Shot-Noise Detection in a Carbon Nanotube Quantum Dot

Onac, E.; Balestro, Franck; Trauzettel, Björn; Lodewijk, C. F. J.; Kouwenhoven, Leo P.

doi:10.1103/physrevlett.96.026803

Cited by 137 publications

(164 citation statements)

References 15 publications

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“…These experiments are technically challenging in the Kondo regime notwithstanding recent progresses [8]. Noise can probe out of equilibrium properties of the model.…”

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confidence: 99%

Current Noise through a Kondo Quantum Dot in aSU(N)Fermi Liquid State

Mora¹,

Leyronas²,

Regnault³

2008

Phys. Rev. Lett.

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The current noise through a mesoscopic quantum dot is calculated and analyzed in the Fermi liquid regime of the SU(N) Kondo model. Results connect the Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and temperature, and show that temperature corrections are sizeable in usual experiments. For the experimentally relevant SU(4) case, quasiparticle interactions are shown to increase the shot noise. PACS numbers: 72.70.+m, 72.15.Qm, 71.10.Ay, 73.63.Fg, 73.63.Kv The Kondo effect [1], i.e. the screening of a local spin by coupling to conduction electrons, is a paradigm for strongly correlated systems as it exhibits sophisticated many-body correlations with a quite simple model. Its tunable realization in mesoscopic quantum dots, semiconductors, or carbon nanotubes, has triggered a renewed interest [2] in Kondo physics probed by transport measurements. In the ground state, the dot spin is screened by a cloud of conduction electrons and forms a singlet. Low energy properties of remaining electrons are described by a local Fermi liquid theory [3]. In this theory, electrons are scattered elastically by the singlet in a similar way as by a resonant level. Electrons also interact through polarization of the spin singlet. The ratio of elastic to inelastic scattering is fixed by universality, i.e. the Kondo temperature T K is the only scale that governs low energy properties of the model. This description applies to SU(2) symmetry but also more generally to SU(N). In that case, both the spin and orbital degrees of freedom are screened by delocalized electrons in the reservoirs. In particular, the SU(4) case has become recently the subject of extensive investigation. Various experimental settings have been proposed [4,5] and its realization has been reported already in vertical quantum dots [6] and carbon nanotubes [7].A promising experimental tool to study Kondo physics is current noise measurement. These experiments are technically challenging in the Kondo regime notwithstanding recent progresses [8]. Noise can probe out of equilibrium properties of the model. This has not been much investigated so far since only a few theoretical methods [9,10,11] apply to the out of equilibrium situation in comparison with the equilibrium case. In particular, the shot-noise at low temperature could provide information on the statistics of charge transfer. Interestingly, a picture has emerged recently [12,13] for the SU(2) Kondo effect at low energy where scattering events of two electrons lead to an effective charge of 5/3 e in the backscattering current. This emphasizes the strong role of interactions for charge transfer even in the vicinity of a Fermi liquid fixed point.The heating due to voltage polarization and the decoupling of phonons to electrons at low energy implies that the temperature of electrons is never really small in practical situations. It is therefore highly desirable to have a theory that holds at finite temperature. The purpose of this letter is to provide a general analysis for the zero-fre...

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“…These experiments are technically challenging in the Kondo regime notwithstanding recent progresses [8]. Noise can probe out of equilibrium properties of the model.…”

mentioning

confidence: 99%

Current Noise through a Kondo Quantum Dot in aSU(N)Fermi Liquid State

Mora¹,

Leyronas²,

Regnault³

2008

Phys. Rev. Lett.

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“…Pioneering measurements [3,4,5] of shot noise in quantum point contacts (QPCs) observed the predicted [6] suppression of shot noise below the Poisson value due to Fermi statistics. In regimes where many-body effects are strong, shot noise measurements have been exploited to directly observe quasiparticle charge in strongly correlated systems [7,8,9] as well as to study coupled localized states in mesoscopic tunnel junctions [10] and cotunneling in nanotube-based quantum dots [11].Paralleling these developments, a large literature has emerged concerning the surprising appearance of an additional plateau in transport through a QPC at zero magnetic field, termed 0.7 structure. Experiment [12,13,14] and theory [15,16] suggest that 0.7 structure is a manybody spin effect.…”

