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Quantum Electronics and Laser Science Conference

Attosecond phase spectroscopy of semiconductor quantum wells

J.J. Baumberg, Albert P. Heberle, Klaus Köhler, Klaus Ploog

Published Jun 7, 1996• 0 citations
OpenAlex

Abstract

Summary form only given. Irreversible absorption of light in any material requires that the coherence of the initial photoexcited state be lost. In quantum-engineered semiconductor systems, decoherence cannot be treated merely phenomenologically, and coherent phenomena play a dramatic role, even in the linear optical properties. We have devised an ultrafast coherent spectroscopy that directly tracks the evolution of the electron-hole phase after excitation with a laser pulse. In high-quality quantum well samples, this general technique uncovers a coherent response differing strongly from that observed on incoherent excitation.

Related papers

Exciton beats and coherent control in GaAs quantum wells

Joaquín Fernández-Rossier, C. Tejedor, Roberto D. Merlin

Summary form only given. The optical properties of semiconductor quantum wells (QW) and, in particular, the coherent dynamics of excitons following resonant excitation with ultrafast laser pulses have attracted much attention in recent years. It is generally accepted that there is a transfer of coherence between the optical field and the QW that disappears in a characteristic time T/sub 2/ (picoseconds for GaAs) after the laser is turned off. However, the questions as to how the coherence is actually induced and that of the nature of the coherent state of the solid are poorly understood. In this work we address these points by re-examining the longstanding problem of the (classical vs. quantum) nature of the ubiquitous beats associated with the light-hole (LX) heavy-hole (HX) excitons, which are observed in transient optical experiments on QW. To this end, we consider the coherent behavior of excitons using the simplest albeit non-trivial model where they are treated as non-interacting bosons. Our results bear directly on studies for which nonlinear effects are not important and are not aimed directly at explaining the fourwave-mixing (FWM) experiments that dominate the field. Nevertheless, since nonlinear effects are, typically, weak compared with harmonic contributions, the free boson picture provides in all cases the correct lowest order wavefunction of the photoexcited solid.

Quantum Electronics and Laser Science Conference•Jan 20, 2003•0 citations

R2.1 Dephasing processes in InGaAs quantum dots

J.H Davies, A.R Long

The dynamics of electrons and holes in semiconductors and semiconductor heterostructures have been extensively discussed in the literature, and are governed by their mutual Coulomb interaction, by their interaction with lattice vibrations (phonons) and by their radiative recombination (for an overview see e.g. Ref. [1]). A powerful technique to study the carrier dynamics in semiconductors utilizes short optical pulses to photoexcite electrons from the valence to the conduction band (i.e. to create electron-hole pairs) that subsequently relax until the photon energy stored in the medium is dissipated and the system has recovered the thermal equilibrium. The dynamics of the carriers photoexcited by the short optical pulse can be followed by monitoring two main optical observables: the interband population difference and the induced polarization. Both quantities decay with time after the photoexcitation due to the carrier dynamics. While the induced polarization (which is an ensemble average over many photoexcited dipole moments) is sensitive to scattering events that break the phase relationship among the individual dipoles and/or with the light field creating them (dephasing processes), the population difference is sensitive only to events that change the energy state of the carriers. Transient coherent optical spectroscopy addresses the time-evolution of the induced polarization in the time-regime during and immediately following the photoexcitation by a short laser pulse, in which the photoexcited dipoles have retained a defined phase relationship among each other and with the exciting coherent radiation.

CRC Press eBooks•May 1, 2003•0 citations

Quantum-Spectroscopy Studies on Semiconductor Nanostructures

Martin Mootz

Quantum spectroscopy utilizes the quantum fluctuations of the light source to characterize and control matter. More specifically, desired many-body states can be directly excited to the semiconductor by adjusting light source's quantum fluctuations. The method is experimentally realizable by projecting an extensive set of classical measurements into a quantum-optical response resulting from any possible quantum source. In this work, quantum spectroscopy is used to identify new classes of many-body states and quantum processes in semiconductor nanostructures. In the first part of this Thesis, the optical properties of semiconductor quantum wells are analyzed with quantum spectroscopy by projecting high-precision optical measurements into quantum-optical responses. It is shown that quantum spectroscopy can characterize the properties of specific stable electron-hole cluster – called quasiparticles – much more sensitively than traditional ultrafast laser spectroscopy. In particular, unambiguous evidence is demonstrated for the identification of a new highly correlated quasiparticle in direct-gap Galliumarsenide quantum wells, the dropleton, that is a quantum droplet consisting of four-to-seven electron-hole pairs. To determine the detectable excitation energetics of such correlated quasiparticles in optically excited semiconductor quantum wells, a new theoretical framework is presented which allows for the computation of the excitation spectrum based on a pair-correlation function formulation of the quasiparticle state. Another study in this Thesis deals with the emission properties of optically pumped quantum-dot microcavities. Experimental and theoretical evidence is shown for a new intriguing quantum-memory effect that is controllable by adjusting pump source's quantum fluctuations. The last part of this Thesis presents a fundamental study about the general applicability of quantum spectroscopy in dissipative systems.

