CAREER: Noise-Tailored Architectures for Fault-Tolerant Continuous-Variable Quantum Computing

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

A computing hardware operating on principles of quantum mechanics opens up the possibility of powerful technologies that can accomplish tasks beyond what is possible with processors based on classical Boolean algebra. However, to fully harness the power of quantum phenomena the computing system must be made robust against inevitable faults in the hardware.

It becomes necessary to correct errors introduced in the system due to faulty-hardware in a fault-tolerant manner so that the computer continues to function reliably even if some of its constituent quantum components have failed. State-of-the-art quantum technologies have led to demonstration of landmark experiments in quantum error correction. However, they are still far away from reaching the stringent performance and resource requirements for fault-tolerance at a large scale needed for practical applications of quantum computing.

The goal of this NSF CAREER program is to apply our expertise in the theory and control of open quantum systems and theory of fault-tolerant error correction in unison to chart a course for practical, scalable fault-tolerant quantum computation with new emerging quantum hardware. To extend the broader impacts of this program, hands-on quantum information science curricula will be developed to engage students in active quantum information research and to draw talent from fields ranging from physics to electrical and computer engineering.

Moreover, to sustain a diverse future quantum workforce, the program will establish a scaffolded education initiative for the local community and youth.

This program takes a bottoms-up approach to accomplish the ambitious task of resource-efficient fault-tolerant quantum error correction. The approach will be developed, in particular, for the emerging superconducting continuous-variable (CV) or bosonic quantum hardware based on storing a bit of quantum information or qubit in quantum states of a superconducting oscillator.

The motivation behind bosonic encodings is that, in principle, they can be made resilient against some sources of noise either by design or by active error correction applied directly to the oscillator mode. Unfortunately, practical experimental noise is more complex and the amount of noise suppression achieved so far in the laboratory is quite limited.

In this program the PI will develop new strategies for robust quantum control of CV qubits taking into account realistic experimental noise. Rather than solely relying on making the CV quantum hardware less noisy, known structures in the noise will be used to design efficient fault-tolerant protocols. This direction is based on the observation that not all errors are equally harmful in a given system.

Some errors are more contagious and spread rapidly in a circuit and then there are also some types of errors that are easier to detect using a particular error-correcting code. Thus, error-correction can be made more effective if the noise channel of a qubit could be tailored to suppress contagious errors, perhaps even at the cost of slightly increasing errors that are nonetheless easier to detect.

Such asymmetric-noise qubits can be realized in a number of ways using CV encoding in superconducting oscillators. Thus, the bottoms-up approach will be taken to develop scalable fault-tolerant architectures with planar topological error correcting codes that can leverage the noise properties of asymmetric-noise CV qubits. This work will not only lead to efficient CV-fault-tolerant error correction, but will also inform the design of next-generation quantum hardware, enabling practical, scalable quantum computing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.