Probing relaxation times in graphene quantum dots

Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, A.; Stampfer, Christoph

doi:10.1038/ncomms2738

Cited by 90 publications

(152 citation statements)

References 36 publications

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“…Using temperature-dependent measurements and calculating with a charge network model, we can extract g C , 2t C , and the lever arms of gates, which altogether give us a calibrated detuning [21,32]. In graphene QDs γ 1 has been reported to be less than 100 MHz [11]. Thus, the only unknown parameter is γ 2 , which is both critical and unexplored for graphene QDs.…”

mentioning

confidence: 99%

“…Various experiments are now underway to study the coherence properties of graphene QDs. For example, using pulsed-gate transient spectroscopy, Volk et al [11] measured a charge relaxation time of 100 ns in a graphene QD device. However, the dephasing times of grapheme QDs, which benchmark their quantum coherence and may be significantly shorter than their relaxation times, have not yet been measured.…”

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confidence: 99%

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Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

et al. 2015

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We use an on-chip superconducting resonator as a sensitive meter to probe the properties of graphene double quantum dots (DQDs) at microwave frequencies. Specifically, we investigate the charge dephasing rates in a circuit quantum electrodynamics (cQED) architecture. The dephasing rates strongly depend on the number of charges in the dots, and the variation has a period of four charges, over an extended range of charge numbers. Although the exact mechanism of this four-fold periodicity in dephasing rates is an open problem, our observations hint at the four-fold degeneracy expected in graphene from its spin and valley degrees of freedom.In recent years, on-chip microwave resonators have emerged as a useful tool both for coupling distant qubits and for sensitive metrology [1]. For example, many experimental studies have recently been performed to study the interaction between quantum dots (QDs) and resonators, in gate-defined carbon-nanotubes [2-4], GaAs [5,6] and InAs nanowire [7,8] structures. Such studies are motivated by considering QDs as promising candidates for quantum information processing. Graphene has also attracted considerable attention in recent years because of its interesting physical properties and potential applications [9]. Like semiconductors, graphene-based QDs have been proposed as potential quantum bits [10]. Various experiments are now underway to study the coherence properties of graphene QDs. For example, using pulsed-gate transient spectroscopy, Volk et al.[11] measured a charge relaxation time of 100 ns in a graphene QD device. However, the dephasing times of grapheme QDs, which benchmark their quantum coherence and may be significantly shorter than their relaxation times, have not yet been measured. In addition, graphene has both spin and valley degrees of freedom, similar to carbon nanotubes [12,13] and Si-based QDs [14]. Spin qubits formed by graphene QDs have been theoretically studied [10], and various valley-related phenomena such as shell filling in carbon nanotubes [12] and valley splitting in silicon [15] have been explored. However, there are no experimental reports on the effects of the four-fold degeneracy caused by the spin and valley degrees in graphene devices.Here, we present an experimental study of a graphene DQD device, which can be considered as a charge qubit that contains a large number of well-defined charge * Corresponding author: gpguo@ustc.edu.cn states. Using the sensitive dispersive readout of a microwave resonator, we measured the charge-state dephasing rates of this DQD in an integrated grapheneresonator device. Applying a quantum model describing the hybrid system, we simultaneously extracted: the DQD-resonator coupling strength, the tunneling rate between each quantum dot, and the charge-state dephasing rates. This microwave spectroscopy overcomes the difficulties of conventional transport techniques and allows us to study DQD dynamics in a large parameter space. In these experiments, we found that the dephasing rates depend on the number of charges in t...

