Compact system development of efficient quantum-entangled photon sources towards deployable and industrial devices

Abstract

Entangled photon pair sources are a key enabling technology for quantum communication and networking, yet their deployment beyond laboratory environments is hindered by system-level complexity, limited operational stability, and insufficient industry compatibility. Here, we demonstrate a rack-based, mobile quantum light source architecture based on a semiconductor quantum dot emitter that directly addresses these challenges through modular system integration and automated operation. The source generates polarization-entangled photon pairs with an entanglement negativity 2n of up to $0.98(1)$, confirming near-maximal entanglement quality. In continuous, hands-off operation over a six-hour time window, the system achieves an average single-photon emission rate of $697(8)$ kHz and a maximum rate of $740(7)$ kHz, while maintaining 2n-value of more than $95$ $\%$. These results are enabled by the integration of optical excitation, collection, cryogenic operation, and control electronics within a standardized rack footprint, together with automated monitoring. By demonstrating simultaneously high entanglement quality, sustained brightness, and long-term operational stability in an industry-aligned system architecture, this work advances semiconductor quantum dot sources toward deployable entangled photon sources for applied quantum photonics.

Figures (10)

• Figure 1: High-level schematic overview of the compact, industry-compatible entangled photon pair source system architecture housed within 19-inch rack systems. The principles and design considerations of the various modules are discussed in the text.
• Figure 2: Illustration of the rack-based quantum dot entangled photon pair source system architecture. (a) Source cryostat and detection rack: Contains the cryostat system together with the associated electronics for the GaAs quantum dot source and single photon time-resolved detection. (b) Optics rack: The optical sub-systems are organized into standardized modules. The automatized polarization projection units and the pulsed 1 GHz clocked Ti:Sa laser system, including its controller, are fully integrated into this rack. and see \ref{['fig:System_Overview']} for their interactions.
• Figure 3: Overview of the employed approach of in situ fiber-coupling of entangled photon pairs sources based on GaAs quantum dots embedded in $\mathrm{Al}_{0.15}\mathrm{Ga}_{0.85}\mathrm{As}$ monolithic microlenses. a) Three-dimensional representation of the cryostat interior design of the in situ fiber coupling system, which includes the fiber-strain-relief unit and free-space-accessible lens for coarse fiber–micro-objective alignment. b) Illustration of the QD-microlens emission collection into a 3D-printed micro objective attached to a single mode fiber. c) A microscopy picture of the monolithic QD-microlens sample chip used in this study. Its dimensions is 1.8 × 1.5 mm, featuring 19200 lenses arranged in 48 fields of 20 $\times$ 20 lenses. d) Scanning electron micrograph under a 45° tilt.
• Figure 4: a) Above-band excitation spectrum of a single GaAs QD-microlens captured using a 3D-printed objective on top of a single-mode fiber. The exciton (X), biexciton (XX), negative and positive trion ($X^-$ and $X^+$) QD emission lines are annotated. b) Schematic illustration of the two-photon resonant excitation (TPE) and entangled photon pair creation scheme. c) Micro-photoluminescence spectrum of the selected QD under two-photon excitation at the $\pi$-pulse excitation. The $\lvert XX\rangle \to \lvert X\rangle$ and the $\lvert X\rangle \to \lvert 0\rangle$ emission lines are shown in back and pink, respectively. d) Normalized CCD count rate as a function of TPE pulse area. The first Rabi $\pi$-pulse is achieved at a power of 9 at a laser repetition rate of 1.
• Figure 5: (a) Representation of the absolute values of two-photon density matrix $\rho$ using 1-clocked two-photon resonant excitation. Both $\rho$ representations for the maximal within a 8 window and lifetime $T_1$-averaged entanglement negativities $2n_{max}$ and $\overline{2n}_{T_1}$, respectively, are shown. (b) 2n as a function of time delay $\delta \tau$ between the X-XX two-photon coincidences. The measured $\rho$ and 2n (blue curve) are derived from the full X-XX two-photon coincidence tomography measurement over all 36.0 detection polarization combinations; the full dataset is shown explicitly in the supplementary materials \ref{['fig:Two-photon X–XX coincidence']}. The green and red curves represent the calculated 2n values of an ideal maximally entangled model with and without considering a limited single-photon detector timing resolution, respectively.