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Applied Physics Letters

Cat-state encoding of a quantum information processor module with cavity–magnon system

Feng‐Yang Zhang, Ye‐Xiong Zeng, Qi‐Cheng Wu, Chui‐Ping Yang

Published Feb 20, 2023• 14 citations
Publisher

Abstract

We propose a scheme to realize the strong coupling between two distant magnons by using coupled cavities as a data bus. This coupling strength can be adjusted by the parameters of the system. One magnon is considered as an information processor, while the other one acts as an information memorizer. This hybrid system is applied to construct a quantum information processor module. Based on the continuous-variable encoding (cat-state encoding) of logical qubits, the information can be transferred from the processor to the memorizer via one step of the operation. This model provides a promising hardware platform for robust quantum information processing.

DOI
10.1063/5.0138391

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We propose a scheme to realize the strong coupling between two distant magnons by using coupled cavities as a data bus. This coupling strength can be adjusted by the parameters of the system. One magnon is considered as an information processor, while the other one acts as an information memorizer. This hybrid system is applied to construct a quantum information processor module. Based on the continuous-variable encoding (cat-state encoding) of logical qubits, the information can be transferred from the processor to the memorizer via one step of the operation. This model provides a promising hardware platform for robust quantum information processing.
Abstract Information transfer between different nodes, particularly parallel information transfer, is fundamental to the realization of quantum networks. In this paper, we propose a scheme for implementing a quantum information parallel transfer that utilizes multimode cat state encoding within a cavity-magnon system. The quantum information parallel transfer module consists of four cavities, each containing a YIG sphere. Our findings indicate that by adjusting the coupling strength and detuning between the magnons and the cavities, the encoded information can be transferred from one pair of cavities to another with high fidelity. The model presented in this study has the potential to serve as a framework for the development of ring networks or one-dimensional cavity chain structures.
Coherent coupling between a ferromagnetic magnon and a superconducting qubit demonstrates a special fascination in the quantum information field. Here, we construct a hybrid system to realize tunable strong coupling between a transmon and a magnon. In a hybrid system, the transmon couples to a cavity while the magnon couples to the other cavity. Meanwhile, the two cavities are coupled via a hopping interaction. In addition, we demonstrate some applications of this system to quantum information. Specifically, a high-fidelity iiiswap${}^{\ifmmode\dagger\else\textdagger\fi{}}$ gate and a maximally entangled state between the transmon and the magnon with this coupling system can be realized even if the dissipation is considered. Moreover, by employing more cavities and magnons, the WWW-type entangled state can be created with multiple transmons. This hybrid system provides an alternative platform for scalable quantum information processing.
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.
Strong long-distance spin-magnon coupling is essential for solid-state quantum information processing and single-qubit manipulation. Here, we propose an approach to realize strong spin-magnon coupling in a hybrid optomechanical cavity-spin-magnon system, where the optomechanical system, consisting of two cavities coupled to a common high-frequency mechanical resonator, acts as quantum interface. By eliminating the mechanical mode, position-position coupling and two-mode squeezing of two cavities are induced. In the squeezing representation, the spin-photon, magnon-photon, and photon-photon coupling strengths are exponentially amplified, thus lower- and upper-branch polaritons (LBP and UBP) are generated by strongly coupled squeezed modes of two cavities. Utilizing the critical property of the LBP, the coupling between the spin qubit (magnon) and LBP is greatly enhanced, while the coupling between the spin qubit (magnon) and UBP is fully suppressed. In the dispersive regime, strong and tunable spin-magnon coupling is induced by the virtual LBP, allowing quantum state exchange between them. Our proposal provides a promising platform to construct magnon-based hybrid systems and realize solid-state quantum information processing with optomechanical interfaces.
Abstract This paper presents a theoretical analysis of remote information transmission based on a cavity-magnon quantum system. We first investigate the dynamics of a two-site coupled-cavity model, where each cavity contains a magnon. Under the condition of large hopping between two cavities or large detuning between the magnon and cavity modes, the state transfer between two distant magnons could be achieved without exciting the cavity field modes. Optimal coherent state transfer is also demonstrated by carefully adjusting parameters to suppress the cavity excitations. Our model could be utilized as the building block for quantum network by extending to one-dimensional coupled cavity chains.
Bosonic quantum error correction encodes a logical qubit in an oscillator, avoiding the hardware overhead of large qubit arrays. Among such encodings, Gottesman-Kitaev-Preskill (GKP) states are paticularly powerful because their phase-space grid structure protects against small displacement errors simultaneously in both conjugate quadratures. Here we provide the first protocol for preparing magnonic GKP states, which involves an ellipsoidal magnetic crystal effectively coupled to a superconducting qubit via a microwave cavity. The geometric anisotropy intrinsically squeezes the magnon mode, while the cavity-mediated qubit control realizes an effective conditional-displacement interaction. We show that two rounds of a conditional-displacement interaction and a qubit projective measurement yield three- and four-component magnonic GKP-like states. We also show how to realize single logical qubit gate operations, such as Pauli, Hadamard and phase gates, completing the logical Pauli basis of the approximate GKP code. Our results establish hybrid magnon-qubit systems as a promising platform for preparing bosonic code states, with applications in magnonic fault-tolerant quantum computation and quantum sensing.