共查询到20条相似文献,搜索用时 15 毫秒
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Amasha S Maclean K Radu IP Zumbühl DM Kastner MA Hanson MP Gossard AC 《Physical review letters》2008,100(4):046803
We demonstrate electrical control of the spin relaxation time T1 between Zeeman-split spin states of a single electron in a lateral quantum dot. We find that relaxation is mediated by the spin-orbit interaction, and by manipulating the orbital states of the dot using gate voltages we vary the relaxation rate W identical withT1(-1) by over an order of magnitude. The dependence of W on orbital confinement agrees with theoretical predictions, and from these data we extract the spin-orbit length. We also measure the dependence of W on the magnetic field and demonstrate that spin-orbit mediated coupling to phonons is the dominant relaxation mechanism down to 1 T, where T1 exceeds 1 s. 相似文献
3.
This paper presents a detailed analysis of the dependence of
degree of strain relaxation of the self-organized InAs/GaAs quantum
dot on the geometrical parameters. Differently shaped quantum dots
arranged with different transverse periods are simulated in this
analysis. It investigates the total residual strain energy that
stored in the quantum dot and the substrate for all kinds of quantum
dots with the same volume, as well as the dependence on both the
aspect ratio and transverse period. The calculated results show that
when the transverse period is larger than two times the base of the
quantum dots, the influence of transverse periods can be ignored.
The larger aspect ratio will lead more efficient strain relaxation.
The larger angle between the faces and the substrate will lead more
efficient strain relaxation. The obtained results can help to
understand the shape transition mechanism during the epitaxial
growth from the viewpoint of energy, because the strain relaxation
is the main driving force of the quantum dot's self-organization. 相似文献
4.
We demonstrate control of the electron number down to the last electron in tunable few-electron quantum dots defined in catalytically grown InAs nanowires. Using low temperature transport spectroscopy in the Coulomb blockade regime, we propose a method to directly determine the magnitude of the spin-orbit interaction in a two-electron artificial atom with strong spin-orbit coupling. Because of a large effective g factor |g(*)|=8+/-1, the transition from a singlet S to a triplet T+ ground state with increasing magnetic field is dominated by the Zeeman energy rather than by orbital effects. We find that the spin-orbit coupling mixes the T+ and S states and thus induces an avoided crossing with magnitude Delta(SO)=0.25+/-0.05 meV. This allows us to calculate the spin-orbit length lambda(SO) approximately 127 nm in such systems using a simple model. 相似文献
5.
We study the effects of magnetic and electric fields on the g factors of spins confined in a two-electron InAs nanowire double quantum dot. Spin sensitive measurements are performed by monitoring the leakage current in the Pauli blockade regime. Rotations of single spins are driven using electric-dipole spin resonance. The g factors are extracted from the spin resonance condition as a function of the magnetic field direction, allowing determination of the full g tensor. Electric and magnetic field tuning can be used to maximize the g-factor difference and in some cases altogether quench the electric-dipole spin resonance response, allowing selective single spin control. 相似文献
6.
A. M. Alcalde Qu Fanyao G. E. Marques 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):228
We have calculated spin-relaxation rates in parabolic quantum dots due to the phonon modulation of the spin–orbit interaction in the presence of an external magnetic field. Both deformation potential and piezoelectric electron–phonon coupling mechanisms are included within the Pavlov–Firsov spin–phonon Hamiltonian. Our results have demonstrated that, in narrow gap materials, the electron–phonon deformation potential and piezoelectric coupling give comparable contributions to spin-relaxation processes. For large dots, the deformation potential interaction becomes dominant. This behavior is not observed in wide or intermediate gap semiconductors, where the piezoelectric coupling, in general, governs the spin-relaxation processes. We have also demonstrated that spin-relaxation rates are particularly sensitive to the Landé g-factor. 相似文献
7.
Chorley SJ Giavaras G Wabnig J Jones GA Smith CG Briggs GA Buitelaar MR 《Physical review letters》2011,106(20):206801
We make use of spin selection rules to investigate the electron spin system of a carbon nanotube double quantum dot. Measurements of the electron transport as a function of the magnetic field and energy detuning between the quantum dots reveal an intricate pattern of the spin state evolution. We demonstrate that the complete set of measurements can be understood by taking into account the interplay between spin-orbit interaction and a single impurity spin coupled to the double dot. The detection and tunability of this coupling are important for quantum manipulation in carbon nanotubes. 相似文献
8.
