118 research outputs found
Engineering of reconfigurable integrated photonics for quantum computation protocols
Over the last decade, integrated optics has emerged as one of the main technologies for quantum optics and more generally quantum computation, quantum cryptography and communication. In particular, it is fundamental for the construction of reconfigurable interferometers with a high number of optical modes. In this thesis we present, on the one hand, the development of a new geometry for the creation of integrated reconfigurable devices with a high number of modes and, on the other hand, the development of quantum computation protocols to be realized in integrated photonic chips. In the first part, two algorithms are proposed for the characterization of integrated circuits in terms of implemented unitary matrix. The first uses a so-called Black Box approach, i.e. one that makes no assumptions about the internal structure of the device under consideration, and it is based on second-order correlation measurements with coherent light. The second is specific to a planar rectangular geometry, first proposed by Clements et al., which has a variety of applications in the literature and is also employed in this thesis. Subsequently, we present the realization of a new 32-mode reconfigurable integrated photonic device with a continuously coupled three-dimensional geometry. Its potential in terms of reconfigurability is tested and a Boson sampling experiment with three and four photons is carried out to show its potential in the field of quantum computation. In the second part, we propose the application of integrated photonic devices to two quantum computation protocols. The first was recently proposed and is the quantum extension of a problem called Bernoulli factory. It consists in the construction of a qubit from qubits in the same unknown state so that there is a predetermined exact relation between the output and input states. In the thesis, we theoretically analyze the computational complexity of the problem in terms of the qubits used and the success probability of the problem. Furthermore, a photonic implementation is proposed and experimentally tested for correctness and resilience to experimental noise. The second application consists of the experimental implementation of a quantum metrology protocol in which three distinct phases are estimated simultaneously, showing that the use of indistinguishable photons leads to an advantage in terms of the variance of the estimates
Characterization of multimode linear optical networks
Multimode optical interferometers represent the most viable platforms for the successful implementation of several quantum information schemes that take advantage of optical processing. Examples range from quantum communication and sensing, to computation, including optical neural networks, optical reservoir computing, or simulation of complex physical systems. The realization of such routines requires high levels of control and tunability of the parameters that define the operations carried out by the device. This requirement becomes particularly crucial in light of recent technological improvements in integrated photonic technologies, which enable the implementation of progressively larger circuits embedding a considerable amount of tunable parameters. We formulate efficient procedures for the characterization of optical circuits in the presence of imperfections that typically occur in physical experiments, such as unbalanced losses and phase instabilities in the input and output collection stages. The algorithm aims at reconstructing the transfer matrix that represents the optical interferometer without making any strong assumptions about its internal structure and encoding. We show the viability of this approach in an experimentally relevant scenario, defined by a tunable integrated photonic circuit, and we demonstrate the effectiveness and robustness of our method. Our findings can find application in a wide range of optical setups, based on both bulk and integrated configurations
Experimental multiparameter quantum metrology in adaptive regime
Relevant metrological scenarios involve the simultaneous estimation of
multiple parameters. The fundamental ingredient to achieve quantum-enhanced
performances is based on the use of appropriately tailored quantum probes.
However, reaching the ultimate resolution allowed by physical laws requires non
trivial estimation strategies both from a theoretical and a practical point of
view. A crucial tool for this purpose is the application of adaptive learning
techniques. Indeed, adaptive strategies provide a flexible approach to obtain
optimal parameter-independent performances, and optimize convergence to the
fundamental bounds with limited amount of resources. Here, we combine on the
same platform quantum-enhanced multiparameter estimation attaining the
corresponding quantum limit and adaptive techniques. We demonstrate the
simultaneous estimation of three optical phases in a programmable integrated
photonic circuit, in the limited resource regime. The obtained results show the
possibility of successfully combining different fundamental methodologies
towards transition to quantum sensors applications
Optimizing quantum-enhanced Bayesian multiparameter estimation in noisy apparata
Achieving quantum-enhanced performances when measuring unknown quantities
requires developing suitable methodologies for practical scenarios, that
include noise and the availability of a limited amount of resources. Here, we
report on the optimization of quantum-enhanced Bayesian multiparameter
estimation in a scenario where a subset of the parameters describes unavoidable
noise processes in an experimental photonic sensor. We explore how the
optimization of the estimation changes depending on which parameters are either
of interest or are treated as nuisance ones. Our results show that optimizing
the multiparameter approach in noisy apparata represents a significant tool to
fully exploit the potential of practical sensors operating beyond the standard
quantum limit for broad resources range
Non-asymptotic Heisenberg scaling: experimental metrology for a wide resources range
Adopting quantum resources for parameter estimation discloses the possibility
to realize quantum sensors operating at a sensitivity beyond the standard
quantum limit. Such approach promises to reach the fundamental Heisenberg
scaling as a function of the employed resources in the estimation process.
Although previous experiments demonstrated precision scaling approaching
Heisenberg-limited performances, reaching such regime for a wide range of
remains hard to accomplish. Here, we show a method which suitably allocates the
available resources reaching Heisenberg scaling without any prior information
on the parameter. We demonstrate experimentally such an advantage in measuring
a rotation angle. We quantitatively verify Heisenberg scaling for a
considerable range of by using single-photon states with high-order orbital
angular momentum, achieving an error reduction greater than dB below the
standard quantum limit. Such results can be applied to different scenarios,
opening the way to the optimization of resources in quantum sensing
Quantum teleportation of a genuine vacuum-one-photon qubit generated via a quantum dot source
Quantum state teleportation represents a pillar of quantum information and a
milestone on the roadmap towards quantum networks with a large number of nodes.
