@inproceedings{43192,
  abstract     = {{The nonlinear optical response of an ensemble of semiconductor quantum dots is analyzed by wave-mixing processes, where we focus on four-wave mixing with two incident pulses. Wave-mixing experiments are often described with semiclassical models, where the light is modeled classically and the material quantum mechanically. Here, however, we use a fully quantized model, where the light is given by a quantum state of light. Quantum light involves more degrees of freedom than classical light as e.g., its photon statistics and quantum correlations, which is a promising resource for quantum devices, such as quantum memories. The light-matter interaction is treated with a Jaynes-Cummings type model and the quantum field is given by a single mode since the quantum dots are embedded in a microcavity. We present numerical simulations of the four-wave-mixing response of a homogeneous system for pulse sequences and find a significant dependence of the result on the photon statistics of the incident pulses. The model constitutes a problem with a large state space which arises from the frequency distribution of the transition energies of the inhomogeneously broadened quantum dot ensemble that is coupled with a quantum light mode. Here we approximate the dynamics by summing over individual quantum dot-microcavity systems. Photon echoes arising from the excitation with different quantum states of light are simulated and compared.}},
  author       = {{Rose, Hendrik and Grisard, S. and Trifonov, A. V. and Reichhardt, R. and Reichelt, Matthias and Bayer, M. and Akimov, I. A.  and Meier, Torsten}},
  booktitle    = {{Ultrafast Phenomena and Nanophotonics XXVII}},
  publisher    = {{SPIE}},
  title        = {{{Theoretical analysis of four-wave mixing on semiconductor quantum dot ensembles with quantum light}}},
  doi          = {{10.1117/12.2647700}},
  volume       = {{12419}},
  year         = {{2023}},
}

@article{45868,
  abstract     = {{Perfect vector vortex beams (PVVBs) have attracted considerable interest due to their peculiar optical features. PVVBs are typically generated through the superposition of perfect vortex beams, which suffer from the limited number of topological charges (TCs). Furthermore, dynamic control of PVVBs is desirable and has not been reported. We propose and experimentally demonstrate hybrid grafted perfect vector vortex beams (GPVVBs) and their dynamic control. Hybrid GPVVBs are generated through the superposition of grafted perfect vortex beams with a multifunctional metasurface. The generated hybrid GPVVBs possess spatially variant rates of polarization change due to the involvement of more TCs. Each hybrid GPVVB includes different GPVVBs in the same beam, adding more design flexibility. Moreover, these beams are dynamically controlled with a rotating half waveplate. The generated dynamic GPVVBs may find applications in the fields where dynamic control is in high demand, including optical encryption, dense data communication, and multiple particle manipulation.}},
  author       = {{Ahmed, Hammad and Ansari, Muhammad Afnan and Li, Yan and Zentgraf, Thomas and Mehmood, Muhammad Qasim and Chen, Xianzhong}},
  issn         = {{2041-1723}},
  journal      = {{Nature Communications}},
  keywords     = {{General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry, Multidisciplinary}},
  number       = {{1}},
  publisher    = {{Springer Science and Business Media LLC}},
  title        = {{{Dynamic control of hybrid grafted perfect vector vortex beams}}},
  doi          = {{10.1038/s41467-023-39599-8}},
  volume       = {{14}},
  year         = {{2023}},
}

@article{45850,
  abstract     = {{Interference between single photons is key for many quantum optics experiments and applications in quantum technologies, such as quantum communication or computation. It is advantageous to operate the systems at telecommunication wavelengths and to integrate the setups for these applications in order to improve stability, compactness and scalability. A new promising material platform for integrated quantum optics is lithium niobate on insulator (LNOI). Here, we realise Hong-Ou-Mandel (HOM) interference between telecom photons from an engineered parametric down-conversion source in an LNOI directional coupler. The coupler has been designed and fabricated in house and provides close to perfect balanced beam splitting. We obtain a raw HOM visibility of (93.5 ± 0.7) %, limited mainly by the source performance and in good agreement with off-chip measurements. This lays the foundation for more sophisticated quantum experiments in LNOI.}},
  author       = {{Babel, Silia and Bollmers, Laura and Massaro, Marcello and Luo, Kai Hong and Stefszky, Michael and Pegoraro, Federico and Held, Philip and Herrmann, Harald and Eigner, Christof and Brecht, Benjamin and Padberg, Laura and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{14}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Demonstration of Hong-Ou-Mandel interference in an LNOI directional coupler}}},
  doi          = {{10.1364/oe.484126}},
  volume       = {{31}},
  year         = {{2023}},
}

