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There are two possible outcomes for the measurement of a qubit—usually taken to have the value "0" and "1", like a bit. However, whereas the state of a bit can only be binary (either 0 or 1), the general state of a qubit according to quantum mechanics can arbitrarily be a coherent superposition of all computable states simultaneously. [2]
[1] [2] A logical qubit is a physical or abstract qubit that performs as specified in a quantum algorithm or quantum circuit [3] subject to unitary transformations, has a long enough coherence time to be usable by quantum logic gates (c.f. propagation delay for classical logic gates). [1] [4] [5]
A qubit is a two-level system, and when we measure one qubit, we can have either 1 or 0 as a result. One corresponds to odd parity, and zero corresponds to even parity. This is what a parity check is. This idea can be generalized beyond single qubits. This can be generalized beyond a single qubit and it is useful in QEC.
In general, the vector space for an n-qubit system is 2 n-dimensional, and this makes it challenging for a classical computer to simulate a quantum one: representing a 100-qubit system requires storing 2 100 classical values.
A 5-qubit code is the smallest possible code that protects a single logical qubit against single-qubit errors. A generalisation of the technique used by Steane , to develop the 7-qubit code from the classical [7, 4] Hamming code , led to the construction of an important class of codes called the CSS codes , named for their inventors: Robert ...
The Schrödinger equation describes how quantum systems that are not observed evolve over time, and is | = ^ | . When the system is in a stable environment, so it has a constant Hamiltonian, the solution to this equation is () = ^ /. [1]: 24–25 If the time is always the same it may be omitted for simplicity, and the way quantum states evolve can be described as | = | , just as in the above ...
The purpose of quantum computing focuses on building an information theory with the features of quantum mechanics: instead of encoding a binary unit of information (), which can be switched to 1 or 0, a quantum binary unit of information (qubit) can simultaneously turn to be 0 and 1 at the same time, thanks to the phenomenon called superposition.
The One Clean Qubit model of computation is performed an qubit system with one pure state and maximally mixed states. [1] This model was motivated by highly mixed states that are prevalent in Nuclear magnetic resonance quantum computers.