Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Applied Physics Letters

Electrical control of singlet-triplet entanglement in lateral quantum dot molecules

Fanyao Qu, Gisele Iorio, Victor Lopez‐Richard, Gilmar Eugenio Marques

Published Aug 24, 2009• 10 citations
Publisher

Abstract

We study effects of spin-orbit coupling and electron-electron correlation, which can be electrically tuned, on the singlet-triplet entanglement in double lateral quantum dots charged with two electrons. We have found that the magnetic character of a double-dot system can be changed from diamagnetic to paramagnetic, only by adjusting the strength of spin-orbit coupling. Coulomb interaction leads to an unusual singlet-triplet energy splitting, accompanied by a shift of this transition energy to the lower magnetic field side in the energy spectrum.

DOI
10.1063/1.3210786

Related papers

Gate-controlled spin-spin interactions in lateral quantum dot molecules

Yun-Pil Shim, Paweł Hawrylak

We present a method of changing the effective spin-spin interactions of electrons localized in quantum dot molecules from antiferromagnetic to ferromagnetic using electrical means. We show that starting with antiferromagnetic interaction of two electrons localized in two quantum dots, the effective spin-spin interaction can change to ferromagnetic by allowing interaction with a third dot containing two spin singlet electrons. The total spin of this four-electron complex can be tuned by changing the third dot potential from singlet to triplet. This is demonstrated using the linear combination of harmonic orbitals combined with the configuration-interaction method mapped onto the Hubbard and an effective $t\text{\ensuremath{-}}J$ model for the triple dot system. All three approaches predict singlet-triplet spin transition, i.e., a mechanism for changing the magnitude and sign of the effective Heisenberg interaction between two localized spins.

Physical Review B•Oct 20, 2008•21 citations

Spin singlet-triplet transition in a Si-based two-electron double quantum dot molecule

S. D. Lee, Kim, S. J., Jian Kang +6 more

We report a successful measurement of the magnetic field-induced spin singlet-triplet transition in silicon-based coupled dot systems. Our specific experimental scheme incorporates a lateral gate-controlled Coulomb-blockaded structure in Si to meet the proposed scheme of Loss and DiVincenzo [1], and a non-equilibrium single-electron tunneling technique to probe the fine energy splitting between the spin singlet and triplet, which varies as a function of applying magnetic fields and interdot coupling constant. Our results, exhibiting the singlet-triplet crossing at a magnetic field for various interdot coupling constants, are in agreement with the theoretical predictions, and give the first experimental demonstration of the possible spin swapping occurring in the coupled double dot systems with magnetic field. *Electronic address: jungchoi@chungbuk.ac.kr [1] D. Loss and D. P. DiVincenzo, Phys. Rev. A 57, 120 (1998).

arXiv:cond-mat/0410044•Oct 2, 2004•0 citations

Competing mechanisms for singlet-triplet transition in artificial molecules

Devis Bellucci, Massimo Rontani, Filippo Troiani +2 more

We study the magnetic field induced singlet/triplet transition for two electrons in vertically-coupled quantum dots by exact diagonalization of the Coulomb interaction. We identify the different mechanisms occurring in the transition, involving either in-plane correlations or localization in opposite dots, depending on the field direction. Therefore, both spin and orbital degrees of freedom can be manipulated by field strength and direction. The phase diagram of realistic devices is determined.

arXiv:cond-mat/0405187•Physical Review B•May 20, 2004•33 citations

Kondo effect and singlet-triplet splitting in coupled quantum dots in a magnetic field

Vitaly N. Golovach, Daniel Loss

We study the interplay between Kondo correlations and the singlet-triplet exchange splitting K between the two spins in a double quantum dot. We calculate the cotunneling current with elastic and inelastic contributions and its renormalization due to Kondo correlations, away and at the degeneracy point K = 0. We show that these Kondo correlations induce pronounced peaks in the conductance G as a function of magnetic field B , inter-dot coupling t H , and temperature. The long-range part of the Coulomb interaction becomes visible due to Kondo correlations resulting in an additional peak in G vs. t H with a strong B -field dependence. These conductance peaks thus provide direct experimental access to K , and thus to a crucial control parameter for spin-based qubits and entanglement.

arXiv:cond-mat/0109155•Europhysics Letters (EPL)•Apr 1, 2003•19 citations

Spin interactions and switching in vertically tunnel-coupled quantum dots

Guido Burkard, Georg Seelig, Daniel Loss

We determine the spin-exchange coupling J between two electrons located in two vertically tunnel-coupled quantum dots, and its variation when magnetic (B) and electric (E) fields (both in-plane and perpendicular) are applied. We predict a strong decrease of J as the in-plane B field is increased, mainly due to orbital compression. Combined with the Zeeman splitting, this leads to a singlet-triplet crossing, which can be observed as a pronounced jump in the magnetization at in-plane fields of a few T, and perpendicular fields of the order of 10 T for typical self-assembled dots. We use harmonic potentials to model the confining of electrons, and calculate the exchange J using the Heitler-London and Hund-Mulliken techniques, including the long-range Coulomb interaction. With our results we provide experimental criteria for the distinction of singlet and triplet states, and therefore for microscopic spin measurements. In the case where dots of different sizes are coupled, we present a simple method to switch the spin coupling on and off with exponential sensitivity using an in-plane electric field. Switching the spin coupling is essential for quantum computation using electronic spins as qubits.

arXiv:cond-mat/9910105•Physical review. B, Condensed matter•Jul 15, 2000•141 citations

