Multiple-scattering has become an exciting platform for quantum optical experiments [1-5]. In wavefront shaping one uses spatial light modulation in combination with strongly scattering materials to achieve control over light in space and time [6]. Recent wavefront-shaping experiments have transformed opaque media in equivalents of waveguides, lenses, waveplates and optical pulse compressors that are inherently robust against disorder and imaging errors. In quantum optics, interference of quantum states is studied in often complicated optical circuits. This requires a close-to-perfect implementation of the setup and provides little flexibility or programmability of the interference. We implement the radically different approach to apply wavefront shaping on quantum light to obtain ample flexibility in optimization and manipulation of the quantum interference. This offers unique opportunities for sample characterization, quantum patterning, secure key generation, or quantum transport through disordered media.
Multiple-scattering has become an exciting platform for quantum optical experiments [1-5]. In wavefront shaping one uses spatial light modulation in combination with strongly scattering materials to achieve control over light in space and time [6]. Recent wavefront-shaping experiments have transformed opaque media in equivalents of waveguides, lenses, waveplates and optical pulse compressors that are inherently robust against disorder and imaging errors. In quantum optics, interference of quantum states is studied in often complicated optical circuits. This requires a close-to-perfect implementation of the setup and provides little flexibility or programmability of the interference. We implement the radically different approach to apply wavefront shaping on quantum light to obtain ample flexibility in optimization and manipulation of the quantum interference. This offers unique opportunities for sample characterization, quantum patterning, secure key generation, or quantum transport through disordered media.
Wavefront shaping allows for ultimate control of light propagation in multiple-scattering media by adaptive manipulation of incident waves. We have demonstrated a method to program general multiport linear optical circuits in multiple-scattering materials by phase modulation of incident wavefronts. Applying this method to quantum light makes it possible to use these optical circuits for adaptive quantum optical experiments, with high flexibility in the control of quantum interference between multiple optical modes. To this end we have constructed a bright single-photon source, producing heralded single-photon states with a measured production rate of > 106 s−1. We have demonstrated that we are able to control the propagation of these single-photon states in random-scattering media, and we are currently investigating Hong-Ou-Mandel interference in these circuits.
Wavefront shaping enables control of classical light through scattering media. Extending these techniques to spatially entangled photons promises new quantum applications, but their fundamental limits, especially when both photons scatter, remain unclear. Here, we theoretically and numerically investigate the enhancement of two-photon correlations through thick scattering media. We analyze configurations where a spatial light modulator shapes one or both photons, either before or after the medium, and show that the optimal enhancement differs fundamentally from classical expectations. For a system with N modes, we show that shaping one photon yields the classical enhancement η≈(π/4)N, while shaping both photons before the medium reduces it to η≈(π/4)2N. However, in some symmetric detection schemes, when both photons are measured at the same mode, perfect correlations are restored with η≈N, resembling digital optical phase conjugation. Conversely, shaping both photons after the medium leads to a complex, NP-hard-like optimization problem, yet achieves superior enhancements, up to η≈4.6N. These results reveal unique quantum effects in complex media and identify strategies for quantum imaging and communication through scattering environments.
This study falls within the emerging field of quantum optics in scattering media. By employing wavefront shaping, researchers successfully transmitted spatially entangled photon pairs through scattering media, mitigating optical disturbances by wavefront shaping. They maintained entanglement with a dimensionality of 17 after propagation, opening avenues for applications in quantum microscopy and quantum communication. Interestingly, this work also shows that in certain cases, quantum entanglement can be transmitted through a complex medium, while classical light remains scattered.
Quantum interference of indistinguishable photons is the foundation of photonic quantum technologies, yet scaling from a few to many identical quantum light sources remains a major challenge. In solid-state platforms, spatial and spectral inhomogeneity and resource-intensive architectures impede scaling. As a result, interference between remote, independent quantum emitters has been thus far limited to pairs. Here we introduce a wavefront-shaping approach that enables scalable interference from multiple indistinguishable quantum dots on the same chip. Using programmable spatial light modulators, we independently excite, collect, and route emission from spatially distinct, yet spectrally degenerate dots. Scaling from two to five indistinguishable emitters, we verify interference through cooperative-emission phenomena and Hong-Ou-Mandel two-photon interference, thereby establishing a route towards large-scale, programmable quantum photonic architectures.
Wavefront manipulation and correction using feedback-based optimization have long been employed in optical applications such as microscopy, optical sensing, astronomical imaging, and communication. With recent advances in quantum optics, wavefront correction has become a crucial tool in quantum imaging, quantum communication, and efficient photon coupling. Consequently, understanding the performance of optimization algorithms under low-photon conditions is essential for the effective deployment of quantum optical systems. This study investigates the performance of two algorithms in the photon-counting regime across varying mean photon rates through experiments and numerical simulations. Furthermore, we propose, simulate, and implement a novel, to the best of our knowledge, augmented algorithm that combines the strengths of both methods and is particularly well suited for quantum applications.
Multiphoton quantum correlations are crucial for quantum information processing and quantum communication protocols in linear optical networks. For large-scale implementation of quantum information processing, such as quantum simulators, boson sampling or programmable quantum logic gates, a programmable functionality of a large multichannel network is required. In this thesis, we describe and demonstrate programmable quantum interference between multiple single-photon states in massively multichannel networks. Using a theoretical analysis we first show that losses in optical networks, which are unavoidable in experiments, introduce new freedom, in that the functionality of the network, and thus also quantum interference in there, is programmable to an extent not possible with lossless networks. We introduce a method to program the functionality of general multichannel linear optical networks by phase modulation of incident wavefronts, which we apply to opaque scattering media as well as integrated optics. To demonstrate quantum interference in massively multichannel networks we require a source of multiple indistinguishable single-photon states. Therefore, we have constructed and characterized a versatile quantum light source based on spontaneous parametric down-conversion. For the first time, we demonstrate two-photon quantum interference in a massively multichannel linear optical network realized in an opaque scattering medium. Using adaptive phase-modulation of the incident photons, the scattering medium is transformed to behave as a fully programmable beam splitter that is freely tunable in functionality. Exploiting this freedom, we not only show the well-known Hong-Ou-Mandel bunching of photons, but also demonstrate that this bunching can be made to vanish, or be transformed into antibunching. Our results establish opaque scattering media as a platform for massively multichannel linear optical networks with programmable quantum correlations. Finally, the high number of available channels offered by opaque scattering media can directly be employed for authentication of secure communication. We present an authenticated protocol for quantum key distribution that removes the need of an initial shared secret for authentication. Moreover, we introduce and demonstrate the first protocol for authenticated and asymmetric quantum communication, based on the quantum-secure readout of a physical unclonable function.