We investigate the idea for probing spin states of two coupled quantum dots (CQDs) by the dc Josephson current flowing through them. This theory requires weak coupling between CQDs and electrodes, but allows arbitrary interdot tunnel coupling, intradot and interdot Coulomb interactions. We find that the Coulomb blockade peaks exhibit a nonmonotonous dependence on the Zeeman splitting of CQDs, which can be understood in terms of Andreev bound states. More importantly, the supercurrent in the Coulomb blockade valleys may provide information on the spin states of CQDs: for CQDs with total electron number $N=1,3$ (odd), the supercurrent will reverse its sign if the CQD becomes a magnetic molecule; for a CQD with $N=2$ (even), the supercurrent will decrease sharply around the transition between the spin singlet and triplet ground states of the CQD.We investigate the idea for probing spin states of two coupled quantum dots (CQDs) by the dc Josephson current flowing through them. This theory requires weak coupling between CQDs and electrodes, but allows arbitrary interdot tunnel coupling, intradot and interdot Coulomb interactions. We find that the Coulomb blockade peaks exhibit a nonmonotonous dependence on the Zeeman splitting of CQDs, which can be understood in terms of Andreev bound states. More importantly, the supercurrent in the Coulomb blockade valleys may provide information on the spin states of CQDs: for CQDs with total electron number $N=1,3$ (odd), the supercurrent will reverse its sign if the CQD becomes a magnetic molecule; for a CQD with $N=2$ (even), the supercurrent will decrease sharply around the transition between the spin singlet and triplet ground states of the CQD.

arXiv:cond-mat/0111209Physical review. B, Condensed matterAug 9, 200221 citations

Anisotropic Spin Exchange in Coupled Quantum Dots

K. Foster, Layla Hormozi

APSMar 1, 20050 citations

Controllable electron spin dephasing due to phonon state distinguishability in a coupled quantum dot system

Michał Gawełczyk, Mateusz Krzykowski, Krzysztof Gawarecki +1 more

We predict a spin pure dephasing channel in electron relaxation between states with unequal Zeeman splittings, exemplified by a spin-preserving electron tunneling between quantum dots in a magnetic field. The dephasing is caused by a mismatch in electron $g$ factors in the dots leading to distinguishability of phonons emitted during tunneling with opposite spins. Combining multiband $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ modeling and dynamical simulations via a master equation, we show that this fundamental effect of spin measurement effected by the phonon bath may be widely controlled by the size and composition of the dots or on demand via tuning of external fields. By comparing the numerically simulated degree of dephasing with the predictions of general theory based on distinguishability of environment states, we show that the proposed mechanism is the dominant phonon-related spin dephasing channel and may limit spin coherence time in tunnel-coupled structures at cryogenic temperatures.We predict a spin pure dephasing channel in electron relaxation between states with unequal Zeeman splittings, exemplified by a spin-preserving electron tunneling between quantum dots in a magnetic field. The dephasing is caused by a mismatch in electron $g$ factors in the dots leading to distinguishability of phonons emitted during tunneling with opposite spins. Combining multiband $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ modeling and dynamical simulations via a master equation, we show that this fundamental effect of spin measurement effected by the phonon bath may be widely controlled by the size and composition of the dots or on demand via tuning of external fields. By comparing the numerically simulated degree of dephasing with the predictions of general theory based on distinguishability of environment states, we show that the proposed mechanism is the dominant phonon-related spin dephasing channel and may limit spin coherence time in tunnel-coupled structures at cryogenic temperatures.

arXiv:1707.06155Physical review. B./Physical review. BAug 3, 201811 citations

Kondo effect in a side-coupled double quantum dot system embedded in a mesoscopic ring

