Relaxation of a Moving Spin Qubit
Recent experimental and theoretical research on spin qubits in
quantum dots have clearly demonstrated that spins have long coherence times and
can be reliably controlled. However, how to achieve long-range quantum
communication for spin qubits thus remains a significant open problem in the scale-up
of spin qubit architectures. One proposed approach involves the transportation
of the electrons themselves, which is attractive because of its conceptual
simplicity and its similarity to the conventional charge-coupled devices.
Here I discuss our recent work on the physics of electron spin
decoherence when the quantum dot is in motion. Specifically, we find that the motion
induced spin decoherence is a pure longitudinal relaxation channel, whose rate
depends on factors such as spin-orbit coupling strength, electron-phonon coupling
strength, disorder in the substrate, the strength of the magnetic field, and the
speed of the quantum dot motion [1,2]. In the case of electron-phonon
interaction induced spin relaxation, we find a range of interesting phenomena originating
from the Doppler effect as we vary the quantum dot speed from the subsonic regime
to the supersonic regime, including frequency shift in emitted phonons, spin
relaxation boom in analogy to sonic boom, and Cherenkov radiation of phonons .
Our results are not only important in identifying how severe a problem
spin decoherence could be when it is in motion, but also reveal interesting
possibilities in coherent control of phonons in a semiconductor
We thank support by US ARO and NSF PIF.
 P. Huang and X. Hu, Phys. Rev. B 88, 075301 (2013).
 X. Zhao, P. Huang, and X. Hu, Sci. Rep. 6, 23169 (2016).