Eckle<i>et al.</i>Reply:

Eckle, Hans-Peter; Johannesson, Henrik; Stafford, Charles

doi:10.1103/physrevlett.88.139702

Cited by 78 publications

(132 citation statements)

References 7 publications

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“…The side-coupled dot was also studied in [20]. The opposite conclusion to ours was reached that the ring would exhibit a perfect persistent current, rather than zero current, at large L/ξ K .…”

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confidence: 86%

Detecting the Kondo Screening Cloud Around a Quantum Dot

2001

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A fundamental prediction of scaling theories of the Kondo effect is the screening of an impurity spin by a cloud of electrons spread out over a mesoscopic distance. This cloud has never been observed experimentally. Recently, aspects of the Kondo effect have been observed in experiments on quantum dots embedded in quantum wires. Since the length of the wire may be of order the size of the screening cloud, such systems provide an ideal opportunity to observe it. We point out that persistent current measurements in a closed ring provide a conceptually simple way of detecting this fundamental length scale.The almost trivial looking problem of a single quantum spin interacting with a gas of otherwise non-interacting electrons has attracted much attention from condensed matter theorists for decades [1]. In particular, it played an important role in the development of scaling and renormalization group (RG) ideas. While the "bare" dimensionless coupling constant, λ is small, the low energy behavior of the system is described by an infinite effective Kondo coupling. This implies that a magnetic impurity makes a large contribution to the resistivity of the metal at low temperatures, corresponding to the "unitary limit". The characteristic energy scale at which the effective coupling constant becomes large defines the Kondo temperature:where D is the bandwidth and we have set Boltzmann's constant to one. Associated with this energy scale is a fundamental length scale:where v F is the Fermi velocity. For a typical metal exhibiting the Kondo effect this length scale can be of order .1 microns or larger. A simple picture of the meaning of this length scale is that a single electron occupying a wave-function extended over this distance forms a spin singlet with the impurity spin (which is assumed to have S = 1/2 here). Physical quantities such as the Knight shift can be expressed in terms of universal scaling functions of r/ξ K where r is the distance from the impurity [2,3]. Recent numerical simulations [2] have explicitly confirmed such scaling behavior. Nevertheless, no experiment has ever directly detected this fundamental length scale. The reason for this is perhaps mainly that this scale is too large. While the original Kondo effect led to a large resistivity at low T , a quite different manifestation of the same physics was predicted in a slightly different experimental configuration, corresponding to a large transmission coefficient [4,5]. A quantum dot can act like an S=1/2 impurity due to the Coulomb blockade. By adjusting a gate voltage on the dot, it can be arranged that the groundstate of the dot has an odd number of electrons, with an unpaired spin pointing up or down, and that the energy cost to add or remove an electron is relatively large. When this quantum dot is connected to leads with weak tunneling matrix elements, the transmission coefficient of the dot is small at most temperatures. This system is essentially equivalent to the Kondo model with the dimensionless coupling constant being of order t ′2 /ǫ 0...

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confidence: 86%

Detecting the Kondo Screening Cloud Around a Quantum Dot

2001

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“…10 The details of the disagreement are well summarized in Refs. [19][20][21]. In a recent Comment 20 the authors doubt the Bethe ansatz result of Ref.…”

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confidence: 87%

“…To rule out the effect of charge fluctuation, we consider the parameter limit of Ϫ d , d ϩUӷ⌫Јϩ⌫ R . In the absence of the reservoir, the Bethe ansatz result 7 shows that the PC is not affected by the QD in the Kondo limit with ␦/T K →0, where T K stands for the Kondo energy scale. For a finite value of ␦/T K , the coupling of the ring to the QD linearly reduces the PC as a function of ␦/T K for small ␦/T K and induces a crossover from the continuum Kondo limit (␦/T K Ӷ1) to an effectively decoupled ring-dot system (␦/T K ӷ1).…”

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confidence: 99%

“…[5][6][7][8][9][10][11] It has been proposed that the spin fluctuation affects the PC in a drastically different manner compared to the case of charge fluctuation. [6][7][8]12 Experimentally, the role of coherent spin fluctuation has been investigated by transport measurements using an AB interferometer setup. 15,16 In this paper, we address the effect of dephasing induced by spin fluctuations.…”

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Spin-fluctuation-induced dephasing in a mesoscopic ring

