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arXiv:2512.22380 · Physical Review A

Creating multicomponent Schrödinger cat states in a coupled qubit-oscillator system

Pavel Stránský, Pavel Cejnar

quant-phSubmitted Dec 26, 2025• Announced Dec 30, 2025• 0 citations• Revised Mar 31, 2026 (v2)
v1 · Dec 26, 2025v2 · Mar 31, 2026
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Abstract

We present a method for preparing various exotic modifications of Schr{ö}dinger cat states by coupling a semiclassical oscillator to a system of qubits. Varying the number of qubits and parameters of the protocol (involving quantum quench of the coupled system and a subsequent spin measurement), we bring the oscillator into a coherent superposition composed of an arbitrary number of wavepackets in tunable proportions and motion relations. The method can be implemented with the aid of current experimental techniques and may find applications in quantum information and sensing protocols.

Journal reference
Phys. Rev. A 113, L040403 (2026)
DOI
10.1103/8yqc-ynp4
Comments
6 pages of the main text, 5 figures; 13 pages of the supplemental material, includes a video file as an additional supplemental material

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Inspired by recent advances in the manipulation of superconducting circuits coupled to mechanical modes in the quantum regime, we propose a protocol for generating superpositions of orthogonally squeezed states in a quantum harmonic oscillator. The protocol relies on a quadratic coupling between the oscillator and a qubit, and is conceptually similar to methods used for preparing cat states in qubit-oscillator systems. We numerically evaluate the robustness of the state-preparation scheme in the presence of decoherence, considering environmental coupling for both the harmonic oscillator and the qubit. As a potential application, we consider a quantum error-correcting code based on conditionally squeezed states and analyze its error correction properties.
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Schr\"odinger-cat states are useful for many applications, ranging from quantum-information processing to high-precision measurements. In this paper we propose a method for creating such cat states, based on photon-assisted Landau-Zener-St\"uckelberg interferometry in a hybrid system consisting of a qubit coupled to a photon cavity. We show that by initializing the qubit in one of its basis states, performing three consecutive sweeps of the qubit energy splitting across the 1-photon resonance, and finally projecting the qubit to the same basis state, the parity of the photon field can be purified to very high degree; when the initial photon state is a coherent state, the final state will then be very close to a Schr\"odinger-cat state. We present numerical simulations that confirm that our protocol could work with high fidelity ($\ensuremath{\sim}0.99$) for coherent states of reasonable size (${|\ensuremath{\alpha}|}^{2}\ensuremath{\sim}10$). Furthermore, we suggest that our protocol can also be used to transfer quantum information between the qubit and a superposition of orthogonal cat states in the cavity.