[Paper Review] Quantum computing 40 years later

John Preskill|arXiv (Cornell University)|Jun 19, 2021

Quantum Computing Algorithms and Architecture36 citations

TL;DR

Preskill reviews the origins of quantum computing, the current NISQ era, and the prospects for scalable fault-tolerant quantum computation, emphasizing applications in quantum simulation and chemistry.

ABSTRACT

Forty years ago, Richard Feynman proposed harnessing quantum physics to build a more powerful kind of computer. Realizing Feynman's vision is one of the grand challenges facing 21st century science and technology. In this article, we'll recall Feynman's contribution that launched the quest for a quantum computer, and assess where the field stands 40 years later.

Motivation & Objective

• Summarize Feynman’s original vision and its historical development toward quantum computation.
• Assess the current state of quantum hardware and the gap to scalable fault-tolerant quantum computing (FTQC).
• Discuss the potential applications of quantum computing, notably quantum simulation and chemistry.

Proposed method

• Historical synthesis of foundational ideas from Feynman, Manin, Benioff, Deutsch, Shor, and others.
• Explanation of core quantum concepts: qubits, tensor products, and the quantum circuit model.
• Discussion of the NISQ era, quantum simulation (analog and digital), and the path to FTQC with error correction.
• Reference to the accuracy-threshold theorem and surface code concepts as drivers for scalability.

Experimental results

Research questions

• RQ1 What is the current status of quantum computing 40 years after Feynman’s proposal?
• RQ2 What roles will NISQ devices play versus fault-tolerant quantum computers in the near and long term?
• RQ3 What are the promising applications of quantum computers, particularly in quantum simulation and chemistry?
• RQ4 What are the principal challenges and requirements (e.g., error rates, qubit counts) to achieve scalable quantum computation?

Key findings

• Quantum computing originated from Feynman’s proposal to simulate quantum systems with a quantum computer, highlighting its potential superiority over classical simulation.
• The field has progressed to the NISQ era, with devices like Google’s Sycamore achieving quantum computational supremacy claims on specific tasks.
• There remains a large gap between NISQ devices and scalable FTQC, with substantial overhead for quantum error correction and potentially hundreds of thousands of physical qubits required for high-impact applications.
• Quantum advantage is most pronounced for simulating quantum dynamics and certain chemistry/physics problems rather than generic NP-hard optimization problems.
• Analog and digital quantum simulators offer complementary near-term approaches, with digital quantum computation providing future flexibility and exact universality.