2002

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We investigate the persistent current in a hybrid Aharonov-Bohm ring-quantum-dot system coupled to a reservoir which provides spin fluctuations. It is shown that the spin exchange interaction between the quantum dot and the reservoir induces dephasing in the absence of direct charge transfer. We demonstrate an anomalous nature of this spin-fluctuation-induced dephasing which tends to enhance the persistent current. We explain our result in terms of the separation of the spin and the charge degrees of freedom. The nature of the spinfluctuation-induced dephasing is analyzed in detail. DOI: 10.1103/PhysRevB.66.075312 PACS number͑s͒: 73.23.Ra, 72.15.Qm, 73.23.Hk Persistent current ͑PC͒ in a mesoscopic Aharonov-Bohm ͑AB͒ ring is an ideal probe of the quantum coherence of electron motion in the equilibrium state. 1 Usually the PC is likely to be suppressed by various dephasing processes. The role of intrinsic dephasing at low temperature has not been well understood until now. 2 An alternative viewpoint to this is to introduce an artificial dephasor, in order to study the effect of decoherence in a controlled manner. 3 A conceptually simple but instructive example for that purpose is an AB ring attached to an electron reservoir which exchanges charges with the ring. 4 In the reservoir electrons are scattered inelastically and there is no phase coherence between electrons absorbed and those emitted by the reservoir. Therefore charge transfer between the ring and reservoir diminishes the coherence and thus the AB oscillation. On the other hand, the effect of spin exchange interactions on the PC has been attracting growing interest in recent years. [5][6][7][8][9][10][11] It has been proposed that the spin fluctuation affects the PC in a drastically different manner compared to the case of charge fluctuation. [6][7][8]12 Experimentally, the role of coherent spin fluctuation has been investigated by transport measurements using an AB interferometer setup. 15,16 In this paper, we address the effect of dephasing induced by spin fluctuations. For this purpose we consider the geometry schematically drawn in Fig. 1, where the spin fluctuation between the ring and reservoir is mediated via antiferromagnetic exchange interactions with the quantum dot ͑QD͒, while direct charge transfer is prohibited by the Coulomb blockade. We find a counterintuitive result that the dephasing tends to enhance the PC rather than to reduce it in this geometry. We argue that this enhancement can be regarded as a signature of the separation of the spin and charge degrees of freedom. Our geometry can be realized in the experiment, for, e.g., by using a two-dimensional electrons gas ͑2DEG͒ system combined with nanofabrication. Actually, a persistent current setup containing an external reservoir ͑without quantum dot͒ was realized in some previous experiments. 17,18 Our model is described by the Hamiltonianwhere H 0 , H R , and T stand for the hybrid dot-ring system, reservoir, and tunneling between the QD and reservoir, respectively. H 0 is decompo...

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“…Methods of generating AB phases have growth in different fields, representing an important role in solid-state interferometers [7,8], nanotubes [9], transmission microscopy [10], AlSb/InAs heterostructures [11], quantum Hall effect regime [12], Kondo resonance [13] and spin transport [14]. Detection of this effect in photonic states [15], optical induction in mesoscopic systems [16] and interaction of AB ring in a high-Q cavity [17,18,19] are examples of the increasing importance of such effect in interacting light-and-matter systems and optical analogues of the AB effect [20].…”

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confidence: 99%

Optical and spin-optical superpositions modulated by Aharonov–Bohm effect

Prudencio

2017

Int. J. Quantum Inform.

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Generation of Aharonov-Bohm (AB) phase has achieved a state-ofthe-art in mesoscopic systems with manipulation and control of the AB effect. The possibility of transfer information enconded in such systems to non-classical states of light increases the possible scenarios where the information can be manipulated and transfered. In this paper we propose a quantum transfer of the AB phase generated in a spintronic device, a topological spin transistor (TST), to an quantum optical device, a coherent state superposition in high-Q cavity and discuss optical and spinoptical superpositions in the presence of an AB phase. We demonstrate that the AB phase generated in the TST can be transfered to the coherent state superposition, considering the interaction with the spin state and the quantum optical manipulation of the coherent state superposition. We show that these cases provide examples of two-qubit states modulated by AB effect and that the phase parameter can be used to control the degree of rotation of the qubit state. We also show under a measurement on the spin basis, an optical one-qubit state that can be modulated by the AB effect. In these cases, we consider a dispesive interaction between a coherent state and a spin state with an acquired AB phase and also discuss a dissipative case where a given Lindblad equation is achieved and solved.

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Eckleet al.Reply:

Cited by 78 publications

References 7 publications

Detecting the Kondo Screening Cloud Around a Quantum Dot

Detecting the Kondo Screening Cloud Around a Quantum Dot

Spin-fluctuation-induced dephasing in a mesoscopic ring

Optical and spin-optical superpositions modulated by Aharonov–Bohm effect

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