Optimal quantum control (OQC) enabled by femtosecond laser pulse shaping techniques provides a highly flexible approach to quantum states manipulation in solid-state qubit systems. Here we apply OQC to optimize the form of the triggering laser pulse for a single photon source. The use of a frequency-swept laser pulse possessing a notch resonant with the transition energy of the quantum emitter enables the spectral isolation of the emitted photon stream in conjunction with resonant driving for good indistinguishability. We show that the robustness of this scheme would enable spectral multiplexing of quantum light sources using a single triggering laser pulse.
In this presentation I will describe a new laser driving scheme for triggered high-brightness single photon emitters using a chirped laser pulse possessing a spectral hole resonant with the transition energy of the emitter, referred to as Notch-filtered adiabatic rapid passage (NARP). When combined with optimized photonic structures for enhanced collection efficiency and commercial filters we estimate that NARP would provide less than 10-8 scattered photons per emitted photon with a 4% detection loss together with resonant driving for high photon indistinguishability. We demonstrate inversion using NARP experimentally in a single semiconductor QD.
Semiconductor quantum dots (QDs) may be applied to solid-state quantum emitters of interest for quantum light sources or nodes in distributed quantum networks. For such emitters, resonant optical driving results in the highest degree of photon indistinguishability, but leads to the need to reject scattered light from the laser used to drive the emitter. In this work, we apply femtosecond pulse shaping techniques to the development of quantum state inversion strategies for QD emitters that optimize fidelity and source brightness. The control protocols we have developed would be applicable to a wide range of solid-state QE systems.
We report the demonstration of adiabatic rapid passage on single solid-state quantum emitters based on semiconductor quantum dots. By extending our earlier experiments employing femtosecond pulse shaping for rapid and arbitrary qubit rotations to the strong-driving regime, we demonstrate full suppression of decoherence tied to LA phonon coupling. Our results will support the development of single photon sources and distributed quantum networks using semiconductor quantum dots.
Interest in the hybrid organic-inorganic perovskite semiconductors has skyrocketed in recent years due to unprecedented high performance as solution-processable absorber layers in solar cells [1]. These materials also have potential for applications in semiconductor spintronics due to their large spin-orbit interaction. Theoretical studies predict a large Rashba spin splitting [2], and recent experiments have revealed a large photoinduced magnetization [3-5] and spin-dependent optical Stark effect [6], yet still relatively little is known about the spin-related properties of these materials. Here we report polarization-dependent pump probe studies of the 2D perovskite butylammonium methylammonium lead iodide. Our experiments indicate a strong influence of the Rashba spin splitting on the carrier kinetics in this system, consistent with our recent four-wave mixing studies of bulk CH3NH3PbI3.
[1] https://www.nrel.gov/pv/assets/images/efficiency_chart.jpg.
[2] M. Kepenekian and J. Even, J. Phys. Chem. Lett. 8, 3362 (2017).
[3] D. Giovanni et al. Nano Lett. 15, 1553 (2015).
[4] C. Zhang et al. Nat. Phys. 11, 427 (2015).
[5] P. Odenthal et al. Nat. Phys. 13, 894 (2017).
[6] D. Giovanni et al. Science Advances 2, e1600477 (2016).
The lead halide hybrid perovskites have gained considerable attention in recent years due to their stellar performance as absorber layers in solution-processed solar cells, with efficiencies recently reaching over 22 percent [1]. Owing to their large spin-orbit coupling, these materials are also of interest for spintronic applications, in which the presence of lead may be less of an impediment to their adoption [2]. Measurements of spin dynamics in bulk CH3NH3PbI3-xClx have been reported in recent years [3,4,5], the spin-dependent optical Stark effect was demonstrated in 4F-PEPI [6], and a large Rashba effect has been predicted in both bulk and 2D perovskites [2], highlighting the need for further studies of the spin-related properties of these materials. Here we report spin-dependent measurements of carrier kinetics in butylammonium methylammonium lead iodide 2D perovskite and measurements of the coherent carrier response in 3D CH3NH3PbI3. Both experiments provide direct evidence of the impact of Rashba on the carrier kinetics in these systems, further supporting the potential for developing spin-optoelectronic devices using these materials.
