A communications system perspective for dynamic mode atomic force microscopy, with applications to high-density storage and nanoimaging

In recent times, the atomic force microscope (AFM) has been used in various fields like biology, chemistry, physics and medicine for obtaining atomic level images. The AFM is a high-resolution microscope which can provide the resolution on the order of fractions of a nanometer. It has applications in the field of material characterization, probe based data storage, nano-imaging etc. The prevalent mode of using the AFM is the static mode where the cantilever is in continuous contact with the sample. This is harsh on the probe and the sample. The problem of probe and sample wear can be partly addressed by using the dynamic mode operation with the high quality factor cantilevers. In the dynamic mode operation, the cantilever is forced sinusoidally using a dither piezo. The oscillating cantilever gently taps the sample which reduces the probe-sample wear. In this dissertation, we demonstrate that viewing the dynamic mode operation from a communication systems perspective can yield huge gains in nano-interrogation speed and fidelity. In the first part of the dissertation, we have considered a data storage system that operates by encoding information as topographic profiles on a polymer medium. A cantilever probe with a sharp tip (few nm radius) is used to create and sense the presence of topographic profiles, resulting in a density of few Tb per square inch. The usage of the static mode is harsh on the probe and the media. In this work, the high quality factor dynamic mode operation, which alleviates the probe-media wear, is analyzed. The read operation is modeled as a communication channel which incorporates system memory due to inter-symbol interference and the cantilever state. We demonstrate an appropriate level of abstraction of this complex nanoscale system that obviates the need for an involved physical model. Next, a solution to the maximum likelihood sequence detection problem based on the Viterbi algorithm is devised. Experimental and simulation results demonstrate that the performance of this detector is several orders of magnitude better than the performance of other existing schemes. In the second part of the dissertation, we have considered another interesting application of the dynamic mode AFM in the field of nano-imaging. Nano-imaging has played a vital role in biology, chemistry and physics as it enables interrogation of material with sub-nanometer resolution. However, current nano-imaging techniques are too slow to be useful in the high speed applications of interest such as studying the evolution of certain biological processes over time that involve very small time scales. In this work, we present a high speed one-bit imaging technique using the dynamic mode AFM with a high quality factor cantilever. We propose a communication channel model for the cantilever based nano-imaging system. Next, we devise an imaging algorithm that incorporates a learned prior from the previous scan line while detecting the features on the current scan line. Experimental results demonstrate that our proposed algorithm provides significantly better image resolution compared to current nano-imaging techniques at high scanning speed. While modeling the probe-based data storage system and the cantilever based nano-imaging system, it has been observed that the channel models exhibit the behavior similar to intersymbol-interference (ISI) channel with data dependent time-correlated noise. The Viterbi algorithm can be adapted for performing maximum likelihood sequence detection in such channels. However, the problem of finding an analytical upper bound on the bit error rate of the Viterbi detector in this case has not been fully investigated. In the third part of the dissertation, we have considered a subset of the class of ISI channels with data dependent Gauss-Markov noise. We derive an upper bound on the pairwise error probability (PEP) between the transmitted bit sequence and the decoded bit sequence that can be expressed as a product of functions depending on current and previous states in the (incorrect) decoded sequence and the (correct) transmitted sequence. In general, the PEP is asymmetric. The average BER over all possible bit sequences is then determined using a pairwise state diagram. Simulations results demonstrate that analytic bound on BER is tight in high SNR regime

Storing, single photons in broadband vapor cell quantum memories

Single photons are an essential resource for realizing quantum technologies. Together with compatible quantum memories granting control over when a photon arrives, they form a foundational component both of quantum communication and quantum information processing. Quality solid-state single photon sources deliver on the high bandwidths and rates required for scalable quantum technology, but require memories that match these operational parameters. In this thesis, I report on quantum memories based on electromagnetically induced transparency and built in warm rubidium vapor, with such fast and high bandwidth interfaces in mind. I also present work on a heralded single photon source based on parametric downconversion in an optical cavity, operated in a bandwidth regime of a few 100s of megahertz. The systems are characterized on their own and together in a functional interface. As the photon generation process is spontaneous, the memory is implemented as a fully reactive device, capable of storing and retrieving photons in response to an asynchronous external trigger. The combined system is used to demonstrate the storage and retrieval of single photons in and from the quantum memory. Using polarization selection rules in the Zeeman substructure of the atoms, the read-out noise of the memory is considerably reduced from what is common in ground-state storage schemes in warm vapor. Critically, the quantum signature in the photon number statistics of the retrieved photons is successfully maintained, proving that the emission from the memory is dominated by single photons. We observe a retrieved single-photon state accuracy of $g_{c,\,\text{ret}}^{(2)}=0.177(23)$ for short storage times, which remains $g_{c,\,\text{ret}}^{(2)}<0.5$ throughout the memory lifetime of $680(50)\,$ns. The end-to-end efficiency of the memory interfaced with the photon source is $\eta_{e2e}=1.1(2)\,\%$, which will be further improved in the future by optimizing the operating regime. With its operation bandwidth of $370\,$MHz, our system opens up new possibilities for single-photon synchronization and local quantum networking experiments at high repetition rates

