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

Chinese Physics B

Quantum Coherence in Triangular Triple Quantum Dots and Its Application to Quantum Circuits

JunqingLi, JianHua Wei

Published Apr 8, 2026• 0 citations
Publisher

Abstract

Abstract Coherence is a fundamental physical quantity that plays a key role in characterizing the superposition and entanglement of quantum states. In this study, we investigate the coherence properties of a triangular triple-quantum-dot system as functions of coupling strength t , Coulomb repulsion U , and temperature T . We compare the coherence in this triangular configuration with that in a series triple quantum dot structure, and find that the triangular arrangement exhibits significantly enhanced coherence. The effect of an external phase on coherence is also examined, revealing periodic modulation. Furthermore, we analyze the implementation of a CSWAP quantum gate within the triangular triple-quantum-dot platform. Leveraging the high-coherence regime, we decompose the CSWAP gate into a sequence of three CNOT gates and two Toffoli gates. By tuning inter-dot couplings and applying magnetic fields, we realize the CSWAP operation and estimate the required gate time. Triangular triple-quantum-dots are considered a promising platform for quantum computing due to their ability to host chiral spin states and maintain robust quantum coherence, which is essential for high fidelity qubit operations. Our results identify optimal parameter regimes for coherence enhancement and provide a theoretical foundation for implementing advanced quantum gates in chiral qubit architectures, paving the way toward scalable quantum computation.

DOI
10.1088/1674-1056/ae5c72

Related papers

Geometric control of concurrence and quantum gate operations in triangular triple quantum dots

Junqing Li, Shuo Dong, Jianhua Wei

Abstract As an important index to measure the degree of entanglement in quantum systems, concurrence plays an important role in practical research. In this paper, we study the concurrence between two qubits in triangular triple quantum dot structure. Through calculation and simulation, it is found that concurrence is mainly affected by the interdot coupling strength t , Coulomb interaction U , temperature T , and electrode coupling Γ . Through comparative studies with parallel triple quantum dot structures, we demonstrate that the triangular geometry exhibits significantly enhanced concurrence under identical conditions. In addition, under the condition that concurrence exceeds 0.9, the functional relationship between t and U is obtained through simulation, which provides theoretical support for quantum dot regulation under high entanglement. Finally, we demonstrate the feasibility of implementing a three-qubit quantum gate, using the Toffoli gate as a representative example, under the condition that the triangular triple quantum dot system maintains high entanglement.

Chinese Physics B•Jul 7, 2025•0 citations

Quantum Circuit Based on Electron Spins in Semiconductor Quantum Dots

Chang‐Yu Hsieh

In this thesis, I present a microscopic theory of quantum circuits based on interacting electron spins in quantum dot molecules. We use the Linear Combination of Harmonic Orbitals-Configuration Interaction (LCHO-CI) formalism for microscopic calculations. We then derive effective Hubbard, t-J, and Heisenberg models. These models are used to predict the electronic, spin and transport properties of a triple quantum dot molecule (TQDM) as a function of topology, gate configuration, bias and magnetic field. With these theoretical tools and fully characterized TQDMs, we propose the following applications: 1. Voltage tunable qubit encoded in the chiral states of a half-filled TQDM. We show how to perform single qubit operations by pulsing voltages. We propose the "chirality-to-charge" conversion as the measurement scheme and demonstrate the robustness of the chirality-encoded qubit due to charge fluctuations. We derive an effective qubit-qubit Hamiltonian and demonstrate the two-qubit gate. This provides all the necessary operations for a quantum computer built with chirality-encoded qubits. 2. Berry's phase. We explore the prospect of geometric quantum computing with chirality-encoded qubit. We construct a Herzberg circuit in the voltage space and show the accumulation of Berry's phase. 3. Macroscopic quantum states on a semiconductor chip. We consider a linear chain of TQDMs, each with 4 electrons, obtained by nanostructuring a metallic gate in a field effect transistor. We theoretically show that the low energy spectrum of the chain maps onto that of a spin-1 chain. Hence, we show that macroscopic quantum states, protected by a Haldane gap from the continuum, emerge. In order to minimize decoherence of electron spin qubits, we consider using electron spins in the p orbitals of the valence band (valence holes) as qubits. We develop a theory of valence hole qubit within the 4-band k.p model. We show that static magnetic fields can be used to perform single qubit operations. We also show that the qubit-qubit interactions are sensitive to the geometry of a quantum dot network. For vertical qubit arrays, we predict that there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.

