Schrodinger's Cat: Two Atoms in One?

James D. Stein

Gary Taubes

Schrödinger's cat has always been an elusive beast, but physicists may have finally trapped one in the laboratory. In the great Austrian physicist's thought experiment, the fate of a cat was linked to the quantum indeterminacy of a radioactive atom—half decayed, half undecayed. The cat, as a result, was both alive and dead. Now physicists at the National Institute of Standards and Technology in Boulder, Colorado, report in this issue ( p. 1131 ) that they have created what one observer calls a “Schrödinger's kitten,” in which they excite an atom into a superposition of quantum states, then ease those two states apart so that the atom appears to be in two distinct physical locations simultaneously.

Ian Colin Percival

Jinyang Li, Selim M. Shahriar

The Schrödinger cat state protocol (SCSP) makes use of a Schrödinger cat (SC) state generated with one-axis-twist squeezing (OATS) to enhance the sensitivity. In principle, the SCSP can magnify the phase shift by a factor N, the number of atoms under interrogation, accompanied by a quantum noise amplification by a factor of root-N, enabling an atomic sensor to reach the Heisenberg limit. However, the current SCSP can reach this benchmark only if the parity of N is known, which is almost impossible for a large ensemble. The reason is the orientation of the SC state generated with the conventional OATS depends on the parity of N. In this paper, we propose a modified OATS (MOATS) operation that generates the SC state aligned in a certain direction regardless of the parity of N.

dong ZHANG

Schrödinger's Cat has acquired many descriptions and interpretations since its introduction in 1935. This paper returns to Schrödinger's original text and separates what Schrödinger explicitly constructed from what is inferred from the construction. Schrödinger specified a steel chamber, “a tiny amount” of radioactive substance, a Geiger counter, relay, hammer, poison, a one-hour interval, equal possibilities that one atom decays or none does, and “the first atomic decay” as the decisive occurrence. He then described the wave function of the entire system as containing the living and dead cat “mixed or smeared in equal parts.” However, not knowing which of two mutually exclusive states is true, or being unable to rule out either, does not imply that both are physically true. The distinction involves not only Schrödinger's Cat but also Schrödinger's YOU—the observer outside the steel chamber who lacks information. Moreover, the causal chain from atomic decay to the cat's death contains additional physical and biological conditions. The original construction should therefore distinguish the physical cat, its quantum-mechanical description, and the information available to YOU.

Peter John Bussey