Multiplexed Control Architecture: A Scalable Solution for Superconducting Quantum Processors

Superconducting quantum processors are a promising technology for quantum computing, but their scalability is hindered by the current control architecture. Each quantum bit (qubit) is controlled by at least one control line, which is not scalable for controlling the thousands or millions of qubits required for fault-tolerance quantum computing. The proposed solution is a multiplexed control architecture that uses shared control lines, reducing the number of control lines required and making the architecture more scalable. This could enable the development of larger, more powerful quantum processors, potentially opening up new possibilities in fields such as cryptography, optimization, and machine learning.

What is the Challenge with Current Superconducting Quantum Processors?

Superconducting quantum processors are a promising technology for quantum computing. However, the current control architecture for these processors presents a significant challenge for scalability. Each quantum bit, or qubit, in these processors is controlled by at least one control line that delivers control pulses from room temperature to the qubits operating at millikelvin temperatures. This strategy has been successful for controlling hundreds of qubits, but it is unlikely to be scalable for controlling thousands or millions of qubits required for fault-tolerance quantum computing.

The limitation is due to the wiring challenge. The number of control lines that can be accommodated is limited by factors such as the cooling power and physical space of the cryogenic system, the control footprint area at the qubit chip level, and others. For instance, to deliver a superconducting quantum processor with just a few thousand qubits, the number of control lines or input/output connections is adequate for controlling one billion transistors in state-of-the-art classical processors.

To address this challenge, strategies have been explored to reduce the control lines running from room temperature to cryogenic temperature. However, implementing successful qubit control at scale while achieving ultra-low power dissipation remains challenging. On-chip control electronics have also been explored to reduce the chip input/output terminals, but this can increase the complexity of wire routing, especially when scaling up.

What is the Proposed Solution to this Challenge?

A multiplexed control architecture for superconducting qubits has been proposed as a solution to this challenge. This architecture introduces two types of shared control lines, row and column lines, providing an efficient approach for parallel controlling N qubits with O(N) control lines. With the combination of these two types of shared lines, unique pairs of control pulses are delivered to qubits on each row-column intersection, enabling parallel qubit addressing.

Unlike traditional gate schemes, both single and two-qubit gates are implemented with pairs of control pulses in this architecture. Considering the inherent parallelism and the control limitations, the integration of this architecture into quantum computing systems should be tailored as much as possible to the specific properties of the quantum circuits to be executed. As such, the architecture could be scalable for executing structured quantum circuits such as quantum error correction circuits.

How Does this Solution Address the Wiring Challenge?

The multiplexed control architecture addresses the wiring challenge by reducing the number of control lines required. By using shared control lines, the architecture can control a larger number of qubits without increasing the number of control lines proportionally. This makes the architecture more scalable, potentially enabling the control of thousands or even millions of qubits.

The architecture also introduces a new way of implementing gates. Instead of using a single control pulse for each gate, the architecture uses pairs of control pulses. This approach allows for more efficient use of the control lines, further enhancing the scalability of the architecture.

What are the Implications of this Solution for Quantum Computing?

The multiplexed control architecture could have significant implications for quantum computing. By addressing the wiring challenge, it could enable the development of larger and more powerful quantum processors. This could, in turn, enable the execution of more complex and powerful quantum algorithms, potentially opening up new possibilities in fields such as cryptography, optimization, and machine learning.

Moreover, the architecture could also make quantum computing more practical and accessible. By reducing the complexity and cost of controlling large numbers of qubits, it could make quantum computing more feasible for a wider range of applications and users.

What are the Next Steps for this Research?

The next steps for this research would be to further develop and test the multiplexed control architecture. This would involve designing and fabricating quantum processors based on the architecture, and then testing these processors to evaluate their performance and scalability.

In addition, further research would be needed to optimize the architecture and tailor it to the specific properties of the quantum circuits to be executed. This could involve developing new algorithms and techniques for generating and delivering the control pulses, as well as new methods for integrating the architecture into quantum computing systems.