We propose an experiment to observe coherent oscillations in a single quantum dot with the oscillations driven by spin-orbit interaction. This is achieved without spin-polarized leads, and relies on changing the strength of the spin-orbit coupling via an applied gate pulse. We derive an effective model of this system which is formally equivalent to the Jaynes-Cummings model of quantum optics. For parameters relevant to an InGaAs dot, we calculate a Rabi frequency of 2 GHz.
We investigate the influence of a perpendicular magnetic field on the spectral and spin properties of a ballistic quasi-one-dimensional electron system with Rashba effect. The magnetic field strongly alters the spin-orbit induced modification to the subband structure when the magnetic length becomes comparable to the lateral confinement. A new subband-dependent energy splitting at k = 0 is found which can be much larger than the Zeeman splitting. This is due to the breaking of a combined spin orbital-parity symmetry.
We predict that phonon subband quantization can be detected in the non-linear electron current through double quantum dot qubits embedded into nano-size semiconductor slabs, acting as phonon cavities. For particular values of the dot level splitting ∆, piezo-electric or deformation potential scattering is either drastically reduced as compared to the bulk case, or strongly enhanced due to phonon van Hove singularities. By tuning ∆ via gate voltages, one can either control dephasing, or strongly increase emission into phonon modes with characteristic angular distributions. PACS numbers: 73.21.La,62.25.+g Coupled semiconductor quantum dots are candidates for controlling quantum superposition and entanglement of electron states. The feasibility of such 'qubits' depends on the control of dephasing due to the coupling to low-energy bosonic excitations of the environment. For example, the electronic transport thorouhg double quantum dots is determined by the spontaneous emission of phonons even at very low temperatures 1 . If two dots are coupled to each other and to external leads, Coulomb blockade guarantees that only one electron at a time can tunnel between the dots and the leads. Dephasing in such a 'pseudo spin'-boson system 2,3 is dominated by the properties of the phonon environment.As a logical step towards the control of dephasing, the control of vibrational properties of quantum dot qubits has been suggested 1 . Recently, considerable progress has been made in the fabrication of nano-structures that are only partly suspended or even free-standing 4,5 . They considerably differ in their mechanical properties from bulk material. For example, phonon modes are split into subbands, and quantization effects become important for the thermal conductivity 6,7,8 . The observation of coherent phonons in dots 9 in nanotubes 10 are other examples of low dimensional mesoscopic systems where phonons become experimentally controllable and are the objects of interest themselves.Double quantum dots are not only tunable phonon emitters 1 but also sensitive high-frequency noise detectors 11 . Together with their successful fabrication within partly free-standing nanostructures 12 , this suggests that they can be used to control both electrons and phonons on a microscopic scale. This opens a path for realizing mechanical counterparts of several quantum optical phenomena, as for instance the generation of nonclassical squeezed phonon states 13 by time-dependent or non-linear interactions with the electrons.In this paper, we demonstrate that phonon confinement can be used to gain control of dissipation in double quantum dots, leading to a considerable reduction of phonon-induced decoherence. More precisely, we show that inelastic scattering and the inelastic current channel for electron transport in the Coulomb blockade regime can be drastically reduced as compared to a bulk environment when double dots are hosted by a semiconductor slab that acts as a phonon cavity. This suppression occurs at specific phonon energies ω 0 when ...
The non-linear electron current through a double quantum dot embedded in a free standing quantum well is investigated. In such a model for a nano-size phonon cavity, the transport at low temperatures is mediated by the spontaneous emission of acoustic phonons. Phonon quantum size effects can be detected as steps in the current. Moreover, for our model we find van-Hove singularities in the phonon density of states that give rise to a strong, tuneable increase of phonon emission into characteristic modes. The emission characteristic, depending on the position of the dots in the cavity, is also considered.
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