Mechanisms and Opportunities for Tunable High-Purity Single Photon Emitters: A Review of Hybrid Perovskites and Prospects for Bright Squeezed Vacuum

TL;DR

The paper addresses the persistent challenge of delivering single-photon emitters with simultaneously high purity, indistinguishability, and tunability for scalable quantum technologies. It introduces a mechanism-based framework to compare SPE platforms, highlighting HOIP QDs as a promising RT source with strong tunability and blinking suppression, while also exploring bright squeezed vacuum (BSV) as a state-engineering avenue to bypass material limits. A RECIQ (Robustness, Efficiency, Control, Integrability, Quality) framework is proposed to standardize performance evaluation and guide integration into photonic architectures. The review concludes that HOIP QDs offer near-term gains, but fundamental scalability hurdles remain, which BSV-based multiplexed schemes could help overcome by enabling parallel, high-purity photon generation across multiple modes. Overall, the work maps a path toward hybrid HOIP- and BSV-based quantum photonics, outlining practical directions for integration into scalable quantum networks and on-chip platforms.

Abstract

Single-photon emitters (SPEs) are central to quantum communication, computing, and metrology, yet their development remains constrained by trade-offs in purity, indistinguishability, and tunability. This review presents a mechanism-based classification of SPEs, offering a physics-oriented framework to clarify the performance limitations of conventional sources, including quantum emitters and nonlinear optical processes. Particular attention is given to hybrid organic-inorganic perovskite quantum dots (HOIP QDs), which provide size- and composition-tunable emission with narrow linewidths and room-temperature operation. Through comparative analysis of physical mechanisms and performance metrics, we show how HOIP QDs may address key limitations of established SPE platforms. Recognizing the constraints of current deterministic sources, we introduce a performance framework to guide the development of scalable SPEs, and examine the theoretical potential of bright squeezed vacuum (BSV) states, discussing how BSV mechanisms could serve as a promising avenue for multiplexable, high-purity photon generation beyond conventional heralded schemes. The review concludes by outlining future directions for integrating HOIP- and BSV-based concepts into scalable quantum photonic architectures.

Figures (18)

• Figure 1: Applications and evolution of single photons sources. (a) Single photons possess indivisibility, low decoherence, fast transmission speed, entanglement capability, and can exist in a superposition of multiple states, which make them highly appealing for advanced applications in quantum communication, computing, metrology, biology, and fundamental physics tests. (b) Timeline highlighting key developments in SPE technologies.
• Figure 2: Characterization techniques for SPEs. (a) HBT setup for assessing single-photon purity. A 50/50 beam splitter directs incoming photons to two detectors; the second-order correlation function $g^{(2)}(0)$ reflects coincidence counts. Lower values indicate higher purity couteau2023applications1. Reproduced with permission from Nat. Rev. Phys. 5, 326 (2023). Copyright 2023 Springer Nature Limited. (b) HOM setup for testing photon indistinguishability. Two identical photons entering a 50/50 beam splitter from different ports interfere quantum mechanically and exit through the same output, leading to suppressed coincidences (HOM dip) couteau2023applications1. Reproduced with permission from Nat. Rev. Phys. 5, 326 (2023). Copyright 2023 Springer Nature Limited. (c) Inverted confocal microscope integrating HBT functionality. Emitters are excited via LED or pulsed laser, and emission is analysed via spectrometer or camera. HBT measurements are conducted using multimode fibres and avalanche photodiodes (APDs). DM: dichroic mirror; PBS: polarizing beam splitter pierini2020highly. Reproduced with permission from ACS Photonics 7, 2265 (2020). Copyright 2020 American Chemical Society. (d) HOM setup for 808 nm photons. Components include FC: fibre coupler; APD: avalanche photodiode; HWP: half-wave plate; BS: beam splitter; M: mirror euler2021spectral. S. Euler et al., Eur. Phys. J. Spec. Top. 230, 1073 (2021); licensed under a Creative Commons Attribution (CC BY) license.
• Figure 3: Mechanism of quantum emitters: (a) Spontaneous Emission: It is initially excited to a higher energy state, naturally decays to its ground state without external influence, emitting a single photon in the process. This emission occurs randomly in time and direction. The energy of the emitted photon corresponds to the energy difference between the two states, defined by $\nu = \frac{\Delta E}{h}$. (b) Stimulated Emission: An incident photon of matching energy interacts with an excited quantum emitter, inducing it to decay to a lower energy state. The result is the emission of a second photon that is coherent with the incident photon, sharing the same phase, frequency, and direction. Although fundamental in laser physics, stimulated emission is less common in SPEs compared to spontaneous emission.
• Figure 4: Single photon Generation Using STIRAP Process. Atoms are first captured and cooled using an MOT, which utilizes laser cooling and magnetic fields to reduce thermal motion and spatially confine the atoms. Once cooled, the MOT is turned off, and the atoms fall under gravity into a high-finesse optical cavity. Here, an optical dipole trap holds a single atom in place. The energy transition is driven by STIRAP, employing two laser pulses: the Stokes pulse (coupling $|e\rangle \longrightarrow |u\rangle$) and the pump pulse (coupling $|g\rangle \longrightarrow |e\rangle$). The Stokes pulse is applied first, creating a pathway, followed by the pump pulse that adiabatically transfers the population to $|u\rangle$while avoiding $|e\rangle$. The atom, now in $|u\rangle$, undergoes a $|u\rangle \longrightarrow |g\rangle$ transition, emitting a photon into the cavity mode enhanced by cQED, resulting in the final state $|g\rangle |1\rangle$.
• Figure 5: QDs confinement and emission mechanisms (a) Electron-hole pairs in QDs and their size-dependent optical and electrical properties. The strong Coulomb attraction between the hole and electron will make them bonded as a quasi-particle. As the size of a QD decreases, its bandgap inversely increases. When the size of the semiconductor crystal is smaller the exciton Bohr radius, it is considered as a quantum dots garcia2021semiconductor. Reproduced with permission from Science 373, eaaz8541 (2021). Copyright 2021 The American Association for the Advancement of Science. (b) The radiative decay of QDs. The electron is first excited to the conduction band, and a hole is formed at the valence band. The exciton they formed will then lose energy gradually in the form of phonons. Finally, the electron and hole will recombine and emit a photon. (c) The non-radiative (Auger) decay of QDs. In the recombination state, instead being in the form of photons, the energy is transferred to another charge carrier, hindering single photon emission.