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Christine Silberhorn

Publications and source records attributed to Christine Silberhorn.

At least 145 records · Page 8Linked to original sources
arXiv2016

Driven Discrete Time Quantum Walks

We introduce the driven discrete time quantum walk, where walkers are added during the walk instead of only at the beginning. This leads to interference in walker number and very different dynamics when compared to the original quantum walk. These dynamics have two regimes, which we illustrate using the one-dimensional line. Then, we explore a search application which has certain advantages over current search protocols, namely that it does not require a complicated initial state nor a specific measurement time to observe the marked state. Finally, we describe a potential experimental implementation using existing technology.

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arXiv2016

Quantum Walks with Dynamical Control: Graph Engineering, Initial State Preparation and State Transfer

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 time-multiplexed finite quantum walks of variable size, the preparation of non-localized 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.

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arXiv2016

Driven Boson Sampling

Sampling the distribution of bosons that have undergone a random unitary evolution is strongly believed to be a computationally hard problem. Key to outperforming classical simulations of this task is to increase both the number of input photons and the size of the network. We propose driven boson sampling, in which photons are input within the network itself, as a means to approach this goal. When using heralded single-photon sources based on parametric down-conversion, this approach offers an $\sim e$-fold enhancement in the input state generation rate over scattershot boson sampling, reaching the scaling limit for such sources. More significantly, this approach offers a dramatic increase in the signal-to-noise ratio with respect to higher-order photon generation from such probabilistic sources, which removes the need for photon number resolution during the heralding process as the size of the system increases.

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arXiv2016

Single-Mode Parametric-Down-Conversion States with 50 Photons as a Source for Mesoscopic Quantum Optics

We generate pulsed, two mode squeezed states in a single spatio-temporal mode with mean photon numbers up to 20. We directly measure photon-number-correlations between the two modes with transition edge sensors up to 80 photons per mode. This corresponds roughly to a state-dimensionality of 6400. We achieve detection efficiencies of 64% in the technologically crucial telecom regime and demonstrate the high quality of our measurements by heralded nonclassical distributions up to 50 photons per pulse and calculated correlation functions up to 40th order.

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arXiv2016

A two-channel, spectrally degenerate polarization entangled source on chip

Integrated optics provides the platform for the experimental implementation of highly complex and compact circuits for quantum information applications. In this context integrated waveguide sources represent a powerful resource for the generation of quantum states of light due to their high brightness and stability. However, the confinement of the light in a single spatial mode limits the realization of multi-channel sources. Due to this challenge one of the most adopted sources in quantum information processes, i.e. a source which generates spectrally indistinguishable polarization entangled photons in two different spatial modes, has not yet been realized in a fully integrated platform. Here we overcome this limitation by suitably engineering two periodically poled waveguides and an integrated polarization splitter in lithium niobate. This source produces polarization entangled states with fidelity of F = 0.973(3) and a test of Bell's inequality results in a violation larger than 14 standard deviations. It can work both in pulsed and continuous wave regime. This device represents a new step toward the implementation of fully integrated circuits for quantum information applications.

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arXiv2015

Dual-path source engineering in integrated quantum optics

Quantum optics in combination with integrated optical devices shows great promise for efficient manipulation of single photons. New physical concepts, however, can only be found when these fields truly merge and reciprocally enhance each other. Here we work at the merging point and investigate the physical concept behind a two-coupled-waveguide system with an integrated parametric down-conversion process. We use the eigenmode description of the linear system and the resulting modification in momentum conservation to derive the state generation protocol for this type of device. With this new concept of state engineering, we are able to effectively implement a two-in-one waveguide source that produces the useful two-photon NOON state without extra overhead such as phase stabilization or narrow-band filtering. Experimentally, we benchmark our device by measuring a two-photon NOON state fidelity of $\mathcal{F} = (84.2 \pm 2.6) \%$ and observe the characteristic interferometric pattern directly given by the doubled phase dependence with a visibility of $V_{\mathrm{NOON}} = (93.3 \pm 3.7) \%$.

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arXiv2015

Quantum walk coherences on a dynamical percolation graph

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.

