Photon antibunching from few quantum dots in a cavity

Abstract

Single quantum dots (QDs) are frequently used as single-photon sources, taking advantage of the final exciton decay in a cascade that produces energetically detuned photons. We propose and analyze a new concept of single-photon source, namely, a few-QD microcavity system driven close to, but below the lasing threshold under strong excitation. Surprisingly, even for two or three QDs inside a cavity, antibunching is observed. To quantify the results, we find that a classification of single-photon emission in terms of antibunching in the autocorrelation function g (2) (0) is insufficient and more details of the photon statistics are required. Our investigations are based on a quantum-optical theory that we solve to obtain the density operator for the quantum-mechanical active medium and radiation field.Introduction. Single-photon sources are key components in quantum-information technologies. They enable the realization of fundamental quantum-mechanical concepts in current applications [1], such as quantum key distribution, quantum teleportation, and Bell measurements. To generate single photons, in many practical applications sources based on parametric down conversion are used [2][3][4]. Alternatively, a single emitter can be driven with a pump pulse to emit exactly one photon on demand per excitation cycle like a turnstile device [5]. Semiconductor quantum dots (QDs) possess distinct properties that make them suited for applications as single-photon sources, such as the possibility of electrical pumping [6]. Resonant excitation schemes have been used to get closer to the ideal case of an isolated "atomlike" single-photon emitter [7]. When using a single QD, a preceding photon from the biexciton recombination can be used to herald the single photon from the exciton recombination, which is always second in the cascade. The extremely high single-photon purity (close to the ideal single-photon Fock state) obtained from these sources comes at the cost of low repetition rates that are limited by the free-space radiative lifetime of hundreds of picoseconds [1,8].QD microcavity laser devices have been demonstrated to exhibit nonclassical features in the light emission around threshold [9,10]. In the following, we explore this quantum regime for single-photon operation from a single-to fewemitter QD medium. The presence of a cavity enhances the emission rate via the Purcell effect [11], and operation in the gigahertz regime has been demonstrated for a single QD in a micropillar resonator [12]. The prospect of achieving single-photon emission with several QD emitters coupling to the cavity reduces the requirement on device fabrication to rely on samples with only a single QD.For single-QD microcavity devices, we identify an optimal balance between cavity-loss rate and light-matter coupling strength that maximizes the emission rate and the degree of antibunching seen in g (2) (0). Next, we explore devices with up to three QDs and quantify their performance in terms of achievable repetition rates, purity of single-photon emi...

Thermal, Quantum Antibunching and Lasing Thresholds from Single Emitters to Macroscopic Devices

“…2c show an anti-bunching regime that exists for a large region of the pump and extends from nano-to macroscopic lasers with β = 1. Anti-bunching has been observed in an experiment with a high cavity Q micropillar containing N ≈ 15 pumped quantum dots [23] and in numerical simulations of quantum dot nanocavities [6], [24]. The observation is consistent with our prediction (Fig.…”

“…pled from the perturbations of the slow variables allowing us to determine analytically the stability of the nonlasing state (see SM Eqs. (22)(23)(24)). The non-lasing state is stable for c † c < c † c th and unstable for c † c > c † c th where…”

Effective second-order correlation function and single-photon detection

“…In semiconductor experiments a light source is said to emit SPs if the second-order correlation function g (2) (τ) fulfills g (2) (0)<1/2 [15]. This criterion is widely used in the semiconductor optics literature for the last 20 years [14][15][16][17][18][19][20][21]. Throughout this time, the information gained from this quantity has varied a lot, ranging from single emitters [15][16][17] to SPs, from a quantitative interpretation as in [20] to a downplay of this quantification as in [18,22].…”

“…This criterion is widely used in the semiconductor optics literature for the last 20 years [14][15][16][17][18][19][20][21]. Throughout this time, the information gained from this quantity has varied a lot, ranging from single emitters [15][16][17] to SPs, from a quantitative interpretation as in [20] to a downplay of this quantification as in [18,22]. There is significant research in trying to lower g (2) (0) further towards ideal zero, see [19] and references therein.…”

Optical detection and storage of entanglement in plasmonically coupled quantum-dot qubits

“…It has been found that the second-order correlation function of photons emitted by coupled QD qubits can be utilized as a "witness" of quantum entanglement formation; specifically, antibunching of photons emitted by the QDs has been numerically predicted [25]. Various QD coupling methods have been proposed including sharing the photon field in an optical microcavity [26] or the interactions with auxiliary plasmonic nanoantennas [14][15][16][17]. However, direct observations of the entanglement of electronic degrees of freedom in QDs remain challenging.…”