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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.
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.
Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field  [PDF]
M. Korkusinski,P. Hawrylak,A. Babinski,M. Potemski,S. Raymond,Z. Wasilewski
Physics , 2007, DOI: 10.1209/0295-5075/79/47005
Abstract: We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla.
High fidelity optical preparation and coherent Larmor precession of a single hole in an InGaAs quantum dot molecule  [PDF]
K. Müller,A. Bechtold,C. Ruppert,C. Hautmann,J. S. Wildmann,T. Kaldewey,M. Bichler,H. J. Krenner,G. Abstreiter,M. Betz,J. J. Finley
Physics , 2012, DOI: 10.1103/PhysRevB.85.241306
Abstract: We employ ultrafast pump-probe spectroscopy with photocurrent readout to directly probe the dynamics of a single hole spin in a single, electrically tunable self-assembled quantum dot molecule formed by vertically stacking InGaAs quantum dots. Excitons with defined spin configurations are initialized in one of the two dots using circularly polarized picosecond pulses. The time-dependent spin configuration is probed by the spin selective optical absorption of the resulting few Fermion complex. Taking advantage of sub-5 ps electron tunneling to an orbitally excited state of the other dot, we initialize a single hole spin with a purity of >96%, i.e., much higher than demonstrated in previous single dot experiments. Measurements in a lateral magnetic field monitor the coherent Larmor precession of the single hole spin with no observable loss of spin coherence within the ~300 ps hole lifetime. Thereby, the purity of the hole spin initialization remains unchanged for all investigated magnetic fields.
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.
Spin Readout and Initialization in a Semiconductor Quantum Dot  [PDF]
Mark Friesen,Charles Tahan,Robert Joynt,M. A. Eriksson
Physics , 2003, DOI: 10.1103/PhysRevLett.92.037901
Abstract: Electron spin qubits in semiconductors are attractive from the viewpoint of long coherence times. However, single spin measurement is challenging. Several promising schemes incorporate ancillary tunnel couplings that may provide unwanted channels for decoherence. Here, we propose a novel spin-charge transduction scheme, converting spin information to orbital information within a single quantum dot by microwave excitation. The same quantum dot can be used for rapid initialization, gating, and readout. We present detailed modeling of such a device in silicon to confirm its feasibility.
Electrically addressing a single self-assembled quantum dot  [PDF]
D. J. P. Ellis,A. J. Bennett,P. Atkinson,D. A. Ritchie,A. J. Shields
Physics , 2006, DOI: 10.1063/1.2190451
Abstract: We report on the use of an aperture in an aluminum oxide layer to restrict current injection into a single self-assembled InAs quantum dot, from an ensemble of such dots within a large mesa. The insulating aperture is formed through the wet-oxidation of a layer of AlAs. Under photoluminescence we observe that only one quantum dot in the ensemble exhibits a Stark shift, and that the same single dot is visible under electroluminescence. Autocorrelation measurements performed on the electroluminescence confirm that we are observing emission from a single quantum dot.
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.
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.
Multi-Exciton Spectroscopy of a Single Self Assembled Quantum Dot  [PDF]
E. Dekel,D. Gershoni,E. Ehrenfreund,D. Spektor J. M. Garcia,P. M. Petroff
Physics , 1998, DOI: 10.1103/PhysRevLett.80.4991
Abstract: We apply low temperature confocal optical microscopy to spatially resolve, and spectroscopically study a single self assembled quantum dot. By comparing the emission spectra obtained at various excitation levels to a theoretical many body model, we show that: Single exciton radiative recombination is very weak. Sharp spectral lines are due to optical transitions between confined multiexcitonic states among which excitons thermalize within their lifetime. Once these few states are fully occupied, broad bands appear due to transitions between states which contain continuum electrons.
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