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Physical Review B

Single quantum dot photocurrent spectroscopy in the cavity quantum electrodynamics regime

P. Gold, Manuel Gschrey, Christian Schneider, Sven Höfling, A. Forchel, Martin Kamp, Stephan Reitzenstein

Published Oct 1, 2012• 6 citations
Publisher

Abstract

We study cavity quantum electrodynamics (cQED) in coupled quantum dot--microcavity systems under electrical readout. Strict resonant excitation of a target quantum dot (QD) allows us to monitor the photocurrent response of a single emitter in the quantum limit of light-matter interaction. We find a strong anticorrelation between radiative recombination and nonradiative tunnel escape of photoexcited carries which can be controlled by cQED effects in the Purcell regime. In fact, cavity-enhanced radiative emission from a QD results in a weaker photocurrent signal which reflects the cQED controlled competition between radiative and nonradiative recombination at the single emitter level.

DOI
10.1103/physrevb.86.161301

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physics.opticsCross-listedarXiv:2607.21012•Jul 24, 2026
We study cavity quantum electrodynamics (cQED) in coupled quantum dot--microcavity systems under electrical readout. Strict resonant excitation of a target quantum dot (QD) allows us to monitor the photocurrent response of a single emitter in the quantum limit of light-matter interaction. We find a strong anticorrelation between radiative recombination and nonradiative tunnel escape of photoexcited carries which can be controlled by cQED effects in the Purcell regime. In fact, cavity-enhanced radiative emission from a QD results in a weaker photocurrent signal which reflects the cQED controlled competition between radiative and nonradiative recombination at the single emitter level.
The strong-coupling regime of cavity-quantum-electrodynamics (cQED) represents the light-matter interaction at the fully quantum level. Adding a single photon shifts the resonance frequencies, a profound nonlinearity. cQED is a test-bed of quantum optics and the basis of photon-photon and atom-atom entangling gates. At microwave frequencies, success in cQED has had a transformative effect. At optical frequencies, the gates are potentially much faster; the photons can propagate over long distances; and the photons can be detected easily, ideal features for quantum networks. Following pioneering work on single atoms, solid-state implementations using semiconductor quantum dots are emerging, an important prospect for quantum technology. We present here a gated, ultralow-loss microcavity-device which forms a highly coherent photon−-−quantum-dot interface with a cooperativity of C=150C=150C=150. The gates allow both the quantum dot charge state and resonance frequency to be controlled electrically; crucially, they eliminate the noise-source which has complicated quantum dot cQED in the past −-− scattering from the bare microcavity mode even at the quantum dot-microcavity resonance. Even in the microcavity, the quantum dot has a linewidth close to the radiative limit. In addition to a very pronounced avoided-crossing in the spectral domain, we observe a clear coherent exchange of a single energy-quantum between the ``atom" and cavity in the time domain (vacuum Rabi-oscillations). Decoherence arises predominantly via the atom and photon loss-channels. The coherence is exploited to probe the transitions between the singly- and doubly-excited photon-atom system via photon-statistics spectroscopy. We propose this system as a platform for quantum technology, for instance a photon-photon entangling gate.
We observe antibunching in the photons emitted from a strongly coupled single quantum dot and pillar microcavity in resonance. When the quantum dot was spectrally detuned from the cavity mode, the cavity emission remained antibunched, and also anticorrelated from the quantum dot emission. Resonant pumping of the selected quantum dot via an excited state enabled these observations by eliminating the background emitters that are usually coupled to the cavity. This device demonstrates an on-demand single-photon source operating in the strong coupling regime, with a Purcell factor of 61+/-7 and quantum efficiency of 97%.
Abstract Inhibition and enhancement of spontaneous emission rate, first proposed by Purcell, is discussed in terms of altered density-of-modes in various types of solid-state cavities and the Purcell factor is derived for two-level atomic system. The conditions for observing Purcell factor and experimental findings in micropillars embedded with Quantum Dots (QD)s are discussed. The strong interaction between photons and matter in the form of QD excitons, dispersion relations for ground and excited states separated by Rabi splitting are discussed. Experimental photoluminescence spectra showing anticrossing of exciton lines and cavity lines by temperature and other tuning methods are used to illustrate the strong light-matter interaction. The Jayness–Cummins model based on second quantization is presented to point out Rabi oscillation, Purcell effect, and other novel features. Microcavity structures for observing cavity quantum electrodynamics effects are mentioned. Microcavity lasers predicting thresholdless operation for unity spontaneous emission coupling factors are discussed.
Theoretical study on entangled photon generation from a quantum dot (QD) embedded in microcavity is briefly reviewed within a strong coupling regime. In this system, entangled photon pairs can be generated through the cascade photon emission via dressed states in the cavity quantum electrodynamics (CQED). Excitation levels of a QD are modeled by a V-type three-level system and four-level system including a biexciton. In contrast to the entangled-photon generation until now, all four Bell states can be generated from an identical cavity system by simply selecting applied-field polarizations and frequencies as characteristic features of the CQED. The CQED effects play a crucial role in providing a high degree of entanglement: (i) spectral fi ltering can be used to extract entangled photons due to the vacuum Rabi splitting and (ii) non-entangled co-polarized photons are strongly suppressed due to the photon blockade effect.
Light-matter interaction on the level of single emitters and single photons has attracted significant scientific interest in recent years. Of particular interest is strong coupling of single emitters in solid state systems and its application to quantum information processing. Due to the enormous progress in semiconductor technology it has become feasible to demonstrate strong coupling of single quantum dots in high-Q microcavity systems. Although it has been argued in these studies that it is very unlikely that several degenerated quantum dots contributed to the observed Rabi-splitting, it was not verified that the system had one and only one emitter. In this work we present proof that the emission from a strongly-coupled QD- microcavity system is dominated by a single quantum emitter.
A cavity quantum electrodynamics (cQED) system consisting of a confined single photon and a single quantum emitter serves as a fundamental block for quantum optics and photonic quantum technologies. The canonical optical mode employed in the conventional cavity quantum electrodynamics features a uniform polarization distribution, leading to the scalar light-matter interaction in most existing experiments. Despite the rapid progress in the generation of structured light with spatially varied polarizations, the structured light-matter interaction, especially at the single quanta level, is highly intriguing yet largely unexplored. Here, we present the structured light-matter interaction at the single-photon level in a semiconductor cavity quantum electrodynamics system. Four distinct structured cavity modes that are spectrally close to each other are constructed in a micropillar cavity. By spatially locating a single epitaxial quantum dot (QD) at the periphery of a semiconductor micropillar cavity and spectrally tuning the QD emission wavelength into the resonances of the structured cavity modes, cavity-enhanced single-photon emissions with spin-locked chiral orbital angular momentum (OAM) and engineerable spin-orbit entanglements are achieved within a single wavelength-scale device. Our work opens an unexplored paradigm of structured quantum light-matter interactions and may further advance chiral quantum optics and high-dimensional photonic quantum technology.