detection system. Here, we
report a realization of homodyne SN spectroscopy enabling shot noise limited SN
measurements. The proof-of-principle measurements on impurities in an
isotopically enriched rubidium atom vapor show that homodyne SN spectroscopy
can be utilized even in the low frequency spectrum which facilitates advanced
semiconductor spin research like higher order SN measurements on spin qubits.
