Qubit–Magnon Dipole Coupling

• Qubit–magnon dipole coupling is a hybrid interaction linking two-level superconducting qubits to collective magnon modes such as the Kittel mode in YIG.
• It employs both electric-dipole and magnetic-dipole interactions, mediated either via a microwave cavity or through direct near-field coupling to establish coherent, strong coupling.
• This coupling enables quantum functionalities including state control, sensing via dispersive shifts, and mediation of quantum gates for scalable superconducting-qubit networks.

Searching arXiv for recent and foundational papers on qubit–magnon dipole coupling to ground the article in the current literature. arxiv_search.query({"^^^^^^^^4search_query4 magnon\" OR ^^^^^^^^4all:\4 magnonics\" OR ^^^^^^^^4all:\4 qubit coupling\"", "start": ^^^^4search_query4^^^^, "max_results": ^^^^4all:\4search_query4^^^^, "sort_by": "submittedDate", "sort_order": "descending"}) Qubit–magnon dipole coupling is the interaction between a two-level qubit and a magnonic collective spin excitation, most commonly the uniform Kittel mode of a yttrium-iron-garnet (YIG) sphere or the uniform mode of a magnetic particle. In superconducting quantum magnonics, this coupling appears in several distinct but related forms: a cavity-assisted interaction in which a transmon couples electrically to a microwave cavity while the magnon couples magnetically to the same cavity mode; a direct near-field magnetic-dipole or inductive interaction between a qubit loop and a ferromagnet; and a direct dispersive PRESERVED_PLACEHOLDER_^^^^4search_query4^^^^-type interaction used to probe noneigenmode magnons. The effective low-energy descriptions are typically a Jaynes–Cummings exchange term, PRESERVED_PLACEHOLDER_^^^^4all:\4^^^^, or a dispersive term, PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^, and these have been used to demonstrate strong coupling, magnon-vacuum-induced Rabi splitting, magnon-number resolution, dissipation-based sensing, squeezing, blockade, and mediated quantum gates (&&&^^^^4search_query4^^^^&&&, &&&^^^^4all:\4^^^^&&&, &&&^^^^4 OR all:\4^^^^&&&, &&&^^^^4 OR all:\4^^^^&&&, Römling et al., 2023).

^^^^4all:\4^^^^. Physical basis and device geometries

The canonical cavity–magnon–qubit architecture consists of a single-mode microwave cavity, a transmon-type superconducting qubit, and a magnon mode in a YIG sphere. In this arrangement the qubit couples to the cavity through an electric-dipole interaction, while the magnon couples to the same cavity through a magnetic-dipole interaction. For the Kittel mode, the magnon corresponds to a uniform precession of all spins in the ferromagnet, so its collective dipole moment is macroscopically enhanced; in the ^^^^4 OR all:\4search_query4all:\44^^^^ experiment the YIG sphere had net spin PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^, yielding a collective magnetic dipole moment $N\mu_B$ (&&&^^^^4all:\4^^^^&&&).

In the rotating-wave approximation, this architecture is described by a three-mode Hamiltonian with cavity operator $a$, magnon operator $m$ or $c$, and qubit Pauli operators or transmon ladder operators. The electric-dipole term has the form $g_{qc}(a^\dagger b+a b^\dagger)$ or $g_q(a\sigma^+ + a^\dagger\sigma^-)$, whereas the magnetic-dipole term has the form PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^ or PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^. The physical distinction is central: the superconducting qubit is tied to the cavity electric field, while the magnon is tied to the cavity magnetic field, so the effective qubit–magnon interaction is a mixed electric–magnetic process mediated by the cavity vacuum field (&&&^^^^4search_query4^^^^&&&, Guo et al., 2023).

A different geometry places a superconducting transmon qubit in the near field of a millimetre-size YIG sphere so that the qubit loop and the collective Kittel-mode magnon share a direct magnetic-dipole interaction. In that case the device Hamiltonian contains a transverse exchange-like term PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^ and a longitudinal term PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^, both derived from the flux dependence of the SQUID Josephson energy and from the flux pull generated by the YIG macrospin fluctuation (Jin et al., 2023).

