arXiv subjects

Sven Rodt

Publications and source records attributed to Sven Rodt.

51 records · Page 3Linked to original sources

arXiv2019

Excitonic complexes in MOCVD-grown InGaAs/GaAs quantum dots emitting at telecom wavelengths

Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metal-organic chemical vapour deposition and emitting at the 1300 nm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the 8-band kp theory combined with the configuration interaction method. The origin of excitonic complexes has been exemplarily confirmed based on magnetooptical and correlation spectroscopy study. Understanding the influence of structural parameters and compositions (of QDs themselves as well as in the neighbouring strain reducing layer) allows to distinguish which of them are crucial to control the emission wavelength to achieve the telecommunication spectral range or to affect binding energies of the fundamental excitonic complexes. The obtained results provide deeper knowledge on control and on limitations of the investigated structures in terms of good spectral isolation of individual optical transitions and the spatial confinement that are crucial in view of QD applications in single-photon sources of high purity at telecom wavelengths.

cond-mat.mes-hall↗

arXiv2019

Indistinguishable photons from deterministically integrated single quantum dots in heterogeneous GaAs/Si$_3$N$_4$ quantum photonic circuits

Silicon photonics enables scaling of quantum photonic systems by allowing the creation of extensive, low-loss, reconfigurable networks linking various functional on-chip elements. Inclusion of single quantum emitters onto photonic circuits, acting as on-demand sources of indistinguishable photons or single-photon nonlinearities, may enable large-scale chip-based quantum photonic circuits and networks. Towards this, we use low-temperature $\textit{in situ}$ electron-beam lithography to deterministically produce hybrid GaAs/Si$_3$N$_4$ photonic devices containing single InAs quantum dots precisely located inside nanophotonic structures, which act as efficient, Si$_3$N$_4$ waveguide-coupled on-chip, on-demand single-photon sources. The precise positioning afforded by our scalable fabrication method furthermore allows observation of post-selected indistinguishable photons. This indicates a promising path towards significant scaling of chip-based quantum photonics, enabled by large fluxes of indistinguishable single-photons produced on-demand, directly on-chip.

physics.app-ph↗

arXiv2019

Directional emission of a deterministically fabricated quantum dot - Bragg reflection multi-mode waveguide system

We report on the experimental study and numerical analysis of chiral light-matter coupling in deterministically fabricated quantum dot (QD) waveguide structures. We apply in-situ electron beam lithography to deterministically integrate single InGaAs/GaAs QDs into GaAs-DBR waveguides to systematically explore the dependence of chiral coupling on the position of the QD inside the waveguide. By a series of micro-photoluminescence measurements, we determine the directionality contrast of emission into left and right traveling waveguide modes revealing a maximum of 0.93 for highly off-center QDs and an oscillatory dependence of this contrast on the QD position. In numerical simulations we obtain insight into chiral light-matter coupling by computing the light field emitted by a circularly polarized source and its overlap with multiple guided modes of the structure, which enables us to calculate directional $β$-factors for the quantum emitters. The calculated dependence of the directionality on the off-center QD position is in good agreement with the experimental data. It confirms the control of chiral effects in deterministically fabricated QD-waveguide systems with high potential for future non-reciprocal on-chip systems required for quantum information processing.

cond-mat.mes-hall↗

arXiv2018

Enhanced photon-extraction efficiency from InGaAs/GaAs quantum dots in deterministic photonic structures at 1.3 μm fabricated by in-situ electron-beam lithography

The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integrated into disc-shaped mesas. Utilizing this approach, an extraction efficiency into free-space (within a numerical aperture of 0.4) of (10${\pm}$2) % has been experimentally obtained in the 1.3 μm wavelength range in agreement with finite-element method calculations.

cond-mat.mes-hall↗

arXiv2018

Numerical optimization of the extraction efficiency of a quantum-dot based single-photon emitter into a single-mode fiber

We present a numerical method for the accurate and efficient simulation of strongly localized light sources, such as quantum dots, embedded in dielectric micro-optical structures. We apply the method in order to optimize the photon extraction efficiency of a single-photon emitter consisting of a quantum dot embedded into a multi-layer stack with further lateral structures. Furthermore, we present methods to study the robustness of the extraction efficiency with respect to fabrication errors and defects.

physics.comp-ph↗

arXiv2018

Generation of maximally entangled states and coherent control in quantum dot microlenses

