The current state of

quantum computing A quantum computer is a computer that exploits quantum mechanical phenomena. On small scales, physical matter exhibits properties of wave-particle duality, both particles and waves, and quantum computing takes advantage of this behavior using s ...

is referred to as the noisy intermediate-scale quantum (NISQ) era, characterized by quantum processors containing up to 1,000

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 syste ...

s which are not advanced enough yet for

fault-tolerance Fault tolerance is the ability of a system to maintain proper operation despite failures or faults in one or more of its components. This capability is essential for high-availability, mission critical, mission-critical, or even life-critical sys ...

or large enough to achieve quantum advantage. These processors, which are sensitive to their environment (noisy) and prone to

quantum decoherence Quantum decoherence is the loss of quantum coherence. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be expla ...

, are not yet capable of continuous quantum error correction. This intermediate-scale is defined by the quantum volume, 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 is derived from Proto-Germanic language, Proto-Germanic ''*gatan'', meaning an opening or passageway. Synonyms include yett (which comes from the same root w ...

fidelity. The term NISQ was coined by John Preskill in 2018. According to Microsoft Azure Quantum's scheme, NISQ computation is considered level 1, the lowest of the quantum computing implementation levels. In October 2023, the 1,000 qubit mark was passed for the first time by Atom Computing's 1,180 qubit quantum processor. However, as of 2024, only two quantum processors have over 1,000 qubits, with sub-1,000 quantum processors still remaining the norm.

Algorithms

NISQ algorithms are

quantum algorithm In quantum computing, a quantum algorithm is an algorithm that runs on a realistic model of quantum computation, the most commonly used model being the quantum circuit model of computation. A classical (or non-quantum) algorithm is a finite seq ...

s designed for quantum processors in the NISQ era. Common examples are the variational quantum eigensolver (VQE) and quantum approximate optimization algorithm (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 contributions ...

and have potential applications in various fields including physics, materials science, data science, cryptography, biology, and finance. However, due to noise during circuit execution, they often require error mitigation techniques. These methods constitute a way of reducing the effect of noise by running a set of circuits and applying post-processing to the measured data. In contrast to quantum error correction, where errors are continuously detected and corrected during the run of the circuit, error mitigation can only use the outcome of the noisy circuits.

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 algorithm for finding the prime factors of an integer. It was developed in 1994 by the American mathematician Peter Shor. It is one of the few known quantum algorithms with compelling potential applications and strong ...

for very large numbers and break RSA encryption. In April 2024, researchers at Microsoft announced a significant reduction in error rates that required only 4 logical qubits, suggesting that quantum computing at scale could be years away instead of decades.

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

Algorithms

Beyond-NISQ era

See also

References

External links