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arXiv:2603.20568

Triply Resonant Photonic Crystal Nanobeam Cavities for Unconditional Photon Blockade

Richard Dong, Abhinav Kala, Andrew Lingenfelter, Michael S. Polania Vivas, Matthew D. Stearns, Arka Majumdar

quant-phphysics.opticsSubmitted Mar 20, 2026• Announced Mar 24, 2026
arXivHTMLPDF

Abstract

The development of many scalable quantum technologies requires single-photon nonlinearity, such as single-photon blockade, in solid-state systems. Recently, it has been shown that single-photon Fock states can, in principle, be unconditionally generated using arbitrarily small intrinsic optical nonlinearities in photonic cavities. We investigate the feasibility of such a scheme in achieving photon blockade in an on-chip silicon photonics platform. We show that a triply resonant nanobeam cavity pumped with three monochromatic lasers could achieve such functionalities with quality factors $\sim 10^7$ and effective mode volumes $\sim 10^{-2} μm^3$, for experimentally feasible incident powers. Using quantum optical simulations, we propose an experimental protocol to generate single photons under this scheme. The constraints on the cavity design and experimental conditions are thoroughly explored to determine feasible regimes of operation.

Comments
9 pages, 4 figures

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The development of many scalable quantum technologies requires single-photon nonlinearity, such as single-photon blockade, in solid-state systems. Recently, it has been shown that single-photon Fock states can, in principle, be unconditionally generated using arbitrarily small intrinsic optical nonlinearities in photonic cavities. We investigate the feasibility of such a scheme in achieving photon blockade in an on-chip silicon photonics platform. We show that a triply resonant nanobeam cavity pumped with three monochromatic lasers could achieve such functionalities with quality factors ∼107\sim 10^7∼107 and effective mode volumes ∼10−2μm3\sim 10^{-2} μm^3∼10−2μm3, for experimentally feasible incident powers. Using quantum optical simulations, we propose an experimental protocol to generate single photons under this scheme. The constraints on the cavity design and experimental conditions are thoroughly explored to determine feasible regimes of operation.
An efficient single-photon nonlinearity is a key resource for photonic quantum technologies. Single-photon nonlinearities have been demonstrated with quantum dots (QDs) across a range of cavity and waveguide geometries. However, none of these realizations simultaneously provide high-efficiency direct fiber coupling and compatibility with scalable on-chip integration. The nanobeam cavity addresses these limitations through its in-plane geometry, which enables highly efficient, direct fiber coupling alongside scalable homogeneous and heterogeneous on-chip integration. Here, we report a single-photon nonlinearity from a nanobeam cavity coupled to a single quantum dot. The nanobeam interfaces directly with a single-mode fiber with an efficiency of 60%. Driven by resonant picosecond pulses, the platform achieves a single-photon nonlinearity with a low threshold of 0.24 incident photons per pulse. The system operates in the strong-coupling regime, exhibiting a coupling rate of g/2π = 29.1 GHz and a cooperativity of C = 3.98. These results establish the nanobeam cavity-QD system as a compact, chip-integrable, and fiber-compatible building block for scalable photonic quantum technologies.
The on-chip generation of nonclassical states of light is a key requirement for future optical quantum hardware. In solid-state cavity quantum electrodynamics, such nonclassical light can be generated from self-assembled quantum dots strongly coupled to photonic crystal cavities. Their anharmonic strong light-matter interaction results in large optical nonlinearities at the single photon level, where the admission of a single photon into the cavity may enhance (photon tunneling) or diminish (photon blockade) the probability for a second photon to enter the cavity. Here, we demonstrate that detuning the cavity and quantum-dot resonances enables the generation of high-purity nonclassical light from strongly coupled systems. For specific detunings we show that not only the purity but also the efficiency of single-photon generation increases significantly, making high-quality single-photon generation by photon blockade possible with current state-of-the-art samples.
The lack of suitable quantum emitters in silicon and silicon-based materials has prevented the realization of room temperature, compact, stable, and integrated sources of single photons in a scalable on-chip architecture, so far. Current approaches rely on exploiting the enhanced optical nonlinearity of silicon through light confinement or slow-light propagation, and are based on parametric processes that typically require substantial input energy and spatial footprint to reach a reasonable output yield. Here we propose an alternative all-silicon device that employs a different paradigm, namely the interplay between quantum interference and the third-order intrinsic nonlinearity in a system of two coupled optical cavities. This unconventional photon blockade allows to produce antibunched radiation at extremely low input powers. We demonstrate a reliable protocol to operate this mechanism under pulsed optical excitation, as required for device applications, thus implementing a true single-photon source. We finally propose a state-of-art implementation in a standard silicon-based photonic crystal integrated circuit that outperforms existing parametric devices either in input power or footprint area.