@inproceedings{34138,
  abstract     = {{Variational Quantum Algorithms (VQAs), such as the Quantum Approximate
Optimization Algorithm (QAOA) of [Farhi, Goldstone, Gutmann, 2014], have seen
intense study towards near-term applications on quantum hardware. A crucial
parameter for VQAs is the depth of the variational ansatz used - the smaller
the depth, the more amenable the ansatz is to near-term quantum hardware in
that it gives the circuit a chance to be fully executed before the system
decoheres. This potential for depth reduction has made VQAs a staple of Noisy
Intermediate-Scale Quantum (NISQ)-era research.
  In this work, we show that approximating the optimal depth for a given VQA
ansatz is intractable. Formally, we show that for any constant $\epsilon>0$, it
is QCMA-hard to approximate the optimal depth of a VQA ansatz within
multiplicative factor $N^{1-\epsilon}$, for $N$ denoting the encoding size of
the VQA instance. (Here, Quantum Classical Merlin-Arthur (QCMA) is a quantum
generalization of NP.) We then show that this hardness persists even in the
"simpler" setting of QAOAs. To our knowledge, this yields the first natural
QCMA-hard-to-approximate problems. To achieve these results, we bypass the need
for a PCP theorem for QCMA by appealing to the disperser-based NP-hardness of
approximation construction of [Umans, FOCS 1999].}},
  author       = {{Bittel, Lennart and Gharibian, Sevag and Kliesch, Martin}},
  booktitle    = {{Proceedings of the 38th Computational Complexity Conference (CCC)}},
  number       = {{34}},
  pages        = {{34:1--34:24}},
  title        = {{{The Optimal Depth of Variational Quantum Algorithms Is QCMA-Hard to Approximate}}},
  doi          = {{10.4230/LIPIcs.CCC.2023.34}},
  volume       = {{264}},
  year         = {{2023}},
}

@article{46138,
  abstract     = {{<jats:p>This work reports a fully guided setup for single-mode squeezing on integrated titanium-indiffused periodically poled nonlinear resonators. A continuous-wave laser beam is delivered and the squeezed field is collected by single-mode fibers; up to −3.17(9) dB of useful squeezing is available in fibers. To showcase the usefulness of such a fiber-coupled device, we applied the generated squeezed light in a fiber-based phase sensing experiment, showing a quantum enhancement in the signal-to-noise ratio of 0.35 dB. Moreover, our investigation of the effect of photorefraction on the cavity resonance condition suggests that it causes system instabilities at high powers.</jats:p>}},
  author       = {{Domeneguetti, Renato and Stefszky, Michael and Herrmann, Harald and Silberhorn, Christine and Andersen, Ulrik L. and Neergaard-Nielsen, Jonas S. and Gehring, Tobias}},
  issn         = {{0146-9592}},
  journal      = {{Optics Letters}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{11}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Fully guided and phase locked Ti:PPLN waveguide squeezing for applications in quantum sensing}}},
  doi          = {{10.1364/ol.486654}},
  volume       = {{48}},
  year         = {{2023}},
}

@inproceedings{46485,
  abstract     = {{We present a miniaturized pulse shaping device that creates an arbitrary dispersion through the interaction of multiple metasurfaces on less than 2 mm<jats:sup>3</jats:sup> volume. For this, a metalens and a grating-metasurface between two silver mirrors are fabricated. The grating contains further phase information to achieve the device's pulse shaping functionality.}},
  author       = {{Geromel, René and Georgi, Philip and Protte, Maximilian and Bartley, Tim and Huang, Lingling and Zentgraf, Thomas}},
  booktitle    = {{CLEO: Fundamental Science 2023}},
  location     = {{San Jose, USA}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Dispersion control with integrated plasmonic metasurfaces}}},
  doi          = {{10.1364/cleo_fs.2023.fth4d.3}},
  year         = {{2023}},
}

