A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

For questions regarding usage, performance, implementation, application or theory related to quantum gates.
For questions relating writing code to be executed on a quantum computer. For questions using or about a specific programming language, consider using also a more specific tag.
Quantum Software Development Kit for writing quantum computing experiments, programs, and applications. If appropriate, also use the [programming] tag.
Quantum systems can mathematically be described by their 'quantum state'. When the system is closed/isolated, the state is 'pure' and can be written as a sum (i.e. 'superposition') of basis vectors. W…
For questions on quantum algorithms. That is, algorithms which in theory can be executed by quantum computers, usually the computers providing 'universal' quantum computation.
For questions about the construction of complex circuits using elementary quantum gates.
for questions about IBM's Quantum Service - Circuit Composer & Quantum Lab. DO NOT use this for questions about general Qiskit issues. As of August 2020, there are 20 processors on th…
For questions about the principle and application of quantum entanglement. It is a physical phenomenon which occurs when pairs or groups of particles are generated, interact, or share spatial proximit…
for questions about mathematics relevant to quantum computing and/or quantum information theory. DO NOT use this tag for general mathematics questions.
For questions related to measurement and its effects as relevant to quantum computation and quantum information.
a collection of techniques to protect quantum information from decoherence and other quantum noise, to realise fault-tolerant quantum computation. Quantum error corre…
currently in the middle of removing this tag, so please don't use it! For questions about the quantum analogues of concepts in information theory, please use the information-theory tag.
182 questions
an algorithm that can perform a search in the order of square root of the input size. This is a provable speed up over the best classical algorithm, which requires a time …
For questions that involve a request for resources to learn anything related to quantum computing or quantum information.
150 questions
For questions about simulating either quantum computers or simulating things on quantum computers.
142 questions
For questions about practical computers or processors that run on a quantum architecture. This is for questions about the machines themselves, not just any computing that could take place on one. You …
a matrix that can be used to describe a quantum system in a mixed state, a statistical ensemble of several quantum states. This should be contrasted with a single state vector that…
For questions about completely positive (CP) linear maps between quantum states. Can also be used for trace-preserving CP maps (quantum channels). For questions about unitary operations, please use qu…
Applies to questions of primarily educational value - styled in the format similar to that found in textbook exercises. This tag should be applied to questions that are (1) stated in the form of an ex…
For questions regarding complexity analysis of quantum algorithms and comparisons with complexities of classical algorithms.
128 questions
For questions about exercises or passages from the popular quantum computing textbook *Quantum Computation and Quantum Information* by Michael Nielsen and Isaac Chuang.
a domain-specific programming language used to express quantum algorithms. This tag should be used for questions related to creating/programming quantum algorithms using the 'Q#' language. If th…
115 questions
For questions about finding (short) gate sequences to implement a specific unitary operation, for example decomposing a complicated multi-qubit gate into a sequence of basic gates. It might apply to o…
106 questions
a class of algorithms that, given a Hermitian matrix A, output a quantum circuit implementing an approximation to the unitary exp[iAt].
For questions related to physical realizations of quantum bits i.e. quantum systems living in a 2-dimensional Hilbert space.
89 questions
For questions about matrix representations of quantum gates.
85 questions
For questions related to building of quantum computers and discussion of the hardware aspects.
81 questions
For questions about the relation between quantum computing and classical computing, such as their relative performance.
81 questions
For questions about different types of noise a quantum computer (or qubits) may experience; how this affects the outcome of the computation; how to reduce a specific type of noise on a specific implem…
79 questions
A python framework for creating, editing, and invoking Noisy Intermediate Scale Quantum (NISQ) circuits. It is a Python library for writing, manipulating, and optimizing quantum circuits and running t…
78 questions
For questions related to the Bloch sphere. In quantum mechanics, the Bloch sphere is a geometrical representation of the pure state space of a two-level quantum mechanical system (qubit), named after …
75 questions
For questions about Pauli matrices in general or Pauli gates in particular, as relevant to quantum computing and/or quantum information theory. The Pauli matrices are a set of three 2 × 2 complex matr…
For questions about cryptography as it relates directly to quantum computing. Not for general cryptographic methods.
74 questions
For questions about how quantum computing could improve or affect machine learning i.e. quantum machine learning. Questions about classical machine learning belong on another site, such as Stack Overf…
72 questions
Shor's algorithm, named after American mathematician Peter Shor, is a quantum algorithm for integer factorization, formulated in 1994. Informally, it solves the following problem: given an integer N, …
71 questions
For questions related to the quantum algorithm for inverting linear systems of equations, developed by Harrow, Hassidim and Lloyd in 2009.
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