On Encoders For Quantum Convolutional Codes

We consider the problem of computing an encoding circuit for a quantum convolutional code given by a polynomial stabilizer matrix S(D) = (X(D) | Z(D)). We present an algorithm that is very similar to a polynomial-time algorithm for computing the Smith form of a polynomial matrix. This is a step towards the conjecture that any quantum convolutional code has an encoder with polynomially bounded depth.