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arXiv:2609.27983

Optical Schrödinger cat states generated using cavity Rydberg quantum photonics

Hendrik Hegels, Mae Eichenberger, Gerhard Rempe, Stephan Dürr

quant-phSubmitted Sep 23, 2026• Announced Sep 24, 2026• 0 citations
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Abstract

We introduce cavity Rydberg quantum photonics as a novel platform for generating hybrid entangled states of optical photons. The system achieves world-record sizes of these states and has the potential to produce yet larger states in the future. In the hybrid entangled state produced here, a superposition of two coherent states is entangled with a polarization qubit carried by a photon in another beam path. We perform quantum state tomography of this hybrid entangled state and evaluate various key properties. By optimizing the decoherence we increase the size compared to previous hybrid entangled states, reaching a size of $α^2= 2.4$. Besides the fundamental interest in Schrödinger cat states, this work is interesting because of potential applications in the field of quantum information processing.

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We introduce cavity Rydberg quantum photonics as a novel platform for generating hybrid entangled states of optical photons. The system achieves world-record sizes of these states and has the potential to produce yet larger states in the future. In the hybrid entangled state produced here, a superposition of two coherent states is entangled with a polarization qubit carried by a photon in another beam path. We perform quantum state tomography of this hybrid entangled state and evaluate various key properties. By optimizing the decoherence we increase the size compared to previous hybrid entangled states, reaching a size of α2=2.4α^2= 2.4α2=2.4. Besides the fundamental interest in Schrödinger cat states, this work is interesting because of potential applications in the field of quantum information processing.
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.
Schrödinger's cat originates from the famous thought experiment querying the counterintuitive quantum superposition of macroscopic objects. As a natural extension, several "cats" (quasi-classical objects) can be prepared into coherent quantum superposition states, which is known as multipartite cat states demonstrating quantum entanglement among macroscopically distinct objects. Here, we present a highly scalable approach to deterministically create flying multipartite Schrödinger's cat states by reflecting coherent-state photons from a microwave cavity containing a superconducting qubit. We perform full quantum state tomography on the cat states with up to four photonic modes and confirm the existence of quantum entanglement among them. We also witness the hybrid entanglement between discrete-variable states (the qubit) and continuous-variable states (the flying multipartite cat) through a joint quantum state tomography. Our work provides an enabling step for implementing a series of quantum metrology and quantum information processing protocols based on cat states.
Schrödinger cat states, consisting of superpositions of macroscopically distinct states, provide key resources for a large number of emerging quantum technologies in quantum information processing. Here we propose how to generate and manipulate mechanical and optical Schrödinger cat states with distinguishable superposition components by exploiting the unique properties of cavity optomechanical systems based on Bose-Einstein condensate. Specifically, we show that in comparison with its solid-state counterparts, almost a 3 order of magnitude enhancement in the size of the mechanical Schrödinger cat state could be achieved, characterizing a much smaller overlap between its two superposed coherent-state components. By exploiting this generated cat state, we further show how to engineer the quadrature squeezing of the mechanical mode. Besides, we also provide an efficient method to create multicomponent optical Schrödinger cat states in our proposed scheme. Our work opens up a new way to achieve nonclassical states of massive objects, facilitating the development of fault-tolerant quantum processors and sensors.
In cavity-quantum-electrodynamics experiments, two-level Rydberg atoms and single-photon microwave fields can be seen as qubits. Quantum gates based on resonant and dispersive atom-field effects have been realized, which implement various kinds of conditional dynamics between these qubits. We have also studied the interaction between a single atom and coherent fields stored in the cavity. By progressively increasing the number of photons in these fields, we have explored various aspects of the quantum-classical boundary. We have realized a complementarity experiment demonstrating the continuous evolution of an apparatus from a quantum to a classical behaviour. We have also prepared 'Schrödinger-cat'-like states of the field made of a few photons, and observed their decoherence. We present a brief review of these experiments along with a proposal to study larger systems, i.e. coherent fields with more photons. Fundamental limits to the size of mesoscopic superpositions of field states in a cavity will be briefly discussed.
Abstract Schrödinger’s cat paradox has revealed the entanglement between microscopic and macroscopic objects. Recently, several approaches have been proposed to generate such hybrid entangled state. In this paper, we demonstrate the generation of generalized hybrid entangled state in a cavity electro–optic system. The hybrid entangled state between the optical cavity and the microwave field is generated by a one-step evolution. Numerical simulations show that the high-fidelity entangled state is obtained even if the decay of the system is considered. Also, this proposal can be applied to generate macroscopic quantum superposition states of the microwave field.
Higher-generation Schrödinger cat states of the quantized electromagnetic field can be produced in a high-Q cavity, starting from a coherent state, through the passage of prepared Rydberg atoms interacting dispersively across it. These states are natural generalizations of the even and odd coherent states, the N th-generations corresponding to specific superpositions of 2 N states on a circle in phase space with well defined parity, and present very peculiar properties. Their photon statistics interchange between super- and sub-Poissonian behaviours and the nature of the photon bunching oscillates as the field intensity in the cavity is varied. For higher-generation even states, the minimum value of the Mandel factor almost reaches −1.0 and the state represents the Fock state |2 N ). Squeezing properties and the Wigner function of these higher-generation Schrödinger cat states are also considered.