Superradiance as a source of collective decoherence in quantum computers

Abstract

We analyze the radiative coupling of qubits to a common radiation bath in free space and discuss that superradiance (collective emission) results in decoherence that scales with the square of the number of qubits. This decoherence mechanism is nonlocal; the collective emission simultaneously decoheres all the qubits in the computer. Because the noise source is not local, the introduced errors are outside the applicability of the threshold theorem. As a result, we argue that the errors due to superradiance cannot be corrected using the current models of fault-tolerant quantum computation.