Experimental Investigation Of Quantum Discord In Deterministic Quantum Computation With One Qubit

Quantum computing has received widespread attention due to the power of surpassing classical computers on certain problems such as factoring large integers.However,it is still unclear what is responsible for the power.Quantum entanglement is a key characteristic to distinguish quantum systems from classical systems,and in the early studies,entangled states are found to play a significant role in quantum communication and quantum computing compared to non-entangled states.As a result,entanglement is considered to be a resource in quantum information and possible source of advantage in quantum computing.However,in 1998,the proposal of the deterministic quantum computation with one qubit(DQC1)algorithm broke this idea.In DQC1 algorithm,there are n qubits in the completely mixed state and one control bit with a polarization a.DQC1 algorithm can estimate the normalized trace of a unitary operator,and has an exponential speedup over classical algorithms even when entanglement is absent.The DQC1 algorithm makes people realize that there are other non-classical correlations besides quantum entanglement.Quantum discord characterizes quantum correlation which is more general than entanglement and there are various important applications of quantum discord in the fields of quantum communication,quantum information theory and quantum metrology.Quantum discord is also considered to be possible source of speedup in the DQC1 algorithm.Although DQC1 has already been realized in several physcial systems and quantum discord has been observed,it is not enough to illustrate the role of quantum discord in the DQC1 algorithm because almost all quantum states have non-zero quantum discord.Based on the electron spin resonance(ESR)technology,this article implements the DQC1 algorithm in a solid-state spin system and observes quantum discord.The experiment also investigates the relationship among quantum discord,quantum Fisher information and a.The quantum Fisher information places an upper bound on estimation precision when the DQC1 is used for parameter estimation and the polarization a is corresponding to the runs of the algorithm for a fixed accuracy of the estimation for the normalized trace.Both quantum Fisher information and a reflect the power of the algorithm.By analyzing power of the algorithm for different quantum discord,we provide further evidence for the key role of discord as a resource in DQC1 and quantum discord might be possible source of quantum advantage.