Spin Decay in a Quantum Dot Coupled to a Quantum Point Contact

TL;DR

This paper investigates how a quantum point contact causes spin decay in a quantum dot through spin-orbit interaction, providing microscopic calculations of relaxation rates and identifying conditions to minimize decay.

Contribution

It offers a detailed microscopic analysis of QPC-induced spin relaxation and decoherence, including their dependence on bias voltage, distance, and orientation.

Findings

Spin relaxation rate is proportional to QPC shot noise at large bias.

Relaxation and decoherence rates can vanish for specific orientations.

Rate scales as the sixth power of the distance between dot and QPC.

Abstract

We consider a mechanism of spin decay for an electron spin in a quantum dot due to coupling to a nearby quantum point contact (QPC) with and without an applied bias voltage. The coupling of spin to charge is induced by the spin-orbit interaction in the presence of a magnetic field. We perform a microscopic calculation of the effective Hamiltonian coupling constants to obtain the QPC-induced spin relaxation and decoherence rates in a realistic system. This rate is shown to be proportional to the shot noise of the QPC in the regime of large bias voltage and scales as $a^{-6}$ where $a$ is the distance between the quantum dot and the QPC. We find that, for some specific orientations of the setup with respect to the crystallographic axes, the QPC-induced spin relaxation and decoherence rates vanish, while the charge sensitivity of the QPC is not changed. This result can be used in experiments to minimize QPC-induced spin decay in read-out schemes.