Non-Hermitian topological quantum states in a reservoir-engineered transmon chain

TL;DR

This paper proposes a method to realize non-Hermitian topological quantum phases in a transmon chain with engineered dissipation, demonstrating observable quantum effects like long-range entanglement through reflection measurements.

Contribution

It introduces a reservoir-engineered transmon chain to achieve and detect non-Hermitian topological phases with tunable dissipation and observable quantum effects.

Findings

Topological end modes are detectable via reflection measurements.

Quantum entanglement persists over long distances in the system.

Dissipation can be tuned in-situ to control topological phases.

Abstract

Dissipation in open systems enriches the possible symmetries of the Hamiltonians beyond the Hermitian framework allowing the possibility of novel non-Hermitian topological phases, which exhibit long-living end states that are protected against disorder. So far, non-Hermitian topology has been explored only in settings where probing genuine quantum effects has been challenging. We theoretically show that a non-Hermitian topological quantum phase can be realized in a reservoir-engineered transmon chain. The spatial modulation of dissipation is obtained by coupling each transmon to a quantum circuit refrigerator allowing in-situ tuning of dissipation strength in a wide range. By solving the many-body Lindblad master equation using a combination of the density matrix renormalization group and third quantization approaches, we show that the topological end modes and the associated phase transition are visible in simple reflection measurements with experimentally realistic parameters. Finally, we demonstrate that genuine quantum effects are observable in this system via robust and slowly decaying long-range quantum entanglement of the topological end modes, which can be generated passively starting from a locally excited transmon.