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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.

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For questions on quantum algorithms. That is, algorithms which in theory can be executed by quantum computers, usually the computers providing 'universal' quantum computation.
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For questions regarding usage, performance, implementation, application or theory related to quantum gates
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For questions related to quantum bits, quantum systems living in a 2-dimensional Hilbert space. Consider also using the 'qubit-state' tag when relevant
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For questions about the principle and application of quantum entanglement, the phenomenon that the states of two qubits can only be described as the state of one system, to quantum computers.
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For questions about quantum information theory. In physics and computer science, quantum information is information that is held in the state of a quantum system. Quantum information is the basic ent…
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For questions related to building of quantum computers and discussion of the hardware aspects
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a collection of techniques to protect quantum information from decoherence and other quantum noise, to realise fault-tolerant quantum computation. Quantum error corre…
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to mark questions that involve a request for resources to learn about Quantum Computing or anything related to that.
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For questions on the manipulation and creation of 'qubits' and the state they represent. These actions may be either from theory or practice, use other tags to indicate this.
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For questions about using the circuit-model of quantum computing, versus, for example, the quantum annealing model or the measurement-based model. Questions which are using the circuit-model but are n…
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For questions relating to the process of assembling quantum programs that can be executed on a quantum computer.
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For questions about existing real-life 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 …
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Quantum Software Development Kit for writing quantum computing experiments, programs, and applications.
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For questions about simulating either quantum computers or simulating things on quantum computers.
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For questions related to measurement and its effects as relevant to quantum computation and quantum information
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For questions about either: comparing the performance of a quantum algorithm with a classical algorithm (or set of classical algorithms) independent of devices; or the ratio of time to solution of a …
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For questions regarding complexity analysis of quantum algorithms and comparisons with complexities of classical algorithms
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For questions about cryptography as it relates directly to quantum computing. Not for general cryptographic methods.
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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…
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For questions about the relation of Quantum Computing and Classical Computing, such as their relative performance.
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an online platform that gives the general public access to a set of IBM’s prototype quantum processors. It is an example of cloud-based quantum computing (from Wikipedia). As o…
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Refers to the state of an isolated quantum system. A quantum state provides a probability distribution for the value of each observable, i.e. for the outcome of each possible measurement on the system…
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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 …
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for questions about mathematics relevant to quantum computing and/or quantum information theory. DO NOT use this tag for general mathematics questions.
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On questions related to experiments with actual quantum computing devices and how to interpret their results. Also appropriate if the question can only be reasonable answered with an experiment (or ex…
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A quantum computing company, based in Burnaby, British Columbia, Canada, mostly known for their quantum annealing computers. An early rendition of these, D-Wave One, was the first commercially availab…
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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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For questions about the set of quantum gates that form a set of gates from which another gate can be produced; this set is analogous the classical set of universal gates (either a NOR gate or a NAND g…
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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, …
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For questions mainly related to qudits, the unit of quantum information in d-level quantum systems.
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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…
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For questions related to Controlled quantum gates. Controlled gates act on 2 or more qubits, where one or more qubits act as a control for some operation. (from Wikipedia)
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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…
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a metaheuristic for finding the global minimum of a given objective function over a given set of candidate solutions (candidate states), by a process using quantum fluctuations. (Wikipedia)
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For questions about the meaning and usage of vocabulary specific to quantum computing or quantum information
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Referring to the loss of quantum coherence, decoherence is often the result of loss of information from a system into the environment (often modelled as a heat bath).