Quantum crystals and spin chains
Energy Technology Data Exchange (ETDEWEB)
Dijkgraaf, Robbert [KdV Institute for Mathematics, University of Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam (Netherlands); Institute for Theoretical Physics, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands); Orlando, Domenico [Institut de Physique, Universite de Neuchatel, Rue Breguet 1, CH-2000 Neuchatel (Switzerland); Reffert, Susanne [Institute for Theoretical Physics, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands)], E-mail: sreffert@gmail.com
2009-04-21
In this article, we discuss the quantum version of the melting crystal corner in one, two, and three dimensions, generalizing the treatment for the quantum dimer model. Using a mapping to spin chains we find that the two-dimensional case (growth of random partitions) is integrable and leads directly to the Hamiltonian of the Heisenberg XXZ ferromagnet. The three-dimensional case of the melting crystal corner is described in terms of a system of coupled XXZ spin chains. We give a conjecture for its mass gap and analyze the system numerically.
Quantum crystals and spin chains
Dijkgraaf, Robbert; Orlando, Domenico; Reffert, Susanne
2009-04-01
In this article, we discuss the quantum version of the melting crystal corner in one, two, and three dimensions, generalizing the treatment for the quantum dimer model. Using a mapping to spin chains we find that the two-dimensional case (growth of random partitions) is integrable and leads directly to the Hamiltonian of the Heisenberg XXZ ferromagnet. The three-dimensional case of the melting crystal corner is described in terms of a system of coupled XXZ spin chains. We give a conjecture for its mass gap and analyze the system numerically.
Quantum spin transistor with a Heisenberg spin chain
Marchukov, O. V.; Volosniev, A. G.; Valiente, M.; Petrosyan, D.; Zinner, N. T.
2016-01-01
Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements. PMID:27721438
Quantum spin transistor with a Heisenberg spin chain
Marchukov, O. V.; Volosniev, A. G.; Valiente, M.; Petrosyan, D.; Zinner, N. T.
2016-10-01
Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements.
Superadiabatic quantum state transfer in spin chains
Agundez, R. R.; Hill, C. D.; Hollenberg, L. C. L.; Rogge, S.; Blaauboer, M.
2017-01-01
In this paper we propose a superadiabatic protocol where quantum state transfer can be achieved with arbitrarily high accuracy and minimal control across long spin chains with an odd number of spins. The quantum state transfer protocol only requires the control of the couplings between the qubits on the edge and the spin chain. We predict fidelities above 0.99 for an evolution of nanoseconds using typical spin-exchange coupling values of μ eV . Furthermore, by building a superadiabatic formalism on top of this protocol, we propose an effective superadiabatic protocol that retains the minimal control over the spin chain and further improves the fidelity.
Magnetocaloric effect in quantum spin-s chains
Directory of Open Access Journals (Sweden)
A. Honecker
2009-01-01
Full Text Available We compute the entropy of antiferromagnetic quantum spin-s chains in an external magnetic field using exact diagonalization and Quantum Monte Carlo simulations. The magnetocaloric effect, i. e., temperature variations during adiabatic field changes, can be derived from the isentropes. First, we focus on the example of the spin-s=1 chain and show that one can cool by closing the Haldane gap with a magnetic field. We then move to quantum spin-s chains and demonstrate linear scaling with s close to the saturation field. In passing, we propose a new method to compute many low-lying excited states using the Lanczos recursion.
Large Deviations in Quantum Spin Chain
Ogata, Yoshiko
2008-01-01
We show the full large deviation principle for KMS-states and $C^*$-finitely correlated states on a quantum spin chain. We cover general local observables. Our main tool is Ruelle's transfer operator method.
Entanglement Entropy in Random Quantum Spin-S Chains
Saguia, A; Continentino, M A; Sarandy, M S
2007-01-01
We discuss the scaling of entanglement entropy in the random singlet phase (RSP) of disordered quantum magnetic chains of general spin-S. Through an analysis of the general structure of the RSP, we show that the entanglement entropy scales logarithmically with the size of a block and we provide a closed expression for this scaling. This result is applicable for arbitrary quantum spin chains in the RSP, being dependent only on the magnitude S of the spin. Remarkably, the logarithmic scaling holds for the disordered chain even if the pure chain with no disorder does not exhibit conformal invariance, as is the case for Heisenberg integer spin chains. Our conclusions are supported by explicit evaluations of the entanglement entropy for random spin-1 and spin-3/2 chains using an asymptotically exact real-space renormalization group approach.
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.;
2000-01-01
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
Generating quantum states through spin chain dynamics
Kay, Alastair
2017-04-01
The spin chain is a theoretical work-horse of the physicist, providing a convenient, tractable model that yields insight into a host of physical phenomena including conduction, frustration, superconductivity, topological phases, localisation, phase transitions, quantum chaos and even string theory. Our ultimate aim, however, is not just to understand the properties of a physical system, but to harness it for our own ends. We therefore study the possibilities for engineering a special class of spin chain, envisaging the potential for this to feedback into the original physical systems. We pay particular attention to the generation of multipartite entangled states such as the W (Dicke) state, superposed over multiple sites of the chain.
Quantum criticality of hot random spin chains.
Vasseur, R; Potter, A C; Parameswaran, S A
2015-05-29
We study the infinite-temperature properties of an infinite sequence of random quantum spin chains using a real-space renormalization group approach, and demonstrate that they exhibit nonergodic behavior at strong disorder. The analysis is conveniently implemented in terms of SU(2)_{k} anyon chains that include the Ising and Potts chains as notable examples. Highly excited eigenstates of these systems exhibit properties usually associated with quantum critical ground states, leading us to dub them "quantum critical glasses." We argue that random-bond Heisenberg chains self-thermalize and that the excited-state entanglement crosses over from volume-law to logarithmic scaling at a length scale that diverges in the Heisenberg limit k→∞. The excited state fixed points are generically distinct from their ground state counterparts, and represent novel nonequilibrium critical phases of matter.
A new correlator in quantum spin chains
Energy Technology Data Exchange (ETDEWEB)
Keating, J P; Mezzadri, F; Novaes, M [School of Mathematics, University of Bristol, Bristol BS8 1TW (United Kingdom)
2006-06-16
We propose a new correlator in one-dimensional quantum spin chains, the s-emptiness formation probability (s-EFP). This is a generalization of the emptiness formation probability (EFP), which is the probability that the first n spins of the chain are all aligned downwards. In the s-EFP we let the spins in question be separated by s sites. The usual EFP corresponds to the special case when s = 1. Taking s > 1 allows us to quantify non-local correlations. We express the s-EFP for the anisotropic XY model in a transverse magnetic field, a system with both critical and non-critical regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find that the magnetic field induces an interesting length scale. (letter to the editor)
Entanglement in Nonunitary Quantum Critical Spin Chains
Couvreur, Romain; Jacobsen, Jesper Lykke; Saleur, Hubert
2017-07-01
Entanglement entropy has proven invaluable to our understanding of quantum criticality. It is natural to try to extend the concept to "nonunitary quantum mechanics," which has seen growing interest from areas as diverse as open quantum systems, noninteracting electronic disordered systems, or nonunitary conformal field theory (CFT). We propose and investigate such an extension here, by focusing on the case of one-dimensional quantum group symmetric or supergroup symmetric spin chains. We show that the consideration of left and right eigenstates combined with appropriate definitions of the trace leads to a natural definition of Rényi entropies in a large variety of models. We interpret this definition geometrically in terms of related loop models and calculate the corresponding scaling in the conformal case. This allows us to distinguish the role of the central charge and effective central charge in rational minimal models of CFT, and to define an effective central charge in other, less well-understood cases. The example of the s l (2 |1 ) alternating spin chain for percolation is discussed in detail.
Spin analogs of superconductivity and integer quantum Hall effect in an array of spin chains
Hill, Daniel; Kim, Se Kwon; Tserkovnyak, Yaroslav
2017-05-01
Motivated by the successful idea of using weakly coupled quantum electronic wires to realize the quantum Hall effects and the quantum spin Hall effects, we theoretically study two systems composed of weakly coupled quantum spin chains within the mean-field approximations, which can exhibit spin analogs of superconductivity and the integer quantum Hall effect. First, a certain bilayer of two arrays of interacting spin chains is mapped, via the Jordan-Wigner transformation, to an attractive Hubbard model that exhibits fermionic superconductivity, which corresponds to spin superconductivity in the original spin Hamiltonian. Secondly, an array of spin-orbit-coupled spin chains in the presence of a suitable external magnetic field is transformed to an array of quantum wires that exhibits the integer quantum Hall effect, which translates into its spin analog in the spin Hamiltonian. The resultant spin superconductivity and spin integer quantum Hall effect can be characterized by their ability to transport spin without any resistance.
Initialization and Readout of Spin Chains for Quantum Information Transport
Kaur, Gurneet
2011-01-01
Linear chains of spins acting as quantum wires are a promising approach to achieve scalable quantum information processors. Nuclear spins in apatite crystals provide an ideal test-bed for the experimental study of quantum information transport, as they closely emulate a one-dimensional spin chain. Nuclear Magnetic Resonance techniques can be used to drive the spin chain dynamics and probe the accompanying transport mechanisms. Here we demonstrate initialization and readout capabilities in these spin chains, even in the absence of single-spin addressability. These control schemes enable preparing desired states for quantum information transport and probing their evolution under the transport Hamiltonian. We further optimize the control schemes by a detailed analysis of $^{19}$F NMR lineshape.
Thermal effects on quantum communication through spin chains
Bayat, A; Bayat, Abolfazl; Karimipour, Vahid
2004-01-01
We study the effect of thermal fluctuations in a recently proposed protocol for transmission of unknown quantum states through quantum spin chains. We develop a low temperature expansion for general spin chains. We then apply this formalism to study exactly thermal effects on short spin chains of four spins. We show that optimal times for extraction of output states are almost independent of the temperature which lowers only the fidelity of the channel. Moreover we show that thermal effects are smaller in the anti-ferromagnetic chains than the ferromagnetic ones.
Time independent universal computing with spin chains: quantum plinko machine
Thompson, K. F.; Gokler, C.; Lloyd, S.; Shor, P. W.
2016-07-01
We present a scheme for universal quantum computing using XY Heisenberg spin chains. Information is encoded into packets propagating down these chains, and they interact with each other to perform universal quantum computation. A circuit using g gate blocks on m qubits can be encoded into chains of length O({g}3+δ {m}3+δ ) for all δ \\gt 0 with vanishingly small error.
Birth and death processes and quantum spin chains
Grünbaum, Alberto F; Zhedanov, Alexei
2012-01-01
This papers underscores the intimate connection between the quantum walks generated by certain spin chain Hamiltonians and classical birth and death processes. It is observed that transition amplitudes between single excitation states of the spin chains have an expression in terms of orthogonal polynomials which is analogous to the Karlin-McGregor representation formula of the transition probability functions for classes of birth and death processes. As an application, we present a characterization of spin systems for which the probability to return to the point of origin at some time is 1 or almost 1.
Long-range interactions in antiferromagnetic quantum spin chains
Bravo, B.; Cabra, D. C.; Gómez Albarracín, F. A.; Rossini, G. L.
2017-08-01
We study the role of long-range dipolar interactions on antiferromagnetic spin chains, from the classical S →∞ limit to the deep quantum case S =1 /2 , including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization, and density matrix renormalization group (DMRG). We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation in both phases, and also close to zero field in the antiferromagnetic phase. In the extreme quantum limit S =1 /2 , extensive DMRG computations show that the main phases remain present with transition lines to saturation significatively shifted to lower fields, in agreement with the bosonization analysis. The overall picture maintains a close analogy with the phase diagram of the anisotropic XXZ spin chain in a transverse field.
Supersymmetric quantum spin chains and classical integrable systems
Tsuboi, Zengo; Zabrodin, Anton; Zotov, Andrei
2015-05-01
For integrable inhomogeneous supersymmetric spin chains (generalized graded magnets) constructed employing Y( gl( N| M))-invariant R-matrices in finite-dimensional representations we introduce the master T-operator which is a sort of generating function for the family of commuting quantum transfer matrices. Any eigenvalue of the master T-operator is the tau-function of the classical mKP hierarchy. It is a polynomial in the spectral parameter which is identified with the 0-th time of the hierarchy. This implies a remarkable relation between the quantum supersymmetric spin chains and classical many-body integrable systems of particles of the Ruijsenaars-Schneider type. As an outcome, we obtain a system of algebraic equations for the spectrum of the spin chain Hamiltonians.
Supersymmetric quantum spin chains and classical integrable systems
Tsuboi, Zengo; Zotov, Andrei
2014-01-01
For integrable inhomogeneous supersymmetric spin chains (generalized graded magnets) constructed employing Y(gl(N|M))-invariant R-matrices in finite-dimensional representations we introduce the master T-operator which is a sort of generating function for the family of commuting quantum transfer matrices. Any eigenvalue of the master T-operator is the tau-function of the classical mKP hierarchy. It is a polynomial in the spectral parameter which is identified with the 0-th time of the hierarchy. This implies a remarkable relation between the quantum supersymmetric spin chains and classical many-body integrable systems of particles of the Ruijsenaars-Schneider type. As an outcome, we obtain a system of algebraic equations for the spectrum of the spin chain Hamiltonians.
Integrable quantum spin chains and their classical continuous counterparts
Avan, Jean; Sfetsos, Konstadinos
2011-01-01
We present certain classical continuum long wave-length limits of prototype integrable quantum spin chains, and define the corresponding construction of classical continuum Lax operators. We also provide two specific examples, i.e. the isotropic and anisotropic Heisenberg models.
Random matrix theory and critical phenomena in quantum spin chains
Hutchinson, J.; Keating, J. P.; Mezzadri, F.
2015-09-01
We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups $U(N)$, $O(N)$ and $Sp(2N)$. In particular we calculate critical exponents $s$, $\
Criticality without Frustration for Quantum Spin-1 Chains
Bravyi, Sergey; Caha, Libor; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter W.
2012-11-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right brackets separated by empty spaces. Entanglement entropy of one half of the chain scales as (1)/(2)logn+O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
Criticality without frustration for quantum spin-1 chains
Bravyi, Sergey; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter
2012-01-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right parentheses separated by empty spaces. Entanglement entropy of one half of the chain scales as log(n)/2 + O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
Energy Technology Data Exchange (ETDEWEB)
Wu, Wei [Zhejiang Institute of Modern Physics and Department of Physics, Zhejiang University, Hangzhou 310027 (China); Beijing Computational Science Research Center, Beijing 100193 (China); Xu, Jing-Bo, E-mail: xujb@zju.edu.cn [Zhejiang Institute of Modern Physics and Department of Physics, Zhejiang University, Hangzhou 310027 (China)
2017-01-30
We investigate the performances of quantum coherence and multipartite entanglement close to the quantum critical point of a one-dimensional anisotropic spin-1/2 XXZ spin chain by employing the real-space quantum renormalization group approach. It is shown that the quantum criticality of XXZ spin chain can be revealed by the singular behaviors of the first derivatives of renormalized quantum coherence and multipartite entanglement in the thermodynamics limit. Moreover, we find the renormalized quantum coherence and multipartite entanglement obey certain universal exponential-type scaling laws in the vicinity of the quantum critical point of XXZ spin chain. - Highlights: • The QPT of XXZ chain is studied by renormalization group. • The renormalized coherence and multiparticle entanglement is investigated. • Scaling laws of renormalized coherence and multiparticle entanglement are revealed.
Quantum correlations and coherence in spin-1 Heisenberg chains
Malvezzi, A. L.; Karpat, G.; ćakmak, B.; Fanchini, F. F.; Debarba, T.; Vianna, R. O.
2016-05-01
We explore quantum and classical correlations along with coherence in the ground states of spin-1 Heisenberg chains, namely the one-dimensional XXZ model and the one-dimensional bilinear biquadratic model, with the techniques of density matrix renormalization group theory. Exploiting the tools of quantum information theory, that is, by studying quantum discord, quantum mutual information, and three recently introduced coherence measures in the reduced density matrix of two nearest neighbor spins in the bulk, we investigate the quantum phase transitions and special symmetry points in these models. We point out the relative strengths and weaknesses of correlation and coherence measures as figures of merit to witness the quantum phase transitions and symmetry points in the considered spin-1 Heisenberg chains. In particular, we demonstrate that, as none of the studied measures can detect the infinite-order Kosterlitz-Thouless transition in the XXZ model, they appear to be able to signal the existence of the same type of transition in the biliear biquadratic model. However, we argue that what is actually detected by the measures here is the SU(3) symmetry point of the model rather than the infinite-order quantum phase transition. Moreover, we show in the XXZ model that examining even single site coherence can be sufficient to spotlight the second-order phase transition and the SU(2) symmetry point.
Matrix product states for su(2) invariant quantum spin chains
Zadourian, Rubina; Fledderjohann, Andreas; Klümper, Andreas
2016-08-01
A systematic and compact treatment of arbitrary su(2) invariant spin-s quantum chains with nearest-neighbour interactions is presented. The ground-state is derived in terms of matrix product states (MPS). The fundamental MPS calculations consist of taking products of basic tensors of rank 3 and contractions thereof. The algebraic su(2) calculations are carried out completely by making use of Wigner calculus. As an example of application, the spin-1 bilinear-biquadratic quantum chain is investigated. Various physical quantities are calculated with high numerical accuracy of up to 8 digits. We obtain explicit results for the ground-state energy, entanglement entropy, singlet operator correlations and the string order parameter. We find an interesting crossover phenomenon in the correlation lengths.
Robust Quantum State Transfer in Random Unpolarized Spin Chains
Yao, Norman Y; Gorshkov, Alexey V; Gong, Zhe-Xuan; Zhai, Alex; Duan, L -M; Lukin, Mikhail D
2010-01-01
We propose and analyze a new approach for quantum state transfer between remote spin qubits. Specifically, we demonstrate that coherent quantum coupling between remote qubits can be achieved via certain classes of random, unpolarized spin chains. Our method is robust to coupling strength disorder and does not require manipulation or control over individual spins. In principle, it can be used to attain perfect state transfer over arbitrarily long range via purely Hamiltonian evolution and may be particularly applicable in a solid-state quantum information processor. As an example, we demonstrate that it can be used to attain strong coherent coupling between Nitrogen-Vacancy centers separated by micrometer distances at room temperature. Realistic imperfections and decoherence effects are analyzed.
Robust quantum state transfer in random unpolarized spin chains.
Yao, N Y; Jiang, L; Gorshkov, A V; Gong, Z-X; Zhai, A; Duan, L-M; Lukin, M D
2011-01-28
We propose and analyze a new approach for quantum state transfer between remote spin qubits. Specifically, we demonstrate that coherent quantum coupling between remote qubits can be achieved via certain classes of random, unpolarized (infinite temperature) spin chains. Our method is robust to coupling-strength disorder and does not require manipulation or control over individual spins. In principle, it can be used to attain perfect state transfer over an arbitrarily long range via purely Hamiltonian evolution and may be particularly applicable in a solid-state quantum information processor. As an example, we demonstrate that it can be used to attain strong coherent coupling between nitrogen-vacancy centers separated by micrometer distances at room temperature. Realistic imperfections and decoherence effects are analyzed.
Frustration-induced quantum phases in mixed spin chain with frustrated side chains
Hida, Kazuo; Takano, Ken'Ichi
2008-08-01
A mixed Heisenberg spin chain with frustrated side chains is investigated by numerical and perturbational calculations. A frustration-induced quantum partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar phase are found adjacent to the conventional Lieb-Mattis-type ferrimagnetic phase or the nonmagnetic singlet cluster solid phases. The partially polarized ferrimagnetic phase has an incommensurate spin structure. Similar structures are commonly found in other frustration-induced partially polarized ferrimagnetic phases. Numerical results also suggest a series of almost critical nonmagnetic ground states in a highly frustrated regime if the side chain spins weakly couple to the main chain.
Sahling, S.; Remenyi, G.; Paulsen, C.; Monceau, P.; Saligrama, V.; Marin, C.; Revcolevschi, A.; Regnault, L. P.; Raymond, S.; Lorenzo, J. E.
2015-03-01
Entanglement is a concept that has defied common sense since the discovery of quantum mechanics. Two particles are said to be entangled when the quantum state of each particle cannot be described independently, no matter how far apart in space and time the two particles are. We demonstrate experimentally that unpaired spins separated by several hundred ångström entangle through a collection of spin singlets made up of antiferromagnetic spin-1/2 chains in a bulk material. Low-temperature magnetization and specific heat studies as a function of magnetic field reveal the occurrence of very dilute spin dimers and at least two quantum phase transitions related to the breaking of excited local triplets. The mechanism at the origin of the unpaired spins inside the quantum chains is the inter-modulation potential between two sublattices, and may be replicated using well-designed synthetic multilayers.
Computational complexity of nonequilibrium steady states of quantum spin chains
Marzolino, Ugo; Prosen, Tomaž
2016-03-01
We study nonequilibrium steady states (NESS) of spin chains with boundary Markovian dissipation from the computational complexity point of view. We focus on X X chains whose NESS are matrix product operators, i.e., with coefficients of a tensor operator basis described by transition amplitudes in an auxiliary space. Encoding quantum algorithms in the auxiliary space, we show that estimating expectations of operators, being local in the sense that each acts on disjoint sets of few spins covering all the system, provides the answers of problems at least as hard as, and believed by many computer scientists to be much harder than, those solved by quantum computers. We draw conclusions on the hardness of the above estimations.
