Using A Dark Line In A Two-Dimensional Magneto-Optical Trap To Produce Dense Cold Atomic Cloud

We present a two-dimensional magneto-optical trap with a dark line, in which the repump light is absent, to increase the atomic density by suppressing the atomic radiation pressure. Optical depth (OD) and duty cycle are used to evaluate the system performance. We demonstrate a 100% increase in OD with the dark line, and obtain an ultrahigh OD of 264 with 10% for duty cycle. Also, with an efficient dark line region, OD could maintain above 100 with duty cycle as high as 30%. The cold atomic ensemble with an ultrahigh OD with a 10%-30% duty cycle is particularly advantageous in quantum information processing and communication.