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**Search for:**quantum-electronics

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#### Simulation of multipartite cavity quantum electrodynamics

, Article IEEE Journal of Quantum Electronics ; Volume 49, Issue 12 , October , 2013 , Pages 1066-1079 ; 00189197 (ISSN) ; Khorasani, S. A ; Aram, M. H ; Sharif University of Technology
2013

Abstract

Cavity quantum electrodynamics of multipartite systems are studied in depth, which consists of an arbitrary number of emitters in interaction with an arbitrary number of cavity modes. The governing model is obtained by taking the full field-dipole and dipole-dipole interactions into account, and is solved in the Schrödinger picture with assumption of vanishing field and dipole interactions at high energies. An extensive code is developed that is able to solve the system and track its evolution in time, while maintaining sufficient degrees of arbitrariness in setting up the initial conditions and interacting partitions. Using this code, we have been able to numerically evaluate various...

#### No-go theorem for iterations of unknown quantum gates

, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 93, Issue 1 , 2016 ; 10502947 (ISSN) ; Karimipour, V ; Sharif University of Technology
American Physical Society

Abstract

We propose a no-go theorem by proving the impossibility of constructing a deterministic quantum circuit that iterates a unitary oracle by calling it only once. Different schemes are provided to bypass this result and to approximately realize the iteration. The optimal scheme is also studied. An interesting observation is that for a large number of iterations, a trivial strategy like using the identity channel has the optimal performance, and preprocessing, postprocessing, or using resources like entanglement does not help at all. Intriguingly, the number of iterations, when being large enough, does not affect the performance of the proposed schemes

#### Evolution of quantum electronic features with the size of silicon nanoparticles embedded in a SiO2 layer obtained by low energy ion implantation

, Article 11th International Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technlogy, GADEST 2005, Giens, 25 September 2005 through 30 September 2005 ; Volume 108-109 , 2005 , Pages 71-76 ; 10120394 (ISSN); 3908451132 (ISBN); 9783908451136 (ISBN) ; Shalchian, M ; BenAssayag, G ; Coffin, H ; Bonafos, C ; Dumas, C ; Atarodi, S. M ; Claverie, A ; Sharif University of Technology
Trans Tech Publications Ltd
2005

Abstract

In this paper, we have studied the evolution of quantum electronic features with the size of silicon nanoparticles embedded in an ultra-thin SiO 2 layer. These nanoparticles were synthesized by ultralow energy (1 KeV) ion implantation and annealing. Their size was modified using the effect of annealing under slightly oxidizing ambient (N2+O2). Material characterization techniques including transmission electron microscopy (TEM) Fresnel imaging and spatially resolved electron energy loss spectroscopy (EELS) have been used to evaluate the effects of oxidation on structural characteristics of nanocrystal layer. Electrical transport characteristics have been measured on few (less than two...

#### From source model to quantum key distillation: An improved upper bound

, Article IWCIT 2014 - Iran Workshop on Communication and Information Theory ; 2014 ; Mahzoon, M ; Gohari, A ; Aref, M.R ; Sharif University of Technology
Abstract

In this paper we derive a new upper bound on the quantum key distillation capacity. This upper bound is an extension of the classical bound of Gohari and Anantharam on the source model problem. Our bound strictly improves the quantum extension of reduced intrinsic information bound of Christandl et al. Although this bound is proposed for quantum settings, it also serves as an upper bound for the special case of classical source model, and may improve the bound of Gohari and Anantharam. The problem of quantum key distillation is one in which two distant parties, Alice and Bob, and an adversary, Eve, have access to copies of quantum systems A, B, E respectively, prepared jointly according to...

