Voltage probe model of spin decay in a chaotic quantum dot with applications to spin-flip noise and entanglement production

Michaelis, B.; Beenakker, C. W. J.

doi:10.1103/physrevb.73.115329

Cited by 10 publications

(10 citation statements)

References 34 publications

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“…[13][14][15] Extensions to spindependent conduction have been proposed more recently. 16,17 As described in Ref. 16, one needs two types of voltage probes to describe spin relaxation and decoherence.…”

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“…16,17 As described in Ref. 16, one needs two types of voltage probes to describe spin relaxation and decoherence. One type of voltage probe is connected to a normal metal reservoir, while the other type of voltage probe is connected to a pair of ferromagnetic reservoirs ͑of opposite polarization, parallel to the polarization of the spin filters in the quantum point contacts͒.…”

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confidence: 99%

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Excess conductance of a spin-filtering quantum dot

Beenakker

2006

Phys. Rev. B

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The conductance G of a pair of single-channel point contacts in series, one of which is a spin filter, increases from 1 / 2 to 2 / 3 ϫ e 2 / h with more and more spin-flip scattering. This excess conductance was observed in a quantum dot by Zumbühl et al., and proposed as a measure for the spin relaxation time T 1 . Here we present a quantum mechanical theory for the effect in a chaotic quantum dot ͑mean level spacing ⌬, dephasing time , charging energy e 2 / C͒, in order to answer the question whether T 1 can be determined independently of and C. We find that this is possible in a time-reversal-symmetry-breaking magnetic field, when the average conductance follows closely the formula ͗G͘ = ͑2e 2 / h͒͑T 1 + h / ⌬͒͑4T 1 +3h / ⌬͒ −1 . DOI: 10.1103/PhysRevB.73.201304 PACS number͑s͒: 73.23.Ϫb, 73.63.Kv, 72.25.Dc, 72.25.Rb The study of spin relaxation in the presence of chaotic scattering is a challenge for theorists and experimentalists. The common goal is to identify transport properties that can be readily measured and that depend as directly as possible on the spin relaxation time ͑T 1 ͒. One line of research is to study how quantum interference effects such as weak localization or universal conductance fluctuations are modified by spin relaxation. 1 A direct relation with T 1 in that context is hindered by the fact that dephasing ͑both of the orbital and of the spin degrees of freedom͒ also modifies the quantum interference effects. Another line of research is to study spinresolved current noise. 2 There a direct relation with T 1 is possible, but the complications involved in the measurement of both time-and spin-dependent current fluctuations have so far prevented an experimental realization. Ideally, one would like to relate T 1 to the time averaged current in a way that is insensitive to dephasing. It is the purpose of this work to present such a relationship.Our research was inspired by the proposal of Zumbühl et al. of a new technique to measure spin relaxation times in confined systems. 3 These authors reported measurements of the conductance of an open two-dimensional GaAs quantum dot in a parallel magnetic field. One of the two point contacts was set to the spin-selective e 2 / h conductance plateau. The other point contact was set to transmit both spins. In this configuration, the classical series conductance of the two point contacts is 1 2 ϫ e 2 / h if there is no spin relaxation and 2 3 ϫ e 2 / h if there is strong spin relaxation. What we will show here is that the ensemble averaged conductance in a timereversal-symmetry-breaking magnetic field varies between these two limits as a rational function of the product of T 1 and the mean level spacing ⌬-largely independent of the presence or absence of dephasing. The geometry of the problem is sketched in Fig. 1. We discuss its various ingredients. Electrons in a twodimensional electron gas ͑2DEG͒ enter and leave the quantum dot via two single-channel quantum point contacts ͑QPC͒. A QPC can operate as a spin filter in a magnetic field, 4,5 as a resu...

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Excess conductance of a spin-filtering quantum dot

Beenakker

2006

Phys. Rev. B

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“…[13][14][15] This has so far not been accomplished experimentally. Thus, the isotropy approximation that has been used here as a way to simplify the calculation of the concurrence also has an experimental implication: 16 By relying on spin isotropy the concurrence can be obtained directly from correlators of time-averaged spin currents. Our demonstration of the accuracy of the isotropy approximation may motivate experimentalists to try this "poor man's method" of entanglement detection-since average spin currents have been measured 17 while spin noise has not.…”

Section: Discussionmentioning

confidence: 99%

Degradation of electron-hole entanglement by spin-orbit coupling

Bardarson

Beenakker

2006

Phys. Rev. B

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Electron-hole pairs produced by tunneling in a degenerate electron gas lose their spin entanglement by spin-orbit coupling, which transforms the fully entangled Bell state into a partially entangled mixed density matrix of the electron and hole spins. We calculate the dependence of the entanglement (quantified by the concurrence) on the spin-orbit coupling time tau_so and on the diffusion time (or dwell time) tau_dwell of electron and hole in the conductors (with conductances >> e^2/h) at the two sides of the tunnel barrier (with conductance << e^2/h). The entanglement disappears when the ratio tau_dwell/tau_so exceeds a critical value of order unity. The results depend on the type of conductor (disordered wire or chaotic quantum dot), but they are independent of other microscopic parameters (number of channels, level spacing). Our analytical treatment relies on an "isotropy approximation" (no preferential basis in spin space), which allows us to express the concurrence entirely in terms of spin correlators. We test this approximation for the case of chaotic dynamics with a computer simulation (using the spin kicked rotator) and find good agreement.Comment: 8 pages, 6 figures. v2. Appendix A expanded, figures adde

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“…10 The effects of voltage probes on entangled states has recently been addressed by Prada, Taddei, and Fazio 11 and also in Ref. 12. In Ref.…”

Section: Introductionmentioning

confidence: 96%

Two-electron-entanglement enhancement by an inelastic scattering process

2007

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In order to assess inelastic effects on two fermion entanglement production, we address an exactly solvable two-particle scattering problem where the target is an excitable scatterer. Useful entanglement, as measured by the two particle concurrence, is obtained from post-selection of oppositely scattered particle states. The S matrix formalism is generalized in order to address nonunitary evolution in the propagating channels. We find the striking result that inelasticity can actually increase concurrence as compared to the elastic case by increasing the uncertainty of the single particle subspace. Concurrence zeros are controlled by either single particle resonance energies or total reflection conditions that ascertain precisely one of the electron states. Concurrence minima also occur and are controlled by entangled resonance situations where the electron becomes entangled with the scatterer, and thus does not give up full information of its state. In this model, exciting the scatterer can never fully destroy phase coherence due to an intrinsic limit to the probability of inelastic events.

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Voltage probe model of spin decay in a chaotic quantum dot with applications to spin-flip noise and entanglement production

Cited by 10 publications

References 34 publications

Excess conductance of a spin-filtering quantum dot

Excess conductance of a spin-filtering quantum dot

Degradation of electron-hole entanglement by spin-orbit coupling

Two-electron-entanglement enhancement by an inelastic scattering process

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