@inbook{47543,
  author       = {{Zentgraf, Thomas and Sain, Basudeb and Zhang, Shuang}},
  booktitle    = {{Fundamentals and Applications of Nonlinear Nanophotonics}},
  editor       = {{Panoiu, Nicoae C.}},
  isbn         = {{978-0-323-90614-2}},
  publisher    = {{Elsevier}},
  title        = {{{Symmetry governed nonlinear selection rules in nanophotonics }}},
  doi          = {{10.1016/B978-0-323-90614-2.00011-0}},
  year         = {{2023}},
}

@inproceedings{43051,
  abstract     = {{We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.}},
  author       = {{Farheen, Henna and Yan, Lok-Yee and Leuteritz, Till and Qiao, Siqi and Spreyer, Florian and Schlickriede, Christian and Quiring, Viktor and Eigner, Christof and Silberhorn, Christine and Zentgraf, Thomas and Linden, Stefan and Myroshnychenko, Viktor and Förstner, Jens}},
  booktitle    = {{Integrated Optics: Devices, Materials, and Technologies XXVII}},
  editor       = {{García-Blanco, Sonia M. and Cheben, Pavel}},
  keywords     = {{tet_topic_opticalantenna}},
  pages        = {{124241E}},
  publisher    = {{SPIE}},
  title        = {{{Tailoring the directive nature of optical waveguide antennas}}},
  doi          = {{10.1117/12.2658921}},
  year         = {{2023}},
}

@article{40513,
  abstract     = {{Geometric-phase dielectric meta-lenses made of silicon with high numerical aperture and short focal lengths are fabricated and characterised. For circularly polarised light, the same meta-lens can act as a converging or diverging lens, depending on the handedness of the circular polarisation. This effect enables application for optical tweezers that trap or release µm-size polymer beads floating in a microfluidic channel on demand. An electrically addressable polarisation converter based on liquid crystals may be used to switch between the two states of polarisation, at which the light transmitted through the meta-lens is focused (trapping) or defocussed (releasing), respectively.}},
  author       = {{Geromel, René and Rennerich, Roman and Zentgraf, Thomas and Kitzerow, Heinz-Siegfried}},
  journal      = {{Liquid Crystals}},
  number       = {{7-10}},
  pages        = {{1193--1203}},
  publisher    = {{Taylor & Francis}},
  title        = {{{Geometric-phase metalens to be used for tunable optical tweezers in microfluidics}}},
  doi          = {{10.1080/02678292.2023.2171146}},
  volume       = {{50}},
  year         = {{2023}},
}

@article{55900,
  author       = {{Scharwald, Dennis and Meier, Torsten and Sharapova, Polina}},
  issn         = {{2643-1564}},
  journal      = {{Physical Review Research}},
  number       = {{4}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Phase sensitivity of spatially broadband high-gain SU(1,1) interferometers}}},
  doi          = {{10.1103/physrevresearch.5.043158}},
  volume       = {{5}},
  year         = {{2023}},
}

@article{31059,
  abstract     = {{In this article we prove meromorphic continuation of weighted zeta functions in the framework of open hyperbolic systems by using the meromorphically continued restricted resolvent of Dyatlov and Guillarmou (2016). We obtain a residue formula proving equality between residues of weighted zetas and invariant Ruelle distributions. We combine this equality with results of Guillarmou, Hilgert and Weich (2021) in order to relate the residues to Patterson-Sullivan distributions. Finally we provide proof-of-principle results concerning the numerical calculation of invariant Ruelle distributions for 3-disc scattering systems.}},
  author       = {{Schütte, Philipp and Weich, Tobias and Barkhofen, Sonja}},
  journal      = {{Communications in Mathematical Physics}},
  pages        = {{655--678}},
  title        = {{{Meromorphic Continuation of Weighted Zeta Functions on Open Hyperbolic Systems}}},
  doi          = {{https://doi.org/10.1007/s00220-022-04538-z}},
  volume       = {{398}},
  year         = {{2023}},
}

