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arxiv: 2606.25511 · v1 · pith:QZ2L3WCHnew · submitted 2026-06-24 · 🪐 quant-ph · cond-mat.mes-hall· physics.optics

Preparing two-mode magnonic Schr\"odinger cat states in a cavity-magnon-qubit system

Gen Li , Gang Liu , Rong-Can Yang , Jie Li This is my paper

Pith reviewed 2026-06-25 21:30 UTC · model grok-4.3

classification 🪐 quant-ph cond-mat.mes-hallphysics.optics
keywords magnonic cat statestwo-mode entanglementcavity magnonicsYIG spheresconditional displacementhybridized magnon modesnon-Gaussian statessuperconducting qubit
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The pith

A cavity-magnon-qubit system generates two-mode magnonic Schrödinger cat states with non-Gaussian entanglement by preparing a bright hybridized mode and measuring the qubit.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows how two identical YIG spheres coupled to one microwave cavity and a superconducting qubit can produce a two-mode magnonic cat state. Adiabatic elimination of the cavity plus resonant qubit driving creates an effective conditional displacement interaction between magnons and the qubit. In the strong magnon-magnon coupling regime the system forms bright and dark hybridized modes; a projective measurement on the qubit leaves the bright mode in a cat state while the dark mode stays in vacuum, which maps to an entangled cat state of the original two magnon modes. The authors verify that the resulting non-Gaussian entanglement survives realistic dissipation with currently accessible parameters.

Core claim

Working in the magnon-magnon strong-coupling regime with two identical magnon frequencies and identical couplings to the cavity produces bright and dark hybridized modes. After the effective magnon-qubit conditional-displacement interaction is established by cavity elimination and qubit driving, a projective measurement on the qubit prepares the bright mode in a cat state while the dark mode remains in vacuum; the corresponding state of the two original magnon modes is therefore a two-mode cat state that carries strong non-Gaussian entanglement.

What carries the argument

Effective magnon-qubit conditional-displacement interaction obtained by adiabatic cavity elimination and resonant qubit driving, which acts on the bright hybridized magnon mode after the strong-coupling regime splits the modes into bright and dark combinations.

If this is right

  • The dark mode remains in vacuum, so all nonclassical features reside in the bright mode and transfer directly to the original magnon pair.
  • Strong non-Gaussian entanglement appears between the two magnon modes as a direct consequence of the cat-state preparation.
  • Dissipation and dephasing reduce but do not eliminate the nonclassicality when realistic device parameters are used.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same bright-dark splitting and conditional-displacement protocol could be applied to three or more magnon modes to produce multi-mode entangled cat states.
  • The resulting non-Gaussian magnon entanglement might serve as a resource for continuous-variable quantum information tasks that require non-Gaussian operations.
  • Measuring the qubit after the interaction provides a direct experimental signature that can be compared against the predicted cat-state fidelity without requiring full tomography of both magnon modes.

Load-bearing premise

The two magnons must have exactly identical frequencies and identical couplings to the cavity so that the hybridized modes cleanly separate into a bright mode that couples to the qubit and a dark mode that does not.

What would settle it

After the qubit is projectively measured in the computational basis, the reconstructed joint Wigner function of the two magnon modes shows no regions of negativity or no interference fringes between the two coherent-state components.

Figures

Figures reproduced from arXiv: 2606.25511 by Gang Liu, Gen Li, Jie Li, Rong-Can Yang.

Figure 1
Figure 1. Figure 1: FIG 1. (a) The cavity-magnon-qubit system, involving a microwave [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG 3. Wigner function of (a) the UHM and (b) the LHM. Two [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG 4. (a) The fidelity [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

