Selective optical charge generation, storage, and readout in a single self-assembled quantum dot

Heiss, D.; Jovanov, V.; Caesar, Markus; Bichler, Max; Abstreiter, G.; Finley, J. J.

doi:10.1063/1.3079658

Cited by 20 publications

(24 citation statements)

References 13 publications

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“…Immediately after exciton generation, the hole escapes the QD within 4 ps [20] leaving behind the single electron spin (|↓⇑ → |↓ ). The implementation of an asymmetric tunnel barrier leads to electron lifetimes extending up to seconds whereas hole lifetimes are unaffected [1]. In our notation, such a spin selective electron preparation is equivalent to the nonzero outcome of the application of the projection operatorQ 0 at t = 0.…”

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confidence: 99%

“…Electronic spins in optically active quantum dots (QDs) have exhibited very long spin lifetimes T 1 , extending beyond a millisecond [1,2], and intrinsic dephasing times T 2 beyond one microsecond when subject to externally applied magnetic fields [3][4][5]. These properties, combined with the potential for ultrafast optical preparation and control [6][7][8], make QD spin qubits very attractive for quantum information processing [9].…”

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confidence: 99%

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Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit

Bechtold

Müller

et al. 2016

Phys. Rev. Lett.

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confidence: 99%

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confidence: 99%

Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit

Bechtold

Müller

et al. 2016

Phys. Rev. Lett.

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“…Optical orientation of carrier spins allowed to realize a programmable QD memory device and exploit it in measurements of longitudinal spin relaxation rates of electrons 3 and holes 4 . Moreover, storage and readout of charge and spin from a single QD was demonstrated 5,6 . It has been pointed out that the leakage of charge from these structures stems from thermal 1 or tunnel escape 6 , photoinduced discharging 7 , or capture by deep levels in the barrier 1 .…”

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confidence: 99%

Dynamics of charge leakage from self-assembled CdTe quantum dots

Kłopotowski

Goryca

Kazimierczuk

et al. 2010

Applied Physics Letters

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We study the leakage dynamics of charge stored in an ensemble of CdTe quantum dots embedded in a field-effect structure. Optically excited electrons are stored and read out by a proper time sequence of bias pulses. We monitor the dynamics of electron loss and find that the rate of the leakage is strongly dependent on time, which we attribute to an optically generated electric field related to the stored charge. A rate equation model quantitatively reproduces the results.PACS numbers: 78.67. Hc, 72.20.Jv, 71.55.Gs Quantum information processing using semiconductor self-assembled quantum dots (QDs) requires a precise control over writting, storage, and readout of electrons from these nanostructures. An experimental testbed for these processes involve QDs embedded in field-effect structures. In such devices, storage of charge carriers was demonstrated and shown to persist over timescales exceeding seconds 1 or even hours 2 . Optical orientation of carrier spins allowed to realize a programmable QD memory device and exploit it in measurements of longitudinal spin relaxation rates of electrons 3 and holes 4 . Moreover, storage and readout of charge and spin from a single QD was demonstrated 5,6 . It has been pointed out that the leakage of charge from these structures stems from thermal 1 or tunnel escape 6 , photoinduced discharging 7 , or capture by deep levels in the barrier 1 . These processes result inevitably in an information loss and therefore their role has to be evaluated and carefully taken into account in designing of any future devices.In this report, we study the escape dynamics of electrons stored in a layer of self-assembled CdTe QDs. We identify the escape mechanism as electron tunneling and propose a theoretical model, which quantitatively reproduces our experimental results. In particular, we address the importance of an optically generated electric field related to the charge stored in the QDs, which substantially modifies the field applied externally and as a result strongly influences the carrier escape. A realization of a QD memory device with II-VI nanostructures is important in view of the possibility of doping these QDs with magnetic ions 8 . Indeed, electrical manipulation of the quantum state of a single magnetic ion or a ferromagnetically coupled system of ions would provide new schemes for quantum computation and quantum information storage 9-11 .The samples were grown by molecular beam epitaxy on a (001)-oriented GaAs substrate. A 4 µm thick pdoped ZnTe buffer layer acted as a back contact. Using a tellurium desorption procedure 12 , a single layer of QDs was grown, separated from the back contact by a 15 nm thick Zn 0.9 Mg 0.1 Te spacer layer. QDs were covered with a 100 nm Zn 0.9 Mg 0.1 Te barrier and another Zn 0.7 Mg 0.3 Te blocking barrier to prevent the escape of carriers to the surface. On top, a 10 nm thick, 20 µm x 100 µm, semitransparent layer of Ti/Au was evaporated to form a Schottky contact. We note that this structure design is analogous to many InAs/GaAs charge-tunable...

