IICQI-10 Program

International Iran Conference on Quantum Information - 2010

 
Abstract-plenary talks
Abstract-keynote talks
Abstract-invited talks
Abstract-contributed talks
Abstract-posters
 

 

Program

 

Registration: 10 Sep. afternoon and 11 Sep. 8:00-9:00 at Hotel Parmis.

 

    14 Sep.   13 Sep.   12 Sep.   11 Sep.  
Mikio Nakahara 9:30 Saverio Pascazio 9:30 Luiz Davidovich 9:30 Vlatko Vedral 9:30
break 10:15 Shao-Ming Fei 10:15 Marcos de Oliveira 10:25 Dan Browne 10:25
Patrick Hayden 10:30 Francesco Ciccarello 10:40 break 11:00 break 11:00
    break 11:05 Dagmar Bruss 11:30 Chiara Macchiavello 11:30
    Tom Stace 11:30 Faisal Khan 12:15 Zahra Shadman 12:15
    Sean Barrett 12:05 lunch 12:40 lunch 12:40
    lunch 12:40 Mahmoud Abdel-Aty 14:30 Seyed Javad Akhtarshenas 14:30
    Ali A. Kamli 14:30 Ugo Marzolino 15:05 Abolfazl Bayat 15:05
    Nigum Arshed 15:05 Yasushi Kondo 15:30 Daniel Burgarth 15:30
    break 15:30 break 15:55 break 15:55
    poster session 16:00-18:30 Abdollah Langari 16:30 Hubert de Guise 16:30
        Archan S. Majumdar 17:05 Akira SaiToh 17:05
 
 
Abstract-plenary talks:

 

Davidovich, Luiz: From Einstein and Schrodinger to Quantum Optics Experiments
 

This talk reviews recent theoretical and experimental findings on the open-system dynamics of entanglement, which can differ in remarkable ways from the dynamics of the individual components of the system. Decoherence leads to non-exponential decay of entanglement, which may vanish even when coherence is still present in the system. These results, which have been recently probed by quantum optics experiments, are relevant for assessing the robustness of applications like quantum communication and computation, as well as for addressing fundamental questions, already raised by Einstein and Schrodinger, concerning the classical limit of quantum mechanics.

 

Hayden, Patrick: Quantum information theory as asymptotic geometry
 

Quantum states are represented as vectors in an inner product space. Because the dimension of that state space grows exponentially with the number of its constituents, quantum information theory is in large part the asymptotic theory of finite dimensional inner product spaces. I'll highlight some examples of how abstract mathematical results on low distortion embeddings of normed spaces manifest themselves in quantum information theory as improvements on the famous "teleportation" procedure, reductions in the amount of shared secret information required to encrypt a quantum message, and counterexamples to the additivity conjecture, among many other applications.

 

Vedral, Vlatko: Quo Vadis Quantum Information?
 

I will talk about three recent developments in quantum information that I think will leave a long-term legacy on science in general. The first is centered on quantum simulations of complex physical systems. The second is regarding the role of quantum coherence in living systems. The third is our emerging, information-based, understanding of the quantum nature of reality. The importance of each of these directions goes well beyond the narrowly defined goal of making faster algorithms, though that goal itself is also worth pursuing. I will speak about concrete open problems within each of these three areas and review some of the key recent findings.

 

Abstract-keynote talks:

 

Bruß, Dagmar: A brief visit to the zoo of multipartite entangled states
 

Entanglement is one of the most fascinating features of quantum mechanics and plays a central role in quantum information processing. Genuine multipartite entanglement comes in various species that populate a rich zoo. In this talk we will visit two less well-known members of this zoo: first, the ``phased Dicke states''. Here, a method for their detection will be explained which uses witness operators that are related to diffractive properties. Second, we will study the ``real equally weighted states'' which appear in quantum algorithms. Here, we will answer the question whether most states of this family are indeed multipartite entangled.

 

Macchiavello, Chiara: Violation of the generalized quantum Hamming bound in quantum error correction with correlated noise
 

The question of whether the quantum Hamming bound, which quantifies the minimum resources needed in order to achieve successful quantum error correction for non-degenerate codes, can be violated with degenerate codes has not been answered for more than a decade. We present a generalization of the quantum Hamming bound, which was originally formulated for the case of noise acting independently on the encoding systems, to a generic noise process. We show in particular that in the presence of correlated noise the bound is violated by employing degenerate codes.

 

Nakahara, Mikio: Neutral Atom Quantum Computer with On-Demand Interaction
 

We discuss an implementation of a neutral atom quantum computer, where atoms are trapped in an array of near-field Fresnel light. The trap light is supplied through an optical fiber attached to each trap. Single-qubit gate operation is realized by the two-photon Raman transition, which is controlled by another laser beam through the same fiber. Selective 2-qubit gate operation is implemented by leaving two atoms in a 1-dimensional optical lattice and then colliding a particular set of quantum states of these atoms to obtain an extra phase. We believe the proposed scheme is realizable within current technology.

