Excitonic Rabi Oscillations Research Articles

Coherent driving of direct and indirect excitons in a quantum dot molecule

Quantum dot molecules (QDMs) are one of the few quantum light sources that promise deterministic generation of one- and two-dimensional photonic graph states. The proposed protocols rely on coherent excitation of the tunnel-coupled and spatially indirect exciton states. Here, we demonstrate power-dependent Rabi oscillations of direct excitons, spatially indirect excitons, and excitons with a hybridized electron wave function. An off-resonant detection technique based on phonon-mediated state transfer allows for spectrally filtered detection under resonant excitation. Applying a gate voltage to the QDM-device enables a continuous transition between direct and indirect excitons and, thereby, control of the overlap of the electron and hole wave function. This does not only vary the Rabi frequency of the investigated transition by a factor of $\approx3$, but also allows to optimize graph state generation in terms of optical pulse power and reduction of radiative lifetimes.

Förster Blockade and Excitation Transfer Behaviors of Two-Photon Rabi Oscillations of Exciton–Biexciton Levels in Coupled Quantum Dots

We provide a theoretical study for the dynamical behavior of two-photon Rabi oscillations in two coupled quantum dots. Each dot is a three-level quantum system (ground, one-exciton, and biexciton states). We describe the optical dynamics within the density matrix formalism framework. The two-photon Rabi oscillations are found to be significantly affected by the strength of the interdot dipolar interaction. Using a detuned laser pulse with an exciton state of the driven quantum dot in our numerical simulations, a direct coherent excitation between the biexciton states can be established, but whether Rabi oscillations can be observed depend mainly on the strength of the dipolar interaction and bandwidth of the excitation laser. When the strength of the dipolar coupling is less than the excitation laser bandwidth, the time-dependent populations of the various two biexciton states of the system exhibit coherent oscillations with several frequencies. However, as we increase the dipolar coupling strength, the population transfer between the quantum dots levels amazingly becomes forbidden, and the excitation gets trapped at the initial state. The reduction of the influence of the dipolar interaction leads to a manipulation of two-photon Rabi oscillation in an ultrashort timescale (∼ps), opening possibilities to achieve ultrafast quantum state control and quantum logic gate generation.

Photoinduced dynamics of excitonic order and Rabi oscillations in the two-orbital Hubbard model

We investigate the condition for the photoinduced enhancement of an excitonic order in a two-orbital Hubbard model, which has been theoretically proposed in our previous work [Phys. Rev. B 97, 115105 (2018)], and analyze it from the viewpoint of the Rabi oscillation. Within the mean-field approximation, we simulate real-time dynamics of an excitonic insulator with a direct gap, where the pair condensation in the initial state is of BEC nature and the photoexcitation is introduced by electric dipole transitions. We first discuss that in the atomic limit our model is reduced to a two-level system that undergoes the Rabi oscillation, so that for single cycle pulses physical quantities after the photoirradiation are essentially determined by the ratio of the Rabi frequency to the pump-light frequency. Then, it is shown that this picture holds even in the case of nonzero transfer integrals where each one-particle state exhibits the Rabi oscillation leading to the enhancement of the excitonic order. We demonstrate that effects of electron-phonon interactions do not alter the results qualitatively. We also examine many-body dynamics by the exact diagonalization method on small clusters, which strongly suggests that our mechanism for the enhancement of the exctionic order survives even when quantum fluctuations are taken into account.

Rabi oscillations of a quantum dot exciton coupled to acoustic phonons: coherence and population readout

While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.

Intrinsic and environmental effects on the interference properties of a high-performance quantum dot single-photon source

We report a joint experimental and theoretical study of the interference properties of a single-photon source based on a In(Ga)As quantum dot embedded in a quasiplanar GaAs microcavity. Using resonant laser excitation with a pulse separation of 2 ns, we find near-perfect interference of the emitted photons, and a corresponding indistinguishability of $\mathcal{I}=(99.6{\phantom{\rule{0.16em}{0ex}}}_{\ensuremath{-}\phantom{\rule{0.16em}{0ex}}1.4}^{+\phantom{\rule{0.16em}{0ex}}0.4})%$. For larger pulse separations, quasiresonant excitation conditions, increasing pump power, or with increasing temperature, the interference contrast is progressively and notably reduced. We present a systematic study of the relevant dephasing mechanisms and explain our results in the framework of a microscopic model of our system. For strictly resonant excitation, we show that photon indistinguishability is independent of pump power, but strongly influenced by virtual phonon-assisted processes which are not evident in excitonic Rabi oscillations.

