Quantum magnonics: when magnon spintronics meets quantum information science

Abstract

Spintronics and quantum information science are two promising candidates for innovating information processing technologies. The combination of these two fields enables us to build solid-state platforms for studying quantum phenomena and for realizing multi-functional quantum tasks. For a long time, however, the intersection of these two fields was limited due to the distinct properties of the classical magnetization, that is manipulated in spintronics, and quantum bits, that are utilized in quantum information science. This situation has changed significantly over the last few years because of the remarkable progress in coding and processing information using magnons. On the other hand, significant advances in understanding the entanglement of quasi-particles and in designing high-quality qubits and photonic cavities for quantum information processing provide physical platforms to integrate magnons with quantum systems. From these endeavours, the highly interdisciplinary field of quantum magnonics emerges, which combines spintronics, quantum optics and quantum information science. Here, we give an overview of the recent developments concerning the quantum states of magnons and their hybridization with mature quantum platforms. First, we review the basic concepts of magnons and quantum entanglement and discuss the generation and manipulation of quantum states of magnons, such as single-magnon states, squeezed states and quantum many-body states including Bose-Einstein condensation and the resulting spin superfluidity. We discuss how magnonic systems can be integrated and entangled with quantum platforms including cavity photons, superconducting qubits, nitrogen-vacancy centers, and phonons for coherent information transfer and collaborative information processing. The implications of these hybrid quantum systems for non-Hermitian physics and parity-time symmetry are highlighted, together with applications in quantum memories and high-precision measurements. Finally, we present an outlook on some of the challenges and opportunities in quantum magnonics.

Dissipation-induced nonreciprocal magnon blockade in a magnon-based hybrid system

“…Owing to great application prospects in quantum technologies, a new class of hybrid quantum systems based on magnons, i.e., the collective spin excitations in ferroand ferrimagnetic crystals such as yttrium iron garnet (YIG), have blossomed in the past few years [1][2][3], where magnons are coherently coupled to microwave potons [4][5][6][7][8][9][10][11][12], phonons [13][14][15][16], optical photons [17,18], and superconducting qubits [19,20]. Benefiting from the advantages of intrinsically good tunability as well as long coherence time, many novel phenomena have been explored in these magnon-based hybrid systems [21][22][23][24][25][26][27][28][29][30][31].…”

Pure dephasing of magnonic quantum states

“…Introduction.-Rapid advancements in control and manipulation of magnons -spin excitations of ordered magnets -have witnessed the experimental generation of their nonclassical states [1][2][3][4]. Strong magnonic coupling to superconducting qubits [3,5], photons [6][7][8][9], and phonons [10][11][12][13] has been demonstrated.…”

“…Strong magnonic coupling to superconducting qubits [3,5], photons [6][7][8][9], and phonons [10][11][12][13] has been demonstrated. This has triggered a wide range of theoretical proposals suggesting the use of magnonic nonclassical states in providing a resource of entanglement and memories for quantum communication and information processing [4,[14][15][16][17][18][19][20][21][22][23].…”

“…Considering, for example, that T * 2 of semiconductor-based spin qubits [33][34][35] is orders of magnitude smaller than their relaxation time T 1 , we anticipate that the magnon dephasing time will become the limiting factor in the generation and usefulness of magnonic quantum states. Understanding magnon dephasing time is thus critical for progress in quantum magnonics [4].…”

“…First, we can calibrate the absorption linewidth of a magnetic sphere by the technique of ferromagnetic resonance, through which we deduce the relaxation time T 1 = 1/(αω r ) with α being the Gilbert damping of the system [54]. Then we prepare a quantum state of magnons and detect its decoherence time T 2 by entangling the magnons with cavity photons and preforming measurements on the cavity output [2,4,20,29]. After subtracting the influence of the relaxation, we have the contribution of pure dephasing as…”