Two-photon diffraction and quantum lithography

We report a proof-of-principle experimental demonstration of quantum lithography. Utilizing the entangled nature of a two-photon state, the experimental results have bettered the classical diffraction limit by a factor of two. This is a quantum mechanical two-photon phenomenon but not a violation of the uncertainty principle.Comment: 5 pages, 5 figures Submitted to Physical Review Letter

Coherent Superposition States as Quantum Rulers

We explore the sensitivity of an interferometer based on a quantum circuit for coherent states. We show that its sensitivity is at the Heisenberg limit. Moreover we show that this arrangement can measure very small length intervals

Entangled-State Lithography: Tailoring any Pattern with a Single State

We demonstrate a systematic approach to Heisenberg-limited lithographic image formation using four-mode reciprocal binominal states. By controlling the exposure pattern with a simple bank of birefringent plates, any pixel pattern on a $(N+1) \times (N+1)$ grid, occupying a square with the side half a wavelength long, can be generated from a $2 N$-photon state.Comment: 4 pages, 4 figure

Two-Photon Interferometry for High-Resolution Imaging

We discuss advantages of using non-classical states of light for two aspects of optical imaging: creating of miniature images on photosensitive substrates, which constitutes the foundation for optical lithography, and imaging of micro objects. In both cases, the classical resolution limit given by the Rayleigh criterion is approximately a half of the optical wavelength. It has been shown, however, that by using multi-photon quantum states of the light field, and multi-photon sensitive material or detector, this limit can be surpassed. We give a rigorous quantum mechanical treatment of this problem, address some particularly widespread misconceptions and discuss the requirements for turning the research on quantum imaging into a practical technology.Comment: Presented at PQE 2001. To appear in Special Issue of Journal of Modern Optic

Positioning and clock synchronization through entanglement

A method is proposed to employ entangled and squeezed light for determining the position of a party and for synchronizing distant clocks. An accuracy gain over analogous protocols that employ classical resources is demonstrated and a quantum-cryptographic positioning application is given, which allows only trusted parties to learn the position of whatever must be localized. The presence of a lossy channel and imperfect photodetection is considered. The advantages in using partially entangled states is discussed.Comment: Revised version. 9 pages, 6 figure

Quantum enhanced positioning and clock synchronization

A wide variety of positioning and ranging procedures are based on repeatedly sending electromagnetic pulses through space and measuring their time of arrival. This paper shows that quantum entanglement and squeezing can be employed to overcome the classical power/bandwidth limits on these procedures, enhancing their accuracy. Frequency entangled pulses could be used to construct quantum positioning systems (QPS), to perform clock synchronization, or to do ranging (quantum radar): all of these techniques exhibit a similar enhancement compared with analogous protocols that use classical light. Quantum entanglement and squeezing have been exploited in the context of interferometry, frequency measurements, lithography, and algorithms. Here, the problem of positioning a party (say Alice) with respect to a fixed array of reference points will be analyzed.Comment: 4 pages, 2 figures. Accepted for publication by Natur

Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption

For dissipation-free photon-photon interaction at the single photon level, we analyze one-photon transition and two-photon transition induced by photon pairs in three-level atoms using two-photon wavefunctions. We show that the two-photon absorption can be substantially enhanced by adjusting the time correlation of photon pairs. We study two typical cases: Gaussian wavefunction and rectangular wavefunction. In the latter, we find that under special conditions one-photon transition is completely suppressed while the high probability of two-photon transition is maintained.Comment: 6 pages, 4 figure

The feasible generation of entangled photon states by using linear optical elements

We present a feasible scheme to produce a polarization-entangled photon states $\frac{1}{\sqrt{2}}(|H>|V>+|V>|H>)$ in a controllable way. This scheme requires single-photon sources, linear optical elements and photon detectors. It generates the entanglement of spatially separated photons. The interaction takes place in the photon detectors. We also show that the same idea can be used to produce the entangled $N$-photon state $\frac{1}{\sqrt{2}}(|0,N>+|N,0>)$Comment: to appear in PR

On building physics-based AI models for the design and SHM of mooring systems

Expert systems in industrial processes are modelled using physics-based approaches, data-driven models or hybrid approaches in which however the underlying physical models generally constitute a separate block with respect to the Artificial Intelligence (AI) technique(s). This work applies the novel concept of “imbrication”-a physics-based AI approach-to the mooring system of offshore renewable energy devices to achieve a complete integration of both perspectives. This approach can reduce the size of the training dataset and computational time while delivering algorithms with higher generalization capability and explicability. We first undertake the design of the mooring system by developing a surrogate model coupled with a Bayesian optimiser. Then, we analyse the structural health monitoring of the mooring system by designing a supervised Deep Neural Network architecture. Herein, we describe the characteristics of the imbrication process, analyse preliminary results of our investigation and provide considerations for orienting further research work and sector applicability

Implementation of Signal Processing Methods in a Structural Health Monitoring (SHM) System based on Ultrasonic Guided Waves for Defect Detection in Different Materials and Structures

The local defect inspection in longitudinal structures such as plates or pipelines implies high economical costs and it is time consuming mainly in underground infrastructures, energy or water, and aerospace sectors. Moreover, if these structures are non-accessible, their local inspection is not possible. Ultrasonic (US) inspection technique based on guided waves is one of the potential alternatives to address this issue. The US inspection based on these type of waves could be applied in many scenarios to monitor the damage state of structures; i.e., in water underground pipelines to identify the wall thickness losses or impact damage detection on Carbon Fiber Reinforced Composites (CFRC). A SHM system based on guided waves requires a special signal processing in order to identify possible damage in the structure. The signal emitted and received is a combination of different propagation modes which are difficult to identify and analyse. However, if the signals are compared to each other (signal related to non-damaged components compared to damaged signal) it is possible to measure their difference as a distance that can be used to estimate the damage level. In this work, signals corresponding to non-damaged samples have been captured and then different types of damage have been applied for different cases. After the data acquisition phase, the comparison between signals has been carried out by applying different mathematical methods and distance metrics (SDC, DTW, Euclidean, Manhattan and Chebyshev), with the aim of detecting defects in different structures and materials. For this purpose, two cases have been analysed: 1) In CFRC plates subjected to impact damage and deformations and 2) In a pipe coated by cement-mortar in order to quantify the wall thickness losses. In both cases ultrasonic PZT sensors, an ultrasonic multichannel pulser/receiver and a software developed ad-hoc have been used. Although the SHM system components were similar, it must be noted that the type of ultrasonic guided waves used were different; in the case of CFRC plates, Lamb waves were excited whereas in the case of the pipeline, Love waves have been used. A comparison between the above mentioned methods is provided. The results show the validity of the approach for damage characterization.Authors would like to acknowledge the Basque Government funding within the ELKARTEK Programme (AIRHEM)