Resonantly driven exciton Rabi oscillation in single quantum dots emitting at 1300 nm**Project supported by the National Basic Research Program, China (Grant No. 2013CB922304), the National Key Research and Development Program of China (Grant No. 2016YFA0301202), and the National Natural Science Foundation of China (Grant Nos. 11474275, 61674135, and 91536101).

We report on the resonance fluorescence (RF) from single InAs quantum dots (QDs) emitting at the telecom band of 1300 nm. The InAs/GaAs QDs are embedded in a planar optical microcavity and the RF is measured by an orthogonal excitation-detection geometry for deeply suppressing the residual laser scattering. An ultra-weak He–Ne laser is necessary to be used as a gate laser for obtaining RF. Rabi oscillation with more than one period is observed through the picosecond (ps) pulsed laser excitation. The resonant control of exciton opens up new possibilities for realizing the on-demand single photon emission and quantum manipulation of solid-state qubits at telecom band.

Pitfalls in the theory of carrier dynamics in semiconductor quantum dots: Single-particle basis versus the many-particle configuration basis

We analyze quantum dot models used in current research for misconceptions that arise from the choice of basis states for the carriers. The examined models originate from semiconductor quantum optics, but the illustrated conceptional problems are not limited to this field. We demonstrate how the choice of basis states can imply a factorization scheme that leads to an artificial dependency between two, actually independent, quantities. Furthermore, we consider an open quantum dot-cavity system and show how the dephasing, generated by the dissipator in the von Neumann Lindblad equation, depends on the choice of basis states that are used to construct the collapse operators. We find that the Rabi oscillations of the s-shell exciton are either dephased by the dissipative decay of the p-shell exciton or remain unaffected, depending on the choice of basis states. In a last step we resolve this discrepancy by taking the full system-reservoir interaction Hamiltonian into account.

Excitonic Rabi oscillations in self-assembled quantum dots in the presence of a local field effect

We experimentally studied the excitonic Rabi oscillations in self-assembled semiconductor quantum dots using two-pulse photon echo spectroscopy. We observed the change in the shape of the Rabi oscillations by the second pulse intensity. Our experimental results were systematically reproduced by numerical calculations taking into account the local field effect arising from the Coulomb interaction between photoinduced charge densities in a quantum dot. Our experimental findings indicated that the local field effect contributes considerably to the coherent optical responses of the excitons in quantum dots.

Excitonic Rabi oscillations in self‐assembled quantum dots studied by photon echoes

AbstractWe report the excitonic Rabi oscillations in self assembled quantum dots observed by photon echo spectroscopy. The amplitude of the observed Rabi oscillations increases with the pulse area, which is different from the results of previous reports.A numerical calculation of the Rabi oscillations including the local field effect in a quantum dot well reproduces the experimental oscillations, indicating that the local field effect is one of the important origins of the modification of the Rabi oscillations in quantum dots (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pronounced enhancement of exciton Rabi oscillation for a two-photon transition based on quantum dot coupling control

We theoretically investigate how to control the Rabi oscillation of excitons of the coupling quantum dots by manipulating static electric fields. Our results show that, for a single-photon process, when direct excitons change into indirect excitons with a bias applied on the sample, the Rabi oscillation rarely alters. However, for the two-photon process, a pronounced enhancement of Rabi oscillation is observed, which can be utilized as the logic gate in quantum information.

Micro-Pump–Probe Spectroscopy of an Exciton in a Single Semiconductor Quantum Dot Using a Heterodyne Technique

A heterodyne detection scheme was applied to micro-pump–probe spectroscopy to study the transient response of an exciton in a single semiconductor quantum dot. The elimination of the pump pulse in the frequency domain provided us a direct probing of the energy relaxation process of the quantum state excited by the pump pulse. The excitonic Rabi oscillations were also monitored by this technique, even in the presence of a strong pump pulse. This spectroscopic technique is suitable for the observation of the optical response and coherent manipulation of a semiconductor quantum dot.