Quantum Critical Spin-2 Chain with Emergent SU(3) Symmetry
Chen, Pochung; Xue, Zhi-Long; McCulloch, I. P.; Chung, Ming-Chiang; Huang, Chao-Chun; Yip, S.-K.
2015-04-01
We study the quantum critical phase of an SU(2) symmetric spin-2 chain obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling of the finite-size energies and entanglement entropy by exact diagonalization and density-matrix renormalization group methods. From the numerical results of the energy spectra, central charge, and scaling dimension we identify the conformal field theory describing the whole critical phase to be the SU (3 )1 Wess-Zumino-Witten model. We find that, while the Hamiltonian is only SU(2) invariant, in this critical phase there is an emergent SU(3) symmetry in the thermodynamic limit.
From Characters to Quantum (Super)Spin Chains via Fusion
Kazakov, Vladimir
2008-01-01
We give an elementary proof of the Bazhanov-Reshetikhin determinant formula for rational transfer matrices of the twisted quantum super-spin chains associated with the gl(K|M) algebra. This formula describes the most general fusion of transfer matrices in symmetric representations into arbitrary finite dimensional representations of the algebra and is at the heart of analytical Bethe ansatz approach. Our technique represents a systematic generalization of the usual Jacobi-Trudi formula for characters to its quantum analogue using certain group derivatives.
Thermodynamics, geometrical frustration and quantum fluctuations in coupled spin chains
Directory of Open Access Journals (Sweden)
J. Sznajd
2009-01-01
Full Text Available The linear-perturbation real space renormalization transformation (LPRG is presented and applied to the study of quantum spin chains coupled by interchain interaction (k1 weaker than intrachain one (k. The method is examined in two exact solvable cases: Ising chains on the square and triangular lattices and quantum XY chain. For the Ising model, in the second order in the cumulant epansion, the deviation of the critical temperature from the exact value is less than 1% for 0.5 k>k1>0.15 k, but even in the case of the standard Ising model (k1=k we found the value of Tc which differs by 2% from the exact one. For the quantum XY chain the deviation of the free energy value found by using LPRG from the exact Katsura result is less than 1% for T/J>1, and for rather low temperature T/J=0.08 is about 6%. The LPRG is used to study the effects of interchain frustration on the phase transition in 2D Heisenberg spin chains with easy axis along the z direction. It is shown that contrary to the pure Ising model in systems with in-plane interactions (XY, the interchain frustration does not destroy the finite-temperature transition. However, such a frustration changes the character of the phase transition from Ising-like to, probably, Kosterlitz-Thouless-like. We have also applied the LPRG method to the calculation of the isothermal magnetocaloric coefficient (MT for several spin models in disordered phases. Is is demonstrated that in the presence of antiferromagnetic fluctuations, MT changes sign at some value of the magnetic field. Generally, MT is negative if magnetic field competes with a short-range order, and consequently it can be an indicator of the change in the short-range correlation.
Quantum Entanglement Channel based on Excited States in a Spin Chain
Institute of Scientific and Technical Information of China (English)
张少良; 杜良辉; 郭光灿; 周幸祥; 周正威
2011-01-01
We study the possibility of using a spin chain to construct a quantum entanglement channel that can be used for quantum state transmission in a solid state system.We analyze the spin chain's states under various z-directional magnetic field and spin interactions to determine the entanglement between Alice and Bob's spins.We derive the conditions under which this entanglement can be distilled,and find that a spin chain of arbitrary length can be used as a quantum channel for quantum state transmission when the number of spin flips in the chain is large.%We study the possibility of using a spin chain to construct a quantum entanglement channel that can be used for quantum state transmission in a solid state system. We analyze the spin chain's states under various z-directional magnetic field and spin interactions to determine the entanglement between Alice and Bob's spins. We derive the conditions under which this entanglement can be distilled, and find that a spin chain of arbitrary length can be used as a quantum channel for quantum state transmission when the number of spin Hips in the chain is large.
Entanglement entropy in quantum spin chains with broken reflection symmetry
Kadar, Zoltan
2010-01-01
We investigate the entanglement entropy of a block of L sites in quasifree translation-invariant spin chains concentrating on the effect of reflection symmetry breaking. The majorana two-point functions corresponding to the Jordan-Wigner transformed fermionic modes are determined in the most general case; from these it follows that reflection symmetry in the ground state can only be broken if the model is quantum critical. The large L asymptotics of the entropy is calculated analytically for general gauge-invariant models, which has, until now, been done only for the reflection symmetric sector. Analytical results are also derived for certain non-gauge-invariant models, e.g. for the Ising model with Dzyaloshinskii-Moriya interaction. We also study numerically finite chains of length N with a non-reflection-symmetric Hamiltonian and report that the reflection symmetry of the entropy of the first L spins is violated but the reflection-symmetric Calabrese-Cardy formula is recovered asymptotically. Furthermore, f...
Random matrix theory and critical phenomena in quantum spin chains.
Hutchinson, J; Keating, J P; Mezzadri, F
2015-09-01
We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups U(N),O(N), and Sp(2N). In particular we calculate critical exponents s,ν, and z, corresponding to the energy gap, correlation length, and dynamic exponent, respectively. We also compute the ground state correlators 〈σ_{i}^{x}σ_{i+n}^{x}〉_{g},〈σ_{i}^{y}σ_{i+n}^{y}〉_{g}, and 〈∏_{i=1}^{n}σ_{i}^{z}〉_{g}, all of which display quasi-long-range order with a critical exponent dependent upon system parameters. Our approach establishes universality of the exponents for the class of systems in question.
Institute of Scientific and Technical Information of China (English)
WANG Zhao-Ming; SHAO Bin; ZOU Jian
2007-01-01
We investigate the entanglement transfer in two parallel 1D spin chains of a quantum spin network,and show that the perfect entanglement transfer can be realized at some special times.In addition,the so-called 'sudden death' phenomenon of entanglement is found in the spin network system.
A direct proof of dimerization in a family of SU(n)-invariant quantum spin chains
Nachtergaele, Bruno; Ueltschi, Daniel
2017-05-01
We study the family of spin-S quantum spin chains with a nearest neighbor interaction given by the negative of the singlet projection operator. Using a random loop representation of the partition function in the limit of zero temperature and standard techniques of classical statistical mechanics, we prove dimerization for all sufficiently large values of S.
2016-01-01
We present a new open-source Python package for exact diagonalization and quantum dynamics of spin(-photon) chains, called QuSpin, supporting the use of various symmetries and (imaginary) time evolution for chains up to 32 sites in length. The package is well-suited to study, among others, quantum quenches at finite and infinite times, the Eigenstate Thermalisation hypothesis, many-body localisation and other dynamical phase transitions, periodically-driven (Floquet) systems, adiabatic and co...
Collective dynamics of solid-state spin chains and ensembles in quantum information processing
Ping, Yuting
This thesis is concerned with the collective dynamics in different spin chains and spin ensembles in solid-state materials. The focus is on the manipulation of electron spins, through spin-spin and spin-photon couplings controlled by voltage potentials or electromagnetic fields. A brief review of various systems is provided to describe the possible physical implementation of the ideas, and also outlines the basis of the adopted effective interaction models. The first two ideas presented explore the collective behaviour of non-interacting spin chains with external couplings. One focuses on mapping the identical state of spin-singlet pairs in two currents onto two distant, static spins downstream, creating distributed entanglement that may be accessed. The other studies a quantum memory consisting of an array of non-interacting, static spins, which may encode and decode multiple flying spins. Both chains could effectively `enhance' weak couplings in a cumulative fashion, and neither scheme requires active quantum control. Moreover, the distributed entanglement generated can offer larger separation between the qubits than more conventional protocols that only exploit the tunnelling effects between quantum dots. The quantum memory can also `smooth' the statistical fluctuations in the effects of local errors when the stored information is spread. Next, an interacting chain of static spins with nearest-neighbour interactions is introduced to connect distant end spins. Previously, it has been shown that this approach provides a cubic speed-up when compared with the direct coupling between the target spins. The practicality of this scheme is investigated by analysing realistic error effects via numerical simulations, and from that perspective relaxation of the nearest-neighbour assumption is proposed. Finally, a non-interacting electron spin ensemble is reviewed as a quantum memory to store single photons from an on-chip stripline cavity. It is then promoted to a full
Boundary Quantum Entanglement of the XXZ Spin Chain with Boundary Impurities
Institute of Scientific and Technical Information of China (English)
ZHUO Wei; WANG Yu-Peng
2007-01-01
The boundary quantum entanglement for the s=1/2 X X Z spin chain with boundary impurities is studied via the density matrix renormalization group(DMRC) method.It is shown that the entanglement entropy of the boundary bond(the impurity and the chain spin next to it)behaves differently in different phases.The relationship between the singular points of the boundary entropy and boundary quantum critical points is discussed.
Boundary-controlled spin chains for robust quantum state transfer
Zwick, Analia; Stolze, Joachim; Osenda, Omar
2011-01-01
Quantum state transfer in the presence of noise is one of the main challenges for building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static randomness. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in boundary-controlled chains only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the noise in the couplings affects the state transfer fidelity depending on the noise model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in boundary-controlled chains without the demanding engineering o...
Using the J1-J2 Quantum Spin Chain as an Adiabatic Quantum Data Bus
Chancellor, Nicholas
2012-01-01
This paper investigates numerically a phenomenon which can be used to transport a single q-bit down a J1-J2 Heisenberg spin chain using a quantum adiabatic process. The motivation for investigating such processes comes from the idea that this method of transport could potentially be used as a means of sending data to various parts of a quantum computer made of artificial spins, and that this method could take advantage of the easily prepared ground state at the so called Majumdar-Ghosh point. We examine several annealing protocols for this process and find similar result for all of them. The annealing process works well up to a critical frustration threshold.
A direct proof of dimerization in a family of SU( n)-invariant quantum spin chains
Nachtergaele, Bruno; Ueltschi, Daniel
2017-09-01
We study the family of spin- S quantum spin chains with a nearest neighbor interaction given by the negative of the singlet projection operator. Using a random loop representation of the partition function in the limit of zero temperature and standard techniques of classical statistical mechanics, we prove dimerization for all sufficiently large values of S.
Quantum discord and quantum phase transition in the XXZ spin chain with three-site interaction
Yang, Jing; Cong, Mei-Yan; Huang, Yan-Xia
2016-12-01
Pairwise quantum discord (QD) and entanglement of the three-qubit XXZ Heisenberg spin chain with two types of three-site interactions and an external magnetic field are investigated. Our study found that both entanglement and quantum discord could detect the quantum critical phenomena of this model. We were able to obtain a nonzero value of quantum discord even at high temperature with the increase of XZX+YZY or XZY-YZX three-site interaction, however, the cooperative effect of XZX+YZY and XZY-YZX interactions is more ideal. Furthermore, in contrast to XZY-YZX and XZX+YZY interactions, the cooperative effect of XZX+YZY and XZY-YZX three-site interactions is more efficient to enhance the maximum value of quantum discord. Likewise, the cooperative effect of XZX+YZY and XZY-YZX interactions is the most optimal to increase the range of magnetic field or anisotropy parameter where quantum discord maintains the maximum value.
An Approach to Loop Quantum Cosmology Through Integrable Discrete Heisenberg Spin Chains
Dantas, Christine C
2012-01-01
The quantum evolution equation of Loop Quantum Cosmology (LQC) -- the quantum Hamiltonian constraint -- is a difference equation. We relate the LQC constraint equation in vacuum Bianchi I separable (locally rotationally symmetric) models with an integrable differential-difference nonlinear Schr\\"odinger type equation, which in turn is known to be associated with integrable, discrete Heisenberg spin chain models in condensed matter physics. We illustrate the similarity between both systems with a simple constraint in the linear regime.
Disordered ground states in a quantum frustrated spin chain with side chains
Takano, Ken'Ichi; Hida, Kazuo
2008-04-01
We study a frustrated mixed spin chain with side chains, where the spin species and the exchange interactions are spatially varied. A nonlinear σ model method is formulated for this model, and a phase diagram with two disordered spin-gap phases is obtained for typical cases. Among them, we examine the case with a main chain, which consists of an alternating array of spin-1 and spin- (1)/(2) sites, and side chains, each of which consists of a single spin- (1)/(2) site, in great detail. Based on numerical, perturbational, and variational approaches, we propose a singlet cluster solid picture for each phase, where the ground state is expressed as a tensor product of local singlet states.
Prethermalization in a Nonintegrable Quantum Spin Chain after a Quench
Marcuzzi, Matteo; Marino, Jamir; Gambassi, Andrea; Silva, Alessandro
2013-11-01
We study the dynamics of a quantum Ising chain after the sudden introduction of a nonintegrable long-range interaction. Via an exact mapping onto a fully connected lattice of hard-core bosons, we show that a prethermal state emerges and we investigate its features by focusing on a class of physically relevant observables. In order to gain insight into the eventual thermalization, we outline a diagrammatic approach which complements the study of the previous quasistationary state and provides the basis for a self-consistent solution of the kinetic equation. This analysis suggests that both the temporal decay towards the prethermal state and the crossover to the eventual thermal one may occur algebraically.
Cheng, Jun-Qing; Wu, Wei; Xu, Jing-Bo
2017-09-01
We investigate the multipartite entanglement and trace distance of the one-dimensional anisotropic spin-1/2 XXZ spin chain with the Dzyaloshinskii-Moriya interaction and find that the Dzyaloshinskii-Moriya interaction can influence the entanglement distribution and increase the proportion of multipartite entanglement in the entanglement structure. Furthermore, we explore the quantum phase transition of the XXZ spin chain with Dzyaloshinskii-Moriya interaction by making use of the multipartite entanglement and trace distance along with the quantum renormalization group method. It is found that the first derivatives of renormalized multipartite entanglement and trace distance for the ground state have dramatic changes near the critical point, and the renormalized multipartite entanglement and trace distance obey the universal finite-size scaling laws in the vicinity of the quantum critical point.
Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain
DEFF Research Database (Denmark)
Stone, M.B.; Reich, D.H.; Broholm, C.
2003-01-01
Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...
Cumulative quantum work-deficit versus entanglement in the dynamics of an infinite spin chain
Energy Technology Data Exchange (ETDEWEB)
Dhar, Himadri Shekhar [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); Ghosh, Rupamanjari [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); School of Natural Sciences, Shiv Nadar University, Gautam Budh Nagar, UP 203207 (India); Sen, Aditi [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India); Sen, Ujjwal, E-mail: ujjwal@hri.res.in [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India)
2014-03-01
We find that the dynamical phase transition (DPT) in nearest-neighbor bipartite entanglement of time-evolved states of the anisotropic infinite quantum XY spin chain, in a transverse time-dependent magnetic field, can be quantitatively characterized by the dynamics of an information-theoretic quantum correlation measure, namely, quantum work-deficit (QWD). We show that only those nonequilibrium states exhibit entanglement resurrection after death, on changing the field parameter during the DPT, for which the cumulative bipartite QWD is above a threshold. The results point to an interesting inter-relation between two quantum correlation measures that are conceptualized from different perspectives.
Ghost spins and quantum critical behavior in a spin chain with local bond deformation
Dai, Jianhui; Wang, Yupeng; Eckern, U.
1999-09-01
We study the impurity-induced critical behavior in an integrable SU(2)-invariant model consisting of an open spin chain of arbitrary spin S (Takhatajian-Babujian model) interacting with an impurity of spin S-->' located at one of the boundaries. For S=1/2 or S'=1/2, the impurity interaction takes a very simple form JS-->1.S-->' that describes the deformed boundary bond between the impurity S-->' and the first bulk spin S-->1 with an arbitrary coupling strength J. For a weak coupling 0S, and S'=J0/[(S+S')2-1/4], the impurity spin is split into two ghost spins. Their cooperative effect leads to a variety of new critical behaviors with different values of \\|S'-S\\|.
Efficient quantum-state transfer in spin-1 chains by adiabatic passage
Eckert, K; Sanpera, A
2007-01-01
We propose a method for quantum state transfer in spin chains using an adiabatic passage technique. Modifying even and odd nearest-neighbor couplings in time allows to achieve transfer fidelities arbitrarily close to one, without the need for a precise control of coupling strengths and timing. We study in detail transfer by adiabatic passage in a spin-1 chain governed by a generalized Heisenberg Hamiltonian. We consider optimization of the transfer process applying optimal control techniques. We discuss a realistic experimental implementation using cold atomic gases confined in deep optical lattices.
Ohanyan, Vadim; Rojas, Onofre; Strečka, Jozef; Bellucci, Stefano
2015-12-01
We examine the general features of the noncommutativity of the magnetization operator and Hamiltonian for small quantum spin clusters. The source of this noncommutativity can be a difference in the Landé g factors for different spins in the cluster, X Y anisotropy in the exchange interaction, and the presence of the Dzyaloshinskii-Moriya term in a direction different from the direction of the magnetic field. As a result, zero-temperature magnetization curves for small spin clusters mimic those for the macroscopic systems with the band(s) of magnetic excitations, i.e., for the given eigenstate of the spin cluster the corresponding magnetic moment can be an explicit function of the external magnetic field yielding the nonconstant (nonplateau) form of the magnetization curve within the given eigenstate. In addition, the X Y anisotropy makes the saturated magnetization (the eigenstate when all spins in cluster are aligned along the magnetic field) inaccessible for finite magnetic field magnitude (asymptotical saturation). We demonstrate all these features on three examples: a spin-1/2 dimer, mixed spin-(1/2,1) dimer, and a spin-1/2 ring trimer. We consider also the simplest Ising-Heisenberg chain, the Ising-X Y Z diamond chain, with four different g factors. In the chain model the magnetization curve has a more complicated and nontrivial structure than that for clusters.
Local quenches in frustrated quantum spin chains: global vs. subsystem equilibration
Diez, Mathias; Haas, Stephan; Venuti, Lorenzo Campos; Zanardi, Paolo
2010-01-01
We study the equilibration behavior following local quenches, using frustrated quantum spin chains as an example of interacting closed quantum systems. Specifically, we examine the statistics of the time series of the Loschmidt echo, the trace distance of the time-evolved local density matrix to its average state, and the local magnetization. Depending on the quench parameters, the equilibration statistics of these quantities show features of good or poor equilibration, indicated by Gaussian, exponential or bistable distribution functions. These universal functions provide valuable tools to characterize the various time-evolution responses and give insight into the plethora of equilibration phenomena in complex quantum systems.
DEFF Research Database (Denmark)
Loft, N. J. S.; Marchukov, O. V.; Petrosyan, D.
2016-01-01
We have developed an efficient computational method to treat long, one-dimensional systems of strongly-interacting atoms forming self-assembled spin chains. Such systems can be used to realize many spin chain model Hamiltonians tunable by the external confining potential. As a concrete...... demonstration, we consider quantum state transfer in a Heisenberg spin chain and we show how to determine the confining potential in order to obtain nearly-perfect state transfer....
Ising Transition in Dimerized XY Quantum Spin Chain
Institute of Scientific and Technical Information of China (English)
YE Fei; DING Guo-Hui; XU Bo-Wei
2002-01-01
We proposed a simple spin-1/2 model which provides an exactly solvable example to study the Ising criticality with central charge c = 1/2.By mapping it onto the real Majorana fermions,the Ising critical behavior is explored explicitly,although its bosonized form is not the double frequency sine-Gordon model.
Hydrogenic spin quantum computing in silicon, and, Damping and diffusion in a chain-boson model
Skinner, Andrew J.
2006-12-01
We propose an architecture for quantum computing with spin-pair encoded qubits in silicon. Electron-nuclear spin-pairs are controlled by a DC magnetic field and electrode-switched on and off hyperfine interaction. This digital processing is insensitive to tuning errors and easy to model. Electron shuttling between donors enables multi-qubit logic. These hydrogenic spin qubits are transferable to nuclear spin-pairs, which have long coherence times, and electron spin-pairs, which are ideally suited for measurement and initialization. The architecture is scaleable to highly parallel operation. We also study the open-system dynamics of a few two-level systems coupled together and embedded in a crystal lattice. In one case, superconducting quantum interference devices, or SQUIDs, exchange their angular momenta with the lattice. Some decaying oscillations can emerge in a lower energy subspace with a longer coherence time. In another case, the exchange coupling between spins-1/2 is strained by lattice distortions. At a critical point energy level crossing, four well-spaced spins dissipate collectively. This is partially true also for the two- or three-SQUID-chain. These collective couplings can improve coherence times.
Entropy Squeezing in the Quantum Heisenberg XY Spin Chains
Institute of Scientific and Technical Information of China (English)
CHANG Ping; SHAO Bin; ZOU Jian
2009-01-01
The time evolution of entropy squeezing for the two-qubit XYZ Heisenberg model in an external uniform magnetic field is investigated in the language of quantum information.The effect of different parameters such as magnetic field and anisotropy parameter on the properties of entropy squeezing and variance squeezing are discussed.It is shown that magnetic field and anisotropy parameter can enhance the entropy squeezing.
A Class of Asymmetric Gapped Hamiltonians on Quantum Spin Chains and its Characterization II
Ogata, Yoshiko
2016-12-01
We give a characterization of the class of gapped Hamiltonians introduced in Part I (Ogata, A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015). The Hamiltonians in this class are given as MPS (Matrix product state) Hamiltonians. In Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), we list up properties of ground state structures of Hamiltonians in this class. In this Part II, we show the converse. Namely, if a (not necessarily MPS) Hamiltonian H satisfies five of the listed properties, there is a Hamiltonian H' from the class by Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), satisfying the following: The ground state spaces of the two Hamiltonians on the infinite interval coincide. The spectral projections onto the ground state space of H on each finite intervals are approximated by that of H' exponentially well, with respect to the interval size. The latter property has an application to the classification problem with open boundary conditions.