A third formulation arises in quantum magnonics models that begin from direct magnetic Zeeman coupling. In the resonance-fluorescence treatment of a qubit and a magnon mode, the coupling strength is extracted from PRESERVED_PLACEHOLDER_^^^^4all:\44^^^^, giving PRESERVED_PLACEHOLDER_^^^^4all:\4^^^^5 with PRESERVED_PLACEHOLDER_^^^^4all:\4^^^^6. In typical circuit-magnon experiments, this yields PRESERVED_PLACEHOLDER_^^^^4all:\4^^^^7–PRESERVED_PLACEHOLDER_^^^^4all:\4 (Ilbuğa et al., 2 Jan 2025).

^^^^4 OR all:\4^^^^. Effective Hamiltonians and the emergence of qubit–magnon exchange

For cavity-assisted systems, the central theoretical step is adiabatic elimination of the far-detuned cavity mode. In the regime PRESERVED_PLACEHOLDER_^^^^4all:\4^^^^9, a second-order Schrieffer–Wolff transformation produces an effective Hamiltonian

PRESERVED_PLACEHOLDER_^^^^4 OR all:\4search_query4^^^^

with

PRESERVED_PLACEHOLDER_^^^^4 OR all:\4all:\4^^^^

The terms proportional to PRESERVED_PLACEHOLDER_^^^^4 OR all:\4 OR all:\4^^^^ and PRESERVED_PLACEHOLDER_^^^^4 OR all:\4 OR all:\4^^^^ are dispersive frequency shifts, while the exchange term is the operative qubit–magnon coupling (Guo et al., 2023).

In the more general asymmetric-detuning form, the same elimination yields

PRESERVED_PLACEHOLDER_^^^^4 OR all:\44^^^^

When PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^5, this reduces to PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^6 (&&&^^^^4all:\4^^^^&&&, &&&^^^^4all:\4 OR all:\4^^^^&&&, &&&^^^^4all:\4 OR all:\4^^^^&&&).

The physical mechanism is explicitly second order. In the cavity-mediated scheme of Guo et al., the qubit and the magnon do not interact directly; rather, the qubit flips and creates or annihilates a virtual cavity photon, and that virtual photon is converted into or from a magnon. This produces the Jaynes–Cummings–type interaction PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^7 (Guo et al., 2023).

In the dispersive limit of the resulting two-mode theory, the exchange interaction is converted into a cross-Kerr-type coupling. For a two-level qubit one obtains

PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^8

or equivalently a dressed Hamiltonian in which the qubit frequency shifts by PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^9 per magnon, with leading-order PRESERVED_PLACEHOLDER_^^^^4 OR all:\4search_query4^^^^. For a weakly anharmonic transmon, the correction PRESERVED_PLACEHOLDER_^^^^4 OR all:\4all:\4^^^^ is also standard in this context (&&&^^^^4 OR all:\4^^^^&&&, &&&^^^^4 OR all:\4^^^^&&&).

Not all dispersive couplings are second order. In the anisotropic-ferromagnet treatment of Romling et al., the interaction Hamiltonian contains a direct first-order term PRESERVED_PLACEHOLDER_^^^^4 OR all:\4 OR all:\4^^^^, arising from the PRESERVED_PLACEHOLDER_^^^^4 OR all:\4 OR all:\4^^^^ part of an interfacial spin–spin exchange. There the dispersive coupling is present already at first order rather than being generated perturbatively from a Jaynes–Cummings exchange (Römling et al., 2023).

^^^^4 OR all:\4^^^^. Coupling regimes and experimental benchmarks

The development of the field can be traced through a sequence of increasingly controlled regimes, from cavity-assisted strong coupling to strong dispersive readout and direct near-field implementations.

Work	Architecture	Reported coupling or signature
(&&&^^^^4all:\4^^^^&&&)	cavity-assisted qubit–magnon hybrid	PRESERVED_PLACEHOLDER_^^^^4 OR all:\44^^^^; tunable PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^5 up to PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^6
(&&&^^^^4search_query4^^^^&&&)	cavity-mediated YIG–transmon system	PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^7 measured; PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^8
(&&&^^^^4all:\4 OR all:\4^^^^&&&)	driven cavity-mediated hybrid	PRESERVED_PLACEHOLDER_^^^^4 OR all:\4^^^^9; vacuum Rabi splitting $N\mu_B$^^^^4search_query4^^^^
(&&&^^^^4 OR all:\4^^^^&&&)	strong-dispersive quantum magnonics	$N\mu_B$^^^^4all:\4^^^^; $N\mu_B$^^^^4 OR all:\4^^^^
(&&&^^^^4 OR all:\4^^^^&&&)	dispersive sensing regime	$N\mu_B$^^^^4 OR all:\4^^^^; sensitivity $N\mu_B$4