#### Is quantum theory compatible with special relativity?

, Article Pramana - Journal of Physics ; Volume 80, Issue 3 , 2013 , Pages 429-437 ; 03044289 (ISSN) ; Shafiee, A ; Saravani, M ; Golshani, M ; Sharif University of Technology
2013

Abstract

How a proposed quantum nonlocal phenomenon could be incompatible with the requirements of special relativity is studied. To show this, the least set of assumptions about the formalism and the interpretation of non-relativistic quantum theory is considered. Then, without any reference to the collapse assumption or any other stochastic processes, an experiment is proposed, involving two quantum systems, that interacted at an arbitrary time, with results which seem to be in conflict with requirements of special relativity

#### Entanglement swapping with local certification: Application to remote micromechanical resonators

, Article 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC ; 2013 ; 978-1-4799-0593-5 (ISBN) ; Pirandola, S ; Tombesi, P ; Vitali, D ; Sharif University of Technology
Abstract

Entanglement swapping allows to entangle two distant systems which never interacted. The standard protocol considers two distant users, Alice and Bob, each possessing a bipartite entangled system, R1B1 for Alice and R2B2 for Bob. The users send their systems B1 and B2 to an intermediate station (Charlie). Here an appropriate Bell measurement is made over the B systems and the outcome communicated back to Alice and Bob. As a result, the two remote systems R 1 and R2 become entangled. A delicate point is the experimental verification of the generated entanglement, which generally involves direct measurements on the two remote systems, R1 and R 2, followed by classical communications. A simple...

#### Analytical and numerical study of quantum transport in an array of nanorings: A case study with double rings

, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 47 , January , 2013 , Pages 297-302 ; 13869477 (ISSN) ; Khoeini, F ; Sharif University of Technology
2013

Abstract

We present an analytical method to obtain an expression for electron transmission through an array of disordered nanorings (ADNRs) sandwiched between two semi-infinite metallic leads in different lead-ring coupling strengths. Our approach is based on the nearest-neighbor tight-binding approximation and transfer matrix method. First, we derive an analytical formula for electron transmission across the system. Next, we apply our approach to study of the electron transport in a perfect double nanoring (PDNR) and design a NOR gate using the magnetic fluxes inputs. The conductance, current-voltage characteristics and threshold voltage of the system are calculated in the weak and strong coupling...

#### Quantum detailed balance conditions and fluctuation relations for thermalizing quantum dynamics

, Article Physical Review E ; Volume 98, Issue 5 , 2018 ; 24700045 (ISSN) ; Benatti, F ; Floreanini, R ; Marcantoni, S ; Golshani, M ; Tayefeh Rezakhani, A ; Sharif University of Technology
American Physical Society
2018

Abstract

Quantum detailed balance conditions and quantum fluctuation relations are two important concepts in the dynamics of open quantum systems: both concern how such systems behave when they thermalize because of interaction with an environment. We prove that for thermalizing quantum dynamics the quantum detailed balance conditions yield validity of a quantum fluctuation relation (where only forward-time dynamics is considered). This implies that to have such a quantum fluctuation relation (which in turn enables a precise formulation of the second law of thermodynamics for quantum systems) it suffices to fulfill the quantum detailed balance conditions. We, however, show that the converse is not...

#### Dzyaloshinskii-Moriya interaction and anisotropy effects on the entanglement of the Heisenberg model

, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 79, Issue 4 , 2009 ; 10502947 (ISSN) ; Jafari, R ; Langari, A ; Sharif University of Technology
2009

Abstract

In this paper the effect of Dzyaloshinskii-Moriya interaction and anisotropy on the entanglement of Heisenberg chain has been studied. While the anisotropy suppresses the entanglement due to favoring of the alignment of spins, the DM interaction restores the spoiled entanglement via creation of the quantum fluctuations. Thermodynamic limit of the model and emerging of nonanalytic behavior of the entanglement have also been probed. The singularities of the entanglement correspond to the critical boundary separating different phases of the model. The singularity of the entanglement derivative approaches the critical point from the gapped phase and will be symmetric if both phases on the...

#### Introduction to the world of Quantum Computers

, Article 5th IEEE International Conference on Cognitive Informatics, ICCI 2006, Beijing, 17 July 2006 through 19 July 2006 ; Volume 2 , 2006 , Pages 760-764 ; Sharif University of Technology
2006

Abstract

The world is changing very fast, and so are the ways of communication and computation. This article is about a new communication and information technology based on the principles of the quantum physics. At first we discuss about some fundamental paradigms of Quantum Computers World, and then introducing the basis of quantum computation: "QBit". Afterthat we will explain some magic properties of this atomic QBit including Quantum Measurement, Superposition, Entanglement, etc. Then we introduce Quantum Gates the basic modules of the next generation computers. Their relation with the ordinary logical gates and the properties of some of the most useful quantum gates. And finally, we will have a...

