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Schrödinger‘s Thought Experiment

In 1935, Austrian physicist Erwin Schrödinger devised a thought experiment to capture the paradoxical nature of quantum physics. He envisioned a cat that can simultaneously be dead and alive. A research team incl. ExQM students lead by Gerhard Rempe, director at the Max Planck Institute of Quantum Optics (MPQ) in Garching has implemented an optical analogue of Schrödinger’s original idea in the laboratory. The results have versatile ap­pli­ca­tions for future quantum communication.

“Flying Optical Cats”

The analogue of Schrödinger’s thought experiment realized at the MPQ was theo­re­ti­cal­ly proposed in 2005 by the theo­re­ti­cians Wang and Duan. The cat is re­pre­sen­ted by coherent laser pulses, which may exist in a superposition of different phases. To create such a superposition, the researchers reflect a laser pulse with a well-defined phase from an optical resonator consisting of two mirrors separated by a slit of only 0.5mm. The re­son­ator contains a single trapped atom initially prepared in a super­po­si­tion of two states. In the re­flec­tion pro­cess, the laser pulse inter­acts with the atom and gets entangled with it. A sub­sequent mea­sure­ment on the atom even­tual­ly allows ge­ne­ra­ting the desired optical cat state.

Applications to Quantum Communication

The results achieved have potential ap­pli­ca­tions in future quantum networks. The experiments show that suitable mea­sure­ments on the atom allow for the generation of a whole zoo of different cat states. These states are not confined to a box as in Schrödinger’s thought experiment. As they are made of light, they can fly between the nodes of a quantum network and even transmit quantum information. Also, cat states may enable quantum error correction schemes. The researchers hope to exploit these features in future experiments.

Text: International Doctorate Program "Exploring Quantum Matter“