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Chapman & Hall/CRC eBooks

Universal quantum gates

Jean-Luc Brylinski, Ranee Kathryn Brylinski

Published Feb 14, 2002• 185 citations
Publisher

Abstract

Abstract In this paper we study universality for quantum gates acting on qudits. Qudits are states in a Hilbert space of dimension d where d can be any integer ≥ 2. We determine which 2-qudit gates V have the properties: (i) the collection of all 1-qudit gates together with V produces all n-qudit gates up to arbitrary precision, or (ii) the collection of all 1-qudit gates together with V produces all n-qudit gates exactly. We show that (i) and (ii) are equivalent conditions on V , and they hold if and only if V is not a primitive gate. Here we say V is primitive if it transforms any decomposable tensor into a decomposable tensor. We discuss some applications and also relations with work of other authors.

DOI
10.1201/9781420035377-5

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Physical Review A•May 12, 2022•11 citations
Abstract In this paper we study universality for quantum gates acting on qudits. Qudits are states in a Hilbert space of dimension d where d can be any integer ≥ 2. We determine which 2-qudit gates V have the properties: (i) the collection of all 1-qudit gates together with V produces all n-qudit gates up to arbitrary precision, or (ii) the collection of all 1-qudit gates together with V produces all n-qudit gates exactly. We show that (i) and (ii) are equivalent conditions on V , and they hold if and only if V is not a primitive gate. Here we say V is primitive if it transforms any decomposable tensor into a decomposable tensor. We discuss some applications and also relations with work of other authors.
In this paper we study universality for quantum gates acting on qudits.Qudits are states in a Hilbert space of dimension d where d can be any integer ≥ 2. We determine which 2-qudit gates V have the properties (i) the collection of all 1-qudit gates together with V produces all n-qudit gates up to arbitrary precision, or (ii) the collection of all 1-qudit gates together with V produces all n-qudit gates exactly.We show that (i) and (ii) are equivalent conditions on V , and they hold if and only if V is not a primitive gate.Here we say V is primitive if it transforms any decomposable tensor into a decomposable tensor.We discuss some applications and also relations with work of other authors.
In this paper we study universality for quantum gates acting on qudits.Qudits are states in a Hilbert space of dimension d where d is at least two. We determine which 2-qudit gates V have the properties (i) the collection of all 1-qudit gates together with V produces all n-qudit gates up to arbitrary precision, or (ii) the collection of all 1-qudit gates together with V produces all n-qudit gates exactly. We show that (i) and (ii) are equivalent conditions on V, and they hold if and only if V is not a primitive gate. Here we say V is primitive if it transforms any decomposable tensor into a decomposable tensor. We discuss some applications and also relations with work of other authors.
We describe criteria for implementation of quantum computation in qudits. A qudit is a -dimensional system whose Hilbert space is spanned by states \ensuremath{\mid}0⟩, \ensuremath{\mid}1⟩, \dots{}, . An important earlier work [] describes how to exactly simulate an arbitrary unitary on multiple qudits using a parameter family of single qudit and two qudit gates. That technique is based on the spectral decomposition of unitaries. Here we generalize this argument to show that exact universality follows given a discrete set of single qudit Hamiltonians and one two-qudit Hamiltonian. The technique is related to the -matrix decomposition of numerical linear algebra. We consider a generic physical system in which the single qudit Hamiltonians are a small collection of and . A coupling graph results taking nodes 0, \dots{}, and edges are allowed Hamiltonians. One qudit exact universality follows iff this graph is connected, and complete universality results if the two-qudit Hamiltonian is also allowed. We discuss implementation in the eight dimensional ground electronic states of and construct an optimal gate sequence using Raman laser pulses.
Quantum computing with qudits, quantum systems with d>2d > 2d>2 levels, offers a powerful extension beyond qubits, expanding the computational possibilities of quantum systems, allowing the simplification of the implementation of several algorithms and, possibly, providing a foundation for optimised error correction. In this work, we propose a novel formulation of qudit gates that is universally applicable for any number of levels ddd, without restrictions on the dimensionality. By extending the mathematical framework of quantum gates to arbitrary dimensions, we derive explicit gate operations that form a universal set for quantum computation on qudits of any size. We demonstrate the validity of our approach through the implementation of the Quantum Fourier Transform (QFT) for arbitrary ddd, verifying both the correctness and utility of our generalized gates. This novel methodology broadens the design space for quantum algorithms and fault-tolerant architectures, paving the way for advancements in qudit-based quantum computing.
We construct solutions of the Yang–Baxter equation in any dimension d≥2d\ge 2d≥2 by directly generalizing the previously found solutions for d=2d=2d=2 . We equip those solutions with unitarity and entangling properties. Being unitary, they can be turned into 222 -qudit quantum logic gates for qudit-based systems. The entangling property enables each of those solutions, together with all 111 -qudit gates, to form a universal set of quantum logic gates.
We establish a relationship between the notion of universal quantum gates and the notion of unitary ttt-designs. We show that a set of qudit gates $\mathcal{S}\ensuremath{\subset}U(d)$ is universal if and only if S\mathcal{S}S forms a $\ensuremath{\delta}$-approximate t(d)t(d)t(d)-design, where $\ensuremath{\delta}<1, t(2)=6$, and t(d)=4t(d)=4t(d)=4 for $d\ensuremath{\ge}3$. Moreover, we argue that from the application point of view sets S\mathcal{S}S with the $\ensuremath{\delta}$ close to 1 should be regarded as nonuniversal. We also provide a second, more algebraic, criterion for the universality verification. It says that $\mathcal{S}\ensuremath{\subset}U(d)$ is universal if and only if the matrices that commute with ${{U}^{\ensuremath{\bigotimes}t(d)}\ensuremath{\bigotimes}{\overline{U}}^{\ensuremath{\bigotimes}t(d)}|U\ensuremath{\in}\mathcal{S}}$ commute also with ${{U}^{\ensuremath{\bigotimes}t(d)}\ensuremath{\bigotimes}{\overline{U}}^{\ensuremath{\bigotimes}t(d)}|U\ensuremath{\in}U(d)}$, where t(2)=3t(2)=3t(2)=3, and t(d)=2t(d)=2t(d)=2 for $d\ensuremath{\ge}3$. Finally, we show that the complexity of checking this algebraic criterion scales polynomially with the dimension ddd.