The integration of entangled photon emitters in nanophotonic structures designed for the broadband enhancement of photon extraction is a major challenge for quantum information technologies. We study the potential of quantum dot (QD) microlenses to act as efficient emitters of maximally entangled photons. For this purpose, we perform quantum tomography measurements on InGaAs QDs integrated deterministically into microlenses. Even though the studied QDs show non-zero excitonic fine-structure splitting (FSS), polarization entanglement can be prepared with a fidelity close to unity. The quality of the measured entanglement is only dependent on the temporal resolution of the used single-photon detectors compared to the period of the excitonic phase precession imposed by the FSS. Interestingly, entanglement is kept along the full excitonic wave-packet and is not affected by decoherence. Furthermore, coherent control of the upper biexcitonic state is demonstrated.

cond-mat.mes-hall↗

arXiv2017

Enhancing the photon-extraction efficiency of site-controlled quantum dots by deterministically fabricated microlenses

We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 $\pm$ 2) $\%$ and a high suppression of multi-photon events with g$^{(2)}$($τ$ = 0) $<$ 0.06 without background subtraction. The demonstrated combination of site-controlled growth of QDs and in-situ electron-beam lithography is relevant for arrays of efficient SPSs which can be applied in photonic quantum circuits and advanced quantum computation schemes.

cond-mat.mes-hall↗

arXiv2017

Deterministic integration of quantum dots into on-chip multi-mode interference beamsplitters using in-situ electron beam lithography

The development of multi-node quantum optical circuits has attracted great attention in recent years. In particular, interfacing quantum-light sources, gates and detectors on a single chip is highly desirable for the realization of large networks. In this context, fabrication techniques that enable the deterministic integration of pre-selected quantum-light emitters into nanophotonic elements play a key role when moving forward to circuits containing multiple emitters. Here, we present the deterministic integration of an InAs quantum dot into a 50/50 multi-mode interference beamsplitter via in-situ electron beam lithography. We demonstrate the combined emitter-gate interface functionality by measuring triggered single-photon emission on-chip with $g^{(2)}(0) = 0.13\pm 0.02$. Due to its high patterning resolution as well as spectral and spatial control, in-situ electron beam lithography allows for integration of pre-selected quantum emitters into complex photonic systems. Being a scalable single-step approach, it paves the way towards multi-node, fully integrated quantum photonic chips.

physics.app-ph↗

arXiv2017

A stand-alone fiber-coupled single-photon source

In this work, we present a stand-alone and fiber-coupled quantum-light source. The plug-and-play device is based on an optically driven quantum dot delivering single photons via an optical fiber. The quantum dot is deterministically integrated in a monolithic microlens which is precisely coupled to the core of an optical fiber via active optical alignment and epoxide adhesive bonding. The rigidly coupled fiber-emitter assembly is integrated in a compact Stirling cryocooler with a base temperature of 35 K. We benchmark our practical quantum device via photon auto-correlation measurements revealing $g^{(2)}(0)=0.07 \pm 0.05$ under continuous-wave excitation and we demonstrate triggered non-classical light at a repetition rate of 80 MHz. The long-term stability of our quantum light source is evaluated by endurance tests showing that the fiber-coupled quantum dot emission is stable within 4% over several successive cool-down/warm-up cycles. Additionally, we demonstrate non-classical photon emission for a user-intervention-free 100-hour test run and stable single-photon count rates up to 11.7 kHz with a standard deviation of 4%.

cond-mat.mes-hall↗

arXiv2017

Accessing the dark exciton spin in deterministic quantum-dot microlenses

The dark exciton state in semiconductor quantum dots constitutes a long-lived solid-state qubit which has the potential to play an important role in implementations of solid-state based quantum information architectures. In this work, we exploit deterministically fabricated QD microlenses with enhanced photon extraction, to optically prepare and readout the dark exciton spin and observe its coherent precession. The optical access to the dark exciton is provided via spin-blockaded metastable biexciton states acting as heralding state, which are identified deploying polarization-sensitive spectroscopy as well as time-resolved photon cross-correlation experiments. Our experiments reveal a spin-precession period of the dark exciton of $(0.82\pm0.01)\,$ns corresponding to a fine-structure splitting of $(5.0\pm0.7)\,μ$eV between its eigenstates $\left|\uparrow\Uparrow\pm\downarrow\Downarrow\right\rangle$. By exploiting microlenses deterministically fabricated above pre-selected QDs, our work demonstrates the possibility to scale up implementations of quantum information processing schemes using the QD-confined dark exciton spin qubit, such as the generation of photonic cluster states or the realization of a solid-state-based quantum memory.

