Showing 1–30 of 30 results for author: Omar, Y

Precision gravimetry via harnessing interaction-induced resonances in optical lattices

Authors: Hassan Manshouri, Moslem Zarei, Mehdi Abdi, Yasser Omar, Sougato Bose, Abolfazl Bayat

Abstract: By confining a Bose-Einstein condensate in a vertical lattice subjected to a gravitational potential, we analyze the quantum Fisher information to determine its scaling with respect to time, system size and particle number. Our results reveal that in the localized phase, on-site interactions $U$ amplify the quantum Fisher information by a factor with respect to resonance condition $U=mh$ where… ▽ More By confining a Bose-Einstein condensate in a vertical lattice subjected to a gravitational potential, we analyze the quantum Fisher information to determine its scaling with respect to time, system size and particle number. Our results reveal that in the localized phase, on-site interactions $U$ amplify the quantum Fisher information by a factor with respect to resonance condition $U=mh$ where $U$ is factor of gradient field amplitude $h$. This precision enhancement can be employed in gravitational acceleration measurements with a finite number of particles trapped in optical lattices. △ Less

Submitted 7 May, 2026; v1 submitted 4 May, 2026; originally announced May 2026.

Thickness effects in the electromechanical stability of charged biological membranes

Authors: Sirui Ning, Yannick A. D. Omar, Karthik Shekhar, Kranthi K. Mandadapu

Abstract: Understanding how electric fields destabilize biological membranes is important for electroporation-based technologies and bioelectronic interfaces. However, theoretical descriptions of this phenomenon remain fragmented. Existing theories treat either electrostatics in membranes of finite thickness or electrohydrodynamic flows at idealized zero-thickness interfaces, leaving unresolved a unified de… ▽ More Understanding how electric fields destabilize biological membranes is important for electroporation-based technologies and bioelectronic interfaces. However, theoretical descriptions of this phenomenon remain fragmented. Existing theories treat either electrostatics in membranes of finite thickness or electrohydrodynamic flows at idealized zero-thickness interfaces, leaving unresolved a unified description that simultaneously incorporates finite membrane thickness, surface charge, and bulk electrohydrodynamics. Here, we apply a recently-developed, dimension-reduction framework that captures the coupled electrohydrodynamic and mechanical effects governing height fluctuations of a charged lipid bilayer of thickness $δ$ in an electrolyte characterized by Debye screening length $λ$. We derive voltage- and charge-dependent renormalizations of the effective surface tension and bending rigidity, along with a dispersion relation governing undulatory instabilities. A wide range of prior theoretical results arise as limiting cases of our more general theory when finite-thickness effects are neglected or screening is asymptotically strong. The key new contribution arises from traction moments generated across the finite membrane thickness, which are absent in zero-thickness descriptions. Under physiological screening ($δ/λ\sim 4$), these contributions account for more than $>70\%$ of the total electrostatic correction to both surface tension and bending rigidity. The theory further reveals that surface charges can stabilize the membrane at physiological ionic strengths, increasing the effective tension and shifting electroporation thresholds in a manner that depends on charge asymmetry between the leaflets. △ Less

Submitted 24 March, 2026; originally announced March 2026.

Comments: 15 pages, 6 figures

Translational diffusion coefficients of membrane protein aggregates in free and supported lipid membranes

Authors: Yannick A. D. Omar

Abstract: There is increasing evidence that numerous membrane proteins can assemble into aggregates that modulate their function and affect many cellular processes such as signal transduction and endocytosis. Here, we present a theoretical description of the instantaneous translational diffusion coefficients of transmembrane protein aggregates on free and supported lipid membranes using Kirkwood-Riseman the… ▽ More There is increasing evidence that numerous membrane proteins can assemble into aggregates that modulate their function and affect many cellular processes such as signal transduction and endocytosis. Here, we present a theoretical description of the instantaneous translational diffusion coefficients of transmembrane protein aggregates on free and supported lipid membranes using Kirkwood-Riseman theory. We find that hydrodynamic interactions within protein aggregates must be accounted for, as neglecting them yields several times lower diffusion coefficients. By deriving hydrodynamic radii for free and supported lipid membranes, we identify effective length scales that accurately characterize aggregate diffusivities in the presence of hydrodynamic interactions. These findings motivate the approximation of an aggregate by its outline and a random particle distribution inside it. We show that this approach provides a practical method to accurately determine aggregate diffusion coefficients when the particle locations cannot be resolved. The results presented in this article have immediate implications for the formation and function of membrane protein aggregates. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Quantum Walks on Arbitrary Spatial Networks with Rydberg Atoms

Authors: Gabriel Almeida, Raul Santos, Lara Janiurek, Yasser Omar

Abstract: Rydberg atoms provide a highly promising platform for quantum computation, leveraging their strong tunable interactions to encode and manipulate information in the electronic states of individual atoms. Key advantages of Rydberg atoms include scalability, reconfigurable connectivity, and native multi-qubit gates, making them particularly well-suited for addressing complex network problems. These p… ▽ More Rydberg atoms provide a highly promising platform for quantum computation, leveraging their strong tunable interactions to encode and manipulate information in the electronic states of individual atoms. Key advantages of Rydberg atoms include scalability, reconfigurable connectivity, and native multi-qubit gates, making them particularly well-suited for addressing complex network problems. These problems can often be framed as graph-based tasks, which can be efficiently addressed using quantum walks. In this work, we propose a general implementation of staggered quantum walks with Rydberg atoms, with a particular focus on spatial networks. We also present an efficient algorithm for constructing the tessellations required for the staggered quantum walk. Finally, we demonstrate that our proposal achieves quadratic speedup in spatial search algorithms. △ Less

Submitted 28 July, 2025; originally announced July 2025.

