Promoting quantum correlations in deterministic quantum computation with a one-qubit model via postselection

Abstract

The deterministic quantum computation with one qubit (DQC1) model is a restricted model of quantum computing able to calculate efficiently the normalized trace of a unitary matrix. In this work we analyse the quantum correlations named entanglement, Bell's nonlocality, quantum discord, and coherence generated by the DQC1 circuit considering only two qubits (auxiliary and control). For the standard DQC1 model only quantum discord and coherence appear. By introducing a filter in the circuit we purify the auxiliary qubit taking it out from the totally mixed state and consequently promoting other quantum correlations between the qubits, such as entanglement and Bell's nonlocality. Through the optimization of the purification process we conclude that even a small purification is enough to generate entanglement and Bell's nonlocality. We obtain, in average, that applying the purification process repeatedly by twelve times the auxiliary qubit becomes 99% pure. In this situation, almost maximally entangled states are achieved, which by its turn, almost maximally violate the Bell's inequality. This result suggests that with a simple modification the DQC1 model can be promoted to a universal model of quantum computing.