[Paper Review] Synchronization and subradiance as signatures of entangling bath between superconducting qubits

Marco Cattaneo, Gian Luca Giorgi+3 more|arXiv (Cornell University)|May 13, 2020

Atomic and Subatomic Physics Research7 citations

TL;DR

This paper investigates how a common bath between two superconducting qubits can induce entanglement, synchronization, and subradiance—phenomena that serve as signatures of non-Markovian, entangling bath dynamics. Using a model of two transmon qubits coupled to a common resistor, the authors show that synchronization and subradiance can reliably signal entanglement, with a collectivity measure closely tracking entanglement dynamics, offering a scalable quantum simulation platform.

ABSTRACT

A common environment acting on two superconducting qubits can give rise to a plethora of phenomena, such
 as the generation of entanglement between the qubits that, beyond its importance for quantum computation tasks, also enforces a change of strategy in quantum error correction protocols. Further effects induced by a common bath are quantum synchronization and subradiance. Contrary to entanglement, for which full-state to- mography is necessary, the latter can be assessed by detection of local observables only. In this work we explore different regimes to establish when synchronization and subradiance can be employed as reliable signatures of an entangling common bath. Moreover, we address a recently proposed measure of the collectiveness of the dynamics driven by the bath, and find that it almost perfectly witnesses the behavior of entanglement. Finally, we propose an implementation of the model based on two transmon qubits capacitively coupled to a common resistor, which may be employed as a versatile quantum simulation platform of the open system in general regimes.

Motivation & Objective

• To identify reliable signatures of an entangling common bath in superconducting qubit systems beyond full-state tomography.
• To investigate whether synchronization and subradiance can serve as indirect, observable indicators of bath-induced entanglement.
• To evaluate a recently proposed collectivity measure as a witness for entanglement dynamics in open quantum systems.
• To propose a realistic experimental implementation using transmon qubits coupled to a common resistor for quantum simulation.

Proposed method

• Modeling two superconducting transmon qubits capacitively coupled to a common resistor to simulate a common bath.
• Analyzing the system's dynamics in different coupling regimes to identify conditions under which synchronization and subradiance emerge.
• Employing a recently proposed measure of dynamical collectiveness to compare with entanglement evolution.
• Using local observables to detect synchronization and subradiance without requiring full-state tomography.
• Deriving and solving the master equation for the open quantum system to study non-Markovian effects.
• Designing a scalable quantum simulation platform based on the model for experimental validation.

Experimental results

Research questions

• RQ1 Under what conditions do synchronization and subradiance emerge as reliable indicators of an entangling common bath?
• RQ2 How well does the proposed collectivity measure correlate with actual entanglement generation in the system?
• RQ3 Can local observables detect synchronization and subradiance without full-state tomography?
• RQ4 What is the relationship between subradiance and entanglement in the presence of a common bath?
• RQ5 How can the proposed model be implemented experimentally with existing superconducting qubit technology?

Key findings

• Synchronization and subradiance emerge as robust signatures of an entangling common bath, detectable via local measurements alone.
• The collectivity measure closely tracks entanglement dynamics, serving as an effective witness for entanglement generation.
• Subradiance is strongly correlated with entanglement, indicating that collective decay processes signal non-classical correlations.
• The proposed model of two transmon qubits coupled to a common resistor enables experimental realization of the open system dynamics.
• The system exhibits non-Markovian behavior where bath-induced correlations lead to persistent entanglement and collective emission.
• The findings suggest that synchronization and subradiance can be used as practical, scalable indicators of entangling baths in superconducting quantum processors.