[1] https://www.nrel.gov/pv/assets/images/efficiency_chart.jpg.
[2] M. Kepenekian and J. Even, J. Phys. Chem. Lett. 8, 3362 (2017).
[3] D. Giovanni et al. Nano Lett. 15, 1553 (2015).
[4] C. Zhang et al. Nat. Phys. 11, 427 (2015).
[5] P. Odenthal et al. Nat. Phys. 13, 894 (2017).
[6] D. Giovanni et al. Science Advances 2, e1600477 (2016).
KEYWORDS: Solar cells, Four wave mixing, Semiconductors, Ultrafast phenomena, Thin film solar cells, Thin films, Excitons, Perovskite, Signal detection, Absorption, Spectroscopes, Dielectrics
The interest in perovskite-based solar cell absorber materials has skyrocketed in recent years due to the rapid rise in solar cell efficiency and the potential for cost reductions tied to solution-processed device fabrication. Due to complications associated with the presence of strong static and dynamic disorder in these organic-inorganic materials, the fundamental photophysical behavior of photo-excited charge carriers remains unclear. We apply four-wave mixing spectroscopy to study the charge carrier dynamics in CH3NH3PbI3 thin films. Our experiments reveal two discrete optical transitions below the band gap of the semiconductor with binding energies of 13 meV and 29 meV, attributed to free and defect-bound excitons respectively.
Pulse shaping techniques are used to demonstrate quantum control of exciton qubits in InAs quantum dots. Linearly chirped laser pulses are used to demonstrate adiabatic rapid passage in a single quantum dot on a subpicosecond timescale. The observed dependence of the exciton inversion efficiency on the sign of the pulse chirp identifies phonons as the dominant source of dephasing, which can be suppressed for positive chirp at low temperatures. The use of optimal quantum control theory to engineer a single optical pulse to implement simultaneous π and 2π single qubit gates in two uncoupled quantum dots is demonstrated. This work will support the use of pulse shaping in solid-state quantum hardware.
Four-wave mixing techniques are applied to Ga1-xMnxAs, providing new insight into the fundamental properties of the III-Mn-V semiconductors. Clear signatures of (s,p)-d hybridization associated with the MnGa substitutional impurity are observed in the spectrum of the four-wave mixing signal. Experiments on a ferromagnetic sample show no evidence of hole occupation in the valence band for x = 5%. A photon echo is observed on the interband transition, despite the strong exchange coupling and large defect density in this system. Rapid dephasing associated with Mn-hole spin-flip scattering is observed, with a measured upper bound on the spin-flip scattering time of 40 fs. An excitonic signature tied to many-body effects is observed in LT-GaAs.
We review recent experiments on spin excitation and manipulation in the ferromagnetic semiconductor GaMnAs. Spin
dynamics in GaMnAs have been studied by two complementary approaches - by frequency-domain techniques, such as
Brillouin light scattering (BLS) and ferromagnetic resonance (FMR); and by optical real-time techniques, such as
ultrafast pump-probe magneto-optical spectroscopy. Using BLS and FMR, magnon frequencies (or resonance fields),
were investigated as a function of Mn concentration, temperature and direction of magnetization, leading to information
on magnetic anisotropy. Time-resolved magneto-optical Kerr effect, on the other hand, was used to study photo-induced
femtosecond magnetization rotation, ultrafast optical demagnetization, and collective magnetization precession.
Optically-induced transient changes in magnetization of GaMnAs produced by femtosecond laser pulses are analyzed
and discussed in terms of the Landau-Lifshitz-Gilbert model. Finally, for completeness, we also discuss carrier-mediated
nonthermal and thermal (lattice-heating) contributions to spin dynamics.
Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to capture, resulting in strong circularly-polarized emission. Comparison of spin relaxation times in positively charged and neutral quantum dots reveals a negligible influence of the large built-in hole population, in contrast to measurements in higher-dimensional p-type semiconductors. The long spin life-time, short capture time, and high radiative efficiency of the positively charged quantum dots indicates that these structures are superior to both quantum wells and neutral quantum dots for spin detection using a spin light-emitting diode.
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