arXiv subjects

A. Kurzmann

Publications and source records attributed to A. Kurzmann.

8 recordsLinked to original sources

arXiv2024

Making Every Photon Count: A Quantum Polyspectra Approach to the Dynamics of Blinking Quantum Emitters at Low Photon Rates Without Binning

The blinking statistics of quantum emitters and their corresponding Markov models play an important role in high resolution microscopy of biological samples as well as in nano-optoelectronics and many other fields of science and engineering. Current methods for analyzing the blinking statistics like the full counting statistics or the Viterbi algorithm break down for low photon rates. We present an evaluation scheme that eliminates the need for both a minimum photon flux and the usual binning of photon events which limits the measurement bandwidth. Our approach is based on higher order spectra of the measurement record which we model within the recently introduced method of quantum polyspectra from the theory of continuous quantum measurements. By virtue of this approach we can determine on- and off-switching rates of a semiconductor quantum dot at light levels 1000 times lower than in a standard experiment and 20 times lower than achieved with a scheme from full counting statistics. Thus a very powerful high-bandwidth approach to the parameter learning task of single photon hidden Markov models has been established with applications in many fields of science.

quant-ph↗

arXiv2021

Quantum polyspectra for modeling and evaluating quantum transport measurements: A unifying approach to the strong and weak measurement regime

Quantum polyspectra of up to fourth order are introduced for modeling and evaluating quantum transport measurements offering a powerful alternative to methods of the traditional full counting statistics. Experimental time-traces of the occupation dynamics of a single quantum dot are evaluated via simultaneously fitting their 2nd-, 3rd-, and 4th-order spectra. The scheme recovers the same electron tunneling and spin relaxation rates as previously obtained from an analysis of the same data in terms of factorial cumulants of the full counting statistics and waiting-time distributions. Moreover, the evaluation of time-traces via quantum polyspectra is demonstrated to be feasible also in the weak measurement regime even when quantum jumps can no longer be identified from time-traces and methods related to the full counting statistics cease to be applicable. A numerical study of a double dot system shows strongly changing features in the quantum polyspectra for the transition from the weak measurement regime to the Zeno-regime where coherent tunneling dynamics is suppressed. Quantum polyspectra thus constitute a general unifying approach to the strong and weak regime of quantum measurements with possible applications in diverse fields as nano-electronics, circuit quantum electrodynamics, spin noise spectroscopy, or quantum optics.

quant-ph↗

arXiv2021

Optical detection of single electron transport dynamics

The unpredictability of a single quantum event lies at the very core of quantum mechanics. Physical information is therefore drawn from a statistical evaluation of many such processes. Nevertheless, recording each single quantum event in a time trace the "random telegraph signal" is of great value, as it allows insight into the underlying physical system. Here, quantum dots have proven to be well suited systems, as they exhibit both single photon emission and single electron charge transport. While single photon emission is generally studied on self-assembled quantum dots, single electron transport studies are focused on gate-defined structures. We investigate, on a single self-assembled quantum dot, the single electron transport in the optical telegraph signal with high bandwidth and observe in the full counting statistics the interplay between charge and spin dynamics in a noninvasive way. In particular, we are able to identify the spin relaxation of the Zeeman-split quantum-dot level in the charge statistics.

cond-mat.mes-hall↗

arXiv2019

Charge detection in gate-defined bilayer graphene quantum dots

We report on charge detection in electrostatically-defined quantum dot devices in bilayer graphene using an integrated charge detector. The device is fabricated without any etching and features a graphite back gate, leading to high quality quantum dots. The charge detector is based on a second quantum dot separated from the first dot by depletion underneath a 150 nm wide gate. We show that Coulomb resonances in the sensing dot are sensitive to individual charging events on the nearby quantum dot. The potential change due to single electron charging causes a step-like change (up to 77 %) in the current through the charge detector. Furthermore, the charging states of a quantum dot with tunable tunneling barriers and of coupled quantum dots can be detected.

cond-mat.mes-hall↗

arXiv2019

Excited states in bilayer graphene quantum dots

We report on ground- and excited state transport through an electrostatically defined few-hole quantum dot in bilayer graphene in both parallel and perpendicular applied magnetic fields. A remarkably clear level scheme for the two-particle spectra is found by analyzing finite bias spectroscopy data within a two-particle model including spin and valley degrees of freedom. We identify the two-hole ground-state to be a spin-triplet and valley-singlet state. This spin alignment can be seen as Hund's rule for a valley-degenerate system, which is fundamentally different to quantum dots in carbon nano tubes and GaAs-based quantum dots. The spin-singlet excited states are found to be valley-triplet states by tilting the magnetic field with respect to the sample plane. We quantify the exchange energy to be 0.35meV and measure a valley and spin g-factor of 36 and 2, respectively.

cond-mat.mes-hall↗

arXiv2018

Photon noise suppression by a built-in feedback loop

Visionary quantum photonic networks need transform-limited single photons on demand. Resonance fluorescence on a quantum dot provides the access to a solid-state single photon source, where the environment is unfortunately the source of spin and charge noise that leads to fluctuations of the emission frequency and destroys the needed indistinguishability. We demonstrate a built-in stabilization approach for the photon stream, which relies solely on charge carrier dynamics of a two-dimensional hole gas inside a micropillar structure. The hole gas is fed by hole tunneling from field-ionized excitons and influences the energetic position of the excitonic transition by changing the local electric field at the position of the quantum dot. The standard deviation of the photon noise is suppressed by nearly 50 percent (noise power reduction of 6 dB) and it works in the developed micropillar structure for frequencies up to 1 kHz. This built-in feedback loop represents an easy way for photon noise suppression in large arrays of single photon emitters and promises to reach higher bandwidth by device optimization.

cond-mat.mes-hall↗

arXiv2016

A charge-driven feedback loop in the resonance fluorescence of a single quantum dot

Semiconductor quantum dots can emit antibunched, single photons on demand with narrow linewidths. However, the observed linewidths are broader than lifetime measurements predict, due to spin and charge noise in the environment. This noise randomly shifts the transition energy and destroys coherence and indistinguishability of the emitted photons. Fortunately, the fluctuations can be reduced by a stabilization using a suitable feedback loop. In this work we demonstrate a fast feedback loop that manifests itself in a strong hysteresis and bistability of the exciton resonance fluorescence signal. Field ionization of photogenerated quantum dot excitons leads to the formation of a charged interface layer that drags the emission line along over a frequency range of more than 30 GHz. This internal charge-driven feedback loop could be used to reduce the spectral diffusion and stabilize the emission frequency within milliseconds, presently only limited by the sample structure, but already faster than nuclear spin feedback.

cond-mat.mes-hall↗

arXiv2016

Optical blocking of electron tunneling into a single self-assembled quantum dot

Time-resolved resonance fluorescence (RF) is used to analyse electron tunneling between a single self-assembled quantum dot (QD) and an electron reservoir. In equilibrium, the RF intensity reflects the average electron occupation of the QD and exhibits a gate voltage dependence that is given by the Fermi distribution in the reservoir. In the time-resolved signal, however, we find that the relaxation rate for electron tunneling is independent of the occupation in the charge reservoir. Using a master equation approach which includes both the electron tunneling and the optical excitation/recombination, we are able to explain the experimental data by optical blocking, i. e. a reduced electron tunneling rate when the QD is occupied by an exciton.

cond-mat.mes-hall↗