Exact Equivalence between Quantum Adiabatic Algorithm and Quantum Circuit Algorithm

We present a rigorous proof that quantum circuit algorithm can be transformed into quantum adiabatic algorithm with the exact same time complexity. This means that from a quantum circuit algorithm of L gates we can construct a quantum adiabatic algorithm with time complexity of O(L). Additionally, our construction shows that one may exponentially speed up some quantum adiabatic algorithms by properly choosing an evolution path.     

Quantum algorithm for a set of quantum 2SAT problems

We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability(Q2SAT)problem,which is a generalization of 2-satisfiability(2SAT)problem.For a Q2SAT problem,we construct the Hamiltonian which is similar to that of a Heisenberg chain.All the solutions of the given Q2SAT problem span the subspace of the degenerate ground states.The Hamiltonian is adiabatically evolved so that the system stays in the degenerate subspace.Our numerical results suggest that the time complexity of our algorithm is O(n^3.9)for yielding non-trivial solutions for problems with the number of clauses m=dn(n-1)/2(d■0.1).We discuss the advantages of our algorithm over the known quantum and classical algorithms.     

绝热演化中一般量子态的几何相位

在绝热演化中的几何相位（即Berry相位）被推广到包括非本征态的一般量子态.这个新的几何相位同时适用于线性量子系统和非线性量子系统.它对于后者尤其重要因为非线性量子系统的绝热演化不能通过本征态的线性叠加来描述.在线性量子系统中,新定义的几何相位是各个本征态Berry相位的权重平均.     

埃弗里特和他的多世界理论

根据多世界理论,宇宙是由无数个平行世界构成的,宇宙中的所有物体无论大小都由波函数描述。     

非线性朗道-基纳隧穿

介绍一种新的量子隧穿———非线性朗道-基纳隧穿.这种隧穿一般发生在有相互作用的二能级系统中,比如光晶格中的玻色-爱因斯坦凝聚物和分子磁体.相对于传统的线性朗道-基纳隧穿,非线性朗道-基纳隧穿由排斥相互作用带来的非线性会增强隧穿的概率.特别是当非线性非常强时,系统的绝热性会遭到破坏;一个无穷小的线性驱动都会造成有限的隧穿概率.     

Matter wave interference of dilute Bose gases in the critical regime

Ultra-cold atomic gases provide a new chance to study the universal critical behavior of phase transition. We study theoretically the matter wave interference for ultra-cold Bose gases in the critical regime. We demonstrate that the interference in the momentum distribution can be used to extract the correlation in the Bose gas. A simple relation between the interference visibility and the correlation length is found and used to interpret the pioneering experiment about the critical behavior of dilute Bose gases [Science 315 1556(2007)]. Our theory paves the way to experimentally study various types of ultra-cold atomic gases with the means of matter wave interference.     

Majorana modes in solid state systems and its dynamics

We review the properties of Majorana fermions in particle physics and point out that Majorana modes in solid state systems are significantly different. The key reason is the concept of anti-particle in solid state systems is different from its counterpart in particle physics. We define Majorana modes as the eigenstates of Majorana operators and find that they can exist both at edges and in the bulk. According to our definition, only one single Majorana mode can exist in a system no matter at edges or in the bulk. Kitaev’s spinless p-wave superconductor is used to illustrate our results and the dynamical behavior of the Majorana modes.     

Logarithmic Quantum Time Crystal

We investigate a time-independent many-boson system, whose ground states are quasi-degenerate and become infinitely degenerate in the thermodynamic limit. Out of these quasi-degenerate ground states we construct a quantum state that evolves in time with a period that is logarithmically proportional to the number of particles,that is, T ～ log N. This boson system in such a state is a quantum time crystal as it approaches the ground state in the thermodynamic limit. The logarithmic dependence of i...     

凝聚态理论和材料计算研究进展

文章介绍了中国科学院物理研究所凝聚态理论与材料计算实验室的历史渊源和发展现状,重点介绍了该室研究人员自2001年以来在表面与半导体物理、强关联物理、自旋与轨道电子学、 冷原子与玻色-爱因斯坦凝聚体、固体物理中的贝里相位效应、低维量子输运与量子信息等方向所做的研究工作.     

Resonant Quantum Search with Monitor Qubits

We present an algorithm for the generalized search problem(searching6)marked items amongitems)based on a continuous Hamiltonian and exploiting resonance.This resonant algorithm has the same time complexity■as the Grover algorithm.A natural extension of the algorithm,incorporating auxiliary"mon√itor"qubits,can determine6)precisely,if it is unknown.The time complexity of our counting algorithm is■,similar to the best quantum approximate counting algorithm,or better,given appropriate physical resou...