The cavity-magnon-qubit system has recently been demonstrated as a new platform for preparing macroscopic quantum states in magnonic systems. Here, we propose to prepare a two-mode magnonic cat state, which is also a non-Gaussian entangled state, based on this practical system involving two yttrium-iron-garnet (YIG) spheres and a superconducting qubit coupled to a common microwave cavity. By adiabatically eliminating the cavity and resonantly driving the qubit, an effective magnon-qubit conditional-displacement interaction is achieved. Further working in the magnon-magnon strong-coupling regime and considering two identical magnon frequencies and coupling strengths to the cavity, two hybridized magnon modes are formed, of which the bright mode is prepared in a cat state after a projective measurement on the qubit, while the dark mode remains in its initial vacuum state. Such a state corresponds to a two-mode cat state of two original magnon modes, which share strong non-Gaussian entanglement. We also discuss practical dissipation and dephasing effects on the cat state. The results indicate that strong nonclassicality and non-Gaussian entanglement are present in the two-mode cat state using fully feasible parameters.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The paper proposes preparing two-mode magnonic Schrödinger cat states (also non-Gaussian entangled states) in a system of two YIG spheres and a superconducting qubit coupled to a common microwave cavity. After adiabatically eliminating the cavity and applying resonant qubit drive to obtain an effective magnon-qubit conditional-displacement interaction, the scheme operates in the magnon-magnon strong-coupling regime under the assumption of identical magnon frequencies and cavity couplings. This produces hybridized bright and dark modes; a projective qubit measurement prepares a cat state in the bright mode (dark mode stays in vacuum), which maps back to a two-mode cat in the original magnon basis. Dissipation and dephasing effects are discussed, with the claim that strong nonclassicality and entanglement persist for feasible parameters.

Significance. If the protocol is robust, the work extends cavity-magnon platforms to two-mode non-Gaussian entanglement, providing a concrete route to macroscopic quantum states with current technology. Explicit discussion of dissipation and dephasing strengthens the feasibility assessment.

major comments (1)
  1. [Abstract and hybridized-modes section] Abstract and the section on hybridized modes: the protocol requires exact equality of the two magnon frequencies and their couplings to the cavity to form clean bright/dark modes with the dark mode remaining in vacuum. No quantitative analysis (e.g., tolerance to frequency mismatch δ or coupling mismatch ε) is provided, yet any deviation mixes the modes and populates the dark mode, undermining the purity of the claimed two-mode cat state and its non-Gaussian entanglement.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback on our manuscript. We address the major comment below.

read point-by-point responses

  1. Referee: [Abstract and hybridized-modes section] Abstract and the section on hybridized modes: the protocol requires exact equality of the two magnon frequencies and their couplings to the cavity to form clean bright/dark modes with the dark mode remaining in vacuum. No quantitative analysis (e.g., tolerance to frequency mismatch δ or coupling mismatch ε) is provided, yet any deviation mixes the modes and populates the dark mode, undermining the purity of the claimed two-mode cat state and its non-Gaussian entanglement.

    Authors: We agree that the protocol as presented assumes identical magnon frequencies and cavity couplings to realize ideal bright and dark modes, and that the original manuscript does not include a quantitative analysis of deviations. In the revised manuscript we have added a new subsection in the hybridized-modes section that provides numerical results for small frequency mismatch δ and coupling mismatch ε. These results show that, within the magnon-magnon strong-coupling regime, mismatches up to approximately 5 % of the coupling strength keep the dark-mode population below a few percent and preserve a Wigner-function negativity above 0.2, indicating that substantial non-Gaussian entanglement survives. The abstract has been updated to note this robustness. revision: yes

Circularity Check

0 steps flagged

No circularity: derivation uses standard quantum-optics steps under explicit assumptions

full rationale

The protocol derives an effective magnon-qubit conditional displacement via adiabatic cavity elimination and resonant qubit drive, then invokes the magnon-magnon strong-coupling regime under the stated assumption of identical frequencies and couplings to obtain clean bright/dark hybridized modes. These steps follow directly from the Hamiltonian and standard approximations without any self-definitional reduction, fitted parameters renamed as predictions, or load-bearing self-citations. The final cat-state claim is conditional on the explicit equality assumption rather than tautological, and the paper remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Based solely on the abstract, the proposal rests on standard domain assumptions in cavity QED without explicit free parameters or new entities identified.

axioms (2)
  • domain assumption Adiabatic elimination of the cavity mode is valid when the cavity is far detuned or strongly coupled
    Invoked to achieve the effective magnon-qubit interaction.
  • domain assumption Identical magnon frequencies and couplings allow formation of bright and dark modes
    Stated as the condition for the hybridized modes and cat state preparation.

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