 

Pascazio, Saverio: Multipartite entanglement and frustration
 

Entanglement is one of the most intriguing features of quantum mechanics. It is widely used in quantum communication and information processing and plays a key role in quantum computation. At the same time, entanglement is not fully understood. It is deeply rooted into the linearity of quantum theory and in the superposition principle and (for pure states) it is essentially related to the impossibility of factorizing the state of the total system in terms of states of its constituents. The characterization and quantification of entanglement is an open and challenging problem. One can give a good definition of bipartite entanglement in terms of the von Neumann entropy or the entanglement of formation. The problem of defining multipartite entanglement is more difficult and no unique definition exists. We introduce the notion of maximally multipartite entangled states (MMES) of n qubits as a generalization of the bipartite case. The bipartite entanglement of a MMES is almost independent of the bipartition and is maximal for all possible bipartitions. Some examples of MMES for few qubits are investigated. For a larger number of qubits the search for MMES becomes more involved and unearths the presence of frustration. MMEs are the solution of an optimization problem that can be recast in terms of classical statistical mechanics. We focus on fundamental issues and possible applications (quantum teamwork).

 

Abstract-invited talks:

 

Abdel-Aty, Mahmoud: Long-lived geometric phase of superconducting qubits with nanomechanical resonators
 

We propose a scheme for environment-induced a long-lived geometric phase using supercoducting artificial atoms.  The system is analogous to a collection of artificial few-level atoms (the Josephson junctions) coupled to the resonators.  In this scheme, the nanomechanical resonator plays an important role to contribute additional auxiliary energy levels to the artificial atoms. Increasing the number of atoms as revealed in a high degree of extinction of propagating waves, plays the opposite role of the environment effect. It is shown that the environment provides a mechanism for the generation of geometric phases.

 

Akhtarshenas, Seyed Javad: Concurrence of Superpositions
 

Recently, Linden, Popescu and Smolin [Phys. Rev. Lett., 97, 100502 (2006)] have raised the following problem: Given a bipartite quantum state and a certain decomposition of it as a superposition of two others, what is the relation between the entanglement of the state and those of the two states in the superposition? In this paper we use the concurrence vector as a measure of entanglement and investigate upper and lower bounds on the concurrence of the state as a function of the concurrence of the superposed states. We show that the concurrence vector enables us to extend the results to the superpositions of two multipartite states.

 

Barrett, Sean: Fault tolerant quantum computation with very high threshold for loss errors
 

Many proposals for fault tolerant quantum computation (FTQC) suffer detectable loss processes. Here we show that topological FTQC schemes, which are known to have high error thresholds, are also extremely robust against losses. We demonstrate that these schemes tolerate loss rates up to 24.9%, determined by bond percolation on a cubic lattice. Our numerical results show that these schemes retain good performance when loss and computational errors are simultaneously present.  This talk is based on the preprint arXiv:1005.2456.

 

Browne, Dan: Linearity and loopholes: On Bell inequalities and measurement-based quantum computation
 

We show [1] that multi-party generalisations of the CHSH inequality can be elegantly derived in a framework similar to measurement-based quantum computation. This gives an operational meaning of what it means to violate a CHSH-type inequality, which allows us to characterise the effect of "loopholes" in Bell inequality experiments. We show that adaptive measurements of the kind which occur in measurement-based quantum computation may be simulated without introducing a loophole, and that this means that one can contrast local hidden variable correlations with a wider class of quantum correlations than traditionally considered.

[1] M. Hoban and D.E. Browne, in preparation

 

de Guise, Hubert: Dynamical symmetry reduction and tomography of three-level atoms
 

I will discuss how the level structure of three-level atoms may the possible tomographic reconstructions of a system of three-level atoms.   The particular case of the ∑ atom will be discussed in greater length with emphasis on the problem of selecting a finite set of transformations that will optimize the reconstruction.(work done in collaboration with Andrei Klimov and Dylan Mahler)

 

de Oliveira, Marcos: Entanglement, quantum discord, and the power of the quantum computer
Universidade Estadual de Campinas, Brazil

We present a direct and general relation between entanglement of formation and quantum discord. By extending the relation to a paradigmatic situation of a bipartite system coupled to the environment we show that in the deterministic quantum computer with one pure qubit (DQC1) the protocol has the ability to rearrange the entanglement and the quantum discord, which are present and distributed following a monogamic relation. This implies that quantum computation can be understood in a different ground- as a coherent dynamics where quantum correlations are distributed between the qubits of the computer. In addition, we extend the discussion for an arbitrary tripartite mixed system, showing the existence of an inequality for the subsystems entropies with stronger bounds than the usual strong subadditivity.  

 

Kamli, Ali: Nonlinear optics with surface polaritons
 

We discuss basic properties of surface polaritons (SP) qubits, namely confinement and losses in the presence of a meta material interface. Using electromagnetically induced transparency technique we show that SPs modes can be controlled, manipulated and slowed down to very low velocities. This enables information encoded in SP qubits to be stored and retrieved according to EIT protocol. Furthermore employing double EIT mechanism we demonstrate that the interaction of two SP qubits can generate large Kerr nonlinearity with phase shift of order π which is essential for application in quantum phase gates a necessary ingredient in quantum computing.