Hanson R Witkamp B Vandersypen LM van Beveren LH Elzerman JM Kouwenhoven LP 《Physical review letters》2003,91(19):196802
We have measured the relaxation time, T1, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit). In a magnetic field, applied parallel to the two-dimensional electron gas in which the quantum dot is defined, Zeeman splitting of the orbital states is directly observed by measurements of electron transport through the dot. By applying short voltage pulses, we can populate the excited spin state with one electron and monitor relaxation of the spin. We find a lower bound on T1 of 50 micros at 7.5 T, only limited by our signal-to-noise ratio. A continuous measurement of the charge on the dot has no observable effect on the spin relaxation. 相似文献
9.
We propose a protocol for a controlled experiment to measure a weak value of the electron's spin in a solid state device. The weak value is obtained by a two step procedure--weak measurement followed by a strong one (postselection), where the outcome of the first measurement is kept provided a second postselected outcome occurs. The setup consists of a double quantum dot and a weakly coupled quantum point contact to be used as a detector. Anomalously large values of the spin of a two electron system are predicted, as well as negative values of the total spin. We also show how to incorporate the adverse effect of decoherence into this procedure. 相似文献
10.
Meunier T Vink IT van Beveren LH Tielrooij KJ Hanson R Koppens FH Tranitz HP Wegscheider W Kouwenhoven LP Vandersypen LM 《Physical review letters》2007,98(12):126601
We observe an experimental signature of the role of phonons in spin relaxation between triplet and singlet states in a two-electron quantum dot. Using both the external magnetic field and the electrostatic confinement potential, we change the singlet-triplet energy splitting from 1.3 meV to zero and observe that the spin relaxation time depends nonmonotonously on the energy splitting. A simple theoretical model is derived to capture the underlying physical mechanism. The present experiment confirms that spin-flip energy is dissipated in the phonon bath. 相似文献
11.
Spin relaxation from a triplet excited state to a singlet ground state in a semiconductor quantum dot is studied by employing an electrical pump-and-probe method. Spin relaxation occurs via co-tunneling when the tunneling rate is relatively large, confirmed by a characteristic square dependence of the relaxation rate on the tunneling rate. When co-tunneling is suppressed by reducing the tunneling rate, the intrinsic spin relaxation is dominated by spin-orbit interaction. We discuss a selection rule of the spin-orbit interaction based on the observed double-exponential decay of the triplet state. 相似文献
12.
Godden TM Quilter JH Ramsay AJ Wu Y Brereton P Boyle SJ Luxmoore IJ Puebla-Nunez J Fox AM Skolnick MS 《Physical review letters》2012,108(1):017402
We demonstrate coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. A superposition of hole-spin states is created by fast (10-100?ps) dissociation of a spin-polarized electron-hole pair. Full control of the hole spin is achieved by combining coherent rotations about two axes: Larmor precession of the hole spin about an external Voigt geometry magnetic field, and rotation about the optical axis due to the geometric phase shift induced by a picosecond laser pulse resonant with the hole-trion transition. 相似文献
13.
Decoherence-free spin entanglement generation and purification in nanowire double quantum dots 下载免费PDF全文
We propose a deterministic generation and purification of decoherence-free spin entangled states with singlet-triplet spins in nanowire double quantum dots via resonator-assisted charge manipulation and measurement techniques. Each spin qubit corresponds to two electrons in a double quantum dot in the nanowire, with the singlet and one of the triplets as the decoherence-free qubit states. The logical qubits are immunized against the dominant source of decoherence-dephasing—while the influences of additional errors are shown by numerical simulations. We analyse the performance and stability of all required operations and emphasize that all techniques are feasible in current experimental conditions. 相似文献
14.
