Optical Multiplexing of Metrological Time and Frequency Signals in a Single 100-GHz-Grid Optical Channel.

In this article, the concept of co-locating all metrological time and frequency signals in a single optical channel of a standard, 100-GHz-spaced optical grid is presented and evaluated. The solution is intended for situations where only a narrow optical bandwidth is available in a fiber heavily loaded with standard data traffic. We localized the optical reference signals in the middle of the channel, with signals related to RF reference and time tags shifted ±12.5 GHz apart. In the experimental evaluation with a 260-km-long fiber, we demonstrate that the stability of frequency signals and the calibration of time tags remained at the very same level of stability and accuracy as for systems utilizing separate channels: the fractional long-term instability for the optical frequency reference was below 5 ×10-20 , that for the RF reference at the level of 10-17, and the mismatch of the time tag calibration was not more than 10 ps. We also identify possible issues, mainly related to a risk of unwanted Brillouin amplification and scattering.

Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables.

Detecting ocean-floor seismic activity is crucial for our understanding of the interior structure and dynamic behavior of Earth. However, 70% of the planet's surface is covered by water, and seismometer coverage is limited to a handful of permanent ocean bottom stations. We show that existing telecommunication optical fiber cables can detect seismic events when combined with state-of-the-art frequency metrology techniques by using the fiber itself as the sensing element. We detected earthquakes over terrestrial and submarine links with lengths ranging from 75 to 535 kilometers and a geographical distance from the earthquake's epicenter ranging from 25 to 18,500 kilometers. Implementing a global seismic network for real-time detection of underwater earthquakes requires applying the proposed technique to the existing extensive submarine optical fiber network.

Observation of Two-Dimensional Localized Jones-Roberts Solitons in Bose-Einstein Condensates.

Jones-Roberts solitons are the only known class of stable dark solitonic solutions of the nonlinear Schrödinger equation in two and three dimensions. They feature a distinctive elongated elliptical shape that allows them to travel without change of form. By imprinting a triangular phase pattern, we experimentally generate two-dimensional Jones-Roberts solitons in a three-dimensional atomic Bose-Einstein condensate. We monitor their dynamics, observing that this kind of soliton is indeed not affected by dynamic (snaking) or thermodynamic instabilities, that instead make other classes of dark solitons unstable in dimensions higher than one. Our results confirm the prediction that Jones-Roberts solitons are stable solutions of the nonlinear Schrödinger equation and promote them for applications beyond matter wave physics, like energy and information transport in noisy and inhomogeneous environments.

Spontaneous pattern formation in an antiferromagnetic quantum gas.

In this Letter we report on the spontaneous formation of surprisingly regular periodic magnetic patterns in an antiferromagnetic Bose-Einstein condensate (BEC). The structures evolve within a quasi-one-dimensional BEC of 87Rb atoms on length scales of a millimeter with typical periodicities of 20…30 µm, given by the spin healing length. We observe two sets of characteristic patterns which can be controlled by an external magnetic field. We identify these patterns as linearly unstable modes within a mean-field approach and calculate their mode structure as well as time and energy scales, which we find to be in good agreement with observations. These investigations open new prospects for controlled studies of symmetry breaking and complex quantum magnetism in bulk BEC.