References:
A. A. Kamli, S. A. Moiseev and B. C. Sanders; Phys. Rev. Lett. 101, 263601 (2008).
S. A. Moiseev, A. A. Kamli and B. C. Sanders; Phys. Rev. A 81, 033839 (2010).

 

Langari, Abdollah: Renormalization of concurrence: Quantum information properties close to quantum critical point via the renormalization group
 

My presentation is a collection of our recent investigations on the quantum information properties of spin models close to the quantum critical points. I first introduce the implementation of quantum renormalization group to get the quantum critical properties of a spin model. This implementation is used to show the evolution and finite size scaling of entanglement and its derivative close to quantum critical point of the Ising model in transverse magnetic field (ITF). The finite size analysis of the entanglement derivative is presented. We have found that the derivative of concurrence between two blocks each containing half of the system size diverges at the critical point with the exponent, which is directly associated with the divergence of the correlation length. From the same point of view the quantum phase transition of XXZ model from the Neel phase to the spin liquid one is presented. The non-analytic behavior comes from the divergence of the first derivative of both measures of entanglement as the size of the system becomes large. The renormalization scheme demonstrates how the minimum value of the first derivative and its position scales with an exponent of the system size. We have also investigated the effect of Dzyaloshinskii-Moriya interaction on the quantum information properties of ITF and XXZ model close to their quantum critical boundaries. Finally, the most recent results are presented on the connection between quantum information property and quantum critical point of the Kondo-necklace model which is obtained by the continuous unitary transformations.

 

Stace, Tom: Quantum error correction thresholds in the presence of loss
 

Toric codes are very powerful error correcting codes, which achieve very high error correction thresholds.  In this talk, I will introduce toric codes as quantum memories, explain how they work, and demonstrate their tolerance against errors.  I will then discuss some recent results that show they are also extremely robust against losses.

 

Abstract-contributed talks:

 

Arshed, Nigum: Channel Capacities of an Exactly Solvable Spin-Star System

We calculate the entanglement-assisted and unassisted channel capacities of an exactly solvable spin star system, which models the quantum dephasing channel. The capacities for this non-Markovian model exhibit a strong dependence on the coupling strengths of the bath spins with the system, the bath temperature, and the number of bath spins. For equal couplings and bath frequencies, the channel becomes periodically noiseless.

 

Bayat, Abolfazl: Entanglement Routers Using Macroscopic Singlets
University College London, UK

We propose a mechanism where high entanglement between very distant boundary spins is generated by suddenly connecting two long Kondo spin chains. We show that this procedure provides an efficient way to route entanglement between multiple distant sites which is useful for quantum computation and multi-party quantum communication. We observe that the key features of the entanglement dynamics of the composite spin chain are remarkably well described using a simple model of two singlets, each formed by two spins. The proposed entanglement routing mechanism is a footprint of the emergence of a Kondo cloud in a Kondo system and can be engineered and observed in varied physical settings.

 

Burgarth, Daniel: Indirect Quantum Tomography of Quadratic Hamiltonians
Imperial College London, UK

A number of many-body problems can be formulated using Hamiltonians that are quadratic in the creation and annihilation operators. Here, we show how such quadratic Hamiltonians can be efficiently estimated indirectly, employing very few resources. We find that almost all properties of the Hamiltonian are determined by its surface, and that these properties can be measured even if the system can only be initialized to a mixed state. Therefore our method can be applied to various physical models, with important examples including coupled nano-mechanical oscillators, hopping fermions in optical lattices, and transverse Ising chains.

 

Ciccarello, Francesco: Optimal and scalable telecloning in a limited-control scenario
University of Palermo, Italy

Quantum telecloning [1] is a Quantum Information Processing task, which allows to achieve optimal spreading among N receivers of the quantum information initially possessed by one sender. So far, to the best of our knowledge, no scheme for the actual implementation of such a process in a scalable way has been proposed. Here, we first show the existence of a class of many-qubit singlets allowing for optimal and scalable telecloning. Next, we illustrate a protocol to prepare such states in a setting where scattering centers possessing a spin degree of freedom interact by means of mobile particles. The scheme is understood simply by resorting to an appropriate coupling scheme for the addition of angular momenta and Hamiltonian symmetries. Major practical advantages of our scheme lie on the management of stationary and well separated spins along with the mild requirement to perform simple Geiger measurements over the mobile particles to establish the necessary multipartite entanglement [3, 4]. We also show strategies that allow generating in the same setting other important many-qubit states such as Aharonov, W and GHZ states.

[1] M. Murao, D. Jonathan, M. B. Plenio, and V. Vedral, Phys. Rev. A 59, 156 (1999).
[2] F. Ciccarello, M. Paternostro, S. Bose, D. Browne, G. M. Palma and M. Zarcone, arXiv:1003.2171 (2010).
[3] F. Ciccarello, M. Paternostro, G. M. Palma and M. Zarcone, New J. Phys. 11, 113053 (2009).
[4] F. Ciccarello, S. Bose and M. Zarcone, Phys. Rev. A 81,  042318 (2010).

