Shape-sensitive Pauli blockade in a bent carbon nanotube

Széchenyi, Gábor; Pályi, András

doi:10.1103/physrevb.91.045431

Cited by 13 publications

(24 citation statements)

References 55 publications

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“…Integrated over a frequency range up to F cutoff ∼ 2/T echo , this requires a total root-mean-square detuning jitter ∆ rms ≥ S ∆∆ F cutoff ∼ 2 mV (25) to explain the measured T echo .…”

Section: Contribution To Decoherencementioning

confidence: 99%

Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube

et al. 2017

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The decay of spin-valley states is studied in a suspended carbon nanotube double quantum dot via leakage current in Pauli blockade and via dephasing and decoherence of a qubit. From the magnetic field dependence of the leakage current, hyperfine and spin-orbit contributions to relaxation from blocked to unblocked states are identified and explained quantitatively by means of a simple model. The observed qubit dephasing rate is consistent with the hyperfine coupling strength extracted from this model and inconsistent with dephasing from charge noise. However, the qubit coherence time, although longer than previously achieved, is probably still limited by charge noise in the device.The co-existence in carbon nanotubes of spin and valley angular momenta opens a host of possibilities for quantum information [1][2][3][4], coherent coupling to mechanics [5,6], and on-chip entanglement [7,8]. Spin-orbit coupling [9] provides electrical control, but introduces a relaxation channel. However, measurements of dephasing and decoherence [10][11][12] show that spin and valley qubit states couple surprisingly strongly to lattice nuclear spins and to uncontrolled electric fields, e.g. from thermal switchers. Realising these possibilities requires such effects to be mitigated. Here we study leakage current in a Pauli blockaded double quantum dot to identify spin-orbit and hyperfine contributions to spin-valley relaxation [3,13,14]. By suspending the nanotube, we decouple it from the substrate [11]. Measuring a spinvalley qubit defined in the double dot, we find dephasing and decoherence rates nearly independent of temperature, and show that charge noise cannot explain the observed dephasing, supporting the conclusion that despite the low density of 13 C spins, hyperfine interaction causes rapid dephasing in nanotubes [10,11].The measured device [ Fig. 1(a-b)] is a carbon nanotube suspended by stamping between two contacts and over five gate electrodes G1-G5 [3,[15][16][17]. Gate voltages V G1 − V G5 , together with Schottky barriers at the contacts, define a double quantum dot potential. The dot potentials are predominantly controlled by gates G1 (for the left dot) and G4-5 (for the right dot), while the interdot tunnel barrier is controlled by gates G2-3. For fast manipulation, gates G1 and G5 are connected via tees to waveform generator outputs and a vector microwave source. The device is measured in a magnetic field B = (B X , B Y , B Z ), with Z chosen along the nanotube and X normal to the substrate. Experiments were in a dilution refrigerator at 15 mK unless stated.To map charge configurations of the double quantum dot, we measure the current I through the nanotube with source-drain bias V SD = 8 mV applied between the contacts [ Fig. 1(c)]. As a function of V G1 and V G4 , the honeycomb Coulomb peak pattern is characteristic of a double quantum dot, with honeycomb vertices marking transitions between particular electron or hole occupations [18]. A horizontal stripe of suppressed current around V G4 = 200 mV indicates depl...

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Section: Contribution To Decoherencementioning

confidence: 99%

Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube

et al. 2017

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“…The spin dephasing due to the hyperfine interaction with 13 C atoms was discussed for charge dynamics in a (0,2e)↔(1e,1e) cycle [28]. The leakage current across Pauli-blocked double dots in straight [29] and bent [30] CNT was also studied. Nevertheless, in CNTs the EDSR was observed only for ambipolar double dots [19,20], with a single electron occupying a n-type dot and a single hole stored in the p-type dot.…”

Section: Introductionmentioning

confidence: 99%

“…The original model [22] of the bend and the subsequent ones [23,30] assumed that the deflection of the CNT does not change along each of the QDs. However, in the experiments the CNT axis is bent due to its deposition above the metal gates [20].…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of (1e,1h) states of carbon nanotube quantum dots

Osika

Szafran

2016

Phys. Rev. B

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We provide an atomistic tight-binding description of a few carriers confined in ambipolar (n-p) double quantum dots defined in a semiconducting carbon nanotube. We focus our attention on the charge state of the system in which Pauli blockade of the current flow is observed [F. Pei et al., Nat. Nanotechnol. 7, 630 (2012); E. A. Laird et al., ibid 8, 565 (2013)] with a single excess electron in the n-dot and a single hole in the p-dot. We use the configuration interaction approach to determine the spin-valley structure of the states near the neutrality point and discuss its consequences for the interdot exchange interaction, the degeneracy of the energy spectrum and the symmetry of the confined states. We calculate the transition energies lifting the Pauli blockade and analyze their dependence on the magnetic field vector. Furthermore, we introduce bending of the nanotube and demonstrate its influence on the transition energy spectra. The best qualitative agreement with the experimental data is observed for nanotubes deflected in the gated areas in which the carrier confinement is induced.

