Schrödinger's Cat Now Lives And Dies In Two Boxes At Once

Schrödinger's Cat Now Lives And Dies In Two Boxes At Once
http://physicsworld.com/cws/article/news/2016/may/27/schroedingers-cat-lives-and-dies-in-two-boxes-at-once

"Schrödinger's cat now has a second box to play in, thanks to an international team of physicists that has created a two-mode "Schrödinger's cat state" for the first time. The experiment brings together two purely quantum properties, in that the "cat" (i.e. the photons) is simultaneously "alive and dead" (in a superposition of states) while also in two locations at once (the two boxes are entangled with one another).

The experiment is a step towards creating the larger and more sophisticated quantum states that are necessary to make quantum computing a reality. The team says that the work also demonstrates a two-logical-qubit system with in-built quantum error correction, making it a great resource for quantum metrology and quantum-communication networks.

Quantum cats

The famous Schrödinger's cat paradox, first proposed in 1935, is based on one of the most basic tenets of quantum mechanics – superposition. This arises because a microscopic particle such as a photon is considered to simultaneously be in all possible "states" (or spatial positions in this experiment) until a measurement is made and its wavefunction collapses. In the real "classical" world, however, macroscopic objects such as cats do not exist in a superposition of states. This is usually explained in terms of "decoherence", whereby a state loses its coherent quantum nature thanks to interactions with the environment. However, just where the boundary between the classical and quantum worlds lies is still a bit of a mystery.

Today, physicists can create multiparticle systems made up of many photons that are collectively in a superposition of two very different or extreme states. These are known as "Schrödinger's cat states" and are easily distinguishable from each other. These systems can be achieved in the lab using harmonic oscillators. The oscillation of a microwave field, for example, can be thought of a swinging pendulum and the two different states are equivalent to the pendulum at the far left or right of its swing. In a cat state, the pendulum is at both distinct positions at once. Such harmonic oscillators are preferable to using atoms to create the two extreme states because the two swing positions are far more distinct and are separated by a distance that can include large numbers of intermediate states.

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