A Class of Asymmetric Gapped Hamiltonians on Quantum Spin Chains and its Characterization II
Ogata, Yoshiko
2016-06-01
We give a characterization of the class of gapped Hamiltonians introduced in Part I (Ogata, A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015). The Hamiltonians in this class are given as MPS (Matrix product state) Hamiltonians. In Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), we list up properties of ground state structures of Hamiltonians in this class. In this Part II, we show the converse. Namely, if a (not necessarily MPS) Hamiltonian H satisfies five of the listed properties, there is a Hamiltonian H' from the class by Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), satisfying the following: The ground state spaces of the two Hamiltonians on the infinite interval coincide. The spectral projections onto the ground state space of H on each finite intervals are approximated by that of H' exponentially well, with respect to the interval size. The latter property has an application to the classification problem with open boundary conditions.
Atomic spin-chain realization of a model for quantum criticality
Toskovic, R.; van den Berg, R.; Spinelli, A.; Eliens, I. S.; van den Toorn, B.; Bryant, B.; Caux, J.-S.; Otte, A. F.
2016-07-01
The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be used as fundamental building blocks for the realization of textbook many-body quantum models, illustrating key concepts such as quantum phase transitions, topological order or frustration as a function of system size. Here, we use low-temperature scanning tunnelling microscopy to construct arrays of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg chains in a transverse field, for which a quantum phase transition from an antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic limit. Site-resolved measurements on these finite-size realizations reveal a number of sudden ground state changes when the field approaches the critical value, each corresponding to a new domain wall entering the chains. We observe that these state crossings become closer for longer chains, suggesting the onset of critical behaviour. Our results present opportunities for further studies on quantum behaviour of many-body systems, as a function of their size and structural complexity.
Optimal control of fast and high-fidelity quantum state transfer in spin-1/2 chains
Zhang, Xiong-Peng; Shao, Bin; Hu, Shuai; Zou, Jian; Wu, Lian-Ao
2016-12-01
Spin chains are promising candidates for quantum communication and computation. Using quantum optimal control (OC) theory based on the Krotov method, we present a protocol to perform quantum state transfer with fast and high fidelity by only manipulating the boundary spins in a quantum spin-1/2 chain. The achieved speed is about one order of magnitude faster than that is possible in the Lyapunov control case for comparable fidelities. Additionally, it has a fundamental limit for OC beyond which optimization is not possible. The controls are exerted only on the couplings between the boundary spins and their neighbors, so that the scheme has good scalability. We also demonstrate that the resulting OC scheme is robust against disorder in the chain.
Optimal control of fast and high-fidelity quantum state transfer in spin-1/2 chains
Energy Technology Data Exchange (ETDEWEB)
Zhang, Xiong-Peng [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Shao, Bin, E-mail: sbin610@bit.edu.cn [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Hu, Shuai; Zou, Jian [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Wu, Lian-Ao [Department of Theoretical Physics and History of Science, The Basque Country University (EHU/UPV), PO Box 644, 48080 Bilbao (Spain); Ikerbasque, Basque Foundation for Science, 48011 Bilbao (Spain)
2016-12-15
Spin chains are promising candidates for quantum communication and computation. Using quantum optimal control (OC) theory based on the Krotov method, we present a protocol to perform quantum state transfer with fast and high fidelity by only manipulating the boundary spins in a quantum spin-1/2 chain. The achieved speed is about one order of magnitude faster than that is possible in the Lyapunov control case for comparable fidelities. Additionally, it has a fundamental limit for OC beyond which optimization is not possible. The controls are exerted only on the couplings between the boundary spins and their neighbors, so that the scheme has good scalability. We also demonstrate that the resulting OC scheme is robust against disorder in the chain.
Robust quantum entanglement generation and generation-plus-storage protocols with spin chains
Estarellas, Marta P.; D'Amico, Irene; Spiller, Timothy P.
2017-04-01
Reliable quantum communication and/or processing links between modules are a necessary building block for various quantum processing architectures. Here we consider a spin-chain system with alternating strength couplings and containing three defects, which impose three domain walls between topologically distinct regions of the chain. We show that—in addition to its useful, high-fidelity, quantum state transfer properties—an entangling protocol can be implemented in this system, with optional localization and storage of the entangled states. We demonstrate both numerically and analytically that, given a suitable initial product-state injection, the natural dynamics of the system produces a maximally entangled state at a given time. We present detailed investigations of the effects of fabrication errors, analyzing random static disorder both in the diagonal and off-diagonal terms of the system Hamiltonian. Our results show that the entangled state formation is very robust against perturbations of up to ˜10 % the weaker chain coupling, and also robust against timing injection errors. We propose a further protocol, which manipulates the chain in order to localize and store each of the entangled qubits. The engineering of a system with such characteristics would thus provide a useful device for quantum information processing tasks involving the creation and storage of entangled resources.
Topological Phases in Graphene Nanoribbons: Junction States, Spin Centers, and Quantum Spin Chains
Cao, Ting; Zhao, Fangzhou; Louie, Steven G.
2017-08-01
We show that semiconducting graphene nanoribbons (GNRs) of different width, edge, and end termination (synthesizable from molecular precursors with atomic precision) belong to different electronic topological classes. The topological phase of GNRs is protected by spatial symmetries and dictated by the terminating unit cell. We have derived explicit formulas for their topological invariants and shown that localized junction states developed between two GNRs of distinct topology may be tuned by lateral junction geometry. The topology of a GNR can be further modified by dopants, such as a periodic array of boron atoms. In a superlattice consisting of segments of doped and pristine GNRs, the junction states are stable spin centers, forming a Heisenberg antiferromagnetic spin 1 /2 chain with tunable exchange interaction. The discoveries here not only are of scientific interest for studies of quasi-one-dimensional systems, but also open a new path for design principles of future GNR-based devices through their topological characters.
New Construction of Eigenstates and Separation of Variables for SU(N) Quantum Spin Chains
Gromov, Nikolay; Sizov, Grigory
2016-01-01
We conjecture a new way to construct eigenstates of integrable XXX quantum spin chains with SU(N) symmetry. The states are built by repeatedly acting on the vacuum with a single operator B^{good}(u) evaluated at the Bethe roots. Our proposal serves as a compact alternative to the usual nested algebraic Bethe ansatz. Furthermore, the roots of the operator B^{good}(u) give the separated variables of the model, explicitly generalizing Sklyanin's approach to the SU(N) case. We present many tests of the conjecture and prove it in several special cases. We focus on rational spin chains with fundamental representation at each site, but expect many of the results to be valid more generally.
Spin-Anisotropy Commensurable Chains Quantum Group Symmetries and N=2 SUSY
Berkovich, A; Sierra, G
1994-01-01
In this paper we consider a class of the 2D integrable models. These models are higher spin XXZ chains with an extra condition of the commensurability between spin and anisotropy. The mathematics underlying this commensurability is provided by the quantum groups with deformation parameter being an Nth root of unity. Our discussion covers a range of topics including new integrable deformations, thermodynamics, conformal behaviour, S-matrices and magnetization. The emerging picture strongly depends on the N-parity. For the N even case at the commensurable point, S-matrices factorize into N=2 supersymmetric Sine-Gordon matrix and an RSOS piece. The physics of the N odd case is rather different. Here, the supersymmetry does not manifest itself and the bootstrap hypothesis fails. Away from the commensurable point, we find an unusual behaviour. The magnetization of our chains depends on the sign of the external magnetic field.
Renes, Joseph M; Brennen, Gavin K; Bartlett, Stephen D
2011-01-01
While solid-state devices offer naturally reliable hardware for modern classical computers, thus far quantum information processors resemble vacuum tube computers in being neither reliable nor scalable. Strongly correlated many body states stabilized in topologically ordered matter offer the possibility of naturally fault tolerant computing, but are both challenging to engineer and coherently control and cannot be easily adapted to different physical platforms. We propose an architecture which achieves some of the robustness properties of topological models but with a drastically simpler construction. Quantum information is stored in the degenerate ground states of spin-1 chains exhibiting symmetry-protected topological order (SPTO), while quantum gates are performed by adiabatic non-Abelian holonomies using only single-site fields and nearest-neighbor couplings. Gate operations respect the SPTO symmetry, inheriting some protection from noise and disorder from the SPTO robustness to local perturbation. A pote...
Pairwise correlations via quantum discord and its geometric measure in a four-qubit spin chain
Directory of Open Access Journals (Sweden)
Abdel-Baset A. Mohamed
2013-04-01
Full Text Available The dynamic of pairwise correlations, including quantum entanglement (QE and discord (QD with geometric measure of quantum discord (GMQD, are shown in the four-qubit Heisenberg XX spin chain. The results show that the effect of the entanglement degree of the initial state on the pairwise correlations is stronger for alternate qubits than it is for nearest-neighbor qubits. This parameter results in sudden death for QE, but it cannot do so for QD and GMQD. With different values for this entanglement parameter of the initial state, QD and GMQD differ and are sensitive for any change in this parameter. It is found that GMQD is more robust than both QD and QE to describe correlations with nonzero values, which offers a valuable resource for quantum computation.
Universal and nonuniversal level statistics in a chaotic quantum spin chain.
Pineda, Carlos; Prosen, Tomaz
2007-12-01
We study the level statistics of an interacting multiqubit system, namely the kicked Ising spin chain, in the regime of quantum chaos. Long range quasienergy level statistics show effects analogous to the ones observed in semiclassical systems due to the presence of short classical periodic orbits, while short range level statistics display perfect statistical agreement with random matrix theory. Even though our system possesses no classical limit, our results suggest existence of an important nonuniversal system specific behavior at short time scale, which clearly goes beyond finite size effects in random matrix theory.
Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling
Del Cima, O M; da Silva, S L L
2015-01-01
The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.
Monthus, Cécile
2017-07-01
When random quantum spin chains are submitted to some periodic Floquet driving, the eigenstates of the time-evolution operator over one period can be localized in real space. For the case of periodic quenches between two Hamiltonians (or periodic kicks), where the time-evolution operator over one period reduces to the product of two simple transfer matrices, we propose a block-self-dual renormalization procedure to construct the localized eigenstates of the Floquet dynamics. We also discuss the corresponding strong disorder renormalization procedure, that generalizes the RSRG-X procedure to construct the localized eigenstates of time-independent Hamiltonians.
Institute of Scientific and Technical Information of China (English)
Shan Chuan-Jia; Cheng Wei-Wen; Liu Tang-Kun; Huang Yan-Xia; Li nong
2008-01-01
By using the method of density-matrix renormalization-group to solve the different spin-spin correlation functions,the nearest-neighbouring entanglement (NNE) and the next-nearest-neighbouring entanglement (NNNE) of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearestneighbouring interaction of exchange couplings,external magnetic fields and the next-nearest neighbouring interaction.For a dimerised ferromagnetic spin chain,the NNNE appears only above a critical dimerized interaction,meanwhile,the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent.We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring (NNN) interaction on the dynamics of NNE and NNNE.The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively,while the antiferromagnetic NNN interaction always reduces the NNE.The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic.
Separation of variables for the quantum SL(2,R) spin chain
Derkachov, S E; Manashov, A N
2003-01-01
We construct representation of the Separated Variables (SoV) for the quantum SL(2,R) Heisenberg closed spin chain and obtain the integral representation for the eigenfunctions of the model. We calculate explicitly the Sklyanin measure defining the scalar product in the SoV representation and demonstrate that the language of Feynman diagrams is extremely useful in establishing various properties of the model. The kernel of the unitary transformation to the SoV representation is described by the same "pyramid diagram" as appeared before in the SoV representation for the SL(2,C) spin magnet. We argue that this kernel is given by the product of the Baxter Q-operators projected onto a special reference state.
Transient Loschmidt Echo and Orthogonality Catastrophe in highly excited Quantum Ising Spin Chains
Schiro, Marco; Lupo, Carla
We study the response to sudden local perturbations of highly excited Quantum Ising Spin Chains. The key quantity encoding this response is the overlap between time-dependent wave functions, which we write as a transient Loschmidt echo. We compute the Echo perturbatively in the case of a weak local quench and study its asymptotics at long times, which contains crucial information about the structure of the highly excited non-equilibrium environment induced by the quench. Our results reveal that the Echo decays exponentially, rather than power law as in the low-energy Orthogonality Catastrophe, a further example of quench-induced decoherence. The emerging decoherence scale is set by the strenght of the local potential and the bulk excitation energy. In addition, the transient evolution features aging behavior at the Ising quantum critical point.
Zwick, A
2009-01-01
One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum $XX$ chain with one impurity. The bipartite entanglement is obtained using the Concurrence and the localization is analyzed using the inverse participation ratio. Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. Our results show that equally localized states do not possess the same bipartite entanglement and suggest that only a restricted class of localizated states allows the storage and transmission of quantum states.
Strečka, Jozef; Verkholyak, Taras
2016-10-01
Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are examined using quantum Monte Carlo simulations for two different quantum spin numbers S=1 and 3/2. The calculated magnetization curves at finite temperatures are confronted with zero-temperature magnetization data obtained within the density matrix renormalization group method, which imply an existence of two quantum critical points determining a breakdown of the gapped Lieb-Mattis ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. While a square root behavior of the magnetization accompanying each quantum critical point is gradually smoothed upon rising temperature, the susceptibility and isothermal entropy change data at low temperatures provide a stronger evidence of the zero-temperature quantum critical points through marked local maxima and minima, respectively.
Phase diagram and spectral properties of a new exactly integrable spin-1 quantum chain
Energy Technology Data Exchange (ETDEWEB)
Alcaraz, Francisco C; Nakamura, Gilberto M [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, CP 369, 13560-970, Sao Carlos, Sao Paulo (Brazil)], E-mail: alcaraz@if.sc.usp.br
2010-04-16
The spectral properties and phase diagram of the exactly integrable spin-1 quantum chain introduced by Alcaraz and Bariev are presented. The model has a U(1) symmetry and its integrability is associated with an unknown R-matrix whose dependence on the spectral parameters is not of a different form. The associated Bethe ansatz equations that fix the eigenspectra are distinct from those associated with other known integrable spin models. The model has a free parameter t{sub p}. We show that at the special point t{sub p} = 1, the model acquires an extra U(1) symmetry and reduces to the deformed SU(3) Perk-Schultz model at a special value of its anisotropy q = exp (i2{pi}/3) and in the presence of an external magnetic field. Our analysis is carried out either by solving the associated Bethe ansatz equations or by direct diagonalization of the quantum Hamiltonian for small lattice sizes. The phase diagram is calculated by exploring the consequences of conformal invariance on the finite-size corrections of the Hamiltonian eigenspectrum. The model exhibits a critical phase ruled by the c = 1 conformal field theory separated from a massive phase by first-order phase transitions.
Criticality-Enhanced Magnetocaloric Effect in Quantum Spin Chain Material Copper Nitrate
Xiang, Jun-Sen; Chen, Cong; Li, Wei; Sheng, Xian-Lei; Su, Na; Cheng, Zhao-Hua; Chen, Qiang; Chen, Zi-Yu
2017-01-01
In this work, a systematic study of Cu(NO3)2·2.5 H2O (copper nitrate hemipentahydrate, CN), an alternating Heisenberg antiferromagnetic chain model material, is performed with multi-technique approach including thermal tensor network (TTN) simulations, first-principles calculations, as well as magnetization measurements. Employing a cutting-edge TTN method developed in the present work, we verify the couplings J = 5.13 K, α = 0.23(1) and Landé factors g∥= 2.31, g⊥ = 2.14 in CN, with which the magnetothermal properties have been fitted strikingly well. Based on first-principles calculations, we reveal explicitly the spin chain scenario in CN by displaying the calculated electron density distributions, from which the distinct superexchange paths are visualized. On top of that, we investigated the magnetocaloric effect (MCE) in CN by calculating its isentropes and magnetic Grüneisen parameter. Prominent quantum criticality-enhanced MCE was uncovered near both critical fields of intermediate strengths as 2.87 and 4.08 T, respectively. We propose that CN is potentially a very promising quantum critical coolant. PMID:28294147
Two-channel spin-chain communication line and simple quantum gates
Stolze, J.; Zenchuk, A. I.
2017-08-01
We consider the remote creation of a mixed state in a one-qubit receiver connected to two two-qubit senders via different channels. Channels are assumed to be chains of spins (qubits) with nearest-neighbor interactions, no external fields are being applied. The problem of sharing the creatable region of the receiver's state-space between two senders is considered for a communication line with the receiver located asymmetrically with respect to these senders (asymmetric communication line). An example of a quantum register realizing simple functions is constructed on the basis of a symmetric communication line. In that setup, the initial states of the two senders serve as input and control signals, respectively, while the state of the receiver at a proper time instant is considered as the output signal.
Quantum chaos in the Heisenberg spin chain: The effect of Dzyaloshinskii-Moriya interaction
Vahedi, J.; Ashouri, A.; Mahdavifar, S.
2016-10-01
Using one-dimensional spin-1/2 systems as prototypes of quantum many-body systems, we study the emergence of quantum chaos. The main purpose of this work is to answer the following question: how the spin-orbit interaction, as a pure quantum interaction, may lead to the onset of quantum chaos? We consider the three integrable spin-1/2 systems: the Ising, the XX, and the XXZ limits and analyze whether quantum chaos develops or not after the addition of the Dzyaloshinskii-Moriya interaction. We find that depending on the strength of the anisotropy parameter, the answer is positive for the XXZ and Ising models, whereas no such evidence is observed for the XX model. We also discuss the relationship between quantum chaos and thermalization.
Quantum Phase Transitions in Alternating-Bond Mixed Diamond Chains with Spins 1 and 1/2
Hida, Kazuo; Takano, Ken'ichi; Suzuki, Hidenori
2010-04-01
We investigate the mixed diamond chain composed of spins 1 and 1/2 when the exchange interaction is alternatingly distorted. Depending on the strengths of frustration and distortion, this system has various ground states. Each ground state consists of an array of spin clusters separated by singlet dimers by virtue of an infinite number of local conservation laws. We determine the ground-state phase diagram by numerically analyzing each spin cluster. In particular, for strong distortions, we find an infinite series of quantum phase transitions using the cluster expansion method and conformal field theory. This leads to an infinite series of steps in the behavior of Curie constant and residual entropy.
Field-driven quantum phase transitions in S =1/2 spin chains
Iaizzi, Adam; Damle, Kedar; Sandvik, Anders W.
2017-05-01
We study the magnetization process of a one-dimensional extended Heisenberg model, the J -Q model, as a function of an external magnetic field h . In this model, J represents the traditional antiferromagnetic Heisenberg exchange and Q is the strength of a competing four-spin interaction. Without external field, this system hosts a twofold-degenerate dimerized (valence-bond solid) state above a critical value qc≈0.85 where q ≡Q /J . The dimer order is destroyed and replaced by a partially polarized translationally invariant state at a critical field value. We find magnetization jumps (metamagnetism) between the partially polarized and fully polarized state for q >qmin , where we have calculated qmin=2/9 exactly. For q >qmin , two magnons (flipped spins on a fully polarized background) attract and form a bound state. Quantum Monte Carlo studies confirm that the bound state corresponds to the first step of an instability leading to a finite magnetization jump for q >qmin . Our results show that neither geometric frustration nor spin anisotropy are necessary conditions for metamagnetism. Working in the two-magnon subspace, we also find evidence pointing to the existence of metamagnetism in the unfrustrated J1-J2 chain (J1>0 ,J20 . While the expected "zero-scale-factor" universality is clearly seen for q =0 and q ≪qmin , for q closer to qmin we find that extremely low temperatures are required to observe the asymptotic behavior, due to the influence of the tricritical point at qmin. In the low-energy theory, one can expect the quartic nonlinearity to vanish at qmin and a marginal sixth-order term should govern the scaling, which leads to a crossover at a temperature T*(q ) between logarithmic tricritical scaling and zero-scale-factor universality, with T*(q ) →0 when q →qmin .
Niccoli, G.
2013-05-01
The antiperiodic transfer matrices associated to higher spin representations of the rational 6-vertex Yang-Baxter algebra are analyzed by generalizing the approach introduced recently in the framework of Sklyanin's quantum separation of variables (SOV) for cyclic representations, spin-1/2 highest weight representations, and also for spin-1/2 representations of the 6-vertex reflection algebra. Such SOV approach allow us to derive exactly results which represent complicate tasks for more traditional methods based on Bethe ansatz and Baxter Q-operator. In particular, we both prove the completeness of the SOV characterization of the transfer matrix spectrum and its simplicity. Then, the derived characterization of local operators by Sklyanin's quantum separate variables and the expression of the scalar products of separate states by determinant formulae allow us to compute the form factors of the local spin operators by one determinant formulae similar to those of the scalar products.
Kumar, Manoranjan; Parvej, Aslam; Soos, Zoltán G
2015-08-12
The spin-1/2 chain with isotropic Heisenberg exchange J1, J2 > 0 between first and second neighbors is frustrated for either sign of J1. Its quantum phase diagram has critical points at fixed J1/J2 between gapless phases with nondegenerate ground state (GS) and quasi-long-range order (QLRO) and gapped phases with doubly degenerate GS and spin correlation functions of finite range. In finite chains, exact diagonalization (ED) estimates critical points as level crossing of excited states. GS spin correlations enter in the spin structure factor S(q) that diverges at wave vector qm in QLRO(q(m)) phases with periodicity 2π/q(m) but remains finite in gapped phases. S(q(m)) is evaluated using ED and density matrix renormalization group (DMRG) calculations. Level crossing and the magnitude of S(q(m)) are independent and complementary probes of quantum phases, based respectively on excited and ground states. Both indicate a gapless QLRO(π/2) phase between -1.2 < J1/|J2| < 0.45. Numerical results and field theory agree well for quantum critical points at small frustration J2 but disagree in the sector of weak exchange J1 between Heisenberg antiferromagnetic chains on sublattices of odd and even-numbered sites.
