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arXiv:2504.08511

Efficient Two Photon Generation from an Emitter in a Cavity

M. I. Mazhari, Rituraj Rituraj

Published Apr 11, 2025• 0 citations
arXivHTMLPDF

Abstract

Two-photon states are essential for fundamental applications in quantum information. One of the primary methods of two-photon generation is based on parametric down-conversion, but this suffers from low efficiency and a large footprint. This work presents a detailed theoretical investigation of an alternative approach: two-photon generation from an emitter in a doubly resonant cavity. The system is modelled by the Lindblad master Equation, and an approximate analytical solution is derived to determine the experimentally achievable limits on efficiency and brightness. Additionally, the optimal cavity parameters for achieving these limits are also identified. For experimentally feasible parameters, the maximum efficiency is approximately 35%, which is significantly higher than that of parametric down-conversion-based methods. The optimal rate and efficiency for two-photon generation are achieved when the outcoupling rate of the cavity mode at the two-photon emission frequency matches the single-photon atom-field coupling strength. Moreover, the outcoupling rate of the cavity mode at the one-photon emission frequency for single photons should be minimized. The cavity field properties are also examined by studying the second-order correlation function at zero time delay and the Mandel Q parameter, revealing highly bunched two-photon emission and super-Poissonian statistics. The quantum-jump framework, combined with Monte Carlo simulations, is used to characterize the mechanism of two-photon emission and the emission spectra of the cavity. Two-photon emission is demonstrated to be a rapid cascade process of quantum jumps, and its spectrum consists of three prominent peaks corresponding to transitions between the dressed states of the system.

