Search

Superconducting qubits have seen a tremendous progress in the last two decades, and yet they remain unable to extract quantum advantage for application scenarios. While algorithms like Shor’s demonstrate quantum advantage in theory, they do not seem to fit modern noisy quantum processors. Then, in order to achieve quantum advantage either modern quantum processors catch up to their expected behaviour, or modern algorithms are tailored to fit the expected behaviour of modern chips. This thesis focuses on the second approach, which is to explore the implementation of algorithms on modern quantum processors. Along all these implementations, we study the errors that cause these algorithms to derail from their ideal results. We attempt to understand, quantify and control these errors, in the hope that this provides useful insights into how to design algorithms for the modern hardware. This thesis starts by introducing the topic of superconducting quantum processors and modern algorithms in the first two chapters. Then we move onto the three experiments, one chapter each, detailing our findings. The first experiment cover an digital-analog implementation of a quantum simulation of light-matter interaction. We present the implementation that makes use of both digital (gates) and analog (evolution) blocks. The accuracy of the Trotterization technique is studied in detail, as well as the capability to study the photon population in the resonator. We manage to implement up to 90 Trotter steps and reproduce the behaviour in the ultra-strong coupling regime. The second experiment presents an error mitigation technique, on an application of great interest to the field (molecular simulations). This application is a fully digital one, within the hot topic of variational algorithms for ground-state preparation. The mitigation technique, which is an invention of our own team (see referenced theoretical works) manages to reduce the algorithm error over an order of mag, QCD/DiCarlo Lab

In this dissertation I will explore the question whether various entities commonly used in quantum field theory can be “constructed". In particular, can spacetime be “constructed" out of building blocks, and can Berezin integral be “constructed" in terms of Riemann integrals. As far as “constructing" spacetime out of building blocks, it has been attempted by multiple scientific communities and various models were proposed. But the common downfall is they break the principles of relativity. I will explore the ways of doing so in such a way that principles of relativity are respected. One of my approaches is to replace points with some entities that have a direction. In one of the sections, those entities are tangent vectors, in the other section they are pairs of points. In both cases, the success of respecting relativity is partial. On the one hand, I successfully removed preferred time axis. But, on the other hand, I still did not restore the symmetry under Lorentz group (or some modification of Lorentz group). For this reason, I also explored a different approach where I designed a matrix model for spacetime. In this case, I successfully restored Eucledian symmetry. Restoring the MInkowksian symmetry proved to be iii more difficult, and, depending on the models, came with the price. In both cases, though, the qestion of whether the resulting quantum field theory approximates the one that we know is left as an open question. There are reasons to hope that it does, but rigorously finding out whether that is the case is left for the future research. As far as constructing Berezin integral in terms of Riemann integrals, this was not attempted nearly as much (although there was one attempt in 1983 by Rabin, and possibly a couple of other isolated attempts). I have attempted to address it in my joint paper with Thomas Scanlon where we supplemented the anticommutting wedge product with Clifford algebra. This essentially amounts to “geometric algebra" mod

Eine wesentliche Komponente eines Quantennetwerks ist die Übertragung von einem Quantenzustand von einer Plattform auf die andere. Insbesondere die Übertragung des Polarisationszustands eines Photons auf den elektronischen Zustand eines Atoms ist ein wichtiger Aspekt für die Realisierung eines hybriden Quantennetzwerks. In dieser Masterarbeit schaffe ich die Grundlagen zur Absorption einzelner Photonen für eine Ion-Resonator Schnittstelle. Abgeschwächte kohärente Pulse können ein wichtiges Mittel sein, um Eigenschaften eines Quantennetzwerks lokal zu testen. Daher haben wir das Ziel, abgeschwächte kohärente Pulse zur Untersuchung der Absorption für eine Ion-Resonator Schnittstelle zu verwenden. In einer numerischen Simulation zeige ich, dass mit abgeschwächten kohärenten Pulsen für einen idealen optischen Resonator eine Absorptionseffizienz von eta_a = 12.8% erreicht werden kann. Wenn die bekannten Verluste unseres aktuellen optischen Resonators berücksichtigt werden, reduziert sich die Absorptionseffizienz um mehr als eine Größenordnung. Anschließend zeige ich, dass abgeschwächte kohärente Pulse mit einer durchschnittlichen Photonenzahl von n_p = 1.01(3) erzeugt werden können. Anhand der Reflexion am Resonator von R_exp = 92.6(6)% der abgeschwächten kohärenten Pulse zeige ich, dass wir die Resonatormode mit Photonen populieren können, was den Weg für zukünftige Experimente zur Absorption von abgeschwächten kohärenten Pulsen mit einem einzelnen Ion ebnet., An essential component of a quantum network is the mapping of quantum information from one platform to the other. In particular, mapping the polarization state of a photon to the electronic state of an atom can be a promising route towards the realization of a hybrid quantum network. In this master’s thesis, I lay the groundwork for the absorption of single photons for an ion-cavity interface. Weak coherent pulses can be an important tool to test features of a quantum network locally, and thus we aim to use weak coherent pulses to test the absorption for an ion-cavity interface. In a numerical simulation, I show that for an ideal cavity, weak coherent pulses can be absorbed with an efficiency of eta_a = 12.8%. When the known losses of our current experimental cavity are included, the absorption efficiency is reduced by more than an order of magnitude. Finally, I show that we can generate weak coherent pulses in the laboratory with an average of n_p = 1.01(3) photons. With a reflection of the weak coherent pulse from the experimental cavity of R_exp = 92.6(6)%, I demonstrate that we can populate the cavity field with weak coherent pulses at the single-photon level, paving the way for future experiments of absorption of weak coherent pulses with a single ion., Masterarbeit Universität Innsbruck 2023

