Coherent communication between quantum registers separated by ∼ 10 μm distances
is one of the requirements for scalability of architectures based on gated quantum dots
. Moving a spin qubit across this distance, e.g. along a chain of tunnel-coupled dots ,
is one of possible solutions. I will discuss our recent theoretical work on such a dot-to-dot
adiabatic charge transfer in presence of realistic amount of charge noise and electron-
phonon coupling [3,4]. The main result is that unless tunnel couplings (defined here as
equal to the gap at the anticrossing of states localized in the two dots) are larger than ≈ 50
μeV, charge noise-induced excitations will be a factor limiting the adiabatic character
of electron transfer across a chain of ∼ 100 QD. I will discuss the close relationship
between non-adiabatic (and thus non-deterministic) character of charge transfer and spin
dephasing caused by dot- and state-specific g-factors, and highlight the differences between
GaAs and Si-based quantum dots caused by stronger electron-phonon coupling in the
former. Finally, I will discuss an alternative qubit shuttling scheme in which gates are
used to create a moving quantum dot [5,6]. I will argue that this scheme is more robust to
electrostatic disorder compared to the one based on pre-existing tunnel coupled quantum
dots, and I will discuss how the valley-orbit coupling in presence of interface roughness
will be the main source of spin qubit dephasing in this scheme .
This work has been funded by the National Science Centre (NCN), Poland under
QuantERA program, Grant No. 2017/25/Z/ST3/03044. Project Si-QuBus has received
funding from the QuantERA ERA-NET Cofund in Quantum Technologies implemented
within the European Union’s Horizon 2020 program.
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