Quantum Discord and the Power of One Qubit

TLDR

The deterministic quantum computation with one qubit (DQC1) model consists of a single pure control qubit coupled to many qubits in a completely mixed state, naturally forming a bipartite split between the control and the mixed qubits. The authors aim to use quantum discord as a figure of merit to characterize the correlations and resources present in the DQC1 computational model. They analyze the quantum discord across the control–mixed qubit split in typical DQC1 circuits to assess nonclassical correlations. They find that, although no entanglement exists between the two parts, the discord is nonzero for typical instances of the DQC1 circuit. Published in Phys.

Abstract

We use quantum discord to characterize the correlations present in the model called deterministic quantum computation with one quantum bit (DQC1), introduced by Knill and Laflamme [Phys. Rev. Lett. 81, 5672 (1998)]. The model involves a collection of qubits in the completely mixed state coupled to a single control qubit that has nonzero purity. The initial state, operations, and measurements in the model all point to a natural bipartite split between the control qubit and the mixed ones. Although there is no entanglement between these two parts, we show that the quantum discord across this split is nonzero for typical instances of the DQC1 ciruit. Nonzero values of discord indicate the presence of nonclassical correlations. We propose quantum discord as figure of merit for characterizing the resources present in this computational model.