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confidence: 99%

Shot-Noise Signatures of 0.7 Structure and Spin in a Quantum Point Contact

et al. 2006

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We report simultaneous measurement of shot noise and dc transport in a quantum point contact as a function of source-drain bias, gate voltage, and in-plane magnetic field. Shot noise at zero field exhibits an asymmetry related to the 0.7 structure in conductance. The asymmetry in noise evolves smoothly into the symmetric signature of spin-resolved electron transmission at high field. Comparison to a phenomenological model with density-dependent level splitting yields good quantitative agreement.Shot noise, the temporal fluctuation of current resulting from the quantization of charge, is sensitive to quantum statistics, scattering and many-body effects [1,2]. Pioneering measurements [3,4,5] of shot noise in quantum point contacts (QPCs) observed the predicted [6] suppression of shot noise below the Poisson value due to Fermi statistics. In regimes where many-body effects are strong, shot noise measurements have been exploited to directly observe quasiparticle charge in strongly correlated systems [7,8,9] as well as to study coupled localized states in mesoscopic tunnel junctions [10] and cotunneling in nanotube-based quantum dots [11].Paralleling these developments, a large literature has emerged concerning the surprising appearance of an additional plateau in transport through a QPC at zero magnetic field, termed 0.7 structure. Experiment [12,13,14] and theory [15,16] suggest that 0.7 structure is a manybody spin effect. Its underlying microscopic origin, however, remains an outstanding problem in mesoscopic physics. This persistently unresolved issue is remarkable given the simplicity of the device.In this Letter, we report simultaneous measurements of the shot noise at 2 MHz and dc transport in a QPC, exploring the noise signature of the 0.7 structure and its evolution with in-plane magnetic field B . A suppression of the noise relative to that predicted by theory for spindegenerate transport [6] is observed near 0.7 × 2e 2 /h at B = 0, in agreement with results from Roche et al. [14] obtained at kHz frequencies. This suppression evolves smoothly with increasing B into the signature of spinresolved transmission. We find quantitative agreement between noise data and a phenomenological model for a density-dependent level splitting [16], with model parameters extracted solely from conductance.Measurements are performed on a gate-defined QPC fabricated on the surface of a GaAs/Al 0.3 Ga 0.7 As heterostructure grown by molecular beam epitaxy (see mi- * These authors contributed equally to this work. FIG. 1: Equivalent circuit near 2 MHz of the noise detection sys-tem measuring QPC noise by cross-correlation on two amplification channels [17]. The scanning electron micrograph shows a device of identical design to the one measured. The QPC is formed by negative voltages V g1 and V g2 applied on two facing electrostatic gates. All other gates on the device are grounded. crograph in Fig. 1). The two-dimensional electron gas 190 nm below the surface has a density of 1.7 × 10 −11 cm −2 and mobility 5.6 × 10 6 cm 2 /Vs. A...

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“…The dc current I gives the average over many switches and is thus related to the stationary probability by I 1 ÿ p 2 I 1 p 2 I 2 . The values of I 1 , I 2 , and I are determined through measurement and p 2 is inferred.When the QPC and qubit are weakly coupled [7,8], a single electron is transferred [9]. This liberates at most energy eV, implying that the rate ÿ 21 is zero when " > eV and the rate ÿ 12 is zero when " < ÿeV.…”

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confidence: 99%

“…When the QPC and qubit are weakly coupled [7,8], a single electron is transferred [9]. This liberates at most energy eV, implying that the rate ÿ 21 is zero when " > eV and the rate ÿ 12 is zero when " < ÿeV.…”

mentioning

confidence: 99%

Polarization of a Charge Qubit Strongly Coupled to a Voltage-Driven Quantum Point Contact

Snyman

Nazarov

2007

Phys. Rev. Lett.

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We study a charge qubit with level splitting ", coupled to a quantum point contact driven by voltage V. In the limit of weak coupling, the qubit polarization shows cusps at " eV. We show that, for stronger couplings, prominent peculiarities occur at fractions " eV=2. Further increase of the coupling leads to a polarization corresponding to a pseudo Boltzmann distribution with an effective temperature eV. DOI: 10.1103/PhysRevLett.99.096802 PACS numbers: 73.23.ÿb, 03.67.Lx, 73.40.Jn, 85.30.Hi The quantum point contact [1] has become a basic concept in the field of quantum transport owing to its simplicity. Its common experimental realization is a narrow constriction that connects two metallic reservoirs. An adequate theoretical description for this setup is a noninteracting one-dimensional electron gas interrupted by a potential barrier. The barrier is completely characterized by its scattering matrix. This enables the scattering approach to quantum transport [2].Despite the correctness of the noninteracting electron description, truly many-body quantum correlations in a QPC do exist and are observable. These manifest themselves in the full counting statistics (FCS) of electron transfers [3] and allow for detection of two-particle entanglement [4] through the measurement of nonlocal current correlations. This suggests that the observation of manybody effects in a QPC crucially relies on a proper detection scheme.In this Letter, we probe a QPC with a charge qubit. Such a device has already been realized using single and double quantum dots. Previously, the QPC has been used as a detector of the qubit state [5,6]. We propose a scheme in which these roles are reversed. Provided the qubit and QPC are coupled strongly, switching between the qubit states is accompanied by severe Fermi-Sea shake-up in the QPC. The ratio of switching rates determines the qubit polarization. The dc current in the QPC reads the qubit polarization. Thereby we obtain information about the Fermi-Sea shake-up in the QPC.For our results to apply, the qubit transition rate induced by the QPC should therefore dominate the rate due to coupling with other environmental modes. We estimate this requirement to be fulfilled already in the weak coupling regime.Before analyzing the system in detail, the following qualitative conclusions can be drawn. The qubit owes its detection capabilities to the following fact: In order to be excited it has to absorb a quantum " of energy from the QPC. Here " is the qubit level splitting, a parameter that can be tuned easily in an experiment by means of a gate voltage. The QPC supplies the energy by transferring charge from the high voltage reservoir to the low voltage reservoir. The transfer of charge q allows qubit transitions for level splittings " < qV, V being the bias-voltage applied. Thus, the creation of excitations in the QPC is correlated with qubit switching.We can assume that successive switchings of the qubit between its states j1i and j2i are rare and uncorrelated. The qubit dynamics are then characte...

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Shot-Noise Detection in a Carbon Nanotube Quantum Dot

Cited by 137 publications

References 15 publications

Current Noise through a Kondo Quantum Dot in aSU(N)Fermi Liquid State

Current Noise through a Kondo Quantum Dot in aSU(N)Fermi Liquid State

Shot-Noise Signatures of 0.7 Structure and Spin in a Quantum Point Contact

Polarization of a Charge Qubit Strongly Coupled to a Voltage-Driven Quantum Point Contact

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