Quantum computers, known for their ability to leverage quantum mechanical phenomena for computations, have shown promise in surpassing classical computers in solving complex computational and optimization problems. While some quantum computers have achieved impressive results in certain tasks, their advantage over classical computers is yet to be definitively and consistently demonstrated. However, a recent theoretical study conducted by Ramis Movassagh, a researcher at Google Quantum AI, formerly at IBM Quantum, aims to mathematically prove the notable advantages of quantum computers. In his paper published in Nature Physics, Movassagh demonstrates that simulating random quantum circuits and estimating their outputs is exceedingly difficult for classical computers, providing insight into the potential power of quantum computing.
One of the fundamental questions in the field of quantum computation is whether quantum computers are exponentially more powerful than classical ones. This question is at the heart of the Quantum Supremacy conjecture, which Movassagh refers to as the Quantum Primacy conjecture. Despite its widespread acceptance, establishing rigorous mathematical proof for this conjecture has been an ongoing challenge.
Researchers have been exploring various ways to demonstrate the advantages of quantum computers over classical ones, employing both theoretical and experimental studies. A crucial step in this endeavor is to prove that classical computers struggle to achieve the precision and accuracy of quantum computers. Movassagh’s interest in this field was piqued during a talk at MIT, where a colleague presented a result providing evidence for the hardness of random circuit sampling (RCS). RCS involves sampling from the output of a random quantum circuit and was being considered as a candidate for demonstrating quantum primacy. Movassagh, though initially skeptical of working in this field, was inspired to find a better proof and contribute to solving the long-standing problem.
Movassagh’s mathematical proof diverged significantly from previous methods. He developed a set of new mathematical techniques that demonstrate that the output probabilities of an average case (random quantum circuit) are as challenging as the worst-case scenario. The key element is the use of the Cayley path, a low-degree algebraic function, to interpolate between the worst-case and average-case circuits. By utilizing the Cayley path, Movassagh showed that the random circuits are essentially as difficult as the worst-case scenario. Unlike previous proofs, Movassagh’s approach does not rely on approximations and provides explicit bounds for errors, enhancing researchers’ ability to assess its robustness.
Since the conception of Movassagh’s proof, both his research group and other teams have further tested and improved its robustness. The proof not only sheds light on the potential computational barriers for the classical simulation of quantum circuits but also introduces new mathematical techniques with applications in quantum cryptography, computation and complexity, and coding theory. Moreover, this proof represents a promising path towards ultimately challenging the Extended-Church Turing thesis, a significant goal in quantum complexity theory.
Movassagh’s recent work marks a crucial contribution to the ongoing exploration of the advantages of quantum computers over classical computers. Moving forward, he plans to leverage his current proof to further demonstrate the immense potential of quantum computers in tackling specific problems. His future studies aim to expand the application of his work to the hardness of other tasks, providing a more comprehensive understanding of the intractability of quantum systems. Additionally, Movassagh is investigating the potential applications of his research in quantum cryptography and aims to prove the quantum primacy conjecture, potentially disproving the Extended Church-Turing thesis.
Ramis Movassagh’s groundbreaking work offers a mathematical proof that showcases the potential of quantum computers. Through innovative techniques and a fresh perspective, he has advanced the understanding of the advantages of quantum computing. As researchers continue to improve and build upon his work, we may inch closer to uncovering the true power and potential of quantum computers, paving the way for a quantum revolution in computation and problem-solving.