•Jan 1, 2012•0 citations

Herzberg circuit and Berry's phase in chirality-based coded qubit in a triangular triple quantum dot

Chang‐Yu Hsieh, Alexandre René, Paweł Hawrylak

We present a theoretical proposal for the Herzberg circuit and controlled accumulation of Berry's phase in a chirality-based coded qubit in a triangular triple quantum dot molecule with one electron each. The qubit is encoded in the two degenerate states of a three-spin complex with total spin $S=1/2$. Using a Hubbard and Heisenberg model the Herzberg circuit encircling the degeneracy point is realized by adiabatically tuning the successive on-site energies of quantum dots and tunnel couplings across a pair of neighboring dots. It is explicitly shown that encircling the degeneracy point leads to the accumulation of the geometrical Berry's phase. We show that only the triangular, not the linear, quantum dot molecule allows for the generation of Berry's phase and we discuss a protocol to detect this geometrical phase.

arXiv:1110.4983•Physical Review B•Sep 6, 2012•23 citations

Control of spin blockade by ac magnetic fields in triple quantum dots

Maria Busl, Rafael Sánchez, Gloria Platero

We analyze coherent spin phenomena in triple quantum dots in triangular configuration under crossed dc and ac magnetic fields. In particular, we discuss the interplay between Aharonov-Bohm current oscillations, coherent electron trapping and spin blockade under two-electron-spin-resonance configurations. We demonstrate an unexpected antiresonant behavior in the current, allowing for both removal and restoration of maximally entangled spin-blockaded states by tuning the ac field frequency. Our theoretical predictions indicate how to manipulate spin qubits in a triangular quantum dot array.

arXiv:0907.0182•Physical Review B•Mar 15, 2010•71 citations

Quantum gates between two spins in a triple-dot system with an empty dot

Jose Garcia Coello, Sougato Bose

We propose a scheme for implementing quantum gates and entanglement between spin qubits in the outer dots of a triple-dot system with an empty central dot. The voltage applied to the central dot can be tuned to realize the gate. Our scheme exemplifies the possibility of quantum gates outside the regime where each dot has an electron, so that spin-spin exchange interaction is not the only relevant mechanism. Analytic treatment is possible by mapping the problem to a $t\ensuremath{-}J$ model. The fidelity of the entangling quantum gate between the spins is analyzed in the presence of decoherence stemming from a bath of nuclear spins, as well as from charge fluctuations. Our scheme provides an avenue for extending the scope of two-qubit gate experiments to triple dots, while requiring minimal control, namely that of the potential of a single dot, and may enhance the qubit separation to ease differential addressability.

arXiv:1104.0716•Physical Review B•Jul 9, 2013•0 citations

Quantum Gates for Quantum Dots

Matthew P. Wardrop

Since the mid-20th century it has been understood that a general-purpose quan- tum computer would be able to efficiently solve problems that will forever be out-of-reach for conventional computers. Since then, many quantum algorithms have been developed with applications in a wide range of domains including cryptography, simulations, machine learning and data analysis. While this has resulted in substantial attention being paid to the development of quantum com- puters, the best architectures to use in their fabrication is not yet clear. Semiconductor quantum dot devices are a particularly promising candidate for use in quantum computing architectures, as it is anticipated that once the funda- mental building blocks are implemented, they might be massively scalable using the existing lithography techniques of the semiconductor industry. So far, how- ever, it is not yet clear how best to implement the high-fidelity gates required for general-purpose quantum computation. In this thesis, we present and characterise novel theoretical proposals for fast, simple and high-fidelity two-qubit gates using magnetic (exchange) coupling for specific semiconductor quantum dot qubits; namely, the singlet-triplet and resonant-exchange qubits. These two-qubit operations are simple enough that it is feasible for them to be implemented in experiments of the near future. Success- ful implementations would significantly extend the experimentally demonstrable frontier of semi-conductor quantum dot devices as relevant to their use in uni- versal quantum computing architectures. We also develop simple parameter estimation schemes by which it is possible to substantially mitigate the dominant sources of error for our proposed gates; namely, low-frequency charge and magnetic noise. We develop the techniques in the context of pseudo-static magnetic field gradient fluctuations in singlet- triplet qubits, and demonstrate that these techniques lead to a several orders of magnitude improvement in single-qubit coherence times. With minimal effort this could be ported to other qubit architectures.

