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

arXiv:cond-mat/0302572 · Physical Review B

Nonequilibrium stabilization of charge states in double quantum dots

Udo Hartmann, Frank K. Wilhelm

Published Apr 28, 2004• 7 citations
arXivHTMLPDF

Abstract

We analyze the decoherence of charge states in double quantum dots due to cotunneling. The system is treated using the Bloch-Redfield generalized master equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the decoherence, characterized through a relaxation ${\ensuremath{\tau}}_{r}$ and a dephasing time ${\ensuremath{\tau}}_{\ensuremath{\varphi}},$ can be controlled through the external voltage and that the optimum point, where these times are maximum, is not necessarily in equilibrium. We outline the mechanism of this nonequilibrium-induced enhancement of lifetime and coherence. We discuss the relevance of our results for recent charge qubit experiments.

DOI
10.1103/physrevb.69.161309

Related papers

Decoherence of Charge States in Double Quantum Dots Due to Cotunneling

U. Hartmann, Frank K. Wilhelm

Solid state quantum bits are a promising candidate for the realization of a scalable quantum computer, however, they are usually strongly limited by decoherence. We consider a double quantum dot charge qubit, whose basis states are defined by the position of an additional electron in the system of two laterally coupled quantum dots. The coupling of these two states can be controlled externally by a quantum point contact between the two dots. We discuss the decoherence through coupling to the electronic leads due to cotunneling processes. We focus on a simple Gedanken experiment, where the system is initially brought into a superposition and then the inter-dot coupling is removed nonadiabatically. We treat the system by invoking the Schrieffer-Wolff transformation in order to obtain a transformed Hamiltonian describing the cotunneling, and then obtain the dynamics of the density matrix using the Bloch-Redfield theory. As a main result, we show that there is energy relaxation even in the absence of inter-dot coupling. This is in contrast to what would be expected from the Spin-Boson model and is due to the fact that a quantum dot is coupled to two distinct baths.

arXiv:cond-mat/0208220•physica status solidi (b)•Oct 1, 2002•14 citations

Non-Markovian decoherence theory for a double-dot charge qubit

Matisse Wei-Yuan Tu, Wei-Min Zhang

In this paper, we develop a nonperturbation theory for describing decoherence dynamics of electron charges in a double quantum dot gated by electrodes. We extend the Feynman-Vernon influence functional theory to fermionic environments and derive an exact master equation for the reduced density matrix of electrons in the double dot for a general spectral density at arbitrary temperature and bias. We then investigate the decoherence dynamics of the double-dot charge qubit with backreaction of the reservoirs being fully taken into account. Time-dependent fluctuations and leakage effects induced from the dot-reservoir coupling are explicitly explored. The charge qubit dynamics from the Markovian to non-Markovian regime is systematically studied under various manipulating conditions. The decay behavior of charge qubit coherence and the corresponding relaxation time ${T}_{1}$ and dephasing time ${T}_{2}$ are analyzed in detail.

arXiv:0809.3490•Physical Review B•Dec 19, 2008•235 citations

Relaxation, dephasing, and quantum control of electron spins in double quantum dots

Jacob M. Taylor, J. R. Petta, Alex C. Johnson +3 more

Recent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here we present a detailed theory for electron-spin dynamics in two-electron double-dot systems that was used to guide those experiments and analyze the results. Specifically, we analyze both spin- and charge-relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron systems. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits.

arXiv:cond-mat/0602470•Physical Review B•Jul 13, 2007•357 citations

Dynamical charge susceptibility in nonequilibrium double quantum dots

Adeline Crépieux C, M. Lavagna

Double quantum dots are one of the promising two-state quantum systems for realizing qubits. In the quest of successfully manipulating and reading information in qubit systems, it is of prime interest to control the charge response of the system to a gate voltage, as filled in by the dynamical charge susceptibility. We theoretically study this quantity for a nonequilibrium double quantum dot by using the functional integral approach and derive its general analytical expression. One highlights the existence of two lines of maxima as a function of the dot level energies, each of them being split under the action of a bias voltage. In the low frequency limit, we derive the capacitance and the charge relaxation resistance of the equivalent quantum RC-circuit with a notable difference in the range of variation for $R$ depending on whether the system is connected in series or in parallel. By incorporating an additional triplet state in order to describe the situation of a double quantum dot with spin, we obtain results for the resonator phase response which are in qualitative agreement with recent experimental observations in spin qubit systems. These results show the wealth of information brought by the knowledge of dynamical charge susceptibility in double quantum dots with potential applications for spin qubits.

arXiv:2204.04943•Physical review. B./Physical review. B•Sep 30, 2022•4 citations

Decoherence by electromagnetic fluctuations in double-quantum-dot charge qubits

Diego C. B. Valente, Eduardo R. Mucciolo, Frank K. Wilhelm

We discuss decoherence due to electromagnetic fluctuations in charge qubits formed by two lateral quantum dots. We use effective circuit model to evaluate correlations of voltage fluctuations in the qubit setup. These correlations allows us to estimate energy $({T}_{1})$ and phase $({T}_{2})$ relaxation times of the qubit system. Our theoretical estimate of the quality factor due to dephasing by electromagnetic fluctuations yields values much higher than those found in recent experiments, indicating that other sources of decoherence play a dominant role.