 

Fei, Shao-Ming: Quantum Entanglement and Experimental Determination
Capital Normal University, China

We discuss quantum entanglement and its experimental determination. In particular the way of experimentally determining the concurrence in terms of the expectation values of local observable, the criteria related to Bell inequalities which are sufficient and necessary for the separability of general pure multipartite quantum states in arbitrary dimensions, as well as the relation between violation of Bell inequalities and distillability properties of quantum states will be investigated.

 

Khan, Faisal: A Game Theoretic Approach to Quantum Markov Processes
Khalifa University of Science, Technology & Research, UAE

In the context of quantum information theory, "quantization" of various mathematical and computational constructions is said to occur upon the replacement, at various points in the construction, of the classical randomization notion of probability distribution with higher order randomization notions from quantum mechanics such as quantum superposition with measurement. For this to be done "properly", a faithful copy of the original construction is required to exist within the new "quantum" one, just as is required when a function is extended to a larger domain. Here procedures for extending history dependent Parrondo games, Markov processes and multiplexing circuits to their "quantum" versions are analyzed from a game theoretic viewpoint, and from this viewpoint, proper quantizations developed.

 

Kondo, Yasushi: Composite Quantum Gates with Vanishing Dynamic Phases
Kinki University, Japan

We show that all composite quantum gates with vanishing dynamic phases are robust against control field strength errors. As examples of this observation, we show (1) how a robust composite rf-pulse in NMR is geometrically constructed and (2) a composite rf-pulse based on Trotter-Suzuki Formulas is a geometric quantum gate.

 

Majumdar, Archan S.: Information processing by single particle hybrid entangled states
Salt Lake, Kolkata, India

We first discuss schemes for generating entanglement between different degrees of freedom of the same particle. Using single particle entangled states as resources we formulate protocols for entanglement swapping and teleportation of usual qubit states. We also present proposals for testing quantum contextuality and nolocality of single particle states generated through atom-photon interactions in cavity quantum electrodynamics.

 

Marzolino, Ugo: Sub-shot-noise quantum metrology with entangled identical particles
University of Trieste, Italy

The usual notion of separability has to be reconsidered when applied to states describing identical particles. A definition of separability not related to any a priori Hilbert space tensor product structure is needed: this can be given in terms of commuting subalgebras of observables. Accordingly, the results concerning the use of the quantum Fisher information in quantum metrology are generalized and physically reinterpreted.

 

SaiToh, Akira: Practical evaluation of an MPS simulation as a classical search tool
Kinki University, Japan

We present our recent results of the studies to evaluate a matrix-product-state (MPS) simulation of a bulk-ensemble search as a classical search tool. The dominant computational cost is the cost to simulate an oracle circuit because the number of queries is not dominant: it is linear in the input size and the number of solutions. The rounding error is avoided by using a multi-precision programming library. The total cost is well characterized by the cube of the maximum Schmidt rank during the simulation. It is known that the upper bound of the maximum Schmidt rank increases exponentially in the depth of mutually overlapping gates in the quantum circuit in MPS simulations in general. We show that the increase is considerably small in practical Oracle circuits for classical satisfiability problems and the variants. Even in hard instances for classical random searches, namely instances with a small number of truth assignments, the increase is shown to be slow in the circuit depth, so far as we could test. In contrast, there are some hard instances for the MPS method, namely those results in a large Schmidt rank that are easy instances for classical random searches.

 

Shadman, Zahra: Non-unitary encoding increases the super dense coding capacity in the presence of noise
D
usseldorf University, Germany

We study an important protocol in quantum information processing, namely super dense coding in the presence of noise. We compare the optimal super dense coding capacity with unitary and non-unitary encoding. We show that in the case of non-unitary encoding, the optimal capacity can be reached by preprocessing on the sender's side followed by a unitary encoding.  We give examples that preprocessing increases the super dense coding capacity.

 

Abstract-posters:

 

01. Abdullah, Shirwan: Entanglement Indicators in Quantum Dots
University of York, UK

We calculate spatial entanglement between two electrons trapped in quantum dots for abroad class of confinement potentials with different type and geometry, we make comparison between entanglement content of the system for different cases. The many-body wave function has been calculated by exact diagonalization of the time independent Schrodinger equation. We show that some physical property of the system could by a good entanglement indicator. Entanglement has an inverse correlation with Coulomb interaction energy in some cases, so it can be used as an entanglement indicator. We show that the wave function at a single highly symmetric point is also a good entanglement indicator. We investigate the possibility of finding a general indicator that will be common for all cases. We study the effect of internal nanostructure parameters and the external fields on entanglement property in systems with different confinement potential type and geometry. This property may be used to tailor nanostructures according to the level of entanglement required by a specific application.

 

02. Ahmadi, Fatemeh: Fidelity for States of Two Spin-1/2 Particles in Moving Frames
Amirkabir University, Iran

 Fidelity for the spin part of states of two spin-1/2 particles is investigated from the view point of moving observers. Using a numerical approach, the behavior of the fidelity in terms of the boost parameter is described for different amounts of spin entanglement and momentum entanglement. It is shown that for the spin entangled states the fidelity decreases less than that of the case of spin product states and there are special cases for which the fidelity remains perfect regardless of moving observers velocity. Generally, in the limit of boosts with speeds close to the speed of light, the fidelity saturates, i.e., it reaches to a constant value that depends on the amount of momentum entanglement and the width of the momentum distribution function.

