Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot

Mavalankar, Aquila; Pei, T.; Gauger, Erik M.; Warner, Jamie H.; Briggs, G. A. D.; Laird, E.

doi:10.1103/physrevb.93.235428

Cited by 16 publications

(21 citation statements)

References 38 publications

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“…Unlike G1 and G5, these gates are not coupled to highfrequency lines and are much better filtered at low temperature (with two-pole 100 kHz RC filters [16]). However, these gates affect inter-dot tunneling more than G1 and G5.…”

Section: Dephasing Due To Voltage Noise On Other Gatesmentioning

confidence: 99%

“…white) over a frequency range extending from zero to a few times 1/T echo . Equation (16) then gives…”

Section: Contribution To Decoherencementioning

confidence: 99%

“…That experiment did not allow conclusive determination of dephasing or decoherence mechanisms, with charge noise [16] and hyperfine coupling [1,10] being leading candidates. In our device, we now show that charge noise does not limit T * [17].)…”

mentioning

confidence: 99%

“…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.…”

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confidence: 99%

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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: Dephasing Due To Voltage Noise On Other Gatesmentioning

confidence: 99%

“…white) over a frequency range extending from zero to a few times 1/T echo . Equation (16) then gives…”

Section: Contribution To Decoherencementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

et al. 2017

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“…6(a)] the final one is (0,2)S ′ when the switching is fast on the τ S scale. The transition has then the Landau-Zener character [32][33][34][35] The charge occupation of the dots is left unchanged for the nonadiabatic abrupt switching. To be more precise, the abrupt potential change leaves a small admixture of (1,1)S state to (0,2)S ′ -which produces oscillations of the charge localized in the left dot in the limits that are marked in the upper panel of Fig.…”

Section: B the Spin Separation And Exchange Sequencementioning

confidence: 99%

Spin separation and exchange for quantum dots in the Overhauser field

Leśnicki

Szafran

2017

Phys. Rev. B

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We describe the spin and charge dynamics of the system of two electrons confined within a double quantum dot defined in a quantum wire. The spin dynamics is driven by the electron motion in presence of the spin-orbit interaction and the randomly varying local Overhauser field due to the nuclear spins. The Schroedinger equation is solved with the time-dependent configuration interaction method that allows for an exact description of the system dynamics. The procedures of the spin separation, exchange and read-out by the spin to charge conversion all induced by the detuning variation are simulated. The rates of the potential variation that are necessary for the spin separation and spin to charge conversion in the context of the Landau-Zener transitions are determined. The average over random configurations of the hyperfine field produce spin exchange results which qualitatively agree with the experimental data.

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Application of quantum dot system: Optically-controlled quantum switch and photon-electron pumping effect

Bai

Chen

et al. 2021

Physica B: Condensed Matter

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Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot

Cited by 16 publications

References 38 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

Spin separation and exchange for quantum dots in the Overhauser field

Application of quantum dot system: Optically-controlled quantum switch and photon-electron pumping effect

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