•Aug 11, 2015•0 citations
Abstract Coherence is a fundamental physical quantity that plays a key role in characterizing the superposition and entanglement of quantum states. In this study, we investigate the coherence properties of a triangular triple-quantum-dot system as functions of coupling strength t , Coulomb repulsion U , and temperature T . We compare the coherence in this triangular configuration with that in a series triple quantum dot structure, and find that the triangular arrangement exhibits significantly enhanced coherence. The effect of an external phase on coherence is also examined, revealing periodic modulation. Furthermore, we analyze the implementation of a CSWAP quantum gate within the triangular triple-quantum-dot platform. Leveraging the high-coherence regime, we decompose the CSWAP gate into a sequence of three CNOT gates and two Toffoli gates. By tuning inter-dot couplings and applying magnetic fields, we realize the CSWAP operation and estimate the required gate time. Triangular triple-quantum-dots are considered a promising platform for quantum computing due to their ability to host chiral spin states and maintain robust quantum coherence, which is essential for high fidelity qubit operations. Our results identify optimal parameter regimes for coherence enhancement and provide a theoretical foundation for implementing advanced quantum gates in chiral qubit architectures, paving the way toward scalable quantum computation.
Abstract As an important index to measure the degree of entanglement in quantum systems, concurrence plays an important role in practical research. In this paper, we study the concurrence between two qubits in triangular triple quantum dot structure. Through calculation and simulation, it is found that concurrence is mainly affected by the interdot coupling strength t , Coulomb interaction U , temperature T , and electrode coupling Γ . Through comparative studies with parallel triple quantum dot structures, we demonstrate that the triangular geometry exhibits significantly enhanced concurrence under identical conditions. In addition, under the condition that concurrence exceeds 0.9, the functional relationship between t and U is obtained through simulation, which provides theoretical support for quantum dot regulation under high entanglement. Finally, we demonstrate the feasibility of implementing a three-qubit quantum gate, using the Toffoli gate as a representative example, under the condition that the triangular triple quantum dot system maintains high entanglement.
In this thesis, I present a microscopic theory of quantum circuits based on interacting electron spins in quantum dot molecules. We use the Linear Combination of Harmonic Orbitals-Configuration Interaction (LCHO-CI) formalism for microscopic calculations. We then derive effective Hubbard, t-J, and Heisenberg models. These models are used to predict the electronic, spin and transport properties of a triple quantum dot molecule (TQDM) as a function of topology, gate configuration, bias and magnetic field. With these theoretical tools and fully characterized TQDMs, we propose the following applications: 1. Voltage tunable qubit encoded in the chiral states of a half-filled TQDM. We show how to perform single qubit operations by pulsing voltages. We propose the "chirality-to-charge" conversion as the measurement scheme and demonstrate the robustness of the chirality-encoded qubit due to charge fluctuations. We derive an effective qubit-qubit Hamiltonian and demonstrate the two-qubit gate. This provides all the necessary operations for a quantum computer built with chirality-encoded qubits. 2. Berry's phase. We explore the prospect of geometric quantum computing with chirality-encoded qubit. We construct a Herzberg circuit in the voltage space and show the accumulation of Berry's phase. 3. Macroscopic quantum states on a semiconductor chip. We consider a linear chain of TQDMs, each with 4 electrons, obtained by nanostructuring a metallic gate in a field effect transistor. We theoretically show that the low energy spectrum of the chain maps onto that of a spin-1 chain. Hence, we show that macroscopic quantum states, protected by a Haldane gap from the continuum, emerge. In order to minimize decoherence of electron spin qubits, we consider using electron spins in the p orbitals of the valence band (valence holes) as qubits. We develop a theory of valence hole qubit within the 4-band k.p model. We show that static magnetic fields can be used to perform single qubit operations. We also show that the qubit-qubit interactions are sensitive to the geometry of a quantum dot network. For vertical qubit arrays, we predict that there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.
