INTRODUCTIONWith the worldwide availability of a large swath of spectrum at the 60 GHz band for unlicensed use, we are starting to see an emergence of new technologies enabling Wi-Fi communication in this frequency band. However, signal propagation at the 60 GHz band significantly differs from that at the 2.4 and 5 GHz bands. Therefore, efficient use of this vast spectrum resource requires a fundamental rethinking of the operation of Wi-Fi and a transition from omnidirectional to directional wireless medium usage. The IEEE 802.11ad amendment addresses these challenges, bringing multi-gigabit-per-second throughput and new application scenarios to Wi-Fi users. These new uses include instant wireless synchronization, high-speed media file exchange between mobile devices without fixed network infrastructure, and wireless cable replacement (e.g., to connect to high definition wireless displays).The most significant difference in 60 GHz propagation behavior is increased signal attenuation. At a typical IEEE 802.11ad range of 10 m, additional attenuation of 22 dB compared to the 5 GHz band is predicted by the Friis transmission equation, resulting from the frequencydependent difference in antenna aperture. In contrast, oxygen absorption plays a minor role over short-range distances, even though it peaks at 60 GHz [1]. Furthermore, 60 GHz communication is characterized by a quasi-optical propagation behavior [2] where the received signal is dominated by the line of sight (LOS) path and first order reflections from strong reflecting materials. As an example, metallic surfaces were found to be strong reflectors and allow non-LOS (NLOS) communication [2]. Concrete materials, on the other hand, cause additional large signal attenuation and can easily create a blockage. Thus, 60 GHz communication is more suitable to in-room environments where sufficient reflectors are present.This article discusses the design assumption resulting from the millimeter-wave (mm-Wave) propagation characteristics and related adaptation to the 802.11 architecture. We further present typical device configurations, an overview of the IEEE 802.11ad physical (PHY) layer, and the newly introduced personal basic service set network architecture. This is followed by an in-depth description of the IEEE 802.11ad beamforming (BF) mechanism and hybrid medium access control (MAC) design, which are the central elements to facilitate directional communication. DIRECTIONAL COMMUNICATIONThe IEEE 802.11ad amendment to the 802.11 standard defines a directional communication scheme that takes advantage of beamforming antenna gain to cope with increased attenuation in the 60 GHz band [1]. With quasi-optical propagation behavior, low reflectivity, and high attenuation, beamforming results in a highly directional signal focus. Based on this behavior, the standard introduces a novel concept of "virtual" antenna sectors [3] that discretize the antenna azimuth. IEEE 802.11ad sectors can be implemented either using precomputed antenna weight vectors for a phased antenna arr...

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Quantum walks constitute a versatile platform for simulating transport phenomena on discrete graphs including topological material properties while providing a high control over the relevant parameters at the same time. To experimentally access and directly measure the topological invariants of quantum walks we implement the scattering scheme proposed by Tarasinski et al. [Phys. Rev. A 89, 042327 (2014)] in a photonic time multiplexed quantum walk experiment. The tunable coin operation provides opportunity to reach distinct topological phases, and accordingly to observe the corresponding topological phase transitions. The ability to read-out the position and the coin state distribution, complemented by explicit interferometric sign measurements, allowed the reconstruction of the scattered reflection amplitudes and thus the computation of the associated bulk topological invariants. As predicted we also find localised states at the edges between two bulks belonging to different topological phases. In order to analyse the impact of disorder we have measured invariants of two different types of disordered samples in large ensemble measurements, demonstrating their constancy in one disorder regime and a continuous transition with increasing disorder strength for the second disorder sample.

Quantum walks are a well-established model for the study of coherent transport phenomena and provide a universal platform in quantum information theory. Dynamically influencing the walker's evolution gives a high degree of flexibility for studying various applications. Here, we present timemultiplexed finite quantum walks of variable size, the preparation of non-localised input states and their dynamical evolution. As a further application, we implement a state transfer scheme for an arbitrary input state to two different output modes. The presented experiments rely on the full dynamical control of a time-multiplexed quantum walk, which includes adjustable coin operation as well as the possibility to flexibly configure the underlying graph structures.

Coherent evolution governs the behaviour of all quantum systems, but in nature it is often subjected to influence of a classical environment. For analysing quantum transport phenomena quantum walks emerge as suitable model systems. In particular, quantum walks on percolation structures constitute an attractive platform for studying open system dynamics of random media. Here, we present an implementation of quantum walks differing from the previous experiments by achieving dynamical control of the underlying graph structure. We demonstrate the evolution of an optical time-multiplexed quantum walk over six double steps, revealing the intricate interplay between the internal and external degrees of freedom. The observation of clear non-Markovian signatures in the coin space testifies the high coherence of the implementation and the extraordinary degree of control of all system parameters. Our work is the proof-of-principle experiment of a quantum walk on a dynamical percolation graph, paving the way towards complex simulation of quantum transport in random media.

The effects of projective measurements on the quantum mechanical evolution of a particle can be simulated with coherent light.

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Detecting light is fundamental to all optical experiments and applications. At the single photon level, the quantised nature of light requires specialised detectors, which typically saturate for more than one photon, rendering the measurement of bright light impossible.Saturation can be partially overcome by multiplexing single-photonsensitive detectors, enabling measurement up to tens of photons [1][2][3][4][5][6][7][8][9][10][11][12]. However, current approaches are still far from bridging the gap to bright light levels. Here, we report on a massively-multiplexed single-photon detector, which exhibits a dynamic range of 123 dB, from optical energies as low as 10 −7 photons per pulse to ∼ 2.5 × 10 5 photons per pulse. This allows us to calibrate a single photon detector directly to a power meter. The use of a single-photon sensitive detector further allows us to characterise the nonclassical features of a variety of quantum states. This device will find application where high dynamic range and single-photon sensitivity are required.Optical detectors are based on a broad range of physical principles, which dictate the range of powers to which they are sensitive. The dynamic range of an optical detector is defined as the difference between its noise floor and saturation intensity. Above the saturation intensity, the detector response is constant, such that different light levels cannot be distinguished. We differentiate saturation from the breakdown intensity of the detector, namely pulse energies above which the detector response is permanently changed (i.e. latched or damaged). For different optical detectors, the saturation intensity and breakdown intensity is determined by its principle of operation. For example, ideal single photon binary ("click, noclick") detectors are saturated when at least one photon is incident. As such, single-photon level detectors cannot be used to measure pulse energies beyond one photon. To overcome this limitation, multiplexing schemes are used to divide an incoming pulse such that the average intensity per multiplexing bin is below the saturation level. Existing multiplexed single-photon detection schemes [1-12] still suffer from saturation effects in that they are not sensitive to photon numbers greater than the number of bins in the multiplexed device [13].In this Letter, we show that we can overcome this saturation limitation, and extend the sensitivity of singlephoton level detectors to 250000 photons per pulse. To do this, we use a detector coupled to a loop of fibre, as first introduced by Banaszek and Walmsley [2]. Below the saturation limit, this detector architecture generates a logarithmic response to the incoming pulse energy [8,14]. However, we show that this device can be pushed beyond its saturation level, and information on the incident pulse energy can still be extracted, limited only by the breakdown level of the click detector. This produces a massively-multiplexed detector with a dynamic range of 123 dB. We perform measurements at low photon-numbers, where this...