Consciousness within the brain hinges on the synchronized activities of millions of neurons, but the mechanism responsible for orchestrating such synchronization remains elusive. In this study we employ cavity quantum electrodynamics to explore entangled biphoton generation through cascade emission in the vibration spectrum of C-H bonds within the lipid molecules' tails. The results indicate that the cylindrical cavity formed by a myelin sheath can facilitate spontaneous photon emission from the vibrational modes and generate a significant number of entangled photon pairs. The abundance of C-H bond vibration units in neurons can therefore serve as a source of quantum entanglement resources for the nervous system. These findings may offer insight into the brain's ability to leverage these resources for quantum information transfer, thereby elucidating a potential source for the synchronized activity of neurons.
Consciousness within the brain hinges on the synchronized activities of millions of neurons, but the mechanism responsible for orchestrating such synchronization remains elusive. In this study we employ cavity quantum electrodynamics to explore entangled biphoton generation through cascade emission in the vibration spectrum of C-H bonds within the lipid molecules' tails. The results indicate that the cylindrical cavity formed by a myelin sheath can facilitate spontaneous photon emission from the vibrational modes and generate a significant number of entangled photon pairs. The abundance of C-H bond vibration units in neurons can therefore serve as a source of quantum entanglement resources for the nervous system. These findings may offer insight into the brain's ability to leverage these resources for quantum information transfer, thereby elucidating a potential source for the synchronized activity of neurons.
Entangled multiphoton states are a critical resource for the emerging applications of quantum science. Generation of reliable sources of such quantum states of light poses both theoretical and practical challenges, particularly in the small scale. We propose a deterministic source of entangled multiphoton states based on spontaneous emission from a ladder of cascaded quantum potential wells. The special ingredient of this scheme compared with a simple ensemble of emitters is the coupling between the two-level systems, creating sublevels in the energy ladder. This enables, via an indistinguishable multipath evolution, the creation of highly entangled multiphoton photon-number combination states in three modes, namely, tripartite entanglement in the frequency degree of freedom. Due to the intricate energy ladder of our proposed structure, we can apply control and switch the entanglement between two multiphoton modes by measuring the third. We further discuss an application as a qubit-pair source with an error-detection ancilla and comment on possible implementations.
The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon pairs. The general postulate is that the emitter generates photons in a nearly maximally entangled state of polarization, ready for application purposes. Here, we demonstrate that this assumption is unjustified. We show that in radiative cascades there exists an interplay between photon polarization and emission wavevector, which can be further amplified by embedding the emitters in micro-cavities. We discuss how the polarization entanglement of photon pairs from a biexciton-exciton cascade in quantum dots strongly depends on their propagation wavevector and we even observe entanglement vanishing for large emission angles. Our experimental results, backed by theoretical modeling, yield a brand-new understanding of cascaded emission for various quantum emitters. In addition, our model provides quantitative guidelines for designing optical microcavities that retain both a high degree of entanglement and collection efficiency, moving the community one step further towards an ideal source of entangled photons for quantum technologies. The assumption that light sources based on radiative cascades provide maximally polarization-entangled photons is not always correct. Here the authors show experimentally in cavity-embedded quantum dots that photon polarization correlates with its emission mode, impacting the degree of entanglement for emitted photon pairs.
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.
A well controlled, triggered source of entangled photons is desirable for many applications in quantum information processing. The two-photon cascade from a biexciton state, two electrons and holes, confined in a quantum dot can be such a source of polarisation-entangled photons provided the two decay paths from the biexciton carry no “which-path” information. In recent years many techniques have been employed to make the two optical decay paths from the biexciton state indistinguishable. A number of these techniques will be discussed and entangled-photon emission from a single quantum dot with a high fidelity in the expected Bell-state from the cascade will be demonstrated. This source of entangled photons allows optical interferometry beyond the limits imposed by the photon wavelength. Interference fringes of the entangled biphoton state reveals a periodicity half of that obtained with the single photon, and much less than that of the pump laser. High fringe visibility indicates that biphoton interference is less sensitive to decoherence than interference of two sequential single photons. The effect of the exciton fine-structure splitting on our entangled photon source will be shown. Surprisingly the entanglement is found to persist despite relatively large separations between the intermediate energy levels of up to 4µeV. Measurements demonstrate that entanglement of the photon pair is robust to the dephasing of the intermediate exciton state responsible for the first order coherence time of either single photon. We distinguish between the first-order coherence time, and a parameter defined as the cross-coherence time, this is illustrated in the figure.
Entanglement plays a crucial role in the development of quantum-enabled devices. One significant objective is the deterministic creation and distribution of entangled states, achieved, for example, through a mechanical oscillator interacting with confined electromagnetic fields. In this study, we explore a cavity resonator containing a two-sided perfect mirror. Although the mirror separates the cavity modes into two independent confined electromagnetic fields, the radiation pressure interaction gives rise to high-order effective interactions across all subsystems. Depending on the chosen resonant conditions, which are also related to the position of the mirror, we study 2n 2 n -photon entanglement generation and bilateral photon pair emission. Demonstrating the non-classical nature of the mechanical oscillator, we provide a pathway to control these phenomena, opening potential applications in quantum technologies. Looking ahead, similar integrated devices could be used to entangle subsystems across vastly different energy scales, such as microwave and optical photons.
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.