State preparation is needed to perform a variety of quantum algorithms. In this thesis, the focus lies on a version that aims to program amplitudes and phases of a superposition consisting of a polynomial number of states. The quantum random access memory (QRAM) a pioneering ansatz, which solves this problem needs an exponential amount of resources. A less general, but not as hardware-intense protocol has been proposed. In this thesis phase development during the adiabatic-diabatic segments of the protocol is studied and the ansatz is extended to include phase programming using only local fields. The necessary field strengths can be calculated analytically and the phases can be controlled very precisely and in more situations compared to the amplitudes. The extended protocol is then benchmarked, where the overlap between the target state and the prepared state is used as a measure of performance. It was shown that the protocol struggles to prepare superposition states, which have eigenstates that contribute to the superposition with a low amplitude, but shows better performance if every eigenstate that contributes to the superposition contributes with similar amplitudes., Gregor Aigner, Masterarbeit Universität Innsbruck 2023

The opinion flows from Introduction to the immunological quantum that requires a historical perspective, to Quantum vaccine algorithms supported by a bibliometric analysis, to Quantum vaccinomics describing from our perspective the different vaccinomics and quantum vaccinomics algorithms. Finally, in the Discussion and conclusions we propose novel platforms and algorithms developed to further advance on quantum vaccinomics. In the paper we refer to protective epitopes or immunological quantum for the design of candidate vaccine antigens, which may elicit a protective response through both cellular and antibody mediated mechanisms of the host immune system. Vaccines are key interventions for the prevention and control of infectious diseases affecting humans and animals worldwide. Biophysics led to quantum biology and quantum immunology reflecting quantum dynamics within living systems and their evolution. In analogy to quantum of light, immune protective epitopes were proposed as the immunological quantum. Multiple quantum vaccine algorithms were developed based on omics and other technologies. Quantum vaccinomics is the methodological approach with different platforms used for the identification and combination of immunological quantum for vaccine development. Current quantum vaccinomics platforms include in vitro, in music and in silico algorithms and top trends in biotechnology for the identification, characterization and combination of candidate protective epitopes. These platforms have been applied to different infectious diseases and in the future should target prevalent and emerging infectious diseases with novel algorithms.

We propose two critical dissipative quantum metrology schemes for single parameter estimation which are based on a quantum probe consisting of a coherently driven ensemble of N spin-1/2 particles under the effect of a collective spin decay. The collective spin system exhibits a dissipative phase transition between thermal and ferromagnetic phases, which is characterized by a nonanalytical behavior of the spin observables. We show that thanks to the dissipative phase transition the sensitivity of the parameter estimation can be significantly enhanced. Furthermore, we show that our steady state is a spin squeezed state which allows one to perform parameter estimation with sub shot-noise limited measurement uncertainty.

Interactions between electrons and nuclei in matter determine all materials' properties. Understanding and modeling these interactions is of paramount importance, particularly in addressing critical scientific questions related to renewable energy solutions, sustainable materials, and semiconductor device modeling. However, simulations of the electronic structure face a common constraint—an accuracy-size tradeoff. While it is possible to simulate materials at the quantum level of accuracy, this is typically limited to a few thousand atoms, even with advanced tools like density functional theory (DFT). On the other hand, large-scale simulations often sacrifice predictive power due to necessary approximations. The Materials Learning Algorithms (MALA) [1] package addresses these challenges by leveraging a combination of neural networks, physically constrained optimization algorithms [2], and efficient post-processing routines. Unlike existing approaches, MALA replaces DFT entirely, providing access to both scalar quantities of interest, such as energies, and volumetric information about the electronic structure, such as the electronic density. Our research has demonstrated that MALA can be applied to systems with arbitrary numbers of atoms (successfully testing up to 100,000 atoms) [3], across various temperature and pressure ranges [4]. We anticipate that MALA will have a significant impact, enabling unprecedented modeling capabilities in the fields of materials science and semiconductor device modeling. [1] L. Fiedler, Z. A. Moldabekov, X. Shao, K. Jiang, T. Dornheim, M. Pavanello, A. Cangi, Phys. Rev. Res. 4, 043033 (2022). [2] L. Fiedler, N. Hoffmann, P. Mohammed, G. A. Popoola, T. Yovell, V. Oles, J. A. Ellis, S. Rajamanickam, A. Cangi, Mach. Learn.: Sci. Technol. 3, 045008 (2022). [3] L. Fiedler, N. A. Modine, S. Schmerler, D. J. Vogel, G. A. Popoola, A. P. Thompson, S. Rajamanickam, A. Cangi, Npj Comput. Mater. 9, 115 (2023). [4] L. Fiedler, N. A. Modine, K. D.

This talk will present our research on merging machine learning with quantum mechanics. Electron-nuclear interactions determine all materials' properties, and accurate simulations of electronic structure are essential to address critical scientific questions related to renewable energy, sustainable materials, and semiconductor devices. However, electronic structure simulations face an accuracy-size tradeoff. I will first present our ongoing efforts on developing the Materials Learning Algorithms (MALA) package to solve the electronic structure problem faster. MALA leverages a combination of neural networks, physically constrained optimization algorithms, and efficient post-processing routines. Next, I will present our work on using physics-informed neural networks to solve the time-dependent Kohn-Sham equations, which describe electron dynamics in response to incident electromagnetic waves.