 

 

03. Akhound , Ahmad: Multi-qubit entanglement and the critical entangling field
Payame Noor  University, Iran

We consider an initial multi-qubit coherent state and study its evolution by the two-axis counter twisting Hamiltonian and investigate its entanglement properties via concurrence in the presence and absence of an external magnetic field. It is observed that in the absence of the external field, the system is not entangled in some time intervals. If the field is increased up to the critical value, the nonexistence periods vanish and barring some separate instances of time, the system becomes continuously entangled. We also define the optimal field at which the time average value of the concurrence assumes the highest possible value [1]. We observe that the fluctuations decrease if the external field is increased, but a tradeoff is involved; the value of the average concurrence is reduced. We plot concurrence versus the external field for several spins and field values.

[1] M. Jafarpour and A. Akhound, Entanglement and squeezing of multi-qubit systems using a two-axis countertwisting Hamiltonian with an external field, Phys. Lett. A 372, (2008).
[2] X. Wang and K. M
olmer, Pairwise entanglement in symmetric multi-qubit systems, Eur. Phys. J. D 18 (2002).

 

04. Alipour, Sahar: Markovianity of quantum channels and quantum estimation
Sharif University of Technology, Iran

We investigate how Markovianity of a quantum dynamics may affect accuracy of the estimation of dynamical parameters. For quantum Markovian dynamics, the time derivative of quantum Fisher information (QFI) is shown to be negative. When symmetric logarithmic derivative (SLD) is taken with respect to a parameter of initial state, this negativity demonstrates loss of distinguishability with time. However, when SLD is taken with respect to a dynamical parameter, the negativity of the rate of QFI shows that the state eventually approaches a stationary fixed state. As a result, in this case the estimation of channel parameters becomes difficult with time. [Joint work with A.T. Rezakhani]

 

05. Annabestani, Mostafa: Shifting position decoherence in one-dimensional discrete time quantum walk
Tarbiat Modares University, Iran

We have investigated the shifting position decoherence in one-dimensional discrete time quantum walk (DTQW) which arise from the tunneling effect in the experimental realization of quantum walk. We proved that the quantum behavior of 1DQW in the presence of tunneling effect doesn't fade, unlike the case in which coin subspace is subject to decoherence where in this case, system transition to classic even for weak strength of noise. We show that quadratic dependency of variance on time, which is pure quantum property of coherent QW, remain quadratic in the presence of tunneling decoherence and coin-position entanglement (CPE), which is another pure quantum property and converge to significant value for any strength of noise. Furthermore we show that this type of decoherence smooth the probability distribution and we represent the compact formula for probability distribution in terms of coherent one-dimensional quantum walk (1DQW).

 

06. Baghbanzadeh, Sima: Bound entanglement in quantum phase transitions
Sharif University of Technology, Iran

Entanglement as a crucial ingredient of quantum many-body systems has different forms, such as free entanglement and bound entanglement. In this study we show that, like free entanglement, bound entanglement can also induce quantum phase transitions. We investigate quantum phase transitions in which a change in the type of entanglement from bound entanglement to either free entanglement or separability may occur. In particular, we present a theoretical method to construct a class of quantum spin-chain Hamiltonians that exhibit this type of quantum criticality. Given parameter-dependent two-site reduced density matrices (with prescribed entanglement properties); we lay out a reverse construction for a compatible pure state for the whole system, as well as a class of Hamiltonians for which this pure state is a ground state. This construction is illustrated through several examples.

 

07. Barzanjeh, Shabir: Dynamical behavior of entanglement in semiconductor microcavities
University of Isfahan, Iran

We investigate evolution of entanglement in a semiconductor cavity QED containing a quantum well. By using Wehrl entropy and introducing generalized concurrence as entanglement measures, we show the influence of the system parameters on the evolution features of entanglement.

 

08. Eslami, Leila: Double quantum ring with Rashba spin-orbit interaction as a quantum NOT gate
Iran University of Science and Technology, Iran

During the last years, many studies have been done on mesoscopic quantum rings made of semiconductors like InGaAs because of their ability to show quantum interference effects such as Aharonov-Bohm oscillations and spin dependent quantum transport (spintronics). The study of electronics and spintronics in mesoscopic systems can be used to improve designing and manufacturing of quantum computing devices. Manipulating spin degree of freedom is one of important fundamental subjects in quantum computing field. One of mechanisms which can control spin transport of electron is Rashba spin-orbit interaction. In previous works spin-polarized persistent current, spin-filtered electron transmission to single quantum ring and also spin separation via a three terminal quantum ring have been proposed using Rashba spin-orbit interaction. In this study we introduce double quantum rings connected each other by a normal lead with perpendicular electric field implied on each of them. Electron beam injected from an incoming lead which is connected to the first quantum ring and transmitted to an outgoing lead connected to the second quantum ring. We use S-matrix formalism to study spin dependent transport of electron through this system. We find that by adjusting parameters of the system (such as the Rashba spin-orbit interaction, geometry of connected rings, strength of coupling constant of leads to the rings and energy of the incident electron beam) properly the system can act as a quantum NOT gate which flips the spin of injected electron from up to down and vice versa.

