In one-way quantum computation (1WQC) model, an initial highly entangled state called a graph state is used to perform universal quantum computations by a sequence of adaptive single-qubit measurements and post-measurement Pauli-X and Pauli-Z corrections. The needed computations are organized as measurement patterns or simply patterns in the 1WQC model. The entanglement operations in a pattern can be shown by a graph which together with the set of its input and output qubits is called the geometry of the pattern. Causal flow is a sufficient condition to identify a dependency structure for measurement sequences in order to obtain determinism. Signal shifting is an optimization technique which uses a set of rewrite rules to propagate the Pauli-Z corrections on the measured qubits to the end of patterns. However, automatically applying these rules has difficulties for implementation and is time consuming due to using many ineffective commutation rules. To overcome this problem, in this paper, a new automatic approach is proposed to perform signal shifting on patterns with flows based on their geometries instead of using rewriting rules. It is shown that the time complexity of the proposed approach is improved compared to the previous ones.
In one-way quantum computation (1WQC) model, an initial highly entangled state called a graph state is used to perform universal quantum computations by a sequence of adaptive single-qubit measurements and post-measurement Pauli-X and Pauli-Z corrections. The needed computations are organized as measurement patterns or simply patterns in the 1WQC model. The entanglement operations in a pattern can be shown by a graph which together with the set of its input and output qubits is called the geometry of the pattern. Causal flow is a sufficient condition to identify a dependency structure for measurement sequences in order to obtain determinism. Signal shifting is an optimization technique which uses a set of rewrite rules to propagate the Pauli-Z corrections on the measured qubits to the end of patterns. However, automatically applying these rules has difficulties for implementation and is time consuming due to using many ineffective commutation rules. To overcome this problem, in this paper, a new automatic approach is proposed to perform signal shifting on patterns with flows based on their geometries instead of using rewriting rules. It is shown that the time complexity of the proposed approach is improved compared to the previous ones.
In the one-way quantum computing model, the information processing is driven by measurements performed on an entangled state, called the resource state. In order to achieve parallelism, one aims to increase the number of simultaneous measurements, such that the effects of decoherence on the resource state are minimised due to the reduction of the time required to run the computation. At the heart of this question is the notion of quantum information flow, which specifies the dependency relations between the measurements in the computations. There exist two well-known techniques for reducing the time required to perform a one-way quantum computation without changing its semantics. The first one, called signal-shifting, transforms the flow of a graph (representing the resource state) within the measurement calculus formalism, whereas the second one, namely finding the maximally-delayed generalised flow, explores the geometry of the graph to increase the number of operations that can be performed simultaneously. In this paper, we show for the first time how these two techniques relate to each other. We prove that the application of the signal-shifting rules to a measurement pattern with flow results in a generalised flow for the pattern. Then, we prove that in the particular case when the input size equals the output size, the gflow obtained using signal-shifting has the lowest possible depth. As a side result, we construct an O(n3)-algorithm for finding maximally delayed gflows on graphs with flow. For those graphs, our algorithm is more efficient than the best previously known algorithm for the same task, which takes O(n4) operations to complete.
In one-way quantum computations (1WQC), quantum correlations in an entangled state, called a cluster or graph state, are exploited to perform universal quantum computations using single-qubit measurements. The choices of bases for these measurements as well as the structure of the entanglements specify a quantum algorithm. The needed computations in this model are organized as patterns. Previously, an approach to extract a 1WQC pattern from a quantum circuit was proposed. The approach takes a quantum circuit consisting of only CZ andj(oc) gates and translates it into a 1WQC pattern after performing some known optimizations. However, most quantum synthesis algorithms decompose circuits using a library containing CNOT and any single-qubit gates. In this paper, we show how this approach can be modified in a way that it can take a circuit consisting of CNOT and any single-qubit gates as well as CZ and J(oc) gates to produce a 1WQC pattern. Experimental results show that adding CNOT gate directly to the pattern decreases the translation run-time.