Deguchi, Tetsuo; Ranjan Giri, Pulak
2016-04-01
Every solution of the Bethe-ansatz equations (BAEs) is characterized by a set of quantum numbers, by which we can evaluate it numerically. However, no general rule is known how to give quantum numbers for the physical solutions of BAE. For the spin-1/2 XXX chain we rigorously derive all the quantum numbers for the complete set of the Bethe-ansatz eigenvectors in the two down-spin sector with any chain length N. Here we obtain them both for real and complex solutions. We also show that all the solutions associated with them are distinct. Consequently, we prove the completeness of the Bethe ansatz and give an exact expression for the number of real solutions which correspond to collapsed bound-state solutions (i.e., two-string solutions) in the sector: 2[(N-1)/2-(N/π ){{tan}}-1(\\sqrt{N-1})] in terms of Gauss’ symbol. Moreover, we prove in the sector the scheme conjectured by Takahashi for solving BAE systematically. We also suggest that by applying the present method we can derive the quantum numbers for the spin-1/2 XXZ chain.
Quantum Cryptography in Spin Networks
Institute of Scientific and Technical Information of China (English)
DENG Hong-Liang; FANG Xi-Ming
2007-01-01
In this paper we propose a new scheme of long-distance quantum cryptography based on spin networks with qubits stored in electron spins of quantum dots. By conditional Faraday rotation, single photon polarization measurement, and quantum state transfer, maximal-entangled Bell states for quantum cryptography between two long-distance parties are created. Meanwhile, efficient quantum state transfer over arbitrary distances is obtained in a spin chain by a proper choice of coupling strengths and using spin memory technique improved. We also analyse the security of the scheme against the cloning-based attack which can be also implemented in spin network and discover that this spin network cloning coincides with the optimal fidelity achieved by an eavesdropper for entanglement-based cryptography.
First order quantum phase transitions of the XX spin-1/2 chain in a uniform transverse field
Energy Technology Data Exchange (ETDEWEB)
Pan Feng [Department of Physics, Liaoning Normal University, Dalian 116029 (China) and Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)]. E-mail: daipan@dlut.edu.cn; Ma Nan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Guan Xin [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Draayer, J.P. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
2007-08-06
Quantum phase transitional behavior of a finite periodic XX spin-12 chain with nearest neighbor interaction in a uniform transverse field is studied based on the simple exact solutions. It is found that there are [N/2] level-crossing points in the ground state, where N is the periodic number of the system and [x] stands for the integer part of x, when the interaction strength and magnitude of the magnetic field satisfy certain conditions. The quantum phase transitional behavior in the thermodynamic is also studied.
2003-01-01
We study the anisotropic Heisenberg (XYZ) spin-1/2 chain placed in a magnetic field pointing along the x-axis. We use bosonization and a renormalization group analysis to show that the model has a non-trivial fixed point at a certain value of the XY anisotropy a and the magnetic field h. Hence, there is a line of critical points in the (a,h) plane on which the system is gapless, even though the Hamiltonian has no continuous symmetry. The quantum critical line corresponds to a spin-flop transi...
Charges and currents in quantum spin chains: late-time dynamics and spontaneous currents
Fagotti, Maurizio
2017-01-01
We review the structure of the conservation laws in noninteracting spin chains and unveil a formal expression for the corresponding currents. We briefly discuss how interactions affect the picture. In the second part, we explore the effects of a localized defect. We show that the emergence of spontaneous currents near the defect undermines any description of the late-time dynamics by means of a stationary state in a finite chain. In particular, the diagonal ensemble does not work. Finally, we provide numerical evidence that simple generic localized defects are not sufficient to induce thermalization.
Many-body localization transition in random quantum spin chains with long-range interactions
Moure, N.; Haas, S.; Kettemann, S.
2015-07-01
While there are well-established methods to study delocalization transitions of single particles in random systems, it remains a challenging problem how to characterize many-body delocalization transitions. Here, we use a generalized real-space renormalization group technique to study the anisotropic Heisenberg model with long-range interactions, decaying with a power α, which are generated by placing spins at random positions along the chain. This method permits a large-scale finite-size scaling analysis. We examine the full distribution function of the excitation energy gap from the ground state and observe a crossover with decreasing α. At αc the full distribution coincides with a critical function. Thereby, we find strong evidence for the existence of a many-body localization transition in disordered antiferromagnetic spin chains with long-range interactions.
Energy Technology Data Exchange (ETDEWEB)
Pan Feng [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Guan Xin [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Ma Nan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Han Wenjuan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Draayer, J P [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
2007-09-26
A simple Mathematica code based on the differential realization of hard-core boson operators for finding exact solutions of the periodic-N spin-1/2 systems with or beyond nearest neighbor interactions is proposed; it can easily be used to study general spin-1/2 interaction systems. As an example, the code is applied to study XXX spin-1/2 chains with nearest neighbor interaction in a uniform transverse field. It shows that there are [N/2] level-crossing points in the ground state, where N is the periodic number of the system and [x] stands for the integer part of x, when the interaction strength and magnitude of the magnetic field satisfy certain conditions. The quantum phase transitional behavior in the ground state of the system in the thermodynamic limit is also studied.
Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.
Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud
2009-04-03
We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.
Wu, Wei; Xu, Jing-Bo
2016-08-01
We investigate the quantum phase transitions of spin systems in one and two dimensions by employing trace distance and multipartite entanglement along with the real-space quantum renormalization group method. As illustration examples, a one-dimensional and a two-dimensional XY models are considered. It is shown that the quantum phase transitions of these spin-chain systems can be revealed by the singular behaviors of the first derivatives of renormalized trace distance and multipartite entanglement in the thermodynamics limit. Moreover, we find that the renormalized trace distance and multipartite entanglement obey certain universal exponential-type scaling laws in the vicinity of the quantum critical points.
Exact matrix product solutions in the Heisenberg picture of an open quantum spin chain
Energy Technology Data Exchange (ETDEWEB)
Clark, S R; Jaksch, D [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Prior, J [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Hartmann, M J [Technische Universitaet Muenchen, Physik Department I, James Franck Strasse, 85748 Garching (Germany); Plenio, M B [Institute for Mathematical Sciences, Imperial College London, SW7 2PG (United Kingdom)], E-mail: s.clark@physics.ox.ac.uk
2010-02-15
In recent work, Hartmann et al (2009 Phys. Rev. Lett. 102 057202) demonstrated that the classical simulation of the dynamics of open 1D quantum systems with matrix product algorithms can often be dramatically improved by performing time evolution in the Heisenberg picture. For a closed system this was exemplified by an exact matrix product operator (MPO) solution of the time-evolved creation operator of a quadratic fermi chain with a matrix dimension of just two. In this work, we show that this exact solution can be significantly generalized to include the case of an open quadratic fermi chain subjected to master equation evolution with Lindblad operators that are linear in the fermionic operators. Remarkably even in this open system the time evolution of operators continues to be described by MPOs with the same fixed dimension as that required by the solution of a coherent quadratic fermi chain for all times. Through the use of matrix product algorithms the dynamical behaviour of operators in this non-equilibrium open quantum system can be computed with a cost that is linear in the system size. We present some simple numerical examples that highlight how useful this might be for the more detailed study of open system dynamics. Given that Heisenberg picture simulations have been demonstrated to offer significant accuracy improvements for other open systems that are not exactly solvable, our work also provides further insight into how and why this advantage arises.
2015-07-15
Progress Report (ONR Award No. N00014-14-1-0804) Quantum Spin Gyroscope August 2014-July 2015 Report Type: Annual Report Primary Contact E-mail... Quantum Spin Gyroscope Grant/Contract Number: N00014-14-1-0804 Principal Investigator Name: Paola Cappellaro Program Manager: Richard Tommy Willis...required large volumes. Our project aims at overcoming these drawbacks by developing a novel solid-state quantum spin gyro- scope associated with the
Djoufack, Z. I.; Tala-Tebue, E.; Nguenang, J. P.; Kenfack-Jiotsa, A.
2016-10-01
We report in this work, an analytical study of quantum soliton in 1D Heisenberg spin chains with Dzyaloshinsky-Moriya Interaction (DMI) and Next-Nearest-Neighbor Interactions (NNNI). By means of the time-dependent Hartree approximation and the semi-discrete multiple-scale method, the equation of motion for the single-boson wave function is reduced to the nonlinear Schrödinger equation. It comes from this present study that the spectrum of the frequencies increases, its periodicity changes, in the presence of NNNI. The antisymmetric feature of the DMI was probed from the dispersion curve while changing the sign of the parameter controlling it. Five regions were identified in the dispersion spectrum, when the NNNI are taken into account instead of three as in the opposite case. In each of these regions, the quantum model can exhibit quantum stationary localized and stable bright or dark soliton solutions. In each region, we could set up quantum localized n-boson Hartree states as well as the analytical expression of their energy level, respectively. The accuracy of the analytical studies is confirmed by the excellent agreement with the numerical calculations, and it certifies the stability of the stationary quantum localized solitons solutions exhibited in each region. In addition, we found that the intensity of the localization of quantum localized n-boson Hartree states increases when the NNNI are considered. We also realized that the intensity of Hartree n-boson states corresponding to quantum discrete soliton states depend on the wave vector.
Topologically protected localised states in spin chains
Estarellas, Marta P.; D’Amico, Irene; Spiller, Timothy P.
2017-02-01
We consider spin chain families inspired by the Su, Schrieffer and Hegger (SSH) model. We demonstrate explicitly the topologically induced spatial localisation of quantum states in our systems. We present detailed investigations of the effects of random noise, showing that these topologically protected states are very robust against this type of perturbation. Systems with such topological robustness are clearly good candidates for quantum information tasks and we discuss some potential applications. Thus, we present interesting spin chain models which show promising applications for quantum devices.
Mussardo, G.; Giudici, G.; Viti, J.
2017-03-01
In this paper we introduce and study the coprime quantum chain, i.e. a strongly correlated quantum system defined in terms of the integer eigenvalues n i of the occupation number operators at each site of a chain of length M. The n i ’s take value in the interval [2,q] and may be regarded as S z eigenvalues in the spin representation j = (q - 2)/2. The distinctive interaction of the model is based on the coprimality matrix \\boldsymbolΦ : for the ferromagnetic case, this matrix assigns lower energy to configurations where occupation numbers n i and n i+1 of neighbouring sites share a common divisor, while for the anti-ferromagnetic case it assigns a lower energy to configurations where n i and n i+1 are coprime. The coprime chain, both in the ferro and anti-ferromagnetic cases, may present an exponential number of ground states whose values can be exactly computed by means of graph theoretical tools. In the ferromagnetic case there are generally also frustration phenomena. A fine tuning of local operators may lift the exponential ground state degeneracy and, according to which operators are switched on, the system may be driven into different classes of universality, among which the Ising or Potts universality class. The paper also contains an appendix by Don Zagier on the exact eigenvalues and eigenvectors of the coprimality matrix in the limit q\\to ∞ .
Energy Technology Data Exchange (ETDEWEB)
Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-01-15
The quantum Hall liquid is a novel state of matter with profound emergent properties such as fractional charge and statistics. Existence of the quantum Hall effect requires breaking of the time reversal symmetry caused by an external magnetic field. In this work, we predict a quantized spin Hall effect in the absence of any magnetic field, where the intrinsic spin Hall conductance is quantized in units of 2 e/4{pi}. The degenerate quantum Landau levels are created by the spin-orbit coupling in conventional semiconductors in the presence of a strain gradient. This new state of matter has many profound correlated properties described by a topological field theory.
Topological Effects on Quantum Phase Slips in Superfluid Spin Transport
Kim, Se Kwon; Tserkovnyak, Yaroslav
2016-03-01
We theoretically investigate effects of quantum fluctuations on superfluid spin transport through easy-plane quantum antiferromagnetic spin chains in the large-spin limit. Quantum fluctuations result in the decaying spin supercurrent by unwinding the magnetic order parameter within the easy plane, which is referred to as phase slips. We show that the topological term in the nonlinear sigma model for the spin chains qualitatively differentiates the decaying rate of the spin supercurrent between the integer versus half-odd-integer spin chains. An experimental setup for a magnetoelectric circuit is proposed, in which the dependence of the decaying rate on constituent spins can be verified by measuring the nonlocal magnetoresistance.
Bazhanov, D. I.; Stepanyuk, O. V.; Farberovich, O. V.; Stepanyuk, V. S.
2016-01-01
We present a study of the magnetic states and exchange coupling in transition-metal Mn, Fe, and Co atomic chains deposited on a self-corrugated C u3N -Cu(110) molecular network by means of first-principles calculations based on the density functional theory. The various adsorption sites on a bumping area of a self-corrugated C u3N layer are investigated where the atomic chains are formed at the initial stage of nanowire growth. We demonstrate, by calculating the ground-state magnetic configurations, that the exchange coupling, magnetic order, and anisotropies in atomic chains depend sensitively on their chemical composition and adsorption sites on the C u3N network. We find that the exchange interactions in atomic chains could lead to ferromagnetic or antiferromagnetic coupling of atomic spins depending on the position of the chain on the surface. The classical spin dynamics is investigated by means of the kinetic Monte Carlo method based on transition-state theory. Moreover we evaluate the Heisenberg-Dirac-Van Vleck quantum spin Hamiltonian for calculations of the magnetic susceptibility, in order to demonstrate the existence of quantum entanglement in the antiferromagnetic atomic chains at low temperatures.
Quantum Spin Models for Copper Oxide Chains in High-T{sub c} Superconductors
Energy Technology Data Exchange (ETDEWEB)
Haugerud, H.
1996-12-31
This doctoral thesis presents some of the most important features of high temperature superconductors, emphasizing the properties of YBa{sub 2}Cu{sub 3}O{sub 6+x} (YBCO). The family of Hubbard-like models is considered and a simplified version of the Emery model derived. This model is applied to fermions on a cyclic chain and solved analytically in the strong correlation limit. For realistic model parameter values the effects of an external magnetic field is investigated by numerical diagonalization. Applying the Emery model to finite cyclic Cu-O chains it is shown that the behaviour of the chains is typical for a 1D Fermi-liquid. The relatively small difference between the values of the local charge and the local magnetic moment indicates that the degree of correlation in this system is very high. The ground state of the Emery model is shown to be antiferromagnetic for half and quarter filling, resembling the ground state of the Heisenberg model. The role of the ensemble of Cu-O chain fragments of the oxygen deficient planes of YBCO is addressed. By applying the Emery model to short Cu-O chains and calculating the free energy of the chains, the parameters of an Ising like lattice gas model are estimated. Several thermodynamical quantities are calculated by applying Monte Carlo technique to the model. The charge transfer from the chains to the planes is shown to correspond to the measured values of T{sub c}. The phase diagram and the average chain length agree well with experiments. The model is also capable of explaining the behaviour of the REBCO series of superconductors, where RE are various rare earth ions. A framework for simultaneously visualizing and computing numerical quantities from lattice simulations is presented and illustrated. 195 refs., 69 figs., 4 tabs.
Zhao, Xu; Zhao, Xing-Dong; Zhou, Lu; Jing, Hui; Zhang, Wei-Ping
2013-07-01
We investigate the quantum interference of spin wave excitations of a spin-1 atomic Bose condensate confined in an optical lattice. Single-channel and dual-channel interactions are employed in our system, and their induced excitations are compared. Also we consider the interplay of magneto-optical excitations, which leads to a constructive or destructive effect for the creation of magnons based on background excitations. The population distributions of excited magnons can be well controlled by steering the long-range dipole-dipole interactions. Such a scheme can be used to demonstrate conventional quantum-optical phenomena like dynamical Casimir effect at finite temperatures.
Institute of Scientific and Technical Information of China (English)
ZHAO Xu; ZHAO Xing-Dong; ZHOU Lu; JING Hui; ZHANG Wei-Ping
2013-01-01
We investigate the quantum interference of spin wave excitations of a spin-1 atomic Bose condensate confined in an optical lattice.Single-channel and dual-channel interactions are employed in our system,and their induced excitations are compared.Also we consider the interplay of magneto-optical excitations,which leads to a constructive or destructive effect for the creation of magnons based on background excitations.The population distributions of excited magnons can be well controlled by steering the long-range dipole-dipole interactions.Such a scheme can be used to demonstrate conventional quantum-optical phenomena like dynamical Casimir effect at finite temperatures.
Realization of a Quantum Integer-Spin Chain with Controllable Interactions
2015-06-17
Haldane phase. ACKNOWLEDGMENTS We thank Brian Neyenhuis, Paul Hess, Alexey Gorshkov, and Zhe -Xuan Gong for critical discussions. A. R. acknowledges the...Lett. 106, 060503 (2011). [35] R. Islam, E. E. Edwards, K. Kim, S. Korenblit, C. Noh, H. Carmichael, G.-D. Lin, L.-M. Duan, C.-C. Joseph Wang , J. K...Chang, C. Noh, H. Carmichael, G.-D. Lin, L.-M. Duan, C.-C. Joseph Wang , J. K. Freericks, and C. Monroe, Quantum Simulation of the Transverse Field Ising
A Quantum Monte Carlo Study on Mixed-Spin Chains of 1/2-1/2-1-1 and 3/2-3/2 -1-1
Institute of Scientific and Technical Information of China (English)
XU Zhao-Xin; ZHANG Jun; YING He-Ping
2003-01-01
The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.
Entanglement in spin-1 Heisenberg XY chain
Institute of Scientific and Technical Information of China (English)
2008-01-01
We investigated the quantum entanglement in spin-1 Heisenberg XY chain for two-spin-qutrit and multi-particle systems. As a measure of the entanglement, the negativity of this state was analyzed as a function of the temperature and the magnetic field. We gave some numerical results and discussed them in detail. We found that the negativity increases monotonously with the coupling constants |J1| and |J2|, and it showed a symmetry with respect to the point of J1=0 and J2=0. In addition to the above features, there is evidence that the critical temperature is independent of the length of the chain.
Entanglement in spin-1 Heisenberg XY chain
Institute of Scientific and Technical Information of China (English)
QIN Meng; TAO YingJuan; HU MingLiang; TIAN DongPing
2008-01-01
We investigated the quantum entanglement in spin-1 Heisenberg XY chain for two-spin-qutrit and multi-particle systems. As a measure of the entanglement, the negativity of this state was analyzed as a function of the temperature and the magnetic field. We gave some numerical results and discussed them in detail. We found that the negativity increases monotonously with the coupling constants |J1|and |J2|, and it showed a symmetry with respect to the point of J1=0 and J2= 0. In addition to the above features, there is evidence that the critical temperature is independent of the length of the chain.
Criticality, factorization and Wigner-Yanase skew information in quantum spin chains
Cheng, W. W.; Li, J. X.; Shan, C. J.; Gong, L. Y.; Zhao, S. M.
2015-07-01
We apply the Wigner-Yanase skew information approach to analyze criticality and factorization phenomenon in the one-dimensional anisotropy model with uniform coupling interaction and periodic-two one. Based on the exact solutions of the ground states, the Wigner-Yanase skew information between two nearest-neighbor lattices is obtained. For the uniform case, the first-order derivative of the Wigner-Yanase skew information is non-analytically around the critical point. The scaling behavior and the universality are verified numerically. In particular, such skew information can also detect the factorization transition in this model. For the periodic-two case, it is found that there exist more than one phase-transition point in some parameter region due to the competition between periodicity and anisotropy. Furthermore, two kinds of phase transitions, i.e., the Ising and anisotropy transitions, driven by external field and the anisotropy parameter , are investigated carefully by the skew information. Our results state that quantum phase transition driven by the anisotropy parameter can belong to the same universality class as the one driven by external field.
Quantum Computation and Quantum Spin Dynamics
Raedt, Hans De; Michielsen, Kristel; Hams, Anthony; Miyashita, Seiji; Saito, Keiji
2001-01-01
We analyze the stability of quantum computations on physically realizable quantum computers by simulating quantum spin models representing quantum computer hardware. Examples of logically identical implementations of the controlled-NOT operation are used to demonstrate that the results of a quantum
Quantum Computation and Quantum Spin Dynamics
Raedt, Hans De; Michielsen, Kristel; Hams, Anthony; Miyashita, Seiji; Saito, Keiji
2001-01-01
We analyze the stability of quantum computations on physically realizable quantum computers by simulating quantum spin models representing quantum computer hardware. Examples of logically identical implementations of the controlled-NOT operation are used to demonstrate that the results of a quantum
Quantum decoration transformation for spin models
Braz, F. F.; Rodrigues, F. C.; de Souza, S. M.; Rojas, Onofre
2016-09-01
It is quite relevant the extension of decoration transformation for quantum spin models since most of the real materials could be well described by Heisenberg type models. Here we propose an exact quantum decoration transformation and also showing interesting properties such as the persistence of symmetry and the symmetry breaking during this transformation. Although the proposed transformation, in principle, cannot be used to map exactly a quantum spin lattice model into another quantum spin lattice model, since the operators are non-commutative. However, it is possible the mapping in the "classical" limit, establishing an equivalence between both quantum spin lattice models. To study the validity of this approach for quantum spin lattice model, we use the Zassenhaus formula, and we verify how the correction could influence the decoration transformation. But this correction could be useless to improve the quantum decoration transformation because it involves the second-nearest-neighbor and further nearest neighbor couplings, which leads into a cumbersome task to establish the equivalence between both lattice models. This correction also gives us valuable information about its contribution, for most of the Heisenberg type models, this correction could be irrelevant at least up to the third order term of Zassenhaus formula. This transformation is applied to a finite size Heisenberg chain, comparing with the exact numerical results, our result is consistent for weak xy-anisotropy coupling. We also apply to bond-alternating Ising-Heisenberg chain model, obtaining an accurate result in the limit of the quasi-Ising chain.