Finite Membrane Thickness Influences Hydrodynamics on the Nanoscale

Authors: Zachary G. Lipel, Yannick A. D. Omar, Dimitrios Fraggedakis

Abstract: Many lipid membrane-mediated transport processes--such as mechanically-gated channel activation and solute transport--involve structural and dynamical features on membrane thickness length scales. Most existing membrane models, however, tend to adopt (quasi-)two-dimensional descriptions that neglect thickness-dependent phenomena relevant to internal membrane mechanics, and thus do not fully accoun… ▽ More Many lipid membrane-mediated transport processes--such as mechanically-gated channel activation and solute transport--involve structural and dynamical features on membrane thickness length scales. Most existing membrane models, however, tend to adopt (quasi-)two-dimensional descriptions that neglect thickness-dependent phenomena relevant to internal membrane mechanics, and thus do not fully account for the complex coupling of lipid membranes with their surrounding fluid media. Therefore, explicitly incorporating membrane thickness effects in lipid membrane models will enable a more accurate description of the influence of membrane/fluid coupling on transport phenomena in the vicinity of the bilayer surfaces. Here, we present a continuum model for membrane fluctuations that accounts for finite membrane thickness and resolves hydrodynamic interactions between the bilayer and its surrounding fluid. By applying linear response analysis, we observe that membrane thickness-mediated effects, such as bending-induced lipid reorientations, can generate shear flows close to the membrane surface that slow down the relaxation of nanometer scale shape fluctuations. Additionally, we reveal the emergence of pressure inversion and flow reversal near the membrane interfaces, accompanied by localized stagnation points. Among these, extensional stagnation points give rise to a novel mode of bulk dissipation, originating from bending-induced compression and expansion of the membrane surfaces and their coupling to shear stresses in the fluid. Our findings identify membrane thickness as a key factor in nanoscale hydrodynamics and suggest that its effects may be detectable in fluctuation spectra and can be relevant to interfacial processes such as solute permeability and contact with solid boundaries or other membranes. △ Less

Submitted 28 August, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: 7 pages, 2 figures

The $(2+δ)$-dimensional theory of the electromechanics of lipid membranes: III. Constitutive models

Authors: Yannick A. D. Omar, Zachary G. Lipel, Kranthi K. Mandadapu

Abstract: This article concludes a three-part series developing a self-consistent theoretical framework of the electromechanics of lipid membranes at the continuum scale. Owing to their small thickness, lipid membranes are commonly modeled as two-dimensional surfaces. However, this approach breaks down when considering their electromechanical behavior as it requires accounting for their thickness. To addres… ▽ More This article concludes a three-part series developing a self-consistent theoretical framework of the electromechanics of lipid membranes at the continuum scale. Owing to their small thickness, lipid membranes are commonly modeled as two-dimensional surfaces. However, this approach breaks down when considering their electromechanical behavior as it requires accounting for their thickness. To address this, we developed a dimension reduction procedure in part 1 to derive effective surface theories explicitly capturing the thickness of lipid membranes. We applied this method to dimensionally reduce Gauss' law and the electromechanical balance laws and referred to the resulting theory as $(2+δ)$-dimensional, where $δ$ indicates the membrane thickness. However, the $(2+δ)$-dimensional balance laws derived in part 2 are general, and specific material models are required to specialize them to lipid membranes. In this work, we devise appropriate three-dimensional constitutive models that capture the in-plane fluid and out-of-plane elastic behavior of lipid membranes. The viscous behavior is recovered by a three-dimensional Newtonian fluid model, leading to the same viscous stresses as strictly two-dimensional models. The elastic resistance to bending is recovered by imposing a free energy penalty on local volume changes. While this gives rise to the characteristic bending resistance of lipid membranes, it differs in its higher-order curvature terms from the Canham-Helfrich-Evans theory. Furthermore, motivated by the small mid-surface stretch of lipid membranes, we introduce reactive stresses that enforce mid-surface incompressibility, resulting in an effective surface tension. Finally, we use the constitutive and reactive stresses to derive the equations of motion describing the electromechanics of lipid membranes. △ Less

Submitted 24 February, 2025; v1 submitted 20 January, 2025; originally announced January 2025.

The $(2+δ)$-dimensional theory of the electromechanics of lipid membranes: II. Balance laws

Authors: Yannick A. D. Omar, Zachary G. Lipel, Kranthi K. Mandadapu

Abstract: This article is the second of a three-part series that derives a self-consistent theoretical framework of the electromechanics of arbitrarily curved lipid membranes. Existing continuum theories commonly treat lipid membranes as strictly two-dimensional surfaces. While this approach is successful in many purely mechanical applications, strict surface theories fail to capture the electric potential… ▽ More This article is the second of a three-part series that derives a self-consistent theoretical framework of the electromechanics of arbitrarily curved lipid membranes. Existing continuum theories commonly treat lipid membranes as strictly two-dimensional surfaces. While this approach is successful in many purely mechanical applications, strict surface theories fail to capture the electric potential drop across lipid membranes, the effects of surface charges, and electric fields within the membrane. Consequently, they do not accurately resolve Maxwell stresses in the interior of the membrane and its proximity. Furthermore, surface theories are generally unable to capture the effects of distinct velocities and tractions at the interfaces between lipid membranes and their surrounding bulk fluids. To address these shortcomings, we apply a recently proposed dimension reduction method to the three-dimensional, electromechanical balance laws. This approach allows us to derive an effective surface theory without taking the limit of vanishing thickness, thus incorporating effects arising from the finite thickness of lipid membranes. We refer to this effective surface theory as $(2 + δ)$-dimensional, where $δ$ indicates the thickness. The resulting $(2 + δ)$-dimensional equations of motion satisfy velocity and traction continuity conditions at the membrane-bulk interfaces, capture the effects of Maxwell stresses, and can directly incorporate three-dimensional constitutive models. △ Less

Submitted 24 February, 2025; v1 submitted 7 September, 2023; originally announced September 2023.

