# program

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• #### 25 October

• P. Schnauber, J. Schall, S. Bounouar, T. Höhne, A. Singh, K. Sirinvasan, M. Davanco, J.-D. Song, S. Burger, S. Rodt, S. Reitzenstein
The deterministic integration of quantum emitters into on-chip photonic elements is crucial for the implementation of scalable on-chip quantum circuits. Recent activities in this field include hybrid QD-waveguides for enhanced photon in-coupling and the controlled integration of QDs using multistep-lithography as well as AFM tip transfer. Here, we report on the deterministic integration of single quantum dots (QD) into on-chip beam splitters using in-situ electron beam lithography (EBL). In this advanced single-step technique, photonic building blocks are patterned on top of chosen QDs immediately after spatial and spectral pre-characterization via cathodoluminescence mapping at 10 K. To realize 50/50 coupling elements, we chose tapered multimode interference (MMI) splitters which feature relaxed fabrication tolerances and robust 50/50 splitting ratio. We demonstrate the functionality of the deterministic QD-waveguide structures by µPL spectroscopy and by studying the photon cross-correlation between the two MMI output ports. The latter confirms single-photon emission and on-chip splitting associated with g(2)(0) ≪ 0.5. Moreover, the deterministic integration of QDs enables the demonstration and controlled study of chiral light-matter effects and directional emission in QD-WGs, as well as the realization of low loss heterogenous QD-WG systems with excellent quantum optical properties in terms of high photon purity and high photon indistinguishability.
Source

• Alessandro Fedrizzi, Francesco Graffitti, Peter Barrow, Alexander Pickston, Massimiliano Proietti, Dmytro Kundys and Agata Branczyk
Frequency encoding of photonic quantum bits allows for denser information storage and thus more robust and powerful quantum information protocols. Here we report the direct generation of pulsed temporal entanglement between photons created in a single-pass parametric downconversion experiment. Tailoring specific time-frequency Schmidt modes typically requires specific phase-matching conditions and pulse shapers. We show that nonlinear crystal domain engineering can be used to generate exact time-frequency modes with exceptional quality and verify the generated entanglement via dispersion spectroscopy and two-photon interference. We demonstrate time-frequency entanglement swapping between independently created photons using this method.
Source

• Sofiane Haffouz, Philip J. Poole, Katharina D. Zeuner, Dan Dalacu, Jeongwan Jin, Lambert Giner, Xiaohua Wu, Khaled Mnaymneh, Jean Lapointe, Val Zwiller and Robin L. Williams
We report on the site-selected growth of single InAsP quantum dots embedded within InP photonic nanowires with unprecedented tuning range from 880 nm to 1550 nm by modifying the dot growth conditions. As an example, high purity single photon source at 1310 nm with low multiphoton emission probability is demonstrated. Alternative approach to achieve light emission in the telecom band where we grow the single InAsxP1-x quantum dot in an InAsyP1-y quantum rod, all embedded in the InP nanowire waveguide will be presented. With this dot-in-a-rod configuration, the 1310 nm-emitter emission intensity was increased from 275,000 cps to 613,000 cps.
Source

• Tina Müller, Matthew Anderson, Jan Huwer, Joanna Skiba-Szymanska, Andrey Krysa, Mark Stevenson, Jon Heffernan, David Ritchie and Andrew Shields
Quantum network technologies rely on interference of indistinguishable photons, demanding sources of highly coherent single photons, with ideal wavelength around 1550 nm for fibre-based applications. Recently, emission of single and entangled photons from semiconductor sources in that band has been reported, but demonstration of sufficiently long coherence times has been outstanding. We show that InAs/InP quantum dots emitting in the telecom C-band can provide photons with coherence times exceeding 1 ns. These values enable near-optimal interference of quantum dot emission with a C-band laser qubit. Using entangled photons we further demonstrate teleportation of such qubits with a fidelity reaching 83.6±2.2%.
Source

• The goal of demonstrating a quantum advantage with currently available technology is an outstanding challenge in quantum information science. Here we discuss examples of such rigorous demonstration of advantage in security and communication efficiency due to the use of quantum resources for useful applications in the context of quantum networks, including quantum cryptographic tasks beyond key distribution and quantum communication complexity. This requires devising novel protocols amenable to experimental implementations, which typically involve encoding in properties of coherent states of light, linear optic circuits and single-photon detection. We further discuss the extension of our results in quantum
Applications

• Kejin Wei, Nora Tischler, Si-Ran Zhao, Yu-Huai Li, Juan Miguel Arrazola, Yang Liu, Weijun Zhang, Hao Li, Lixing You, Zhen Wang, Yu-Ao Chen, Barry Sanders, Qiang Zhang, Geoff Pryde, Feihu Xu and Jian-Wei Pan
We experimentally demonstrate exponentially superior quantum communication complexity by realizing a superposition of communication directions for a two-party distributed computation. Our photonic demonstration employs $d$-dimensional quantum systems, qudits, up to $d=2^{13}$ dimensions and demonstrates a communication complexity advantage, requiring less than $(0.696 \pm 0.006)$ times the communication of any causally ordered protocol. These results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures.
Applications

• Daniele Cozzolino, Emanuele Polino, Mauro Valeri, Gonzalo Carvacho, Davide Bacco, Nicoló Spagnolo, Leif Katsuo Oxenløwe and Fabio Sciarrino
Distribution of photonic entangled states using optical fiber links is fundamental for quantum networks. The orbital angular momentum (OAM) is one of the most promising degree of freedom due to its capability to encode high-dimensional states. We demonstrate fiber distribution of hybrid polarization-vector vortex entangled photon pairs by exploiting an air-core fiber which supports OAM modes. Distribution of the entangled states is demonstrated by performing quantum state tomographies, by violations of Bell inequalities and multipartite entanglement tests. The present results open new scenarios for quantum applications where correlated complex states can be transmitted by exploiting the vectorial nature of light.
Applications

• Caterina Vigliar, Daniel Llewellyn, Benjamin Slater, Beatrice Da Lio, Stefano Paesani, Jorge Barreto, Dondu Sahin, John Rarity, Leif Katsuo Oxenløwe, Karsten Rottwitt, Jianwei Wang, Yunhong Ding, Mark Thompson, Davide Bacco and Massimo Borghi
In this work we report the first chip-to-chip high-dimensional entanglement distribution of path-encoded quantum states of light through multicore fibres. We build a system composed of two integrated silicon chips, a transmitter and a receiver, linked by a five-meter long seven-core fibre. Maximally entangled two- and four-dimensional quantum states, prepared and measured over the two chips, are succesfully verified. These results mark a key step towards the development of distributed quantum applications.
Applications

• Asimina Arvanitaki, Masha Baryakhtar, Karl Berggren, Ilya Charaev, Jeff Chiles, Marco Colangelo, Andrew Dane, Junwu Huang, Robert Lasenby, Sae Woo Nam, Ken Van Tillburg and Varun Verma
In recent years, the development of fast and low-dark-count single-photon detectors for photonic quantum information applications promise a radical improvement in our capacity to search for dark matter. The advent of superconducting nanowire detectors, which have fewer than 10 dark counts per day and have demonstrated sensitivity from the mid-infrared to the ultraviolet wavelength band, provides an opportunity to search for bosonic dark matter in the neighborhood of 1 eV. We present recent theoretical and experimental progress in this direction.
Applications

Detector

• Enrico Conca, Vincenzo Sesta, Federica Villa, Mauro Buttafava, Simone Tisa, Alberto Dalla Mora, Davide Contini, Alessandro Torricelli, Antonio Pifferi, Laura Di Sieno, Paola Taroni, Franco Zappa and Alberto Tosi
We present an integrated circuit designed for compact and low-cost TD-NIRS systems, combining a fast-gated single-photon detector array (based on SPADs) with 8.6 mm2 active area, a Time-to-Digital Converter (TDC) with 72 ps resolution and integrated histogram builder, fabricated in a 0.35 µm CMOS technology. This fully-digital photodetector combines the fast-gating capability of SPAD detectors, previously only demonstrated for single pixels, with the large area typically found in detectors like Silicon Photomultipliers (SiPMs), earning the name of “fast-gated digital SiPM”. We use a novel frontend circuit to maximize fill factor and reduce power consumption.
Detector