#### On dimension bounds for auxiliary quantum systems

, Article IEEE Transactions on Information Theory ; Vol. 60, Issue. 1 , Jan , 2014 , PP . 368-387 ; ISSN: 00189448 ; Gohari, A ; Sharif University of Technology
Abstract

Expressions of several capacity regions in quantum information theory involve an optimization over auxiliary quantum registers. Evaluating such expressions requires bounds on the dimension of the Hilbert space of these auxiliary registers, for which no nontrivial technique is known; we lack a quantum analog of the Carathéodory theorem. In this paper, we develop a new non-Carathéodory-type tool for evaluating expressions involving a single quantum auxiliary register and several classical random variables. As we show, such expressions appear in problems of entanglement-assisted Gray-Wyner and entanglement-assisted channel simulation, where the question of whether entanglement helps in these...

#### Dissipative quantum metrology in manybody systems of identical particles

, Article New Journal of Physics ; Vol. 16, issue , January , 2014 ; Alipour, S ; Rezakhani, A. T ; Sharif University of Technology
Abstract

Estimation of physical parameters is essential in almost any part of science and technology. The enhancement of performance in this task (e.g. beating the standard classical shot-noise limit) using available physical resources is a major goal in metrology. Quantum metrology in closed systems has indicated that entanglement in such systems may be a useful resource. However, whether in open quantum systems such enhancements may still show up is not yet fully understood. Here, we consider a dissipative (open) quantum system of identical particles in which a parameter of the open dynamics itself is to be estimated. We employ a recently developed dissipative quantum metrology framework, and...

#### Quantum metrology in open systems: Dissipative cramer-rao bound

, Article Physical Review Letters ; Volume 112, Issue 12 , 2014 ; 00319007 (ISSN) ; Mehboudi, M ; Rezakhani, A. T ; Sharif University of Technology
American Physical Society
2014

Abstract

Estimation of parameters is a pivotal task throughout science and technology. The quantum Cramér-Rao bound provides a fundamental limit of precision allowed to be achieved under quantum theory. For closed quantum systems, it has been shown how the estimation precision depends on the underlying dynamics. Here, we propose a general formulation for metrology scenarios in open quantum systems, aiming to relate the precision more directly to properties of the underlying dynamics. This feature may be employed to enhance an estimation precision, e.g., by quantum control techniques. Specifically, we derive a Cramér-Rao bound for a fairly large class of open system dynamics, which is governed by a...

#### Highly sensitive dispersion map extraction from highly nonlinear fibers using BOTDA probing of parametric amplification

, Article 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013 ; 2013 ; Vedadi, A ; Denisov, A ; Soto, M. A ; Mehrany, K ; Bres, C. S ; Thevenaz, L ; Sharif University of Technology
2013

Abstract

The performance of devices based on highly nonlinear fibers (HNLF) can be drastically impeded by even tiny fluctuations of the zero dispersion wavelength (ZDW) along the fiber. Being able to measure ZDW fluctuations along an HNLF is therefore essential for the design of efficient nonlinear optics based devices such as fiber optical parametric amplifiers (FOPA), regenerators and limiters. Different schemes using complex distributed sensing of localized nonlinear interactions have been used in order to derive the ZDW fluctuations along the fiber [1-2]. In [3], the distributed gain of a pulsed pump FOPA along an HNLF was measured using a Brillouin Optical-Time Domain Analysis (BOTDA) based...

#### Quantum interface between optics and microwaves with optomechanics

, Article 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, Munich, 12 May 2013 through 16 May 2013 ; 2013 ; Abdi, M ; Milburn, G. J ; Tombesi, P ; Vitali, D ; Sharif University of Technology
IEEE Computer Society
2013

Abstract

A number of schemes for a quantum interface between light at different wavelengths have been demonstrated and very recently various solutions for interfacing optics and microwaves have been proposed [1-3]. We describe here a reversible quantum interface between optical and microwave photons based on a micro-mechanical resonator in a superconducting circuit, simultaneously interacting with an optical and a microwave cavity [3]. When the cavities are appropriately driven, the mechanical resonator mediates an effective parametric amplifier interaction, entangling an optical signal and a microwave idler. Such continuous variable (CV) entanglement can be then exploited to implement CV...