Low-Dissipation Data Bus via Coherent Quantum Dynamics

Authors: Dylan Lewis, João P. Moutinho, António Costa, Yasser Omar, Sougato Bose

Abstract: The transfer of information between two physical locations is an essential component of both classical and quantum computing. In quantum computing the transfer of information must be coherent to preserve quantum states and hence the quantum information. We establish a simple protocol for transferring one- and two-electron encoded logical qubits in quantum dot arrays. The theoretical energetic cost… ▽ More The transfer of information between two physical locations is an essential component of both classical and quantum computing. In quantum computing the transfer of information must be coherent to preserve quantum states and hence the quantum information. We establish a simple protocol for transferring one- and two-electron encoded logical qubits in quantum dot arrays. The theoretical energetic cost of this protocol is calculated - in particular, the cost of freezing and unfreezing tunnelling between quantum dots. Our results are compared with the energetic cost of shuttling qubits in quantum dot arrays and transferring classical information using classical information buses. Only our protocol can manage constant dissipation for any chain length. This protocol could reduce the cooling requirements and constraints on scalable architectures for quantum dot quantum computers. △ Less

Submitted 5 April, 2023; originally announced April 2023.

Comments: 10 pages, 6 figures

Journal ref: Phys. Rev. B 108, 075405 (2023)

The $(2 + δ)$-dimensional theory of the electromechanics of lipid membranes: I. Electrostatics

Authors: Yannick A. D. Omar, Zachary G. Lipel, Kranthi K. Mandadapu

Abstract: The coupling of electric fields to the mechanics of lipid membranes gives rise to intriguing electromechanical behavior, as, for example, evidenced by the deformation of lipid vesicles in external electric fields. Electromechanical effects are relevant for many biological processes, such as the propagation of action potentials in axons and the activation of mechanically-gated ion channels. Current… ▽ More The coupling of electric fields to the mechanics of lipid membranes gives rise to intriguing electromechanical behavior, as, for example, evidenced by the deformation of lipid vesicles in external electric fields. Electromechanical effects are relevant for many biological processes, such as the propagation of action potentials in axons and the activation of mechanically-gated ion channels. Currently, a theoretical framework describing the electromechanical behavior of arbitrarily curved and deforming lipid membranes does not exist. Purely mechanical models commonly treat lipid membranes as two-dimensional surfaces, ignoring their finite thickness. While holding analytical and numerical merit, this approach cannot describe the coupling of lipid membranes to electric fields and is thus unsuitable for electromechanical models. In a sequence of articles, we derive an \textit{effective} surface theory of the electromechanics of lipid membranes, named a $(2+δ)$-dimensional theory, which has the advantages of surface descriptions while accounting for finite thickness effects. The present article proposes a new, generic dimension-reduction procedure relying on low-order spectral expansions. This procedure is applied to the electrostatics of lipid membranes to obtain a $(2+δ)$-dimensional theory that captures potential differences across and electric fields within lipid membranes. This new model is tested on different geometries relevant for lipid membranes, showing good agreement with the corresponding three-dimensional electrostatics theory. △ Less

Submitted 23 January, 2023; originally announced January 2023.

Journal ref: Phys. Rev. E 109, 054401 (2024)

Quantum dynamics for energetic advantage in a charge-based classical full-adder

Authors: João P. Moutinho, Marco Pezzutto, Sagar Pratapsi, Francisco Ferreira da Silva, Silvano De Franceschi, Sougato Bose, António T. Costa, Yasser Omar

Abstract: We present a proposal for a one-bit full-adder to process classical information based on the quantum reversible dynamics of a triple quantum dot system. The device works via the repeated execution of a Fredkin gate implemented through the dynamics of a single time-independent Hamiltonian. Our proposal uses realistic parameter values and could be implemented on currently available quantum dot archi… ▽ More We present a proposal for a one-bit full-adder to process classical information based on the quantum reversible dynamics of a triple quantum dot system. The device works via the repeated execution of a Fredkin gate implemented through the dynamics of a single time-independent Hamiltonian. Our proposal uses realistic parameter values and could be implemented on currently available quantum dot architectures. We compare the estimated energy requirements for operating our full-adder with those of well-known fully classical devices, and argue that our proposal may provide a consistently better energy efficiency. Our work serves as a proof of principle for the development of energy-efficient information technologies operating through coherent quantum dynamics. △ Less

Submitted 29 July, 2022; v1 submitted 28 June, 2022; originally announced June 2022.

Comments: V2: Minor updates. -- Keywords: energy-efficient computing, quantum dynamics, quantum gates, semiconductor quantum dots, quantum technologies

Journal ref: PRX Energy 2, 033002 (2023)

Open-Air Microwave Entanglement Distribution for Quantum Teleportation

Authors: Tasio Gonzalez-Raya, Mateo Casariego, Florian Fesquet, Michael Renger, Vahid Salari, Mikko Möttönen, Yasser Omar, Frank Deppe, Kirill G. Fedorov, Mikel Sanz

Abstract: Microwave technology plays a central role in current wireless communications, standing among them mobile communication and local area networks (LANs). The microwave range shows relevant advantages with respect to other frequencies in open-air transmission, such as low absorption losses and low energy consumption, and it is additionally the natural working frequency in superconducting quantum techn… ▽ More Microwave technology plays a central role in current wireless communications, standing among them mobile communication and local area networks (LANs). The microwave range shows relevant advantages with respect to other frequencies in open-air transmission, such as low absorption losses and low energy consumption, and it is additionally the natural working frequency in superconducting quantum technologies. Entanglement distribution between separate parties is at the core of secure quantum communications. Therefore, understanding its limitations in realistic open-air settings, specially in the rather unexplored microwave regime, is crucial for transforming microwave quantum communications into a mainstream technology. Here, we investigate the feasibility of an open-air entanglement distribution scheme with microwave two-mode squeezed states. First, we study the reach of direct entanglement transmission in open-air, obtaining a maximum distance of approximately 500 meters in a realistic setting with state-of-the-art experimental parameters. Afterwards, we adapt entanglement distillation and entanglement swapping protocols to microwave technology in order to reduce environmental entanglement degradation. While entanglement distillation helps to increase quantum correlations in the short-distance low-squeezing regime by up to $46\%$, entanglement swapping increases the reach by $14\%$. Then, we compute the fidelity of a continuous-variable quantum teleportation protocol using open-air-distributed entanglement as a resource. Finally, we adapt the machinery to explore the limitations of quantum communication between satellites, where the thermal noise impact is substantially reduced and diffraction losses are dominant. △ Less

Submitted 14 March, 2022; originally announced March 2022.

