In a conventional atomic interferometer employing
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to nonfederal websites. Their policies may differ from this site.

$N$ atoms, the phase sensitivity is at the standard quantum limit:$1/\sqrt{N}$ . Under usual spin squeezing, the sensitivity is increased by lowering the quantum noise. It is also possible to increase the sensitivity by leaving the quantum noise unchanged while producing phase amplification. Here we show how to increase the sensitivity, to the Heisenberg limit of$1/N$ , while increasing the quantum noise by$\sqrt{N}$ and amplifying the phase by a factor of$N$ . Because of the enhancement of the quantum noise and the large phase magnification, the effect of excess noise is highly suppressed. The protocol uses a Schrödinger cat state representing a maximally entangled superposition of two collective states of$N$ atoms. The phase magnification occurs when we use either atomic state detection or collective state detection; however, the robustness against excess noise occurs only when atomic state detection is employed. We show that for one version of the protocol, the signal amplitude is$N$ when$N$ is even, and is vanishingly small when$N$ is odd, for both types of detection. We also show how the protocol can be modified to reverse the nature of the signal for odd versus even values of$N$ . Thus, formore »