Superconducting qubits with 1 second coherence time using rotation codes

Introduction

Quantum computers use highly entangled qubits to achieve their exceptional computational power. However, the qubits also easily entangle with their environment, leading to errors. Future quantum computers can be protected against such errors by encoding each logical qubit redundantly in thousands of physical qubits. This daunting overhead can be reduced exponentially by improving the quality of the physical qubits.

Cavity Qubits

We can also replace the two-level physical qubits with cavities, which are described by continuous variables. This built-in redundancy can further reduce the overhead for fault-tolerant quantum computation.

Proposal Overview

In this proposal, I aim to develop a qubit based on superconducting cavities with a coherence time of 1 second - three orders of magnitude higher than the current state of the art. I will achieve this goal by tackling the problem of errors in quantum computers on three fronts:

1. Developing a qubit with suppressed intrinsic loss mechanisms by harnessing recent developments in cavities for particle accelerators.
2. Using quantum control to mitigate the effect of dominant error mechanisms.
3. Developing and implementing bosonic rotation codes, a novel blueprint for quantum error correction tailored to the error structure of the cavity qubit. These codes are unique in that they treat photon loss errors and phase noise errors on equal footing.

Design Considerations

My proposal requires a radical rethinking of the cavity design, its interaction with quantum circuits, and how quantum information is encoded and manipulated. It combines advances in quantum information science, superconductivity, and materials science.

Broader Impact

Beyond providing a novel approach to quantum computing, the proposal will impact a broad range of fields ranging from quantum-enhanced sensing to the simulation of photochemical reactions.