Dephasing in a quantum dot due to coupling with a quantum point contact

Levinson, Y.

doi:10.1209/epl/i1997-00351-x

Cited by 136 publications

(177 citation statements)

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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%

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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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“…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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“…IV is that of dephasing of a quantum dot. Following Levinson 42,43 we outline here how one arrives in that case at the expressions for the dephasing rate used in Sec. IV.…”

Section: Appendix: Derivation Of Dephasing Rate For a Quantum Dotmentioning

confidence: 99%

Nonequilibrium charge noise and dephasing from a spin-incoherent Luttinger liquid

Fiete

Kindermann

2007

Phys. Rev. B

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We theoretically investigate the charge noise and dephasing in a metallic device in close proximity to a spin incoherent Luttinger liquid with a small but finite current. The frequency dependence of the charge noise exhibits a loss of frequency peaks corresponding to the 2k F part of the density correlations in the electron liquid when the temperature T is increased from values below the magnetic exchange energy J of the electron gas to values above it. The dephasing rate in a nearby metallic nanostructure also shows a crossover for T ϳ J and may exhibit a nonmonotonic temperature dependence. For a range of temperatures the dephasing rate decreases with increasing temperatures. The proposed experiments provide a convenient approach to probe the spin-incoherent Luttinger liquid and should be implementable in a wide variety of systems.

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“…More recently, the charge fluctuations in two nearby mesoscopic conductors was treated with this approach and the effect of quantum dephasing due to charge fluctuations was calculated within this approach [41,38]. The results can be compared with other theoretical works [42] and with experiments [43].…”

Section: Partial Density Of States Matrixmentioning

confidence: 98%

The Local Larmor Clock, Partial Densities of States, and Mesoscopic Physics

Büttiker

Time in Quantum Mechanics

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Abstract. Starting from the Larmor clock we introduce a hierarchy of density of states. At the bottom of this hierarchy are the partial densities of states which represent the contribution to the local density of states if both the incident and the out-going scattering channel is prescribed. We discuss the role of the partial densities of states in a number of electrical conduction problems in phase coherent mesoscopic systems: The partial densities of states play a prominent role in measurements with a scanning tunneling microscope on multiprobe conductors in the presence of current flow. The partial densities of states determine the degree of dephasing generated by a weakly coupled voltage probe. We show that the partial densities of states determine the frequency-dependent response of mesoscopic conductors in the presence of slowly oscillating voltages applied to the contacts of the sample. We introduce the off-diagonal elements of the partial density of states matrix to describe fluctuation processes. These examples demonstrate that the analysis of the Larmor clock has a wide range of applications.

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Dephasing in a quantum dot due to coupling with a quantum point contact

Cited by 136 publications

References 12 publications

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

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

Nonequilibrium charge noise and dephasing from a spin-incoherent Luttinger liquid

The Local Larmor Clock, Partial Densities of States, and Mesoscopic Physics

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