We present a novel application of the HHL (Harrow-Hassidim-Lloyd) algorithm --- a quantum algorithm solving systems of linear equations --- in solving an open problem about quantum walks, namely computing hitting (or absorption) probabilities of a general (not only Hadamard) one-dimensional quantum walks with two absorbing boundaries. This is achieved by a simple observation that the problem of computing hitting probabilities of quantum walks can be reduced to inverting a matrix. Then a quantum algorithm with the HHL algorithm as a subroutine is developed for solving the problem, which is faster than the known classical algorithms by numerical experiments.We present a novel application of the HHL (Harrow-Hassidim-Lloyd) algorithm --- a quantum algorithm solving systems of linear equations --- in solving an open problem about quantum walks, namely computing hitting (or absorption) probabilities of a general (not only Hadamard) one-dimensional quantum walks with two absorbing boundaries. This is achieved by a simple observation that the problem of computing hitting probabilities of quantum walks can be reduced to inverting a matrix. Then a quantum algorithm with the HHL algorithm as a subroutine is developed for solving the problem, which is faster than the known classical algorithms by numerical experiments.

arXiv:2009.03618Quantum Information and ComputationMar 22, 20216 citations

Improved upper bounds for the hitting times of quantum walks

Yosi Atia, Shantanav Chakraborty

Continuous-time quantum walks have proven to be an extremely useful framework for the design of several quantum algorithms. Often, the running time of quantum algorithms in this framework is characterized by the quantum hitting time: the time required by the quantum walk to find a vertex of interest with a high probability. In this article, we provide improved upper bounds for the quantum hitting time that can be applied to several continuous-time quantum walk (CTQW) based quantum algorithms. In particular, we apply our techniques to the glued-trees problem, improving their hitting time upper bound by a polynomial factor: from $O({n}^{5})$ to $O({n}^{2}logn)$ . Furthermore, our methods also help to exponentially improve the dependence on precision of the CTQW based algorithm to find a marked node on any ergodic, reversible Markov chain by Chakraborty et al. [Phys. Rev. A 102, 022227 (2020)].Continuous-time quantum walks have proven to be an extremely useful framework for the design of several quantum algorithms. Often, the running time of quantum algorithms in this framework is characterized by the quantum hitting time: the time required by the quantum walk to find a vertex of interest with a high probability. In this article, we provide improved upper bounds for the quantum hitting time that can be applied to several continuous-time quantum walk (CTQW) based quantum algorithms. In particular, we apply our techniques to the glued-trees problem, improving their hitting time upper bound by a polynomial factor: from $O({n}^{5})$ to $O({n}^{2}logn)$. Furthermore, our methods also help to exponentially improve the dependence on precision of the CTQW based algorithm to find a marked node on any ergodic, reversible Markov chain by Chakraborty et al. [Phys. Rev. A 102, 022227 (2020)].

arXiv:2005.04062Physical Review ASep 21, 20219 citations

Improved Simulation of Quantum Random Walks

Uğur Küçük, A. C. Cem Say

Lecture notes in computer scienceJan 1, 20050 citations

QUANTUM HITTING TIME ON THE COMPLETE GRAPH

Raqueline A. M. Santos, Renato Portugal

Quantum walks play an important role in the area of quantum algorithms. Many interesting problems can be reduced to searching marked states in a quantum Markov chain. In this context, the notion of quantum hitting time is very important, because it quantifies the running time of the algorithms. Markov chain-based algorithms are probabilistic, therefore the calculation of the success probability is also required in the analysis of the computational complexity. Using Szegedy's definition of quantum hitting time, which is a natural extension of the definition of the classical hitting time, we present analytical expressions for the hitting time and success probability of the quantum walk on the complete graph.Quantum walks play an important role in the area of quantum algorithms. Many interesting problems can be reduced to searching marked states in a quantum Markov chain. In this context, the notion of quantum hitting time is very important, because it quantifies the running time of the algorithms. Markov chain-based algorithms are probabilistic, therefore the calculation of the success probability is also required in the analysis of the computational complexity. Using Szegedy's definition of quantum hitting time, which is a natural extension of the definition of the classical hitting time, we present analytical expressions for the hitting time and success probability of the quantum walk on the complete graph.

arXiv:0912.1217International Journal of Quantum InformationAug 1, 201025 citations

O({n}^{5})

O({n}^{2}logn)

. Furthermore, our methods also help to exponentially improve the dependence on precision of the CTQW based algorithm to find a marked node on any ergodic, reversible Markov chain by Chakraborty et al. [Phys. Rev. A 102, 022227 (2020)].