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Journal of Jinggangshan University

THE SINGLET DECOHERENCE EFFECT OF QUANTUM DOT KONDO CAUSED BY THE PHASE MEASUREMENT

Lü Rong

Published Jan 1, 2011• 0 citations
OpenAlex

Abstract

For the singlet decoherence intensity of quantum dot Kondo in the QPC experiment,the difference is thirty times between experiment measurement and theory calculation and the cause is undiscovered until now.In this paper,we calculate the transport properties of quantum dot on QPC equipment and find that the phase measurement is a possible cause about the mystery.

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For the singlet decoherence intensity of quantum dot Kondo in the QPC experiment,the difference is thirty times between experiment measurement and theory calculation and the cause is undiscovered until now.In this paper,we calculate the transport properties of quantum dot on QPC equipment and find that the phase measurement is a possible cause about the mystery.
To investigate the decoherence of Kondo singlet, we once again check a model, an Aharonov–Bohm interferometer with a quantum dot coupling to left–right electrodes, which is designed by Yacoby to measure phase-sensitive of a quantum dot. By employing the cluster expansion, the equations of motion of Green's functions are transformed into the corresponding equations of connected Green's functions, which contain the correlation of two conducting electrons. With the method, we show that the Kondo singlet is suppressed by phase-sensitive detection of Aharonov–Bohm interferometer. Our numerical results have provided a qualitative explanation with the anomalous features observed in an experiment by Avinun-Kalish et al. [Phys. Rev. Lett.92 (2004) 156801].
We investigate the effect of the charge state measurement of the Kondo singlet in a quantum dot transistor via a capacitively coupled quantum point contact detector. By employing the variational ansatz for the singlet ground state of the quantum dot combined with the density matrix formulation for the coupled system, we show that the coherent Kondo singlet is destroyed by the phase-sensitive as well as the current-sensitive detection in the transmission and reflection coefficients at the quantum point contact. We argue that the phase-sensitive component of the decoherence rate may explain the anomalous features observed in a recent experiment by Avinun-Kalish et al. [Phys. Rev. Lett. 92, 156801 (2004)]. We also discuss the correlations of the shot noise at the quantum point contact detector and the decoherence in the quantum dot.
In this document we present a study of the thermodynamic and transport properties of two kinds of quantum impurity systems in the Kondo regime.The first system consists of a spin-1 molecule in which mechanical stretching along the transport axis produces a magnetic anisotropy.We find that a generic coupling between a vibrational mode along this axis and the molecular spin induces a correction to the magnetic anisotropy, driving the ground state of the system into a non-Fermi-liquid phase.A transition into a Fermi-liquid ground state can then be induced by means of stretching, going through an underscreened spin-1 Kondo ground state at zero effective anisotropy.In the second system we study the effects of a charge detector, implemented by a quantum point-contact (QPC), on the Kondo state of a nearby spin-1/2 quantum dot (QD).While making the charge detection possible, the Coulomb interaction between the electrons traversing the QPC and those within the QD contribute to decoherence of the Kondo state.By modeling the QPC as two metallic terminals connected to an intermediate localized level, we can explore three transport regimes of the detector: a zero-conductance regime, a finite-conductance regime in mixed valence, and unitary conductance in a Kondo ground state that has been suggested as an explanation to the "0.7 anomaly" in QPCs.Transitions between these different ground states can be achieved by tuning the strength of a capacitive coupling that parameterizes the electrostatic interaction.
We investigate various aspects of the Kondo singlet in a quantum dot (QD) electrostatically coupled to a mesoscopic detector. The two subsystems are represented by an entangled state between the Kondo singlet and the charge-dependent detector state. We show that the phase-coherence of the Kondo singlet is destroyed in a way that is sensitive to the charge-state information restored both in the magnitude and in the phase of the scattering coefficients of the detector. We also introduce the notion of the 'conditional evolution' of the Kondo singlet under projective measurement on the detector. Our study reveals that the state of the composite system is disentangled upon this measurement. The Kondo singlet evolves into a particular state with a fixed number of electrons in the QD. Its relaxation time is shown to be sensitive only to the QD-charge dependence of the transmission probability in the detector, which implies that the phase information is erased in this conditional evolution process. We discuss implications of our observations in view of the possible experimental realization.