Successful photonic demonstrations of this protocol have been carried out
employing different qubit encodings. However, demonstrations in the Fock basis
encoding are challenging, due to the impossibility of creating a coherent
superposition of vacuum-one photon states on a single mode with linear optics.
Previous realizations using such an encoding strongly relied on ancillary modes
of the electromagnetic field, which only allowed the teleportation of
subsystems of entangled states. Here, we enable quantum teleportation of
genuine vacuum-one photon states avoiding ancillary modes, by exploiting
coherent control of a resonantly excited semiconductor quantum dot in a
micro-cavity. Within our setup, we can teleport vacuum-one-photon qubits and
perform entanglement swapping in such an encoding. Our results may disclose new
potentialities of quantum dot single-photon sources for quantum information
applications.Comment: 10 pages, 4 figures + Supplementary Informatio
Witnesses of coherence and dimension from multiphoton indistinguishability tests
Quantum coherence marks a deviation from classical physics, and has been studied as a resource for metrology and quantum computation. Finding reliable and effective methods for assessing its presence is then highly desirable. Coherence witnesses rely on measuring observables whose outcomes can guarantee that a state is not diagonal in a known reference basis. Here, we experimentally measure a type of coherence witness that uses pairwise state comparisons to identify superpositions in a basis-independent way. Our experiment uses a single interferometric setup to simultaneously measure the three pairwise overlaps among three single-photon states via Hong-Ou-Mandel tests. Aside from coherence witnesses, we show the measurements also serve as a Hilbert-space dimension witness. Our results attest to the effectiveness of pooling many two-state comparison tests to ascertain various relational properties of a set of quantum states
Boson Sampling in a reconfigurable continuously-coupled 3D photonic circuit
Boson Sampling is a computational paradigm representing one of the most
viable and pursued approaches to demonstrate the regime of quantum advantage.
Recent results have demonstrated significant technological leaps in
single-photon generation and detection, leading to progressively larger
experimental instances of Boson Sampling experiments in different photonic
systems. However, a crucial requirement for a fully-fledged platform solving
this problem is the capability of implementing large scale interferometers,
that must simultaneously exhibit low losses, high degree of reconfigurability
and the realization of arbitrary transformations. In this work, we move a step
forward in this direction by demonstrating the adoption of a novel compact and
reconfigurable 3D-integrated platform for photonic Boson Sampling. We perform
3- and 4-photon experiments by using such platform, showing the possibility of
programming the circuit to implement a large number of unitary transformations.
These results show that such compact and highly-reconfigurable layout can be
scaled up to experiments with larger number of photon and modes, and can
provide a viable direction for hybrid computing with photonic processors.Comment: 17 pages, 14 figure
Detection of infectious disease outbreaks in twenty-two fragile states, 2000-2010: a systematic review.
Fragile states are home to a sixth of the world's population, and their populations are particularly vulnerable to infectious disease outbreaks. Timely surveillance and control are essential to minimise the impact of these outbreaks, but little evidence is published about the effectiveness of existing surveillance systems. We did a systematic review of the circumstances (mode) of detection of outbreaks occurring in 22 fragile states in the decade 2000-2010 (i.e. all states consistently meeting fragility criteria during the timeframe of the review), as well as time lags from onset to detection of these outbreaks, and from detection to further events in their timeline. The aim of this review was to enhance the evidence base for implementing infectious disease surveillance in these complex, resource-constrained settings, and to assess the relative importance of different routes whereby outbreak detection occurs.We identified 61 reports concerning 38 outbreaks. Twenty of these were detected by existing surveillance systems, but 10 detections occurred following formal notifications by participating health facilities rather than data analysis. A further 15 outbreaks were detected by informal notifications, including rumours.There were long delays from onset to detection (median 29 days) and from detection to further events (investigation, confirmation, declaration, control). Existing surveillance systems yielded the shortest detection delays when linked to reduced barriers to health care and frequent analysis and reporting of incidence data.Epidemic surveillance and control appear to be insufficiently timely in fragile states, and need to be strengthened. Greater reliance on formal and informal notifications is warranted. Outbreak reports should be more standardised and enable monitoring of surveillance systems' effectiveness
COVID19 Disease Map, a computational knowledge repository of virus-host interaction mechanisms.
Funder: Bundesministerium für Bildung und ForschungFunder: Bundesministerium für Bildung und Forschung (BMBF)We need to effectively combine the knowledge from surging literature with complex datasets to propose mechanistic models of SARS-CoV-2 infection, improving data interpretation and predicting key targets of intervention. Here, we describe a large-scale community effort to build an open access, interoperable and computable repository of COVID-19 molecular mechanisms. The COVID-19 Disease Map (C19DMap) is a graphical, interactive representation of disease-relevant molecular mechanisms linking many knowledge sources. Notably, it is a computational resource for graph-based analyses and disease modelling. To this end, we established a framework of tools, platforms and guidelines necessary for a multifaceted community of biocurators, domain experts, bioinformaticians and computational biologists. The diagrams of the C19DMap, curated from the literature, are integrated with relevant interaction and text mining databases. We demonstrate the application of network analysis and modelling approaches by concrete examples to highlight new testable hypotheses. This framework helps to find signatures of SARS-CoV-2 predisposition, treatment response or prioritisation of drug candidates. Such an approach may help deal with new waves of COVID-19 or similar pandemics in the long-term perspective
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