I-Ling Tsai, Chung‐Hou Chung

We study finite-size effect of the Kondo screening cloud in a double quantum dot setup via a large- $N$ slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size $L$ and the other dot is side coupled to the embedded dot via an antiferromagnetic spin-spin-exchange coupling with a strength $K$ . The antiferromagnetic coupling favors local spin-singlet state and suppresses the Kondo screening. The mean-field phase diagram as a function of $1/L$ and $K$ shows a crossover to the local spin-singlet ground state from the Kondo phase to occur at $K<{K}_{c}$ $(L=4n,4n+1,4n+3)$ and at $K>{K}_{c}$ $(L=4n+2)$ . The effective Kondo temperature ${T}_{k}$ (proptotional to inverse of the Kondo screening cloud size) shows the Kosterlitz-Thouless (KT) scaling at finite sizes for $L=4n,4n+2$ , indicating quantum transition of the KT type between the Kondo screened phase for $K\ensuremath{\le}{K}_{c}$ and a local spin-singlet phase for $K\ensuremath{\ge}{K}_{c}$ in the thermodynamic limit with ${K}_{c}$ being the critical value. The local density of states on the embedded quantum dot and the persistent current at finite sizes with different values of $K$ are calculated in the crossover region.We study finite-size effect of the Kondo screening cloud in a double quantum dot setup via a large-$N$ slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size $L$ and the other dot is side coupled to the embedded dot via an antiferromagnetic spin-spin-exchange coupling with a strength $K$. The antiferromagnetic coupling favors local spin-singlet state and suppresses the Kondo screening. The mean-field phase diagram as a function of $1/L$ and $K$ shows a crossover to the local spin-singlet ground state from the Kondo phase to occur at $K<{K}_{c}$ $(L=4n,4n+1,4n+3)$ and at $K>{K}_{c}$ $(L=4n+2)$. The effective Kondo temperature ${T}_{k}$ (proptotional to inverse of the Kondo screening cloud size) shows the Kosterlitz-Thouless (KT) scaling at finite sizes for $L=4n,4n+2$, indicating quantum transition of the KT type between the Kondo screened phase for $K\ensuremath{\le}{K}_{c}$ and a local spin-singlet phase for $K\ensuremath{\ge}{K}_{c}$ in the thermodynamic limit with ${K}_{c}$ being the critical value. The local density of states on the embedded quantum dot and the persistent current at finite sizes with different values of $K$ are calculated in the crossover region.

arXiv:0908.0589Physical Review BMay 4, 20100 citations

“Which-way” Spin Decoherence in a Coupled Quantum Dot System

Mateusz Krzykowski, Michał Gawełczyk, Krzysztof Gawarecki +1 more

Quantum Information and Measurement (QIM)Jan 1, 20190 citations

N=1,3

(odd), the supercurrent will reverse its sign if the CQD becomes a magnetic molecule; for a CQD with

N=2

(even), the supercurrent will decrease sharply around the transition between the spin singlet and triplet ground states of the CQD.

g

factors in the dots leading to distinguishability of phonons emitted during tunneling with opposite spins. Combining multiband $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ modeling and dynamical simulations via a master equation, we show that this fundamental effect of spin measurement effected by the phonon bath may be widely controlled by the size and composition of the dots or on demand via tuning of external fields. By comparing the numerically simulated degree of dephasing with the predictions of general theory based on distinguishability of environment states, we show that the proposed mechanism is the dominant phonon-related spin dephasing channel and may limit spin coherence time in tunnel-coupled structures at cryogenic temperatures.

We study finite-size effect of the Kondo screening cloud in a double quantum dot setup via a large-

N

slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size

L

and the other dot is side coupled to the embedded dot via an antiferromagnetic spin-spin-exchange coupling with a strength

K

. The antiferromagnetic coupling favors local spin-singlet state and suppresses the Kondo screening. The mean-field phase diagram as a function of

1/L

and

K

shows a crossover to the local spin-singlet ground state from the Kondo phase to occur at

K<{K}_{c}

(L=4n,4n+1,4n+3)

and at

K>{K}_{c}

(L=4n+2)

. The effective Kondo temperature

{T}_{k}

(proptotional to inverse of the Kondo screening cloud size) shows the Kosterlitz-Thouless (KT) scaling at finite sizes for

L=4n,4n+2

, indicating quantum transition of the KT type between the Kondo screened phase for $K\ensuremath{\le}{K}_{c}$ and a local spin-singlet phase for $K\ensuremath{\ge}{K}_{c}$ in the thermodynamic limit with

{K}_{c}

being the critical value. The local density of states on the embedded quantum dot and the persistent current at finite sizes with different values of

K

are calculated in the crossover region.