Journal ref: Phys. Rev. Applied 18, 044002 (2022)

Quantum Link Prediction in Complex Networks

Authors: João P. Moutinho, André Melo, Bruno Coutinho, István A. Kovács, Yasser Omar

Abstract: Predicting new links in physical, biological, social, or technological networks has a significant scientific and societal impact. Path-based link prediction methods utilize explicit counting of even and odd-length paths between nodes to quantify a score function and infer new or unobserved links. Here, we propose a quantum algorithm for path-based link prediction, QLP, using a controlled continuou… ▽ More Predicting new links in physical, biological, social, or technological networks has a significant scientific and societal impact. Path-based link prediction methods utilize explicit counting of even and odd-length paths between nodes to quantify a score function and infer new or unobserved links. Here, we propose a quantum algorithm for path-based link prediction, QLP, using a controlled continuous-time quantum walk to encode even and odd path-based prediction scores. Through classical simulations on a few real networks, we confirm that the quantum walk scoring function performs similarly to other path-based link predictors. In a brief complexity analysis we identify the potential of our approach in uncovering a quantum speedup for path-based link prediction. △ Less

Submitted 25 November, 2022; v1 submitted 9 December, 2021; originally announced December 2021.

Comments: Keywords: Complex Networks, Quantum Algorithms, Link Prediction, Social Networks, Protein-Protein Interaction Networks

Benchmarking Machine Learning Algorithms for Adaptive Quantum Phase Estimation with Noisy Intermediate-Scale Quantum Sensors

Authors: Nelson Filipe Costa, Yasser Omar, Aidar Sultanov, Gheorghe Sorin Paraoanu

Abstract: Quantum phase estimation is a paradigmatic problem in quantum sensing andmetrology. Here we show that adaptive methods based on classical machinelearning algorithms can be used to enhance the precision of quantum phase estimation when noisy non-entangled qubits are used as sensors. We employ the Differential Evolution (DE) and Particle Swarm Optimization (PSO) algorithms to this task and we identi… ▽ More Quantum phase estimation is a paradigmatic problem in quantum sensing andmetrology. Here we show that adaptive methods based on classical machinelearning algorithms can be used to enhance the precision of quantum phase estimation when noisy non-entangled qubits are used as sensors. We employ the Differential Evolution (DE) and Particle Swarm Optimization (PSO) algorithms to this task and we identify the optimal feedback policies which minimize the Holevo variance. We benchmark these schemes with respect to scenarios that include Gaussian and Random Telegraph fluctuations as well as reduced Ramsey-fringe visibility due to decoherence. We discuss their robustness against noise in connection with real experimental setups such as Mach-Zehnder interferometry with optical photons and Ramsey interferometry in trapped ions,superconducting qubits and nitrogen-vacancy (NV) centers in diamond. △ Less

Submitted 17 August, 2021; v1 submitted 16 August, 2021; originally announced August 2021.

Journal ref: EPJ Quantum Technol. 8, 16 (2021)

Robustness of Noisy Quantum Networks

Authors: Bruno C. Coutinho, William J. Munro, Kae Nemoto, Yasser Omar

Abstract: Quantum networks are a new paradigm of complex networks, allowing us to harness networked quantum technologies and to develop a quantum internet. But how robust is a quantum network when its links and nodes start failing? We show that quantum networks based on typical noisy quantum-repeater nodes are prone to discontinuous phase transitions with respect to the random loss of operating links and no… ▽ More Quantum networks are a new paradigm of complex networks, allowing us to harness networked quantum technologies and to develop a quantum internet. But how robust is a quantum network when its links and nodes start failing? We show that quantum networks based on typical noisy quantum-repeater nodes are prone to discontinuous phase transitions with respect to the random loss of operating links and nodes, abruptly compromising the connectivity of the network, and thus significantly limiting the reach of its operation. Furthermore, we determine the critical quantum-repeater efficiency necessary to avoid this catastrophic loss of connectivity as a function of the network topology, the network size, and the distribution of entanglement in the network. In particular, our results indicate that a scale-free topology is a crucial design principle to establish a robust large-scale quantum internet. △ Less

Submitted 4 March, 2021; originally announced March 2021.

Comments: quantum Internet, complex quantum networks, phase transitions, percolation theory

Quantum field thermal machines

Authors: M. Gluza, J. Sabino, N. H. Y. Ng, G. Vitagliano, M. Pezzutto, Y. Omar, I. Mazets, M. Huber, J. Schmiedmayer, J. Eisert

