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Spotlight on Optics: Generation of highly pure Schrödinger's cat states and real-time quadrature measurements via optical filtering



Thomas Gerrits


Schrödinger cat states are fundamental quantum states with no classical analogues. Schrödinger Gedanken experiment of 1935 described a cat apparently held in a superposition of alive and dead states [1], but we now use Schrödinger cat to refer to a quantum state that is a superposition of two highly distinguishable classical states. Such states could be useful for quantum information processing and metrology beyond the quantum limit. Making Schrödinger cat states in travelling optical modes is especially desirable, because they can be used for quantum communication, computing and interferometry. In their experiment, Asavanant et al. demonstrate the generation of high-purity optical Schrödinger cat states in a travelling optical mode using a continuous wave (CW) squeezer and subsequent photon subtraction. The non-Gaussian operation of photon subtraction projects the squeezed vacuum into a squeezed single photon state, a close approximation to the desired optical Schrödinger cat state. High purities can be achieved with such CW sources. However, the cat state’s location in time could only be determined in post-processing until now. Asavanant et al. demonstrate CW-squeezing mode matching through optical and electrical filtering, and consequently observe a cat state in real-time without the need of post-processing. Thus, the cat state generated from the CW squeezer has a deterministic appearance in time, in principle allowing for feed-forward operation and interference on beam splitters, a necessary ingredient for continuous variable quantum computing. [1] Schrödinger, E. Die gegenwartige Situation in der Quantenmechanik. Naturwissenschaften 23, 807-812 (1935)
Optics Express


Gerrits, T. (2017), Spotlight on Optics: Generation of highly pure Schrödinger's cat states and real-time quadrature measurements via optical filtering, Optics Express, [online], (Accessed June 21, 2024)


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Created December 25, 2017, Updated November 10, 2018