Scientists Drive Dual Rail Qubits For Longer Coherence Times, Better Error Correction

Insider Summary

• Scientists from the AWS Center for Quantum Computing are leading a promising research project on dual-rail qubits that can facilitate longer coherence times and better fault management.
• Dual-rail qubits consist of a pair of transmons coupled resonantly.
• The researchers demonstrated that double-rail qubits remain coherent for milliseconds, which is a long time for a quantum state.

Quantum computing, with its enormous promise and potential, has always faced a daunting obstacle: noise. The fragile nature of the quantum state makes it susceptible to errors, leading to loss of information and computing power. Quantum error correction (QEC) is an important area of ​​research that aims to reduce these errors and bring quantum computers closer to their full potential.

A research team, led by scientists from the AWS Center for Quantum Computing, now report that the “dual-rail qubit” approach may offer a promising new pathway to longer qubit coherence times and better quantum error correction.

According to the research team, which published its findings in pre-press the ArXiv server, traditional error correction methods involve identifying and correcting errors that occur in the subspace of quantum computing. However, this approach may not be the most efficient for all qubit types. Qubit deletion introduces a major fault mode involving leakage from the computational subspace. Taking advantage of the unique advantages of erasing error correction could be a game changer for quantum computing.

In the Quantum World, One Millisecond Is a Lifetime

The researchers demonstrated the feasibility of dual rail qubits as highly coherent erasing qubits. This qubit is composed of a pair of resonantly coupled transmons, and its distinctive feature is that nearly all errors manifest as deletion errors. Double-rail qubits display millisecond-scale coherence within their subspace, a remarkable feat considering that for a quantum state, a millisecond is a lifetime.

The main advantage of erasing qubits lies in their ability to achieve more favorable error thresholds compared to standard error correction methods. The suppression of residual dephasing in these dual-rail qubits ensures that deletion errors become the dominant error type, making them easier to detect and correct. Single qubit gates are mainly affected by erase errors, with a very low erase probability per gate.

One of the more exciting advances reported in this paper is the system’s ability to detect wipe faults in real-time during mid-circuit operation, a feat previously considered very challenging. The recognition of dephasing errors per check is less than 0.1%, ensuring that the detection process does not compromise the coherence of the qubits.

The ability of these dual-rail qubits to maintain high coherence over a wide tunable operating range also offers unique advantages. By reducing the possibility of frequency collisions, it provides increased capacity to avoid errors caused by environmental noise.

More work is likely to follow, according to the team.

They write: “Future studies could complement the toolbox for operating deletion surface codes, including developing two-qubit gates between double-rail pairs, reinitializing double-rail qubits after deletion errors, and exploring novel deletion detection mechanisms.”

The AWS team is also joined by scientists from Hebrew University of Jerusalem, Pritzker School of Molecular Engineering, University of Chicago; Quantum Materials and Information Institute, California Institute of Technology, Thomas J. Watson, Sr., Applied Physics Laboratory and Kavli Nanoscience Institute.