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A Charge and Spin Readout Scheme For Single Self-Assembled Quantum Dots  [PDF]
D. Heiss,V. Jovanov,M. Bichler,G. Abstreiter,J. J. Finley
Physics , 2008, DOI: 10.1103/PhysRevB.77.235442
Abstract: We propose an all optical spin initialization and readout concept for single self assembled quantum dots and demonstrate its feasibility. Our approach is based on a gateable single dot photodiode structure that can be switched between charge and readout mode. After optical electron generation and storage, we propose to employ a spin-conditional absorption of a circularly polarized light pulse tuned to the single negatively charged exciton transition to convert the spin information of the resident electron to charge occupancy. Switching the device to the charge readout mode then allows us to probe the charge state of the quantum dot (1e, 2e) using non-resonant luminescence. The spin orientation of the resident electron is then reflected by the photoluminescence yield of doubly and singly charged transitions in the quantum dot. To verify the feasibility of this spin readout concept, we have applied time gated photoluminescence to confirm that selective optical charging and efficient non perturbative measurement of the charge state can be performed on the same dot. The results show that, by switching the electric field in the vicinity of the quantum dot, the charging rate can be switched between a regime of efficient electron generation and a readout regime, where the charge occupancy and, therefore, the spin state of the dot can be tested via PL over millisecond timescales, without altering it.
Selective Optical Charge Generation, Storage and Readout in a Single Self Assembled Quantum Dot  [PDF]
D. Heiss,V. Jovanov,M. Caesar,M. Bichler,G. Abstreiter,J. J. Finley
Physics , 2008, DOI: 10.1063/1.3079658
Abstract: We report the investigation of a single quantum dot charge storage device. The device allows selective optical charging of a single dot with electrons, storage of these charges over timescales much longer than microseconds and reliable optical readout of the charge occupancy using a time gated photoluminescence technique. This device enables us to directly investigate the electric field dependent tunneling escape dynamics of electrons at high electric fields over timescales up to 4 us. The results demonstrate that such structures and measurement techniques can be used to investigate charge and spin dynamics in single quantum dots over microsecond timescales.
Probing spin relaxation in an individual InGaAs quantum dot using a single electron optical spin memory device  [PDF]
D. Heiss,V. Jovanov,F. Klotz,D. Rudolph,M. Bichler,G. Abstreiter,M. S. Brandt,J. J. Finley
Physics , 2010, DOI: 10.1103/PhysRevB.82.245316
Abstract: We demonstrate all optical electron spin initialization, storage and readout in a single self-assembled InGaAs quantum dot. Using a single dot charge storage device we monitor the relaxation of a single electron over long timescales exceeding 40{\mu}s. 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.
Phase readout of a charge qubit capacitively coupled to an open double quantum dot  [PDF]
C. Kreisbeck,F. J. Kaiser,S. Kohler
Physics , 2009, DOI: 10.1103/PhysRevB.81.125404
Abstract: We study the dynamics of a charge qubit that is capacitively coupled to an open double quantum dot. Depending on the qubit state, the transport through the open quantum dot may be resonant or off-resonant, such that the qubit affects the current through the open double dot. We relate the initial qubit state to the magnitude of an emerging transient current peak. The relation between these quantities enables the readout of not only the charge but also the phase of the qubit.
Charge and spin state readout of a double quantum dot coupled to a resonator  [PDF]
K. D. Petersson,C. G. Smith,D. Anderson,P. Atkinson,G. A. C. Jones,D. A. Ritchie
Physics , 2010, DOI: 10.1021/nl100663w
Abstract: State readout is a key requirement for a quantum computer. For semiconductor-based qubit devices it is usually accomplished using a separate mesoscopic electrometer. Here we demonstrate a simple detection scheme in which a radio-frequency resonant circuit coupled to a semiconductor double quantum dot is used to probe its charge and spin states. These results demonstrate a new non-invasive technique for measuring charge and spin states in quantum dot systems without requiring a separate mesoscopic detector.