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“…However, when the two electrons in the (1, 1) configuration occupy one of the triplet states |T 0 or |T ± [18], given by |T 0 = (|⇑ L |⇓ R + |⇓ L |⇑ R ) / √ 2, |T + = |⇑ L |⇑ R , and |T − = |⇓ L |⇓ R , the (1, 1) → (0, 2) transition is forbidden due to the Pauli exclusion principle. In such a Pauli-blockade regime [63], the spin-conserving tunneling between the two quantum dots can be described bŷ…”

mentioning

confidence: 99%

“…with the tunneling rate J between the singlet states |S = (|⇓ L |⇑ R − |⇑ L |⇓ R ) / √ 2 in the (1, 1) configuration and the corresponding singlet state S g in the (0, 2) configuration. In the case α R = −α L = α and B = (0, 0, B z ), on which we will focus, |T ± couple with the singlet state |S , while |T 0 remains blocked [63,64]. Assisted by such a T 0 -blockade mechanism, as well as the dipole-dipole coupling between the NV centers and the quantum dots, a maximally entangled steady state of the NV-center electron spins can be achieved.…”

mentioning

confidence: 99%

Nanotube double quantum dot spin transducer for scalable quantum information processing

Song

Liu

et al. 2020

New J. Phys.

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One of the key challenges for the implementation of scalable quantum information processing is the design of scalable architectures that support coherent interaction and entanglement generation between distant quantum systems. We propose a nanotube double quantum dot spin transducer that allows to achieve steady-state entanglement between nitrogen-vacancy center spins in diamond with spatial separations over micrometers. The distant spin entanglement further enables us to design a scalable architecture for solid-state quantum information processing based on a hybrid platform consisting of nitrogen-vacancy centers and carbon-nanotube double quantum dots. PACS numbers: 76.30.Mi,73.63.Kv,03.67.Bg Introduction.-Quantum computing with potential revolutionary applications [1, 2] has raised increasing interest over the past decades and intensive efforts are devoted to the implementation of quantum information processing. A large variety of physical systems provide promising candidates to construct the basic building blocks for quantum-information processing devices, e.g., photons [3][4][5][6], atoms [7-9], trapped ions [10][11][12][13], superconducting circuits [14-16], quantum dots [17][18][19], and spins in solids [20][21][22][23][24]. Despite their individual advantages, each of these physical systems is accompanied by its own drawbacks. These shortcomings call for the development of hybrid quantum systems [25][26][27][28][29] that combine the advantages of its constituents in order to overcome the difficulties toward the implementation of powerful quantum information processing devices. One well recognised severe challenge in terms of scalability is the implementation of coherent coupling between spatially separated quantum systems.Nitrogen-vacancy (NV) centers in diamond consist of both an electron spin and an intrinsic nuclear spin, where the electron spins can serve as a register to process quantum information, due to their excellent coherent controllability [30], and the nuclear spins can serve as a memory to store quantum information, due to their superb coherence time [31]. Unfortunately, the prospect of using NV centers for scalable quantum computing is hindered by the fact that the direct coupling between NV centers decays rapidly with their distance [32]. In order to overcome this obstacle, several schemes have been proposed using microwave and optical cavities [33][34][35][36][37][38], mechanical oscillators [39][40][41][42][43][44][45][46], spin-photon interface [47] to mediate the coupling between distant NV centers. However, the goal of long-range coupling between solid-state spins in a deterministic and scalable manner remains challenging to achieve due to e.g. the influence of cavity losses and the thermalization of mechanical oscillators.In this work, we propose an efficient strategy for steadystate entanglement generation between NV-center electron spins at micrometer distances, which is mediated by the leakage current of a carbon-nanotube double quantum dot (DQD) [48][49][50][51][52][53][54][55]...

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Shape-sensitive Pauli blockade in a bent carbon nanotube

Cited by 13 publications

References 55 publications

Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube

Hyperfine and Spin-Orbit Coupling Effects on Decay of Spin-Valley States in a Carbon Nanotube

Electronic structure of (1e,1h) states of carbon nanotube quantum dots

Nanotube double quantum dot spin transducer for scalable quantum information processing

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