arXiv:1005.0861•Physical Review B•Sep 3, 2010•12 citations

Controlled decoherence of a charge qubit in a double quantum dot

T. Fujisawa, T. Hayashi, Y. Hirayama

We investigate coherent time evolution of a charge qubit in a semiconductor double quantum dot. A high-speed voltage pulse controls the energy bias and strength of the decoherence of the system. The qubit is effectively isolated from the electrodes in the Coulomb blockade regime, while it is affected by dissipative tunneling processes in the single-electron tunneling regime. We discuss the importance of the controlled decoherence by means of density matrix simulations.

Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena•Jul 1, 2004•36 citations
We analyze the decoherence of charge states in double quantum dots due to cotunneling. The system is treated using the Bloch-Redfield generalized master equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the decoherence, characterized through a relaxation \ensuremathτr{\ensuremath{\tau}}_{r}\ensuremathτr​ and a dephasing time \ensuremathτ\ensuremathφ,{\ensuremath{\tau}}_{\ensuremath{\varphi}},\ensuremathτ\ensuremathφ​, can be controlled through the external voltage and that the optimum point, where these times are maximum, is not necessarily in equilibrium. We outline the mechanism of this nonequilibrium-induced enhancement of lifetime and coherence. We discuss the relevance of our results for recent charge qubit experiments.
Solid state quantum bits are a promising candidate for the realization of a scalable quantum computer, however, they are usually strongly limited by decoherence. We consider a double quantum dot charge qubit, whose basis states are defined by the position of an additional electron in the system of two laterally coupled quantum dots. The coupling of these two states can be controlled externally by a quantum point contact between the two dots. We discuss the decoherence through coupling to the electronic leads due to cotunneling processes. We focus on a simple Gedanken experiment, where the system is initially brought into a superposition and then the inter-dot coupling is removed nonadiabatically. We treat the system by invoking the Schrieffer-Wolff transformation in order to obtain a transformed Hamiltonian describing the cotunneling, and then obtain the dynamics of the density matrix using the Bloch-Redfield theory. As a main result, we show that there is energy relaxation even in the absence of inter-dot coupling. This is in contrast to what would be expected from the Spin-Boson model and is due to the fact that a quantum dot is coupled to two distinct baths.
In this paper, we develop a nonperturbation theory for describing decoherence dynamics of electron charges in a double quantum dot gated by electrodes. We extend the Feynman-Vernon influence functional theory to fermionic environments and derive an exact master equation for the reduced density matrix of electrons in the double dot for a general spectral density at arbitrary temperature and bias. We then investigate the decoherence dynamics of the double-dot charge qubit with backreaction of the reservoirs being fully taken into account. Time-dependent fluctuations and leakage effects induced from the dot-reservoir coupling are explicitly explored. The charge qubit dynamics from the Markovian to non-Markovian regime is systematically studied under various manipulating conditions. The decay behavior of charge qubit coherence and the corresponding relaxation time T1{T}_{1}T1​ and dephasing time T2{T}_{2}T2​ are analyzed in detail.
Recent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here we present a detailed theory for electron-spin dynamics in two-electron double-dot systems that was used to guide those experiments and analyze the results. Specifically, we analyze both spin- and charge-relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron systems. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits.
Double quantum dots are one of the promising two-state quantum systems for realizing qubits. In the quest of successfully manipulating and reading information in qubit systems, it is of prime interest to control the charge response of the system to a gate voltage, as filled in by the dynamical charge susceptibility. We theoretically study this quantity for a nonequilibrium double quantum dot by using the functional integral approach and derive its general analytical expression. One highlights the existence of two lines of maxima as a function of the dot level energies, each of them being split under the action of a bias voltage. In the low frequency limit, we derive the capacitance and the charge relaxation resistance of the equivalent quantum RC-circuit with a notable difference in the range of variation for RRR depending on whether the system is connected in series or in parallel. By incorporating an additional triplet state in order to describe the situation of a double quantum dot with spin, we obtain results for the resonator phase response which are in qualitative agreement with recent experimental observations in spin qubit systems. These results show the wealth of information brought by the knowledge of dynamical charge susceptibility in double quantum dots with potential applications for spin qubits.
We discuss decoherence due to electromagnetic fluctuations in charge qubits formed by two lateral quantum dots. We use effective circuit model to evaluate correlations of voltage fluctuations in the qubit setup. These correlations allows us to estimate energy (T1)({T}_{1})(T1​) and phase (T2)({T}_{2})(T2​) relaxation times of the qubit system. Our theoretical estimate of the quality factor due to dephasing by electromagnetic fluctuations yields values much higher than those found in recent experiments, indicating that other sources of decoherence play a dominant role.