quant-ph↗

arXiv2017

Path-controlled time reordering of paired photons in a dressed three-level cascade

The two-photon dressing of a "three-level ladder" system, here the ground state, the exciton and the biexciton of a semiconductor quantum dot, leads to new eigenstates and allows one to manipulate the time ordering of the paired photons without unitary post processing. We show that, after spectral post-selection of the single dressed states, the time ordering of the cascaded photons can be removed or conserved. Our joint experimental and theoretical study demonstrates the high potential of a "ladder" system to be a versatile source of orthogonally polarized, bunched or antibunched pairs of photons.

quant-ph↗

arXiv2017

Resonance fluorescence of a site-controlled quantum dot realized by the buried-stressor growth technique

Site-controlled growth of semiconductor quantum dots (QDs) represents a major advancement to achieve scalable quantum technology platforms. One immediate benefit is the deterministic integration of quantum emitters into optical microcavities. However, site-controlled growth of QDs is usually achieved at the cost of reduced optical quality. Here, we show that the buried-stressor growth technique enables the realization of high-quality site-controlled QDs with attractive optical and quantum optical properties. This is evidenced by performing excitation power dependent resonance fluorescence experiments at cryogenic temperatures showing QD emission linewidths down to 10 $μ$eV. Resonant excitation leads to the observation of the Mollow triplet under CW excitation and enables coherent state preparation under pulsed excitation. Under resonant $π$-pulse excitation we observe clean single photon emission associated with $g^{(2)}(0)=0.12$ limited by non-ideal laser suppression.

cond-mat.mes-hall↗

arXiv2017

A bright triggered twin-photon source in the solid state

A non-classical light source emitting pairs of identical photons represents a versatile resource of interdisciplinary importance with applications in quantum optics and quantum biology. Emerging research fields, which benefit from such type of quantum light source, include quantum-optical spectroscopy or experiments on photoreceptor cells sensitive to photon statistics. To date, photon twins have mostly been generated using parametric downconversion sources, relying on Poissonian number distributions, or atoms, exhibiting low emission rates. Here, we propose and experimentally demonstrate the efficient, triggered generation of photon twins using the energy-degenerate biexciton-exciton radiative cascade of a single semiconductor quantum dot. Deterministically integrated within a microlens, this nanostructure emits highly-correlated photon pairs, degenerate in energy and polarization, at a rate of up to (234 $\pm$ 4) kHz. Furthermore, we verify a significant degree of photon-indistinguishability and directly observe twin-photon emission by employing photon-number-resolving detectors, which enables the reconstruction of the emitted photon number distribution.

quant-ph↗

arXiv2016

Two-photon interference from remote deterministic quantum dot microlenses

We report on two-photon interference (TPI) experiments using remote deterministic single-photon sources. Employing 3D in-situ electron-beam lithography, we fabricate quantum-light sources at specific target wavelengths by integrating pre-selected semiconductor quantum dots within monolithic microlenses. The individual single-photon sources show TPI visibilities of 49% and 22%, respectively, under pulsed p-shell excitation at 80 MHz. For the mutual TPI of the remote sources, we observe an uncorrected visibility of 29%, in quantitative agreement with the pure dephasing of the individual sources. Due to its efficient photon extraction within a broad spectral range (> 20 nm), our microlens-based approach is predestinated for future entanglement swapping experiments utilizing entangled photon pairs emitted by distant biexciton-exciton radiative cascades.

cond-mat.mes-hall↗

arXiv2016

CSAR 62 as negative-tone resist for high-contrast e-beam lithography at temperatures between 4 K and room temperature

The temperature dependence of the electron-beam sensitive resist CSAR 62 is investigated in its negative-tone regime. The writing temperatures span a wide range from 4 K to room temperature with the focus on the liquid helium temperature regime. The importance of low temperature studies is motivated by the application of CSAR 62 for deterministic nanophotonic device processing by means of in-situ electron-beam lithography. At low temperature, CSAR 62 exhibits a high contrast of 10.5 and a resolution of 49 nm. The etch stability is almost temperature independent and it is found that CSAR 62 does not suffer from peeling which limits the low temperature application of the standard electron-beam resist PMMA. As such, CSAR 62 is a very promising negative-tone resist for in-situ electron-beam lithography of high quality nanostructures at low temperature.

cond-mat.mtrl-sci↗