Schrodinger’s Cat Is Alive: The Path Back to Classical Physics

Jörg Wrachtrup

Yanhua H. Shih

In quantum theory, a particle is allowed to be in a state of coherent superposition among a set of orthogonal states. A vivid picture of this concept is the “Schrödinger cat”: a cat is alive and dead simultaneously. This would be no surprise if one means a large number of an ensemble of cats with 50% alive and 50% dead. But, “Schrödinger cat” is a cat. People are talking about a cat being alive and dead simultaneously. In mathematics, the best word to characterize the relationship between states “alive” and “dead” is perhaps “orthogonal”. In quantum mechanics, the superposition of orthogonal states is used to describe the state of a quantum object, or a particle. The superposition principle is indeed a mystery compared to our everyday classical life experience. Beyond the superposition of orthogonal single-particle states, the superposition of orthogonal multi-particle states represents an even more troubling concept in classical theory.

Gregory R. Mulhauser

Ken Krechmer

E. Schrödinger proposed a thought experiment to illustrate the discontinuity, not fully understood, that appears in quantum mechanics when a measurement process occurs. The cats in his thought experiment appear to be both alive and dead. This unreasonable appearance has not been satisfactorily explained before. Calibration, which is required in metrology, is not treated in physics theory. This paper illustrates how calibration to a non-local time standard explains the alive and dead appearance of Schrödinger's cats.

Jeffrey Bub

Ian S. Osborne

Quantum Physics The story of Schrodinger's cat being hidden away in a box and being both dead and alive is often invoked to illustrate the how peculiar the quantum world can be. On a twist of the dead/alive behavior, Wang et al. now show that the cat can be in two separate locations at the same time. Constructing their cat from coherent microwave photons, they show that the state of the “electromagnetic cat” can be shared by two separated cavities. Going beyond common-sense absurdities of the classical world, the ability to share quantum states in different locations could be a powerful resource for quantum information processing. Science , this issue p. [1087][1] [1]: /lookup/doi/10.1126/science.aaf2941