Quantum register

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In quantum computing, a quantum register is a system comprising multiple qubits[1]. It is the quantum analog of the classical processor register. Quantum computers perform calculations by manipulating qubits within a quantum register.


An size quantum register is a quantum system comprising qubits.

The Hilbert space, , in which the data stored in a quantum register is given by .[2]

Quantum vs. Classical Register[edit]

First, there's a conceptual difference between the quantum and classical register. An size classical register refers to an array of flip flops. An size quantum register is merely a collection of qubits.

Moreover, while an size classical register is able to store a single value of the possibilities spanned by classical pure bits, a quantum register is able to store all possibilities spanned by quantum pure qubits in the same time.

For example, consider a 2-bit-wide register. A classical register is able to store only one of the possible values represented by 2 bits - accordingly.

If we consider 2 pure qubits in superpositions and , using the quantum register definition it follows that it is capable of storing all the possible values spanned by two qubits simultaneously.


  1. ^ Ekert, Artur; Hayden, Patrick; Inamori, Hitoshi (2008). "Basic concepts in quantum computation". arXiv:quant-ph/0011013.
  2. ^ Major, Günther W., V.N. Gheorghe, F.G. (2009). Charged particle traps II : applications. Berlin: Springer. p. 220. ISBN 978-3540922605.