The role of phonons for exciton and biexciton generation in an optically driven quantum dot

Reiter, Doris E.; Kuhn, Thomas; Glässl, Martin; Axt, Vollrath M.

doi:10.1088/0953-8984/26/42/423203

Cited by 70 publications

(88 citation statements)

References 223 publications

(488 reference statements)

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“…At the highest pulse areas, however, the theory predicts essentially perfect RAP independent of the sign of the chirp. The interpretation is that the splittings between the branches at the avoided crossings are energetically so large that they lie well above the energy range of the phonons which are efficiently coupled to the exciton system [34]. In other words, the wavelength of the phonons required for scattering between the dressed states becomes much smaller than the size of the QD at high pulse area.…”

Section: -2mentioning

confidence: 99%

“…We use standard GaAs parameters and take the excitation parameters from the experiment leaving the QD size as the only fitting parameter. This model has been successfully used to describe the phonon influence on Rabi rotations [34] and on the population inversion via RAP [12,27]. For the occupations of the exciton and biexciton states as well as for the coherences between all involved states a set of equations of motion is derived within a well-established fourth-order correlation expansion method [35].…”

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Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage

et al. 2017

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A biexciton in a semiconductor quantum dot is a source of polarization-entangled photons with high potential for implementation in scalable systems. Several approaches for nonresonant, resonant, and quasiresonant biexciton preparation exist, but all have their own disadvantages; for instance, low fidelity, timing jitter, incoherence, or sensitivity to experimental parameters. We demonstrate a coherent and robust technique to generate a biexciton in an InGaAs quantum dot with a fidelity close to 1. The main concept is the application of rapid adiabatic passage to the ground-state-exciton-biexciton system. We reinforce our experimental results with simulations which include a microscopic coupling to phonons. DOI: 10.1103/PhysRevB.95.161302 Entangled photon pairs are a powerful resource, especially for quantum teleportation and quantum key distribution protocols. Spontaneous parametric down-conversion in nonlinear optics is a source of entangled photon pairs [1], but success is not guaranteed-the emission is a probabilistic process-and the error rate is high. In contrast, semiconductor quantum dots (QDs) are bright, on-demand sources of both single photons [2] and entangled photon pairs and hence have enormous potential in quantum computing and quantum cryptography [3].A biexciton in a QD is the starting point for a two-photon cascade: when perfectly prepared, biexciton decay leads to the subsequent emission of two photons [ Fig. 1(f)]. In a QD without a significant fine-structure splitting (FSS), the two photons are polarization entangled [4]. The majority of InGaAs QDs show a FSS due to a reduced symmetry [5][6][7]. However, sophisticated techniques were developed to compensate for the FSS with strain [8], electric [9], or magnetic fields [10,11] and with special growth conditions [7].Several approaches for biexciton preparation have been proposed [12][13][14][15] and demonstrated [4,[16][17][18][19][20]. Resonant two-photon schemes involving Rabi rotations [4,17,18] are sensitive to fluctuations in both laser power and QD optical frequency. They are likely to suffer from an imperfect biexciton preparation resulting in undesired exciton photons unrelated to the cascade process.A more robust scheme using phonon-assisted excitation was reported by several groups recently [18][19][20][21][22]. An impressively high biexciton occupation of up to 95% was demonstrated using this quasiresonant scheme [20]. But the strength here is also a weakness. The scheme relies on the coupling to the phonon bath in the semiconductor environment: it is an inherently incoherent process. Also, a dependence on relaxation processes in the state preparation results in a timing jitter. In some cases, charge-carrier relaxation times can reach values of up to a nanosecond [23].We present here a coherent technique to create a biexciton with high probability, low jitter, and weak dependence on the * timo.kaldewey@unibas.ch excitation and system parameters. The technique is based on rapid adiabatic passage (RAP). RAP allows the robust creatio...