• Fabio Acerbi, Massimo Capasso, Alberto Mazzi, Giovanni Paternoster, Nicola Zorzi and Alberto Gola
Silicon photomultipliers (SiPMs) are arrays of many SPADs, each one with integrated quenching. They are single-photon detector but the output proportional to the number of photons. They have easy scalability, for microcell size (5 to 100 µm) and the overall active area (1mm2 to 100mm2). SiPMs emerged as a promising solution for LIDAR, spectroscopy, physics experiments, etc. In this work we will talk about SiPMs operated at low (cryogenic) temperatures (down to liquid nitrogen temperature) showing the performance of different FBK SiPM technologies, discussing the trends. DCR reaches values of less than 1cps/mm2 with good PDE and dynamic range.
Detector

• Simon Grosse
Detectors based on SPAD technology offer a high time resolution and sensitivity for applications that require time-resolved single-photon measurements. The integration of SPADs into the CMOS process (CSPAD) allows for efficient on-chip signal processing and high flexibility for custom detector designs. Fraunhofer IMS endeavors include active research and development in the fields of LiDAR, Quantum Imaging, microscopy, spectroscopy and more. The approach of utilizing a wafer-to-wafer bonding process with a backside-illuminated CSPAD wafer and a read-out wafer will enable significant improvements of the detector performance as well as the possibility of combining different technologies.
Detector

• Fabrizio Piacentini, Alessio Avella, Enrico Rebufello, Salvatore Virzì, Muriel de Souza, Rudi Lussana, Federica Villa, Alberto Tosi, Marco Gramegna, Giorgio Brida, Matteo Paris, Eliahu Cohen, Jan Dziewior, Lev Vaidman, Ivo Pietro Degiovanni and Marco Genovese
Measurement has a crucial role in quantum mechanics. In this talk, we present the experimental implementation of three novel quantum measurement paradigms: the first one is Protective Measurement, showing unprecedented measurement capability and demonstrating how the expectation value of an observable can be obtained without statistics. Afterwards, we introduce the Genetic Quantum Measurement, presenting analogies with the typical mechanisms of genetic algorithms. Finally, we present Robust Weak value Measurement, a protocol able to extract a weak value not as an average on an ensemble of weakly measured particles, but even from a single particle."
Metrology

• Lynden Shalm, Yanbao Zhang, Mohammad Alhejji, Michael Mazurek, Martin Stevens, Carlos Abellán, Morgan Mitchell, Sae Woo Nam and Emanuel Knill
I will discuss our recent work using a photonic-based Bell experiment to perform the first device-independent randomness expansion. Our experiment is able to produce more certified random output bits than input bits consumed. These expansion protocols have more demanding requirements compared to regular device-independent randomness generation, and several theoretical and experimental innovations were required in order to realize randomness expansion. After taking 130 hours of data, we have achieved certified randomness expansion. Our work opens the way for other novel device-independent protocols, and has the potential for use in quantum networked applications.
Metrology

• Christopher Chunnilall, Elizabeth Laier-English, Anthony Vaquero-Stainer and Adrian Wonfor
NPL is developing single-photon metrology of the quantum-optical layer in QKD hardware. NPL uses fibre links to provide a time signal traceable to UTC to the finance sector, and to enable remote frequency comparison between optical clocks. These applications normally use signal powers around 0 dBm (1 mW). NPL and the UK Quantum Communications Hub are investigating the ability to operate QKD over fibres carrying time signals. Initial investigations are being performed on spools of fibre, with the aim of implementation over installed fibre links. We report on progress towards our objective, and characterisation of the link and hardware parameters."
Metrology

• Mikolaj Lasota, Marta Misiaszek and Piotr Kolenderski
We report on the theory and experimental verification of a novel approach to the problem of estimating the statistics of photons emitted from an unknown source of light. In particular, we investigate two types of detection systems, based on photon-number resolved single photon detectors and spatial multiplexing with four bucket detectors.
Metrology

• Given the fast progress made in improvement of superconducting nanowire single photon detectors (SNSPD) in the last decade, renewed effort has focused on understanding the fundamental limits of the detection process. A wide range of experiments have been performed across many groups to push beyond the state of the art in individual metrics, such as dark count rate, efficiency, photon number resolution, long wavelength sensitivity and timing resolution. These results have triggered significant improvements in understanding of the detection mechanism, however, gaps between experiment and theory still remain and leaves the door open for further investigations. Timing resolution in particular can be as good as 2.6±0.2 ps for visible wavelengths and 4.3±0.2 ps at 1550 nm. This has an impact on many applications including classical and quantum communication, higher spatial resolution in laser ranging with fewer photons, observation of shorter-lived fluorophores in biomedical applications and fast optical waveform capture. Encouragingly, it is not believed that fundamental limits have been reached yet. The limits of photon energy cut-off are also an ongoing topic of study and single photon response has been observed out to 9.9 μm which is promising for a number of applications, including exoplanet transient spectroscopy.
Detector

• Varun Verma, Emma Wollman, Adriana Lita, Boris Korzh, Matthew Shaw, Richard Mirin and Sae Woo Nam
Recently we have begun to develop arrays of SNSPDs for applications in astronomy and chemical sensing in the mid-infrared (2 – 11 µm wavelength range). We report on the fabrication and characterization of a 32 x 32 WSi SNSPD array (1024 pixels) with an active area of 1.6 mm x 1.6 mm. The first array tested functioned as designed with a pixel yield of 99.4%. Although this array has not yet been optimized for the mid-infrared, we will show preliminary results demonstrating saturated internal detection efficiency of a single-pixel WSi detector at a wavelength of 10 µm.
Detector

• Devin Hugh Smith, David S. Phillips, Paolo Mennea, Varun B. Verma, Adriana Lita, Thomas Gerrits, Richard P. Mirin, Rex H.S. Bannerman, Paul C. Gow, Jelmer Renema, Robert J.A. Francis-Jones, Raj B. Patel, Santiago Sempere-Llagostena, Peter G.R. Smith, Sae Woo Nam, Ian A. Walmsley and James C. Gates
We report the first superconducting nanowire single-photon detectors (SNSPD) on an integrated silica platform. Four WSi detectors were deposited atop each of a set of waveguides inscribed by direct-UV writing, each providing a weak measurement of the guided mode. The detectors operated with a jitter of about 200 ps and a dead time of 180 ns, while the detectors each detected approximately 0.12% of the passing light with a dark count rate of 0.4/s operating at 1550 nm.
Detector

• Alessandro Gaggero, Francesco Martini, Francesco Mattioli, Fabio Chiarello, Robert Cernansky, Alberto Politi and Roberto Leoni
The realization of large-scale photonic circuits for quantum optics experiments at telecom wavelengths requires an increasing number of integrated detectors. SNSPDs can be easily integrated onchip, and they can efficiently detect the light propagating inside waveguides. The thermal budget of cryostats poses a limit on the maximum number of elements that can be integrated on the same chip due to the thermal impact of the readout electronics. We propose and implement a novel amplitude-multiplexing scheme allowing the efficient reading of several SNSPDs with only one readout port, thus enabling the realization of photonic circuits with a large number of modes
Detector

• Sergey Polyakov, Ivan Burenkov, M.V. Jabir and Abdella Battou
We present the unconditional violation of the lowest standard quantum limit for a family of coherent frequency shift keying communication protocols with the alphabet sizes of M=4 and M=8. Not only this protocol is more energy efficient for large alphabets, but also it scales more favorably with the alphabet size than legacy classical communication protocols.
Metrology

