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Quantum Communications and Quantum Imaging

Cavity-mediated quantum correlation between QDs

Kyu Young Kim, Jinhee Lee, Woong Bae Jeon, Dong Hyun Park, Suk In Park, Jin Dong Song, Changhyoup Lee, Je‐Hyung Kim

Published Jul 31, 2025• 0 citations
Publisher

Abstract

Cooperative phenomena, such as super(sub)radiance in quantum systems, arise from interactions among quantum emitters. Superradiance has been intensively studied from various platforms. While superradiance provides a good insight into the collective effect in quantum systems, exploiting the entangled state is not easy because of its strong radiative nature. In contrast, subradiance remains largely unexplored due to its inherent dark nature, despite its long lifetime and robustness against dephasing. Here, we experimentally demonstrate a long-lived subradiance among multiple quantum dots coupled to a low-Q cavity. The directional cavity mode provides a constant momentum condition, similar to a waveguide, and facilitates a shared radiative field among the quantum dots. By balancing cavity dissipation, incoherent pumping, and coupling strength, we realize steady-state subradiance rather than superradiance. As a key signature of subradiance, we observe a stark change in the photon statistics, with photon bunching exceeding the classical limit of 2. Additionally, we engineer the coupled system by changing detuning and incoherent pumping. Furthermore, modifying the pumping mechanism allows us to manipulate the dephasing of quantum dots involved in the cooperative process. Our experimental study on cavity-mediated cooperative phenomena among multiple quantum dots introduces a novel approach to generating quantum correlations with long-lived entanglement, offering potential applications in quantum storage and metrology.

