Energy-efficient quantum computing

Abstract

In the near future, one of the major challenges in the realization of large-scale quantum computers operating at low temperatures is the management of harmful heat loads owing to thermal conduction of cabling and dissipation at cryogenic components. This naturally raises the question that what are the fundamental limitations of energy consumption in scalable quantum computing. In this work, we derive the greatest lower bound for the gate error induced by a single application of a bosonic drive mode of given energy. Previously, such an error type has been considered to be inversely proportional to the total driving power, but we show that this limitation can be circumvented by introducing a qubit driving scheme which reuses and corrects drive pulses. Specifically, our method serves to reduce the average energy consumption per gate operation without increasing the average gate error. Thus our work shows that precise, scalable control of quantum systems can, in principle, be implemented without the introduction of excessive heat or decoherence. The energy efficiency of a large-scale quantum computer can be improved by using fewer pulses to control more qubits. Joni Ikonen and co-workers from Aalto University (Finland) and Yale University (United States) present a theoretical scheme to manipulate qubits using a single itinerant control pulse. This is in contrast to the current mainstream prototypes where each qubit is usually controlled from room temperature through dedicated transmission lines and control pulses. The study finds that a single pulse can be recycled since its quantum state does not significantly change after interactions with the qubits. Therefore, compared to controlling qubits individually, the recycling method requires in total less energy for gate operations of equal precision. Designs based on similar redistribution of pulses may offer more efficient utilization of the control hardware in future large-scale quantum computers.