The ^^^^4 OR all:\4search_query4all:\44^^^^ demonstration of coherent coupling between a ferromagnetic magnon and a superconducting qubit used a re-entrant rectangular copper microwave cavity with TE$N\mu_B$5 mode frequency $N\mu_B$6, a transmon qubit at $N\mu_B$7 with $N\mu_B$8, and a YIG sphere realizing the Kittel mode with $N\mu_B$9. Using $a$^^^^4search_query4^^^^, the effective-coupling estimate was $a$^^^^4all:\4^^^^, while the observed static coupling was $a$^^^^4 OR all:\4^^^^. The measured linewidths were $a$^^^^4 OR all:\4^^^^, $a$4, and $a$5, so $a$6 and the system was in the strong-coupling regime (&&&^^^^4all:\4^^^^&&&).

In the ^^^^4 OR all:\4search_query4all:\4^^^^5 “single-magnon limit” experiment, the TE$a$7 cavity–magnon coupling was $a$8, the TE$a$9 qubit–cavity coupling was $m$^^^^4search_query4^^^^, the effective detuning was $m$^^^^4all:\4^^^^, and the resulting qubit–magnon coupling was measured as $m$^^^^4 OR all:\4^^^^, with a predicted value $m$^^^^4 OR all:\4^^^^. At the qubit–magnon degeneracy point the observed splitting was $m$4. The same work reported magnon–cavity cooperativity $m$5 and qubit–magnon cooperativity $m$6 (&&&^^^^4search_query4^^^^&&&).

The ^^^^4 OR all:\4search_query4all:\4^^^^9 driven qubit–magnon experiment reported a larger cavity–qubit coupling $m$7 and cavity–magnon coupling $m$8, with detuning $m$9 and effective qubit–magnon coupling $c$^^^^4search_query4^^^^. In the absence of drive, the vacuum Rabi splitting was $c$^^^^4all:\4^^^^ (&&&^^^^4all:\4 OR all:\4^^^^&&&).

Representative far-detuned parameters for the two-tone squeezing proposal are cavity frequency $c$^^^^4 OR all:\4^^^^, qubit and magnon frequencies $c$^^^^4 OR all:\4^^^^, couplings $c$4 and $c$5, and detuning $c$6, which give $c$7. Dissipation rates were quoted as magnon linewidth $c$8 and qubit decay $c$9 (Guo et al., 2023).

4. Spectroscopy, dispersive readout, and number resolution

The most direct signature of coherent qubit–magnon exchange is an avoided crossing or vacuum-Rabi splitting at resonance. In both the ^^^^4 OR all:\4search_query4all:\44^^^^ and ^^^^4 OR all:\4search_query4all:\4^^^^5 cavity-mediated experiments, qubit spectroscopy revealed the hybridization of a single qubit excitation with a single magnon, thereby establishing strong coupling at the single-excitation level (&&&^^^^4all:\4^^^^&&&, &&&^^^^4search_query4^^^^&&&).

Moving away from resonance into the large-detuning regime yields the strong-dispersive regime of quantum magnonics. In the ^^^^4 OR all:\4search_query4all:\4^^^^6 number-state-resolution experiment, the lowest-order model was

$g_{qc}(a^\dagger b+a b^\dagger)$^^^^4search_query4^^^^

which in the limit $g_{qc}(a^\dagger b+a b^\dagger)$^^^^4all:\4^^^^ reduces to

$g_{qc}(a^\dagger b+a b^\dagger)$^^^^4 OR all:\4^^^^

The reported values were $g_{qc}(a^\dagger b+a b^\dagger)$^^^^4 OR all:\4^^^^, $g_{qc}(a^\dagger b+a b^\dagger)$4, $g_{qc}(a^\dagger b+a b^\dagger)$5, $g_{qc}(a^\dagger b+a b^\dagger)$6, and narrowed qubit linewidth $g_{qc}(a^\dagger b+a b^\dagger)$7. Because $g_{qc}(a^\dagger b+a b^\dagger)$8, the qubit spectral line split into well-resolved peaks spaced by $g_{qc}(a^\dagger b+a b^\dagger)$9 per magnon. The same experiment reported that resolving $g_q(a\sigma^+ + a^\dagger\sigma^-)$^^^^4search_query4^^^^ magnons corresponds to detecting the flip of one spin among $g_q(a\sigma^+ + a^\dagger\sigma^-)$^^^^4all:\4^^^^ (&&&^^^^4 OR all:\4^^^^&&&).