We report electronic control and measurement of an imbalance between spin-up and spin-down electrons in micron-scale open quantum dots. Spin injection and detection were achieved with quantum point contacts tuned to have spin-selective transport, with four contacts per dot for realizing a nonlocal spin-valve circuit. This provides an interesting system for studies of spintronic effects since the contacts to reservoirs can be controlled and characterized with high accuracy. We show how this can be used to extract in a single measurement the relaxation time for electron spins inside a ballistic dot (tau(sf) approximately equal to 300 ps) and the degree of spin polarization of the contacts (P approximately equal to 0.8). 相似文献
15.
Hai-Zhou Lu Rong Lü Shun-Qing Shen 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(1):69-75
Dynamics of two quantum dots coupled to electrodes with spin bias is
investigated theoretically by means of the master equations. The two dots are coupled via exchange interaction. When the
exchange interaction is much smaller than the lead-dot 2 coupling and dot 2 is under a symmetric spin bias,
an initially fully polarized electron spin in dot 1 undergoes an oscillation with ignorable
attenuation. Meanwhile, the direction of charge current flowing through dot 2 oscillates in
the same period as that of the spin in dot 1. This allows to reverse or nearly noninvasively read
out the spin in dot 1, by switching on and off the exchange
interaction for a duration of half-integer or integer periods of the
oscillation, respectively. 相似文献
16.
We present a spin current generator based on a T-shaped double quantum dot (TDQD) molecule connected with two leads, and the coherent spin-flip effect is taken into account within the TDQD. The spin current from the right output terminal is obtained, more importantly, the properties of the spin current are investigated in detail, these results offer us a way to manipulate the spin current with the system parameters. 相似文献
17.
Alexej Chernikov Swantje Horst Stephan W. Koch Sangam Chatterjee Wolfgang W. Rühle Julian Sweet Benjamin Richards Josh Hendrickson Galina Khitrova Hyatt M. Gibbs Dimitri Litvinov Dagmar Gerthsen Martin Wegener 《Solid State Communications》2009,149(35-36):1485-1492
An ensemble of InAs quantum dots with ground state transition energies centered at 1.216 eV and density 1011dots/cm2 has been studied by time-resolved photoluminescence (PL). The wavelength of the 100-fs excitation pulse was tuned through the ground (excited) state transitions, resulting in resonant (optical phonon sideband) PL. The decay of the PL was time resolved with a streak camera in the interval 1.5–3 ns to avoid scattered laser light. The intensity of the PL was recorded with its polarization both parallel with and perpendicular to the excitation polarization (along one of the crystal’s cleave axes); the ratio is 2.22 at low temperatures and low excitation. A phenomenological rate equation analysis is made, separating the excitations into two classes, one polarized along the excitation polarization and the other unpolarized (either that way immediately after the excitation pulse or scattered from the first class). Excellent fits to the data lead to the conclusion that both classes decay radiatively with a lifetime of 1 ns, and a transfer from the polarized to the unpolarized species takes place with a distribution time of 12 ns at low temperatures and low excitation, dropping rapidly toward zero for temperatures above 30 K and for intense excitation levels. The polarization of a coherently excited ground state exciton should dephase with a rate equal to the sum of the radiative rate plus the inverse of this distribution time. 相似文献
18.
Laird EA Petta JR Johnson AC Marcus CM Yacoby A Hanson MP Gossard AC 《Physical review letters》2006,97(5):056801
We measure singlet-triplet dephasing in a two-electron double quantum dot in the presence of an exchange interaction which can be electrically tuned from much smaller to much larger than the hyperfine energy. Saturation of dephasing and damped oscillations of the spin correlator as a function of time are observed when the two interaction strengths are comparable. Both features of the data are compared with predictions from a quasistatic model of the hyperfine field. 相似文献
19.
《Superlattices and Microstructures》1999,25(1-2):247-250
We have studied single electron and hole storage in self-assembled InAs quantum dots (QDs) embedded in GaAs/n-AlGaAs field effect transistors (QD-FETs). We prepared two types of QD-FETs. A single electron and a photo-generated single hole can be stored in each QD in Type 1. In the new Type II, single-electron discharge processes can be controlled by a surface gate voltage (Vg) as well as single-electron storage processes. We demonstrate possible application to novel photo devices and quantum dot memory devices. 相似文献
20.
Korenev VL 《Physical review letters》2007,99(25):256405
Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins-the nuclear spin nanomagnet. 相似文献