Beyond quantum supremacy: the hunt for useful quantum computers

Rajit Nair, Ramgopal Kashyap, Preeti Sharma Nair

P. Roushan

C. Neill, P. Roushan, Kostyantyn Kechedzhi +29 more

A key step toward demonstrating a quantum system that can address difficult problems in physics and chemistry will be performing a computation beyond the capabilities of any classical computer, thus achieving so-called quantum supremacy. In this study, we used nine superconducting qubits to demonstrate a promising path toward quantum supremacy. By individually tuning the qubit parameters, we were able to generate thousands of distinct Hamiltonian evolutions and probe the output probabilities. The measured probabilities obey a universal distribution, consistent with uniformly sampling the full Hilbert space. As the number of qubits increases, the system continues to explore the exponentially growing number of states. Extending these results to a system of 50 qubits has the potential to address scientific questions that are beyond the capabilities of any classical computer.

Mikio Nakahara

Benjamin Villalonga, Dmitry I. Lyakh, Sergio Boixo +6 more

Abstract Noisy intermediate-scale quantum (NISQ) computers are entering an era in which they can perform computational tasks beyond the capabilities of the most powerful classical computers, thereby achieving ‘quantum supremacy’, a major milestone in quantum computing. NISQ supremacy requires comparison with a state-of-the-art classical simulator. We report HPC simulations of hard random quantum circuits (RQC), which have been recently used as a benchmark for the first experimental demonstration of quantum supremacy, sustaining an average performance of 281 Pflop/s (true single precision) on Summit, currently the fastest supercomputer in the world. These simulations were carried out using qFlex, a tensor-network-based classical high-performance simulator of RQCs. Our results show an advantage of many orders of magnitude in energy consumption of NISQ devices over classical supercomputers. In addition, we propose a standard benchmark for NISQ computers based on qFlex.

Ayekpam Malemnganbi Chanu, Vinod Kumar

At our current technological pace, it's become increasingly hard to make more compact classical computers. Proceeding with this as one of the motivations for developing quantum computers, recent years have seen a surge in interest and therefore investment in the field with aims to surpass the capabilities of its classical counterpart. The term quantum supremacy, although it gets thrown around quite often, is a very intricate concept. Assessing all its parts to establish a robust definition and foundational ground rules is crucial as we go further. Theoretically discussed wonders that can be achieved by quantum computer sounds promising-from the rapid acceleration in the development of artificial intelligence and cryptography to quantum chemistry and modelling chemical reactions. But how far do we need to go for it to become a reality? Are we there yet? All these questions arise as there have been claims of quantum supremacy which are contentious at the least. A major reason for worry is the intractability of quantum computers that makes sceptics wonder if it's a pursuit equivalent to chasing the wind. Quantum computers will not make classical computers obsolete is another view point which does hold water as quantum computers seem to be useful only in solving specific problems. Even though the endeavour for quantum supremacy is still ongoing, companies have also gravitated towards Quantum advantage. This paper lays out an idiosyncratic view of what we can achieve and what we already have.