Stable Modes in a Magnon Bose–Einstein Condensate Self-Generator

Recently, we have obtained a permanently existing Bose–Einstein condensate (BEC) of magnons in the self-generation mode. We have shown that magnon relaxation processes do not disturb the coherent state of the BEC when magnon relaxation is compensated by exciting new magnons under the effect of an amplified signal of magnon BEC emission applied to the sample. This is due to the boson enhancement effect, whereby only magnons corresponding to the quantum state of the BEC are excited in the presence of the BEC. In this work, we report the new studies, where a set of stable condensate states that are determined by the phase relationship of the radio-frequency signal emitted by the BEC and the amplified signal fed back have been obtained. The formation of stable regions of BEC generation corresponding to a phase jump multiple of 2π on the feedback line has been experimentally detected. A theoretical model has been constructed to describe the process of transition between BEC states in a self-generator. This model has much in common with the well-known washboard model for phase qubits.