Low energy spin dynamics of a quantum ferrimagnetic chain, NiCu(pba)(H 2O) 32H 2O
Fujiwara, N.; Hagiwara, M.
2000-01-01
Nuclear magnetic resonance (NMR) for 1H nuclei was performed in a Heisenberg chain with alternating spins S=1 and 1/2, NiCu(pba)(H 2O) 32H 2O (pba=1,3-propylenebis (oxamato)) from 4.2 to 280 K. The relaxation rate (1/ T1) is proportional to 1/ H ( H is applied field), whereas the temperature dependence is weak and is almost constant at high temperatures. The temperature and field dependences are investigated on the basis of the spin-wave theory.
Valinevich, P. A.; Derkachov, S. É.; Kulish, P. P.; Uvarov, E. M.
2016-11-01
We consider the problem of seeking the eigenvectors for a commuting family of quantum minors of the monodromy matrix for an SL(n,ℂ)-invariant inhomogeneous spin chain. The algebra generators and elements of the L-operator at each site of the chain are implemented as linear differential operators in the space of functions of n(n-1)/2 variables. In the general case, the representation of the sln(ℂ) algebra at each site is infinite-dimensional and belongs to the principal unitary series. We solve this problem using a recursive procedure with respect to the rank n of the algebra. We obtain explicit expressions for the eigenvalues and eigenvectors of the commuting family. We consider the particular cases n = 2 and n = 3 and also the limit case of the one-site chain in detail.
Salberger, Olof
2016-01-01
We introduce a new model of interacting spin 1/2. It describes interaction of three nearest neighbors. The Hamiltonian can be expressed in terms of Fredkin gates. The Fredkin gate (also known as the CSWAP gate) is a computational circuit suitable for reversible computing. Our construction generalizes the work of Ramis Movassagh and Peter Shor. Our model can be solved by means of Catalan combinatorics in the form of random walks on the upper half of a square lattice [Dyck walks]. Each Dyck path can be mapped to a wave function of the spins. The ground state is an equally weighted superposition of Dyck walks [instead of Motzkin walks]. We can also express it as a matrix product state. We further construct the model of interacting spins 3/2 and greater half-integer spins. The models with higher spins require coloring of Dyck walks. We construct SU(k) symmetric model [here k is the number of colors]. The leading term of the entanglement entropy is then proportional to the square root of the length of the lattice ...
Blockspin Cluster Algorithms for Quantum Spin Systems
Wiese, U J
1992-01-01
Cluster algorithms are developed for simulating quantum spin systems like the one- and two-dimensional Heisenberg ferro- and anti-ferromagnets. The corresponding two- and three-dimensional classical spin models with four-spin couplings are maped to blockspin models with two-blockspin interactions. Clusters of blockspins are updated collectively. The efficiency of the method is investigated in detail for one-dimensional spin chains. Then in most cases the new algorithms solve the problems of slowing down from which standard algorithms are suffering.
Quantum annealing with manufactured spins.
Johnson, M W; Amin, M H S; Gildert, S; Lanting, T; Hamze, F; Dickson, N; Harris, R; Berkley, A J; Johansson, J; Bunyk, P; Chapple, E M; Enderud, C; Hilton, J P; Karimi, K; Ladizinsky, E; Ladizinsky, N; Oh, T; Perminov, I; Rich, C; Thom, M C; Tolkacheva, E; Truncik, C J S; Uchaikin, S; Wang, J; Wilson, B; Rose, G
2011-05-12
Many interesting but practically intractable problems can be reduced to that of finding the ground state of a system of interacting spins; however, finding such a ground state remains computationally difficult. It is believed that the ground state of some naturally occurring spin systems can be effectively attained through a process called quantum annealing. If it could be harnessed, quantum annealing might improve on known methods for solving certain types of problem. However, physical investigation of quantum annealing has been largely confined to microscopic spins in condensed-matter systems. Here we use quantum annealing to find the ground state of an artificial Ising spin system comprising an array of eight superconducting flux quantum bits with programmable spin-spin couplings. We observe a clear signature of quantum annealing, distinguishable from classical thermal annealing through the temperature dependence of the time at which the system dynamics freezes. Our implementation can be configured in situ to realize a wide variety of different spin networks, each of which can be monitored as it moves towards a low-energy configuration. This programmable artificial spin network bridges the gap between the theoretical study of ideal isolated spin networks and the experimental investigation of bulk magnetic samples. Moreover, with an increased number of spins, such a system may provide a practical physical means to implement a quantum algorithm, possibly allowing more-effective approaches to solving certain classes of hard combinatorial optimization problems.
Langari, A; Pollmann, F; Siahatgar, M
2013-10-09
We study the phase diagram of the anisotropic spin-1 Heisenberg chain with single ion anisotropy (D) using a ground-state fidelity approach. The ground-state fidelity and its corresponding susceptibility are calculated within the quantum renormalization group scheme where we obtained the renormalization of fidelity preventing calculation of the ground state. Using this approach, the phase boundaries between the antiferromagnetic Néel, Haldane and large-D phases are obtained for the whole phase diagram, which justifies the application of quantum renormalization group to trace the symmetry-protected topological phases. In addition, we present numerical exact diagonalization (Lanczos) results in which we employ a recently introduced non-local order parameter to locate the transition from Haldane to large-D phase accurately.
Thermal quantum discord in the Heisenberg chain with impurity
Energy Technology Data Exchange (ETDEWEB)
Gong, Jia-Min, E-mail: jmgong@yeah.net; Hui, Zhan-Qiang
2014-07-01
We study thermal quantum discord (TQD) in the Heisenberg chain with spin site or magnetic impurity. The former one of which may induce inhomogeneous exchange interactions between the neighboring spins, while the latter one may model a spin chain with nonuniform magnetic field. In contrast to one's traditional understanding, we found that the spin impurity can be used to enhance the TQD greatly for all the bipartition schemes of the chain, while the magnetic impurity located on one spin can make the TQD between the other two spins approaching its maximum 1 for the antiferromagnetic chain.
Spin supersolid in an anisotropic spin-one Heisenberg chain.
Sengupta, P; Batista, C D
2007-11-23
We consider an S=1 Heisenberg chain with strong exchange (Delta=J(z)/J(perpendicular)) and single-ion uniaxial anisotropy (D) in a magnetic field (B) along the symmetry axis. The low-energy spectrum is described by an effective S=1/2 XXZ model that acts on two different low-energy sectors for a finite range of fields. The vacuum of each sector exhibits Ising-like antiferromagnetic ordering coexisting with the finite spin stiffness obtained from the exact solution of the XXZ model. In this way, we demonstrate the existence of a spin supersolid phase. We also compute the full Delta-B quantum phase diagram using a quantum Monte Carlo method.
Decoherence in quantum spin systems
De Raedt, H; Dobrovitski, VV; Landau, DP; Lewis, SP; Schuttler, HB
2003-01-01
Computer simulations of decoherence in quantum spin systems require the solution of the time-dependent Schrodinger equation for interacting quantum spin systems over extended periods of time. We use exact diagonalization, the Chebyshev polynomial technique, four Suzuki-formula algorithms, and the sh
Spin Chains and Gustafson's Integrals
Derkachov, S E
2016-01-01
The Gustafson's integrals are the multidimensional generalization of the classical Mellin--Barnes integrals. We show that some of these integrals arise from relations between matrix elements in the Sklyanin's representation of Separated Variables in the spin chain models. We also present several new integrals.
Kono, Y; Sakakibara, T; Aoyama, C P; Hotta, C; Turnbull, M M; Landee, C P; Takano, Y
2015-01-23
High-precision dc magnetization measurements have been made on Cu(C4H4N2) (NO3)2 in magnetic fields up to 14.7 T, slightly above the saturation field Hs=13.97 T, in the temperature range from 0.08 to 15 K. The magnetization curve and differential susceptibility at the lowest temperature show excellent agreement with exact theoretical results for the spin-1/2 Heisenberg antiferromagnet in one dimension. A broad peak is observed in magnetization measured as a function of temperature, signaling a crossover to a low-temperature Tomonaga-Luttinger-liquid regime. With an increasing field, the peak moves gradually to lower temperatures, compressing the regime, and, at Hs, the magnetization exhibits a strong upturn. This quantum critical behavior of the magnetization and that of the specific heat withstand quantitative tests against theory, demonstrating that the material is a practically perfect one-dimensional spin-1/2 Heisenberg antiferromagnet.
Quantum Correlations in Heisenberg XY Chain
Institute of Scientific and Technical Information of China (English)
ZHU Yin-Yan; ZHANG Yong
2013-01-01
Quantum correlations measured by quantum discord (QD),measurement-induced distance (MID),and geometric measure of quantum discord (GMQD) in two-qubit Heisenberg XY spin chain are investigated.The effects of DM interaction and anisotropic on the three correlations are considered.Characteristics of various correlation measures for the two-qubit states are compared.The increasing Dz increases QD,MID and GMQD monotonously while the increasing anisotropy both increases and decreases QD and GMQD.The three quantum correlations are always existent at very high temperature.MID is always larger than QD,but there is no definite ordering between QD and GMQD.
BPS Monopoles and Open Spin Chains
Doikou, Anastasia
2010-01-01
We construct SU(n+1) BPS monopoles with minimal symmetry breaking by solving the full Weyl equation. In this context, we explore and discuss the existence of an open spin chain-like part within the Weyl equation. For instance, in the SU(3) case the relevant spin chain is the 2-site spin 1/2 XXX chain with open boundary conditions. We exploit the existence of such a spin chain part in order to solve the full Weyl equation.
Quantum spin liquids: a review
Savary, Lucile; Balents, Leon
2017-01-01
Quantum spin liquids may be considered ‘quantum disordered’ ground states of spin systems, in which zero-point fluctuations are so strong that they prevent conventional magnetic long-range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, which is of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects, such as non-local excitations, topological properties, and more. In this review, we discuss the nature of such phases and their properties based on paradigmatic models and general arguments, and introduce theoretical technology such as gauge theory and partons, which are conveniently used in the study of quantum spin liquids. An overview is given of the different types of quantum spin liquids and the models and theories used to describe them. We also provide a guide to the current status of experiments in relation to study quantum spin liquids, and to the diverse probes used therein.
Quantum information storage and state transfer based on spin systems
Song, Z
2004-01-01
The idea of quantum state storage is generalized to describe the coherent transfer of quantum information through a coherent data bus. In this universal framework, we comprehensively review our recent systematical investigations to explore the possibility of implementing the physical processes of quantum information storage and state transfer by using quantum spin systems, which may be an isotropic antiferromagnetic spin ladder system or a ferromagnetic Heisenberg spin chain. Our studies emphasize the physical mechanisms and the fundamental problems behind the various protocols for the storage and transfer of quantum information in solid state systems.
Spin network quantum simulator
Energy Technology Data Exchange (ETDEWEB)
Marzuoli, Annalisa; Rasetti, Mario
2002-12-30
We propose a general setting for a universal representation of the quantum structure on which quantum information stands, whose dynamical evolution (information manipulation) is based on angular momentum recoupling theory. Such scheme complies with the notion of 'quantum simulator' in the sense of Feynman, and is shown to be related with the topological quantum field theoretical approach to quantum computation.
Erlingsson, S.I.
2003-01-01
The main theme of this thesis is the hyperfine interaction between the many lattice nuclear spins and electron spins localized in GaAs quantum dots. This interaction is an intrinsic property of the material. Despite the fact that this interaction is rather weak, it can, as shown in this thesis, stro
Spin chains and string theory.
Kruczenski, Martin
2004-10-15
Recently, an important test of the anti de Sitter/conformal field theory correspondence has been done using rotating strings with two angular momenta. We show that such a test can be described more generally as the agreement between two actions: one a low energy description of a spin chain appearing in the field theory side, and the other a limit of the string action in AdS5xS5. This gives a map between the mean value of the spin in the boundary theory and the position of the string in the bulk, and shows how a string action can emerge from a gauge theory in the large-N limit.
Quantum state transfer in a q-deformed chain
Energy Technology Data Exchange (ETDEWEB)
L' Innocente, Sonia [Dipartimento di Matematica ed Informatica, Universita di Camerino, 62032 Camerino (Italy); Lupo, Cosmo; Mancini, Stefano [Dipartimento di Fisica, Universita di Camerino, 62032 Camerino (Italy)], E-mail: sonia.linnocente@unicam.it, E-mail: cosmo.lupo@unicam.it, E-mail: stefano.mancini@unicam.it
2009-11-27
We investigate the quantum state transfer in a chain of particles satisfying the q-deformed oscillators algebra. This general algebraic setting includes the spin chain and the bosonic chain as limiting cases. We study conditions for perfect state transfer depending on the number of sites and excitations on the chain. They are formulated by means of irreducible representations of a quantum algebra realized through Jordan-Schwinger maps. Playing with deformation parameters, we can study the effects of nonlinear perturbations or interpolate between the spin and bosonic chains.
Entanglement Enhancement in an XY Spin Chain
Institute of Scientific and Technical Information of China (English)
SU Xiao-Qiang
2011-01-01
We study evolution of entanglement in an XY-type spin channel and find that the entanglement can be enhanced by the spin channel. The parameter regions of the initial states for different numbers of sites are obtained.Furthermore, we consider a common spin environment coupling to the spin chains and find that the entanglement enhancement can also be implemented only for the chains with the odd numbers of sites.%@@ We study evolution of entanglement in an XY-type spin channel and find that the entanglement can be enhanced by the spin channel.The parameter regions of the initial states for different numbers of sites are obtained.Furthermore,we consider a common spin environment coupling to the spin chains and find that the entanglement enhancement can also be implemented only for the chains with the odd numbers of sites.
Systematic classical continuum limits of integrable spin chains and emerging novel dualities
Avan, Jean; Sfetsos, Konstadinos
2010-01-01
We examine certain classical continuum long wave-length limits of prototype integrable quantum spin chains. We define the corresponding construction of classical continuum Lax operators. Our discussion starts with the XXX chain, the anisotropic Heisenberg model and their generalizations and extends to the generic isotropic and anisotropic gl_n magnets. Certain classical and quantum integrable models emerging from special "dualities" of quantum spin chains, parametrized by c-number matrices, are also presented.
Directory of Open Access Journals (Sweden)
Tetsuo Deguchi
2011-06-01
Full Text Available We show some symmetry relations among the correlation functions of the integrable higher-spin XXX and XXZ spin chains, where we explicitly evaluate the multiple integrals representing the one-point functions in the spin-1 case. We review the multiple-integral representations of correlation functions for the integrable higher-spin XXZ chains derived in a region of the massless regime including the anti-ferromagnetic point. Here we make use of the gauge transformations between the symmetric and asymmetric R-matrices, which correspond to the principal and homogeneous gradings, respectively, and we send the inhomogeneous parameters to the set of complete 2s-strings. We also give a numerical support for the analytical expression of the one-point functions in the spin-1 case.
Fatollahi, Amir H
2016-01-01
The general theoretical ground for the models based on the compact angle coordinates is presented. It is observed that the proper dependence on compact coordinates has to be through the group elements and is achieved most naturally in a discrete-time formulation of the theory. By the construction, the discrete worldline inlaid by compact coordinates resembles the spin chains of magnetic systems. As examples, the models based on the groups U(1), $\\mathbb{Z}_N$ and SU(2) are explicitly constructed and their exact energy spectra are obtained. As the consequence of minima in the spectra, the models exhibit a phase transition of first-order. The dynamics by U(1) group is attempted to be fitted to the proposed role for monopoles in the dual Meissner effect of confinement mechanism.
Energy Technology Data Exchange (ETDEWEB)
Fatollahi, Amir H. [Alzahra University, Department of Physics, P. O. Box 19938, Tehran (Iran, Islamic Republic of)
2017-03-15
The general theoretical ground for models based on compact angle coordinates is presented. It is observed that the proper dependence on compact coordinates has to be through the group elements and is achieved most naturally in a discrete-time formulation of the theory. By the construction, the discrete worldline inlaid by compact coordinates resembles the spin chains of magnetic systems. As examples, the models based on the groups U(1), Z{sub N} and SU(2) are explicitly constructed and their exact energy spectra are obtained. As the consequence of the minima in the spectra, the models exhibit a phase transition of first order. We attempt to fit the dynamics by the U(1) group to the proposed role for monopoles in the dual Meissner effect of the confinement mechanism. (orig.)
Spin squeezing and quantum correlations
Indian Academy of Sciences (India)
K S Mallesh; Swarnamala Sirsi; Mahmoud A A Sbaih; P N Deepak; G Ramachandran
2002-08-01
We discuss the notion of spin squeezing considering two mutually exclusive classes of spin- states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin- states using 2 spinors oriented along different axes. Taking the case of = 1, we show that the `non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.
Extended cluster spin-1/2 XXZ chain
Tahvili, Masoumeh; Mahdavifar, Saeed
2017-01-01
We study the quantum phase transitions in the extended cluster spin-1/2 XXZ chain, which is equivalent to a 1D spin-1/2 XXZ model with three-spin interaction. The ground state phase diagram of the 1D spin-1/2 anisotropic XXZ model is known. Depending on the value of the anisotropy parameter, the ground state exhibits the ordering of the Luttinger liquid (LL), the Neel and the saturated ferromagnetic phases. In the absence of the anisotropy, it was shown that the three-spin interaction induces a quantum phase transition between two kinds of the LL phases. In the presence of the anisotropy, by using the analytical and numerical methods, the extended ground state phase diagram of the model is obtained.
Bethe vectors for XXX-spin chain
Burdík, Čestmír; Fuksa, Jan; Isaev, Alexei
2014-11-01
The paper deals with algebraic Bethe ansatz for XXX-spin chain. Generators of Yang-Baxter algebra are expressed in basis of free fermions and used to calculate explicit form of Bethe vectors. Their relation to N-component models is used to prove conjecture about their form in general. Some remarks on inhomogeneous XXX-spin chain are included.
Symmetric Telecloning and Entanglement Distribution of Spin Quantum States
Institute of Scientific and Technical Information of China (English)
WANG Qiong; LI Ji-Xin; ZANG Hao-Sheng
2008-01-01
@@ We propose a physical realization of symmetric telecloning machine for spin quantum states. The concept of area average fidelity is introduced to describe the telecloning quality. It is indicated that for certain input states this quantity may come to an enough high level to satisfy the need of quantum information processing. We also study the properties of entanglement distribution via the spin chain for arbitrary two-qubit entangled pure states as inputs and find that the decay ratio of entanglement for the output states is only determined by the parameters of spin chain and waiting time, independent of the initial input states.
Indian Academy of Sciences (India)
Victor Mukherjee; Uma Divakaran; Amit Dutta; Diptiman Sen
2008-08-01
In this paper we review the quenching dynamics of a quantum spin-1/2 chain in the presence of a transverse field, when the transverse field or the anisotropic interaction is quenched at a slow but uniform rate. We also extend the results to the cases in which the system starts with any arbitrary initial condition as opposed to the initial fully magnetically aligned state which has been extensively studied earlier. The evolution is non-adiabatic in the time interval when the parameters are close to their critical values, and is adiabatic otherwise. The density of defects produced due to non-adiabatic transitions is calculated by mapping the many-particle system to an equivalent Landau–Zener problem. We show that in one dimension the density of defects in the final state scales as $1/\\sqrt{}$ irrespective of the initial condition, where is the quenching time-scale. However, the magnitude of density of defects is found to depend on the initial condition.
Liu, Guang-Hua; You, Wen-Long; Li, Wei; Su, Gang
2015-04-29
Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform Dzyaloshinskii-Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1; while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually.
Spin waves and spin instabilities in quantum plasmas
Andreev, P A
2014-01-01
We describe main ideas of method of many-particle quantum hydrodynamics allows to derive equations for description of quantum plasma evolution. We also present definitions of collective quantum variables suitable for quantum plasmas. We show that evolution of magnetic moments (spins) in quantum plasmas leads to several new branches of wave dispersion: spin-electromagnetic plasma waves and self-consistent spin waves. Propagation of neutron beams through quantum plasmas is also considered. Instabilities appearing due to interaction of magnetic moments of neutrons with plasma are described.
A Quantum Monte Carlo Study on Mixed-Spin Chains of 1／2-1／2-1-1 and 3／2-3／2-1-1
Institute of Scientific and Technical Information of China (English)
XUZhao-Xin; ZHANGJun; YINGHe-Ping
2003-01-01
The ground-state and thermodynamic properties of quantum mixed-spin chains of 1/2-1/2-1-1 and 3/2-3/2-1-1 are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it hastwo phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain,the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameter α=J2/J1.
