  We investigate theoretically the effect of a magnetic field on intersubband
polaritons in an asymmetric quantum well placed inside an optical resonator. It
is demonstrated that the field-induced diamagnetic shift of electron subbands
in the well increases the broadening of optical lines corresponding to
intersubband electron transitions. As a consequence, the magnetic field can
switch the polariton system from the regime of strong light-matter coupling to
the regime of weak one. This effect paves a way to the effective control of
polaritonic devices with a magnetic field.
