title: A quantum algorithm for obtaining the energy spectrum of a physical system without guessing its eigenstates.
abstract: We present a quantum algorithm that provides a general approach for obtaining the energy spectrum of a physical system without making a guess on its eigenstates. In this algorithm, a probe qubit is coupled to a quantum register R which consists of one ancilla qubit and an n-qubit register that represents the system. R is prepared in a general reference state, and a general excitation operator that acts on R is constructed. The probe exhibits a dynamical response only when it is resonant with a transition from the reference state to an excited state of R which contains the eigenstates of the system. By varying the probe's frequency, the energy spectrum and the eigenstates of the system can be obtained.
authors: Department of Applied Physics, Xian Jiaotong University, Xi'an 710049, China. wanghf@mail.xjtu.edu.cn.
authors: Hefeng
authors: H
authors: Wang