Interactions between electrons and nuclei in matter determine all materials' properties. Understanding and modeling these interactions is of paramount importance, particularly in addressing critical scientific questions related to renewable energy solutions, sustainable materials, and semiconductor device modeling. However, simulations of the electronic structure face a common constraint—an accuracy-size tradeoff. While it is possible to simulate materials at the quantum level of accuracy, this is typically limited to a few thousand atoms, even with advanced tools like density functional theory (DFT). On the other hand, large-scale simulations often sacrifice predictive power due to necessary approximations. The Materials Learning Algorithms (MALA) [1] package addresses these challenges by leveraging a combination of neural networks, physically constrained optimization algorithms [2], and efficient post-processing routines. Unlike existing approaches, MALA replaces DFT entirely, providing access to both scalar quantities of interest, such as energies, and volumetric information about the electronic structure, such as the electronic density. Our research has demonstrated that MALA can be applied to systems with arbitrary numbers of atoms (successfully testing up to 100,000 atoms) [3], across various temperature and pressure ranges [4]. We anticipate that MALA will have a significant impact, enabling unprecedented modeling capabilities in the fields of materials science and semiconductor device modeling. [1] L. Fiedler, Z. A. Moldabekov, X. Shao, K. Jiang, T. Dornheim, M. Pavanello, A. Cangi, Phys. Rev. Res. 4, 043033 (2022). [2] L. Fiedler, N. Hoffmann, P. Mohammed, G. A. Popoola, T. Yovell, V. Oles, J. A. Ellis, S. Rajamanickam, A. Cangi, Mach. Learn.: Sci. Technol. 3, 045008 (2022). [3] L. Fiedler, N. A. Modine, S. Schmerler, D. J. Vogel, G. A. Popoola, A. P. Thompson, S. Rajamanickam, A. Cangi, Npj Comput. Mater. 9, 115 (2023). [4] L. Fiedler, N. A. Modine, K. D.

© 2015 Elsevier Inc. Support from the Ministerio de Economia y Competitividad (Spain) under Project Nos. FIS2011-29596-C02-01 (AS) and FIS2012-35583 (AL), and a "Ramon y Cajal" Research Fellowship with Ref. RYC-2010-05768 (AS) is acknowledged., Weak-measurement-based experiments (Kocsis et al., 2011) have shown that, at least for pure states, the average evolution of independent photons in Young's two-slit experiment is in compliance with the trajectories prescribed by the Bohmian formulation of quantum mechanics. But, what happens if the same experiment is repeated assuming that the wave function associated with each particle is different, i.e., in the case of mixed (incoherent) states? This question is investigated here by means of two alternative numerical simulations of Young's experiment, purposely devised to be easily implemented and tested in the laboratory. Contrary to what could be expected a priori, it is found that even for conditions of maximal mixedness or incoherence (total lack of interference fringes), experimental data will render a puzzling and challenging outcome: the average particle trajectories will still display features analogous to those for pure states, i.e., independently of how mixedness arises, the associated dynamics is influenced by both slits at the same time. Physically this simply means that weak measurements are not able to discriminate how mixedness arises in the experiment, since they only provide information about the averaged system dynamics., Ministerio de Economía y Competitividad (MINECO), España, Programa Ramon y Cajal, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

We study resonating valence bond (RVB) states in the projected entangled pair states (PEPS) formalism. Based on symmetries in the PEPS description, we establish relations between the toric code state, the orthogonal dimer state, and the SU(2) singlet RVB state on the kagome lattice: We prove the equivalence of toric code and dimer state, and devise an interpolation between the dimer state and the RVB state. This interpolation corresponds to a continuous path in Hamiltonian space, proving that the RVB state is the fourfold degenerate ground state of a local Hamiltonian on the (finite) kagome lattice. We investigate this interpolation using numerical PEPS methods, studying the decay of correlation functions, the change of overlap, and the entanglement spectrum, none of which exhibits signs of a phase transition., Unión Europea. FP7, Comunidad de Madrid, Alexander von Humboldt Foundation, Caltech Institute for Quantum Information and Matter (an NSF Physics Frontiers Center), Gordon and Betty Moore Foundation, NSF, Agence Nationale de la Recherche, DFG Forschergruppe, CALMIP (Toulouse), Caixa Manresa, Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