#### Topological code autotune

, Article Physical Review X ; Volume 2, Issue 4 , October , 2012 ; 21603308 (ISSN) ; Whiteside, A. C ; McInnes, A. L ; Rabbani, A ; Sharif University of Technology
2012

Abstract

Many quantum systems are being investigated in the hope of building a large-scale quantum computer. All of these systems suffer from decoherence, resulting in errors during the execution of quantum gates. Quantum error correction enables reliable quantum computation given unreliable hardware. Unoptimized topological quantum error correction (TQEC), while still effective, performs very suboptimally, especially at low error rates. Hand optimizing the classical processing associated with a TQEC scheme for a specific system to achieve better error tolerance can be extremely laborious. We describe a tool, AUTOTUNE, capable of performing this optimization automatically, and give two highly...

#### Phase diagram of J1-J2 transverse field Ising model on the checkerboard lattice: a plaquette-operator approach

, Article European Physical Journal B ; Volume 88, Issue 10 , October , 2015 ; 14346028 (ISSN) ; Langari, A ; Sharif University of Technology
springer berlin
2015

Abstract

We study the effect of quantum fluctuations by means of a transverse magnetic field (Γ) on the antiferromagnetic J1-J2 Ising model on the checkerboard lattice, the two dimensional version of the pyrochlore lattice. The zero-temperature phase diagram of the model has been obtained by employing a plaquette operator approach (POA). The plaquette operator formalism bosonizes the model, in which a single boson is associated to each eigenstate of a plaquette and the inter-plaquette interactions define an effective Hamiltonian. The excitations of a plaquette would represent an-harmonic fluctuations of the model, which lead not only to lower the excitation energy compared with a single-spin flip but...

#### Stable local moments of vacancies, substitutional and hollow site impurities in graphene

, Article Journal of Physics Condensed Matter ; Volume 27, Issue 15 , 2015 ; 09538984 (ISSN) ; Jafari, S. A ; Sharif University of Technology
Institute of Physics Publishing
2015

Abstract

The two-sublattice nature of graphene lattice in conjunction with three-fold rotational symmetry, allows for the p-wave hybridization of the impurity state with the Bloch states of carbon atoms. Such an opportunity is not available in normal metals where the wave function is scalar. The p-wave hybridization function V (-k) appears when dealing with vacancies, substitutional adatoms and the hollow site impurities while the s-wave mixing on graphene lattice pertains only to the top site impurities. In this work, we compare the local moment formation in these two cases and find that the local moments formed by p-wave mixing compared to the s-wave one are robust against the changes in the...

#### Investigation of readout cell configuration and parameters on functionality and stability of bi-directional RSFQ TFF

, Article IEEE Transactions on Applied Superconductivity ; Volume 26, Issue 3 , 2016 ; 10518223 (ISSN) ; Zandi, H ; Foroughi, F ; Bozbey, A ; Fardmanesh, M ; Sharif University of Technology
Abstract

Considering the two main categories of rapid single flux quantum gates with destructive and nondestructive readout process, we have investigated the effects of readout cell topology and involved critical parameters on the proper functionality and stability of the states of the newly developed bidirectional T flip-flops (TFFs). It is observed that instabilities and fluctuations in the state of the gate (memory of TFF) after each transition determine the minimum time intervals between the clock pulses set by the ac bias current, further limiting the ultimate operation frequency of the circuits. The absolute values of the current levels of the junctions at each state, which play an important...

#### Thermal effects on coherence and excitation transfer

, Article Physical Review A ; Volume 96, Issue 4 , 2017 ; 24699926 (ISSN) ; Mani, A ; Sharif University of Technology
Abstract

To control and utilize quantum features in small scale for practical applications such as quantum transport, it is crucial to gain a deep understanding of the quantum characteristics of states such as coherence. Here by introducing a technique that simplifies solving the dynamical equation, we study the dynamics of coherence in a system of qubits interacting with each other through a common bath at nonzero temperature. Our results demonstrate that depending on the initial state, the environment temperature affects coherence and excitation transfer in different ways. We show that when the initial state is incoherent, as time goes on, coherence and the probability of excitation transfer...