DOI
10.48550/arxiv.2504.08511

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Two-photon states are essential for fundamental applications in quantum information. One of the primary methods of two-photon generation is based on parametric down-conversion, but this suffers from low efficiency and a large footprint. This work presents a detailed theoretical investigation of an alternative approach: two-photon generation from an emitter in a doubly resonant cavity. The system is modelled by the Lindblad master Equation, and an approximate analytical solution is derived to determine the experimentally achievable limits on efficiency and brightness. Additionally, the optimal cavity parameters for achieving these limits are also identified. For experimentally feasible parameters, the maximum efficiency is approximately 35%, which is significantly higher than that of parametric down-conversion-based methods. The optimal rate and efficiency for two-photon generation are achieved when the outcoupling rate of the cavity mode at the two-photon emission frequency matches the single-photon atom-field coupling strength. Moreover, the outcoupling rate of the cavity mode at the one-photon emission frequency for single photons should be minimized. The cavity field properties are also examined by studying the second-order correlation function at zero time delay and the Mandel Q parameter, revealing highly bunched two-photon emission and super-Poissonian statistics. The quantum-jump framework, combined with Monte Carlo simulations, is used to characterize the mechanism of two-photon emission and the emission spectra of the cavity. Two-photon emission is demonstrated to be a rapid cascade process of quantum jumps, and its spectrum consists of three prominent peaks corresponding to transitions between the dressed states of the system.
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Abstract Spontaneous two-photon emission is a process in which the transition between two quantum states happens via simultaneous emissions of two identical photons. Such second-order quantum radiation is of paramount importance in astrophysics, atomic physics, and quantum technology. In particular, on-demand spontaneous two-photon emission from single quantum emitters has long been envisioned to revolutionize photonic quantum science and technology. To date, experimental realizations of two-photon emission at the single quanta level are still highly challenging yet elusive due to their low probabilities. In this work, we explore spontaneous two-photon emission from a single semiconductor quantum dot deterministically coupled to a high-quality microcavity in which the cavity resonances greatly enhance both excitation and emission processes. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity mode drives the biexciton to the ground state and simultaneously emits two photons into the cavity mode, resulting in two-photon emissions with a record brightness comparable to the competing single-photon process and sub-nanowatt power consumption. For the first time, the quantum nature associated with spontaneous two-photon emissions in the cavity quantum electrodynamics regime has been investigated via photon statistics measurements. Furthermore, spontaneous two-photon emission is exploited to build unconventional entangled quantum light sources with the unique advantage of combining the best of two worlds: near-unity entanglement fidelity for spontaneous parametric down-conversion source and on-demand photon emissions for atomic quantum emitters. Our work provides unprecedented insights into the two-photon process in the quantum regime and opens an unexplored avenue for pursuing optically reconfigurable quantum light sources with nonlinear quantum radiations.
Motivated by recent advances in the development of single photon emitters for quantum information sciences, here we design and formulate a quantum cascade model that describes cascade emission by a quantum dot (QD) in a cavity structure while preserving entanglement that stores information needed for single photon emission. The theoretical approach is based on a photonic structure that consists of two orthogonal cavities in which resonance with either the first or second of the two emitted photons is possible, leading to amplification and rerouting of the entangled light. The cavity-QD scheme uses a four-level cascade emitter that involves three levels for each polarization, leading to two spatially entangled photons for each polarization. By solving the Schrodinger equation, we identify the characteristic properties of the system, which can be used in conjunction with optimization techniques to achieve the "best" design relative to a set of prioritized criteria or constraints in our optical system. The theoretical investigations include an analysis of emission spectra in addition to the joint spectral density profile, and the results demonstrate the ability of the cavities to act as frequency filters for the photons that make up the entanglements and to modify entanglement properties. The results provide new opportunities for the experimental design and engineering of on-demand single photon sources.
The spontaneous emission spectrum from two quantum dots (QDs) that are strongly coupled with a single-mode nanocavity is investigated using rigorous numerical calculations and simple analytical solutions of quantum dynamics. The emission spectra both from the side and along the axis of the cavity are considered. Modification of two parameters, the coupling strength and the detuning between the transition frequencies of the two quantum dots, allows us to efficiently control the shape of the spontaneous emission spectrum. Different profiles and their physical origins can be well understood in the dressed-state picture for the light—QD interaction in the on-resonance and off-resonance situations. In the on-resonance situation, the emission spectra exhibit symmetric features, and they are not altered by the asymmetry in the coupling parameters. The axis spectra show two emission peaks while the side spectra have three emission peaks. In the off-resonance situation, the emission spectra always show an asymmetrical three-peak feature. When the two QDs have different decay parameters, singular features (a peak or a dip) can take place at the frequency of the cavity mode, and this is attributed to the unbalanced process of the emission and absorption of a single photon.
We theoretically investigate the photon statistics in a cavity quantum electrodynamics system of a single quantum dot (QD) coupled to photonic molecule. Our previous work [Wen Zhang et.al, Phys. Rev. A 89, 043832 (2014)] has shown that QD-bimodal cavity system can generate ultrastrongly sub-Poissonian light by regulating the ratio between driving strengths of two cavity modes. Here we study two coupled single-mode nanocavities with a QD coupling to one of them as a photonic molecule system. Statistical character of photon emission is presented by evaluating the zero-delay secondorder correlation function g2(0). When both cavities with/without QD are driven, the sub-Poissonian character can be optimized by regulating the ratio between driving strengths of each cavities. We also present the dependences of other system parameters on the photon statistics. The physical mechanism of both effects is to optimize the combination of super-Poissonian and coherent light which results in sub-Poissonian light generation. As a result g2(0) can be reduced up to several orders of magnitude compared with the QD coupled one-mode-cavity system.
We have demonstrated high-speed controlled generation of single photons in a coupled atom-cavity system. A single 85Rb atom, pumped with a nanosecond-pulse laser, generates a single photon into the cavity mode, and the photon is then emitted out the cavity rapidly. By employing cavity parameters for a moderate coupling regime, the single-photon emission process was optimized for both high efficiency and fast bit rates up to 10 MHz. The temporal single-photon wave packet was studied by means of the photon-arrival-time distribution relative to the pump pulse and the efficiency of the single-photon generation was investigated as the pump power. The single-photon nature of the emission was confirmed by the second-order correlation of emitted photons.