Decoherence of an entangled state of a strongly-correlated double quantum dot structure through tunneling processes

TL;DR

This paper investigates how entanglement between two electrons in a double quantum dot decays due to tunneling processes, analyzing the effects of voltage and tunneling on decoherence using advanced simulation methods.

Contribution

It provides a detailed analysis of entanglement decay mechanisms in strongly-correlated quantum dots under non-equilibrium conditions, comparing real-time dynamics with two computational approaches.

Findings

Decoherence occurs exponentially fast under large voltage and current conditions.

Virtual tunneling leads to slower coherence loss at low voltages.

Results from density matrix renormalization group and master-equation methods agree well.

Abstract

We consider two quantum dots described by the Anderson-impurity model with one electron per dot. The goal of our work is to study the decay of a maximally entangled state between the two electrons localized in the dots. We prepare the system in a perfect singlet and then tunnel-couple one of the dots to leads, which induces the non-equilibrium dynamics. We identify two cases: if the leads are subject to a sufficiently large voltage and thus a finite current, then direct tunneling processes cause decoherence and the entanglement as well as spin correlations decay exponentially fast. At zero voltage or small voltages and beyond the mixed-valence regime, virtual tunneling processes dominate and lead to a slower loss of coherence. We analyze this problem by studying the real-time dynamics of the spin correlations and the concurrence using two techniques, namely the time-dependent density matrix renormalization group method and a master-equation method. The results from these two approaches are in excellent agreement in the direct-tunneling regime for the case in which the dot is weakly tunnel-coupled to the leads. We present a quantitative analysis of the decay rates of the spin correlations and the concurrence as a function of tunneling rate, interaction strength, and voltage.