©2008 The American Physical Society. We acknowledge financial support from the Spanish MEC project No. FIS2006-04885, the project No. CAM-UCM/910758 (A.B. and M.A.M.D.) and the UCM project No. PR1-A/07-15378 (A.L.). Additionally, we acknowledge support from a FPU MEC grant (A.B.), and the ESF Science Programme INSTANS 2005-2010 (M.A.M.D.)., We study the nonrelativistic limit of a paradigmatic model in relativistic quantum mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a different kind of Zitterbewegung which persists in this nonrelativistic regime, and leads to an observable deformation of the particle orbit. This effect can be interpreted in terms of a Ramsey-interferometric phenomenon, allowing an insightful connection between relativistic quantum mechanics and quantum optics. Furthermore, subsequent corrections to the nonrelativistic limit, which account for the usual spin-orbit Zitterbewegung, can be neatly understood in terms of a Mach-Zehnder interferometer., Ministerio de Educación y Ciencia (MEC), España, Universidad Complutense de Madrid (UCM), Comunidad de Madrid (CAM), European Science Foundation (ESF), Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© 1996 The American Physical Society. A. L. acknowledges the support of a grant from the Dirección General de Investigación Científica y Técnica del Ministerio Español de Educación y Ciencia and the kind hospitality from the Optics Department of the Palacký University. J. P. acknowledges partial support of the Grant No. 202y96y0421 of Czech Grant Agency., Two examples are presented where the photon emission on spontaneous parametric down-conversion is prevented when attempts are made to infer the moment of emission. This inhibition is analyzed in terms of the disturbance caused on the system by the modifications that must be introduced in order to make possible such inference., Dirección General de Investigación Científica y Técnica (DGICYT), España, Czech Grant Agency, Ministerio de Educación y Ciencia (MEC), España, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© 1993 The American Physical Society. We are much indebted to Professor E. Bernabeu for his continual advice and interest in the present work., An alternative derivation of the Pegg-Barnett phase operator is presented. This approach is based on the properties of the representation in quantum mechanics of a nonlinear nonbijective canonical transformation. It does not use as its starting point either a finite-dimensional space or the definition of phase states. The features of this formalism are analyzed in terms of this transformation., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© Atlantis Press. One of us (FC) would like to thank Francois Leyvraz for several illuminating discussions. The research reported in this paper has profited from visits by each of the two authors in the Department of the other performed in the framework of the exchange program among our two Universities. The research of DGU is supported in part by the Ramón y Cajal program of the Ministerio de Ciencia y Tecnología and by the DGI under grants FIS2005-00752 and MTM2006-00478., Mechanisms are elucidated underlying the existence of dynamical systems whose generic solutions approach asymptotically (at large time) isochronous evolutions: all their dependent variables tend asymptotic ally to functions periodic with the sa m e fixed period. We focus on two such mechanisms, emphasizing their generality and illustrating each of them via a representative example. The first example belongs to a recently discovered class of integrable indeed solvable many-body problems. The second example consists of a broad class of (generally nonintegrable) models obtained by deforming appropriately the well-known (integrable and isochronous) many-body problem with inverse-cube two-body forces and a one-body linear ("harmonic oscillator") force., Ministerio de Ciencia y Tecnologia. Ramón y Cajal program, DGI, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2015 American Physical Society. We thank G. Toth, H. de Guise, and B.-G. Englert for fruitful discussions. Z.H. and J.R. are thankful for the financial assistance of the Grant Agency of the Czech Republic (Grant No. 15-031945) and the IGA Project of the Palacky University (Grant No. PrF_2015_002). G.L. is partially funded by EU FP7 (Grant No. Q-ESSENCE). Finally, P.H. and L.L.S.-S. acknowledge the support from the Spanish MINECO (Grant No. FIS2011-26786) and UCM-Banco Santander Program (Grant No. GR3/14)., Rotated quadratures carry the phase-dependent information of the electromagnetic field, so they are somehow conjugate to the photon number. We analyze this noncanonical pair, finding an exact uncertainty relation, as well as a couple of weaker inequalities obtained by relaxing some restrictions of the problem. We also find the intelligent states saturating that relation and complete their characterization by considering extra constraints on the second-order moments of the variables involved. Using these moments, we construct performance measures tailored to diagnose photon-added and Schrodinger-cat-like states, among others., Unión Europea. FP7, Ministerio de Economía y Competitividad (MINECO), España, Grant Agency of the Czech Republic, IGA Project of the Palacky University, Universidad Complutense de Madrid (UCM), Banco Santander Central Hispano (BSCH), Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We are grateful to Professors A Smerzi, L Maccone, M Tsang and M J W Hall for useful discussions. We acknowledge financial support from the project QUITEMAD S2009-ESP-1594 of the Consejeria de Educacion de la Comunidad de Madrid. AR acknowledges support from MICINN FIS2009-10061. AL acknowledges support from project no. FIS2008-01267 of the Spanish Direccion General de Investigacion del Ministerio de Ciencia e Innovacion., We provide evidence that the uncertainty in detection of small and deterministic phase-shift deviations from a working point can be lower than the Heisenberg bound, for a fixed finite mean number of photons. We achieve that by exploiting nonlinearity of estimators and coherence with the vacuum., Comunidad de Madrid, Ministerio de Ciencia e Innovacion (MICINN), España, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

©2013 American Physical Society. M. A. P. acknowledges support from Projects No. MTM2012-39101-C02-01 and No. FIS2010-22082 of the Ministerio de Economia y Competitividad of Spain. A. L. acknowledges support from Projects No. FIS2012-35583 of the Spanish Ministerio de Economia y Competitividad and QUITEMAD No. S2009-ESP-1594 of the Consejeria de Educacion de la Comunidad de Madrid. I. G. acknowledges support from Project No. FIS2010-22082. We thank Dr. H. Canabal and Dr. F. Carreno for technical assistance., We provide theoretical and experimental evidence of a classical-optics realization of quantum Zeno dynamics. In contrast to other approaches, the classical implementation is extremely simple and adaptable. Frequently monitoring the transverse spreading of the light emitted by an extended source results in a nontrivial dynamics where spreading and all other transverse effects associated with light propagation as the increase of spatial coherence tends to be inhibited. This is fully equivalent to a quantum Zeno dynamics where monitoring whether a quantum free particle at rest remains in a spatial interval causes inhibition of the quantum-state evolution, including the degree of purity., Comunidad de Madrid, Ministerio de Economia y Competitividad (MINECO), Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

©2007 The American Physical Society. This work was supported by grants FIS2006-12783-C03-01 from Ministerio de Educación y Ciencia of Spain, and 200650M012 from Comunidad de Madrid and CSIC. A.R. is supported by the Spanish program “Juan de la Cierva”. R.A.M. is supported by the I3P program funded by the European Social Fund., We investigate the decoherence properties of a central system composed of two spins 1/2 in contact with a spin bath. The dynamical regime of the bath ranges from a fully integrable limit to complete chaoticity. We show that the dynamical regime of the bath determines the efficiency of the decoherence process. For perturbative regimes, the integrable limit provides stronger decoherence, while in the strong coupling regime the chaotic limit becomes more efficient. We also show that the decoherence time behaves in a similar way. On the contrary, the rate of decay of magnitudes like linear entropy or fidelity does not depend on the dynamical regime of the bath. We interpret the latter results as due to a comparable complexity of the Hamiltonian for both the integrable and the fully chaotic limits., Ministerio de Educación y Ciencia, Comunidad de Madrid, CSIC, Spanish program “Juan de la Cierva”, European Social Fund, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Supplementary material: http://eprints.sim.ucm.es/38062, The spectral gap-the energy difference between the ground state and first excited state of a system-is central to quantum many-body physics. Many challenging open problems, such as the Haldane conjecture, the question of the existence of gapped topological spin liquid phases, and the Yang-Mills gap conjecture, concern spectral gaps. These and other problems are particular cases of the general spectral gap problem: given the Hamiltonian of a quantum many-body system, is it gapped or gapless? Here we prove that this is an undecidable problem. Specifically, we construct families of quantum spin systems on a two-dimensional lattice with translationally invariant, nearest-neighbour interactions, for which the spectral gap problem is undecidable. This result extends to undecidability of other low-energy properties, such as the existence of algebraically decaying ground-state correlations. The proof combines Hamiltonian complexity techniques with aperiodic tilings, to construct a Hamiltonian whose ground state encodes the evolution of a quantum phase-estimation algorithm followed by a universal Turing machine. The spectral gap depends on the outcome of the corresponding 'halting problem'. Our result implies that there exists no algorithm to determine whether an arbitrary model is gapped or gapless, and that there exist models for which the presence or absence of a spectral gap is independent of the axioms of mathematics., Comunidad de Madrid, Royal Society, Ministerio de Economía y Competitividad (MINECO), European Research Council (ERC) under the European Union, John Templeton Foundation, Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