In the one-way model of measurement-based quantum computation (MBQC), computation proceeds via single-qubit measurements on a resource state.Flow conditions ensure that the overall computation is deterministic in a suitable sense, and are required for efficient translation into quantum circuits.Procedures that rewrite MBQC patterns -e.g. for optimisation, or adapting to hardware constraints -thus need to preserve the existence of flow.Most previous work has focused on rewrites that reduce the number of qubits in the computation, or that introduce new Pauli-measured qubits.Here, we consider the insertion of planar-measured qubits into MBQC patterns, i.e. arbitrary measurements in a plane of the Bloch sphere spanned by a pair of Pauli operators; such measurements are necessary for universal MBQC.We extend the definition of causal flow, previously restricted to XY -measurements only, to also permit Y Z-measurements and derive the conditions under which a Y Z-insertion preserves causal flow.Then we derive conditions for Y Z-insertion into patterns with gflow or Pauli flow, in which case the argument straightforwardly extends to XZ-insertions as well.We also show that the 'vertex splitting' or 'neighbour unfusion' rule previously used in the literature can be derived from Y Z-insertion and pivoting.This work contributes to understanding the broad properties of flow-preserving rewriting in MBQC and in the ZX-calculus more broadly, and it will enable more efficient optimisation, obfuscation, or routing.
The one-way model of Measurement-Based Quantum Computing and the gate-based circuit model give two different presentations of how quantum computation can be performed. There are known methods for converting any gate-based quantum circuit into a one-way computation, whereas the reverse is only efficient given some constraints on the structure of the measurement pattern. Causal flow and generalised flow have already been shown as sufficient, with efficient algorithms for identifying these properties and performing the circuit extraction. Pauli flow is a weaker set of conditions that extends generalised flow to use the knowledge that some vertices are measured in a Pauli basis. In this paper, we show that Pauli flow can similarly be identified efficiently and that any measurement pattern whose underlying graph admits a Pauli flow can be efficiently transformed into a gate-based circuit without using ancilla qubits. We then use this relationship to derive simulation results for the effects of graph-theoretic rewrites in the ZX-calculus using a more circuit-like data structure we call the Pauli Dependency DAG.
One-way quantum computation (1WQC) is a model of universal quantum computations in which a specific highly entangled state called acluster stateallows for quantum computation by single-qubit measurements. The needed computations in this model are organized as measurement patterns. The traditional approach to obtain a measurement pattern is by translating a quantum circuit that solely consists of CZ andJ(α) gates into the corresponding measurement patterns and then performing some optimizations by using techniques proposed for the 1WQC model. However, in these cases, the input of the problem is a quantum circuit, not an arbitrary unitary matrix. Therefore, in this article, we focus on the first phase—that is, decomposing a unitary matrix into CZ andJ(α) gates. Two well-known quantum circuit synthesis methods, namely cosine-sine decomposition and quantum Shannon decomposition are considered and then adapted for a library of gates containing CZ andJ(α), equipped with optimizations. By exploring the solution space of the combinations of these two methods in a bottom-up approach of dynamic programming, a multiobjective quantum circuit synthesis method is proposed that generates a set of quantum circuits. This approach attempts to simultaneously improve the measurement pattern cost metrics after the translation from this set of quantum circuits.
In one-way quantum computation (1WQC) model, universal quantum computations are performed using measurements to designated qubits in a highly entangled state. The choices of bases for these measurements as well as the structure of the entanglements specify a quantum algorithm. As scalable and reliable quantum computers have not been implemented yet, quantum computation simulators are the only widely available tools to design and test quantum algorithms. However, simulating the quantum computations on a standard classical computer in most cases requires exponential memory and time. In this paper, a general direct simulator for 1WQC, called OWQS, is presented. Some techniques such as qubit elimination, pattern reordering and implicit simulation of actions are used to considerably reduce the time and memory needed for the simulations. Moreover, our simulator is adjusted to simulate the measurement patterns with a generalized flow without calculating the measurement probabilities which is called extended one-way quantum computation simulator (EOWQS). Experimental results validate the feasibility of the proposed simulators and that OWQS and EOWQS are faster as compared with the well-known quantum circuit simulators, i.e., QuIDDPro and libquantum for simulating 1WQC model.