@article{61252,
  abstract     = {{<jats:title>Abstract</jats:title><jats:p>The biexciton‐exciton emission cascade commonly used in quantum‐dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work, it focuses on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishability. It achieves this goal by selectively reducing the biexciton lifetime with an optical resonator. It demonstrates that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and twofold degenerate optical modes. The in‐depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum‐dot cavity excitation dynamics with full access to photon properties. It reports non‐trivial dependencies on system parameters and use the predictive power of the combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values, here specifically for the telecom C‐band at 1550 nm.</jats:p>}},
  author       = {{Bauch, David and Siebert, Dustin and Jöns, Klaus D. and Förstner, Jens and Schumacher, Stefan}},
  issn         = {{2511-9044}},
  journal      = {{Advanced Quantum Technologies}},
  number       = {{1}},
  publisher    = {{Wiley}},
  title        = {{{On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs}}},
  doi          = {{10.1002/qute.202300142}},
  volume       = {{7}},
  year         = {{2023}},
}

@article{61266,
  abstract     = {{<jats:p>This review examines the use of continuous-variable spectroscopy techniques for investigating quantum coherence and light-matter interactions in semiconductor systems with ultrafast dynamics. Special emphasis is placed on multichannel homodyne detection as a powerful tool to measure the quantum coherence and the full density matrix of a polariton system. Observations, such as coherence times that exceed the nanosecond scale obtained by monitoring the temporal decay of quantum coherence in a polariton condensate, are discussed. Proof-of-concept experiments and numerical simulations that demonstrate the enhanced resourcefulness of the produced system states for modern quantum protocols are assessed. The combination of tailored resource quantifiers and ultrafast spectroscopy techniques that have recently been demonstrated paves the way for future applications of quantum information technologies.</jats:p>}},
  author       = {{Lüders, Carolin and Barkhausen, Franziska and Pukrop, Matthias and Rozas, Elena and Sperling, Jan and Schumacher, Stefan and Aßmann, Marc}},
  issn         = {{2159-3930}},
  journal      = {{Optical Materials Express}},
  number       = {{11}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Continuous-variable quantum optics and resource theory for ultrafast semiconductor spectroscopy [Invited]}}},
  doi          = {{10.1364/ome.497006}},
  volume       = {{13}},
  year         = {{2023}},
}

@article{38541,
  author       = {{Barkhofen, Sonja and Brecht, Benjamin and Silberhorn, Christine}},
  journal      = {{Physik in unserer Zeit}},
  number       = {{1}},
  pages        = {{10--11}},
  publisher    = {{Wiley}},
  title        = {{{Verschränkung wie am Fließband}}},
  doi          = {{https://doi.org/10.1002/piuz.202370107}},
  volume       = {{54}},
  year         = {{2023}},
}

@article{36471,
  abstract     = {{<jats:p>Superconducting nanowire single-photon detectors (SNSPDs) show near unity efficiency, low dark count rate, and short recovery time. Combining these characteristics with temporal control of SNSPDs broadens their applications as in active de-latching for higher dynamic range counting or temporal filtering for pump-probe spectroscopy or LiDAR. To that end, we demonstrate active gating of an SNSPD with a minimum off-to-on rise time of 2.4 ns and a total gate length of 5.0 ns. We show how the rise time depends on the inductance of the detector in combination with the control electronics. The gate window is demonstrated to be fully and freely, electrically tunable up to 500 ns at a repetition rate of 1.0 MHz, as well as ungated, free-running operation. Control electronics to generate the gating are mounted on the 2.3 K stage of a closed-cycle sorption cryostat, while the detector is operated on the cold stage at 0.8 K. We show that the efficiency and timing jitter of the detector is not altered during the on-time of the gating window. We exploit gated operation to demonstrate a method to increase in the photon counting dynamic range by a factor 11.2, as well as temporal filtering of a strong pump in an emulated pump-probe experiment.</jats:p>}},
  author       = {{Hummel, Thomas and Widhalm, Alex and Höpker, Jan Philipp and Jöns, Klaus and Chang, Jin and Fognini, Andreas and Steinhauer, Stephan and Zwiller, Val and Zrenner, Artur and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{1}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Nanosecond gating of superconducting nanowire single-photon detectors using cryogenic bias circuitry}}},
  doi          = {{10.1364/oe.472058}},
  volume       = {{31}},
  year         = {{2023}},
}