DOI
10.1117/12.3063739

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Cooperative phenomena, such as super(sub)radiance in quantum systems, arise from interactions among quantum emitters. Superradiance has been intensively studied from various platforms. While superradiance provides a good insight into the collective effect in quantum systems, exploiting the entangled state is not easy because of its strong radiative nature. In contrast, subradiance remains largely unexplored due to its inherent dark nature, despite its long lifetime and robustness against dephasing. Here, we experimentally demonstrate a long-lived subradiance among multiple quantum dots coupled to a low-Q cavity. The directional cavity mode provides a constant momentum condition, similar to a waveguide, and facilitates a shared radiative field among the quantum dots. By balancing cavity dissipation, incoherent pumping, and coupling strength, we realize steady-state subradiance rather than superradiance. As a key signature of subradiance, we observe a stark change in the photon statistics, with photon bunching exceeding the classical limit of 2. Additionally, we engineer the coupled system by changing detuning and incoherent pumping. Furthermore, modifying the pumping mechanism allows us to manipulate the dephasing of quantum dots involved in the cooperative process. Our experimental study on cavity-mediated cooperative phenomena among multiple quantum dots introduces a novel approach to generating quantum correlations with long-lived entanglement, offering potential applications in quantum storage and metrology.
Cooperative effects such as super(or sub)radiance in quantum systems arise from the interplay among quantum emitters. While bright superradiant states have been extensively studied and have yielded important insights into cooperative phenomena, subradiant states remain less explored due to their inherently dark state nature. However, subradiance holds significant potential as a valuable quantum resource exploiting long-lived and large-scale entanglement, which is a key for advancing quantum information technologies. Here, we demonstrate strong collective emission from a cavity-mediated steady-state subradiant state. In a tailored photonic environment with balanced cavity dissipation, emitter-field coupling strength, and incoherent pumping, two quantum dots coupled to a low-Q cavity exhibit a steady-state population in a subradiant state with a highly negative cooperativity parameter among the emitters. As a key signature of steady-state subradiance, the system shows strong photon bunching ( g(2)(0)>8{{{\rm{g}}}}^{\left(2\right)}\left(0\right) > 8g(2)(0)>8 ) and suppressed single-photon decay (36 ns). Furthermore, we investigate that such collective interactions can be manipulated by controlling various system parameters, such as detuning and dephasing, supported by numerical simulations. Our approach to inducing cavity-mediated subradiance paves the way for generating and harnessing quantum correlations among quantum emitters via controlled dissipation. Subradiance is a cooperative effect in systems of quantum emitters, which is the opposite of superradiance, or enhanced emission, but has been less explored. Here, the authors demonstrate a steady-state subradiant state in a system of two InAs quantum dots coupled to a low-Q nanophotonic cavity.
We theoretically investigate the emission properties of a single-mode cavity coupled to a mesoscopic number of incoherently pumped quantum emitters. We propose an operational measure for the medium cooperativity, valid both in the bad- and in the good-cavity regimes. We show that the opposite regimes of subradiance and super-radiance correspond to negative and positive cooperativity, respectively. The lasing regime is shown to be characterized by non-negative cooperativity. In the bad-cavity regime we show that the cooperativity defines the transitions from subradiance to super-radiance. In the good-cavity regime it helps to define the lasing threshold, also providing distinguishable signatures indicating the lasing regime. Increasing the quality factor of the cavity mode induces a crossover from the solely super-radiant to the lasing regime. Furthermore, we verify that lasing is manifested in a wide range of positive cooperative behavior, showing that stimulated emission and super-radiance can coexist. The robustness of the cooperativity is studied with respect to experimental imperfections, such as inhomogeneous broadening and pure dephasing.
When multiple quantum emitters couple to a common electromagnetic environment, interference in their collective radiative dynamics gives rise to superradiance and subradiance. In regimes where coherent interactions and collective dissipation compete, the microscopic many-body dynamics and quantum correlations among the emitters that underlie superradiance and subradiance are theoretically challenging and remain experimentally elusive, even though collective emission has been observed in many physical systems. Here, we realize a superconducting qubit array coupled to a common microwave waveguide that mediates collective dissipation, with simultaneous access to coherent interactions and microscopic measurements of many-body dynamics. Engineered qubit-waveguide couplings with tunable amplitude and phase enable control of collective interference and the resulting super- and subradiant states. Leveraging site-resolved control and readout, we directly observe the microscopic decay dynamics of multi-qubit states across different excitation manifolds and track the evolution of populations and tunable quantum correlations. We reveal collective decay in regimes beyond the ideal Dicke model, where strong qubit-qubit interactions stabilize superradiance and subradiance against local dephasing and reshape decay pathways through spatially and spectrally structured many-body eigenstates. Our results establish a flexible platform for exploring collective phenomena in many-body quantum optics and driven-dissipative approaches to robust quantum information processing.
When quantum emitters couple indistinguishably to light, they can synchronize into a collective light matter system with radiative properties profoundly different from those of independent particles. To date, the resulting collective effects have largely been confined to point like or homogeneous ensembles. Here, we open access to a qualitatively new collective regime by realizing geometrically ordered, spatially extended atom arrays with subwavelength spacing. This establishes a fundamentally new platform in which collective emission is no longer confined to a single Dicke mode but instead emerges from an ordered network of photon mediated interactions. We find that 2D atom arrays undergo strong super and subradiant emission. Despite subwavelength spacing, we achieve site resolved imaging and directly observe the buildup of spatial correlations, demonstrating the transformation of cooperative decay into a strongly correlated many-body process. We observe extensive scaling of superradiance, uncover superradiant revivals, and reveal the ferromagnetic nature of superradiance and the antiferromagnetic nature of subradiance. Our results realize a novel programmable platform for exploring and utilizing dissipative many-body quantum physics, opening new possibilities for photon capture, storage, and atom photon entanglement.
We study the temporal correlations of the field emitted by an electromagnetic resonator coupled to a mesoscopic number of two-level emitters that are incoherently pumped by a weak external drive. We solve the master equation of the system for increasing number of emitters and as a function of the cavity quality factor, and we identify three main regimes characterized by well-distinguished statistical properties of the emitted radiation. For small cavity decay rates, the emission events are uncorrelated and the number of photons in the emitted field becomes larger than one, resembling the build-up of a laser field inside the cavity. At intermediate decay rates (as compared with the emitter–cavity coupling) and for a few emitters, the statistics of the emitted radiation is bunched and strikingly dependent on the parity of the number of emitters. The latter property is related to the cooperativity of the emitters mediated by their coupling to the cavity mode, and its connection with steady-state subradiance is discussed. Finally, in the bad cavity regime the typical situation of emission from a collection of individual emitters is recovered. We also analyze how the cooperative behavior evolves as a function of pure dephasing, which allows us to recover the case of a classical source made of an ensemble of independent emitters, similar to what is obtained for a very leaky cavity. State-of-the-art techniques of Q -switch of resonant cavities, allied with the recent capability of tuning single emitters in and out of resonance, suggest this system to be a versatile source of different quantum states of light.