Abstract: Recent years have enjoyed an overwhelming interest in quantum thermodynamics, a field of research aimed at understanding thermodynamic tasks performed in the quantum regime. Further progress, however, seems to be obstructed by the lack of experimental implementations of thermal machines in which quantum effects play a decisive role. In this work, we introduce a blueprint of quantum field machines,… ▽ More Recent years have enjoyed an overwhelming interest in quantum thermodynamics, a field of research aimed at understanding thermodynamic tasks performed in the quantum regime. Further progress, however, seems to be obstructed by the lack of experimental implementations of thermal machines in which quantum effects play a decisive role. In this work, we introduce a blueprint of quantum field machines, which - once experimentally realized - would fill this gap. Even though the concept of the QFM presented here is very general and can be implemented in any many body quantum system that can be described by a quantum field theory. We provide here a detailed proposal how to realize a quantum machine in one-dimensional ultra-cold atomic gases, which consists of a set of modular operations giving rise to a piston. These can then be coupled sequentially to thermal baths, with the innovation that a quantum field takes up the role of the working fluid. In particular, we propose models for compression on the system to use it as a piston, and coupling to a bath that gives rise to a valve controlling heat flow. These models are derived within Bogoliubov theory, which allows us to study the operational primitives numerically in an efficient way. By composing the numerically modelled operational primitives we design complete quantum thermodynamic cycles that are shown to enable cooling and hence giving rise to a quantum field refrigerator. The active cooling achieved in this way can operate in regimes where existing cooling methods become ineffective. We describe the consequences of operating the machine at the quantum level and give an outlook of how this work serves as a road map to explore open questions in quantum information, quantum thermodynamic and the study of non-Markovian quantum dynamics. △ Less

Submitted 19 July, 2021; v1 submitted 1 June, 2020; originally announced June 2020.

Comments: 48 pages, 18 figures, replaced by published version

Journal ref: PRX Quantum 2, 030310 (2021)

Topologically protected quantization of work

Authors: Bruno Mera, Krzysztof Sacha, Yasser Omar

Abstract: The transport of a particle in the presence of a potential that changes periodically in space and in time can be characterized by the amount of work needed to shift a particle by a single spatial period of the potential. In general, this amount of work, when averaged over a single temporal period of the potential, can take any value in a continuous fashion. Here we present a topological effect ind… ▽ More The transport of a particle in the presence of a potential that changes periodically in space and in time can be characterized by the amount of work needed to shift a particle by a single spatial period of the potential. In general, this amount of work, when averaged over a single temporal period of the potential, can take any value in a continuous fashion. Here we present a topological effect inducing the quantization of the average work. We find that this work is equal to the first Chern number calculated in a unit cell of a space-time lattice. Hence, this quantization of the average work is topologically protected. We illustrate this phenomenon with the example of an atom whose center of mass motion is coupled to its internal degrees of freedom by electromagnetic waves. △ Less

Submitted 10 July, 2019; v1 submitted 14 February, 2019; originally announced February 2019.

Comments: 10 pages (including Supplemental Material), 1 figure, 1 table; closer to published version

Journal ref: Phys. Rev. Lett. 123, 020601 (2019)

Arbitrary Lagrangian--Eulerian finite element method for curved and deforming surfaces. I. General theory and application to fluid interfaces

Authors: Amaresh Sahu, Yannick A. D. Omar, Roger A. Sauer, Kranthi K. Mandadapu

Abstract: An arbitrary Lagrangian--Eulerian (ALE) finite element method for arbitrarily curved and deforming two-dimensional materials and interfaces is presented here. An ALE theory is developed by endowing the surface with a mesh whose in-plane velocity need not depend on the in-plane material velocity, and can be specified arbitrarily. A finite element implementation of the theory is formulated and appli… ▽ More An arbitrary Lagrangian--Eulerian (ALE) finite element method for arbitrarily curved and deforming two-dimensional materials and interfaces is presented here. An ALE theory is developed by endowing the surface with a mesh whose in-plane velocity need not depend on the in-plane material velocity, and can be specified arbitrarily. A finite element implementation of the theory is formulated and applied to curved and deforming surfaces with in-plane incompressible flows. Numerical inf--sup instabilities associated with in-plane incompressibility are removed by locally projecting the surface tension onto a discontinuous space of piecewise linear functions. The general isoparametric finite element method, based on an arbitrary surface parametrization with curvilinear coordinates, is tested and validated against several numerical benchmarks. A new physical insight is obtained by applying the ALE developments to cylindrical fluid films, which are computationally and analytically found to be stable to non-axisymmetric perturbations, and unstable with respect to long-wavelength axisymmetric perturbations when their length exceeds their circumference. A Lagrangian scheme is attained as a special case of the ALE formulation. Though unable to model fluid films with sustained shear flows, the Lagrangian scheme is validated by reproducing the cylindrical instability. However, relative to the ALE results, the Lagrangian simulations are found to have spatially unresolved regions with few nodes, and thus larger errors. △ Less

Submitted 20 March, 2020; v1 submitted 12 December, 2018; originally announced December 2018.

Comments: 59 pages, 16 figures

Journal ref: Journal of Computational Physics 407 (2020) 109253

An out-of-equilibrium non-Markovian Quantum Heat Engine

Authors: Marco Pezzutto, Mauro Paternostro, Yasser Omar

Abstract: We study the performance of a quantum Otto cycle using a harmonic work medium and undergoing collisional dynamics with finite-size reservoirs. We span the dynamical regimes of the work strokes from strongly non-adiabatic to quasi-static conditions, and address the effects that non-Markovianity of the open-system dynamics of the work medium can have on the efficiency of the thermal machine. While s… ▽ More We study the performance of a quantum Otto cycle using a harmonic work medium and undergoing collisional dynamics with finite-size reservoirs. We span the dynamical regimes of the work strokes from strongly non-adiabatic to quasi-static conditions, and address the effects that non-Markovianity of the open-system dynamics of the work medium can have on the efficiency of the thermal machine. While such efficiency never surpasses the classical upper bound valid for finite-time stochastic engines, the behaviour of the engine shows clear-cut effects induced by both the finiteness of the evolution time, and the memory-bearing character of the system-environment evolution. △ Less

Submitted 18 February, 2019; v1 submitted 26 June, 2018; originally announced June 2018.

