Kasper H. Nielsen, Ying Wang, Edward C. R. Deacon, Patrik Isene Sund, Zhe Liu, Sven Scholz, Andreas Dirk Wieck, Arne Ludwig, Leonardo Midolo, Anders Søndberg Sørensen, Stefano Paesani, Peter Lodahl
The lack of interactions between single photons prohibits direct nonlinear operations in quantum optical circuits, representing a central obstacle in photonic quantum technologies. Here, we demonstrate multi-mode nonlinear photonic circuits where both linear and direct nonlinear operations can be programmed with high precision at the single-photon level. Nonlinear interaction is realised with a tunable quantum dot embedded in a nanophotonic waveguide mediating interactions between individual photons within a temporal linear optical interferometer. We demonstrate the capability to reprogramme the nonlinear photonic circuits and implement protocols where strong nonlinearities are required, in particular for quantum simulation of anharmonic molecular dynamics, thereby showcasing the new key functionalities enabled by our technology. Adding tunable photon-photon nonlinearities to programmable photonic circuits would greatly extend their capabilities. Here, the authors demonstrate this by embedding a photonic-crystal waveguide nanostructure hosting an InAs quantum dot within a programmable linear optical circuit, and using it to realise a proof-of-concept quantum simulation of anharmonic molecular vibrational dynamics.
The lack of interactions between single photons prohibits direct nonlinear operations in quantum optical circuits, representing a central obstacle in photonic quantum technologies. Here, we demonstrate multi-mode nonlinear photonic circuits where both linear and direct nonlinear operations can be programmed with high precision at the single-photon level. Nonlinear interaction is realised with a tunable quantum dot embedded in a nanophotonic waveguide mediating interactions between individual photons within a temporal linear optical interferometer. We demonstrate the capability to reprogramme the nonlinear photonic circuits and implement protocols where strong nonlinearities are required, in particular for quantum simulation of anharmonic molecular dynamics, thereby showcasing the new key functionalities enabled by our technology. Adding tunable photon-photon nonlinearities to programmable photonic circuits would greatly extend their capabilities. Here, the authors demonstrate this by embedding a photonic-crystal waveguide nanostructure hosting an InAs quantum dot within a programmable linear optical circuit, and using it to realise a proof-of-concept quantum simulation of anharmonic molecular vibrational dynamics.
Light-matter interaction at the quantum level provides a versatile interface driving photonic quantum technologies toward practical applications. We demonstrate multi-mode photonic circuits that enable precise programming of linear and nonlinear phase configurations at the single-photon level. The nonlinearity operation is realized using a solid-state quantum emitter, a self-assembled quantum dot, integrated into a nanophotonic device. The quantum dot interfaces with a temporal linear optical interferometer, creating a programmable nonlinear photonic platform that is necessary for implementing quantum protocols that require strong nonlinearities, such as the quantum simulation of anharmonic molecular dynamics.
The generation of indistinguishable single photons and control of photon-photon interactions are key requirements for photonic quantum networks. Nano-photonic waveguide-based architectures, in which few-level solid state systems provide both single photon generation and the nonlinearity through which two or more photons interact, offer a scalable route to such networks. However, it is a challenge to maintain the optical quality of the embedded photon sources whilst also providing fine-tuning of the emission frequency and optical nonlinearity in a waveguide geometry. We demonstrate a tunable solid-state platform for scalable photonic quantum networks which allows local electrical control of both single photon generation and optical nonlinearity at the single photon level. Electrical tuning and switching of coherent photon scattering from a quantum dot embedded in a nano-photonic waveguide is demonstrated, with a transmission extinction as large as 40±2% measured on resonance. Observation of a clear, voltage-controlled bunching signal in the photon statistics of the transmitted light demonstrates the single photon character of the nonlinearity. The deterministic nature of the nonlinearity is particularly attractive for the future realization of photonic gates for scalable nano-photonic waveguide-based quantum information processing.