The ^^^^4 OR all:\4search_query4 OR all:\4search_query4^^^^ dissipation-based sensing experiment used the same dispersive principle but focused on qubit dephasing induced by magnon-number fluctuations. There the effective qubit–magnon coupling was $g_q(a\sigma^+ + a^\dagger\sigma^-)$^^^^4 OR all:\4^^^^ and the dispersive shift per magnon was $g_q(a\sigma^+ + a^\dagger\sigma^-)$^^^^4 OR all:\4^^^^, extracted from $g_q(a\sigma^+ + a^\dagger\sigma^-)$4. With qubit linewidth $g_q(a\sigma^+ + a^\dagger\sigma^-)$5 and magnon linewidth $g_q(a\sigma^+ + a^\dagger\sigma^-)$6, Ramsey interferometry yielded a steady-state magnon-population sensitivity $g_q(a\sigma^+ + a^\dagger\sigma^-)$7 (&&&^^^^4 OR all:\4^^^^&&&).

A complementary spectroscopic regime is resonance fluorescence. For a weakly driven qubit–magnon Jaynes–Cummings system,

$g_q(a\sigma^+ + a^\dagger\sigma^-)$8

the steady-state qubit and magnon spectra show two sidebands at $g_q(a\sigma^+ + a^\dagger\sigma^-)$9 and a central PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4search_query4^^^^-function “Heitler peak” at PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4all:\4^^^^ with vanishing linewidth in the weak-driving limit. The sideband splitting is PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4 OR all:\4^^^^, and the effect persists at both strong and weak coupling (Ilbuğa et al., 2 Jan 2025).

The dispersive paradigm has also been generalized to noneigenmode magnons in anisotropic ferromagnets. There the qubit frequency depends on the bare-magnon number even though the true eigenmode is a squeezed-magnon Bogoliubov mode. Qubit excitation spectroscopy can then resolve the even bare-magnon Fock components of the squeezed-magnon ground state through transitions PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4 OR all:\4^^^^ (Römling et al., 2023).

5. Drive engineering, tunability, and nonclassical-state generation

Time-dependent control of qubit–magnon dipole coupling has become a central method for generating nonclassical magnon states. In the ^^^^4 OR all:\4search_query4all:\44^^^^ experiment, when the qubit and magnon were detuned by PRESERVED_PLACEHOLDER_^^^^4all:\4search_query44^^^^ so that the static coupling was negligible, a microwave drive at

PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^5

activated a third-order nonlinearity of the transmon. On two-photon resonance this produced a tunable interaction with experimentally observed PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^6 up to PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^7 and slope PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^8 (&&&^^^^4all:\4^^^^&&&).

Guo et al. proposed a two-tone-driving protocol in a cavity–magnon–qubit system to generate magnon squeezing. After cavity elimination, the qubit–magnon interaction is driven so as to engineer an effective parametric Hamiltonian PRESERVED_PLACEHOLDER_^^^^4all:\4search_query4^^^^9 with PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4search_query4^^^^ and PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4all:\4^^^^. The required conditions are PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4 OR all:\4^^^^, together with residual-detuning tuning to cancel fast phases. Numerically, moderate squeezing with variance PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4 OR all:\4^^^^ vacuum was found for PRESERVED_PLACEHOLDER_^^^^4all:\4all:\44^^^^ and PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^5, with PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^6 and drive strengths in the hundreds of MHz range. The proposal states that the generated squeezed states involve more than PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^7 spins and are therefore macroscopic quantum states (Guo et al., 2023).

Driven qubit–magnon coupling can also produce double dressing. In the ^^^^4 OR all:\4search_query4all:\4^^^^9 experiment, a coherent drive resonant with the qubit led first to classical dressing of the qubit and then to hybridization of the dressed states with the magnon. The resulting four eigenmodes formed two “particle-like” and two “hole-like” branches whose splittings depended on the drive power through PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^8, creating a particle–hole symmetry and enabling quantum simulation of composite fermion-boson quasi-particles (&&&^^^^4all:\4 OR all:\4^^^^&&&).

For directly coupled transmon–YIG devices, driving can instead be used to generate strong antibunching. Under the optimized condition PRESERVED_PLACEHOLDER_^^^^4all:\4all:\4^^^^9 and with probe and drive amplitudes satisfying PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4search_query4^^^^, the equal-time second-order correlation function is analytically minimized. The reported optimum reaches PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4all:\4^^^^, and the robustness of the blockade was analyzed in the presence of thermal noise and moderate longitudinal coupling (Jin et al., 2023).

