A method to digitally simulate an evolving quantum state of a qubit register of a quantum computer is enacted in a computer system. The quantum state is represented as an array of complex-valued amplitudes, where each amplitude is associated with an individual qubit of the qubit register, and where the quantum state is separable as a product of the individual quantum states of each qubit. One or more quantum-program instructions corresponding to a quantum circuit are received, and the amplitudes of the array are adjusted to reflect a change in the quantum state pursuant to execution of the quantum circuit, the change preserving the separability of the quantum state as a product of individual quantum states of each qubit. One or more of the adjusted amplitudes are then outputted computationally, in such form as to be receivable as input to a computer program.