Ultrafast few-fermion optoelectronics in a single self-assembledInGaAs/GaAsquantum dot

We report a comprehensive study of the ultrafast optoelectronic response of a single self-assembled InGaAs/GaAs quantum dot embedded in a $n\text{\ensuremath{-}}i$-Schottky photodiode device. While manipulation of the artificial atom relies on two independently tunable picosecond pulse trains, sensitive all electrical readout is achieved via photocurrent. We apply our methods to probe the temporal evolution of the quantum dot absorption spectrum following coherent optical generation of a $s$-shell exciton. Our measurements reveal the biexciton absorption as well as previously unobserved $p$-shell transitions that appear in the presence of $s$-shell population. Furthermore, time-resolved measurements allow us to directly monitor the picosecond tunneling times of electrons and holes out of the dot. Beyond these incoherent phenomena, we also demonstrate the potential of our techniques for coherent quantum dot manipulations. Beginning with excitonic Rabi oscillations driven by a single pulse tuned to the neutral exciton we move on to demonstrate the coherent generation of the biexciton via a two-photon nonlinearity, before realizing conditional Rabi oscillations in the exciton-biexciton state manifold. The results provide significant potential for realizing and utilizing conditional coherent dynamics in quantum dot nanostructures for all optical, ultrafast quantum information processing.

Preface: Phys. Status Solidi C 6/S1

AbstractICOOPMA 2008 is the third in the ICOOPMA series, an International Conference on Optical, Optoelectronic and Photonic Materials and Applications (also known as The International Conference on Optical and Optoelectronic Properties of Materials and Applications), originally sponsored by Springer, that was held for the first time in Darwin, Australia, in July 2006. The ICOOPMA series arose from a need for such a conference for those researchers who sought a truly international conference that covered a wide range of materials and applications in optics, optoelectronics and photonics. One of the goals is to provide discussions between re‐searchers working on different classes of materials that have similar applications; or have been character‐ized by similar techniques. The conference has a large number of invited speakers to allow such cross‐fertilization between researchers working on different classes of materials. The conference also seeks papers in interesting or novel applications, or papers that enhance material properties for applications. The In‐ternational and Local Organizing Committees have the responsibility of ensuring an in‐depth scientific coverage with invited and contributed papers from various countries and in various disciplines; and en‐suring an enjoyable scientific program. The Second ICOOPMA was held in London, England, 29 July–3 August 2007, and had over 250 participants, and five plenary lectures. The Third ICOOPMA was held in Edmonton, Canada, 20–25 July 2008, and again had nearly 250 participants and had seven plenary talks. TRLabs in Edmonton was responsible for organizing and man‐aging the conference and there were a number of ma‐jor sponsors without whom this conference would not have had the success it deserves. We thank TRLabs for their organization, and our sponsors for their gra‐cious contributions and commitment to the ICOOPMA. There were three parallel oral sessions from Monday to Thursday, and a poster session on Tuesday to cover all the 300 papers. The current Pro‐ceedings represent a collection of papers that have been presented at the conference, and have been fully refereed for inclusion in the proceedings. With the agreement of the journal's Chief Editor and the authors, a selection of papers have been transferred to physica status solidi (a) 206(5) (May 2009). The papers in both issues cover not only topics on fundamental concepts, including various optical properties (luminescence being the most popular) of a wide class of materials, e.g. organics, glasses, semi‐conductors, nanocrystals, quantum wells, wires and dots etc., but also a number of interesting applications from photonics modulators to X‐ray detectors. There were four best poster prizes that were given during the conference to J. E. Cunningham and Edmund Lin‐field et al. (University of Leeds, UK) on “Terahertz imaging and spectroscopy using on‐chip systems”; Shabnam Homampour et al. (McMaster University, Canada) on “Thermal tuning of planar Bragg gratings in silicon‐on‐insulator rib waveguides”; Mamiko Kujiraoka et al. (National Institute of Information and Commu‐nications Technology, Japan) on “Ensemble effect on Rabi oscillations of exciton in quantum dots”; Osamu Kojima et al. (Kobe University, Japan) on “Lengthening of photoluminescence decay time owing to expansion of electron envelope functions in stacked quantum dots”.Timely publication of conference papers in an easily accessible journal is one of the attractions in presenting one's latest work at conferences. It allows the work to appear relatively quickly after it has been discussed at the conference. The papers in the proceedings were therefore prepared in publica‐tion‐ready form. However, it is also important to en‐sure that proper refereeing has been done before a paper has been accepted. We specifically allowed pa‐per submissions to continue well after the conference date to ensure that the papers included discussions during the conference. We thank the many referees who have unselfishly dedicated their valuable time in reviewing some ninety‐five manuscripts and, in many cases, reviewing the revised versions as well. We are grateful to the editorial team at Wiley‐VCH, in par‐ticular Stefan Hildebrandt in Berlin, for their help in getting the proceedings out as soon as possible once the refereeing of the papers were complete (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ensemble effect on Rabi oscillations of excitons in quantum dots