Introduction to quantum spin systems
Directory of Open Access Journals (Sweden)
A. Langari
2008-06-01
Full Text Available This manuscript is the collection of lectures given in the summer school on strongly correlated electron systems held at Isfahan university of technology, June 2007. A short overview on quantum magnetism and spin systems is presented. The numerical exact diagonalization (Lanczos alghorithm is explained in a pedagogical ground. This is a method to get some ground state properties on finite cluster of lattice models. Two extensions of Lanczos method to get the excited states and also finite temperature properties of quantum models are also explained. The basic notions of quantum phase transition is discussed in term of Ising model in transverse field. Its phase diagram and critical properties are explained using the quantum renormalization group approach. Most of the topics are in tutorial level with hints to recent research activities.
Experimental Realization of a Quantum Spin Pump
DEFF Research Database (Denmark)
Watson, Susan; Potok, R.; M. Marcus, C.;
2003-01-01
We demonstrate the operation of a quantum spin pump based on cyclic radio-frequency excitation of a GaAs quantum dot, including the ability to pump pure spin without pumping charge. The device takes advantage of bidirectional mesoscopic fluctuations of pumped current, made spin......-dependent by the application of an in-plane Zeeman field. Spin currents are measured by placing the pump in a focusing geometry with a spin-selective collector....
Entanglement in spin-one Heisenberg chains
Wang, X G; Sun, Z; Li, Y Q; Wang, XiaoGuang; Li, HaiBin; Sun, Zhe; Li, You-Quan
2005-01-01
By using the concept of negativity, we study entanglement in spin-one Heisenberg chains. Both the bilinear chain and the bilinear-biquadratic chain are considered. Due to the SU(2) symmetry, the negativity can be determined by two correlators, which greatly facilitate the study of entanglement properties. Analytical results of negativity are obtained in the bilinear model up to four spins and the two-spin bilinear-biquadratic model, and numerical results of negativity are presented. We determine the threshold temperature before which the thermal state is doomed to be entangled.
Path integrals for dimerized quantum spin systems
Energy Technology Data Exchange (ETDEWEB)
Foussats, Adriana, E-mail: afoussats@gmail.co [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Greco, Andres [Facultad de Ciencias Exactas, Ingenieria y Agrimensura and Instituto de Fisica Rosario (UNR-CONICET), Av. Pellegrini 250, 2000 Rosario (Argentina); Muramatsu, Alejandro [Institut fuer Theoretische Physik III, Universitaet Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart (Germany)
2011-01-11
Dimerized quantum spin systems may appear under several circumstances, e.g. by a modulation of the antiferromagnetic exchange coupling in space, or in frustrated quantum antiferromagnets. In general, such systems display a quantum phase transition to a Neel state as a function of a suitable coupling constant. We present here two path-integral formulations appropriate for spin S=1/2 dimerized systems. The first one deals with a description of the dimers degrees of freedom in an SO(4) manifold, while the second one provides a path-integral for the bond-operators introduced by Sachdev and Bhatt. The path-integral quantization is performed using the Faddeev-Jackiw symplectic formalism for constrained systems, such that the measures and constraints that result from the algebra of the operators is provided in both cases. As an example we consider a spin-Peierls chain, and show how to arrive at the corresponding field-theory, starting with both an SO(4) formulation and bond-operators.
Spin photocurrents in quantum wells
Ganichev, S D
2003-01-01
Spin photocurrents generated by homogeneous optical excitation with circularly polarized radiation in quantum wells (QWs) are reviewed. The absorption of circularly polarized light results in optical spin orientation due to the transfer of the angular momentum of photons to electrons of a two-dimensional electron gas. It is shown that in QWs belonging to one of the gyrotropic crystal classes a non-equilibrium spin polarization of uniformly distributed electrons causes a directed motion of electrons in the plane of the QW. A characteristic feature of this electric current, which occurs in unbiased samples, is that it reverses its direction upon changing the radiation helicity from left-handed to right-handed and vice versa. Two microscopic mechanisms are responsible for the occurrence of an electric current linked to a uniform spin polarization in a QW: the spin polarization-induced circular photogalvanic effect and the spin-galvanic effect. In both effects the current flow is driven by an asymmetric distribut...
Semiconductor quantum dots for electron spin qubits
van der Wiel, Wilfred Gerard; Stopa, M.; Kodera, T.; Hatano, T.; Tarucha, S.
2006-01-01
We report on our recent progress in applying semiconductor quantum dots for spin-based quantum computation, as proposed by Loss and DiVincenzo (1998 Phys. Rev. A 57 120). For the purpose of single-electron spin resonance, we study different types of single quantum dot devices that are designed for
Quantum spin transport in semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Schindler, Christoph
2012-05-15
In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.
Free spin quantum computation with semiconductor nanostructures
Zhang, W M; Soo, C; Zhang, Wei-Min; Wu, Yin-Zhong; Soo, Chopin
2005-01-01
Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.
Spin transport through quantum dots
Energy Technology Data Exchange (ETDEWEB)
Lima, A.T. da Cunha; Anda, Enrique V. [Pontificia Univ. Catolica do Rio de Janeiro (PUC-Rio), RJ (Brazil)
2003-07-01
Full text: We investigate the spin polarized transport properties of a nanoscopic device constituted by a quantum dot connected to two leads. The electrical current circulates with a spin polarization that is modulated via a gate potential that controls the intensity of the spin-orbit coupling, the Rashba effect. We study a polarized field-effect transistor when one of its parts is constituted by a small quantum dot, which energies are controlled by another gate potential operating inside the confined region. The high confinement and correlation suffered by the charges inside the dot gives rise to novel phenomena. We show that through the manipulation of the gate potential applied to the dot it is possible to control, in a very efficient way, the intensity and polarization of the current that goes along the system. Other crucial parameters to be varied in order to understand the behavior of this system are the intensity of the external applied electric and magnetic field. The system is represented by the Anderson Impurity Hamiltonian summed to a spin-orbit interaction, which describes the Rashba effect. To obtain the current of this out-of-equilibrium system we use the Keldysh formalism.The solution of the Green function are compatible with the Coulomb blockade regime. We show that under the effect of a external magnetic field, if the dot is small enough the device operates as a complete spin filter that can be controlled by the gate potential. The behavior of this device when it is injected into it a polarized current and modulated by the Rashba effect is as well studied. (author)
Open quantum spin systems in semiconductor quantum dots and atoms in optical lattices
Energy Technology Data Exchange (ETDEWEB)
Schwager, Heike
2012-07-04
In this Thesis, we study open quantum spin systems from different perspectives. The first part is motivated by technological challenges of quantum computation. An important building block for quantum computation and quantum communication networks is an interface between material qubits for storage and data processing and travelling photonic qubits for communication. We propose the realisation of a quantum interface between a travelling-wave light field and the nuclear spins in a quantum dot strongly coupled to a cavity. Our scheme is robust against cavity decay as it uses the decay of the cavity to achieve the coupling between nuclear spins and the travelling-wave light fields. A prerequiste for such a quantum interface is a highly polarized ensemble of nuclear spins. High polarization of the nuclear spin ensemble is moreover highly desirable as it protects the potential electron spin qubit from decoherence. Here we present the theoretical description of an experiment in which highly asymmetric dynamic nuclear spin pumping is observed in a single self-assembled InGaAs quantum dot. The second part of this Thesis is devoted to fundamental studies of dissipative spin systems. We study general one-dimensional spin chains under dissipation and propose a scheme to realize a quantum spin system using ultracold atoms in an optical lattice in which both coherent interaction and dissipation can be engineered and controlled. This system enables the study of non-equilibrium and steady state physics of open and driven spin systems. We find, that the steady state expectation values of different spin models exhibit discontinuous behaviour at degeneracy points of the Hamiltonian in the limit of weak dissipation. This effect can be used to dissipatively probe the spectrum of the Hamiltonian. We moreover study spin models under the aspect of state preparation and show that dissipation drives certain spin models into highly entangled state. Finally, we study a spin chain with
Circuit quantum electrodynamics with a spin qubit.
Petersson, K D; McFaul, L W; Schroer, M D; Jung, M; Taylor, J M; Houck, A A; Petta, J R
2012-10-18
Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.
Quantum Optimization of Fully Connected Spin Glasses
Venturelli, Davide; Mandrà, Salvatore; Knysh, Sergey; O'Gorman, Bryan; Biswas, Rupak; Smelyanskiy, Vadim
2015-07-01
Many NP-hard problems can be seen as the task of finding a ground state of a disordered highly connected Ising spin glass. If solutions are sought by means of quantum annealing, it is often necessary to represent those graphs in the annealer's hardware by means of the graph-minor embedding technique, generating a final Hamiltonian consisting of coupled chains of ferromagnetically bound spins, whose binding energy is a free parameter. In order to investigate the effect of embedding on problems of interest, the fully connected Sherrington-Kirkpatrick model with random ±1 couplings is programmed on the D-Wave TwoTM annealer using up to 270 qubits interacting on a Chimera-type graph. We present the best embedding prescriptions for encoding the Sherrington-Kirkpatrick problem in the Chimera graph. The results indicate that the optimal choice of embedding parameters could be associated with the emergence of the spin-glass phase of the embedded problem, whose presence was previously uncertain. This optimal parameter setting allows the performance of the quantum annealer to compete with (and potentially outperform, in the absence of analog control errors) optimized simulated annealing algorithms.
Quantum Optimization of Fully Connected Spin Glasses
Directory of Open Access Journals (Sweden)
Davide Venturelli
2015-09-01
Full Text Available Many NP-hard problems can be seen as the task of finding a ground state of a disordered highly connected Ising spin glass. If solutions are sought by means of quantum annealing, it is often necessary to represent those graphs in the annealer’s hardware by means of the graph-minor embedding technique, generating a final Hamiltonian consisting of coupled chains of ferromagnetically bound spins, whose binding energy is a free parameter. In order to investigate the effect of embedding on problems of interest, the fully connected Sherrington-Kirkpatrick model with random ±1 couplings is programmed on the D-Wave Two^{TM} annealer using up to 270 qubits interacting on a Chimera-type graph. We present the best embedding prescriptions for encoding the Sherrington-Kirkpatrick problem in the Chimera graph. The results indicate that the optimal choice of embedding parameters could be associated with the emergence of the spin-glass phase of the embedded problem, whose presence was previously uncertain. This optimal parameter setting allows the performance of the quantum annealer to compete with (and potentially outperform, in the absence of analog control errors optimized simulated annealing algorithms.
Spin flips and quantum information for anti-parallel spins
Gisin, Nicolas
1999-01-01
We consider two different ways to encode quantum information, by parallel or anti-parallel pairs of spins. We find that there is more information in the anti-parallel ones. This purely quantum mechanical effect is due to entanglement, not of the states but occuring in the course of the measuring process. We also introduce a range of quantum information processing machines, such as spin-flip and anti-cloning.
Implementation of State Transfer Hamiltonians in Spin Chains with Magnetic Resonance Techniques
Cappellaro, Paola
2014-01-01
Nuclear spin systems and magnetic resonance techniques have provided a fertile platform for experimental investigation of quantum state transfer in spin chains. From the first observation of polarization transfer, predating the formal definition of quantum state transfer, to the realization of state transfer simulations in small molecules and in larger solid-state spin systems, the experiments have drawn on the strengths of nuclear magnetic resonance (NMR), in particular on its long history o...
Oeiras, R. Y.; da Silva, E. Z.
2014-04-01
Carbon linear atomic chains attached to graphene have experimentally been produced. Motivated by these results, we study the nature of the carbon bonds in these nanowires and how it affects their electrical properties. In the present study we investigate chains with different numbers of atoms and we observe that nanowires with odd number of atoms present a distinct behavior than the ones with even numbers. Using graphene nanoribbons as leads, we identify differences in the quantum transport of the chains with the consequence that even and odd numbered chains have low and high electrical conduction, respectively. We also noted a dependence of current with the wire size. We study this unexpected behavior using a combination of first principles calculations and simple models based on chemical bond theory. From our studies, the electrons of carbon nanowires present a quasi-free electron behavior and this explains qualitatively the high electrical conduction and the bond lengths with unexpected values for the case of odd nanowires. Our study also allows the understanding of the electric conduction dependence with the number of atoms and their parity in the chain. In the case of odd number chains a proposed π-bond (MpB) model describes unsaturated carbons that introduce a mobile π-bond that changes dramatically the structure and transport properties of these wires. Our results indicate that the nature of bonds plays the main role in the oscillation of quantum electrical conduction for chains with even and odd number of atoms and also that nanowires bonded to graphene nanoribbons behave as a quasi-free electron system, suggesting that this behavior is general and it could also remain if the chains are bonded to other materials.
Energy Technology Data Exchange (ETDEWEB)
Oeiras, R. Y.; Silva, E. Z. da [Institute of Physics “Gleb Wataghin”, University of Campinas-Unicamp, 13083-859 Campinas, SP (Brazil)
2014-04-07
Carbon linear atomic chains attached to graphene have experimentally been produced. Motivated by these results, we study the nature of the carbon bonds in these nanowires and how it affects their electrical properties. In the present study we investigate chains with different numbers of atoms and we observe that nanowires with odd number of atoms present a distinct behavior than the ones with even numbers. Using graphene nanoribbons as leads, we identify differences in the quantum transport of the chains with the consequence that even and odd numbered chains have low and high electrical conduction, respectively. We also noted a dependence of current with the wire size. We study this unexpected behavior using a combination of first principles calculations and simple models based on chemical bond theory. From our studies, the electrons of carbon nanowires present a quasi-free electron behavior and this explains qualitatively the high electrical conduction and the bond lengths with unexpected values for the case of odd nanowires. Our study also allows the understanding of the electric conduction dependence with the number of atoms and their parity in the chain. In the case of odd number chains a proposed π-bond (MpB) model describes unsaturated carbons that introduce a mobile π-bond that changes dramatically the structure and transport properties of these wires. Our results indicate that the nature of bonds plays the main role in the oscillation of quantum electrical conduction for chains with even and odd number of atoms and also that nanowires bonded to graphene nanoribbons behave as a quasi-free electron system, suggesting that this behavior is general and it could also remain if the chains are bonded to other materials.
Magnetic monopoles in quantum spin ice
Petrova, Olga; Moessner, Roderich; Sondhi, Shivaji
Typical spin ice materials can be modeled using classical Ising spins. The geometric frustration of the pyrochlore lattice causes the spins to satisfy ice rules, whereas a violation of the ice constraint constitutes an excitation. Flipping adjacent spins fractionalizes the excitation into two monopoles. Long range dipolar spin couplings result in Coulombic interactions between charges, while the leading effect of quantum fluctuations is to provide the monopoles with kinetic energy. We study the effect of adding quantum dynamics to spin ice, a well-known classical spin liquid, with a particular view of how to best detect its presence in experiment. For the weakly diluted quantum spin ice, we find a particularly crisp phenomenon, namely, the emergence of hydrogenic excited states in which a magnetic monopole is bound to a vacancy at various distances.
Enhancement of entanglement transfer in a spin chain by phase shift control
Maruyama, K; Nori, F
2006-01-01
We study the effect of a phase shift on the amount of transferrable two-spin entanglement in a spin chain. We consider a ferromagnetic Heisenberg/XY spin chain, both numerically and analytically, and two mechanisms to generate a phase shift, the Aharonov-Casher effect and the Dzyaloshinskii-Moriya interaction. In both cases, the maximum attainable entanglement is shown to be significantly enhanced, suggesting its potential usefulness in quantum information processing.
Effect of Dzialoshinski-Moriya interaction on thermal entanglement of a mixed-spin chain
Institute of Scientific and Technical Information of China (English)
2008-01-01
The effect of Dzialoshinski-Moriya (DM) interaction on thermal entanglement of a mixed-spin chain in an external magnetic field is investigated. It is found that DM interaction may enhance quantum thermal entanglement to a maximal value even though the magnetic field plays a positive role in shrinking thermal entanglement in the mixed-spin chain. Furthermore, the effect of inhomogeneity of the magnetic field on quantum entanglement is analyzed. Our analysis will shed some light on the understanding of the effect of the DM interaction on thermal entanglement of a mixed-spin chain.
Quantum Spin Transport in Mesoscopic Interferometer
Directory of Open Access Journals (Sweden)
Zein W. A.
2007-10-01
Full Text Available Spin-dependent conductance of ballistic mesoscopic interferometer is investigated. The quantum interferometer is in the form of ring, in which a quantum dot is embedded in one arm. This quantum dot is connected to one lead via tunnel barrier. Both Aharonov- Casher and Aharonov-Bohm e ects are studied. Our results confirm the interplay of spin-orbit coupling and quantum interference e ects in such confined quantum systems. This investigation is valuable for spintronics application, for example, quantum information processing.
Ground-State and Thermal Entanglement in Three-Spin Heisenberg-XXZ Chain with Three-Spin Interaction
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The entanglement properties of a three-spin X X Z Heisenberg chain with three-spin interaction are studied by means of concurrence of pairwise entanglement. We show that ground-state pairwise entanglement, pairwise thermal entanglement, or quantum phase transition is not present in antiferromagnetic spin chain. For the ferromagnetic case, quantum phase transition takes place at △ = 1 for anisotropic interaction and at some values of three-spin coupling strength, and pairwise thermal entanglement increases when the value of J/T increases and with anisotropic interaction and three-spin interaction decrease. In addition, we find that increasing the anisotropic interaction and the three-spin interaction will decrease critical temperature.
Electron Spins in Semiconductor Quantum Dots
Hanson, R.
2005-01-01
This thesis describes a series of experiments aimed at understanding and controlling the behavior of the spin degree of freedom of single electrons, confined in semiconductor quantum dots. This research work is motivated by the prospects of using the electron spin as a quantum bit (qubit), the basic
Integrable Deformations of the XXZ Spin Chain
Beisert, Niklas; de Leeuw, Marius; Loebbert, Florian
2013-01-01
We consider integrable deformations of the XXZ spin chain for periodic and open boundary conditions. In particular, we classify all long-range deformations and study their impact on the spectrum. As compared to the XXX case, we have the z-spin at our disposal, which induces two additional deformations: the short-range magnetic twist and a new long-range momentum-dependent twist.
Quantum state transfer in a XX chain with impurities
Energy Technology Data Exchange (ETDEWEB)
Zwick, Analia; Osenda, Omar, E-mail: zwick@famaf.unc.edu.ar, E-mail: osenda@famaf.unc.edu.ar [Facultad de Matematica, AstronomIa y Fisica, Universidad Nacional de Cordoba and IFEG-CONICET, Ciudad Universitaria, X5016LAE, Cordoba (Argentina)
2011-03-11
One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum XX chain with one impurity. The bipartite entanglement is obtained using the concurrence and the localization is analyzed using the inverse participation ratio (IPR). Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. The analysis of the IPR allows us to identify scenarios where the transmission of quantum states or entanglement can be achieved with a high degree of fidelity. In particular, we identify a regime where the transmission of quantum states between the extremes of the chain is executed in a short transmission time {approx}N/2, where N is the number of spins in the chain, and with a large fidelity.
Quantum Computing with Electron Spins in Quantum Dots
Vandersypen, L M K; Van Beveren, L H W; Elzerman, J M; Greidanus, J S; De Franceschi, S; Kouwenhoven, Leo P
2002-01-01
We present a set of concrete and realistic ideas for the implementation of a small-scale quantum computer using electron spins in lateral GaAs/AlGaAs quantum dots. Initialization is based on leads in the quantum Hall regime with tunable spin-polarization. Read-out hinges on spin-to-charge conversion via spin-selective tunneling to or from the leads, followed by measurement of the number of electron charges on the dot via a charge detector. Single-qubit manipulation relies on a microfabricated wire located close to the quantum dot, and two-qubit interactions are controlled via the tunnel barrier connecting the respective quantum dots. Based on these ideas, we have begun a series of experiments in order to demonstrate unitary control and to measure the coherence time of individual electron spins in quantum dots.
Shortcuts to adiabaticity in cutting a spin chain
Ren, Feng-Hua; Wang, Zhao-Ming; Gu, Yong-Jian
2017-01-01
"Shortcuts to adiabaticity" represents a strategy for accelerating a quantum adiabatic process, is useful for preparing or manipulating a quantum state. In this paper, we investigate the adiabaticity in the dynamics of an XY spin chain. During the process of cutting one long chain into two short chains, a "shortcut" can be obtained by applying a sequence of external pulses. The fidelity which measures the adiabaticity can be dramatically enhanced by increasing the pulse strength or pulse duration time. This reliability can be kept for different types of pulses, such as random pulse time interval or random strength. The free choice of the pulse can be explained by the adiabatic representation of the Hamiltonian, and it shows that the control effects are determined by the integral of the control function in the time domain.
Spectrum of a duality-twisted Ising quantum chain
Grimm, U
2002-01-01
The Ising quantum chain with a peculiar twisted boundary condition is considered. This boundary condition, first introduced in the framework of the spin-1/2 XXZ Heisenberg quantum chain, is related to the duality transformation, which becomes a symmetry of the model at the critical point. Thus, at the critical point, the Ising quantum chain with the duality-twisted boundary is translationally invariant, similar as in the case of the usual periodic or antiperiodic boundary conditions. The complete energy spectrum of the Ising quantum chain is calculated analytically for finite systems, and the conformal properties of the scaling limit are investigated. This provides an explicit example of a conformal twisted boundary condition and a corresponding generalised twisted partition function.
Quantum Monte Carlo Study of Random Antiferromagnetic Heisenberg Chain
Todo, Synge; Kato, Kiyoshi; Takayama, Hajime
1998-01-01
Effects of randomness on the spin-1/2 and 1 antiferromagnetic Heisenberg chains are studied using the quantum Monte Carlo method with the continuous-time loop algorithm. We precisely calculated the uniform susceptibility, string order parameter, spatial and temporal correlation length, and the dynamical exponent, and obtained a phase diagram. The generalization of the continuous-time loop algorithm for the systems with higher-S spins is also presented.
