The field of quantum computing has made significant progress in recent years, but building a fully functional, error-corrected quantum computer that can outperform classical computers for a wide range of applications remains a formidable challenge. The current status of quantum computing can be summarized as follows:
Quantum Supremacy: In 2019, Google claimed to have achieved quantum supremacy, which means demonstrating a quantum computer's ability to solve a specific problem that is infeasible for classical computers to solve within a reasonable time frame. Google's experiment involved performing a calculation with a quantum computer that would take thousands of years for the fastest classical supercomputers.
Noisy Intermediate-Scale Quantum (NISQ) Computers: Current quantum computers, known as NISQ computers, have a limited number of qubits (the basic units of quantum information) and suffer from high error rates due to noise and decoherence. However, researchers have been able to perform certain calculations and simulations on these devices, showcasing their potential in specific areas like quantum chemistry simulations, optimization problems, and cryptography.
Quantum Error Correction: One of the key challenges in quantum computing is the fragility of qubits. Researchers are actively working on developing quantum error correction techniques that can protect quantum information from errors caused by noise and decoherence. Implementing error correction is crucial for scaling up quantum computers and achieving greater computational power.
Scaling and Quantum Volume: Increasing the number of qubits and reducing error rates are critical for building more powerful quantum computers. The concept of "quantum volume" is often used as a metric to measure a quantum computer's computational capability, which takes into account the number of qubits, gate fidelities, and connectivity between qubits.
As for the timeline, it is challenging to provide an exact estimate of when we will have a fully functional, fault-tolerant quantum computer that can solve complex real-world problems efficiently. The development of quantum technologies is highly dynamic, and breakthroughs can occur unexpectedly. However, many experts believe that it will likely take several more years, possibly decades, to achieve practical, error-corrected quantum computers that can outperform classical computers across a broad range of applications.
It's worth mentioning that even before the advent of fault-tolerant quantum computers, intermediate milestones and quantum advantage in specific applications can be achieved, providing value in areas such as optimization, simulation, and cryptography. Quantum computing remains an active and exciting area of research and development, with many companies, academic institutions, and governments investing in advancing the field.