Copyright © 1994 Published by Elsevier B.V. FRR was supported by FOM, The Netherlands. The authors are also grateful to CICyT, Spain for partial support., We show that the renormalized vacuum expectation value of he Wilson loop for topologically massive abelian gauge theory in R3 can be defined so that its large-mass limit is the renormalized vacuum expectation value of the Wilson loop for abelian Chern-Simons theory also in R3., FOM,Netherlands, CICyT,Spain, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2010 The American Physical Society. This work has been supported by project No. FIS2008-01267 of the Spanish Direccion General de Investigacion del Ministerio de Ciencia e Innovacion, and by project QUITEMAD S2009-ESP-1594 of the Consejeria de Educacion de la Comunidad de Madrid., We examine the relation between second-order coherence and resolution in the interferometric detection of phase shifts. While for classical thermal light resolution and second-order coherence are synonymous, we show that for quantum light beams reaching optimum precision second-order coherence and resolution become antithetical., Comunidad de Madrid, Ministerio de Ciencia e Innovación (MCINN), España, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© 1998 The American Physical Society. We wish to thank Professor G. García-Alcaine for a careful reading of the manuscript., Two examples are presented where the observation of the emission in parametric down-conversion leads to its enhancement instead of its inhibition. The improvement is analyzed in terms of the quantum features of the observation., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

For every Matrix Product State (MPS) one can always construct a so-called parent Hamiltonian. This is a local, frustration free, Hamiltonian which has the MPS as ground state and is gapped. Whenever that parent Hamiltonian has a degenerate ground state space (the so-called non-injective case), we construct another ’uncle’ Hamiltonian which is also local and frustration free, has the same ground state space, but is gapless, and its spectrum is R +. The construction is obtained by linearly perturbing the matrices building up the state in a random direction, and then taking the limit where the perturbation goes to zero. For MPS where the parent Hamiltonian has a unique ground state (the so-called injective case) we also build such uncle Hamiltonian with the same properties in the thermodynamic limit., Comunidad de Madrid, Ministerio de Ciencia e Innovación (MICINN), European CHIST-ERA, Unión Europea. FP7, NSF, ARO, Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

The ability to communicate securely across the internet is owing to the security of the RSA cryptosystem, among others. This cryptosystem relies on the difficulty of integer factorization to provide secure communication. Peter Shor’s quantum integer factorization algorithm threatens to upend this. A special case of the hidden subgroup problem, the algorithm provides an exponential speedup in the integer factorization problem, destroying RSA’s security. Robert McEliece’s cryptosystem has been proposed as an alternative. Based upon binary Goppa codes instead of integer factorization, his cryptosystem uses code scrambling and error introduction to hinder decrypting a message without the private key. This cryptosystem cannot be reduced to the hidden subgroup problem and stands as a viable post-quantum alternative to RSA encryption.

This study critically reevaluates the Harlow-Hayden (HH) solution to the black hole information paradox and its articulation in the firewall paradox. The exploration recognizes the HH solution as a revolutionary approach in black hole physics, steering away from traditional constraints to depict the event horizon as a computational rather than a physical barrier. The paper first maps the initial physical dilemma that instigated the HH journey, introducing Alice, an observer facing intricate computational challenges as she approaches the black hole. I then depict the evolution of the narrative, describing how Alice was facilitated with a quantum computer to surmount the computational challenges and further detailing the augmented complexities arising from the integration of the physical dynamics of the black hole. Yet, HH's research applies the AdS/CFT correspondence to explore the dynamic unitary transformation in solving the firewall paradox through decoding Hawking radiation. However, it identifies a contradiction; the eternal perspective of black holes from the AdS/CFT theory challenges the firewall paradox's foundation. Finally, I narrate a paradigm shift as HH reframes Alice's task within the realms of error-correcting codes, illustrating a remarkable transition from a physical problem in black hole physics to a computational predicament in computer science. The study revisits pivotal moments in understanding black hole physics ten years later through this reexamination.

This paper explores the enduring black hole information and firewall paradoxes, challenges that have prompted many proposals, conjectures, and theories. Noteworthy among these are the ER = EPR conjecture and AdS/CFT correspondence, which suggest possible avenues toward the yet-to-be-realized unified theory of quantum gravity. This discourse offers a comprehensive analysis of the aforementioned paradoxes, drawing upon insights from efforts to reconcile the schism between general relativity and quantum mechanics.

