A verification scheme for universal quantum computers

We present a new verification scheme for universal quantum computers that yields the number of working qubits and measures the noise expected when executing quantum circuits. It is based on detecting the standard deviation of the meta-probability distribution of output values for a single qubit probed by random quantum gates involving all the qubits of the quantum computer. This result is generated directly from the output statistics of the quantum computer and thus does not require any assistance from classical computers. With current technology quantum computers with up to 40 qubits could be tested employing this method, but in future, given faster quantum processors, it might be used to demonstrate quantum supremacy. Our results have been successfully demonstrated on a real quantum computer (IBM-Cairo).