 

09. Fasihi Aghbolagh, Mohammad A.: Entanglement of Fermionic Coherent States for Pseudo Hermitian Hamiltonian
Kinki University, Japan

In this paper the entanglement of multi-qubit fermionic pseudo Hermitian coherent states (FPHCS) described by anticommutative Grassmann numbers is studied. The pseudo-Hermitian versions of the well-known maximally entangled pure states such as GHZ, W, Bell and biseparable states are introduced through integrating over tensor product of FPHCSs with suitable choice of Grassmannian weight function. Meanwhile to clarify the issue, as an example, a two level pseudo Hermitian Hamiltonian is introduced and using its bi-orthogonal eigen-vectors we construct all possible pseudo Hermitian versions of Bell, W and GHZ states as a tensor product of them. Then using the concurrence measure for two qubit states, entanglement of these states is calculated as a function of the parameters of the pseudo Hermitian Hamiltonian and it is shown that in some special points, the amount of their entanglement coincide with maximal value. Using average entropy the same results are deduced for pseudo W and GHZ states constructed by bi-orthogonal eigen-vectors of pseudo Hermitian Hamiltonian and it is shown that, as a limit point, the maximal values are achieved for Hermitian one.

 

10. Gutschow, Johannes: Performance of quantum convolutional coding with memory constraints
Universitat Hannover, Germany

Quantum convolutional error-correcting codes [1] are often said to outperform block codes in terms of code rate and decoding complexity. However, there is no general proof of this. For example many promising examples of convolutional codes turn out to have bad properties, such as being catastrophic and thus spreading errors infinitely. The question we address here is the memory requirements of the encoding and decoding procedures for quantum convolutional codes.  We introduce a description of convolutional stabilizer codes (CSC) by Clifford channels with memory that enables us to relate properties of the encoders to simple conditions on the classical representation of the channel. For example, the encoder of a CSC is non-catastrophic, if and only if the channel describing it is strictly forgetful, i.e., the influence of the original memory input vanishes after finitely many uses of the channel. This is in turn true, if and only if the memory-to-memory reduction of the channel is a nilpotent matrix. Using this description, we present a Hamming bound for convolutional stabilizer codes and discuss it with respect to coding under memory constraints.  We show that convolutional codes are especially suitable in asymmetric setups, because, to use the power of the convolutional scheme, the decoder requires more memory than the encoder. Finally we illustrate our findings with examples of convolutional stabilizer codes.

[1] Harold Ollivier and Jean-Pierre Tillich. Quantum convolutional codes: fundamentals. preprint, Jan  2004; arXiv:quant-ph/0401134

 

11. Haibati, Ozra: Measuring Entanglement between Two Cavities Quantum Electrodynamics
Zanjan University, Iran

We propose a new experimental setup of the Mach-Zendher interferometer for the three levels Rydberg atoms. The three levels Rydberg atomic systems are interacted with two entangled cavities quantum electrodynamics. In our proposal the state of incoming atoms and entangled cavities (C1 and C2) are denoted by |g> and a |0, 1> + b |1, 0>, respectively. The amount of entanglement is measured by the imaginary parameters a, b. We have |a|=|b|=1/√2 for maximum entanglement, a = 1, b = 0 (or a = 0, b = 1) for no entanglement and otherwise partially entanglement states. One of the cavities is placed in clockwise path of interferometer and the other one is placed in counter-clockwise path. In each path two cavities are sandwiching Ci (i = 1, 2) that Ri (i = 1, 2 or i = 3, 4) are identical low Q cavities. In this case, the Rydberg atoms interact classically with the resonance cavities Ri and quantum mechanically with the out of resonance cavities Ci. For a specific phase difference in Ri cavities, the entangled parameters are involved in the outgoing state of atom. It is shown that the measurement of the state of individual outgoing atoms give us the entanglement parameters a, b as well as the phase difference between two paths. Furthermore, the result is given in terms of the value of the Wigner function at the origin.

 

12. Herrera Marti, David: A photonic Implementation of the Topological Cluster State Computer
Imperial College London, UK

A new experimental implementation of the topological cluster state quantum computer is suggested, in which the basic elements are linear optics, measurements, and a two-dimensional array of light strobed quantum dots. This overcomes the need of non-linear devices to create a lattice of entangled photons.

 

13. Heshami, Khabat: Quantum memory based on controllable transition dipole moment
University of Calgary, Canada

To build quantum memory for light with atomic ensembles one need to map single photons into atomic excitations and freeze them until releasing them back to photons on demand. Here we present an idea for realizing this storage-recall procedure by directly turning transition dipole moment on and off in a two-level system. An analytical treatment of the problem is performed and the physical requirements on the proposed scheme are discussed. Employing a magneto-dependent transition dipole moment in Tm3+: YAG crystal, we show a good instructive quantum memory using this simple idea.