@article{63043,
  abstract     = {{Spatial modes of light have become highly attractive to increase the dimension and, thereby, security and information capacity in quantum key distribution (QKD). So far, only transverse electric field components have been considered, while longitudinal polarization components have remained neglected. Here, we present an approach to include all three spatial dimensions of electric field oscillation in QKD by implementing our tunable, on-a-chip vector beam decoder (VBD). This inversely designed device pioneers the "preparation" and "measurement" of three-dimensionally polarized mutually unbiased basis states for high-dimensional (HD) QKD and paves the way for the integration of HD QKD with spatial modes in multifunctional on-a-chip photonics platforms.}},
  title        = {{{Tunable vector beam decoder by inverse design for high-dimensional quantum key distribution with 3D polarized spatial modes}}},
  doi          = {{10.48550/ARXIV.2304.12296}},
  year         = {{2023}},
}

@inproceedings{45578,
  abstract     = {{A frequency-flexible Nyquist pulse synthesizer is presented with optical pulse bandwidths up to fopt=100 GHz and repetition rates equal to fopt/9, fabricated in an electronic-photonic co-integrated platform utilizing linear on-chip drivers.}},
  author       = {{Kress, Christian and Schwabe, Tobias and Silberhorn, Christine and Scheytt, J. Christoph}},
  booktitle    = {{ Conference on Lasers and Electro-Optics (CLEO) 2023}},
  location     = {{San Jose, CA, USA}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Generation of 100 GHz Periodic Nyquist Pulses using Cascaded Mach-Zehnder Modulators in a Silicon Electronic-Photonic Platform}}},
  doi          = {{https://doi.org/10.1364/CLEO_SI.2023.SF1P.6}},
  year         = {{2023}},
}

@article{46468,
  author       = {{Lange, Nina Amelie and Schapeler, Timon and Höpker, Jan Philipp and Protte, Maximilian and Bartley, Tim}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{2}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Degenerate photons from a cryogenic spontaneous parametric down-conversion source}}},
  doi          = {{10.1103/physreva.108.023701}},
  volume       = {{108}},
  year         = {{2023}},
}

@article{44081,
  author       = {{Serino, Laura and Gil López, Jano and Stefszky, Michael and Ricken, Raimund and Eigner, Christof and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{2691-3399}},
  journal      = {{PRX Quantum}},
  keywords     = {{General Physics and Astronomy, Mathematical Physics, Applied Mathematics, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, General Computer Science}},
  number       = {{2}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Realization of a Multi-Output Quantum Pulse Gate for Decoding High-Dimensional Temporal Modes of Single-Photon States}}},
  doi          = {{10.1103/prxquantum.4.020306}},
  volume       = {{4}},
  year         = {{2023}},
}

@article{42648,
  abstract     = {{In real photonic quantum systems losses are an unavoidable factor limiting the scalability to many modes and particles, restraining their application in fields as quantum information and communication. For this reason, a considerable amount of engineering effort has been taken in order to improve the quality of particle sources and system components. At the same time, data analysis and collection methods based on post-selection have been used to mitigate the effect of particle losses. This has allowed for investigating experimentally multi-particle evolutions where the observer lacks knowledge about the system's intermediate propagation states. Nonetheless, the fundamental question how losses affect the behaviour of the surviving subset of a multi-particle system has not been investigated so far. For this reason, here we study the impact of particle losses in a quantum walk of two photons reconstructing the output probability distributions for one photon conditioned on the loss of the other in a known mode and temporal step of our evolution network. We present the underlying theoretical scheme that we have devised in order to model controlled particle losses, we describe an experimental platform capable of implementing our theory in a time multiplexing encoding. In the end we show how localized particle losses change the output distributions without altering their asymptotic spreading properties. Finally we devise a quantum civilization problem, a two walker generalisation of single particle recurrence processes.}},
  author       = {{Pegoraro, Federico and Held, Philip and Barkhofen, Sonja and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{0031-8949}},
  journal      = {{Physica Scripta}},
  number       = {{3}},
  publisher    = {{IOP Publishing}},
  title        = {{{Dynamic conditioning of two particle discrete-time quantum walks}}},
  doi          = {{10.1088/1402-4896/acbcaa}},
  volume       = {{98}},
  year         = {{2023}},
}