We present a theoretical proposal for the Herzberg circuit and controlled accumulation of Berry's phase in a chirality-based coded qubit in a triangular triple quantum dot molecule with one electron each. The qubit is encoded in the two degenerate states of a three-spin complex with total spin S=1/2S=1/2S=1/2. Using a Hubbard and Heisenberg model the Herzberg circuit encircling the degeneracy point is realized by adiabatically tuning the successive on-site energies of quantum dots and tunnel couplings across a pair of neighboring dots. It is explicitly shown that encircling the degeneracy point leads to the accumulation of the geometrical Berry's phase. We show that only the triangular, not the linear, quantum dot molecule allows for the generation of Berry's phase and we discuss a protocol to detect this geometrical phase.
We analyze coherent spin phenomena in triple quantum dots in triangular configuration under crossed dc and ac magnetic fields. In particular, we discuss the interplay between Aharonov-Bohm current oscillations, coherent electron trapping and spin blockade under two-electron-spin-resonance configurations. We demonstrate an unexpected antiresonant behavior in the current, allowing for both removal and restoration of maximally entangled spin-blockaded states by tuning the ac field frequency. Our theoretical predictions indicate how to manipulate spin qubits in a triangular quantum dot array.
We propose a scheme for implementing quantum gates and entanglement between spin qubits in the outer dots of a triple-dot system with an empty central dot. The voltage applied to the central dot can be tuned to realize the gate. Our scheme exemplifies the possibility of quantum gates outside the regime where each dot has an electron, so that spin-spin exchange interaction is not the only relevant mechanism. Analytic treatment is possible by mapping the problem to a $t\ensuremath{-}J$ model. The fidelity of the entangling quantum gate between the spins is analyzed in the presence of decoherence stemming from a bath of nuclear spins, as well as from charge fluctuations. Our scheme provides an avenue for extending the scope of two-qubit gate experiments to triple dots, while requiring minimal control, namely that of the potential of a single dot, and may enhance the qubit separation to ease differential addressability.
Since the mid-20th century it has been understood that a general-purpose quan- tum computer would be able to efficiently solve problems that will forever be out-of-reach for conventional computers. Since then, many quantum algorithms have been developed with applications in a wide range of domains including cryptography, simulations, machine learning and data analysis. While this has resulted in substantial attention being paid to the development of quantum com- puters, the best architectures to use in their fabrication is not yet clear. Semiconductor quantum dot devices are a particularly promising candidate for use in quantum computing architectures, as it is anticipated that once the funda- mental building blocks are implemented, they might be massively scalable using the existing lithography techniques of the semiconductor industry. So far, how- ever, it is not yet clear how best to implement the high-fidelity gates required for general-purpose quantum computation. In this thesis, we present and characterise novel theoretical proposals for fast, simple and high-fidelity two-qubit gates using magnetic (exchange) coupling for specific semiconductor quantum dot qubits; namely, the singlet-triplet and resonant-exchange qubits. These two-qubit operations are simple enough that it is feasible for them to be implemented in experiments of the near future. Success- ful implementations would significantly extend the experimentally demonstrable frontier of semi-conductor quantum dot devices as relevant to their use in uni- versal quantum computing architectures. We also develop simple parameter estimation schemes by which it is possible to substantially mitigate the dominant sources of error for our proposed gates; namely, low-frequency charge and magnetic noise. We develop the techniques in the context of pseudo-static magnetic field gradient fluctuations in singlet- triplet qubits, and demonstrate that these techniques lead to a several orders of magnitude improvement in single-qubit coherence times. With minimal effort this could be ported to other qubit architectures.