 

14. Houshmand, Monireh: Minimal memory requirements for pearl necklace encoders of quantum convolutional codes
Ferdowsi University of Mashhad, Iran

One of the major goals in quantum computer science is to reduce the overhead associated with the implementation of quantum computers, and inevitably, routines for quantum error correction will account for most of this overhead. A particular technique for quantum error correction that may be useful in the outer layers of a concatenated scheme for fault tolerance is quantum convolutional coding. The encoder for a quantum convolutional code has a representation as a convolutional encoder or as a pearl necklace encoder. In the pearl necklace representation, it has not been particularly clear in the research literature how much quantum memory such an encoder would require for implementation. Here, we offer an algorithm that answers this question. The algorithm first constructs a weighted, directed acyclic graph where each vertex of the graph corresponds to a gate string in the pearl necklace encoder, and each path through the graph represents a non-commutative path through gates in the encoder. We show that the longest path through the graph corresponds to the minimal amount of memory needed to implement the encoder. A dynamic programming search through this graph determines the longest path. The running time for the construction of the graph and search through it is quadratic in the number of gate strings in the pearl necklace encoder.

 

15. Jafarpour, Mojtaba: Optimal and critical squeezing fields for a multi-qubit spin system
Shahid Chamran University, Iran

We consider a multi-qubit spin system initially in a coherent state, whose internal interactions are described by a one-axis twisting Hamiltonian [1, 2]. We study its squeezing dynamics and calculate its squeezing parameter in the presence and absence of an external magnetic field. A critical magnetic field is introduced for this system; if the external field is increased up to, the system becomes continuously squeezed. We also introduce an optimal field, at which the average depth of the squeezing parameter is maximized. We may increase the external field to the values higher than to decrease the squeezing fluctuations, but a tradeoff is involved; the squeezing depth is decreased as a result.

[1] M. Kitagawa and M. Ueda, Squeezed spin states, Phys. Rev. A 47, 5138-5143 (1993).
[2] A. Akhound and M. Jafarpour, Spin squeezing Hamiltonian and optimal spin squeezing parameters, IL NuovoCimento B 122 (6), 885-896, Doi 10.1393/ncb/i2007-10398-2 (2007).

 

16. Lupo, Cosmo: Memory effects in attenuation and amplification quantum processes
University of Camerino, Italy

With increasing communication rates via quantum channels, memory effects become unavoidable whenever the use rate of the channel is comparable with the typical relaxation time of the channel environment. We then introduce a model of bosonic memory channel, describing correlated noise effects in quantum optical processes via attenuating or amplifying media. To study such a channel model we make use of a proper set of collective field variables, which allows us to unravel the memory effects, mapping the n-fold concatenation of the memory channel to a, unitarily equivalent, direct product of n single-mode bosonic channels. We hence estimate the channel capacities by relying on known results for the memoryless setting. Our findings show that the model is characterized by two different regimes, in which the cross-correlations induced by the noise among different channel uses are either exponentially enhanced or exponentially reduced.

 

17. Mahdian, Mohammad: Quantifying spin-momentum correlation in single-particle quantum states using non-linear entanglement witnesses
University of Tabriz, Iran

We present a unifying approach to the quantification of spin-momentum correlation of single spin half and one particle by using the Non-Linear entanglement witnesses (NLEWs) which have been constructed based on convex optimization method. Likewise, we show that for quantum mixed states which are made by means of two types of degrees of freedom spin and momentum, the effect of the Lorentz transformation is to decrease both the amount and the region of entanglement.

 

18. Maleki, Yusef: Entanglement of Grassmannian Coherent States
Mohaghegh Ardabili University, Iran

In this paper we investigate the entanglement of multi-partite Grassmannian coherent states (GCS) described by Grassmann numbers. Choosing an appropriate weight function, we show that it is possible to construct some entangled pure states, consisting of GHZ, W, Bell, cluster type and biseparable states, by tensor product of GCSs. It is shown that for three level systems, the Grassmann creation and annihilation operators b and b together with bz form a closed deformed algebra SUq (2) with q = e2 π i / 3 which is useful to construct entangled qutrit-states. The same argument hold for three level squeezed states. Moreover combining the Grassmann and bosonic coherent states we construct maximal entangled supersymmetric coherent states. Finally a comparison with maximal entangled bosonic coherent states is presented and it is shown that in some cases they have fermionic counterpart which are maximal entangled after integration with suitable weight functions.

 

19. Mani, Azam: Time-Dependent Memory Channel
Sharif University of Technology, Iran

We present a model for memory channels which is more realistic than the studied ones. In this model, the quantum system of our interest is coupled to a classical environment so that the state of both system and environment changes with time. During the relaxation process of environment, two qubits interact with it at different times and thus are affected by different channels. In other words, we have time dependent memory channel which relaxes to a specific channel. We consider the role of time interval between sending the qubits in the relaxation time of environment and thus behavior of the resulting channel.