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Section: -2mentioning

confidence: 99%

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confidence: 99%

Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage

et al. 2017

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“…The excitonic QD states are promising candidates to be used as qubits for quantum computing [2][3][4][5][6][7] , while the radiative decay from the biexciton cascade offers the possibility of an on-demand creation of indistinguishable entangled photon pairs [8][9][10] . It has been shown that both exciton and biexciton states of a QD can be prepared by using ultra-fast laser pulses under a variety of excitation conditions 11,12 . The most commonly known schemes for this purpose are resonant excitation leading to Rabi rotations [13][14][15][16] , different protocols using chirped laser pulses exploiting the adiabatic rapid passage effect [17][18][19][20][21][22][23][24][25] , and phonon-assisted off-resonant driving [26][27][28][29] .…”

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confidence: 99%

Fast and selective phonon-assisted state preparation of a quantum dot by adiabatic undressing

et al. 2016

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We investigate theoretically the temporal behavior of a quantum dot under off-resonant optical excitation targeted at fast acoustic phonon-assisted state preparation. We demonstrate that in a preparation process driven by short laser pulses three processes can be identified: a dressing of the states during the switch on of the laser pulse, a subsequent phonon-induced relaxation and an undressing at the end of the pulse. By analyzing excitation scenarios with different pulse shapes we highlight the decisive impact of an adiabatic undressing on the final state in short pulse protocols. Furthermore, we show that in exciton-biexciton systems the laser characteristics such as the pulse detuning and the pulse length as well as the biexciton binding energy can be used to select the targeted quantum dot state.

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“…Quantum control of the exciton, an electron-hole pair, proceeds on picosecond timescales well before spontaneous emission takes place (timescale ∼1 ns). Phonons lead to a deterioration of the exciton preparation fidelity for schemes using resonant excitation [1,[6][7][8][9][10]. In fact, the interaction with the phonons is sufficiently strong that an exciton state can be prepared by relying on it (phonon-mediated relaxation following excitation with a detuned pulse) [11][12][13][14][15].…”

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Demonstrating the decoupling regime of the electron-phonon interaction in a quantum dot using chirped optical excitation

et al. 2017

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Excitation of a semiconductor quantum dot with a chirped laser pulse allows excitons to be created by rapid adiabatic passage. In quantum dots this process can be greatly hindered by the coupling to phonons. Here we add a high chirp rate to ultrashort laser pulses and use these pulses to excite a single quantum dot. We demonstrate that we enter a regime where the exciton-phonon coupling is effective for small pulse areas, while for higher pulse areas a decoupling of the exciton from the phonons occurs. We thus discover a reappearance of rapid adiabatic passage, in analogy to the predicted reappearance of Rabi rotations at high pulse areas. The measured results are in good agreement with theoretical calculations. DOI: 10.1103/PhysRevB.95.241306 In semiconductors, a driven electron is damped by the interaction with phonons. In the context of quantum control, phonons lead to dephasing. The electron-phonon interaction is therefore important in the development of quantum technology with semiconductors. It is a rich and subtle subject.One possible way to suppress electron-phonon damping is to drive the electronic system so quickly that the relatively large inertia of the phonons prevents them from reacting to the driven electron. In the context of Rabi oscillations, the driven oscillations of a two-level system, a "reappearance" has been predicted [1]. As the drive is increased, the Rabi oscillations are initially damped more and more by the phonons, but then the damping decreases and is eventually suppressed. The reappearance regime represents phonon-free quantum control. It has, however, never been observed experimentally. Here, we demonstrate the experimental realization of the reappearance regime. Validation comes from a full microscopic theory.Our quantum system is a single self-assembled quantum dot (QD), an emitter of highly coherent single photons [2,3] and polarization-entangled photon pairs [4,5]. Quantum control of the exciton, an electron-hole pair, proceeds on picosecond timescales well before spontaneous emission takes place (timescale ∼1 ns). Phonons lead to a deterioration of the exciton preparation fidelity for schemes using resonant excitation [1,[6][7][8][9][10]. In fact, the interaction with the phonons is sufficiently strong that an exciton state can be prepared by relying on it (phonon-mediated relaxation following excitation with a detuned pulse) [11][12][13][14][15]. In a Rabi experiment, phonons lead to a clear damping [6,7]. The specific dephasing mechanism was identified as a coupling to longitudinal acoustic (LA) phonons. For higher pulse areas, theory predicts that the electronic oscillations become so fast such that the phonons decouple and the Rabi oscillations recover, the reappearance phenomenon. The existence of a pulse area for which the coupling to the phonons is maximal is a consequence of the nonmonotonic electron-phonon coupling [1,16].For the pulses used so far experimentally (pulses of 1-10 ps duration), the reappearance regime for Rabi oscillations can only be entered at ex...

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The role of phonons for exciton and biexciton generation in an optically driven quantum dot

Cited by 70 publications

References 223 publications

Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage

Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage

Fast and selective phonon-assisted state preparation of a quantum dot by adiabatic undressing

Demonstrating the decoupling regime of the electron-phonon interaction in a quantum dot using chirped optical excitation

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