Physical and logical qubits
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In quantum computing, a qubit is a unit of information analogous to a bit (binary digit) in classical computing, but it is affected by quantum mechanical properties such as superposition and entanglement which allow qubits to be in some ways more powerful than classical bits for some tasks. Qubits are used in quantum circuits and quantum algorithms composed of quantum logic gates to solve computational problems, where they are used for input, output and intermediate computations.
A physical qubit is a physical device that behaves as a two-state quantum system, used as a component of a computer system.[1] A logical qubit is a physical or abstract qubit that performs as specified in a quantum algorithm or quantum circuit 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).[2]
As of September 2018[update], most technologies used to implement qubits face issues of stability, decoherence, fault tolerance and scalability.[3] Because of this, many physical qubits are needed for the purposes of error-correction to produce an entity which behaves logically as a single qubit would in a quantum circuit or algorithm (see: quantum error correction). Thus, contemporary logical qubits typically consist of many physical qubits to provide stability, error-correction and fault tolerance needed to perform useful computations.
The approach of topological qubits, which takes advantage of topological effects in quantum mechanics, has been proposed as needed many fewer or even a single physical qubit per logical qubit.[3] Topological qubits rely on a class of particles called anyons which have spin that is neither half-integral (fermions) nor integral (bosons), and therefore obey neither the Fermi–Dirac statistics nor the Bose–Einstein statistics of particle behavior.[4] Anyons exhibit braid symmetry in their world lines, which has desirable properties for the stability of qubits. Notably, anyons must exist in systems constrained to two spatial dimensions or fewer, according to the spin–statistics theorem, which states that in 3 or more spatial dimensions, only fermions and bosons are possible.[4]
See also
- Quantum error correction
- Quantum threshold theorem
- Quantum computing:
- Superconductive quantum computing
- Trapped-ion quantum computing
- Semiconductor quantum computing
- Topological quantum computing
References
- ^ "Achieving scalability in quantum computing". Microsoft Cloud Blogs. Microsoft. 2018-05-16. Retrieved 2018-09-18.
- ^ "LogiQ". www.iarpa.gov. Retrieved 2018-09-18.
- ^ a b Mishmash, Ryan; Alicea, Jason (2017-08-16). "Topological qubits: Arriving in 2018?". Quantum Fronteirs. Retrieved 2018-09-17.
{{cite web}}: Cite has empty unknown parameter:|dead-url=(help) - ^ a b Wilczek, Frank (2018-02-27). "How 'Anyon' Particles Emerge From Quantum Knots | Quanta Magazine". Quanta Magazine. Retrieved 2018-09-18.
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| This article, Physical and logical qubits, has recently been created via the Articles for creation process. Please check to see if the reviewer has accidentally left this template after accepting the draft and take appropriate action as necessary.
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