Quantum information processing and quantum cryptography are expected to realize highly secure future information networks. How to control photon qubits will be one of the major issues for this direction, but the technologies related to generations and detections of individual photons are still being developed. Semiconductor quantum dots (QDs) have been expected to play major role for on-demand generations of single photons as well as entangled photon pairs. In this talk, photon generation processes from a single QD will be studied for the control of the quantum states of generated photons. Generation of entangled photon pairs from QDs based on biexciton-exciton cascade recombination processes is presently in a difficult situation due to exciton states energy splitting related to growth-related issues. An approach to open new paradigm will be discussed with preliminary results.
Quantum information processing and quantum cryptography are expected to realize highly secure future information networks. How to control photon qubits will be one of the major issues for this direction, but the technologies related to generations and detections of individual photons are still being developed. Semiconductor quantum dots (QDs) have been expected to play major role for on-demand generations of single photons as well as entangled photon pairs. In this talk, photon generation processes from a single QD will be studied for the control of the quantum states of generated photons. Generation of entangled photon pairs from QDs based on biexciton-exciton cascade recombination processes is presently in a difficult situation due to exciton states energy splitting related to growth-related issues. An approach to open new paradigm will be discussed with preliminary results.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton–exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton-exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Semiconductor quantum dots (QDs) are able to confine single charges on the nanoscale in all three dimensions of space, making them excellent systems for exploring quantum phenomena. In particular, QDs have demonstrated outstanding performance as sources of entangled and indistinguishable photon pairs, properties highly desired in the fields of quantum communication and -information processing. Here I report on the advances of QDs as potential resources for photonic quantum networks, which allow to overcome the fundamental range limitations of single photon-based applications. After an introduction to the underlying mechanisms of entangled photon pair generation, I demonstrate several building blocks of quantum networks, with quantum key distribution as a prime application.
Emitters based on semiconductor quantum dots are promising sources for both single photons and pairs of polarization-entangled photons. Typically, single photons are generated through a photon emission event bringing the electronic system from a single-exciton state back to the ground state. In the case of entangled photons two photons are generated through a cascaded emission from the biexciton to either one of the single-exciton states and then back to the ground state. Alternatively, emission of two photons can also be achieved through a higher-order two-photon process bringing the quantum dot directly from the biexciton state (through a virtual intermediate state) back to the ground state. Here we discuss in particular how this two-photon process can lead to certain conceptual advantages in both the generation of polarization-entangled photon pairs and generation of single photons.
Among different solid-state emitters of quantum light, epitaxial GaAs quantum dots (QDs) have recently emerged as nearly-ideal sources of triggered polarization entangled photon pairs [1]. This property, combined with the strongly suppressed probability of multiphoton emission under resonant excitation [2] has allowed the implementation of quantum teleportation using photons subsequently emitted by a single QD [3]. In this talk I will discuss the peculiar properties of GaAs QDs [4,5], their performance as emitters of both single and entangled photons, as well as possible methods to engineer their light emission characteristics [1,4] to meet the demanding requirements imposed by photonic quantum technologies. [1] D. Huber et al. Phys. Rev. Lett. 121, 033902 (2018). [2] L. Schweickert et al. Appl. Phys. Lett. 112, 093106 (2018). [3] M. Reindl et al. Science Adv. (2018). [4] X. Yuan et al. Nat. Comm. 9, 3058 (2018). [5] M. Reindl et al. https://arxiv.org/abs/1901.11251.
Semiconductor Quantum dots are potentially an attractive source of non-classical light. They can confine bound electron-hole pairs, excitons, in all three spatial dimensions giving them discrete optical emission energies, much like the electronic states in atomic systems. The semiconductor nature of the system allows quantum dots to be integrated into complicated device structures including optical cavities [1] and electrical injection [2]. The radiative exciton emission from a semiconductor quantum dot can provide the simplest form of quantum light, a single photon source [2]. The finite re-excitation time following the radiative decay of an exciton in a quantum dot prevents the dot from emitting more than one photon if excited with a short optical or electronic pulse. In a similar fashion excitation of the biexciton state, consisting of two electrons and holes, in the quantum dot results in the emission of a pair of photons at the energy of the biexciton and exciton transitions. The biexciton state was, in fact, proposed as a possible source of polarisation-entangled photons in 2000 by Benson et al. [3] as it consists of two polarisation-correlated decay paths which could potentially be indistinguishable. The condition of indistinguishability is fundamental to the generation of entangled photons and is, in general, not true of the two decay paths from the biexciton state in a quantum dot; physical anisotropy causes the intermediate exciton states to hybridise and separate in energy providing ‘which-path’ information about the route taken through the biexciton decay. We demonstrate how the splitting between the intermediate exciton states in a single InAs quantum dot can be controlled by growth [4], rapid thermal annealing [5] and the application of an external magnetic field [6]. Each of these three techniques can be used to make the intermediate exciton states degenerate allowing the biexciton decay to produce singe pairs of entangled photons triggered by short laser pulses [7,8]. Entangled photon pair sources are essential for applications such as entanglement based quantum key distribution, and optical quantum computing. For these applications it is important that no more than one entangled photon pair is generated in a cycle, a requirement met by our quantum dot source which is not possible with traditional methods for generating entangled pairs of photons. Entanglement also enables quantum interferometry and metrology, the basis of image resolution beyond that possible with equivalent classical light. Biphoton interferometry using entangled emission from the biexciton decay reveals fringes with half the period of classical light [9], and less that that of the laser. In addition, interferometry suggests that this type of entangled light source is not limited by decoherence, we fine the biphoton is surprising robust against dephasing, in stark contrast to the devastating effect of decoherence upon single photons emitted by similar structures.