5,872 research outputs found
Efficient Circuits for Quantum Walks
We present an efficient general method for realizing a quantum walk operator
corresponding to an arbitrary sparse classical random walk. Our approach is
based on Grover and Rudolph's method for preparing coherent versions of
efficiently integrable probability distributions. This method is intended for
use in quantum walk algorithms with polynomial speedups, whose complexity is
usually measured in terms of how many times we have to apply a step of a
quantum walk, compared to the number of necessary classical Markov chain steps.
We consider a finer notion of complexity including the number of elementary
gates it takes to implement each step of the quantum walk with some desired
accuracy. The difference in complexity for various implementation approaches is
that our method scales linearly in the sparsity parameter and
poly-logarithmically with the inverse of the desired precision. The best
previously known general methods either scale quadratically in the sparsity
parameter, or polynomially in the inverse precision. Our approach is especially
relevant for implementing quantum walks corresponding to classical random walks
like those used in the classical algorithms for approximating permanents and
sampling from binary contingency tables. In those algorithms, the sparsity
parameter grows with the problem size, while maintaining high precision is
required.Comment: Modified abstract, clarified conclusion, added application section in
appendix and updated reference
Efficient quantum walk on a quantum processor
The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor
One-Dimensional Lazy Quantum walk in Ternary System
Quantum walks play an important role for developing quantum algorithms and
quantum simulations. Here we present one dimensional three-state quantum
walk(lazy quantum walk) and show its equivalence for circuit realization in
ternary quantum logic for the first of its kind. Using an appropriate logical
mapping of the position space on which a walker evolves onto the multi-qutrit
states, we present efficient quantum circuits considering the nearest neighbour
position space for the implementation of lazy quantum walks in one-dimensional
position space in ternary quantum system. We also address scalability in terms
of -qutrit ternary system with example circuits for a three qutrit state
space.Comment: 13 pages, 12 figures, and 10 table
The Power Of Quantum Walk Insights, Implementation, And Applications
In this thesis, I investigate quantum walks in quantum computing from three aspects: the insights, the implementation, and the applications. Quantum walks are the quantum analogue of classical random walks. For the insights of quantum walks, I list and explain the required components for quantizing a classical random walk into a quantum walk. The components are, for instance, Markov chains, quantum phase estimation, and quantum spectrum theorem. I then demonstrate how the product of two reflections in the walk operator provides a quadratic speed-up, in comparison to the classical counterpart. For the implementation of quantum walks, I show the construction of an efficient circuit for realizing one single step of the quantum walk operator. Furthermore, I devise a more succinct circuit to approximately implement quantum phase estimation with constant precision controlled phase shift operators. From an implementation perspective, efficient circuits are always desirable because the realization of a phase shift operator with high precision would be a costly task and a critical obstacle. For the applications of quantum walks, I apply the quantum walk technique along with other fundamental quantum techniques, such as phase estimation, to solve the partition function problem. However, there might be some scenario in which the speed-up of spectral gap is insignificant. In a situation like that that, I provide an amplitude amplification-based iii approach to prepare the thermal Gibbs state. Such an approach is useful when the spectral gap is extremely small. Finally, I further investigate and explore the effect of noise (perturbation) on the performance of quantum walk
An efficient quantum circuit analyser on qubits and qudits
This paper presents a highly efficient decomposition scheme and its
associated Mathematica notebook for the analysis of complicated quantum
circuits comprised of single/multiple qubit and qudit quantum gates. In
particular, this scheme reduces the evaluation of multiple unitary gate
operations with many conditionals to just two matrix additions, regardless of
the number of conditionals or gate dimensions. This improves significantly the
capability of a quantum circuit analyser implemented in a classical computer.
This is also the first efficient quantum circuit analyser to include qudit
quantum logic gates
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