•Jan 1, 2014•0 citations

Direct observation of the excitonic ac Stark splitting in a semiconductor quantum well

Michele Saba, Francesco Quochi, Cristiano Ciuti +5 more

Summary form only given. In the excitonic ac Stark shift in quantum wells the excitonic absorption line is blueshifted by shining on the sample an intense laser pulse, whose frequency is lower than the exciton transition frequency. The effect is bigger when the laser spectrum approaches the resonance with the excitonic absorption. But if the laser and excitonic absorption spectra sensibly overlap, a great amount of electronic population is excited and consequently the Coulomb nonlinearities due to the interaction between excited carries or excitons dramatically increase. One prominent effect under these conditions is the excitation- induced dephasing which can destroy the coherence of the electronic system and therefore the coupling between excitons and light, which is inherently coherent. Some evidence for the resonant Stark effect was already reported, but the direct observation of the spectral splitting was still missing. This observation demonstrates that the coherent exciton light coupling in semiconductors can be strong enough to survive the fast dephasing, and that therefore an efficient ultrafast manipulation of the exciton absorption in the coherent transient is possible. In order to magnify the ac Stark effect and its visibility a special sample was designed: a single In/sub 0.04/Ga/sub 0.96/As quantum well is grown on the top of an AlAs/AlGaAs distributed Bragg reflector; two /spl lambda//2 spacers separate the quantum well from the mirror and from the air. In this configuration the light field incident on the sample and the one reflected by the mirror constructively interfere at the quantum well position, giving a high effective absorption.

Quantum Electronics and Laser Science Conference•Nov 13, 2002•0 citations

Optical coherent control in semiconductors

John Erland, Vadim G. Lyssenko, J. M. Hvam

Summary form only given. The developments with coherent control (CC) techniques in optical spectroscopy have recently demonstrated population control and coherence manipulations when the induced optical phase is explored with phase-locked laser pulses. These and other developments have been guiding the new research field of quantum control including the recent applications to semiconductors and nanostructures. We study the influence of inhomogeneous broadening in semiconductors on CC results. Photoluminescence (PL) and the coherent emission in four-wave mixing (FWM) is recorded after resonant excitation with phase-locked laser pulses. The sample is a narrow GaAs single quantum well.

Quantum Electronics and Laser Science Conference•Nov 13, 2002•0 citations

Ultrafast manipulation of coherent excitons in quantum wells by pulse shaping technique

Kazuhiro Komori, Takashi ASAHARA, Takeyoshi Sugaya +2 more

The development of both the ultrafast lasers and the growth technique of high quality semiconductor nano-structures gives us the ability to manipulate the quantum dynamics by a coherent control[l] and the possibility to apply the coherent phenomena to ultrafast novel devices.