Deformed Fredkin Spin Chain with Extensive Entanglement
Salberger, Olof; Zhang, Zhao; Katsura, Hosho; Klich, Israel; Korepin, Vladimir
2016-01-01
We introduce a new spin chain which is a deformation of the Fredkin spin chain and has a phase transition between bounded and extensive entanglement entropy scaling. In this chain, spins have a local interaction of three nearest neighbors. The Hamiltonian is frustration-free and its ground state can be described analytically as a weighted superposition of Dyck paths. In the purely spin $1/2$ case, the entanglement entropy obeys an area law: it is bounded from above by a constant, when the size of the block $n$ increases (and $t>1$). When a local color degree of freedom is introduced the entanglement entropy increases linearly with the size of the block (and $t>1$). The entanglement entropy of half of the chain is tightly bounded by ${ n}\\log s$ where $n$ is the size of the block, and $s$ is the number of colors. Our chain fosters a new example for a significant boost to entropy and for the existence of the associated critical rainbow phase where the entanglement entropy scales with volume that has recently be...
Excitation of bond-alternating spin-1/2 Heisenberg chains by tunnelling electrons.
Gauyacq, J-P; Lorente, N
2014-10-01
Inelastic electron tunneling spectra (IETS) are evaluated for spin-1/2 Heisenberg chains showing different phases of their spin ordering. The spin ordering is controlled by the value of the two different Heisenberg couplings on the two sides of each of the chain's atoms (bond-alternating chains). The perfect anti-ferromagnetic phase, i.e. a unique exchange coupling, marks a topological quantum phase transition (TQPT) of the bond-alternating chain. Our calculations show that the TQPT is recognizable in the excited states of the chain and hence that IETS is in principle capable of discriminating the phases. We show that perfectly symmetric chains, such as closed rings mimicking infinite chains, yield the same spectra on both sides of the TQPT and IETS cannot reveal the nature of the spin phase. However, for finite size open chains, both sides of the TQPT are associated with different IETS spectra, especially on the edge atoms, thus outlining the transition.
Effects of Intrinsic Decoherence on Information Transport in a Spin Chain
Institute of Scientific and Technical Information of China (English)
ZENG Tian-Hai; SHAO Bin; ZOU Jian
2009-01-01
Considering Milburn's intrinsic decoherence effect on quantum communication through a spin chain, we show that the transfer quality for quantum state and entanglement will obviously decrease with the increasing intrinsic decoherence rate. Some odd chains are much higher than even ones for the state transfer efficiency. The state transfer of a long chain is very sensitive to the intrinsic decoherence, which turns out to be an obstacle for information transport.
Robustness of spin-coupling distributions for perfect quantum state transfer
Energy Technology Data Exchange (ETDEWEB)
Zwick, Analia [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Facultad de Matematica, Astronomia y Fisica and Instituto de Fisica Enrique Gaviola, Universidad Nacional de Cordoba, 5000 Cordoba (Argentina); Alvarez, Gonzalo A.; Stolze, Joachim [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Osenda, Omar [Facultad de Matematica, Astronomia y Fisica and Instituto de Fisica Enrique Gaviola, Universidad Nacional de Cordoba, 5000 Cordoba (Argentina)
2011-08-15
The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling distributions of spin chain channels designed for perfect quantum state transfer. In particular, we study the transfer of an initial state from one end of the chain to the other end. We quantify the robustness of different coupling distributions against perturbations and we relate it to the properties of the energy eigenstates and eigenvalues. We find that the localization properties of the systems play an important role for robust quantum state transfer.
Nimbalkar, Manoj; Neves, Jorge L; Elavarasi, S Begam; Yuan, Haidong; Khaneja, Navin; Dorai, Kavita; Glaser, Steffen J
2011-01-01
We study multiple-spin coherence transfers in linear Ising spin chains with nearest neighbor couplings. These constitute a model for efficient information transfers in future quantum computing devices and for many multi-dimensional experiments for the assignment of complex spectra in nuclear magnetic resonance spectroscopy. We complement prior analytic techniques for multiple-spin coherence transfers with a systematic numerical study where we obtain strong evidence that a certain analytically-motivated family of restricted controls is sufficient for time-optimality. In the case of a linear three-spin system, additional evidence suggests that prior analytic pulse sequences using this family of restricted controls are time-optimal even for arbitrary local controls. In addition, we compare the pulse sequences for linear Ising spin chains to pulse sequences for more realistic spin systems with additional long-range couplings between non-adjacent spins. We experimentally implement the derived pulse sequences in th...
Anisotropic Spin Splitting in Step Quantum Wells
Institute of Scientific and Technical Information of China (English)
HAO Ya-Fei; CHEN Yong-Hai; HAO Guo-Dong; WANG Zhan-Guo
2009-01-01
By the method of finite difference,the anisotropic spin splitting of the Alx Ga1-x As/GaAs/Aly Ga1-y As/Alx Ga1-x As step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field.We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field.The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin.The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.
Feynman propagator for spin foam quantum gravity.
Oriti, Daniele
2005-03-25
We link the notion causality with the orientation of the spin foam 2-complex. We show that all current spin foam models are orientation independent. Using the technology of evolution kernels for quantum fields on Lie groups, we construct a generalized version of spin foam models, introducing an extra proper time variable. We prove that different ranges of integration for this variable lead to different classes of spin foam models: the usual ones, interpreted as the quantum gravity analogue of the Hadamard function of quantum field theory (QFT) or as inner products between quantum gravity states; and a new class of causal models, the quantum gravity analogue of the Feynman propagator in QFT, nontrivial function of the orientation data, and implying a notion of "timeless ordering".
The entanglement negativity in random spin chains
Ruggiero, Paola; Calabrese, Pasquale
2016-01-01
We investigate the logarithmic negativity in strongly-disordered spin chains in the random-singlet phase. We focus on the spin-1/2 random Heisenberg chain and the random XX chain. We find that for two arbitrary intervals the disorder-averaged negativity and the mutual information are proportional to the number of singlets shared between the two intervals. Using the strong-disorder renormalization group (SDRG), we prove that the negativity of two adjacent intervals grows logarithmically with the intervals length. In particular, the scaling behavior is the same as in conformal field theory, but with a different prefactor. For two disjoint intervals the negativity is given by a universal simple function of the cross ratio, reflecting scale invariance. As a function of the distance of the two intervals, the negativity decays algebraically in contrast with the exponential behavior in clean models. We confirm our predictions using a numerical implementation of the SDRG method. Finally, we also implement DMRG simula...
Grimm, U; Grimm, Uwe; Schuetz, Gunter M.
1993-01-01
The finite-size scaling spectra of the spin-1/2 XXZ Heisenberg chain with toroidal boundary conditions and an even number of sites provide a projection mechanism yielding the spectra of models with a central charge c<1 including the unitary and non-unitary minimal series. Taking into account the half-integer angular momentum sectors - which correspond to chains with an odd number of sites - in many cases leads to new spinor operators appearing in the projected systems. These new sectors in the XXZ chain correspond to a new type of frustration lines in the projected minimal models. The corresponding new boundary conditions in the Hamiltonian limit are investigated for the Ising model and the 3-state Potts model and are shown to be related to duality transformations which are an additional symmetry at their self-dual critical point. By different ways of projecting systems we find models with the same central charge sharing the same operator content and modular invariant partition function which however diffe...
Topological magnon bound-states in quantum Heisenberg chains
Qin, Xizhou; Ke, Yongguan; Zhang, Li; Lee, Chaohong
2016-01-01
It is still an outstanding challenge to characterize and understand the topological features of strongly correlated states such as bound-states in interacting multi-particle quantum systems. Recently, bound states of elementary spin waves (magnons) in quantum magnets have been experimentally observed in quantum Heisenberg chains comprising ultracold Bose atoms in optical lattices. Here, we explore an unprecedented topological state called topological magnon bound-state in the quantum Heisenberg chain under cotranslational symmetry. We find that the cotranslational symmetry allows us to formulate a direct topological invariant for the multi-particle quantum states, which can be used to characterize the topological features of multi-magnon excitations. We calculate energy spectra, density distributions, correlations and topological invariants of the two-magnon bound-states and show the existence of topological magnon bound-states. Our study not only opens a new prospect to pursue topological bound-states, but a...
Adiabatic Evolution in XXX Spin Chain is Fast
Korepin, V
2004-01-01
Adiabatic theorem of quantum mechanics was used by E. Farhi, J. Goldstone, S. Gutmann and M. Sipser to design quantum algorithms of a new kind. A quantum computer evolves slowly enough, so that it remains in its instantaneous ground state, which tells the solution. We consider XXX Heisenberg spin chain. We rotate magnetic field and change its magnitude. The ground state evolves from a ferromagnetic one into a nontrivial ground state of XXX anti-ferromagnet. This adiabatic evolution goes very gently. Because of SU(2) symmetry and integrability only one mode get exited. We prove that the time of the evolution scales as a square root of number of qubits. This is faster then other known examples.
Spin dynamics and spin freezing at ferromagnetic quantum phase transitions
Schmakat, P.; Wagner, M.; Ritz, R.; Bauer, A.; Brando, M.; Deppe, M.; Duncan, W.; Duvinage, C.; Franz, C.; Geibel, C.; Grosche, F. M.; Hirschberger, M.; Hradil, K.; Meven, M.; Neubauer, A.; Schulz, M.; Senyshyn, A.; Süllow, S.; Pedersen, B.; Böni, P.; Pfleiderer, C.
2015-07-01
We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1- y Fe2+ y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1- x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.
Lopez, G V
2012-01-01
We study the simulation of a single qubit rotation and Controlled-Not gate in a solid state one-dimensional chain of nuclear spins system interacting weakly through an Ising type of interaction with a modular component of the magnetic field in the z-direction, characterized by $B_z(z,t)=Bo(z)\\cos\\delta t$. These qubits are subjected to electromagnetic pulses which determine the transition in the one or two qubits system. We use the fidelity parameter to determine the performance of the Not (N) gate and Controlled-Not (CNOT) gate as a function of the frequency parameter $\\delta$. We found that for $|\\delta|\\le 10^{-3} MHz$, these gates still have good fidelity.
Robustness of spin-coupling distributions for perfect quantum state transfer
Zwick, Analia; Stolze, Joachim; Osenda, Omar
2011-01-01
The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling distributions of spin chain channels designed for perfect quantum state transfer. In particular, we study the transfer of an initial state from one end of the chain to the other end. We quantify the robustness of different coupling distributions against perturbations and we relate it to the properties of the energy eigenstates and eigenvalues. We find that the localization properties of the systems play an important role f...
Entanglement dynamics in critical random quantum Ising chain with perturbations
Energy Technology Data Exchange (ETDEWEB)
Huang, Yichen, E-mail: ychuang@caltech.edu
2017-05-15
We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique. - Highlights: • We study the dynamical quantum phase transition between many-body localized phases. • We simulate the dynamics of a very long random spin chain with matrix product states. • We observe numerically super-logarithmic growth of entanglement entropy with time.
Quantum limited heterodyne detection of spin noise
Cronenberger, S.; Scalbert, D.
2016-09-01
Spin noise spectroscopy is a powerful technique for studying spin relaxation in semiconductors. In this article, we propose an extension of this technique based on optical heterodyne detection of spin noise, which provides several key advantages compared to conventional spin noise spectroscopy: detection of high frequency spin noise not limited by detector bandwidth or sampling rates of digitizers, quantum limited sensitivity even in case of very weak probe power, and possible amplification of the spin noise signal. Heterodyne detection of spin noise is demonstrated on insulating n-doped GaAs. From measurements of spin noise spectra up to 0.4 Tesla, we determined the distribution of g-factors, Δg/g = 0.49%.
Magnetizing and heating quantum spin ladders
Indian Academy of Sciences (India)
Andrey Zheludev
2008-11-01
Quasi-one-dimensional quantum spin liquids, such as weakly coupled even-legged S=1/2 spin ladders or spin tubes, have a singlet non-magnetic ground state and gap in the excitation spectrum. Their low-temperature properties can be described in terms of triplet massive quasiparticles. These magnons possess some unique features due to the peculiar topology of one dimension. For example, two-particle interactions totally destroy single-particle states for certain energy and momentum transfers, resulting in the so-called termination of the magnon spectrum. At high field a Bose–Einstein condensation of these magnons produces a `quantum spin solid' phase, where `conventional` antiferromagnetic order coexists with excitations that are totally outside conventional spin wave theory. At finite temperatures strong repulsion between quasiparticles leads to a universal renormalization of their masses and lifetimes. These diverse phenomena are best probed by neutron scattering experiments that directly measure the spin correlation functions and excitation spectra.
Quantum Computing with an Electron Spin Ensemble
DEFF Research Database (Denmark)
Wesenberg, Janus; Ardavan, A.; Briggs, G.A.D.
2009-01-01
We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized...
Topological basis realization for BMW algebra and Heisenberg XXZ spin chain model
Liu, Bo; Xue, Kang; Wang, Gangcheng; Liu, Ying; Sun, Chunfang
2015-04-01
In this paper, we study three-dimensional (3D) reduced Birman-Murakami-Wenzl (BMW) algebra based on topological basis theory. Several examples of BMW algebra representations are reviewed. We also discuss a special solution of BMW algebra, which can be used to construct Heisenberg XXZ model. The theory of topological basis provides a useful method to solve quantum spin chain models. It is also shown that the ground state of XXZ spin chain is superposition state of topological basis.
Thermodynamics of Inozemtsev's elliptic spin chain
Klabbers, Rob
2016-06-01
We study the thermodynamic behaviour of Inozemtsev's long-range elliptic spin chain using the Bethe ansatz equations describing the spectrum of the model in the infinite-length limit. We classify all solutions of these equations in that limit and argue which of these solutions determine the spectrum in the thermodynamic limit. Interestingly, some of the solutions are not selfconjugate, which puts the model in sharp contrast to one of the model's limiting cases, the Heisenberg XXX spin chain. Invoking the string hypothesis we derive the thermodynamic Bethe ansatz equations (TBA-equations) from which we determine the Helmholtz free energy in thermodynamic equilibrium and derive the associated Y-system. We corroborate our results by comparing numerical solutions of the TBA-equations to a direct computation of the free energy for the finite-length hamiltonian. In addition we confirm numerically the interesting conjecture put forward by Finkel and González-López that the original and supersymmetric versions of Inozemtsev's elliptic spin chain are equivalent in the thermodynamic limit.
On the semi-classical limit of scalar products of the XXZ spin chain
Jiang, Yunfeng; Brunekreef, Joren
2017-03-01
We study the scalar products between Bethe states in the XXZ spin chain with anisotropy |Δ| > 1 in the semi-classical limit where the length of the spin chain and the number of magnons tend to infinity with their ratio kept finite and fixed. Our method is a natural yet non-trivial generalization of similar methods developed for the XXX spin chain. The final result can be written in a compact form as a contour integral in terms of Faddeev's quantum dilogarithm function, which in the isotropic limit reduces to the classical dilogarithm function.
On the Semi-Classical Limit of Scalar Products of the XXZ Spin Chain
Jiang, Yunfeng
2016-01-01
We study the scalar products between Bethe states in the XXZ spin chain with anisotropy $|\\Delta|>1$ in the semi-classical limit where the length of the spin chain and the number of magnons tend to infinity with their ratio kept finite and fixed. Our method is a natural yet non-trivial generalization of similar methods developed for the XXX spin chain. The final result can be written in a compact form as a contour integral in terms of Faddeev's quantum dilogarithm function, which in the isotropic limit reduces to the classical dilogarithm function.
Weinberg, Phillip
2016-01-01
We present a new open-source Python package for exact diagonalization and quantum dynamics of spin(-photon) chains, called $\\mathcal{Q}^{\\mathrm{u}}\\!\\mathcal{S}\\mathcal{P}\\mathcal{I}\\mathcal{N}$, supporting the use of various symmetries and (imaginary) time evolution. The package is well-suited to study, among others, quantum quenches at finite and infinite times, the Eigenstate Thermalisation hypothesis, many-body localisation and other dynamical phase transitions, periodically-driven (Floquet) systems, adiabatic and counter-diabatic ramps, and spin-photon interactions. Moreover, $\\mathcal{Q}^{\\mathrm{u}}\\!\\mathcal{S}\\mathcal{P}\\mathcal{I}\\mathcal{N}$'s user-friendly interface can easily be used in combination with other Python packages which makes it amenable to a high-level customisation. We explain how to use $\\mathcal{Q}^{\\mathrm{u}}\\!\\mathcal{S}\\mathcal{P}\\mathcal{I}\\mathcal{N}$ using three detailed examples: (i) adiabatic ramping of parameters in the many-body localised XXZ model, (ii) heating in the ...
Quantum coherence and uncertainty in the anisotropic XY chain
Karpat, G.; ćakmak, B.; Fanchini, F. F.
2014-09-01
We explore the local quantum coherence and the local quantum uncertainty, based on Wigner-Yanase skew information, in the ground state of the anisotropic spin-1/2 XY chain in a transverse magnetic field. We show that the skew information, as a figure of merit, supplies the necessary information to reveal the occurrence of the second-order phase transition and the completely factorized ground state in the XY model. Additionally, in the same context, we also discuss the usefulness of a simple experimentally friendly lower bound of local quantum coherence. Furthermore, we demonstrate how the connection between the appearance of nonanalyticities in the local quantum uncertainty of the ground state and the quantum phase transitions does not hold in general, by providing explicit examples of the situation. Lastly, we discuss the ability of the local quantum coherence to accurately estimate the critical point of the phase transition, and we investigate the robustness of the factorization phenomenon at low temperatures.
Quantum Spin Liquid in Frustrated One-Dimensional LiCuSbO4
DEFF Research Database (Denmark)
Dutton, S. E.; Kumar, M.; Mourigal, M.;
2012-01-01
A quantum magnet, LiCuSbO4, with chains of edge-sharing spin-1/2CuO6 octahedra is reported. While short-range order is observed for T2 K data.......A quantum magnet, LiCuSbO4, with chains of edge-sharing spin-1/2CuO6 octahedra is reported. While short-range order is observed for T2 K data....
Quantum computation with nuclear spins in quantum dots
Energy Technology Data Exchange (ETDEWEB)
Christ, H.
2008-01-24
The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin
Energy Technology Data Exchange (ETDEWEB)
Barmettler, Peter; Gritsev, Vladimir [Department of Physics, University of Fribourg, CH-1700 Fribourg (Switzerland); Punk, Matthias [CPHT, Ecole Polytechnique, 91128 Palaiseau (France); Demler, Eugene [Department of Physics, Harvard University, Cambridge, MA 02138 (United States); Altman, Ehud, E-mail: peter.barmettler@cpht.polytechnique.f [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel)
2010-05-15
Recent experimental achievements in controlling ultracold gases in optical lattices open a new perspective on quantum many-body physics. In these experimental setups, it is possible to study coherent time evolution of isolated quantum systems. These dynamics reveal new physics beyond the low-energy properties that are usually relevant in solid-state many-body systems. In this paper, we study the time evolution of antiferromagnetic order in the Heisenberg chain after a sudden change of the anisotropy parameter, using various numerical and analytical methods. As a generic result, we find that the order parameter, which can show oscillatory or non-oscillatory dynamics, decays exponentially except for the effectively non-interacting case of the XX limit. For weakly ordered initial states, we also find evidence for an algebraic correction to the exponential law. The study is based on numerical simulations using a numerical matrix product method for infinite system sizes (iMPS), for which we provide a detailed description and an error analysis. Additionally, we investigate in detail the exactly solvable XX limit. These results are compared to approximative analytical approaches including an effective description by the XZ model as well as by mean-field, Luttinger-liquid and sine-Gordon theories. The comparison reveals which aspects of non-equilibrium dynamics can, as in equilibrium, be described by low-energy theories and which are the novel phenomena specific to quantum quench dynamics. The relevance of the energetically high part of the spectrum is illustrated by means of a full numerical diagonalization of the Hamiltonian.
One-way quantum deficit and quantum coherence in the anisotropic XY chain
Ye, Biao-Liang; Li, Bo; Zhao, Li-Jun; Zhang, Hai-Jun; Fei, Shao-Ming
2017-03-01
In this study, we investigate pairwise non-classical correlations measured using a one-way quantum deficit as well as quantum coherence in the XY spin-1/2 chain in a transverse magnetic field for both zero and finite temperatures. The analytical and numerical results of our investigations are presented. In the case when the temperature is zero, it is shown that the one-way quantum deficit can characterize quantum phase transitions as well as quantum coherence. We find that these measures have a clear critical point at λ = 1. When λ ≤ 1, the one-way quantum deficit has an analytical expression that coincides with the relative entropy of coherence. We also study an XX model and an Ising chain at the finite temperatures.
Dynamical spin-spin coupling of quantum dots
Grigoryan, Vahram; Xiao, Jiang; A spintronics Group Team
2014-03-01
We carried out a nested Schrieffer-Wolff transformation of an Anderson two-impurity Hamiltonian to study the spin-spin coupling between two dynamical quantum dots under the influence of rotating transverse magnetic field. As a result of the rotating field, we predict a novel Ising type spin-spin coupling mechanism between quantum dots, whose strength is tunable via the magnitude of the rotating field. Due to its dynamical origin, this new coupling mechanism is qualitatively different from the all existing static couplings such as RKKY, while the strength could be comparable to the strength of the RKKY coupling. The dynamical coupling with the intristic RKKY coupling enables to construct a four level system of maximally entangled Bell states in a controllable manner. This work was supported by the special funds for the Major State Basic Research Project of China (No. 2011CB925601) and the National Natural Science Foundation of China (Grants No. 11004036 and No. 91121002).
