A CNOT gate between multiphoton qubits encoded in two cavities

TL;DR

This paper demonstrates a fast, high-fidelity CNOT gate between two logical qubits encoded in single microwave cavities, advancing quantum computing with error-protected, high-dimensional qubits.

Contribution

It introduces a method to implement a CNOT gate between cavity-encoded multiphoton qubits using a transmon, achieving operation within 190 ns.

Findings

CNOT gate achieved between cavity-encoded qubits

Gate operation time is 190 ns, much shorter than decoherence time

High-fidelity operation demonstrated

Abstract

Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits encoded in high-dimensional systems. Typically, logical qubits are encoded in multiple two-level systems, but entangling gates operating on such qubits are highly complex and have not yet been demonstrated. Here, we realize a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities. In this approach, we encode a qubit in the high-dimensional space of a single cavity mode, rather than in multiple two-level systems. We couple two such encoded qubits together through a transmon, which is driven by an RF pump to apply the gate within 190 ns. This is two orders of magnitude shorter than the decoherence time of the transmon, enabling a high-fidelity gate operation. These results are an important step towards universal algorithms on error-corrected logical qubits.