A CNOT gate between multiphoton qubits encoded in two cavities.

Research paper by S S Rosenblum, Y Y YY Gao, P P Reinhold, C C Wang, C J CJ Axline, L L Frunzio, S M SM Girvin, Liang L Jiang, M M Mirrahimi, M H MH Devoret, R J RJ Schoelkopf

Indexed on: 15 Feb '18Published on: 15 Feb '18Published in: Nature communications


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.