Quantum Cryptography

Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues.Comment: 55 pages, 32 figures; to appear in Reviews of Modern Physic

Formulation, implementation considerations, and first performance evaluation of algorithmic solutions - D4.1

Deliverable D4.1 del projecte Europeu OneFIT (ICT-2009-257385)This deliverable contains a first version of the algorithmic solutions for enabling opportunistic networks. The presented algorithms cover the full range of identified management tasks: suitability, creation, QoS control, reconfiguration and forced terminations. Preliminary evaluations complement the proposed algorithms. Implementation considerations towards the practicality of the considered algorithms are also included.Preprin

An On-chip PVT Resilient Short Time Measurement Technique

As the CMOS technology nodes continue to shrink, the challenges of developing manufacturing tests for integrated circuits become more difficult to address. To detect parametric faults of new generation of integrated circuits such as 3D ICs, on-chip short-time intervals have to be accurately measured. The accuracy of an on-chip time measurement module is heavily affected by Process, supply Voltage, and Temperature (PVT) variations. This work presents a new on-chip time measurement scheme where the undesired effects of PVT variations are attenuated significantly. To overcome the effects of PVT variations on short-time measurement, phase locking methodology is utilized to implement a robust Vernier delay line. A prototype Time-to-Digital Converter (TDC) has been fabricated using TSMC 0.180 µm CMOS technology and experimental measurements have been carried out to verify the performance parameters of the TDC. The measurement results indicate that the proposed solution reduces the effects of PVT variations by more than tenfold compared to a conventional on-chip TDC. A coarse-fine time interval measurement scheme which is resilient to the PVT variations is also proposed. In this approach, two Delay Locked Loops (DLLs) are utilized to minimize the effects of PVT on the measured time intervals. The proposed scheme has been implemented using CMOS 65nm technology. Simulation results using Advanced Design System (ADS) indicate that the measurement resolution varies by less than 0.1ps with ±15% variations of the supply voltage. The proposed method also presents a robust performance against process and temperature variations. The measurement accuracy changes by a maximum of 0.05ps from slow to fast corners. The implemented TDC presents a robust performance against temperature variations too and its measurement accuracy varies a few femto-seconds from -40 ºC to +100 ºC. The principle of robust short-time measurement was used in practice to design and implement a state-of-the-art Coordinate Measuring Machine (CMM) for an industry partner to measure geometrical features of transmission parts with micrometer resolution. The solution developed for the industry partner has resulted in a patent and a product in the market. The on-chip short-time measurement technology has also been utilized to develop a solution to detect Hardware Trojans

Development of a new trigger system for spin-filtering studies

Polarized antiprotons allow unique access to a number of fundamental physics observables. One example is the transversity distribution which is the last missing piece to complete the knowledge of the nucleon partonic structure at leading twist in the QCD-based parton model. The transversity is directly measurable via Drell-Yan production in double polarized antiproton-proton collisions. This and a multitude of other findings, which are accessible via ~p ~p scattering experiments, led the Polarized Antiproton eXperiments (PAX) Collaboration to propose such investigations at the High Energy Storage Ring (HESR) of the Facility for Antiproton and Ion Research (FAIR). Futhermore the production of intense polarized antiproton beams is still an unsolved problem, which is the core of the PAX proposal. In this frame, an intense work on the feasibility of this ambitious project is going on at COSY (COoler SYnchrotron of the Institut für KernPhysik –IKP– of the Forschungs Zentrum Jülich) (FZJ) where the work of this thesis has been performed. Presently, the only available method to polarize an antiproton beam is by means of the mechanism of spin-filtering exploiting the spin dependence of the (p p) interaction via the repeated interaction with a polarized hydrogen target. Since the total cross section is different for parallel and antiparallel orientation of the beam particle spins relative to the direction of the target polarization, one spin direction is depleted faster than the other, so that the circulating beam becomes increasingly polarized, while the intensity decreases with time. A spin-filtering experiment with protons has been prepared and finally realized in 2011 at the COSY ring in Jülich. Aims of the spin-filtering experiments at COSY performed by the PAX Collaboration were two. The first was to confirm the present understanding of the spin filtering processes in storage rings, and the second was the commissioning of the experimental setup, which will be used for the experiments with the antiprotons. The major part of my PhD work consisted in the development and commissioning of a new trigger board to be implemented in the Data Acquisition System (DAQ) of the experiment. The motivation for the project was the replacement of the existing old-fashioned trigger system based on NIM logic modules, with a modern system based on FPGA programmable chips. This, also in perspective of the more complex detection system that the Collaboration is planning to realize for the future experimental activity. The trigger board was designed and realized by the electronic workshop of the University of Ferrara and INFN of Ferrara. My first task was to write the control-software of the board. After that I performed a series of development and commissioning tests which successfully demonstrated the full efficiency of the board and gave green light for the implementation of the board in the experimental setup

Formulations and identification of algorithmic solutions for enabling opportunistic networks - M4.1

Milestone M4.1 del projecte Europeu OneFIT (ICT-2009-257385).This document contains a detailed description of the algorithms to be implemented to manage the opportunistic networks. There are defined according to the functional and system architecture (WP2) to fulfil the technical challenges. These algorithms will implemented during the WP4.2 and validated during the WP4.3Postprint (published version