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arXiv2015

A versatile design for resonant guided-wave parametric down-conversion sources for quantum repeaters

Quantum repeaters - fundamental building blocks for long-distance quantum communication - are based on the interaction between photons and quantum memories. The photons must fulfil stringent requirements on central frequency, spectral bandwidth and purity in order for this interaction to be efficient. We present a design scheme for monolithically integrated resonant photon-pair sources based on parametric down-conversion in nonlinear waveguides, which facilitate the generation of such photons. We investigate the impact of different design parameters on the performance of our source. The generated photon spectral bandwidths can be varied between several tens of MHz up to around $1\,$GHz, facilitating an efficient coupling to different memories. The central frequency of the generated photons can be coarsely tuned by adjusting the pump frequency, poling period and sample temperature and we identify stability requirements on the pump laser and sample temperature that can be readily fulfilled with off-the-shelve components. We find that our source is capable of generating high-purity photons over a wide range of photon bandwidths. Finally, the PDC emission can be frequency fine-tuned over several GHz by simultaneously adjusting the sample temperature and pump frequency. We conclude our study with demonstrating the adaptability of our source to different quantum memories.

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arXiv2015

Analysis of photon triplet generation in pulsed cascaded parametric down-conversion sources

We analyze the generation rates and preparation fidelities of photon triplet states in pulsed cascaded parametric down-conversion (PDC) under realistic experimental circumstances. As a model system, we assume a monolithically integrated device with negligible interface loss between the two consecutive PDC stages. We model the secondary down-conversion process in terms of a lossy channel and provide a detailed analysis of noise contributions. Taking variable pump powers into account, we estimate the impact of higher-order photon contributions and conversion processes on the achievable coincidence probabilities. At mean photon numbers of $\langle m\rangle\sim0.25$ photons per pulse behind the first PDC stage, we expect around $4.0$ genuine photon triplets per hour. Additionally, we discuss fundamental limitations of our model system as well as feasible improvements to the detectable photon triplet rate.

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arXiv2015

Direct generation of genuine single-longitudinal-mode narrowband photon pairs

The practical prospect of quantum communication and information processing relies on sophisticated single photon pairs which feature controllable waveform, narrow spectrum, excellent purity, fiber compatibility and miniaturized design. For practical realizations, stable, miniaturized, low-cost devices are required. Sources with one or some of above performances have been demonstrated already, but it is quite challenging to have a source with all of the described characteristics simultaneously. Here we report on an integrated single-longitudinal-mode non-degenerate narrowband photon pair source, which exhibits all requirements needed for quantum applications. The device is composed of a periodically poled Ti-indiffused lithium niobate waveguide with high reflective dielectric mirror coatings deposited on the waveguide end-faces. Photon pairs with wavelengths around 890 nm and 1320 nm are generated via type II phase-matched parametric down-conversion. Clustering in this dispersive cavity restricts the whole conversion spectrum to one single-longitudinal-mode in a single cluster yielding a narrow bandwidth of only 60 MHz. The high conversion efficiency in the waveguide, together with the spectral clustering in the doubly resonant waveguide, leads to a high brightness of $3\times10^4~$pairs/(s$\cdot$mW$\cdot$MHz). This source exhibits prominent single-longitudinal-mode purity and remarkable temporal shaping capability. Especially, due to temporal broadening, we can observe that the coherence time of the two-photon component of PDC state is actually longer than the one of the single photon states. The miniaturized monolithic design makes this source have various fiber communication applications.

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arXiv2015

Storage of hyperentanglement in a solid-state quantum memory

Two photons can simultaneously share entanglement between several degrees of freedom such as polarization, energy-time, spatial mode and orbital angular momentum. This resource is known as hyperentanglement, and it has been shown to be an important tool for optical quantum information processing. Here we demonstrate the quantum storage and retrieval of photonic hyperentanglement in a solid-state quantum memory. A pair of photons entangled in polarization and energy-time is generated such that one photon is stored in the quantum memory, while the other photon has a telecommunication wavelength suitable for transmission in optical fibre. We measured violations of a Clauser-Horne-Shimony-Holt (CHSH) Bell inequality for each degree of freedom, independently of the other one, which proves the successful storage and retrieval of the two bits of entanglement shared by the photons. Our scheme is compatible with long-distance quantum communication in optical fibre, and is in particular suitable for linear-optical entanglement purification for quantum repeaters.

