Spontaneous pattern formation in a driven atomic cloud at ultracold temperatures of 10nK or less. By fast modulation of an external magnetic field, we can modulate the interaction strength between atoms from repulsive to attractive to generate density wave patterns which are spontaneously formed in an initially uniform sample. Different density wave patterns can be generated by changing the modulation scheme. This work is a demonstration of quantum simulation of 2D matter in a laboratory using ultracold gases. Contributors: Zhendong Zhang, Kai-Xuan Yao, Lei Feng, Jiazhong Hu, Shu Nagata, Cheng Chin