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“…We performed our experiments using a single dot charge storage device (see Refs. 21,22). These devices are grown by molecular beam epitaxy and consist of a single layer of self-assembled In 0.5 Ga 0.5 As quantum dots embedded into the intrinsic region of an n-type GaAs Schottky phoarXiv:1009.0207v1 [cond-mat.mes-hall] 1 Sep 2010…”

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confidence: 99%

“…Initially, in phase (i) of the measurement the dot is emptied of all stored charge. 22 During the spingeneration phase a single electron is optically created in the dot using a single frequency diode laser resonant with X 0 . In practice, the laser frequency is fixed close to the X 0 resonance and we tune the QD transition into resonance using the DC Stark effect.…”

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confidence: 99%

Optically monitoring electron spin relaxation in a single quantum dot using a spin memory device

et al. 2010

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We demonstrate all optical electron spin initialization, storage and readout in a single selfassembled InGaAs quantum dot. Using a single dot charge storage device we monitor the relaxation of a single electron over long timescales exceeding 40µs. The selective generation of a single electron in the quantum dot is performed by resonant optical excitation and subsequent partial exciton ionization; the hole is removed from the quantum dot whilst the electron remains stored. When subject to a magnetic field applied in Faraday geometry, we show how the spin of the electron can be prepared with a polarization up to 65% simply by controlling the voltage applied to the gate electrode. After generation, the electron spin is stored in the quantum dot before being read out using an all optical implementation of spin to charge conversion technique, whereby the spin projection of the electron is mapped onto the more robust charge state of the quantum dot. After spin to charge conversion, the charge state of the dot is repeatedly tested by pumping a luminescence recycling transition to obtain strong readout signals. In combination with spin manipulation using fast optical pulses or microwave pulses, this provides an ideal basis for probing spin coherence in single self-assembled quantum dots over long timescales and developing optimal methods for coherent spin control. The spin of charges trapped in semiconductor quantum dots (QDs) is one of the most promising solid state qubits, 1 primarily due to the robust quantum coherence and excellent scaling prospects.2-11 Several groups have demonstrated electrical methods to initialize, control and readout QD spin qubits.2,5,6,12 However, optically active dots are particularly attractive since pulsed lasers can be used to selectively address spin qubits over ultrafast timescales.9,13-16 Optical readout of a single spin is extremely challenging and sensitive techniques based on resonant light scattering 17 and Faraday/Kerr 15,18 rotation have been applied. Such measurements are typically repeated at high frequencies (>10MHz) to provide enough signal, limiting their potential to probe slow spin dynamics occurring over timescales >1µs. Recent experiments using time-resolved resonance fluorescence showed spin detection 19 in a single QD over much longer timescales. Nevertheless, in such approaches the QDs are tunnel coupled to a Fermi reservoir and co-tunneling leads to enhanced spin relaxation close to the edge of the charging thresholds. Thus, the electric field regime where the device can be operated is rather limited potentially posing problems when moving from a single dot to few QD systems where electric field also allows tuning of dot-dot tunnel coupling.20 Here, we demonstrate an all optical spin memory device that allows us to prepare a single spin in an individual QD, store it over millisecond timescales and read it out with high fidelity. Readout is based on spin to charge conversion, whereby spin is first mapped onto the charge status of the dot before charge is repeatedly m...

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Selective optical charge generation, storage, and readout in a single self-assembled quantum dot

Cited by 20 publications

References 13 publications

Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit

Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit

Dynamics of charge leakage from self-assembled CdTe quantum dots

Optically monitoring electron spin relaxation in a single quantum dot using a spin memory device

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