ocessor based on electrically addressable ferroelectric-nematic liquid-crystal (FNLC) nonlinear elements. The architecture combines continuous-wave spontaneous parametric down-conversion with shallow cascaded photon-generation modules, time-resolved heralding, parallel processing panels, and measurement-mediated electrical coupling between panels. Rather than increasing the depth of a single nonlinear cascade, scalability is achieved predominantly by increasing the number of independently operating modules and interconnected panels. Quantum correlations are generated locally within nonlinear modules, while detection outcomes from one part of the processor can be used by a classical controller to modify the voltages and hence the subsequent quantum-optical states generated in other parts. This event-driven organization allows probabilistically generated quantum resources to be selected and processed without requiring simultaneous successful generation throughout the entire device. Recent demonstrations of continuouswave SPDC, quasi-phase matching, and electrical control of entangled-photon generation in FNLCs provide the experimental basis for the proposed architecture. The key unresolved parameter is the probability of secondary single-photon-pumped down-conversion in an FNLC element. Its measurement provides a direct quantitative test of the feasibility of cascaded FNLC processing. The proposed system is therefore formulated as an adaptive quantum-photonic processor rather than a universal gate-based quantum computer, with coherent photonic interconnects and quantum storage representing possible future extensions.
ocessor based on electrically addressable ferroelectric-nematic liquid-crystal (FNLC) nonlinear elements. The architecture combines continuous-wave spontaneous parametric down-conversion with shallow cascaded photon-generation modules, time-resolved heralding, parallel processing panels, and measurement-mediated electrical coupling between panels. Rather than increasing the depth of a single nonlinear cascade, scalability is achieved predominantly by increasing the number of independently operating modules and interconnected panels. Quantum correlations are generated locally within nonlinear modules, while detection outcomes from one part of the processor can be used by a classical controller to modify the voltages and hence the subsequent quantum-optical states generated in other parts. This event-driven organization allows probabilistically generated quantum resources to be selected and processed without requiring simultaneous successful generation throughout the entire device. Recent demonstrations of continuouswave SPDC, quasi-phase matching, and electrical control of entangled-photon generation in FNLCs provide the experimental basis for the proposed architecture. The key unresolved parameter is the probability of secondary single-photon-pumped down-conversion in an FNLC element. Its measurement provides a direct quantitative test of the feasibility of cascaded FNLC processing. The proposed system is therefore formulated as an adaptive quantum-photonic processor rather than a universal gate-based quantum computer, with coherent photonic interconnects and quantum storage representing possible future extensions.
We propose a Liquid-Crystal Quantum-Photonic Processor (LCQPP) architecture based on a parallel array of independently electrically addressable ferroelectric-nematic liquid-crystal (FNLC) cells. A common optical initialization is combined with local information encoding through voltages applied independently to individual cells. Each cell generates a voltage-dependent signal–idler photon-pair state, followed by parallel quantum-optical readout and classical feedback. The architecture builds on experimentally demonstrated SPDC, electrically tunable photon-pair entanglement, and quasi-phase matching in ferroelectric-nematic liquid crystals, and organizes these capabilities into a programmable quantum-photonic processing matrix. Version v3: The processor architecture has been clarified by explicitly introducing measurement-mediated inter-cell feedback. Measurement outcomes from one FNLC cell can be processed by the classical controller and used to modify the control voltages, and hence the subsequent quantum-optical states, of other cells. The distinction between intra-cell quantum entanglement and inter-cell measurement-mediated coupling has been made explicit.
Entangled photon pair sources relying on spontaneous parametric down-conversion (SPDC) are an essential ingredient for optical quantum technologies. Currently, the vast majority of SPDC sources is based on solid-state crystals. However, their rigid nature implies a careful design of the source as well as it limits the two-photon state that can be generated, without much possibility of tuning it. Here, we demonstrate a new generation of efficient, highly tunable sources of entangled photons based on recently discovered liquid crystal materials called ferroelectric nematic liquid crystals (FNLC). In addition to other highly desirable properties that liquid crystals possess, such as the ability to self-assemble into complex structures, strong response to the electric field and integrability into complex optical systems, FNLCs also possess considerable optical nonlinearity. This, as we demonstrate, enables also efficient SPDC generation and opens the door for promising new functionalities in quantum technologies. This work demonstrates the first-ever realization of SPDC in soft, organic matter, with the possibility of controlling the molecular order and thus tuning the two-photon polarization state. We show that almost any polarization state can be generated by simply adjusting the twist of the molecular orientation along the sample. Additionally, by applying only a few volts, we can drastically alter both the emission rate and the generated state of photon pairs, which enables real-time tunability. Developed concepts could lead to complex multi-pixel devices generating quantum light with real time tunability and therefore hold the potential to have a huge impact in the field of quantum technologies.