The same two-tone-control logic has been extended to multimagnetic-mode settings. In a system with one transmon, two YIG spheres, and one cavity mode, adiabatic elimination gives qubit–magnon couplings

PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4 OR all:\4^^^^

and a cavity-mediated magnon–magnon beam-splitter coupling PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4 OR all:\4^^^^. Under two-tone driving of the qubit and appropriate detuning choices, a fourth-order elimination yields an effective two-mode-squeezing term

PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\44^^^^

with PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^5. For the quoted parameters, PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^6, PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^7, PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^8, and PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^9–PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4search_query4^^^^ (&&&^^^^4all:\4 OR all:\4^^^^&&&).

6. Conceptual distinctions, applications, and extensions

A recurring conceptual distinction is that “qubit–magnon dipole coupling” does not refer to a single microscopic mechanism. In cavity-assisted YIG–transmon systems, the operative interaction is second order and mediated by virtual cavity photons, combining electric-dipole qubit coupling and magnetic-dipole magnon coupling. In direct transmon–YIG geometries, the dominant couplings are transverse and longitudinal terms generated by the flux response of a SQUID to the YIG stray field. In anisotropic-ferromagnet treatments, a direct first-order dispersive term can exist independently of Jaynes–Cummings exchange. This suggests that the same low-energy algebra can arise from physically different microscopic couplers (Guo et al., 2023, Jin et al., 2023, Römling et al., 2023).

The applications already established or proposed in the cited literature are correspondingly diverse. The earliest cavity-mediated work identified quantum control and measurement of magnon excitations, including generation of single-magnon Fock states, Bell states, and arbitrary superpositions using standard circuit-QED pulse sequences, with the ferromagnetic mode functioning as a quantum memory at the single-excitation level (&&&^^^^4all:\4^^^^&&&). Subsequent work emphasized non-classical magnon states, strong-dispersive number resolution, and a coherent interface between superconducting qubits and optical photons (&&&^^^^4search_query4^^^^&&&, &&&^^^^4 OR all:\4^^^^&&&).

Sensing and spectroscopy form a second major branch. Dissipation-based interferometry turns magnon-induced dephasing into a metrological resource at the PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4all:\4^^^^ scale (&&&^^^^4 OR all:\4^^^^&&&), while resonance-fluorescence theory shows that elastic qubit-to-magnon scattering can produce a magnonic analog of the Heitler effect and indicates a path toward coherent magnon sources (Ilbuğa et al., 2 Jan 2025). Direct dispersive access to noneigenmode magnons further enables spectroscopy of equilibrium squeezing and deterministic generation of squeezed even Fock states (Römling et al., 2023).

A third branch uses magnons as mediators rather than endpoints. In NV-center/YIG-film hybrids, the Hamiltonian

PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4 OR all:\4^^^^

describes dipolar NV–magnon coupling, and the magnon-induced self-energy determines an effective NV–NV interaction

PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4 OR all:\4^^^^

The experimentally extracted value at PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\44^^^^ was PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^5, compared with direct dipole–dipole coupling PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^6 (Fukami et al., 2023).

For superconducting-qubit networks, a related idea is to use a magnetic particle as a magnonic bus. In the transmon–magnet hybrid analyzed by Dols et al., inductive qubit–magnon couplings PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^7 and PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^8 lead, after a Schrieffer–Wolff transformation, to three effective qubit–qubit interactions: transverse PRESERVED_PLACEHOLDER_^^^^4all:\4 OR all:\4^^^^9, longitudinal PRESERVED_PLACEHOLDER_^^^^4all:\44search_query4^^^^, and mixed PRESERVED_PLACEHOLDER_^^^^4all:\44all:\4^^^^. Under realistic parameters the proposed gate performances were average fidelity PRESERVED_PLACEHOLDER_^^^^4all:\44 OR all:\4^^^^ for iSWAP and CZ, and PRESERVED_PLACEHOLDER_^^^^4all:\44 OR all:\4^^^^ for iCNOT (Dols et al., 2024).

Taken together, these results define qubit–magnon dipole coupling as a family of hybrid interactions that link superconducting or spin qubits to collective magnetic excitations across resonant, dispersive, and parametrically driven regimes. The common technical theme is the conversion of a macroscopically large magnetic mode into a controllable quantum degree of freedom without sacrificing single-quantum addressability.