Novel Lasers and Devices - Basic Aspects•Jan 1, 1999•0 citations
Summary form only given. Irreversible absorption of light in any material requires that the coherence of the initial photoexcited state be lost. In quantum-engineered semiconductor systems, decoherence cannot be treated merely phenomenologically, and coherent phenomena play a dramatic role, even in the linear optical properties. We have devised an ultrafast coherent spectroscopy that directly tracks the evolution of the electron-hole phase after excitation with a laser pulse. In high-quality quantum well samples, this general technique uncovers a coherent response differing strongly from that observed on incoherent excitation.
Summary form only given. The optical properties of semiconductor quantum wells (QW) and, in particular, the coherent dynamics of excitons following resonant excitation with ultrafast laser pulses have attracted much attention in recent years. It is generally accepted that there is a transfer of coherence between the optical field and the QW that disappears in a characteristic time T/sub 2/ (picoseconds for GaAs) after the laser is turned off. However, the questions as to how the coherence is actually induced and that of the nature of the coherent state of the solid are poorly understood. In this work we address these points by re-examining the longstanding problem of the (classical vs. quantum) nature of the ubiquitous beats associated with the light-hole (LX) heavy-hole (HX) excitons, which are observed in transient optical experiments on QW. To this end, we consider the coherent behavior of excitons using the simplest albeit non-trivial model where they are treated as non-interacting bosons. Our results bear directly on studies for which nonlinear effects are not important and are not aimed directly at explaining the fourwave-mixing (FWM) experiments that dominate the field. Nevertheless, since nonlinear effects are, typically, weak compared with harmonic contributions, the free boson picture provides in all cases the correct lowest order wavefunction of the photoexcited solid.
The dynamics of electrons and holes in semiconductors and semiconductor heterostructures have been extensively discussed in the literature, and are governed by their mutual Coulomb interaction, by their interaction with lattice vibrations (phonons) and by their radiative recombination (for an overview see e.g. Ref. [1]). A powerful technique to study the carrier dynamics in semiconductors utilizes short optical pulses to photoexcite electrons from the valence to the conduction band (i.e. to create electron-hole pairs) that subsequently relax until the photon energy stored in the medium is dissipated and the system has recovered the thermal equilibrium. The dynamics of the carriers photoexcited by the short optical pulse can be followed by monitoring two main optical observables: the interband population difference and the induced polarization. Both quantities decay with time after the photoexcitation due to the carrier dynamics. While the induced polarization (which is an ensemble average over many photoexcited dipole moments) is sensitive to scattering events that break the phase relationship among the individual dipoles and/or with the light field creating them (dephasing processes), the population difference is sensitive only to events that change the energy state of the carriers. Transient coherent optical spectroscopy addresses the time-evolution of the induced polarization in the time-regime during and immediately following the photoexcitation by a short laser pulse, in which the photoexcited dipoles have retained a defined phase relationship among each other and with the exciting coherent radiation.
Quantum spectroscopy utilizes the quantum fluctuations of the light source to characterize and control matter. More specifically, desired many-body states can be directly excited to the semiconductor by adjusting light source's quantum fluctuations. The method is experimentally realizable by projecting an extensive set of classical measurements into a quantum-optical response resulting from any possible quantum source. In this work, quantum spectroscopy is used to identify new classes of many-body states and quantum processes in semiconductor nanostructures. In the first part of this Thesis, the optical properties of semiconductor quantum wells are analyzed with quantum spectroscopy by projecting high-precision optical measurements into quantum-optical responses. It is shown that quantum spectroscopy can characterize the properties of specific stable electron-hole cluster – called quasiparticles – much more sensitively than traditional ultrafast laser spectroscopy. In particular, unambiguous evidence is demonstrated for the identification of a new highly correlated quasiparticle in direct-gap Galliumarsenide quantum wells, the dropleton, that is a quantum droplet consisting of four-to-seven electron-hole pairs. To determine the detectable excitation energetics of such correlated quasiparticles in optically excited semiconductor quantum wells, a new theoretical framework is presented which allows for the computation of the excitation spectrum based on a pair-correlation function formulation of the quasiparticle state. Another study in this Thesis deals with the emission properties of optically pumped quantum-dot microcavities. Experimental and theoretical evidence is shown for a new intriguing quantum-memory effect that is controllable by adjusting pump source's quantum fluctuations. The last part of this Thesis presents a fundamental study about the general applicability of quantum spectroscopy in dissipative systems.
Summary form only given. In the excitonic ac Stark shift in quantum wells the excitonic absorption line is blueshifted by shining on the sample an intense laser pulse, whose frequency is lower than the exciton transition frequency. The effect is bigger when the laser spectrum approaches the resonance with the excitonic absorption. But if the laser and excitonic absorption spectra sensibly overlap, a great amount of electronic population is excited and consequently the Coulomb nonlinearities due to the interaction between excited carries or excitons dramatically increase. One prominent effect under these conditions is the excitation- induced dephasing which can destroy the coherence of the electronic system and therefore the coupling between excitons and light, which is inherently coherent. Some evidence for the resonant Stark effect was already reported, but the direct observation of the spectral splitting was still missing. This observation demonstrates that the coherent exciton light coupling in semiconductors can be strong enough to survive the fast dephasing, and that therefore an efficient ultrafast manipulation of the exciton absorption in the coherent transient is possible. In order to magnify the ac Stark effect and its visibility a special sample was designed: a single In/sub 0.04/Ga/sub 0.96/As quantum well is grown on the top of an AlAs/AlGaAs distributed Bragg reflector; two /spl lambda//2 spacers separate the quantum well from the mirror and from the air. In this configuration the light field incident on the sample and the one reflected by the mirror constructively interfere at the quantum well position, giving a high effective absorption.
Summary form only given. The developments with coherent control (CC) techniques in optical spectroscopy have recently demonstrated population control and coherence manipulations when the induced optical phase is explored with phase-locked laser pulses. These and other developments have been guiding the new research field of quantum control including the recent applications to semiconductors and nanostructures. We study the influence of inhomogeneous broadening in semiconductors on CC results. Photoluminescence (PL) and the coherent emission in four-wave mixing (FWM) is recorded after resonant excitation with phase-locked laser pulses. The sample is a narrow GaAs single quantum well.