Dr. Ata Ulhaq’s research reveals fundamental limitations of elementary quantum systems!

Quantum – an alluring word that elicits fascination not only for the academic but the pop culture community as well. At the bleeding edge of research, quantum mechanics continues to elude our intuition, serving our intellect with increasingly onerous revelations, the deeper we probe it. However, where it has kept the academicians busy with toilsome research, it continues to hold promise for great technological advancements also. Our understanding of any physical discipline is incomplete without also understanding its basic, fundamental limits.

Dr. Ata Ulhaq, Assistant Professor of Physics, has co-authored a paper revealing insights into the fundamental limitations of elementary quantum systems. This paper has been published in Nature’s NPJ Quantum Information journal. By setting up a quantum dot (a man-made electron transporter of nanoscale proportions), experiments reveal fundamental limits and trade-offs of quantum dot spin dynamics, while reduced tunneling can be used to achieve longer lifetimes of electron spin qubits, exceeding one second.

Experiments presented in this study establish a comprehensive picture of electron–nuclear spin relaxation in self-assembled quantum dots in a wide range of practically accessible conditions. Current experiments require a magnetic field intensity greater than 0.15 T to initialize the spins. In these experiments, electron spin relaxation is fundamentally limited by phonon coupling in. However, nuclear spin relaxation studied in Dr. Ata’s work is specific to III-V quantum dots and is governed by noncollinear hyperfine interaction. The techniques employed in this study can also be applied to establish the less explored fundamental limits of nuclear spin dynamics in electron-charged strain-free quantum dots, where noncollinear interaction will be small, but nuclear spin diffusion might be more prominent.

The electron-nuclear spin relaxation attained in this work provides a roadmap for design of the optimal operating conditions in quantum dot spin qubits.

Reference: Gillard, G., Griffiths, I.M., Ragunathan, G. et al. Fundamental limits of electron and nuclear spin qubit lifetimes in an isolated self-assembled quantum dot. npj Quantum Inf 7, 43 (2021). https://doi.org/10.1038/s41534-021-00378-2