At the quantum limit of nonlinear optics, where single photons interact with individual emitters, new phenomena are found. One-dimensional, subwavelength waveguides have recently emerged as a promising quantum optical platform capable of both guiding and confining photons, leading to efficient light-matter interactions and enhancing quantum optical nonlinearities. We explore this regime using both single organic molecules and epitaxially grown quantum dots coupled to nanoscale waveguides. In the first case, two-color experiments allow us to observe distinctly quantum nonlinearities such as Stark shifts of the molecular resonances or amplification without population inversion, although we are limited by relatively weak molecule-waveguide coupling. In contrast, quantum dots can be nearly perfectly coupled to waveguides, allowing us to demonstrate optical nonlinearities at the true single photon level. These, as we discuss, can be used as a basis for novel on-chip quantum technologies.
Abstract : Photons play a central role in many areas of quantum information processing and quantum sensing, ranging from linear optics quantum computing and quantum simulation to quantum communications. A central problem in many of these applications is the need to control many spatial and temporal modes with high efficiency and precision. Photonic integrated circuits can contain closely-spaced and extremely phase-stable components that enable precision control of many spatial and temporal modes in dielectric waveguides. This program developed photonic integrated circuits (PICs) based on the silicon-on-insulator platform. We developed large-scale PICs with cascaded Mach-Zehnder interferometers (MZI) with precision electro-optic modulators. These PICs have very low internal losses (0.1 dB/MZI) and achieve exceptionally high contrast interference ( 80 dB) over tens of spatial modes. These fully programmable mode transformers have driven experimental and theoretical advances in quantum simulation, cluster-state quantum computing, all-optical quantum repeaters, neuromorphic computing, and other applications. In addition, we developed new schemes for ballistic quantum computation, new methods for high-efficiency single photon sources, a new approach for 3-photon cluster state generation that forms the essential ingredient for percolation-based generation of scalable cluster states, and quantum logic gates based on weak optical nonlinearities.
Programmable photonic integrated circuits are emerging as increasingly large and versatile interferometric processors operating at room temperature. However, their native operations are linear, while many computational tasks require nonlinear input-output transformations that typically rely on nonlinear optical materials or resonant devices. Here, we establish a direct mapping between quantum signal processing (QSP) and the native two-mode operations of programmable interferometric photonic integrated circuits, showing that the SU(2) structure required by QSP can be realized through programmable phase control and mode mixing. We experimentally demonstrate this correspondence using dual-rail single-photon encoding on a 24-mode programmable photonic integrated circuit, realizing QSP sequences up to depth L=11 and synthesizing STEP, ReLU and SELU functions through programmable phase control. The optical transformation remains linear, while repeated encoding of the input variable and coherent interference produce a nonlinear dependence of the output probabilities on the encoded variable. Across all accessible circuit depths, the measured responses follow the programmed QSP transformations, with hardware-induced mean squared errors between 10−3 and 10−2, all remaining below the intrinsic finite-depth approximation error. These results establish an algorithm-to-hardware mapping of QSP on programmable photonic processors. They also demonstrate an algorithmic route to programmable nonlinear functions of encoded variables on linear photonic hardware.
Quantum photonics is a rapidly developing platform for future quantum network applications. Waveguide-based architectures, in which embedded quantum emitters act as both nonlinear elements to mediate photon–photon interactions and as highly coherent single-photon sources, offer a highly promising route to realize such networks. A key requirement for the scale-up of the waveguide architecture is local control and tunability of individual quantum emitters. Here, we demonstrate electrical control, tuning, and switching of the nonlinear photon–photon interaction arising due to a quantum dot embedded in a single-mode nano-photonic waveguide. A power-dependent waveguide transmission extinction as large as 40±2% is observed on resonance. Photon statistics measurements show clear, voltage-controlled bunching of the transmitted light and antibunching of the reflected light, demonstrating the single-photon, quantum character of the nonlinearity. Importantly, the same architecture is also shown to act as a source of highly coherent, electrically tunable single photons. Overall, the platform presented addresses the essential requirements for the implementation of photonic gates for scalable nano-photonic-based quantum information processing.