Impurity effects on semiconductor quantum bits in coupled quantum dots

Nga T. T. Nguyen, S. Das Sarma

We theoretically consider the effects of having unintentional charged impurities in laterally coupled two-dimensional double (GaAs) quantum-dot systems, where each dot contains one or two electrons and a single charged impurity. Using molecular orbital and configuration interaction methods, we calculate the effect of the impurity on the two-electron energy spectrum of each individual dot as well as on the spectrum of the coupled-double-dot two-electron system. We find that the singlet-triplet exchange splitting between the two lowest-energy states, both for the individual dots and the coupled-dot system, depends sensitively on the location of the impurity and its coupling strength (i.e. the effective charge). A strong electron-impurity coupling breaks down the equality of the two doubly occupied singlets in the left and the right dots, leading to a mixing between different spin singlets. As a result, the maximally entangled qubit states are no longer fully obtained in the zero-magnetic-field case. Moreover, a repulsive impurity results in a triplet-singlet transition as the impurity effective charge increases or the impurity position changes. We comment on the impurity effect in spin qubit operations in the double-dot system based on our numerical results.

arXiv:1103.0767•Physical Review B•Jun 14, 2011•44 citations
We study effects of spin-orbit coupling and electron-electron correlation, which can be electrically tuned, on the singlet-triplet entanglement in double lateral quantum dots charged with two electrons. We have found that the magnetic character of a double-dot system can be changed from diamagnetic to paramagnetic, only by adjusting the strength of spin-orbit coupling. Coulomb interaction leads to an unusual singlet-triplet energy splitting, accompanied by a shift of this transition energy to the lower magnetic field side in the energy spectrum.
We present a method of changing the effective spin-spin interactions of electrons localized in quantum dot molecules from antiferromagnetic to ferromagnetic using electrical means. We show that starting with antiferromagnetic interaction of two electrons localized in two quantum dots, the effective spin-spin interaction can change to ferromagnetic by allowing interaction with a third dot containing two spin singlet electrons. The total spin of this four-electron complex can be tuned by changing the third dot potential from singlet to triplet. This is demonstrated using the linear combination of harmonic orbitals combined with the configuration-interaction method mapped onto the Hubbard and an effective $t\text{\ensuremath{-}}J$ model for the triple dot system. All three approaches predict singlet-triplet spin transition, i.e., a mechanism for changing the magnitude and sign of the effective Heisenberg interaction between two localized spins.
We report a successful measurement of the magnetic field-induced spin singlet-triplet transition in silicon-based coupled dot systems. Our specific experimental scheme incorporates a lateral gate-controlled Coulomb-blockaded structure in Si to meet the proposed scheme of Loss and DiVincenzo [1], and a non-equilibrium single-electron tunneling technique to probe the fine energy splitting between the spin singlet and triplet, which varies as a function of applying magnetic fields and interdot coupling constant. Our results, exhibiting the singlet-triplet crossing at a magnetic field for various interdot coupling constants, are in agreement with the theoretical predictions, and give the first experimental demonstration of the possible spin swapping occurring in the coupled double dot systems with magnetic field. *Electronic address: jungchoi@chungbuk.ac.kr [1] D. Loss and D. P. DiVincenzo, Phys. Rev. A 57, 120 (1998).
We study the interplay between Kondo correlations and the singlet-triplet exchange splitting K between the two spins in a double quantum dot. We calculate the cotunneling current with elastic and inelastic contributions and its renormalization due to Kondo correlations, away and at the degeneracy point K = 0. We show that these Kondo correlations induce pronounced peaks in the conductance G as a function of magnetic field B , inter-dot coupling t H , and temperature. The long-range part of the Coulomb interaction becomes visible due to Kondo correlations resulting in an additional peak in G vs. t H with a strong B -field dependence. These conductance peaks thus provide direct experimental access to K , and thus to a crucial control parameter for spin-based qubits and entanglement.
We determine the spin-exchange coupling J between two electrons located in two vertically tunnel-coupled quantum dots, and its variation when magnetic (B) and electric (E) fields (both in-plane and perpendicular) are applied. We predict a strong decrease of J as the in-plane B field is increased, mainly due to orbital compression. Combined with the Zeeman splitting, this leads to a singlet-triplet crossing, which can be observed as a pronounced jump in the magnetization at in-plane fields of a few T, and perpendicular fields of the order of 10 T for typical self-assembled dots. We use harmonic potentials to model the confining of electrons, and calculate the exchange J using the Heitler-London and Hund-Mulliken techniques, including the long-range Coulomb interaction. With our results we provide experimental criteria for the distinction of singlet and triplet states, and therefore for microscopic spin measurements. In the case where dots of different sizes are coupled, we present a simple method to switch the spin coupling on and off with exponential sensitivity using an in-plane electric field. Switching the spin coupling is essential for quantum computation using electronic spins as qubits.
We theoretically consider the effects of having unintentional charged impurities in laterally coupled two-dimensional double (GaAs) quantum-dot systems, where each dot contains one or two electrons and a single charged impurity. Using molecular orbital and configuration interaction methods, we calculate the effect of the impurity on the two-electron energy spectrum of each individual dot as well as on the spectrum of the coupled-double-dot two-electron system. We find that the singlet-triplet exchange splitting between the two lowest-energy states, both for the individual dots and the coupled-dot system, depends sensitively on the location of the impurity and its coupling strength (i.e. the effective charge). A strong electron-impurity coupling breaks down the equality of the two doubly occupied singlets in the left and the right dots, leading to a mixing between different spin singlets. As a result, the maximally entangled qubit states are no longer fully obtained in the zero-magnetic-field case. Moreover, a repulsive impurity results in a triplet-singlet transition as the impurity effective charge increases or the impurity position changes. We comment on the impurity effect in spin qubit operations in the double-dot system based on our numerical results.