Quantum Paradigm of the Foldover Magnetic Resonance

Abstract

The explosive development of quantum magnonics requires considering several previously known effects from a new angle. In this article, we revise the phenomenon of "foldover" (bi-stable) magnetic resonance from the point of view of quantum magnonics. The density of magnons under strong excitation can exceed the critical value for the formation of a magnon Bose condensate. Under these conditions, the effect of quantum transport of magnons should be considered. In particular, the effect of spin superfluidity, discovered earlier in super fluid 3He should lead to spatial redistribution of the precessing magnetization. Our experimental results confirm a significant change in properties of the foldover magnetic resonance in yttrium iron garnet (YIG) due to superfluid magnetization transport. This discovery paves the way for many quantum applications of supermagnonics, such as magnetic Josephson effect, long-distance spin transport, Q-bit, quantum logics, magnetic sensors, and others.

Magnon Tunneling Between Two Magnon Bose-Einstein Condensates

“…A complete verification of the quantum behavior of nonequilibrium magnon gas was performed in antiferromagnetic superfluid 3 He, the results of which were awarded by the prestigious F. London prize. An experimental verification for the quantum behavior of nonequilibrium magnon gas in YIG was described in 9 .…”

“…At a permanent RF pumping the chemical potential of mBEC is determined by the RF frequency, which determines the density of nonequilibrium magnons, and therefore the angle of magnetization deflection. In other words, magnon density is determined by the frequency of excitation, and not on its intensity, while RF power is enough to compensate for magnons relaxation, as shown in 9 . Of course, only a part of non-equilibrium magnons condenses.…”

“…However, these phenomena are not directly related to superfluidity of 3 He and can be found in other magnetic materials. Thus, mBEC and magnon superfluidity was observed in solid materials, including antiferromagnets with a coupling nuclear electron precession [23][24][25][26] and YIG film, magnetized in plane 27,28 and out of plane 9,29 .…”

Inverse “Foldover” Resonance in an Yttrium Iron Garnet Film

“…In this case, different types of Bose-Einstein condensation of magnons should be taken into account [21]. In conclusion, using the magnon Bose-Einstein condensate, it is possible to construct a quantum qubit operating at room temperatures, as proposed in [22]. Possible practical implementations of such a qubit were considered in [23].…”