arXiv subjects

M. Geller

Publications and source records attributed to M. Geller.

13 recordsLinked to original sources

arXiv2025

Quantum stochastic resonance in a single-photon emitter

Stochastic resonance is a phenomenon in which fluctuations enhance an otherwise weak signal. It has been found in many different systems in paleoclimatology, biology, medicine, and physics. The classical stochastic resonance due to thermal noise has recently been experimentally extended to the quantum regime, where the fundamental randomness of individual quantum events provides the noise source. Here, we demonstrate quantum stochastic resonance in the single-electron tunneling dynamics of a periodically driven single-photon emitter, consisting of a self-assembled quantum dot that is tunnel-coupled to an electron reservoir. Such highly-controllable quantum emitters are promising candidates for future applications in quantum information technologies. We monitor the charge dynamics by resonant optical excitation and identify quantum stochastic resonance with the help of full counting statistics of tunneling events in terms of the Fano factor and extend the statistical evaluation to factorial cumulants to gain a deeper understanding of this far-reaching phenomenon.

cond-mat.mes-hall↗

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↗

arXiv2022

Quantum Zeno Manipulation of Quantum Dots

We investigate whether and how the quantum Zeno effect, i.e., the inhibition of quantum evolution by frequent measurements, can be employed to isolate a quantum dot from its surrounding electron reservoir. In contrast to the often studied case of tunneling between discrete levels, we consider the tunnelling of an electron from a continuum reservoir to a discrete level in the dot. Realizing the quantum Zeno effect in this scenario can be much harder because the measurements should be repeated before the wave packet of the hole left behind in the reservoir moves away from the vicinity of the dot. Thus, the required repetition rate could be lowered by having a flat band (with a slow group velocity) in resonance with the dot or a sufficiently small Fermi velocity or a strong external magnetic field. We also consider the anti-Zeno effect, i.e., how measurements can accelerate or enable quantum evolution.

cond-mat.mes-hall↗

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↗

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↗

arXiv2012

Transverse rectification in density-modulated two-dimensional electron gases

We demonstrate tunable transverse rectification in a density-modulated two-dimensional electron gas (2DEG). The density modulation is induced by two surface gates, running in parallel along a narrow stripe of 2DEG. A transverse voltage in the direction of the density modulation is observed, i.e. perpendicular to the applied source-drain voltage. The polarity of the transverse voltage is independent of the polarity of the source-drain voltage, demonstrating rectification in the device. We find that the transverse voltage $U_{y}$ depends quadratically on the applied source-drain voltage and non-monotonically on the density modulation. The experimental results are discussed in the framework of a diffusion thermopower model.

cond-mat.mes-hall↗

arXiv2010

Non-equilibrium many-particle spin states in self-assembled quantum dot hydrogen, helium and lithium

We introduce an all-electrical measurement technique, which makes it possible to prepare and detect the ground and excited many-particle states in self-assembled InAs QDs at 4K. This way, the pure-electron spectra of QD-hydrogen, -helium and -lithium are resolved. Comparison with detailed many-body calculations enables us to identify the different charge configurations and in particular detect the singlet and triplet spin states of QD helium. Furthermore, the time-resolved evolution of the density of states from non-equilibrium to equilibrium charge occupation is shown.

cond-mat.mes-hall↗

arXiv2007

Excitonic Mott transition in type-II quantum dots

Photoluminescence spectra measured on a type-II GaSb/GaAs quantum dot ensemble at high excitation power indicate a Mott transition from the low density state comprising of spatially-indirect excitons to a high density electron-plasma state. Under the influence of a very high magnetic field, the electron-plasma that is formed at high excitation powers is `frozen-out' into a state of optically inactive magneto-excitons.

cond-mat.other↗

arXiv1996

An Optical/X--ray Study of A576, a Galaxy Cluster with a Cold Core

We analyze the galaxy population and dynamics of the galaxy cluster Abell 576 using 281 redshifts (230 new), R band CCD galaxy photometry over a 2h^{-1} Mpc by 2h^{-1} Mpc region centered on the cluster, an Einstein IPC image, and an Einstein MPC spectrum. The cluster galaxies with emission lines in their spectra have a larger velocity dispersion and are significantly less clustered on this 2h^{-1} Mpc scale than galaxies without emission lines. We show that excluding the emission line galaxies decreases the velocity dispersion by 18% and the virial mass estimate by a factor of two. The central cluster region contains a non--emission galaxy population and an intracluster medium which are significantly cooler (sigma_{core}=387^{+250}_{-105}~km/s and T_X=1.6^{+0.4}_{-0.3}~keV at 90\% confidence) than the global populations (sigma=977^{+124}_{-96}~km/s for the non--emission population and T_X>4~keV at 90% confidence). Because (1) the low dispersion population is no more luminous than the global population and (2) the evidence for a cooling flow is weak, we suggest that the cluster core may contain the remnants of a lower mass subcluster. We examine the cluster mass, baryon fraction and luminosity function. The cluster virial mass varies significantly depending on the galaxy sample used. Consistency between the hydrostatic and virial estimators can be achieved if (1) the gas temperature at r\sim1h^{-1}~Mpc is T_X\sim8keV (the best fit value) and (2) several velocity outliers are excluded from the virial calculation. Although the best fit Schechter function parameters and the ratio of galaxy to gas mass are typical of other clusters, the baryon fraction is relatively low. Using a lower limit to the binding mass, we show that the gas mass fraction is \le3h^{-3/2}% and the baryon fraction is \le6%.

astro-ph↗

arXiv1994

Analysis of the 3d6 4s(6D)4f-5g Supermultiplet of Fe I in Laboratory and Solar Infrared Spectra

The combined laboratory and solar analysis of the highly-excited subconfigurations 4f and 5g of Fe I has allowed us to classify 87 lines of the 4f-5g supermultiplet in the spectral region 2545-2585 cm-1. The level structure of these JK-coupled configurations is predicted by semiempirical calculations and the quadrupolic approximation. Semiempirical gf-values have been calculated and are compared to gf values derived from the solar spectrum. The solar analysis has shown that these lines, which should be much less sensitive than lower excitation lines to departures from LTE and to temperature uncertainties, lead to a solar abundance of iron which is consistent with the meteoritic value (A_Fe = 7.51).

astro-ph↗