Abstract Liquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation 1 . The recently discovered ferroelectric nematic liquid crystals 2,3 also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics 4,5 . Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies 6 . However, spontaneous parametric down-conversion, the basic source of entangled photons 7 , heralded single photons 8 and squeezed light 9 , has so far not been observed in liquid crystals—or in any liquids or organic materials. Here we implement spontaneous parametric down-conversion in a ferroelectric nematic liquid crystal and demonstrate electric-field tunable broadband generation of entangled photons, with an efficiency comparable to that of the best nonlinear crystals. The emission rate and polarization state of photon pairs is markedly varied by applying a few volts or twisting the molecular orientation along the sample. A liquid-crystal source enables a special type of quasi-phase matching 10 , which is based on the molecular twist structure and is therefore reconfigurable for the desired spectral and polarization properties of photon pairs. Such sources promise to outperform standard nonlinear optical materials in terms of functionality, brightness and the tunability of the generated quantum state. The concepts developed here can be extended to complex topological structures, macroscopic devices and multi-pixel tunable quantum light sources.
Abstract Quantum nonreciprocity—a fundamental phenomenon enabling directional control of quantum states and photon correlations—has long been recognized as pivotal for quantum technologies. However, the experimental realization of nonreciprocal quantum photon-pair generation, as a critical prerequisite for advancing quantum systems, continues to be an outstanding challenge that remains unaddressed in practice. Here, we experimentally implement a highly-efficient nonreciprocal quantum photon source in a micro/nano-scale helical structured nonlinear optical fluid. Intriguing helical quasi-phase matching is achieved by deliberately engineering the pitch of the chiral ferroelectric structure, thus enabling spontaneous parametric down-conversion with record-high brightness (5,801.6 Hz∙mW −1 , 10,071% enhancement over phase-mismatched systems) and high coincidence-to-accidental ratio, rivaling state-of-the-art centimeter-scale nonlinear crystals. In particular, by tailoring the ferroelectric helix structure with orthogonally aligned head and tail polarization vectors, we demonstrate up to 22.6 dB isolation in biphoton generation coupled with nonreciprocal quantum polarization states, while maintaining classical optical reciprocity . This quantum liquid-crystal-based platform, combining flexible tunability and superior performance of purely quantum nonreciprocity at micro/nano scales, builds a bridge between a wide range of soft-matter systems, nonreciprocal physics, and emerging quantum photonic technologies.
Quantum nonreciprocity-a fundamental phenomenon enabling directional control of quantum states and photon correlations-has long been recognized as pivotal for quantum technologies. However, the experimental realization of nonreciprocal quantum photon-pair generation, as a critical prerequisite for advancing quantum systems, continues to be an outstanding challenge that remains unaddressed in practice. Here, we experimentally implement a highly-efficient nonreciprocal quantum photon source in a micro/nano-scale helical structured nonlinear optical fluid. Intriguing helical quasi-phase matching is achieved by deliberately engineering the pitch of the chiral ferroelectric structure, thus enabling spontaneous parametric down-conversion with record-high brightness (5,801.6 Hz*mW-1, 10,071% enhancement over phase-mismatched systems) and high coincidence-to-accidental ratio, rivaling state-of-the-art centimeter-scale nonlinear crystals. In particular, by tailoring the ferroelectric helix structure with orthogonally aligned head and tail polarization vectors, we demonstrate up to 22.6 dB isolation in biphoton generation coupled with nonreciprocal quantum polarization states, while maintaining classical optical reciprocity. This quantum liquid-crystal-based platform, combining flexible tunability and superior performance of purely quantum nonreciprocity at micro/nano scales, builds a bridge between a wide range of soft-matter systems, nonreciprocal physics, and emerging quantum photonic technologies.
For high-intensity photon pair generation via spontaneous parametric down-conversion, phase matching or quasi-phase-matching must be realized. The most common method is to use periodically poled crystals, where quasi-phase-matching is achieved through the periodic modulation of the nonlinear susceptibility. In contrast to solid-state materials typically employed, an alternative approach is demonstrated here by using chiral ferroelectric nematic liquid crystals (FNLCs). It involves the spontaneous formation of a twisted periodic arrangement of liquid crystal molecules that depends only on the concentration of chiral dopants. This enables the rapid and scalable fabrication of nonlinear optical media with a tunable periodicity of the structure. We show that within only 20 µ m , we can enhance the signal by 2 orders of magnitude compared to the maximal achievable rate for the non-phase-matched case. This process enables us to achieve a significantly enhanced photon pair generation rate of over 1200 Hz/mW in a very short interaction length while simultaneously maintaining a high degree of polarization entanglement. These results establish chiral FNLCs as a versatile, reconfigurable, and low-cost platform for nonlinear and quantum photonics.