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arXiv:2410.22423 · Physical Review Applied

Engineering propagating cat states with driven four-level systems inside a cavity

Seigo Kikura, Hayato Goto, Takao Aoki

Published Jun 20, 2025• 3 citations
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Abstract

We propose a method for generating optical cat states in propagating pulses based on cavity quantum electrodynamics (QED). This scheme uses multiple four-level systems (FLSs) inside an optical cavity as a light source. Time-modulating driving stimulates it to produce a superposition of coherent states entangled with the FLSs. The postselection of an appropriate state of the FLSs leads to a multicomponent cat state in a propagating pulse. Taking atomic decay and cavity loss into account, we optimize the cavity external coupling rate to maximize the fidelity. We find that its optimum value is formulated similarly to those of other generation methods for propagating states, suggesting a universal property of cavity-QED systems interacting with fields outside the cavity.

DOI
10.1103/d9wz-b2ph

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We propose a method for generating optical cat states in propagating pulses based on cavity quantum electrodynamics (QED). This scheme uses multiple four-level systems (FLSs) inside an optical cavity as a light source. Time-modulating driving stimulates it to produce a superposition of coherent states entangled with the FLSs. The postselection of an appropriate state of the FLSs leads to a multicomponent cat state in a propagating pulse. Taking atomic decay and cavity loss into account, we optimize the cavity external coupling rate to maximize the fidelity. We find that its optimum value is formulated similarly to those of other generation methods for propagating states, suggesting a universal property of cavity-QED systems interacting with fields outside the cavity.
Deep in the ultrastrong light-matter coupling regime, it has been predicted that the ground state of a two-level atom interacting with a cavity mode takes the form of a "virtual" Schrödinger cat entangled state between light and matter. We propose a method to convert this Schrödinger cat state from virtual to real, and back again, by driving the atom with optimally chosen pulses. Our system consists of a four-level atom, with two of these levels ultrastrongly coupled to a cavity mode. We show that the Schrödinger cat state can be converted between virtual and real by making use of either an ideal ultrafast pulse or a multi-tone π-pulse. In addition to allowing us to observe these unusual virtual states this method could also be used to generate entangled cat states on demand for quantum information processing.
We propose a scheme to engineer quantum superpositions of coherent states (``Schr\"odinger-cat states'') of propagating optical pulses. Multidimensional and multipartite cat states can be generated simply by reflecting coherent optical pulses successively from a single-atom cavity. The influences of various sources of noise, including atomic spontaneous emission and pulse-shape distortion, are characterized through detailed numerical simulation, which demonstrates the practicality of this scheme within the reach of current experimental technology.
In the context of cavity quantum electrodynamics (QED),a potential scheme is proposed to generate entangled coherent states. The scheme includes twice interactions of two-level atoms with cavities. In the first interaction,two atoms are sent into a microwave cavity with the large detuning respectively. And then the second interaction is that the two atoms enter another microwave cavity and are driven by a resonant classical field meantime. When we choose the proper interaction time and make measurement on the two atoms,the two microwave cavity mode fields are determinatively entangled. In addition,it is easy to generalize the scheme to multi-cavity and multi-atom.
Schrödinger cat states, representing coherent superpositions of macroscopically distinguishable states, are indispensable nonclassical resources for continuous-variable quantum information processing. Existing generation protocols typically rely on strong nonlinear interactions, complicated control techniques, or engineered dissipation, posing challenges for experimental implementation. Here, we propose a simple measurement-based protocol for generating Schrödinger cat states in a cavity-QED system by combining coherent driving, dispersive atom--cavity interactions, and atomic postselection. The atom--cavity interaction establishes coherent correlations between the atomic and photonic degrees of freedom, while the subsequent atomic postselection projects the cavity field onto a non-Gaussian superposition state with pronounced Wigner negativity. Numerical simulations based on the Lindblad master equation show that the generated Schrödinger cat states remain robust against moderate cavity dissipation. Our results demonstrate that conditional atomic measurements provide an effective and experimentally accessible approach for preparing nonclassical cavity states without relying on strong optical nonlinearities or engineered dissipation.
We propose a scheme to engineer Schrödinger-cat states of propagating optical pulses. Multi-dimensional and multi-partite cat states can be generated simply by reflecting coherent optical pulses successively from a single-atom cavity. The influences of various sources of noise, including the atomic spontaneous emission and the pulse shape distortion, are characterized through detailed numerical simulation, which demonstrates practicality of this scheme within the reach of current experimental technology.