This paper introduces several new classes of mathematical structures that have close connections with physics and with the theory of dynamical systems. The most general of these structures, called generalized stochastic systems, collectively encompass many important kinds of stochastic processes, including Markov chains and random dynamical systems. This paper then states and proves a new theorem that establishes a precise correspondence between any generalized stochastic system and a unitarily evolving quantum system. This theorem therefore leads to a new formulation of quantum theory, alongside the Hilbert-space, path-integral, and quasiprobability formulations. The theorem also provides a first-principles explanation for why quantum systems are based on the complex numbers, Hilbert spaces, linear-unitary time evolution, and the Born rule. In addition, the theorem suggests that by selecting a suitable Hilbert space, together with an appropriate choice of unitary evolution, one can simulate any generalized stochastic system on a quantum computer, thereby potentially opening up an extensive set of novel applications for quantum computing.

Piccinini's Usability Constraint states that physical processes must have ``physically constructible manifestation[s]" to be included in epistemically useful models of physical computation. But to determine what physical processes can be implemented on physical systems (as parts of computations), we must already know what physical processes can be implemented on physical systems (as parts of processes for constructing computing systems). We need additional assumptions about what qualifies as a building process. Piccinini implicitly assumes a classical computational understanding of executable processes, but this is an assumption imposed on physical theories and may artificially limit our picture of epistemically useful physical computation.

Arguments by Sorkin and Borsten, Jubb, and Kells establish that a natural extension of quantum measurement theory from non-relativistic quantum mechanics to relativistic quantum theory leads to the unacceptable consequence that expectation values in one region depend on which non-selective measurement is performed in a spacelike separated region. Sorkin labels such scenarios `impossible measurements'. We explicitly present these arguments as a no-go result with the logical form of a reductio argument and investigate the consequences for measurement in quantum field theory (QFT). Sorkin-type impossible measurement scenarios clearly illustrate the moral that Microcausality is not by itself sufficient to rule out superluminal signalling in relativistic quantum theories that use L{\"u}ders' rule. We review three different approaches to formulating an account of measurement for QFT and analyze their responses to the `impossible measurements' problem. Two of the approaches are recent proposals for measurement theories for QFT: a measurement theory based on detector models proposed in Polo-G{\'o}mez, Garay, and Mart{\'i}n-Mart{\'i}nez and a measurement framework for algebraic QFT proposed in Fewster and Verch. Of particular interest for foundations of QFT is that they share common features that may hold general morals about how to represent measurement in QFT, in spite of being much different in spirit and in details such as the form taken by the state update rules. Careful attention to the dynamics is an important component of both strategies for responding to the `impossible measurements' problem. Both also abandon the traditional operational interpretation of a local algebra of observables $\mathcal{A}(O)$ as representing possible operations carried out in region $O$. Their respective state update rules cannot be literally interpreted as representing a physical change of state of the system upon measurement that occurs in any region of spacetime. The third response to t

RISC-V is an open-source Instruction Set Architecture that offers a simple, modular, and scalable design. Its extensions allow for customization and optimization based on specific execution workloads. One of these workloads could be quantum computing, which exploits the concepts of superposition and entanglement to manipulate qubits and perform computations that would be infeasible for classical computers. The customization offered by RISC-V presents a remarkable opportunity to develop specialized architectures that can efficiently address the execution of quantum algorithms, bridging the gap between classical and quantum computation. In this thesis work, a RISC-V 32-bit instruction set extension called qRV32 is developed to address the control of diamond qubits, based on an existing QISA. The architecture defines the encoding syntax for the machine-level instructions and the exchange protocol for control and data in the system. Accordingly to this specification, the hardware of a control core processing the ISE has been designed. Custom functional units and necessary peripherals have been added to the base core CV32E40P in order to implement the desired control functionalities. The thesis also proposed additional work to ease the complete design and functionality of the system. In particular, an assembler targeting qRV32 has been developed, enabling the automated translation of assembly instructions to machine-level code. Furthermore, an experimental model is developed to evaluate the parallelism of the system. The resulting architecture is eventually tested and evaluated. Software simulations are used to test the functionality of the control core and the custom components. Eventually, a simplified version of the model is used to estimate the parallelism of the core, which can control 23605 network nodes when operating at fclk = 55MHz., Computer Engineering

This study aims to describe the concept of quantum learning model, the steps of applying quantum learning model, the role of quantum learning in increasing multiple learning targets, and the advantages and disadvantages of quantum learning model. Quantum learning model is a learning model that can make students directly experience problems, find their own answers to problems and activities in accordance with the competencies to be achieved. The research method used is descriptive qualitative research method. Qualitative descriptive research method according to Kirk and Miller, defines that qualitative research is a certain tradition in social science that fundamentally relies on observations of humans both in their areas and in their terms. The research subjects were the English teacher, and the principal. The object of research is the students of class X-4 SMA PGRI Cicurug. The results showed that the success of quantum learning depends on the teacher's ability to understand the concept and implement quantum learning steps in their learning activities. Its application in English subjects is enough to show that there is an increase in student learning targets, Penelitian ini bertujuan untuk mendeskripsikan tentang konsep model pembelajaran quantum learning, langkah-langkah penerapan model quantum learning, peran quantum learning dalam meningkatkan secara berlipat target belajar, dan kelebihan kekurangan model pembelajaran quantum learning. Model pembelajaran Quantum Learning merupakan suatu model pembelajaran yang dapat membuat siswa langsung mengalami permasalahan, menemukan sendiri jawaban atas permasalahan dan beraktivitas sesuai dengan kompetensi yang ingin dicapai. Metode penelitian yang digunakan yaitu metode penelitian deskriptif kualitatif. Metode penelitian deskriptif kualitatif menurut Kirk dan Miller, mendefinisikan bahwa penelitian kualitatif adalah tradisi tertentu dalam ilmu pengetahuan sosial yang secara fundamental bergantung dari pengamatan pada manusia baik dalam kawasannya maupun dalam peristilahannya. Subjek penelitian adalah guru bahasa Inggris, dan kepala sekolah. Adapun objek penelitiannya yaitu siswa kelas X-4 SMA PGRI Cicurug. Hasil penelitian menunjukkan bahwa keberhasilan pembelajaran quantum tergantung pada kemampuan guru dalam memahami konsep dan mengimplementasikan langkah-langkah pembelajaran quantum dalam kegiatan pembelajarannya. Penerapannya dalam mata pelajaran bahasa Inggris cukup menunjukkan bahwa terdapat peningkatan pada target belajar siswa

