Physics:Quantum Qubit: Difference between revisions
Normalize Book I Quantum page structure |
Normalize Quantum book page structure and short text |
||
| Line 111: | Line 111: | ||
* enables superposition and interference | * enables superposition and interference | ||
* forms the foundation of quantum computation and communication | * forms the foundation of quantum computation and communication | ||
== Description == | |||
'''Qubit''' is a matter-scale concept used to organize how quantum theory describes atoms, particles, fields, condensed matter, plasma, or spacetime-related systems. In the Quantum Collection it is placed by scale so the reader can move from materials and molecules down to subatomic degrees of freedom. | |||
== Quantum context == | |||
At this scale, the relevant behavior is controlled by quantized states, interactions, conservation laws, and the way excitations or particles are observed. The concept is normally linked to measurable properties such as energy, momentum, charge, spin, spectra, scattering rates, or collective modes. | |||
== Role in the collection == | |||
This page provides a compact reference point for related pages in Book II. It should be read together with nearby matter-scale topics and the corresponding foundations in [[Physics:Quantum mechanics|quantum mechanics]].<ref name="matter-wiki">{{cite web |url=https://en.wikipedia.org/wiki/Quantum_mechanics |title=Quantum mechanics |website=Wikipedia |access-date=2026-05-20}}</ref> | |||
=See also= | =See also= | ||
Revision as of 23:06, 19 May 2026
A qubit (quantum bit) is the fundamental unit of quantum information. It is realized by a two-level quantum system and forms the quantum analogue of the classical bit.[1]
Definition
A qubit is described by a state vector in a two-dimensional complex Hilbert space with orthonormal basis states and .[2][3]
A general qubit state is
where satisfy the normalization condition
The coefficients and are probability amplitudes.[4]
Comparison with a classical bit
A classical bit can take only one of two values, 0 or 1. A qubit, however, can exist in a coherent superposition of both basis states.[1]
Upon measurement:
- is obtained with probability
- is obtained with probability
Unlike a classical bit, measurement generally disturbs the qubit state and destroys quantum coherence.[1]
Bloch sphere representation
Any pure qubit state can be written as
This allows a geometric representation on the Bloch sphere, where and specify the state.[1]
Pure states lie on the surface of the Bloch sphere, while the global phase has no observable physical effect.[1]
Mixed states
A qubit may also be in a mixed state, described by a density matrix
Mixed states arise from statistical uncertainty or from interaction with an environment, and correspond to points inside the Bloch sphere.[1]
Quantum operations
Quantum states evolve according to unitary transformations:
where is a unitary operator.[1]
In quantum computing, these transformations are implemented as quantum gates. Examples include:
- Pauli gates ()
- Hadamard gate
- Controlled-NOT (CNOT) gate
These operations enable interference, superposition control, and the creation of entanglement.
Physical realizations
Qubits can be implemented in various physical systems, including:
- electron spin
- photon polarization
- trapped ions
- superconducting circuits
- quantum dots
Different implementations are used depending on the application in quantum computing, communication, or sensing.[1][5]
Quantum registers
A collection of qubits forms a quantum register. For qubits, the state space has dimension , allowing complex superpositions and correlations.[2]
Physical significance
The qubit:
- is the basic carrier of quantum information
- enables superposition and interference
- forms the foundation of quantum computation and communication
Description
Qubit is a matter-scale concept used to organize how quantum theory describes atoms, particles, fields, condensed matter, plasma, or spacetime-related systems. In the Quantum Collection it is placed by scale so the reader can move from materials and molecules down to subatomic degrees of freedom.
Quantum context
At this scale, the relevant behavior is controlled by quantized states, interactions, conservation laws, and the way excitations or particles are observed. The concept is normally linked to measurable properties such as energy, momentum, charge, spin, spectra, scattering rates, or collective modes.
Role in the collection
This page provides a compact reference point for related pages in Book II. It should be read together with nearby matter-scale topics and the corresponding foundations in quantum mechanics.[6]
See also
Table of contents (217 articles)
Index
Full contents
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Nielsen, Michael A.; Chuang, Isaac L. (2010). Quantum Computation and Quantum Information. Cambridge University Press. ISBN 978-1-107-00217-3.
- ↑ 2.0 2.1 Yanofsky, Noson S.; Mannucci, Mirco A. (2013). Quantum Computing for Computer Scientists. Cambridge University Press. pp. 138–144. ISBN 978-0-521-87996-5.
- ↑ Seskir, Zeki C.; Migdał, Piotr; Weidner, Carrie; Anupam, Aditya; Case, Nicky; Davis, Noah; Decaroli, Chiara; Ercan, İlke et al. (2022). "Quantum games and interactive tools for quantum technologies outreach and education". Optical Engineering 61 (8). doi:10.1117/1.OE.61.8.081809. Bibcode: 2022OptEn..61h1809S.
- ↑ Williams, Colin P. (2011). Explorations in Quantum Computing. Springer. pp. 9–13. ISBN 978-1-84628-887-6.
- ↑ Preskill, John (1998). Lecture Notes for Physics 229: Quantum Information and Computation.
- ↑ "Quantum mechanics". https://en.wikipedia.org/wiki/Quantum_mechanics.
Source attribution: Physics:Quantum Qubit
