Dissipation and Dephasing of Interacting Photons in Transmon Arrays

TL;DR

This paper investigates how dissipation and dephasing affect the many-body quantum dynamics of transmon arrays, emphasizing the importance of higher excited states and providing insights for improving coherence in quantum computing applications.

Contribution

It offers a detailed analysis of dissipation and dephasing effects on transmon arrays, including higher excited states, using analytical and numerical methods, and assesses their impact on quantum information tasks.

Findings

Many-body decoherence limits observable unitary dynamics.

State-of-the-art transmon arrays can demonstrate coherent many-body dynamics.

Improving coherence is necessary for advanced quantum computing with transmons.

Abstract

Transmon arrays are one of the most promising platforms for quantum information science. Despite being often considered simply as qubits, transmons are inherently quantum mechanical multilevel systems. Being experimentally controllable with high fidelity, the higher excited states beyond the qubit subspace provide an important resource for hardware-efficient many-body quantum simulations, quantum error correction, and quantum information protocols. Alas, dissipation and dephasing phenomena generated by couplings to various uncontrollable environments yield a practical limiting factor to their utilization. To quantify this in detail, we present here the primary consequences of single-transmon dissipation and dephasing to the many-body dynamics of transmon arrays. We use analytical methods from perturbation theory and quantum trajectory approach together with numerical simulations, and deliberately consider the full Hilbert space including the higher excited states. The three main non-unitary processes are many-body decoherence, many-body dissipation, and heating/cooling transitions between different anharmonicity manifolds. Of these, the many-body decoherence -- being proportional to the squared distance between the many-body Fock states -- gives the strictest limit for observing effective unitary dynamics. Considering experimentally relevant parameters, including also the inevitable site-to-site disorder, our results show that the state-of-the-art transmon arrays should be ready for the task of demonstrating coherent many-body dynamics using the higher excited states. However, the wider utilization of transmons for ternary-and-beyond quantum computing calls for improving their coherence properties.