Comments: Close to published version. Added Figure 8b

Journal ref: Quantum Science and Technology 4, 025002 (2019)

Exciton transport in the PE545 complex: insight from atomistic QM/MM-based quantum master equations and elastic network models

Authors: Sima Pouyandeh, Stefano Iubini, Sandro Jurinovich, Yasser Omar, Benedetta Mennucci, Francesco Piazza

Abstract: In this paper we work out a parameterization of the environment noise within the Haken-Strobl-Reinenker (HSR) model for the PE545 light-harvesting complex based on atomic-level quantum mechanics/molecular mechanics (QM/MM) simulations. We use this approach to investigate the role of different auto- and cross-correlations in the HSR noise tensor, confirming that site-energy autocorrelations (pure d… ▽ More In this paper we work out a parameterization of the environment noise within the Haken-Strobl-Reinenker (HSR) model for the PE545 light-harvesting complex based on atomic-level quantum mechanics/molecular mechanics (QM/MM) simulations. We use this approach to investigate the role of different auto- and cross-correlations in the HSR noise tensor, confirming that site-energy autocorrelations (pure dephasing) terms dominate the noise-induced exciton mobility enhancement, followed by site energy-coupling cross-correlations for specific triplets of pigments. Interestingly, several cross-correlations of the latter kind, together with coupling-coupling cross-correlations, display clear low-frequency signatures in their spectral densities in the region 30-70 inverse centimeters. These slow components lie at the limits of validity of the HSR approach, requiring that environmental fluctuations be faster than typical exciton transfer time scales. We show that a simple coarse-grained elastic-network-model (ENM) analysis of the PE545 protein naturally spotlights collective normal modes in this frequency range, that represent specific concerted motions of the subnetwork of cysteines that are covalenty linked to the pigments. This analysis strongly suggests that protein scaffolds in light-harvesting complexes are able to express specific collective, low-frequency normal modes providing a fold-rooted blueprint of exciton transport pathways. We speculate that ENM-based mixed quantum classical methods, such as Ehrenfest dynamics, might be promising tools to disentangle the fundamental designing principles of these dynamical processes in natural and artificial light-harvesting structures. △ Less

Submitted 29 May, 2017; originally announced June 2017.

Comments: 20 pages, 8 figures, submitted to Phys. Biol

Universality of Black Hole Quantum Computing

Authors: Gia Dvali, Cesar Gomez, Dieter Lust, Yasser Omar, Benedikt Richter

Abstract: By analyzing the key properties of black holes from the point of view of quantum information, we derive a model-independent picture of black hole quantum computing. It has been noticed that this picture exhibits striking similarities with quantum critical condensates, allowing the use of a common language to describe quantum computing in both systems. We analyze such quantum computing by allowing… ▽ More By analyzing the key properties of black holes from the point of view of quantum information, we derive a model-independent picture of black hole quantum computing. It has been noticed that this picture exhibits striking similarities with quantum critical condensates, allowing the use of a common language to describe quantum computing in both systems. We analyze such quantum computing by allowing coupling to external modes, under the condition that the external influence must be soft-enough in order not to offset the basic properties of the system. We derive model-independent bounds on some crucial time-scales, such as the times of gate operation, decoherence, maximal entanglement and total scrambling. We show that for black hole type quantum computers all these time-scales are of the order of the black hole half-life time. Furthermore, we construct explicitly a set of Hamiltonians that generates a universal set of quantum gates for the black hole type computer. We find that the gates work at maximal energy efficiency. Furthermore, we establish a fundamental bound on the complexity of quantum circuits encoded on these systems, and characterize the unitary operations that are implementable. It becomes apparent that the computational power is very limited due to the fact that the black hole life-time is of the same order of the gate operation time. As a consequence, it is impossible to retrieve its information, within the life-time of a black hole, by externally coupling to the black hole qubits. However, we show that, in principle, coupling to some of the internal degrees of freedom allows acquiring knowledge about the micro-state. Still, due to the trivial complexity of operations that can be performed, there is no time advantage over the collection of Hawking radiation and subsequent decoding. △ Less

Submitted 4 May, 2016; originally announced May 2016.

Comments: 25+5 pages

Report number: LMU-ASC 03/16, MPP-2016-1

Journal ref: Fortschr. Phys. 65, 1600111 (2017)

Quantum Thermal Machines Fuelled by Vacuum Forces

Authors: Hugo Terças, Sofia Ribeiro, Marco Pezzutto, Yasser Omar

Abstract: We propose a quantum thermal machine composed of two nanomechanical resonators (NMR) (two membranes suspended over a trench in a substrate), placed a few $μ$m from each other. The quantum thermodynamical cycle is powered by the Casimir interaction between the resonators and the working fluid is the polariton resulting from the mixture of the flexural (out-of-plane) vibrations. With the help of pie… ▽ More We propose a quantum thermal machine composed of two nanomechanical resonators (NMR) (two membranes suspended over a trench in a substrate), placed a few $μ$m from each other. The quantum thermodynamical cycle is powered by the Casimir interaction between the resonators and the working fluid is the polariton resulting from the mixture of the flexural (out-of-plane) vibrations. With the help of piezoelectric cells, we select and sweep the polariton frequency cyclically. We calculate the performance of the proposed quantum thermal machines and show that high efficiencies are achieved thanks to (i) the strong coupling between the resonators and (ii) the large difference between the membrane stiffnesses. Our findings can be of particular importance for applications in nanomechanical technologies where a sensitive control of temperature is needed. △ Less

Submitted 29 April, 2016; originally announced April 2016.