• Sacha Schwarz, Jean-Philippe MacLean and Kevin Resch
The generation of ultrafast laser pulses and their reconstruction is essential for many applications in modern optics. Quantum optical fields can also be generated on ultrafast time scales, however, the methods available for strong laser pulses are not appropriate for measuring the properties of weak, possibly entangled pulses. Here, we demonstrate a method to reconstruct the joint-spectral amplitude and phase of a two-photon energy-time entangled state from joint measurements in frequency and time. Our reconstruction method is based on a modified Gerchberg-Saxton algorithm. Such techniques are essential to measure and control the shape of ultrafast entangled photon pulses.
Metrology

• David Fuster, José M. Llorens, Yolanda González and Benito Alén
A plug&play single photon device based on a electro-optical pumping scheme will be presented. It is based on a vertical multijunction heterostructure comprising two separated electrical injection and electrical tuning regions. The connection between them is purely optical and thus, it naturally avoids sheet resistance problems when applied to nanophotonic devices. We will show finite element simulations of different electrical and photonic designs together with results obtained in the first fabricated devices. Our initial prototypes show single photon emission with g2(0)<0.1 at injection currents as low as 100 mA/cm2 and fully linear conversion between electrical power and single photon flux.
Metrology

• Hélène Ollivier, Ilse Maillette, Guillaume Coppola, Stephen Wein, Paul Hilaire, Abdelmounaim Harouri, Aristide Lemaître, Isabelle Sagnes, Loïc Lanco, Sarah Thomas, Juan Loredo, Carlos Anton, Niccolo Somaschi and Pascale Senellart
Quantum dots are promising candidates to generate the single photons needed to implement quantum networks. Although quantum dot indistinguishable single photon sources have already allowed an exponential speedup of quantum optics experiments, such as Boson Sampling, so far only single photons emitted by one quantum dot source have been used. Indeed, it remains to demonstrate that this technology can be reproducibly fabricated for widespread applications, an important challenge since quantum dots show natural inhomogeneity. In this presentation, we show that it is possible to produce multiple sources presenting homogeneous characteristics.
Metrology

• Marco Lucamarini, Zhiliang Yuan, James F. Dynes, Andrew J. Shields
Since its inception in 2012, Measurement-Device-Independent (MDI) Quantum Key Distribution (QKD) has grown into a well-established technique that features several remarkable properties: it overcomes all the implementation loopholes related to using sensitive detection apparatuses; it partially removes the restriction of a trusted-node architecture in a quantum network, using a single untrusted node (Charlie) to connect distant users (Alice and Bob); it improves the signal to noise ratio of point-to-point QKD, thus slightly extending its transmission range in the asymptotic scenario. The practicality of MDI-QKD has been convincingly proven in various experiments. Nevertheless, its overall key rate remains quite modest due to a coincidence detection Charlie has to perform on the two photons sent by Alice and Bob. Moreover, MDI-QKD key rate scales only linearly with the channel transmission 𝜂, similarly to the direct-link QKD, while the presence of an intermediate node could lead, in principle, to a better scaling. Theoretical papers have shown that MDI-QKD endowed with a quantum memory has the potential to approach the scaling law of a single repeater, 𝑂(√𝜂), but the realization of this proposal is still elusive. Recently, a far more efficient form of MDI-QKD named “Twin-Field” (TF) QKD has been introduced. This new technique inherits all the security-related benefits of MDI-QKD but, as an extra, it also features the single-repeater scaling law 𝑂(√𝜂) without employing a quantum memory, using only currently available technology. This makes it possible to overcome at long distance the Repeaterless Secret Key Capacity (RSKC), a bound that is unsurpassable with point-to-point QKD only. Overcoming this bound is the benchmark of a quantum repeater. Therefore, experiments performing TF-QKD beyond the RSKC limit, are considered the first realizations of an “effective quantum repeater”. In this talk, I will introduce the TF type of MDI-QKD protocols and rationalise the recent literature in this rapidly evolving research area. Starting from observations on the requirements of practical implementation, I will move towards security proofs and experimental results that compose the current landscape of TF quantum cryptography.
Applications

• Mariella Minder, Mirko Pittaluga, George Roberts, Marco Lucamarini, James Dynes, Zhiliang Yuan and Andrew Shields
Quantum key distribution (QKD) allows users to generate shared encryption keys that are guaranteed to be theoretically secure by the laws of quantum mechanics. There is a fundamental rate-distance limit in practical QKD that was thought to be unsurpassable with current technology. The recent Twin-Field QKD (TF-QKD) protocol promises to overcome this limit and predicts the same square root dependence of key rate on channel loss as a quantum repeater, using twin light fields to carry quantum information. Here we provide the first experimental validation of this by implementing TF-QKD over channel losses exceeding 90dB.
Applications

• Marco Avesani, Davide G. Marangon, Hamid Tebyanian, Giuseppe Vallone and Paolo Villoresi
Randomness is an invaluable resource for many applications. Quantum random number generators (QRNG) offer an advantage over other solutions because they exploit the intrinsic randomness of quantum mechanics to generate secure random numbers. However, practical QRNG usually require to trust the inner working of their components and their security can be completely compromised in case of malfunction or malicious external actions. Here we describe a series of works where the source is untrusted and the security is evaluated in the Source-Device-Independent scenario. We experimentally realized the protocols with photonic implementations, reaching secure rates that match the requirements of practical applications.
Applications

• Sören Wengerowsky, Siddarth Koduru Joshi, Fabian Steinlechner, Julien R. Zichi, Sergiy M. Dobrovolsky, Rene van der Molen, Johannes W. N. Los, Val Zwiller, Marijn A. M. Versteegh, Alberto Mura, Davide Calonico, Massimo Inguscio, Bo Liu, Thomas Scheidl, Hannes Hübel, Anton Zeilinger, André Xuereb and Rupert Ursin
We present the distribution of polarisation-entangled photons between Malta and Sicily using a 96 km-long submarine telecommunications as a quantum channel. We were able to observe around 260 photon pairs per second, with a polarisation visibility above 86%. In a second experiment we send one of the entangled photons through this cable back and forth such that two of the deployed fibres were used consecutively as a loop. Our experiment demonstrates the feasibility of using deployed submarine telecommunications optical fibres as long-distance quantum channels for polarisation-entangled photons. This opens up possibilities for future experiments and technological applications using existing infrastructure.
Applications

• Soeren Wengerowsky, Siddarth Koduru Joshi, Fabian Steinlechner, Hannes Hübel and Rupert Ursin
We present a proof-of-principle experiment consisting of four users in a novel network architecture which enables scalable quantum communication based on polarization-entangled photon pairs at telecommunications wavelength. Our scheme uses frequency multiplexing to share 6 two-photon entangled states between each pair of clients in a mesh-like network topology using only one fiber per client. As clients need minimal resources - one polarization detection module and single-mode fiber each, the physical topology of the network outside the source scales linearly if a user is added, while the logical topology scales quadratically with N(N-1) network connections between N users."
Applications

• Klaus Suhling, Jakub Nedbal, Liisa M. Hirvonen
Time-correlated single photon counting (TCSPC) is a widely used, sensitive, precise and robust technique to detect photon arrival times in fluorescence spectroscopy and microscopy. In confocal or multiphoton excitation fluorescence microscopy, it is often implemented with beam scanning and single point detectors. However, we have implemented a camera-based wide-field TCSPC method, where the position and the arrival time of the photons are recorded simultaneously. This has some advantages for certain types of microscopy. We employ a photon counting image intensifier in combination with a 1 MHz frame rate CMOS camera, thus combining an ultra-fast frame rate with single photon sensitivity. Compatibility of this method with live-cell imaging was demonstrated by imaging europium-containing beads with a lifetime of 570 μs in living HeLa cells, as well as decays of ruthenium compound Ru(dpp) with lifetimes from around 1 to 5 μs. Moreover, the invariant phosphor decay of the image intensifier screen can be used for accurate timing of photon arrival well below the camera exposure time. By taking ratios of the intensity of the photon events in two subsequent frames, decays of ruthenium and iridium-containing compounds with lifetimes of around 1 μs were measured with 18.5 μs frame exposure time (54 kHz camera frame rate), including in living HeLa cells. These approaches bring together advantageous features for time-resolved live cell imaging such as low excitation intensity, single photon sensitivity, ultra-fast camera frame rates and short acquisition times. We also report on nanosecond fluorescence lifetime imaging (FLIM) microscopy based on a 40 mm diameter crossed delay line anode detector with picosecond time resolution, where the readout is performed by three standard TCSPC boards. We apply this wide-field TCSPC detector to FLIM of cells labelled with membrane dyes imaged with a TIRF microscope. Moreover, we demonstrate FLIM lightsheet microscopy with this detector.
Applications