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arXiv2015

Probing spectral-temporal correlations with a versatile integrated source of parametric down-conversion states

The spectral-temporal correlation and the correlation time of a biphoton wavepacket generated in the process of parametric down-conversion (PDC), is of great importance for a broad range of quantum experiments. We utilise an integrated PDC source to generate biphotons with different types of spectral-temporal correlations and probe their respective correlation times. The outcomes confirms that the correlation time is independent of the coherence time of the pump light, and it is only determined by the waveguide length and its dispersion properties. Furthermore, we investigate the properties of the PDC biphoton wavepacket exhibiting different types of spectral-temporal correlations and their suitability for quantum-enhanced applications.

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arXiv2015

Observation of Topological Structures in Photonic Quantum Walks

Phases of matter with non-trivial topological order are predicted to exhibit a variety of exotic phenomena, such as the existence robust localized bound states in 1D systems, and edge states in 2D systems, which are expected to display spin-helicity, immunity to back-scattering, and weak anti-localization. In this Letter, we present an experimental observation of topological structures generated via the controlled implementation of two consecutive non-commuting rotations in photonic discrete-time quantum walks. The second rotation introduces valley-like Dirac points in the system, allowing to create the non-trivial topological pattern. By choosing specific values for the rotations, it is possible to coherently drive the system between topological sectors characterized by different topological invariants. We probe the full topological landscape, demonstrating the emergence of localized bound states hosted at the topological boundaries, and the existence of extremely localized or delocalized non-Gaussian quantum states. Our results pave the way for the study of valley-based electronics and applications of topological mechanisms in robust optical-device engineering.

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arXiv2014

N00N states from a single non-linear directional coupler

In the quest for applicable quantum information technology miniaturised, compact and scalable sources are of paramount importance. Here, we present the concept for the generation of 2-photon N00N states without further post-processing in a single non-linear optical element. Based upon a periodically poled waveguide coupler, we present the principle of state generation via type-0 parametric down-conversion inside this type of devices. With the eigenmode description of the linear optical element, we utilise the delocalised photon pair generation to generate a N00N state in the measurement basis. We show, that we are able to eliminate the need for narrow-band spectral filtering, as well as for phase-stabilisation of the pump light, making this approach an elegant way to produce 2-photon N00N states.

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arXiv2014

Demonstration of coherent time-frequency Schmidt mode selection using dispersion-engineered frequency conversion

Time-frequency Schmidt (TFS) modes of ultrafast quantum states are naturally compatible with high bit-rate integrated quantum communication networks. Thus they offer an attractive alternative for the realization of high dimensional quantum optics. Here, we present a quantum pulse gate based on dispersion-engineered ultrafast frequency conversion in a nonlinear optical waveguide, which is a key element for harnessing the potential of TFS modes. We experimentally retrieve the modal spectral-temporal structure of our device and demonstrate a single-mode operation fidelity of 80\%, which is limited by experimental shortcomings. In addition, we retrieve a conversion efficiency of 87.7\% with a high signal-to-noise ratio of 8.8 when operating the quantum pulse gate at the single-photon level.

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arXiv2014

Driven Quantum Walks

In this letter we introduce the concept of a driven quantum walk. This work is motivated by recent theoretical and experimental progress that combines quantum walks and parametric down- conversion, leading to fundamentally different phenomena. We compare these striking differences by relating the driven quantum walks to the original quantum walk. Next, we illustrate typical dynamics of such systems and show these walks can be controlled by various pump configurations and phase matchings. Finally, we end by proposing an application of this process based on a quantum search algorithm that performs faster than a classical search.

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arXiv2014

Theory of filtered type-II PDC in the continuous-variable domain: Quantifying the impacts of filtering

Parametric down-conversion (PDC) forms one of the basic building blocks for quantum optical experiments. However, the intrinsic multimode spectral-temporal structure of pulsed PDC often poses a severe hindrance for the direct implementation of the heralding of pure single-photon states or, for example, continuous-variable entanglement distillation experiments. To get rid of multimode effects narrowband frequency filtering is frequently applied to achieve a single-mode behavior. A rigorous theoretical description to accurately describe the effects of filtering on PDC, however, is still missing. To date, the theoretical models of filtered PDC are rooted in the discrete-variable domain and only account for filtering in the low gain regime, where only a few photon pairs are emitted at any single point in time. In this paper we extend these theoretical descriptions and put forward a simple model, which is able to accurately describe the effects of filtering on PDC in the continuous-variable domain. This developed straightforward theoretical framework enables us to accurately quantify the trade-off between suppression of higher-order modes, reduced purity and lowered Einstein-Podolsky-Rosen (EPR) entanglement, when narrowband filters are applied to multimode type-II PDC.

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