Magnon qubit and quantum computing on magnon Bose-Einstein condensates

Recently, great progress has been made in the creation of a solid-state quantum computer using superconducting qubits on Cooper pairs of charged electrons. However, this approach has met limitations due to decoherence effects caused by the strong Coulomb interaction of the superconducting qubit with the environment. Here, we propose the solution of this problem by switching to another Bose-Einstein condensate (BEC), uncharged long-lived magnons, wherein the magnon BEC qubit can be realized due to the magnon blockade isolating a pair of the magnon condensate energy levels in the mesoscopic and nanoscopic ferromagnetic dielectric sample. We demonstrate the single-qubit gates by operating quantum transition between these states in the external microwave field. We also consider implementation of the two-qubit gates by using the interaction between such magnon BEC qubits due to exchange by virtual photons in a microwave cavity. Finally, we discuss the condition for long-lived magnon BEC qubits, a scalable architecture, and promising advantages of the multiqubit quantum computer based on the magnon qubit.

Figure 1

Layout of magnon BEC single-qubit gate (MBEC: magnon Bose-Einstein condensate; LP: laser pumping; MWR: microwave resonator; J: current in magnetic coil; ${\mathrm{B}}_0$: magnetic field). Here, magnon BEC is excited by the laser pulse and qubit rotation is achieved by the interaction with a standing microwave field in a high-quality resonator.

Figure 2

Scheme of quantum computer on magnon BEC qubits and multiqubit atomic quantum memory in waveguide microwave resonator (PN: processor node; QM: quantum memory). Dashed lines show interaction between two qubits and reversible transfer of quantum information between PN and QM via the interaction with virtual photons.