Experimental Study Of Small-Scale Quantum Processor On The Solid-state Spin System

The rapid development of quantum information science cannot be divorced from the support of quantum mechanics theory.Unlike the classical system,the system described by quantum mechanics can show more abundant and unusual physical phenomena,contrary to intuitive experience,so it has been widely concerned.For example,compared with classical computing,the parallelism of quantum computing makes it have the property of exponential acceleration.The coherence of quantum states is an important feature that distinguishes quantum systems from classical systems.So what strange physical phenomena can these differences produce?What is the boundary between quantum mechanics description and classical mechanics description?These critical issues are worthy of our in-depth study.As one of the essential candidate systems in the physical implementation of the quantum computer,the spin system has attracted much attention.The nitrogen-vacancy(NV)center in diamond is a unique system in the solid spin system.The ground state of the NV center inherently has a spin triplet structure.It also has good spin coherence at room temperature,optical spin polarization and readout mechanism,and the ability to manipulate by microwave and radio frequency pulse.The current research topics based on the NV center system include quantum algorithms,quantum control,quantum sensing,quantum simulation,magnetic resonance spectroscopy,biophysics and biomagnetism,magnetic field imaging,magnetic navigation,paleomagnetism and dark matter detection,and so on.This paper mainly studies the difference between the quantum system and classical system based on the small-scale quantum processor and quantum control method constructed by NV center in diamond and primarily includes the following two works:1.We show an experimental study of the Leggett-Garg inequality in a three-level system using an NV center in diamond based on quantum manipulation technology.Unlike previous related studies of Leggett-Garg inequality,which are based on two-level systems,we take advantage of the three-level system with spin 1 in both the electron spin and the nuclear spin of the NV center in the diamond.In the experiment,the maximum value of Leggett-Garg inequality can reach K3exp=1.625±0.022,which exceeds the Lüders bound that the two-level system can reach.It is shown that the NV center in a diamond can be helpful for the experimental exploration of the fundamentals of quantum information physics.2.The continuous-time quantum random walk algorithm is experimentally realized through the programmable quantum control method.The programmable quantum processor based on the spin qubit of the NV center realizes the quantum random walk algorithm by changing the system parameters in the general quantum circuit.Experimental results indicate that the quantum random walk produces the oscillating behavior,which is reversible and periodic,while the classical counterpart is essentially dissipative.This work illustrates the difference between quantum random walk and classical walk and verifies the flexibility of programmable quantum control methods.In short,the research in this paper helps investigate and understand the essential difference between the classical world and the quantum world by constructing smallscale quantum processors based on solid-state spins.