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International Conference on Quantum Information

Detecting “Schrödinger’s Cat” States of Light: Insights from the Retrodictive Approach

Taoufik Amri, Julien Laurat, Claude Fabre

Published Jan 1, 2011• 1 citation
Publisher

Abstract

We show how the retrodictive approach of quantum physics allows to study detectors of strongly non-classical states of light, such as “Schrödinger’s Cat” states of light, which can be useful for quantum metrology.
DOI
10.1364/icqi.2011.qtue6

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Using the retrodictive approach of quantum physics, we show that the state retrodicted from the response of a measurement apparatus is a convenient tool to fully characterize its quantum properties. We translate in terms of this state some interesting aspects of the quantum behavior of a detector, such as the nonclassicality or the non-gaussian character of its measurements. We also introduce estimators--the projectivity, the ideality, the fidelity, or the detectivity of measurements performed by the apparatus--which directly follow from the retrodictive approach. Beyond their fundamental significance for describing general quantum measurements, these properties are crucial in several protocols, in particular, in the conditional preparation of nonclassical states of light or in measurement-driven quantum information processing.
While the interface between strong-field physics and quantum optics offers a unique regime for combining extreme nonlinearity with quantum optical resources, its potential for generating non-classical states of light remains largely unexplored. Standard protocols for generating optical Schrödinger cat states, such as photon subtraction from squeezed light, are inherently limited in the achievable macroscopicity of the state and its scalability. In this work, we bridge this gap by demonstrating that above-threshold ionization driven by bright squeezed light provides a strong-field analogue of photon subtraction, where photoelectron detection acts as a high-intensity heralding mechanism, enabling the generation of large amplitude optical Schrödinger cat states. We characterize the resulting non-Gaussian features and show that they can be tuned via the detected photoelectron momentum, and study their robustness against the experimental imperfections arising from finite momentum resolution at the heralding step. Despite the noise, we show that the generated states can be manipulated to violate a Bell inequality, thereby highlighting their potential for foundational and practical applications. Our results establish strong-field processes as a scalable platform for macroscopic quantum state engineering, opening a route to quantum optics in previously inaccessible regimes.