Coulomb interaction signatures in self-assembled lateral quantum dot molecules  [PDF]
Xinran. Zhou,Jihoon. Lee,Gregory. J. Salamo,Miquel. Royo,Juan. I. Climente,Matthew. F. Doty
Physics , 2012, DOI: 10.1103/PhysRevB.87.125309
Abstract: We use photoluminescence spectroscopy to investigate the ground state of single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage along the growth direction that allows us to control the total charge occupancy of the quantum dot molecule. Using a combination of computational modeling and experimental analysis, we assign the observed discrete spectral lines to specific charge distributions. We explain the dynamic processes that lead to these charge configurations through electrical injection and optical generation. Our systemic analysis provides evidence of inter-dot tunneling of electrons as predicted in previous theoretical work.
Probing single charge fluctuations in a semiconductor with laser spectroscopy on a quantum dot  [PDF]
J. Houel,A. Kuhlmann,L. Greuter,F. Xue,M. Poggio,B. D. Gerardot,P. A. Dalgarno,A. Badolato,P. M. Petroff,A. Ludwig,D. Reuter,A. D. Wieckand,R. J. Warburton
Physics , 2011, DOI: 10.1103/PhysRevLett.108.107401
Abstract: We probe local charge fluctuations in a semiconductor via laser spectroscopy on a nearby self-assembled quantum dot. We demonstrate that the quantum dot is sensitive to changes in the local environment at the single charge level. By controlling the charge state of localized defects, we are able to infer the distance of the defects from the quantum dot with +-5 nm resolution. The results identify and quantify the main source of charge noise in the commonly-used optical field-effect devices. Based on this understanding we achieve routinely close-totransform-limited quantum dot optical linewidths.
Absorption and photoluminescence spectroscopy on a single self-assembled charge-tunable quantum dot  [PDF]
S. Seidl,M. Kroner,P. A. Dalgarno,A. H?gele,J. M. Smith,M. Ediger,B. D. Gerardot,J. M. Garcia,P. M. Petroff,K. Karrai,R. J. Warburton
Physics , 2005, DOI: 10.1103/PhysRevB.72.195339
Abstract: We have performed detailed photoluminescence (PL) and absorption spectroscopy on the same single self-assembled quantum dot in a charge-tunable device. The transition from neutral to charged exciton in the PL occurs at a more negative voltage than the corresponding transition in absorption. We have developed a model of the Coulomb blockade to account for this observation. At large negative bias, the absorption broadens as a result of electron and hole tunneling. We observe resonant features in this regime whenever the quantum dot hole level is resonant with two-dimensional hole states located at the capping layer-blocking barrier interface in our structure.
Waveguide-Coupled Photonic Crystal Cavity for Quantum Dot Spin Readout  [PDF]
R. J. Coles,N. Prtljaga,B. Royall,I. J. Luxmoore,A. M. Fox,M. S. Skolnick
Physics , 2013, DOI: 10.1364/OE.22.002376
Abstract: We present a waveguide-coupled photonic crystal H1 cavity structure in which the orthogonal dipole modes couple to spatially separated photonic crystal waveguides. Coupling of each cavity mode to its respective waveguide with equal efficiency is achieved by adjusting the position and orientation of the waveguides. The behavior of the optimized device is experimentally verified for where the cavity mode splitting is larger and smaller than the cavity mode linewidth. In both cases, coupled Q-factors up to 1600 and contrast ratios up to 10 are achieved. This design may allow for spin state readout of a self-assembled quantum dot positioned at the cavity center or function as an ultra-fast optical switch operating at the single photon level.
GHz bandwidth electro-optics of a single self-assembled quantum dot in a charge-tunable device  [PDF]
Jonathan H. Prechtel,Paul A. Dalgarno,Robert H. Hadfield,Jamie McFarlane,Antonio Badolato,Pierre M. Petroff,Richard J. Warburton
Physics , 2011, DOI: 10.1063/1.3687375
Abstract: The response of a single InGaAs quantum dot, embedded in a miniaturized charge-tunable device, to an applied GHz bandwidth electrical pulse is investigated via its optical response. Quantum dot response times of 1.0 \pm 0.1 ns are characterized via several different measurement techniques, demonstrating GHz bandwidth electrical control. Furthermore a novel optical detection technique based on resonant electron-hole pair generation in the hybridization region is used to map fully the voltage pulse experienced by the quantum dot, showing in this case a simple exponential rise.
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