• Dmitry Tabakaev, Geraldine Haack, Hugo Zbinden and Robert Thew
The recently developed theory of entangled two-photon absorption (ETPA) predicts a linear dependence of its rate on the entangled pair flux in the low-power regime, and provides a tool for two-photon studies even on sensitive samples. We experimentally observed this signature for ETPA-induced fluorescence of Rhodamine 6G and its dependence on inter-photon delay, concentration and polarization to find out which degrees of freedom play a role in ETPA. The developed methods have possible applications in sensing, spectroscopy, imaging and fluorescence microscopy, especially for biological objects in vivo and in vitro, that could be susceptible to damage from intense laser schemes.
Applications

• Atul Ingle, Andreas Velten and Mohit Gupta
Single-photon avalanche diodes (SPADs) are an emerging sensor technology and are becoming increasingly popular in low light and active imaging applications. We propose passive free-running SPAD (PF-SPAD) that, unlike conventional active imaging applications, uses SPADs in ambient light to capture 2D intensity images. Surprisingly, a PF-SPAD can operate at much higher flux levels than previously thought possible and provide over 2 orders of magnitude higher dynamic range than conventional image sensors. Thus, SPADs have the potential to be used as general-purpose passive image sensors in a variety of consumer and scientific applications that deal with extreme dynamic range.
Applications

• David Lindell, Matthew O'Toole and Gordon Wetzstein
Imaging objects outside a camera's direct line of sight enables new capabilities in autonomous vehicle navigation, remote sensing, medical imaging, and many other domains. Recent approaches to non-line-of-sight (NLOS) imaging demonstrate impressive results using time-resolved single-photon detectors with ultrafast pulsed lasers. However, the size and quality of scenes which can be captured and reconstructed is limited because conventional inversion methods are typically slow or make restrictive assumptions about the scene. We introduce efficient methods for NLOS imaging based on a confocal sampling scheme and experimentally validate our approach with NLOS imaging of room-sized scenes outdoors and imaging at interactive rates.

• Andrew White
We introduce a hardware processor capable of analysing the continuous output signal from transition edge-sensors (TES's), giving us near-real information about photon number. We discriminate up to 15 photons, with certainties ranging from 99.9999996% for 2 photons, to 98.0% for 13 photons. We implement a general imaging method by measuring the complex degree of coherence using linear optics and our photon-number-resolving detectors. Testing our method on by measuring the size and position of a small distant source of pseudo-thermal light, we find it outperforms the traditional imaging method by an order of magnitude in precision.
Applications

• J Tasker, J Frazer, G Ferranti, J C F Matthews
Silicon quantum photonics is emerging as a sophisticated platform to perform quantum information technology demonstrations and quantum optics experiments. Recent efforts have brought together on-chip generation of correlated photon pairs using four-wave mixing, with the inherent stability of nested interferometers to program electrically the manipulation quantum states to implement large scale quantum optics experiments . For example, one such recent device is a fully programmable two-qubit quantum processor that comprises more than 200 photonic components, and was used to implement 98 different two-qubit unitary operations (with an average quantum process fidelity of 93.2±4.5%), demonstrate a two-qubit quantum approximate optimization algorithm, and simulation of Szegedy directed quantum walks. A requirement of any integrated quantum optics platform is the integration into the monolithic architecture of methods to measure quantum states and characterise quantum processes. To this end, we will discuss efforts to realise homodyne detection integrated with silicon-on-insulator quantum photonics in large-scale photonic circuits. We report measured performance characteristics that are sufficient to perform quantum optics experiments. We will discuss how these performance characteristics can be improved by use of integrated electronics to perform the low noise amplification component of the detector, and we will show how this may perform beyond the state of the art with bulk optics and discrete electronics.
Applications

• Francesco Ceccarelli, Simone Atzeni, Francesco Pellegatta, Andrea Crespi and Roberto Osellame
Femtosecond laser micromachining (FLM) allows rapid and cost-effective fabrication of 3D photonic integrated circuits employed today in diverse single-photon applications. However, when a thermal phase shifter is exploited to reconfigure an FLM device, its operation requires many hundreds of milliwatts. This issue strongly limits the scalability of these circuits. With this work, we present a new FLM fabrication process that takes advantage of thermal isolation microstructures (i.e. trenches and bridge waveguides) to demonstrate low propagation losses (0.29 dB/cm at 1550 nm), along with a power dissipation for a 2π phase shift down to 37 mW.
Applications

• Peter Connolly, Gerald Buller, Yash Shah and David Cumming
The ability to extract multispectral data from single-photon imaging systems is one which is of great interest in many areas of research including remote depth profiling, fluorescence lifetime imaging and astrophysical spectroscopy. We present the first realisation of a mosaic filter array integrated with a single-photon avalanche diode (SPAD) array. The mosaic filter array is fabricated in a single-step process utilising an e-beam written plasmonic metasurface which permits high efficiency transmission. Filters were bonded to two CMOS Si-SPAD arrays and a bespoke algorithm was able to reconstruct colour images of a four colour target using single-photon counting.
Applications

• Segolene Olivier, Corrado Sciancalepore, El Dirani Houssein, Karim Hassan, Raouia Rhazi, Costantino Agnesi, Giuseppe Vallone, Davide Bacco, Yunhong Ding, Karsten Rottwitt, Frederico Sabattoli, Matteo Galli and Daniele Bajoni
Silicon photonics technology is very attractive to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of MDI-QKD protocols. It has now reached a high level of maturity for datacom and telecom applications. Building further on this platform, we aim at developing a versatile quantum-grade platform for fully integrated quantum transmitter and receiver circuits based either on superposition or entanglement approaches and combining both quantum and classical channels. We present first experimental results of Hong-Ou-Mandel interference between weak coherent pulses generated by hybrid III-V/Si lasers and the emission of photon pairs by high-Q silicon microring resonators.
Applications

• Jelmer Renema
Gaussian boson sampling is the most feasible way of demonstrating a quantum advantage using photonics. However, much is unknown regarding the hardness of this experiment. I will extend simulability results on boson sampling to the regime of Gaussian boson sampling. I will show that Gaussian boson sampling has the same susceptibility to noise as regular boson sampling. I will also show that strong squeezing constitutes an imperfection, and give an upper bound on the permissible level of squeezing in a boson sampler. I will discuss the implications of these results imply for experimental resources necessary to demonstrate a quantum advantage."
Applications

