Abstract
Long-distance transfer of quantum information in architectures based on quantum dot spin qubits will be necessary for their scalability. One way of achieving it is to simply move the electron between two quantum registers. Precise control over the electron shuttling through a chain of tunnel-coupled quantum dots is possible when interdot energy detunings are changed adiabatically. Deterministic character of shuttling is however endangered by coupling of the transferred electron to thermal reservoirs: sources of fluctuations of electric fields, and lattice vibrations. We theoretically analyse how the electron transfer between two quantum dots is affected by electron-phonon scattering, and interaction with sources of $1/f$ and Johnson charge noise in both detuning and tunnel coupling. The electron-phonon scattering turns out to be irrelevant in Si quantum dots, while a competition between the effects of charge noise and Landau-Zener effect leads to an existence of optimal detuning sweep rate, at which probability of leaving the electron behind is minimal. In GaAs quantum dots, on the other hand, coupling to phonons is strong enough to make the phonon-assisted processes of interdot transfer dominate over influence of charge noise. The probability of leaving the electron behind depends then monotonically on detuning sweep rate, and values much smaller than in silicon can be obtained for slow sweeps. However, after taking into account limitations on transfer time imposed by need for preservation of electron's spin coherence, minimal probabilities of leaving the electron behind in both GaAs- and Si-based double quantum dots turn out to be of the same order of magnitude. Bringing them down below $10^{-3}$ requires temperatures $\leq \! 100$ mK and tunnel couplings above $20$ $\mu$eV.
Highlights
In quantum computing architectures based on voltagecontrolled quantum dots (QDs) developed in GaAs/AlGaAs [1,2,3], Si/SiGe [4], and Silicon-Metal-Oxide-Semiconductor (SiMOS) [5,6,7,8] structures, scalability will be possible only if quantum information is transferred between few-qubit registers, separated by distances much larger than the typical QD size
As we show in this paper, interactions with sources of electric field noise and phonons in realistic Si- and GaAs-based structures are dominating the physics of charge transfer in a wide range of sweep rates, with nonadiabatic effects described by the LZ theory being relevant only for very fast sweeps
We focus on QDs based on silicon and GaAs and employ realistic models of charge noise and phonon interaction with an electron confined in a double QD
Summary
In quantum computing architectures based on voltagecontrolled quantum dots (QDs) developed in GaAs/AlGaAs [1,2,3], Si/SiGe [4], and Silicon-Metal-Oxide-Semiconductor (SiMOS) [5,6,7,8] structures, scalability will be possible only if quantum information is transferred between few-qubit registers, separated by distances much larger than the typical QD size. We address the situation of lower temperatures/larger tunnel couplings, taking into account the quantum limit [69] of both 1/ f noise from two-level fluctuators (TLFs) present in the nanostructure and Johnson noise from reservoirs of free electrons, while considering the coupling of the moving electron to phonons Coupling to all these thermal reservoirs gives transition rates, +/−( ) for transfer of energy from/to the environment, that nontrivially depend on. We give there a discussion of expected amplitude of 1/ f noise at GHz frequencies relevant for transitions during electron transfer in realistic GaAs- and silicon-based QDs. in Sec. IV we use these rates to calculate the dynamics of the electron driven adiabatically through an anticrossing of levels associated with the two dots and show a qualitative difference between resulting probability of leaving the electron behind between GaAs- and silicon-based QDs. In the last section, we discuss some of the implications of these results for experimental efforts aimed at using chains of QDs for coherent shuttling of electron spin qubits
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