We present a mechanism that harnesses extremely weak Kerr-type nonlinearities in a single driven cavity to deterministically generate single-photon Fock states and more general photon-blockaded states. Our method is effective even for nonlinearities that are orders-of-magnitude smaller than photonic loss. It is also completely distinct from so-called unconventional photon blockade mechanisms, as the generated states are non-Gaussian, exhibit a sharp cutoff in their photon number distribution, and can be arbitrarily close to a single-photon Fock state. Our ideas require only standard linear and parametric drives and are hence compatible with a variety of different photonic platforms.
Photon blockade (PB) is generally classified into conventional and unconventional types based on their distinct physical mechanisms. Recent studies have aimed to bridge the two regimes to realize a universal photon blockade (universal PB) that combines their respective advantages. Here, we propose a scheme for achieving universal PB based on second-order nonlinearity. The second-order nonlinear coupling between two cavity modes mediates the fundamental interaction, while an optical parametric amplifier embedded in one cavity introduces additional quantum interference pathways. We analytically derive the optimal conditions for universal PB, and the analytical results show excellent agreement with numerical simulations. By comparing universal PB with conventional PB, we highlight its unique performance advantages: the scheme operates effectively in both strong and weak coupling regimes, relaxes experimental constraints, and achieves an ultra-low equal-time second-order correlation function g (2) (0) down to 10 −7 , while maintaining a moderate mean photon number N a ∼ 10 −2 . This work provides a feasible and tunable platform for realizing high-purity single-photon sources and exploring quantum statistical properties in nonlinear cavity systems.
On-chip generation of non-classical states of light is a fundamental building block for the development of quantum information [1]. A convenient method harnesses resonantly enhanced parametric processes, since they operate at room temperature. We consider here spontaneous Four-Wave-Mixing (FWM). The generation of time correlated, entangled photons pairs and heralded single photons via FWM has been demonstrated on silicon and on different III-V semiconductor ring resonators with very large efficiency [2], [3]. Here, an alternative type of cavity is used: a Photonic Crystal (PhC) cavity. These periodic structures offer the possibility to reduce the mode volume V in all-dielectric structure, with a micrometer-scale footprint, which strongly increases the efficiency of the nonlinear process(∝Q3/V2)(\propto Q^{3}/V^{2})(∝Q3/V2)if high quality factor Q is preserved. We achieve it with a bichromatic Photonic Crystal cavity depicted in fig. 1.a). The cavity is located between two lines of holes with reduced perioda′a^{\prime}a′compared to the rest of the holes with periodaaa; while light propagates in a waveguide created with a missing line of holes ended by a reflector [4]. This design imposes an effective parabolic potential for the optical field, that ultimately leads to equispaced resonances in frequency, which is a strict condition for efficient resonant enhancement of the interaction imposed by the energy conservation of FWM. The cavity is pumped with a CW laser with pump power level ofP0P_{0}P0​transferred to the cavity. A self thermal tuning technique is used to compensate for any residual frequency mismatch of the resonance triplet [4] after fabrication. After the chip, the generated photon pairs encounter an unbalanced Mach-Zehnder “Franson” interferometer [5]. At the output, they are time-energy entangled. They travel through a filtering stage to suppress any residual pump photons before being detected by superconducting nanowire single-photon detectors. The efficiency of our source is measured by bypassing the Franson interferometer. Taking into account the losses between the cavity and the detectors, it is estimated to be 16 GHz/mW2and is comparable to the state-of-the-art of semiconductor based resonators for photon pair generation (20 GHz/mW2, fig. 1.b)) [2]; while our average Q-factor (2.1 × 105) is five times smaller for this sample but could be larger (up to 7 × 105). Comparable efficiency is achieved because the resonator volume is at least one order of magnitude smaller than in ring resonators. Consequently, the footprint is very small(<70μm2,≈600(< 70\mu \mathrm{m}^{2}, \approx 600(<70μm2,≈600and 300 m2in [2] and [3]), which is an important asset for scalability. The entangled nature of the photon pair is quantified with two-photon interferences depicted in fig. 1.c). For pump power of 15μW\mu \mathrm{W}μW, large net visibility is measured up to 96.6 ± 4.2 %. This work shows that PhC cavities are novel and promising sources for integrated quantum optics.