The utilization of atom interferometry for gyroscopes is of considerable interest because the detection of inertial rotations via the Sagnac effect has a potential
1010 greater sensitivity than optical gyroscopes. Here we analyze, in the presence of a rotation $\ensuremath{\Omega}$, phase-coherent transport of atomic matter waves in a one-dimensional chain of
N ring interferometers in which the sizes of the rings are chirped symmetrically about the center ring. The gyroscope scale factor of the area-chirped array for $N\ensuremath{\lesssim}10$ is several orders of magnitude larger than that for the unchirped array, which itself is larger than the scale factor of a Mach-Zehnder interferometer with the same enclosed area. This enhancement is achieved with total enclosed areas that are larger or smaller than that of the unchirped array by less than 25
. As such, the area chirp achieves rotation sensitivities with $N\ensuremath{\lesssim}10$ interferometers that would normally require $N\ensuremath{\gg}100$ rings of identical sizes.
Experiments in our laboratory have arrived at squeezing in a pulse-excited fiber ring. The pulse excitation suppresses stimulated Brillouin scattering, and at the low frequencies used for the measurement, which are made possible by the pump separation, guided acoustic-wave Brillouin scattering is ineffective. It is likely that large squeezing can be realized by using solitons in the same fiber-ring configuration, because solitons assure better squeezing phase profiles. These findings encouraged us to "design" a fiber gyro that performs below the standard quantum limit. It consists of two fiber-ring reflectors; the first acts as a squeezer, and the second acts as a Sagnac interferometer. We use the theory of quantization of solitons.1 The pulse injected into the first fiber ring is a sech adjusted so as to travel as a pair of countertraveling solitons in the squeezing ring.2 The ring acts like a Mach-Zehnder interferometer folded back on itself. The pump is reflected from the pump port, and the vacuum port has squeezed vacuum emerging from it. The pump is recycled in the second Sagnac ring to act as the signal for the rotation sensing. The squeezed vacuum from the first ring is injected into the vacuum port of the Sagnac interferometer. Because practical design considerations dictate fiber lengths on the order of 100 m for both rings, the nonlinearity in the Sagnac ring cannot be neglected. It produces its own squeezing but in the wrong phase for detector noise reduction. However, by proper adjustment of the squeezing in both interferometers, it is possible to counteract the harmful squeezing effect in the Sagnac interferometer and still arrive at a net reduction of the detector noise.