Comments: Quantum thermal machines, Casimir effect, mechanical resonators, finite-time thermodynamics

Journal ref: Phys. Rev. E 95, 022135 (2017)

Transport of quantum excitations coupled to spatially extended nonlinear many-body systems

Authors: Stefano Iubini, Octavi Boada, Yasser Omar, Francesco Piazza

Abstract: The role of noise in the transport properties of quantum excitations is a topic of great importance in many fields, from organic semiconductors for technological applications to light-harvesting complexes in photosynthesis. In this paper we study a semi-classical model where a tight-binding Hamiltonian is fully coupled to an underlying spatially extended nonlinear chain of atoms. We show that the… ▽ More The role of noise in the transport properties of quantum excitations is a topic of great importance in many fields, from organic semiconductors for technological applications to light-harvesting complexes in photosynthesis. In this paper we study a semi-classical model where a tight-binding Hamiltonian is fully coupled to an underlying spatially extended nonlinear chain of atoms. We show that the transport properties of a quantum excitation are subtly modulated by (i) the specific type (local vs non-local) of exciton-phonon coupling and by (ii) nonlinear effects of the underlying lattice. We report a non-monotonic dependence of the exciton diffusion coefficient on temperature, in agreement with earlier predictions, as a direct consequence of the lattice-induced fluctuations in the hopping rates due to long-wavelength vibrational modes. A standard measure of transport efficiency confirms that both nonlinearity in the underlying lattice and off-diagonal exciton-phonon coupling promote transport efficiency at high temperatures, preventing the Zeno-like quench observed in other models lacking an explicit noise-providing dynamical system. △ Less

Submitted 21 November, 2016; v1 submitted 13 May, 2015; originally announced May 2015.

Journal ref: New Journal of Physics 17, 113030 (2015)

Quantum walks in synthetic gauge fields with 3D integrated photonics

Authors: Octavi Boada, Leonardo Novo, Fabio Sciarrino, Yasser Omar

Abstract: There is great interest in designing photonic devices capable of disorder-resistant transport and information processing. In this work we propose to exploit 3D integrated photonic circuits in order to realize 2D discrete-time quantum walks in a background synthetic gauge field. The gauge fields are generated by introducing the appropriate phase shifts between waveguides. Polarization-independent p… ▽ More There is great interest in designing photonic devices capable of disorder-resistant transport and information processing. In this work we propose to exploit 3D integrated photonic circuits in order to realize 2D discrete-time quantum walks in a background synthetic gauge field. The gauge fields are generated by introducing the appropriate phase shifts between waveguides. Polarization-independent phase shifts lead to an Abelian or magnetic field, a case we describe in detail. We find that, in the disordered case, the magnetic field enhances transport due to the presence of topologically protected chiral edge states which do not localize. Polarization-dependent phase shifts lead to effective non-Abelian gauge fields, which could be adopted to realize Rashba-like quantum walks with spin-orbit coupling. Our work introduces a flexible platform for the experimental study of multi-particle quantum walks in the presence of synthetic gauge fields, which paves the way towards topologically robust transport of many-body states of photons. △ Less

Submitted 10 March, 2016; v1 submitted 24 March, 2015; originally announced March 2015.

Comments: This version contains results for the case of two-particle quantum walks

Journal ref: Phys. Rev. A 95, 013830 (2017)

Measurement-Assisted Quantum Communication in Spin Channels with Dephasing

Authors: Abolfazl Bayat, Yasser Omar

Abstract: We propose a protocol for countering the effects of dephasing in quantum state transfer over a noisy spin channel weakly coupled to the sender and receiver qubits. Our protocol, based on performing regular global measurements on the channel, significantly suppresses the nocuous environmental effects and offers much higher fidelities than the traditional no-measurement approach. Our proposal can al… ▽ More We propose a protocol for countering the effects of dephasing in quantum state transfer over a noisy spin channel weakly coupled to the sender and receiver qubits. Our protocol, based on performing regular global measurements on the channel, significantly suppresses the nocuous environmental effects and offers much higher fidelities than the traditional no-measurement approach. Our proposal can also operate as a robust two-qubit entangling gate over distant spins. Our scheme counters any source of dephasing, including those for which the well established dynamical decoupling approach fails. Our protocol is probabilistic, given the intrinsic randomness in quantum measurements, but its success probability can be maximized by adequately tuning the rate of the measurements. △ Less

Submitted 21 October, 2015; v1 submitted 11 February, 2015; originally announced February 2015.

Comments: 8 pages, 9 figures

Journal ref: New J. Phys. 17, 103041 (2015)

Graphene Enabled Low-Control Quantum Gates between Static and Mobile Spins

Authors: G. Cordourier-Maruri, Y. Omar, R. de Coss, S. Bose

Abstract: We show that the feature of Klein tunneling makes graphene a unique interface for implementing low control quantum gates between static and mobile qubits. A ballistic electron spin is considered as the mobile qubit, while the static qubit is the electronic spin of a quantum dot fixed in a graphene nanoribbon. Scattering is the low control mechanism of the gate, which, in other systems, is really d… ▽ More We show that the feature of Klein tunneling makes graphene a unique interface for implementing low control quantum gates between static and mobile qubits. A ballistic electron spin is considered as the mobile qubit, while the static qubit is the electronic spin of a quantum dot fixed in a graphene nanoribbon. Scattering is the low control mechanism of the gate, which, in other systems, is really difficult to exploit because of both back-scattering and the momentum dependence of scattering. We find that Klein tunneling enables the implementation of quasi-deterministic quantum gates regardless of the momenta or the shape of the wave function of the incident electron. The Dirac equation is used to describe the system in the one particle approximation with the interaction between the static and the mobile spins modelled by a Heisenberg Hamiltonian. Furthermore, we discuss an application of this model to generate entanglement between two well separated static qubits. △ Less

Submitted 30 June, 2013; originally announced July 2013.

