  Beyond the quantum limit, many-body effects are expected to induce unusual
electronic phase transitions. Materials possessing metallic ground states with
strong interactions between localized and itinerant electronic states are
natural candidates for the realization of such quantum phases. However, the
electronic correlations responsible for increasing the likelihood of novel
phases simultaneously place the quantum limit beyond the reach of laboratory
magnets. Here we propose these difficulties can be surmounted in materials with
strong correlations and insulating ground states. Strong correlations in
insulators and high magnetic fields conspire to fill Landau levels in the
reverse order compared to conventional metals, such that the lowest Landau
level is the first observed. Consequently, the quantum limit in strongly
correlated insulators is reached in reverse and at fields accessible in
laboratories. Quantum oscillations measured at high fields in YbB12 are shown
to have features consistent with the reverse quantum limit. These include how
quantum oscillations move in lock step with the angular evolution of the
insulator-metal transition and the field dependence of the quantum oscillation
frequency. We argue that close to the insulator-metal transition, the
insulating state should be viewed through the lens of a magnetic field-induced
electronic instability affecting the lowest Landau level states in the quantum
limit.
