We propose a new one-dimensional composite right/left-handed (CRLH) transmission line active metamaterial based upon a sub-wavelength metal waveguide loaded with quantum-cascade material that provides terahertz gain via stimulated emission. Finite element simulations were performed to design and characterize a one-dimensional CRLH metamaterial supporting Â¿backwardÂ¿ waves in the range of 1-2 THz. The addition of capacitive gaps in the top metal and inductive virtual current paths from top contact to the ground plane of a metal-metal quantum-cascade waveguide introduces propagating negative index and zero-index modes. We evaluate the feasibility of a zero-index terahertz quantum-cascade laser, based on a CRLH resonator, which exhibits a uniform spatial mode that is immune to spatial hole burning. An alternate balanced design for traveling-wave applications is also discussed.