• I. P. Degiovanni, P. Traina, E. Moreva, J. Forneris, F. Piacentini, S. Ditalia Tchernij, E. Bernardi, G. Brida, I. Burenkov, E. A. Goldshmidt, S. V. Polyakov, P. Olivero, M. Genovese
In single-photon metrology the characterization of the emission statistics of the sources in order to quantifying the non-classical properties is of the utmost importance, i. e. the quality of the single photon state produced. This is particularly relevant in quantum cryptography, where uncontrolled fluctuations in the number of photons may open serious security issues. The most used parameter for this characterization is the second order Glauber’s correlation function (g(2)), which, despite having the advantage of being independent of the quantum efficiency of the detectors, has also several drawbacks, especially when one aims at the characterization of clusters of emitters or single emitters in noisy background. For these systems, new tools based on parameters that are resilient to noise and exploiting multifold coincidence events are being proven to be effective in specific contexts. In this framework we will report on the first experimental demonstration of a recently proposed criterion (Filip’s θ function) [4] addressed to detect nonclassical behavior in the fluorescence emission of ensembles of single-photon emitters (applied in particular to clusters of Nitrogen-Vacancy centres in diamond) [5]. In a nutshell, the difference between the Glauber’s and the Filip’s functions is that the former relies on the multi-detection of photons in coincidence, while the latter relies on simultaneous “non-detection” of photons. We will introduce simulation results on the application of a novel technique exploiting higher order Glauber’s and Filip’s functions (θ(n) and g(n) with n > 2) simultaneously to entirely reconstruct the modes hidden in more complex optical fields such as, e.g., single photon sources in a noise-bath. This mode reconstruction method is based on optimisation algorithms requiring as input data, as said, higher order Glauber’s and Filip’s functions (that are somehow connected to high order moments of the statistics of the input photons), whose associated uncertainties increase with the order. We show that the use of both θ(n) and g(n) (rather than using only g(n) as it was done in the past) allows to reduce the functions order necessary to carry on the reconstruction, hence improving its performances.
Metrology

• Ya-Li Mao, Qi-Chao Sun, Qiang Zhang, Jingyun Fan and Jian-Wei Pan
We derive a state-dependent error-disturbance tradeoff based on statistical distance in the sequential measurements of a pair of noncommutative observables and experimentally verify the relation with a photonic qubit system.
Metrology

• Anna Paterova, Hongzhi Yang, Chengwu An, Dmitry Kalashnikov and Leonid Krivitskiy
Nonlinear interference of spontaneous parametric down-conversion photons (SPDC) has been studied over the last few decades. It is shown that due to the effect of induced coherence, the interference pattern for the signal SPDC photons is determined by idler SPDC photons too. Based on this concept, we demonstrate the method of IR metrology with visible light using a nonlinear Michelson interferometer. Current configuration of the interferometer allows multiple type of measurements, including IR spectroscopy, IR optical coherence tomography (OCT), IR imaging and IR polarimetry. The developed IR metrology technique is relevant to material research, optical inspection and quality control.
Metrology

• Kaisa Laiho, Marco Schmidt, Holger Suchomel, Martin Kamp, Sven Höfling, Christian Schneider, Joern Beyer, Gregor Weihs and Stephan Reitzenstein
We measure the joint photon statistics of parametric down-conversion from a Bragg-reflection waveguide with transition-edge sensors, being true photon-number resolving detectors. Further, we utilize the normalized factorial moments of photon-number, which can be measured independent of losses, and the loss-corrected mean photon-number of the target state for reconstructing the photon-number parity of heralded single photons loss-tolerantly via the moment generating function. We take into account imperfections in the heralded state preparation and manipulation as well as investigate the boundaries of the method used for the state reconstruction.
Metrology

• Brian Aull, Erik Duerr, Jonathan Frechette, Chris Leitz, Abigail Licht, Alex McIntosh, Kevin Ryu, Daniel Schuette, Vyshnavi Suntharalingam, Richard Younger
MIT Lincoln Laboratory develops photon-counting image sensors for lidar, passive imaging, wavefront sensing, and communications. These sensors are based on hybridizing or 3D integrating custom arrays of Geiger-mode avalanche photodiodes (GmAPDs) with all-digital CMOS circuits. This presentation reviews ongoing technology development work at the Laboratory on three fronts: (1) Silicon and InGaAsP/InP GmAPD arrays, (2) Novel readout circuits architectures for lidar and photon-starved passive imaging, and (3) 3D integration and rapid prototyping techniques.
Detector

• Chan-Yong Park, Soohyun Baek, Jung-Hyun Kim, Bora Jeon, Seung-Chul Yang, Chulwoo Park and Seok-Beom Cho
Room temperature operation of single photon avalanche diode is very important in the points that it provides low cost solution and small size of module. We fabricated a high performance SPAD having small active volume. Using conventional gating technology, the dark count probability(DCP)/gate was measured to be 2E-6 at -40C and 3E-5 at room temperature for 30% photon detection efficiency(PDE), respectively. We will present various other performances in the workshop.
Detector

• Gerald Buller
Germanium layers have been used to extend the operational wavelength of silicon-based single-photon avalanche diode (SPAD) detectors. We present a novel planar geometry device which has shown a significant improvements in comparison to all previous mesa geometry Ge-on-Si SPAD detectors. The single-photon detection efficiency is as high a 38% in these prototype devices, with significant improvements demonstrated in dark count rate and jitter in comparison with previously published Ge-on-Si SPADs. An afterpulsing comparison with alternative InGaAs/InP SPADs will be presented, as well as a study of the spectral response. We will discuss future device iterations for further performance enhancements.
Detector

• Giulia Acconcia, Angelo Gulinatti, Massimo Ghioni and Ivan Rech
Single Photon Avalanche Diodes (SPADs) offer clear advantages in single-photon measurements, but their operation at high rates is still an open challenge. Targeting the exploitation of our custom-technology SPADs, we designed a fully integrated Active Quenching Circuit (AQC) able to achieve a rate as high as 160Mcps. In timing, we designed an AQC with a tunable dead time to avoid pile-up distortion and a fully differential pick-up circuit providing picoseconds timing jitter even at high count rates. Exploiting a Si-Ge 0.35µm technology we also developed a Time-to-Amplitude Converter able to provide a state-of-art timing precision of less than 4.3ps rms.
Detector

• Matteo Salomoni, Etiennette Auffray, Paul Lecoq, Stefan Enoch, Alberto Gola, Stefan Gundacker, Marco Toliman Lucchini, Alberto Mazzi and Marco Paganoni
We present the advancements obtained in trying to minimize the time jitter and photo-detection efficiency of Silicon photo-multipliers (SiPM). SiPM suffers from non-homogeneity of the avalanche generation as a function of the e-h generation position and from non-optimal detection efficiency, particularly at low over-voltages. Using light concentrator tuned on the single photo-avalanche diode shape could minimize the jitter by confining the photo-conversion region in the vicinity of the high field. Combining this with the inclusion of hyperbolic meta-material inside or in the vicinity of the high field region has the potential to produce a leap in performance of these devices.
Detector

• Carlos Anton Solanas, Juan Loredo, Guillaume Coppola, Niko Viggianiello, Hélène Ollivier, Abdelmounaim Harouri, Niccolo Somaschi, Andrea Crespi, Isabelle Sagnes, Aristide Lemaître, Loïc Lanco, Roberto Osellame, Fabio Sciarrino and Pascale Senellart
We report the interfacing of an integrated solid-state single-photon source with an integrated, reconfigurable photonic tritter demonstrating a highly efficient three photon colaescence.
Source

• Timm Kupko, Lucas Rickert, Martin V. Helversen, Alexander Schlehahn, Sven Rodt, Christian Schneider, Sven Höfling, Markus Rau, Harald Weinfurter, Stephan Reitzenstein and Tobias Heindel
Engineered solid-state-based non-classical light sources show prospects to push the performance of implementations of quantum information to a new level. In this contribution, we will present proof-of-concept quantum key distribution (QKD) experiments using electrically-pumped quantum-dot single-photon sources (SPSs). In addition, we present stand-alone fiber-coupled SPSs and discuss our recent progress in their development. We show how to optimize the performance of single-photon QKD and demonstrate real-time security monitoring using sub-poissonian light sources by evaluating the photon statistics during key generation. These results represent important contributions towards the development of functional quantum-secured communication networks based on quantum-light sources.
Source

