Spectroscopy of size dependent many-particle effects in single self-assembled semiconductor quantum dots

Single InAs quantum dots (QDs) grown with the Stranski-Krastanov method in a InGaAs quantum well embedded in GaAs and emitting in the near infrared have been optically investigated. Photoluminescence of the QDs was excited non resonantly with a He-Ne laser and single dot spectroscopy was carried out at temperatures below 60 K. To perform QD spectroscopy at low temperatures a very stable micro-photoluminescence microscope set-up fully integrated in a liquid helium cryostate has been developed. The experimental set-up allows mapping of the optical emission by recording spectra for every point of a scan grid. This mapping mode is used to acquire optical images and to locate a particular dot for investigation. At low excitation power a single sharp line arising from recombination of a single exciton in the dot is observed. Varying the excitation density the spectra become more complex, with appearance of the biexciton emission line, followed by emission from excitons occupying higher shells in the dot. A statistics of biexciton binding energies over a dozen of dots was acquired and the results compared with single QD spectroscopy data available in the literature, for III-V material systems. Despite the impossibility to obtain precise information about the dimensions of the particular QD under investigation, from the analysis of these data a general trend can be found in the dependency of the biexciton binding energy on the size of InAs QDs, parameterised with their emission energy.Einzelne selbstorganisierte InAs Quantenpunkte gewachsen in einem InGaAs Quantenschicht, die in GaAs eingebettet ist, sind untersucht worden. Die Quantenpunkte emittieren im nahinfraroten Spektralbereich. Photolumineszenz wird nicht-resonant mit einem He-Ne Laser angeregt und Experimente an einzelnen Quantenpunkten werden bei Temperaturen unter 60 K durchgeführt. Das experimentelle System, bestehend aus einem sehr stabilen Mikrophotolumineszenz-Mikroskop, das in einem mit flüssigem Helium gekühlten Kryostat eingebaut ist, ermöglicht rasterspektroskopische Untersuchungen mit der Aufnahme von einem Spektrum für jeden Punkt eines Rasters. Dieser Betriebsmodus wird für die Aufnahme von optischen Bildern und die Lokalisierung von einzelnen Quantenpunkten verwendet. Bei niedriger Anregungsleistung wird in den Spektren eine einzelne scharfe Emissionslinie beobachtet, die von der Rekombinierung eines Exzitons in einem einzelnen Quantenpunkt stammt. Mit steigender Anregungsleistung tauchen andere Emissionslinien in den Spektren auf; als Erste die Biexziton-Emissionslinie und folgend die Emissionslinien der angeregten Zustände. Die gemessenen Werte für die Biexziton-Bindungsnergie wurden mit den Ergebnissen von ähnlichen Experimenten an einzelnen Quantenpunkten aus der Literatur verglichen. Die Analyse von diesen führt zu einem generellen Verlauf für die Abhängigkeit von der Größe der Biexziton-Bindungsenergie in InAs Quantenpunkten

Open-cavity in closed-cycle cryostat as a quantum optics platform

The introduction of an optical resonator can enable efficient and precise interaction between a photon and a solid-state emitter. It facilitates the study of strong light-matter interaction, polaritonic physics and presents a powerful interface for quantum communication and computing. A pivotal aspect in the progress of light-matter interaction with solid-state systems is the challenge of combining the requirements of cryogenic temperature and high mechanical stability against vibrations while maintaining sufficient degrees of freedom for in-situ tunability. Here, we present a fiber-based open Fabry-P\'{e}rot cavity in a closed-cycle cryostat exhibiting ultra-high mechanical stability while providing wide-range tunability in all three spatial directions. We characterize the setup and demonstrate the operation with the root-mean-square cavity length fluctuation of less than $90$ pm at temperature of $6.5$ K and integration bandwidth of $100$ kHz. Finally, we benchmark the cavity performance by demonstrating the strong-coupling formation of exciton-polaritons in monolayer WSe$_2$ with a cooperativity of $1.6$. This set of results manifests the open-cavity in a closed-cycle cryostat as a versatile and powerful platform for low-temperature cavity QED experiments.Comment: 10 pages, 8 figure

Open-Cavity in Closed-Cycle Cryostat as a Quantum Optics Platform

The introduction of an optical resonator can enable efficient and precise interaction between a photon and a solid-state emitter. It facilitates the study of strong light-matter interaction, polaritonic physics and presents a powerful interface for quantum communication and computing. A pivotal aspect in the progress of light-matter interaction with solid-state systems is the challenge of combining the requirements of cryogenic temperature and high mechanical stability against vibrations while maintaining sufficient degrees of freedom for in situ tunability. Here, we present a fiber-based open Fabry-Pérot cavity in a closed-cycle cryostat exhibiting ultrahigh mechanical stability while providing wide-range tunability in all three spatial directions. We characterize the setup and demonstrate the operation with the root-mean-square cavitylength fluctuation of less than 90 pm at temperature of 6.5 K and integration bandwidth of 100 kHz. Finally, we benchmark the cavity performance by demonstrating the strong-coupling formation of exciton polaritons in monolayer WSe2 with a cooperativity of 1.6. This set of results manifests the open cavity in a closed-cycle cryostat as a versatile and powerful platform for low-temperature cavity QED experiments