Electronic properties of aperiodic quantum dot chains
Korotaev, P. Yu.; Vekilov, Yu. Kh.; Kaputkina, N. E.
2012-04-01
The electronic spectral and transport properties of aperiodic quantum dot chains are investigated. The systems with singular continuous energy spectrum are considered: Thue-Morse chain, double-periodic chain, Rudin-Shapiro chain. The influence of electronic energy in quantum dot on the spectral properties, band structure, density of states and spectral resistivity, is discussed. Low resistivity regions correspond to delocalized states and these states could be current states. Also we discuss the magnetic field application as the way to tune electronic energy in quantum dot and to obtain metallic or insulating conducting states of the systems.
Quantum Computation and Spin Electronics
DiVincenzo, David P.; Burkard, Guido; Loss, Daniel; Sukhorukov, Eugene V.
1999-01-01
In this chapter we explore the connection between mesoscopic physics and quantum computing. After giving a bibliography providing a general introduction to the subject of quantum information processing, we review the various approaches that are being considered for the experimental implementation of quantum computing and quantum communication in atomic physics, quantum optics, nuclear magnetic resonance, superconductivity, and, especially, normal-electron solid state physics. We discuss five ...
Exact diagonalization of quantum-spin models
Lin, H. Q.
1990-10-01
We have developed a technique to replace hashing in implementing the Lanczös method for exact diagonalization of quantum-spin models that enables us to carry out numerical studies on substantially larger lattices than previously studied. We describe the algorithm in detail and present results for the ground-state energy, the first-excited-state energy, and the spin-spin correlations on various finite lattices for spins S=1/2, 1, 3/2, and 2. Results for an infinite system are obtained by extrapolation. We also discuss the generalization of our method to other models.
Spin storage in quantum dot ensembles and single quantum dots
Energy Technology Data Exchange (ETDEWEB)
Heiss, Dominik
2009-10-15
This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h
Unconventional spin texture in a noncentrosymmetric quantum spin Hall insulator
Mera Acosta, C.; Babilonia, O.; Abdalla, L.; Fazzio, A.
2016-07-01
We propose that the simultaneous presence of both Rashba and band inversion can lead to a Rashba-like spin splitting formed by two bands with the same in-plane helical spin texture. Because of this unconventional spin texture, the backscattering is forbidden in edge and bulk conductivity channels. We propose a noncentrosymmetric honeycomb-lattice quantum spin Hall (QSH) insulator family formed by the IV, V, and VII elements with this property. The system formed by Bi, Pb, and I atoms is mechanically stable and has both a large Rashba spin splitting of 60 meV and a large nontrivial band gap of 0.14 eV. Since the edge and the bulk states are protected by the time-reversal (TR) symmetry, contrary to what happens in most doped QSH insulators, the bulk states do not contribute to the backscattering in the electronic transport, allowing the construction of a spintronic device with less energy loss.
Observation of Prethermalization in Long-Range Interacting Spin Chains
Neyenhuis, B; Lee, A C; Zhang, J; Richerme, P; Hess, P W; Gong, Z -X; Gorshkov, A V; Monroe, C
2016-01-01
Statistical mechanics can predict thermal equilibrium states for most classical systems, but for an isolated quantum system there is no general understanding on how equilibrium states dynamically emerge from the microscopic Hamiltonian. For instance, quantum systems that are near-integrable usually fail to thermalize in an experimentally realistic time scale and, instead, relax to quasi-stationary prethermal states that can be described by statistical mechanics when approximately conserved quantities are appropriately included in a generalized Gibbs ensemble (GGE). Here we experimentally study the relaxation dynamics of a chain of up to 22 spins evolving under a long-range transverse field Ising Hamiltonian following a sudden quench. For sufficiently long-ranged interactions the system relaxes to a new type of prethermal state that retains a strong memory of the initial conditions. In this case, the prethermal state cannot be described by a GGE, but rather arises from an emergent double-well potential felt by...
Geometric Quantum Discord in the Heisenberg XX Model with Three-Spin Interactions
Xie, Yu-Xia; Liu, Jing; Sun, Yu-Hang
2017-02-01
Quantum discord is a resource for quantum information processing tasks, and seeking flexible ways to control it is of practical significance. We investigate the trace distance, Bures distance, and Hellinger distance geometric quantum discords (GQDs) for thermal states of the Heisenberg XX chain with three-spin interactions. The results show that both the XZX + YZY and XZY - YZX types of three-spin interactions can be used to enhance evidently the GQDs for the boundary spins of the chain. The optimal strengths of three-spin interactions for which the maximum enhancement of the GQDs are achieved are strongly dependent on the GQD measures we adopted and the number of spins in the chain.
Geometric Quantum Discord in the Heisenberg XX Model with Three-Spin Interactions
Xie, Yu-Xia; Liu, Jing; Sun, Yu-Hang
2016-11-01
Quantum discord is a resource for quantum information processing tasks, and seeking flexible ways to control it is of practical significance. We investigate the trace distance, Bures distance, and Hellinger distance geometric quantum discords (GQDs) for thermal states of the Heisenberg XX chain with three-spin interactions. The results show that both the XZX + YZY and XZY -YZX types of three-spin interactions can be used to enhance evidently the GQDs for the boundary spins of the chain. The optimal strengths of three-spin interactions for which the maximum enhancement of the GQDs are achieved are strongly dependent on the GQD measures we adopted and the number of spins in the chain.
Ajoy, Ashok; Cappellaro, Paola
2013-05-31
We propose a method for Hamiltonian engineering that requires no local control but only relies on collective qubit rotations and field gradients. The technique achieves a spatial modulation of the coupling strengths via a dynamical construction of a weighting function combined with a Bragg grating. As an example, we demonstrate how to generate the ideal Hamiltonian for perfect quantum information transport between two separated nodes of a large spin network. We engineer a spin chain with optimal couplings starting from a large spin network, such as one naturally occurring in crystals, while decoupling all unwanted interactions. For realistic experimental parameters, our method can be used to drive almost perfect quantum information transport at room temperature. The Hamiltonian engineering method can be made more robust under decoherence and coupling disorder by a novel apodization scheme. Thus, the method is quite general and can be used to engineer the Hamiltonian of many complex spin lattices with different topologies and interactions.
Spins of Andreev states in double quantum dots
Su, Zhaoen; Chen, Jun; Yu, Peng; Hocervar, Moira; Plissard, Sebastien; Car, Diana; Tacla, Alexandre; Daley, Andrew; Pekker, David; Bakkers, Erik; Frolov, Sergey
Andreev (or Shiba) states in coupled double quantum dots is an open field. Here we demonstrate the realization of Andreev states in double quantum dots in an InSb nanowire coupled to two NbTiN superconductors. The magnetic field dependence of the Andreev states has been explored to resolve the spins in different double dot configurations. The experiment helps to understand the interplay between pair correlation, exchange energy and charging energy with a well-controlled system. It also opens the possibility to implement Majorana modes in Kitaev chains made of such dots.
The master T-operator for inhomogeneous XXX spin chain and mKP hierarchy
Zabrodin, A
2014-01-01
Following the approach of [1], we show how to construct the master T-operator for the quantum GL(N)-invariant inhomogeneous XXX spin chain with twisted boundary conditions. It satisfiesthe bilinear identity and Hirota equations for the classical mKP hierarchy. We also characterize the class of solutions to the mKP hierarchy that correspond to eigenvalues of the master T-operator and study dynamics of their zeros as functions of the spectral parameter. This implies a remarkable connection between the quantum spin chain and the classical Ruijsenaars-Schneider system of particles.
Finite size and finite temperature studies of the osp(1|2) spin chain
Tavares, T. S.; Ribeiro, G. A. P.
2017-08-01
We studied a quantum spin chain invariant by the superalgebra osp (1 | 2). We derived non-linear integral equations for the row-to-row transfer matrix eigenvalue in order to analyze its finite size scaling behavior and we determined its central charge. We also studied the thermodynamical properties of the spin chain via non-linear integral equations for the quantum transfer matrix eigenvalue. We numerically solved these NLIE and evaluated the specific heat and magnetic susceptibility. The analytical low temperature analysis was performed providing the effective central charge. The computed values are in agreement with the numerical predictions in the literature.
Optical nuclear spin polarization in quantum dots
Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei
2016-10-01
Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time. Project partially supported by the National Natural Science Foundations of China (Grant Nos. 11374039 and 11174042) and the National Basic Research Program of China (Grant Nos. 2011CB922204 and 2013CB632805).
Consequences of Kondo exchange on quantum spins
Delgado Acosta, Fernando; Hirjibehedin, Cyrus F.; Fernández Rossier, Joaquín
2014-01-01
When individual quantum spins are placed in close proximity to conducting substrates, the localized spin is coupled to the nearby itinerant conduction electrons via Kondo exchange. In the strong coupling limit this can result in the Kondo effect — the formation of a correlated, many body singlet state — and a resulting renormalization of the density of states near the Fermi energy. However, even when Kondo screening does not occur, Kondo exchange can give rise to a wide variety of other pheno...
Thermodynamics of Inozemtsev's Elliptic Spin Chain
Klabbers, Rob
2016-01-01
We study the thermodynamic behaviour of Inozemtsev's long-range elliptic spin chain using the Bethe ansatz equations describing the spectrum of the model in the infinite-length limit. We classify all solutions of these equations in that limit and argue which of these solutions determine the spectrum in the thermodynamic limit. Interestingly, some of the solutions are not selfconjugate, which puts the model in sharp contrast to one of the model's limiting cases, the Heisenberg xxx spin chain. Invoking the string hypothesis we derive the thermodynamic Bethe ansatz equations (TBA-equations) from which we determine the Helmholtz free energy in thermodynamic equilibrium and derive the associated Y-system. We corroborate our results by comparing numerical solutions of the TBA-equations to a direct computation of the free energy for the finite-length hamiltonian. In addition we confirm numerically the interesting conjecture put forward by Finkel and Gonz\\'alez-L\\'opez that the original and supersymmetric versions of...
Quantum coherence and uncertainty in the anisotropic XY chain
2014-01-01
We explore the local quantum coherence and the local quantum uncertainty, based on Wigner-Yanase skew information, in the ground state of the anisotropic spin-1/2 XY chain in transverse magnetic field. We show that the skew information, as a figure of merit, supplies the necessary information to reveal the occurrence of the second order phase transition and the completely factorized ground state in the XY model. Additionally, in the same context, we also discuss the usefulness of a simple exp...
Spin and topological order in a periodically driven spin chain
Russomanno, Angelo; Friedman, Bat-el; Dalla Torre, Emanuele G.
2017-07-01
The periodically driven quantum Ising chain has recently attracted a large attention in the context of Floquet engineering. In addition to the common paramagnet and ferromagnet, this driven model can give rise to new topological phases. In this work, we systematically explore its quantum phase diagram by examining the properties of its Floquet ground state. We specifically focus on driving protocols with time-reversal invariant points, and demonstrate the existence of an infinite number of distinct phases. These phases are separated by second-order quantum phase transitions, accompanied by continuous changes of local and string order parameters, as well as sudden changes of a topological winding number and of the number of protected edge states. When one of these phase transitions is adiabatically crossed, the correlator associated to the order parameter is nonvanishing over a length scale which shows a Kibble-Zurek scaling. In some phases, the Floquet ground state spontaneously breaks the discrete time-translation symmetry of the Hamiltonian. Our findings provide a better understanding of topological phases in periodically driven clean integrable models.
Bending strain engineering in quantum spin hall system for controlling spin currents
Huang, Bing; Jin, Kyung-Hwan; Cui, Bin; Zhai, Feng; Mei, Jiawei; Liu, Feng
2017-06-01
Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. Here the concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. We show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Furthermore, the curved quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.
Nonequilibrium Spin Magnetization Quantum Transport Equations
Buot, F A; Otadoy, R E S; Villarin, D L
2011-01-01
The classical Bloch equations of spin magnetization transport is extended to fully time-dependent and highly-nonlinear nonequilibrium quantum distribution function (QDF) transport equations. The leading terms consist of the Boltzmann kinetic equation with spin-orbit coupling in a magnetic field together with spin-dependent scattering terms which do not have any classical analogue, but should incorporate the spatio-temporal-dependent phase-space dynamics of Elliot-Yafet and D'yakonov-Perel scatterings. The resulting magnetization QDF transport equation serves as a foundation for computational spintronic and nanomagnetic device applications, in performing simulation of ultrafast-switching-speed/low-power performance and reliability analyses.
Applying classical geometry intuition to quantum spin
Durfee, Dallin S.; Archibald, James L.
2016-09-01
Using concepts of geometric orthogonality and linear independence, we logically deduce the form of the Pauli spin matrices and the relationships between the three spatially orthogonal basis sets of the spin-1/2 system. Rather than a mathematically rigorous derivation, the relationships are found by forcing expectation values of the different basis states to have the properties we expect of a classical, geometric coordinate system. The process highlights the correspondence of quantum angular momentum with classical notions of geometric orthogonality, even for the inherently non-classical spin-1/2 system. In the process, differences in and connections between geometrical space and Hilbert space are illustrated.
Quantum computing with an electron spin ensemble.
Wesenberg, J H; Ardavan, A; Briggs, G A D; Morton, J J L; Schoelkopf, R J; Schuster, D I; Mølmer, K
2009-08-14
We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper pair box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.
Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets.
Gingras, M J P; McClarty, P A
2014-05-01
The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare-earth pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic state with an emergent gauge freedom. Spin ices provide one of very few experimentally realized examples of fractionalization because their elementary excitations can be regarded as magnetic monopoles and, over some temperature range, spin ice materials are best described as liquids of these emergent charges. In the presence of quantum fluctuations, one can obtain, in principle, a quantum spin liquid descended from the classical spin ice state characterized by emergent photon-like excitations. Whereas in classical spin ices the excitations are akin to electrostatic charges with a mutual Coulomb interaction, in the quantum spin liquid these charges interact through a dynamic and emergent electromagnetic field. In this review, we describe the latest developments in the study of such a quantum spin ice, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found.
Quantum Markov Chain Mixing and Dissipative Engineering
DEFF Research Database (Denmark)
Kastoryano, Michael James
2012-01-01
This thesis is the fruit of investigations on the extension of ideas of Markov chain mixing to the quantum setting, and its application to problems of dissipative engineering. A Markov chain describes a statistical process where the probability of future events depends only on the state...... of the system at the present point in time, but not on the history of events. Very many important processes in nature are of this type, therefore a good understanding of their behaviour has turned out to be very fruitful for science. Markov chains always have a non-empty set of limiting distributions...... (stationary states). The aim of Markov chain mixing is to obtain (upper and/or lower) bounds on the number of steps it takes for the Markov chain to reach a stationary state. The natural quantum extensions of these notions are density matrices and quantum channels. We set out to develop a general mathematical...
Effects of Spin Quantum Force in Magnetized Quantum Plasma
Institute of Scientific and Technical Information of China (English)
杨秀峰; 姜虹; 祁学宏; 段文山
2011-01-01
Starting from the governing equations for a quantum magnetoplasma including the electron spin -1/2 effects and quantum Bohm potential, we derive Korteweg-de Vries （KdV） equation of the system of quantum magneto- hydrodynamics （QMHD）. The amplitude and width of magnetosonic soliton with different parameters in the system are studied. It is found that the normalized Zeeman energy E plays a crucial role, for E ≥ 1 the amplitude τmξ and the width we of solitary wave all decrease as E increases. That is, the introduction of spin quantum force modifies the shape of solitary magnetosonic waves and makes them more narrower and shallower.
Topological Excitations in Quantum Spin Systems
Directory of Open Access Journals (Sweden)
Ranjan Chaudhury
2013-01-01
Full Text Available The origin and significance of topological excitations in quantum spin models in low dimensions are presented in detail. Besides a general review, our own work in this area is described in great depth. Apart from theoretical analysis of the existence and properties of spin vortices and antivortices, the possible experimental consequences and signatures are also highlighted. In particular, the distinguishing features between the even and odd charged topological excitations are brought out through a detailed analysis of the topological term in the quantum action. Moreover, an interesting symmetry property is predicted between the excitations from a ferromagnetic model and an antiferromagnetic model. Through a novel approach of ours, a bridge is established between field theoretical formalism and the well-known statistical mechanical treatment of Berezinskii-Kosterlitz-Thouless (BKT transition involving these topological excitations. Furthermore, a detailed phenomenological analysis of the experimentally observed static and dynamic magnetic properties of the layered magnetic materials, possessing XY anisotropy in the in-plane spin-spin couplings, is undertaken to test the theoretical predictions regarding the behaviour of these excitations. The importance and the crucial role of quantum spin fluctuations in these studies are also brought out very clearly by our analysis.
Spin & Statistics in Nonrelativistic Quantum Mechanics, II
Kuckert, B; Kuckert, Bernd; Mund, Jens
2004-01-01
Recently a sufficient and necessary condition for Pauli's spin- statistics connection in nonrelativistic quantum mechanics has been established [quant-ph/0208151]. The two-dimensional part of this result is extended to n-particle systems and reformulated and further simplified in a more geometric language.
Temperature dependence of the NMR spin-lattice relaxation rate for spin-1/2 chains
Coira, E.; Barmettler, P.; Giamarchi, T.; Kollath, C.
2016-10-01
We use recent developments in the framework of a time-dependent matrix product state method to compute the nuclear magnetic resonance relaxation rate 1 /T1 for spin-1/2 chains under magnetic field and for different Hamiltonians (XXX, XXZ, isotropically dimerized). We compute numerically the temperature dependence of the 1 /T1 . We consider both gapped and gapless phases, and also the proximity of quantum critical points. At temperatures much lower than the typical exchange energy scale, our results are in excellent agreement with analytical results, such as the ones derived from the Tomonaga-Luttinger liquid (TLL) theory and bosonization, which are valid in this regime. We also cover the regime for which the temperature T is comparable to the exchange coupling. In this case analytical theories are not appropriate, but this regime is relevant for various new compounds with exchange couplings in the range of tens of Kelvin. For the gapped phases, either the fully polarized phase for spin chains or the low-magnetic-field phase for the dimerized systems, we find an exponential decrease in Δ /(kBT ) of the relaxation time and can compute the gap Δ . Close to the quantum critical point our results are in good agreement with the scaling behavior based on the existence of free excitations.
Disentanglement of Two Qubits Coupled to an XY Spin Chain at Finite Temperature
Institute of Scientific and Technical Information of China (English)
NIE Jing; WANG Lin-Cheng; YI Xue-Xi
2009-01-01
The disentanglement evolution of bipartite spin-1/2 system coupled to a common surrounding XY chain in transverse fields at nonzero temperature is studied in this letter. The dynamical process of the entanglement is numerically and anaiytically investigated. We find that thermal effects can enhance disentanglement if the entangled initial state of the central spins does not in the decoherenee free space. The critical phenomenon of quantum phase transitions reflected in the disentanglement can be washed out by the thermal effect eventually.
Coherent spin dynamics in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Amand, T.; Senes, M.; Marie, X.; Renucci, P. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique-LPMC, INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Urbaszek, B. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique-LPMC, INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Krebs, O.; Laurent, S.; Voisin, P. [Laboratoire de Photonique et Nanostructures, route de Nozay, 91460 Marcoussis (France); Warburton, R.J. [Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)
2005-05-01
The anisotropic exchange interaction (AEI) between electrons and holes is shown to play a central role in quantum dots (QDs) spin dynamics. In neutral QDs, AEI is at the origin of spin quantum beats observed under resonant excitation between the lowest energy doublet of linearly dipole-active eigenstates. In negatively charged QDs, AEI is at the origin of QD emission with opposite helicity to the optic al excitation, under non-resonant excitation conditions. Finally, the possibility of leaving a spin information in the system after recombination of the photo-injected electron-hole pair is discussed with respect to the type and the level of the doping. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Quantum computing with acceptor spins in silicon.
Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie
2016-06-17
The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time [Formula: see text] as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.
Integrable spin chains and scattering amplitudes
Energy Technology Data Exchange (ETDEWEB)
Bartels, J.; Prygarin, A. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Lipatov, L.N. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Petersburg Nuclear Physics Institute (Russian Federation); Sankt-Peterburgskij Univ., St. Petersburg (Russian Federation)
2011-04-15
In this review we show that the multi-particle scattering amplitudes in N=4 SYM at large N{sub c} and in the multi-Regge kinematics for some physical regions have the high energy behavior appearing from the contribution of the Mandelstam cuts in the complex angular momentum plane of the corresponding t-channel partial waves. These Mandelstam cuts or Regge cuts are resulting from gluon composite states in the adjoint representation of the gauge group SU(N{sub c}). In the leading logarithmic approximation (LLA) their contribution to the six point amplitude is in full agreement with the known two-loop result. The Hamiltonian for the Mandelstam states constructed from n gluons in LLA coincides with the local Hamiltonian of an integrable open spin chain. We construct the corresponding wave functions using the integrals of motion and the Baxter-Sklyanin approach. (orig.)
Off-diagonal Bethe ansatz solution of the XXX spin chain with arbitrary boundary conditions
Cao, Junpeng; Yang, Wen-Li; Shi, Kangjie; