Decoherence in Solid State Qubits

TL;DR

This review explores how environmental interactions cause decoherence in solid state qubits, focusing on spin-qubits in quantum dots and superconducting qubits, and discusses mechanisms and effects on quantum device performance.

Contribution

It provides a comprehensive analysis of decoherence mechanisms in solid state qubits, highlighting differences between spin-based and superconducting implementations.

Findings

Decoherence in spin-qubits mainly arises from phonon interactions and nuclear spin baths.

Superconducting qubits experience decoherence from control parameter fluctuations and circuit losses.

Understanding these mechanisms is crucial for improving quantum device coherence times.

Abstract

Interaction of solid state qubits with environmental degrees of freedom strongly affects the qubit dynamics, and leads to decoherence. In quantum information processing with solid state qubits, decoherence significantly limits the performances of such devices. Therefore, it is necessary to fully understand the mechanisms that lead to decoherence. In this review we discuss how decoherence affects two of the most successful realizations of solid state qubits, namely, spin-qubits and superconducting qubits. In the former, the qubit is encoded in the spin 1/2 of the electron, and it is implemented by confining the electron spin in a semiconductor quantum dot. Superconducting devices show quantum behavior at low temperatures, and the qubit is encoded in the two lowest energy levels of a superconducting circuit. The electron spin in a quantum dot has two main decoherence channels, a (Markovian) phonon-assisted relaxation channel, due to the presence of a spin-orbit interaction, and a (non-Markovian) spin bath constituted by the spins of the nuclei in the quantum dot that interact with the electron spin via the hyperfine interaction. In a superconducting qubit, decoherence takes place as a result of fluctuations in the control parameters, such as bias currents, applied flux, and bias voltages, and via losses in the dissipative circuit elements.