Superpositions of macroscopically distinct quantum states, introduced in Schrödinger's famous Gedankenexperiment, are an epitome of quantum ‘strangeness’ and a natural tool for determining the validity limits of quantum physics. The optical incarnation of Schrödinger's cat (SC)—the superposition of two opposite-amplitude coherent states—is also the backbone of continuous-variable quantum information processing. However, the existing preparation methods limit the amplitudes of the component coherent states, which curtails the state's usefulness for fundamental and practical applications. Here, we convert a pair of negative squeezed SC states of amplitude 1.15 to a single positive SC state of amplitude 1.85 with a success probability of ∼0.2. The protocol consists in bringing the initial states into interference on a beamsplitter and a subsequent heralding quadrature measurement in one of the output channels. Our technique can be realized iteratively, so arbitrarily high amplitudes can, in principle, be reached.
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We thank Y. Kurochkin and A. Turlapov for discussions. We acknowledge financial support from the Ministry of Education and Science of the Russian Federation (Agreement 14.582.21.0009, ID RFMEFI58215X0009). A.I.L. is supported by the Natural Sciences and Engineering Research Council of Canada and is a Canadian Institute for Advanced Research Fellow.
The authors declare no competing financial interests.
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Sychev, D., Ulanov, A., Pushkina, A. et al. Enlargement of optical Schrödinger's cat states. Nature Photon 11, 379–382 (2017). https://doi.org/10.1038/nphoton.2017.57
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