AbstractWe observed excitonic Rabi oscillations (ROs) in quantum dots (QDs) by four‐wave mixing (FWM) and pump‐probe techniques. When a large number of QDs are excited by a spatially nonuniform laser, the inhomogeneous distribution of the transition dipole moments of the QD excitons and the spatial distribution of the input electric field induce distribution of the Rabi frequencies. We investigated this ensemble effect on the ROs of the excitonic polarization and the excitonic population observed in the FWM and pump‐probe signals. By calculating the FWM and pump‐probe signals including the Gaussian distribution of the pulse area, we first showed that a part of the ensemble effect can be cancelled out only in case of the ROs of the excitonic polarization. This reflects the differences between the characteristics of excitonic polarization and population. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The excitonic population transfer in an interacting charge-transfer exciton system

We investigate the effects of the coupling of charge-transfer excitons on the excitonic population dynamics of a charge-transfer exciton system coupled by either CW or pulsed chirped electromagnetic fields. Owing to the strong coupling, at exact resonance with the CW fields, there is a critical value of the Rabi frequency above which the excitonic Rabi oscillations with complete population transfer to the excited state could be achieved. For the pulsed chirped field, if the coupling is considered, it has also been shown that the excitonic population transfer can be obtained in a wide range of both negative and positive values of chirped rate.

Signatures of energy transfer and multi-exciton states on exciton Rabi oscillation in semiconductor nanocrystals

The theory of coherent energy transfer in nanocrystal (NC) systems is generalised for multi-exciton states. We study the effect of the Forster coupling between two individual semiconductor nanocrystals on the pump and induced Rabi oscillations (ROs). The relevant excitonic states in an isolated NC can be described by an effective four-state system, consisting of the ground state, the exciton state, the biexciton state and the triexciton state. The dynamics of a single donor-acceptor pair is described using a density matrix approach that incorporates dipole coupling to multi-exciton states. Our study shows that for short pulse the multi-exciton states play an important role in the dynamics. We also show that the amplitude and the period of the ROs in both dots are heavily influenced by Forster coupling strength. The quality factor of the induced ROs in the acceptor yields information on the energy transfer rate between the two dots. We present result for a variety of sample materials and realistic structure parameters.

Correlation effect of Rabi oscillations of excitons in quantum dots

We performed a transient four-wave mixing experiment on a strain-compensated InAs quantum dot (QD) ensemble over a wide range of excitation intensities. Under the resonant excitation of an exciton ground state, an extremely long dephasing time of 1 ns was found. By increasing the areas of the excitation pulses, Rabi oscillations of excitonic polarizations were clearly observed. The corresponding Rabi frequency is three orders of magnitude higher than the measured dephasing rate. For larger pulse areas, we found that the deviation of experimental data from two-level predictions became significant. The deviations cannot be explained by taking into account, as has been suggested in other research, excitation density-dependent dephasing or Hartree–Fock-type Coulomb interactions between excitons.

Acoustic phonon-assisted damping of Rabi oscillations in InAs quantum dots

Excitonic ground state Rabi oscillations in InAs quantum dots are studied via an ultrafast spectral hole burning technique. From comparison with frequency domain data, we find that acoustic phonon-induced dephasing processes damp the oscillations.

Exciton Rabi oscillation observed in spontaneous emissions after resonant excitation

We observed Rabi oscillations of ground-state excitons in single GaAs quantum dots (QDs). We temporally resolved emissions from the ground-state excitons after exciting the same level by picosecond short pulses. To capture weak emissions from single QDs, the reflection signals of an excitation laser were reduced by applying obliquely incident geometry and crossed polarization configuration. Rabi oscillations were observed in the emissions as a function of excitation amplitude.

Exciton Rabi Oscillation in Single Pair of InAs/GaAs Coupled Quantum Dots

We measured the optical properties of exciton states and the exciton Rabi oscillation in a single pair of coupled quantum dots (CQDs). We compared the transition dipole moments of exciton in a single quantum dot (SQD) and CQDs. The transition dipole moment estimated from the experimental result in a single pair of CQDs was 72 D, which is larger than that for SQD. We concluded that the large transition dipole moment is attributed to the large coherence volume in CQDs.