Résumé We present the current status of the BMV experiment. Our apparatus is based on an up-todate resonant optical cavity coupled to a transverse magnetic field. We detail our data acquisition and analysis procedure which takes into account the symmetry properties of the raw data with respect to the orientation of the magnetic field and the sign of the cavity birefringence. The measurement result of the vacuum magnetic linear birefringence kCM presented in this paper was obtained with about 200 magnetic pulses and a maximum field of 6.5 T, giving a noise floor of about 8 × 10 −21 T −2 at 3σ confidence level.PACS. 12.20.Fv Experimental tests -78.20.Ls Magneto-optical effects -42.25.Lc Birefringence

In this paper we present the realization of further steps towards the measurement of the magnetic birefringence of the vacuum using pulsed fields. After describing our experiment, we report the calibration of our apparatus using nitrogen gas and we discuss the precision of our measurement giving a detailed error budget. Our best present vacuum upper limit is ∆n ≤ 5.0 × 10 −20 T −2 per 4 ms acquisition time. We finally discuss the improvements necessary to reach our final goal.