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Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

et al. 2015

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“…For example, electron-phonon scattering has been shown to limit the charge-carrier mobility in graphene samples [33] and has also been argued to be the main mechanism for charge relaxation in QDs [27]. To gain an estimate of the charge relaxation times in graphene quantum dots, we thus focus on relaxation processes due to electron-phonon interaction.…”

Section: Electron-phonon Interaction and Charge Relaxation Timesmentioning

confidence: 99%

“…So far, Coulomb blockade [16][17][18][19], excited states [20][21][22], charge sensing [23,24], and spin-filling sequences [25] have been studied in detail in etched graphene quantum dot devices. More recently, also charge pumps [26] and charge relaxation times of excited states [27] in graphene quantum dots have been investigated experimentally. The extracted lifetimes are a factor of 5-10 larger, with an extracted lower bound of around 60-100 ns compared to III/V quantum dots [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Modeling charge relaxation in graphene quantum dots induced by electron-phonon interaction

Reichardt

Stampfer

2016

Phys. Rev. B

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We study and compare two analytic models of graphene quantum dots for calculating charge relaxation times due to electron-phonon interaction. Recently, charge relaxation processes in graphene quantum dots have been probed experimentally and here we provide a theoretical estimate of relaxation times. By comparing a model with pure edge confinement to a model with electrostatic confinement, we find that the latter features much larger relaxation times. Interestingly, relaxation times in electrostatically defined quantum dots are predicted to exceed the experimentally observed lower bound of ∼100 ns.

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“…In a recent investigation, the Ref. [18] analyzes how the sublattices or chiral symmetries 19 (SLS) affect the electronic transport through a chaotic quantum (Dirac) billiard 20,21 , which henceforth we call chaotic Dirac Billiard (DB) 22 . Through this device, the wave functions of the electrons are described by massless Dirac equation of the corresponding relativistic quantum mechanics, instead of Schrödinger equation.…”

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Anomalous entanglement in chaotic Dirac billiards

Ramos¹,

Silva²,

Barbosa³

2014

Phys. Rev. B

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We present analytical and numerical results that demonstrate the presence of anomalous entanglement behavior on the Dirac Billiards. We investigate the statistical distribution of the characteristic entangled measures, focusing on the mean, on the variance and on the quantum interference terms. We show a quite distinct behavior of the Dirac Billiard compared with the non-relativist (Schrödinger) ones. Particularly, we show a very plausible Bell state and a sharp amplitude of quantum interference term on entangled electrons left from the Dirac Billiards. The results have remarkable relevance to the novel quantum dots build of materials like graphene or topological insulators.PACS numbers: 73.21.La,05.45.Mt The entanglement is one the most fundamental effect on quantum mechanics, with no classical analog 1 . Two or more particles are entangled if they support a nonlocal correlation which cannot be acquired by the dynamics of classical mechanics 2 . Because its non-classical characteristics, the control of entangled states has attracted the interest of numerous science communities 3 . The technological applications of the effect has a broad range as quantum computation, teleportation, telecommunication and cryptography [2][3][4] .A large number of mechanism to entangle electronic particles, with or without interaction, can be found in the literature 4-6 , and the quantum chaotic devices are a promising option 7,8 . In a recent work, Beenakker et al.9 proposed the possibility to entangle two noninteracting electrons using, as an orbital entangler, a quantum (Schrödinger) chaotic billiard or, as we will call henceforth, the Schrödinger Billiard (SB). They obtained the averages and variances of concurrence and entanglement. However the results were found to be nearly invariant under the presence or absence of time-reversal symmetry (TRS). This means that the quantum interference corrections (weak-localization) of two arbitrary entanglement measures are approximately null, in contrast with another physical observables of electronic transport as conductance and shot-noise power. Nevertheless, the Ref.[10] has argued that the two first moments of entanglement measures do not capture the full information about quantum dynamics, and the complete information about fundamental symmetries of nature emerges only on the distribution probabilities. More recently, the effects of tunneling barriers 11,12 on statistic of concurrence and joint probability distribution of concurrence and squared norm 12,13 for SB were also studied. 22 . Through this device, the wave functions of the electrons are described by massless Dirac equation of the corresponding relativistic quantum mechanics, instead of Schrödinger equation. The two categories of billiards show blunt differences on the corresponding electronic transport statistics, which leads us to suspect that a subtle difference occurs also on the quantum entanglement statistical moments.In this work, we analyze the concurrence and entanglement statistics of two non-interacting electro...

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Probing relaxation times in graphene quantum dots

Cited by 90 publications

References 36 publications

Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

Modeling charge relaxation in graphene quantum dots induced by electron-phonon interaction

Anomalous entanglement in chaotic Dirac billiards

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