Stationary quantum information sources emit sequences of correlatedqudits---that is, structured quantum stochastic processes. If an observer performs identical measurements on a qudit sequence, the outcomes are a realization of a classical stochastic process. We introduce quantum-information-theoretic properties for separable qudit sequences that serve as bounds on the classical information properties of subsequent measured processes. For sources driven by hidden Markov dynamics we describe how an observer can temporarily or permanently synchronize to the source's internal state using specific positive operator-valued measures or adaptive measurement protocols. We introduce a method for approximating an information source with an independent and identically-distributed, Markov, or larger memory model through tomographic reconstruction. We identify broad classes of separable processes based on their quantum information properties and the complexity of measurements required to synchronize to and accurately reconstruct them.

Random walks have been used in a number of different fields for a long time. With the rise of of quantum random walks a lot of these applications have been made more efficient. Recently there have been a lot of improvements in the realization of these quantum random walks in real world systems. In this research, the effect of uncertainty in the measurement time and measurement frequency are studied on three problems that make use of a quantum random walk. These problems are the network centrality problem, the graph isomorphism problem and the spatial search problem. These effects are studied by first looking at the theory behind these problems after which the theoretical results of these three problems are calculated. These theoretical results will then be compared to simulated results that have a certain level of uncertainty in the measurement time or frequency. For both the network centrality problem and the spatial search problem we concluded that only a small error is made when uncertainties are introduced in the system. This implies that these problems are solvable in realizations of the quantum random walk in real world systems. For the Graph isomorphism problem we saw that the error that is made when uncertainties are introduced was large which implies that this problem would only be solvable for small uncertainties., Applied Mathematics | Applied Physics

Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines., QC 20230704

Eine wesentliche Komponente eines Quantennetwerks ist die Übertragung von einem Quantenzustand von einer Plattform auf die andere. Insbesondere die Übertragung des Polarisationszustands eines Photons auf den elektronischen Zustand eines Atoms ist ein wichtiger Aspekt für die Realisierung eines hybriden Quantennetzwerks. In dieser Masterarbeit schaffe ich die Grundlagen zur Absorption einzelner Photonen für eine Ion-Resonator Schnittstelle. Abgeschwächte kohärente Pulse können ein wichtiges Mittel sein, um Eigenschaften eines Quantennetzwerks lokal zu testen. Daher haben wir das Ziel, abgeschwächte kohärente Pulse zur Untersuchung der Absorption für eine Ion-Resonator Schnittstelle zu verwenden. In einer numerischen Simulation zeige ich, dass mit abgeschwächten kohärenten Pulsen für einen idealen optischen Resonator eine Absorptionseffizienz von eta_a = 12.8% erreicht werden kann. Wenn die bekannten Verluste unseres aktuellen optischen Resonators berücksichtigt werden, reduziert sich die Absorptionseffizienz um mehr als eine Größenordnung. Anschließend zeige ich, dass abgeschwächte kohärente Pulse mit einer durchschnittlichen Photonenzahl von n_p = 1.01(3) erzeugt werden können. Anhand der Reflexion am Resonator von R_exp = 92.6(6)% der abgeschwächten kohärenten Pulse zeige ich, dass wir die Resonatormode mit Photonen populieren können, was den Weg für zukünftige Experimente zur Absorption von abgeschwächten kohärenten Pulsen mit einem einzelnen Ion ebnet., An essential component of a quantum network is the mapping of quantum information from one platform to the other. In particular, mapping the polarization state of a photon to the electronic state of an atom can be a promising route towards the realization of a hybrid quantum network. In this master’s thesis, I lay the groundwork for the absorption of single photons for an ion-cavity interface. Weak coherent pulses can be an important tool to test features of a quantum network locally, and thus we aim to use weak coherent pulses to test the absorption for an ion-cavity interface. In a numerical simulation, I show that for an ideal cavity, weak coherent pulses can be absorbed with an efficiency of eta_a = 12.8%. When the known losses of our current experimental cavity are included, the absorption efficiency is reduced by more than an order of magnitude. Finally, I show that we can generate weak coherent pulses in the laboratory with an average of n_p = 1.01(3) photons. With a reflection of the weak coherent pulse from the experimental cavity of R_exp = 92.6(6)%, I demonstrate that we can populate the cavity field with weak coherent pulses at the single-photon level, paving the way for future experiments of absorption of weak coherent pulses with a single ion., Masterarbeit Universität Innsbruck 2023

Includes Supplementary Material, The use of cyber deception is a powerful but underutilized practice for spoiling cyber-attacker activity from initial reconnaissance to actions on an objective. This dissertation applies exploratory data analysis techniques to network traffic data collected during the Tularosa study, the largest experiment of defensive cyber deception involving human subjects to date. Using a network-graph–based information technology artifact developed for this research temporal variables of latency, frequency, and duration for system interactions were extracted from over 200 gigabytes of network traffic collected during the Tularosa study. Analysis of the data bolsters previous assertions that decoy-based deception is significantly more effective against cyber-attackers when presence of deception is known and suggests this impact is enduring. Distinct temporal patterns for aggregated network traffic for each experimental group were also identified. This research also provides the first application of factor analysis to data collected during the Tularosa study, which highlighted the key role of technical experience in explaining observed variance. Finally, quantum probability theory is explored as a potential model to explain variations in latency observed between the control and experimental groups which may be the result of interference effect and/or order effect phenomena. Cyber-defenders can apply findings from this research to impede cyber-attacker activity., Lieutenant Colonel, United States Army, Approved for public release. Distribution is unlimited.

