We consider deterministic and {\em randomized} quantum algorithms simulating $e^{-iHt}$ by a product of unitary operators $e^{-iA_jt_j}$, $j=1,...,N$, where $A_j\in\{H_1,...,H_m\}$, $H=\sum_{i=1}^m H_i$ and $t_j > 0$ for every $j$. Randomized algorithms are algorithms approximating the final state of the system by a mixed quantum state. First, we provide a scheme to bound the trace distance of the final quantum states of randomized algorithms. Then, we show some randomized algorithms, which have the same efficiency as certain deterministic algorithms, but are less complicated than their opponentes. Moreover, we prove that both deterministic and randomized algorithms simulating $e^{-iHt}$ with error $\e$ at least have $Ω(t^{3/2}\e^{-1/2})$ exponentials.
Randomized query complexity of sabotaged and composed functions
我们研究了有界错误随机查询复杂度的合成问题:对于所有的布尔函数f和g,R(f o g)= Omega(R(f)R(g))吗?我们表明,插入一个简单的布尔函数h,其查询复杂度只有Theta(log R(g)),在f和g之间允许我们证明R(f o h o g)= Omega(R(f)R(h)R(g))。我们证明了这一点,使用一个新的下界测量随机查询复杂性,我们称之为随机破坏复杂性,RS(f)。随机破坏复杂度具有几个期望的性质,例如完美合成定理,RS(f o g)>= RS(f)RS(g),以及具有随机查询复杂度的合成定理,R(f o g)= Omega(R(f)RS(g))。它也是全函数的二次紧下界,并且可以二次优于分区界,这是随机查询复杂度的最佳已知一般下界。使用这种技术,我们还表明提升定理的影响,通信复杂性。我们证明了零错误随机化协议的一般提升定理隐含了有界错误协议的一般提升定理。
Improved Bounds on the Randomized and Quantum Complexity of Initial-Value Problems
我们处理的问题,开始在[8],寻找随机和量子复杂性的初值问题。我们在[8]中表明,在最坏情况下的确定性复杂度上,两种设置都有可能加速。在本文中,我们证明,通过定义新的算法,可以实现进一步的改进,在上界的随机化和量子复杂性。在具有r个连续有界偏导数的右手函数的Hölder类中,其中r阶导数是指数为ρ的Hölder函数,ε-复杂度在随机设置下为O((1/ε)^{1/(r+ρ+1/3)}),在量子计算机上为O((1/ε)^{1/(r+ρ+1/2)})(直到对数因子)。这是对文献[8]结果的改进。对于一个特殊的问题,进一步讨论了复杂性上界和下界之间的差距。我们考虑标量自治问题,其目的是计算积分区间的端点处的解。对于这个问题,我们通过建立(本质上)匹配的复杂性上限和下限来填补空白。我们证明了这种情况下的复杂性在随机设置中为(1/ε)^{1/(r+ p +1/2)}阶,在量子设置中为(1/ε)^{1/(r+ p +1)}阶(再次达到对数因子)。
New upper and lower bounds for randomized and quantum Local Search
Local Search problem, which finds a local minimum of a black-box function on a given graph, is of both practical and theoretical importance to combinatorial optimization, complexity theory and many other areas in theoretical computer science. In this paper, we study the problem in the randomized and quantum query models and give new lower and upper bound techniques in both models. The lower bound technique works for any graph that contains a product graph as a subgraph. Applying it to the Boolean hypercube {0,1}^n and the constant dimensional grids [n]^d, two particular product graphs that rec…