The current state of quantum computing is referred to as the noisy intermediate-scale quantum (NISQ) era,
characterized by
quantum processors containing 50-100
qubit
In quantum computing, a qubit () or quantum bit is a basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device. A qubit is a two-state (or two-level) quantum-mechanical system, ...
s which are not yet advanced enough for
fault-tolerance
Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
or large enough to achieve
quantum supremacy
In quantum computing, quantum supremacy or quantum advantage is the goal of demonstrating that a programmable quantum device can solve a problem that no classical computer can solve in any feasible amount of time (irrespective of the usefulness of ...
.
These processors, which are sensitive to their environment (noisy) and prone to
quantum decoherence, are not yet capable of continuous
quantum error correction
Quantum error correction (QEC) is used in quantum computing to protect quantum information from errors due to decoherence and other quantum noise. Quantum error correction is theorised as essential to achieve fault tolerant quantum computing tha ...
. This intermediate-scale is defined by the
quantum volume
Quantum volume is a metric that measures the capabilities and error rates of a quantum computer. It expresses the maximum size of square quantum circuits that can be implemented successfully by the computer. The form of the circuits is independent ...
, which is based on the moderate number of qubits and
gate
A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include '' yett and port''. The concept originally referred to the gap or hole in the wal ...
fidelity. The term NISQ was coined by
John Preskill
John Phillip Preskill (born January 19, 1953) is an American theoretical physicist and the Richard P. Feynman Professor of Theoretical Physics at the California Institute of Technology, where he is also the Director of the Institute for Quantum In ...
in 2018.
Algorithms
NISQ algorithms are designed for quantum processors in the NISQ era, such as the
variational quantum eigensolver In quantum computing, the variational quantum eigensolver (VQE) is a quantum algorithm for quantum chemistry, quantum simulations and optimization problems. It is a hybrid algorithm that uses both classical computers and quantum computers to find t ...
(VQE) and
quantum approximate optimization algorithm
Quantum optimization algorithms are quantum algorithms that are used to solve optimization problems. Mathematical optimization deals with finding the best solution to a problem (according to some criteria) from a set of possible solutions. Mostly ...
(QAOA), which use NISQ devices but offload some calculations to classical processors.
These algorithms have been successful in
quantum chemistry
Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contribution ...
and have potential applications in various fields including physics, material science, data science, cryptography, biology, and finance.
However, they often require error mitigation techniques to produce accurate results.
Beyond-NISQ era
The creation of a computer with tens of thousands of qubits and enough error correction would eventually end the NISQ era.
These beyond NISQ devices would be able to, for example, implement
Shor's algorithm
Shor's algorithm is a quantum computer algorithm for finding the prime factors of an integer. It was developed in 1994 by the American mathematician Peter Shor.
On a quantum computer, to factor an integer N , Shor's algorithm runs in polynomial ...
for very large numbers and break
RSA
RSA may refer to:
Organizations Academia and education
* Rabbinical Seminary of America, a yeshiva in New York City
*Regional Science Association International (formerly the Regional Science Association), a US-based learned society
*Renaissance S ...
encryption.
See also
*
Quantum supremacy
In quantum computing, quantum supremacy or quantum advantage is the goal of demonstrating that a programmable quantum device can solve a problem that no classical computer can solve in any feasible amount of time (irrespective of the usefulness of ...
References
External links
John Preskill lecture on NISQ era
{{History of physics
Computer architecture statements
History of computing hardware
Quantum computing
Quantum information science
Computational complexity theory