• Sviatoslav Ditalia Tchernij, Jacopo Forneris, Natko Skukan, Milko Jaksic, Giampiero Amato, Luca Boarino, Ivo Degiovanni, Emanuele Enrico, Ekaterina Moreva, Paolo Traina, Marco Genovese and Paolo Olivero
In this work we present our results on the electrical control of diamond color centers, particularly of the Nitrogen - vacancy (NV) center. The application of an electric field and the injection of an electrical current in an insulating material such as diamond, was achieved using graphitic micro electrodes fabricated by means of ion beam lithography. Regarding the NV centers we report the following: - Charge state conversion; - Electroluminescence stimulation; - Electric field sensing. These results provide promising perspectives on the utilization of integrated electrical structures for the stimulation and control of deep color centers in diamond."
Source

• Sebastian Ecker, Frédéric Bouchard, Lukas Bulla, Florian Brandt, Oskar Kohout, Fabian Steinlechner, Robert Fickler, Mehul Malik, Yelena Guryanova, Rupert Ursin and Marcus Huber
The distribution of single photons over long distances is a cornerstone of practical quantum communication. However, both loss across the link and background photons limit the channel distance and capacity. By utilizing high-dimensional entanglement in spatiotemporal properties of photon pairs we are able to overcome levels of noise which are prohibitive for qubits to be transmitted. We identify two pathways to noise resilience based on increasing the resolution of the state space and using additional measurement bases in high dimensions. These pathways are showcased in an experiment employing energy-time entanglement and another one utilizing entanglement in the orbital angular momentum.
Source

• P. Lombardi, M. Colautti, M. Lopez, S. Kück, C. Toninelli
In this contribution we discuss the state of the art of single-molecule based single photon sources developed in Florence. In particular we will present our latest results concerning the integration of organic molecules into different photonic architectures, from optical planar antennas, to silicon nitride waveguide and polymeric structures. Finally we will elaborate on the applications of such single photon sources for quantum metrology. The science and technology of measuring accurately light at the few photon level is one of the fields where non-classical light states might be more beneficial than classical sources. Intrinsic intensity squeezing in the emission from single quantum object will guarantee a precise definition and measurement of photon fluxes in the fW range. We will hence present a molecule-based single photon source that, operated at 3 K, delivers a constant stream of photons with beyond 1-Mcps flux at the detector, a spectrometer-limited bandwidth of 0.2 nm and single photon high purity. This source is used to calibrate a silicon avalanche photodiode directly against an analog photodetector, previously referred to the primary standard.
Source

• Ross Schofield, Sebastien Boissier, Lin Jin, Anna Ovvyan, Salahuddin Nur, Kyle Major, Frank Koppens, Costanza Toninelli, Wolfram Pernice, Ed Hinds and Alex Clark
Here we present the coupling of single dibenzoterrylene (DBT) molecules to nanophotonic silicon nitride waveguides by filling a gap in the waveguide with a mixture of DBT in anthracene via an on-chip micro-capillary. When cooled to cryogenic temperature, we observe narrow resonances from many molecules via fluorescence. Sending light through the waveguide we can excite single molecules, and by monitoring the transmission we observe coherent extinction of the light. This allows us to measure a coupling to the waveguide of ~7%. We will also discuss the addition of holes to form nanobeam cavities to further enhance this interaction.
Source

• Hamza Abudayyeh, Boaz Lubotzky, Somak Majumder, Niko Nikolay, Jennifer Hollingsworth, Oliver Benson and Ronen Rapaport
Several challenges face room-temperature quantum emitters such as nanocrystal quantum dots and color centers including low photon extraction efficiency, low emission rates and relatively low single photon purities. In this talk I will review our efforts in overcoming these technical difficulties using several complementary methods including designing several nanoantenna devices that enhance the directionality and emission rate of the nanoemitter approaching record high collection efficiencies. In addition, we developed several temporal heralding techniques to overcome the hurdle of low single photon purity in nanocrystal quantum dots in an effort to produce highly pure, bright and efficient single photon sources on-chip.
Source

• Hui Wang, Chao-Yang Lu and Jian-Wei Pan
We develop single- and entangled-photon sources that simultaneously combines high purity, efficiency, and indistinguishability. We demonstrate entanglement among 12 single photons. We construct high-performance multi-photon boson sampling machines to race against classical computers.
Source

• Glenn Solomon, Tobias Huber, Markus Müller, Yichen Shuai and Marcelo Davanco
We have fabricated and tested an integrated chip-scale single-photon source based on the coupling of micro-pillar cavities containing QDs connected to ridge waveguides. This geometry allows us to resonantly excite single QDs in several cavities in the chip plane via a single waveguide, while the quantum light is directed vertically off-chip. Our measurements are completely filter-free: QD light is directly collected from the sample and (broadband) fiber-coupled into our detection scheme. Furthermore, while cross-polarization, with its 50% loss, is required in most resonant excited QD cavity structures, it is eliminated here. Autocorrelation measurements demonstrates zero (within error) multi-photon light contribution.
Source

• Applications

• Jeremy Adcock, Caterina Vigliar, Samuel Morley-Short, Raffaele Santagati, Josh Silverstone and Mark Thompson
Quantum computers promise a paradigm shift humanity’s information processing capability. Measurement-based quantum computing—built on graph states—is the prevailing architecture for large-scale quantum computation. Meanwhile, silicon quantum photonics is a high-performance, scalable quantum technology platform, boasting circuits of unparalleled size. We present the first integrated device to wield four-photon entanglement, generating every type of four-qubit graph states. We also verify our photon's indistinguishability via high-visibility on-chip quantum interference. Finally, we bound the leading sources of error, combining a detailed model of the device with Bayesian parameter estimation, paving the way to scalability.
Applications

• Gautam Kavuri, Martin Stevens, Paul Kwiat, Saewoo Nam and Lynden Shalm
A loophole-free Bell test shrunk to a tabletop would open the door to new tests of fundamental physics, such as a loophole-free chained Bell experiment, and exciting practical applications, such as randomness beacons. The major challenge in building such a system is the need for a low-loss high-bandwidth polarization switch. We will present a scheme for an all-optical switch that can simultaneously meet the challenging requirements of less than 5% loss and a GHz bandwidth that are demanded by this experiment.
Applications

• Zi-Heng Xiang, Jan Huwer, Mark Stevenson, Joanna Skiba-Szymanska, Martin B. Ward, Ian Farrer, David Ritchie and Andrew Shields
Semiconductor-based quantum dots (QDs) are considered to be one of the most important quantum emitters due to their single photon-emission property and integrability. However, the generated single photons from the QDs are not yet used for large-scale quantum communication systems. To explore such application, we transmit entangled photons from a telecom QD device over the Cambridge Fiber Network. A polarization stabilization system is operated for compensating fiber birefringence changes. High-fidelity (91.3%) entanglement is successfully maintained under field environment over one week of continuous operation, indicating great potential and reliability of QD emitters for application in quantum networks.
Applications

• Single-photon detectors are an essential tool for a wide range of applications in physics, chemistry, biology, communications, computing, imaging, medicine, and remote sensing. Ideally, a single photon detector generates a measurable signal only when a single photon is absorbed. Furthermore, the ideal detector would have 100% detection efficiency, no false positive (dark counts), and transform-limited timing resolution. Since the first reported detection of a single photon using a superconducting nanowire in 2001[1], steady progress has been made in the development and application of superconducting nanowire single photon detectors (SNSPD or SSPD) with ideal properties. I will briefly describe progress in detector developments, use of these detectors in new applications, and opportunities for future work.
Detector

• Matthieu Perrenoud, Misael Caloz, Claire Autebert, Christian Schonenberger, Hugo Zbinden and Félix Bussières
Achieving ultra-high detection rate with high efficiency is crucial for many applications requiring fast single photon detection, such as Quantum Key Distribution. We report on parallely-connected SNSPDs, using a new approach to mitigate the effects of electrical cross-talk and the latching it can cause. Using this method, we will report on MoSi-based SNSPDs with high efficiency at 1550 nm and detection rates as high as 200 MHz."
Detector

