Noise effects and tomography of remote entangled spins in quantum dots

TL;DR

This paper studies how decoherence impacts entanglement between quantum dots in micro cavities and introduces a tomography scheme to measure the entangled state, emphasizing the importance of timing in photon exchange and measurement.

Contribution

It proposes a practical tomographic method for entangled quantum dots that is robust against pure-dephasing noise and allows multiple measurements to improve accuracy.

Findings

Entanglement is sensitive to photon exchange timing due to dephasing.

The tomography scheme can reconstruct the full quantum state with single spin rotations.

Additional photons can be used for enhanced measurement without strict timing constraints.

Abstract

We investigate how decoherence affects the entanglement established between two quantum dots in micro cavities, and propose a tomographic scheme able to measure the entangled state. The scheme we consider establishes the entanglement via the exchange and measurement of a photon. Making the realistic assumption of noise dominated by pure-dephasing processes, we find that the photon must be exchanged and measured on timescales shorter than the quantum dots' characteristic dephasing time for appreciable levels of entanglement to be achieved. The tomographic scheme is able to reconstruct the full density matrix of the quantum dots, and requires only single spin rotations and the injection of an additional photon. Remarkably, we find that the additional photon need not be exchanged and measured on a timescale shorter than the dephasing time for accurate tomography, and also allows many to be used in order to increase the measurement signal.