We consider a quantum fully packed loop model on the square lattice with a frustration-free projector Hamiltonian and ring-exchange interactions acting on plaquettes. A boundary Hamiltonian is added to favor domain-wall boundary conditions and link ground state properties to the combinatorics and six-vertex model literature. We discuss how the boundary term fractures the Hilbert space into Krylov subspaces, and we prove that the Hamiltonian is ergodic within each subspace, leading to a series of energy-equidistant exact eigenstates in the lower end of the spectrum. Among them we systematically classify both finitely entangled eigenstates and product eigenstates. Using a recursion relation for enumerating half-plane configurations, we compute numerically the exact entanglement entropy of the ground state, confirming area law scaling. Finally, the spectrum is shown to be gapless in the thermodynamic limit with a trial state constructed by adding a twist to the ground state superposition.

The model of continuous spontaneous localization (CSL) is the most prominent consistent modification of quantum mechanics predicting an objective quantum-to-classical transition. Here we show that precision interferometry with Bose-Einstein-condensed atoms can serve to lower the current empirical bound on the localization rate parameter by several orders of magnitude. This works by focusing on the atom count dis-tributions rather than just mean population imbalances in the interferometric signal of squeezed Bose-Einstein condendates, without the need for highly entangled Greenberger-Horne-Zeilinger-like states. In fact, the interplay between CSL-induced diffusion and dispersive atom-atom interactions results in an amplified sensitivity of the condensate to CSL. We discuss experimentally realistic measurement schemes utilizing state-of-the-art experimental techniques to test new regions of parameter space and, pushed to the limit, to probe and potentially rule out large relevant parameter regimes of CSL.

We consider a quantum fully packed loop model on the square lattice with a frustration-free projector Hamiltonian and ring-exchange interactions acting on plaquettes. A boundary Hamiltonian is added to favor domain-wall boundary conditions and link ground state properties to the combinatorics and six-vertex model literature. We discuss how the boundary term fractures the Hilbert space into Krylov subspaces, and we prove that the Hamiltonian is ergodic within each subspace, leading to a series of energy-equidistant exact eigenstates in the lower end of the spectrum. Among them we systematically classify both finitely entangled eigenstates and product eigenstates. Using a recursion relation for enumerating half-plane configurations, we compute numerically the exact entanglement entropy of the ground state, confirming area law scaling. Finally, the spectrum is shown to be gapless in the thermodynamic limit with a trial state constructed by adding a twist to the ground state superposition.

State preparation is needed to perform a variety of quantum algorithms. In this thesis, the focus lies on a version that aims to program amplitudes and phases of a superposition consisting of a polynomial number of states. The quantum random access memory (QRAM) a pioneering ansatz, which solves this problem needs an exponential amount of resources. A less general, but not as hardware-intense protocol has been proposed. In this thesis phase development during the adiabatic-diabatic segments of the protocol is studied and the ansatz is extended to include phase programming using only local fields. The necessary field strengths can be calculated analytically and the phases can be controlled very precisely and in more situations compared to the amplitudes. The extended protocol is then benchmarked, where the overlap between the target state and the prepared state is used as a measure of performance. It was shown that the protocol struggles to prepare superposition states, which have eigenstates that contribute to the superposition with a low amplitude, but shows better performance if every eigenstate that contributes to the superposition contributes with similar amplitudes., Masterarbeit Universität Innsbruck 2023

With the development in Quantum Computing, the current strength of public key cryptography is challenged. Large-scale Quantum computers will be able to break many of the public-key cryptosystems currently in use and it would threaten the confidentiality and integrity of digital communications on the public networks. The literature review studies the hypothesis based on which it is predicted that Quantum Computing will challenge current use of public key cryptography. The review also analyzes research by NIST, and several other researchers to analyze the impact of Quantum Computing to cryptography in use by businesses, time it may take to break the current strength of cryptography and what business should do to protect data. The literature review concludes with recommendations for the businesses on approach and transition from current cryptography to Quantum safe cryptography.

The minimum vertex cover problem (MinVertexCover) is an important optimization problem in graph theory, with applications in numerous fields outside of mathematics. As MinVertexCover is an NP-hard problem, there currently exists no efficient algorithm to find an optimal solution on arbitrary graphs. We consider quantum optimization algorithms, such as the Quantum Alternating Operator Ansatz (QAOA+), to find good minimum vertex covers. This thesis presents new 'second degree' mixing Hamiltonians for MinVertexCover in the QAOA+ framework, which allow mixing between solutions Hamming distance 2 apart. The performance of these new Hamiltonians is evaluated on a small graph. Methods to extend this idea by constructing Hamiltonians which allow mixing between solutions at Hamming distance n are also presented, along with a generalization of second degree mixing Hamiltonians to other optimization problems., Applied Mathematics

With the development in Quantum Computing, the current strength of public key cryptography is challenged. Large-scale Quantum computers will be able to break many of the public-key cryptosystems currently in use and it would threaten the confidentiality and integrity of digital communications on the public networks. The literature review studies the hypothesis based on which it is predicted that Quantum Computing will challenge current use of public key cryptography. The review also analyzes research by NIST, and several other researchers to analyze the impact of Quantum Computing to cryptography in use by businesses, time it may take to break the current strength of cryptography and what business should do to protect data. The literature review concludes with recommendations for the businesses on approach and transition from current cryptography to Quantum safe cryptography.