Comments: Comments welcome, 6 pages, 3 figures

Journal ref: Phys. Rev. B 89, 075426 (2014)

Implementing quantum gates through scattering between a static and a flying qubit

Authors: G. Cordourier-Maruri, F. Ciccarello, Y. Omar, M. Zarcone, R. de Coss, S. Bose

Abstract: We investigate whether a two-qubit quantum gate can be implemented in a scattering process involving a flying and a static qubit. To this end, we focus on a paradigmatic setup made out of a mobile particle and a quantum impurity, whose respective spin degrees of freedom couple to each other during a one-dimensional scattering process. Once a condition for the occurrence of quantum gates is derived… ▽ More We investigate whether a two-qubit quantum gate can be implemented in a scattering process involving a flying and a static qubit. To this end, we focus on a paradigmatic setup made out of a mobile particle and a quantum impurity, whose respective spin degrees of freedom couple to each other during a one-dimensional scattering process. Once a condition for the occurrence of quantum gates is derived in terms of spin-dependent transmission coefficients, we show that this can be actually fulfilled through the insertion of an additional narrow potential barrier. An interesting observation is that under resonance conditions the above enables a gate only for isotropic Heisenberg (exchange) interactions and fails for an XY interaction. We show the existence of parameter regimes for which gates able to establish a maximum amount of entanglement can be implemented. The gates are found to be robust to variations of the optimal parameters. △ Less

Submitted 25 November, 2010; v1 submitted 13 August, 2010; originally announced August 2010.

Comments: 7 pages, 3 figures

Journal ref: Phys. Rev. A 82, 052313 (2010)

Quanta of Local Conformational Change: Conformons in alpha-helical proteins

Authors: Victor Atanasov, Yasser Omar

Abstract: We propose the conformon as a quantum of conformational change for energy transfer in alpha-helical proteins. The underlying mechanism of interaction between the quantum of excitation and the conformational degrees of freedom is nonlinear and leads to solitary wave packets of conformational energy. The phenomenon is specific to alpha-helices and not to beta-sheets in proteins due to the three st… ▽ More We propose the conformon as a quantum of conformational change for energy transfer in alpha-helical proteins. The underlying mechanism of interaction between the quantum of excitation and the conformational degrees of freedom is nonlinear and leads to solitary wave packets of conformational energy. The phenomenon is specific to alpha-helices and not to beta-sheets in proteins due to the three strands of hydrogen bonds constituting the alpha-helical backbone. △ Less

Submitted 8 January, 2010; v1 submitted 2 June, 2009; originally announced June 2009.

Journal ref: New J. Phys. 12, 055003 (2010)

Effect of Static Disorder in an Electron Fabry-Perot Interferometer with Two Quantum Scattering Centers

Authors: Francesco Ciccarello, G. Massimo Palma, Michelangelo Zarcone, Yasser Omar, Vitor Rocha Vieira

Abstract: In a recent paper -- F. Ciccarello \emph{et al.}, New J. Phys. \textbf{8}, 214 (2006) -- we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such effect is of particular interest in the control of transmission of quan… ▽ More In a recent paper -- F. Ciccarello \emph{et al.}, New J. Phys. \textbf{8}, 214 (2006) -- we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such effect is of particular interest in the control of transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme. △ Less

Submitted 3 July, 2007; v1 submitted 24 January, 2007; originally announced January 2007.

Comments: 4 pages, 5 figures

Journal ref: Las. Phys. 17, 889 (2007)

Electron Fabry-Perot interferometer with two entangled magnetic impurities

Authors: F. Ciccarello, G. M. Palma, M. Zarcone, Y. Omar, V. R. Vieira

Abstract: We consider a one-dimensional (1D) wire along which single conduction electrons can propagate in the presence of two spin-1/2 magnetic impurities. The electron may be scattered by each impurity via a contact-exchange interaction and thus a spin-flip generally occurs at each scattering event. Adopting a quantum waveguide theory approach, we derive the stationary states of the system at all orders… ▽ More We consider a one-dimensional (1D) wire along which single conduction electrons can propagate in the presence of two spin-1/2 magnetic impurities. The electron may be scattered by each impurity via a contact-exchange interaction and thus a spin-flip generally occurs at each scattering event. Adopting a quantum waveguide theory approach, we derive the stationary states of the system at all orders in the electron-impurity exchange coupling constant. This allows us to investigate electron transmission for arbitrary initial states of the two impurity spins. We show that for suitable electron wave vectors, the triplet and singlet maximally entangled spin states of the impurities can respectively largely inhibit the electron transport or make the wire completely transparent for any electron spin state. In the latter case, a resonance condition can always be found, representing an anomalous behaviour compared to typical decoherence induced by magnetic impurities. We provide an explanation for these phenomena in terms of the Hamiltonian symmetries. Finally, a scheme to generate maximally entangled spin states of the two impurities via electron scattering is proposed. △ Less

Submitted 3 July, 2007; v1 submitted 2 November, 2006; originally announced November 2006.

Comments: 19 pages

Journal ref: J. Phys. A: Math. Theor. 40, 7993 (2007)

Entanglement Controlled Single-Electron Transmittivity

Authors: Francesco Ciccarello, Massimo Palma, Michelangelo Zarcone, Yasser Omar, Vitor Rocha Vieira

Abstract: We consider a system consisting of single electrons moving along a 1D wire in the presence of two magnetic impurities. Such system shows strong analogies with a Fabry - Perot interferometer in which the impurities play the role of two mirrors with a quantum degree of freedom: the spin. We have analysed the electron transmittivity of the wire in the presence of entanglement between the impurity s… ▽ More We consider a system consisting of single electrons moving along a 1D wire in the presence of two magnetic impurities. Such system shows strong analogies with a Fabry - Perot interferometer in which the impurities play the role of two mirrors with a quantum degree of freedom: the spin. We have analysed the electron transmittivity of the wire in the presence of entanglement between the impurity spins. The main result of our analysis is that, for suitable values of the electron momentum, there are two maximally entangled state of the impurity spins the first of which makes the wire transparent whatever the electron spin state while the other strongly inhibits the electron transmittivity. Such predicted striking effect is experimentally observable with present day technology. △ Less

Submitted 10 October, 2006; v1 submitted 17 March, 2006; originally announced March 2006.

Comments: Published version (6 figures)

Journal ref: New J. Phys. 8, 214 (2006)