Quantum computers in the presence of resource constraints – QuRes
Quantum computing is currently the object of high expectations from major companies and governments worldwide. The confidence in the successful implementation of universal, scalable quantum computers is founded on the ability to do Quantum Error Correction (QEC), and to carry out Fault-Tolerant Quantum Computation (FTQC), to mitigate the adverse effects of noise. There are various Fault-Tolerant Quantum Computing schemes, but all involve huge physical overheads, e.g., ancilla and data qubits, as well as the use of classical information processing in the course of quantum computation. Large-scale Fault-Tolerant Quantum Computing will thus likely incur high resource costs, like large energetic bills.
Despite being a crucial practical constraint, the issue of resource consumption has largely been ignored thus far, as the past focus of the community had been to understand if quantum computation would be possible in principle. Nowadays, prototype quantum computers are taking shape and the question of scaling up to large-scale, useful quantum computers becomes of practical relevance. There is thus a growing need to quantify and minimize the resources needed to achieve the desired computational performance. Reciprocally, we need to better understand what limits nature imposes on quantum computation when resource constraints are taken into account.
To address these questions, we aim to build a general framework to assess the various physical resources needed for Fault-Tolerant Quantum Computing, and relating them to computational performance. We shall take inspiration from Quantum Thermodynamics, which investigates the fundamental interplay between energy, entropy, and information in the quantum realm. Thermodynamics can be seen as a “resource theory”, describing how to perform useful tasks in the presence of resource constraints and providing practical strategies to minimize resource costs.
Our French-Singaporean consortium is based on a long term and fruitful collaboration, and gathers the interdisciplinary expertise (Fault-Tolerant Quantum Computing, Quantum Thermodynamics, Quantum Optics in the Solid-State) to address these timely questions. Namely, the QuRes project targets two main objectives, respectively operating at the full-stack and fundamental levels:
OBJECTIVE 1. We will develop a complete framework to ASSESS HOW RESOURCE CONSTRAINTS MAY LIMIT QUANTUM COMPUTING POWER in standard fault-tolerant schemes, and optimize the resource consumption for a given target computing accuracy. We shall focus on realistic scenarios taken from the superconducting qubits platform, at the intermediate scale that will be relevant for the first generation of fault-tolerant quantum computers. We will adopt a “full-stack” approach involving resource costs like the energy costs from cryogeny and heat dissipation by the classical information processing unit, amplifiers and attenuators.
OBJECTIVE 2. We will explore STRATEGIES TO OVERCOME THE RESOURCE-IMPOSED LIMITS through novel approaches such as autonomous error correction. This holds the promise to perform quantum error correction without the use of classical information processing; i.e., removing the errors by purely quantum processes. This context is well adapted to derive universal, technology-independent fundamental bounds that will set a minimal resource cost to achieve a prescribed computing performance. It is also well adapted to the study of smart scenarios for resource savings, such as reversible computing.
Our framework being technological- and computational-scheme agnostic, it will ultimately allow the benchmarking of various scenarios of Fault-Tolerant Quantum Computing, and suggest possible developments to overcome constraints on the power of quantum computing.
Robert Whitney (LABORATOIRE DE PHYSIQUE ET MODELISATION DES MILIEUX CONDENSES)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LPM2C LABORATOIRE DE PHYSIQUE ET MODELISATION DES MILIEUX CONDENSES
Yale-NUS College / Science Division (Physics)
NEEL Institut Néel
Help of the ANR 218,158 euros
Beginning and duration of the scientific project: April 2022 - 36 Months