 

20. Marvian Mashhad, Milad: Generalizing Quantum Secret Sharing Using Secure Carriers
Sharif University of Technology, Iran

We generalize the secret sharing scheme of reference [1] to more general access structures, namely a large class of (k, n) threshold schemes. The basic property of our scheme and that of [1] is that the entanglement is not used as a resource, but can be re-generated after each round of the protocol by suitable unitary operations of all the dealers. In effect an entangled state shared between all the participants plays the role of a carrier to which information is hooked by the sender and unhooked by the legitimate parties, by suitable operations. In view of the high cost of entanglement generation, our scheme may find useful applications in the future.

[1] Saber Bagherinezhad, Vahid Karimipour, Quantum secret sharing based on reusable GHZ states as secure carriers Physical Rev. A 67, 044302 (2003).

 

21. Mehri-Dehnavi, Hossein: Entanglement of pseudo-pure spinor state in accelerated frames
Kinki University, Japan

We study the entanglement of a class of pseudo-pure stats in non-inertial frames. We will show that logarithmic negativity decrease with respect to acceleration and we can show that there are some initially entangled states can be observed as separable states in non-inertial frames with finite acceleration. Also, it can be shown that the mutual information tends to half of its initial value in the limit of infinite acceleration.

 

22. Memarzadeh Esfahani, Laleh: Quantum information reclaiming by classical feedback from the environment
University of Camerino, Italy

We investigate the quantum information reclaim from the environment after amplitude damping has occurred. In particular we address the question of optimal measurement on the environment to perform the best possible correction on two and three dimensional quantum systems. Depending on the dimension we show that the entanglement fidelity (the measure quantifying the correction performance) is or is not the same for all possible measurements and uncover the optimal measurement leading to the maximum entanglement fidelity. Furthermore, we study random unitary channel acting on nqubits by using the classical result of measurement on the environment of m.

 

23. Mohammady, Mohammad H.: Bismuth in silicon qubits: the role of EPR cancellation resonances
University College London, UK

We investigate theoretically and experimentally the electron paramagnetic resonance (EPR) spectra of bismuth doped silicon (Si:Bi) at intermediate magnetic fields, B ≈ 0.05-0.6 T. We identify a previously unexplored EPR regime of "cancellation-resonances"- where part of the hyperfine coupling is resonant with the external field-induced splitting. We show this regime has interesting and experimentally accessible consequences for spectroscopy and quantum information applications. These include reduction of decoherence, fast manipulation of the coupled nuclear-electron qubit system and line narrowing in the multi-qubit case. We test our theoretical analysis by comparing with experimental X-band (9.7 GHz) EPR spectra obtained in the intermediate field regime.

 

24. Moradi, Shahpoor: Two accelerated observers and degradation of entanglement
Razi University, Iran

We study the entanglement of free scalar and Dirac fields as seen by two accelerated parties. We also study the entanglement distillability of bipartite mixed states of two modes of a free Dirac field, seen by two accelerated parties in the context of Werner states. We conclude that if we considered two accelerated observers instead one, the density matrix would be mixed to a higher degree, resulting in a higher degradation of entanglement.

 

25. Najarbashi, Ghader: Maximal Entanglement of Two-qubit States Constructed by Linearly Independent
University of Mohaghegh Ardabili, Iran

In this work, we find the necessary and sufficient condition for the maximal entanglement of the state, |ψ> = μ|α>|β> + λ|α>|δ> + ρ|ϒ>|β> + ν|ϒ>|δ>, constructed by linearly independent coherent states with real parameters when <α|ϒ>=<β|δ>. To this aim we use the concurrence.

 

26. Rezaei Karamati, Mahdi: Molecular solution for the subset-sum problem on DNA based quantum computing
University of Tabriz, Iran

Feynman in 1961 and in 1982 respectively proposed molecular computation and one of the most important problems in computation theory, that is, whether computing devices based on quantum theory are able to finish computations faster than the standard Turing machines. In 1994, Adleman succeeded to solve an instance of the Hamiltonian path problem in a test tube, just by handling DNA strands. Deutsch denoted a general model of quantum computation - the quantum Turing machine. Molecular solution for the subset-sum problem on DNA based supercomputing has been offered in Weng-long Chang et al. 2003 articles. Here, it is demonstrated that the DNA-based algorithm of an n-bit parallel adder and a DNA based algorithm of an n-bit parallel comparator to formally verify our designed molecular solutions for the subset-sum problem can be implemented by Hadamard gates, NOT gates, CNOT gates, CCNOT gates, Grovers operators, and quantum measurements on a quantum computer.

 

27. Sadeghi, Parvin: Tesallis entropy in the Husimi and Wigner representations
Zanjan University, Iran

In this paper the Tesallis entropy is developed into the phase space picture of quantum mechanics, for an ordinary range of q-parameters. We apply the Tesallis entropy for the Schrodinger Cat State (SCS) in the Husimi and Wigner representations. It will reduce to the Whrel and linear entropies for a corresponding q-parameter. The variations of the Tesallis entropy in terms of the nonlinear effect and strong field for the SCS are compared with the corresponding SCS quantum signature which is introduced by Kenfack et al. We find a suitable q-parameter for the Tesallis entropy which has a best fitting with the quantum signature.

 

 

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Updated 08 September 2010 by K. Heshami