• Sonia Buckley, Jeffrey T. Chiles, Adam N. McCaughan, Alex N. Tait, Richard P. Mirin, Sae Woo Nam and Jeffrey M. Shainline
We have previously proposed a superconducting opto-electronic platform for neuromorphic computing which utilizes semiconductor LED light sources coupled to integrated waveguides for communication, and super-conducting single photon detectors and superconducting electronics for computation. In this talk we will review the progress in realizing this platform.
Detector

• Takahiro Takumi, Fumihiro China, Masahiro Yabuno, Shigehito Miki, Hirotaka Terai and Ryosuke Shimizu
We present the experimental demonstration of a time-resolved measurement of a single-photon wave packet with a sub-picosecond resolution by means of an optical Kerr gating. Cross-phase modulation induced in a photonic crystal fiber, placed in a Sagnac interferometer, is used in our method. We measure the wave packet of a heralded single-photon from a PPKTP crystal. The observed single-photon wave packet shows the temporal width of ~4 ps, which is a good agreement with the theoretically expected one. In addition, we estimate the temporal resolution of our system to be ~400 fs.
Detector

• Eric Fossum, Jiaju Ma and Stanley Chan
The Dartmouth Quanta Image Sensor (QIS) was presented at SPW2017 in Boulder. This is a CMOS room-temperature, megapixel resolution, small pixel pitch, very low dark count, photon-number-resolving image sensor. The purpose of this paper is to update the single-photon-detector community of progress made since SPW2017.
Detector

• Simon Verghese, Caner Onal and James Dunphy
This talk will review some history of Waymo's self driving car project and describe a few use-cases for automotive LIDARs on Waymo cars. Out of that will emerge key differences between single photon sensors for self-driving and traditional applications (biochemistry, astrophysics, mapping lidar) which could provide opportunities for optimizing single photon sensitive detectors for automotive LIDAR receiver implementations. We will discuss some of the unique requirements and challenges of using such detectors in high-dynamic-range environments, keeping in mind the scalability and durability constraints for long term deployment in a Level 4 fully autonomous self driving fleet.
Applications

• Gabriella Musarra, Alex Turpin, Ilya Starshynov, Ashley Lyons, Enrico Conca, Federica Villa and Daniele Faccio
We report a new paradigm for LIDAR. We demonstrate full-3D information of a flash-illuminated scene from a single temporal histogram, measured with a single SPAD detector, via deep learning."
Applications

• Aurora Maccarone, Aongus McCarthy, Julián Tachella, Francesco Mattioli Della Rocca, Yoann Altmann, Stephen McLaughlin, Robert Henderson and Gerald Buller
Time-correlated single photon counting (TCSPC) has emerged as a critical optical detection technology for lidar and depth profiling due to its high sensitivity and excellent surface-to-surface resolution. We have applied this technique to measure three-dimensional underwater scenes of stationary and moving targets in highly scattering conditions. We present depth and intensity profiles obtained using two systems: a single pixel monostatic transceiver scanning system; and a camera based on a CMOS single photon SPAD detector array with picosecond timing. We also describe advanced computational imaging approaches that are optimised for underwater scenes to demonstrate real-time processing of three-dimensional moving images.
Applications

• Rachael Tobin, Aongus McCarthy, Abderrahim Halimi, Julian Tachella, Yoann Altmann, Martin Laurenzis, Frank Christnacher, Philip Soan, Kenneth McEwan, Stephen McLaughlin and Gerald Buller
Single-photon LIDAR operating in the short-wave infrared (SWIR) offers great potential for kilometre range three-dimensional imaging with improved penetration through atmospheric obscurants. The use of SWIR single-photon imaging provides an eye-safe technique with superior surface-to-surface resolution compared to alternative LIDAR approaches. We present two optical configurations for imaging in highly attenuating environments, such as fog. Three-dimensional target profiles were obtained in high levels of scattering media, and for targets hidden behind camouflage netting at ranges of hundreds of metres. Bespoke algorithms allow for sparse photon data reconstruction using short acquisition times, and for real time reconstruction of dynamic complex scenes.
Applications

• Martin Laurenzis, Stephane Schertzer, Emmanuel Bacher and Frank Christnacher
Single Photon Counting Avalanche Diode (SPAD) sensors can be driven with reverse bias voltages beyond the breakdown point to count single photon events by triggering an avalanche effect. The event time can be read out with sub-nanosecond to a few 10 picosecond precision. Thus, SPAD sensors have the potential to revolutionize optical sensing by combining high sensitivity and high timing precision, and they can be used for computational imaging. In our experiments we used InGaAs SPAD devices as gated single diodes as well as 32x32 array detectors to perform active imaging at a laser wavelength of 1.5 µm."
Applications

• Johan Rothman, Salvatore Pes, Pierre Bluet, Julie Abergel, Sylvain Gout, Philippe Ballet Jean-Louis Santailler, Jean-Alain Nicolas, Jean-Pierre Rostaing, Sebastien Renet, Lydie Mathieu, Jérôme Le Perchec
The high gain and low excess noise factor in HgCdTe APDs enables down to single photon detection with a detection efficiency that are expected to exceed 90%. As the detection is done in linear mode these detectors conserve a high dynamic range that enables to detect multi-photon states on a single detector and do not exhibit a dead-time after the detection of one or a number of photons. The latter means that the detection rate is only limited by the bandwidth of the APD and the pre-amplifier, which is why rates in excess of 1 GHz can be achieved in such detectors, surpassing other single photon detection technologies by a factor 10 to 1000. Such high count-rates makes HgCdTe APDs and interesting candidate both for classical free space optical communications and for quantum optics application such as quantum cryptography and quantum computing. The GHz single photon rate landmark has been approached at CEA/Leti by the development of a detection module for deep space FSO in collaboration of ESA. The detection module is a four quadrant HgCdTe APDs, designed to minimize the collection time of the carriers and hybridized to a dedicated CMOS circuit with resistive trans-impedance amplifier (RTIA). The bandwidth and count rate of each channel is limited to 400 MHz by the low noise RTIA. Single photon detection has been demonstrated up to count rates of 500 MHz with such module, implying a cumulated detection rate of 2 GHz if the signal is dispatched over all four quadrants. The aim of this communication is to discuss the expected optimal performance of HgCdTe APDs at GHz count rates in perspective of the most recent results, such as detection efficiency jitter, dark-count rate and maximum count-rate, which have been measured on present detector modules.
Detector

• Leonardo Gasparini, Majid Zarghami, Matteo Perenzoni, Luca Parmesan, Manuel Moreno Garcia, Valentin Mitev, Laurent Balet, Nicolas Torcheboeuf, Dmitri Boiko, Manuel Unternährer, Bänz Bessire and André Stefanov
SUPERTWIN is a H2020 European FET-OPEN project that aims at building an all-solid-state super-resolution quantum microscope exploiting the non-classical correlations existing among entangled N-photon states. The project poses significant challenges on the detector in terms of efficiency. The parameters of interest include photon detection efficiency (PDE), timing resolution, spatial resolution and duty cycle. The SUPERTWIN detectors are arrays of Single-Photon Avalanche Diodes in CMOS technology that indentify N-photon states by means of the time of arrival of photons at a relatively high efficiency.
Detector

• Majid Zarghami, Leonardo Gasparini, Matteo Perenzoni and Lucio Pancheri
High Dynamic Range (HDR) operation is required for applications such as automotive to cover a large variation of illumination intensity. The capability to count single photons up to 100’s Mphotons/s enabled Single Photon Avalanche Diodes (SPADs) to achieve a HDR. This work exploits the excellent timing resolution of SPADs to extend the dynamic range beyond the saturation level by extracting the intensity of light from the photon interarrival times, reaching 138.7-dB dynamic range within 30-ms integration time.
Detector

• Gobinath Jegannathan, Hans Ingelberts and Maarten Kuijk
A novel type of SPAD, fabricated in 350 nm CMOS technology, is presented consisting of a small 1-fF avalanche diode in its center and surrounded by a large collection volume for photo-generated minority carriers. A current-assisted drift field guides each photo-generated electron in the collection volume towards the center diode for the purpose of triggering a diode breakdown.
Detector

• Giorgio Tortarolo, Marco Castello, Sami Koho, Mauro Buttafava, Eli Slenders, Alessandro Rossetta, Paolo Bianchini, Federica Villa, Alberto Diaspro, Alberto Tosi and Giuseppe Vicidomini
Laser scanning microscopy uses single-element detectors to record the fluorescent light generated by raster scanning an excitation spot across the sample. Since such a detector spatially and temporally integrates the light at any sample position, important information are cancelled out. To address this limitation, we replace the single-element detector with a SPAD array detector. The novel spatial information allows improving the resolution of confocal microscopy, mitigating photo-damaging in STED microscopy, and compensating aberrations in TPE microscopy. The temporal information allows to combine intensity and fluorescence lifetime imaging. Lastly, we discuss the application of the proposed microscope in single-molecule imaging/tracking/spectroscopy."
Applications

• The emission of semiconductor quantum dots (QDs) has been shown to exhibit excellent properties in terms of single photon purity, photon indistinguishability and entanglement fidelity, i.e. essential prerequisites for quantum communication. Emission in the telecom O- or C-band will boost the range of communication schemes due to the favourable absorption and dispersion properties of silica fibers employed in the existing global fiber network. By metal-organic vapor-phase epitaxy, we have fabricated InAs quantum dots on InGaAs/GaAs metamorphic buffer layers on a GaAs substrate with area densities that allow addressing single quantum dots. The photoluminescence emission from the quantum dots is shifted to the telecom C-band at 1.55 μm with a high yield due to the reduced stress in the quantum dots. Single- and polarization-entangled photon emission is demonstrated. Furthermore, the coherence properties of photons emitted by InAs/InGaAs QDs emitting directly in the telecom C-band, are examined under above-band excitation and in resonance fluorescence. The average linewidth is reduced from 9.74 GHz in above-band excitation to 3.5 GHz in resonance fluorescence. Two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of g(2)(0) = 0.07 and a postselected degree of indistinguishability of VHOM = 0.89 are determined for the biexciton transitions. Finally, to boost the extraction efficiency, the applicability of an approach combining a nano-membrane containing QDs, with a GaP hemispherical lens is presented for a sample emitting in the telecom O-band.
Source

• Saverio Francesconi, Florent Baboux, Arnault Raymond, Nicolas Fabre, Aristide Lemaître, Perola Milman, Maria Amanti and Sara Ducci
High-dimensional nonclassical states of light are key resources for quantum information technologies thanks to their robustness to decoherence and the easy transmission, and thus a versatile way to generate and manipulate them is desirable. In this work we present a new technique to control the frequency entangled two-photon state generated by Spontaneous Parametric Down Conversion in a semiconductor AlGaAs microcavity under a transvers pump geometry. This technique allows to generate different types of frequency states (correlated, anti-correlated and separable) and to control the exchange statistics of the two photons (bosonic and fermionic), directly at the generation stage without any post-selection.
Source

• Colin P. Lualdi, Fumihiro Kaneda, Joseph C. Chapman and Paul G. Kwiat
Heralded single-photon sources (HSPSs) via spontaneous parametric down-conversion have long served as single-photon sources in the laboratory, but their probabilistic nature makes them unsuitable for large-scale optical quantum information processing applications. We use time-multiplexing techniques to overcome this limitation by pairing an ultra-low loss, adjustable delay line with our high-efficiency HSPS generating highly indistinguishable (~90%) photons. We report our most current results and ongoing improvement efforts, which include a 66.7±2.4% presence probability of single-photon states collected into a single-mode optical ﬁber, a ten-fold enhancement over the non-multiplexed case.
Source

• Claire Marvinney, Matthew Feldman and Benjamin Lawrie
Hexagonal boron nitride (hBN) is a 2D material of interest for quantum photonic and phononic applications because its defect-based single photon emitters are bright, have narrow linewidths, and are stable at room temperature, and because, for isotopically pure samples, the phonon interactions can have ultra-low losses. To create a description of the combined photonic and phononic quantum state in hBN of varying isotopic concentration, measurements of spectrally resolved correlation functions are employed to study the electron-phonon and electron-electron interactions in isotopically enriched and naturally abundant hBN samples.
Source

• Joel Grim, Allan Bracker, Maxim Zalalutdinov, Samuel Carter, Alexander Kozen, Mijin Kim, Chul Soo Kim, Jerome Mlack, Michael Yakes, Bumsu Lee and Daniel Gammon
We demonstrate scalable quantum interactions between quantum dots (QDs) embedded in the same photonic crystal waveguide. The QDs are tuned into resonance using laser-patterned strain with a tuning step size down to the homogeneous linewidth and sub-micron spatial resolution.
Source

• Quantum communication can provide unconditional security based on the basic law of quantum mechanics. One of the main goal of the field is to extend the transmission distance to large scale, like 1000 km. Here in this talk, I shall review the single photon transmission, interference, frequency conversion technology developed in our group and their applications in long distance quantum communication, including MDI-QKD, quantum repeater and free space quantum communication.
Applications

• Zheng-Da Li, Rui Zhang, Xu-Fei Yin, Li-Zheng Liu, Yi Hu, Yu-Qiang Fang, Yue-Yang Fei, Xiao Jiang, Jun Zhang, Feihu Xu, Yu-Ao Chen and Jian-Wei Pan
Quantum repeaters – important component of the quantum internet – enable the entanglement to be distributed over long distances. A standard quantum repeater relies on a necessary demanding requirement of quantum memory. Despite significant progress, the limited performance of quantum memory makes practical quantum repeaters still a challenge. Remarkably, a proposed all-photonic quantum repeater avoids the need for quantum memory. Here we perform an experimental demonstration of an all-photonic quantum repeater by manipulating a 12-photon interferometer and observe an 89% enhancement of entanglement-generation rate over the parallel entanglement swapping. These results open a new way towards realizing practical quantum repeaters.
Applications

• Alessia Scriminich, Mael Flament, Sonali Gera, Youngshin Kim, Mehdi Namazi, Steven Sagona-Stophel, Giuseppe Vallone, Paolo Villoresi and Eden Figueroa
We measure Hong-Ou-Mandel interference between polarization qubits encoded in weak coherent pulses after storage and retrieval from two independent room-temperature rubidium vapor quantum memories, operating via Electromagnetically-Induced Transparency. We obtain an interference visibility of 41.9% with few-photon-level inputs, and 25.9% with single-photon-level inputs. The results obtained open the way to the implementation of our system in a cryptographic network exploiting for instance memory-assisted MDI-QKD, or for Quantum Repeater applications.
Applications

• Samuele Grandi, Jelena Rakonjac, Dario Lago-Rivera, Alessandro Seri and Hugues de Riedmatten
A reliable way of transferring quantum information between distant locations is becoming ever more crucial, with optical losses and no-cloning theorem still posing a great challenge. We present here our efforts towards the realisation of a quantum repeater, based on a rare-earth quantum memory. Entangled photon-pairs are generated from cavity-enhanced spontaneous down-conversion, where the signal photon is stored as a collective spin excitation in the quantum memory, while the idler is in the telecom band. The entanglement analysis will be made through time-bin qubits analysers made of a fibre-based Mach-Zehnder interferometer, for the former, and a solid-state for the latter.
Applications

• Mohsen Falamarzi Askarani, Marcel.Li Grimau Puigibert, Jacob H. Davidson, Thomas Lutz, Gustavo C. Amaral, Daniel Oblak and Wolfgang Tittel
Entangling quantum systems with different characteristics through the exchange of photons is a prerequisite for building future quantum networks. Proving the presence of entanglement between quantum memories for light working at different wavelengths furthers this goal. Here, we report on a series of experiments with a thulium-doped crystal, serving as a quantum memory for 794 nm photons, an erbium-doped fibre, serving as a quantum memory for telecommunication wavelength photons at 1535 nm, and a source of photon pairs created via spontaneous parametric down-conversion.
Applications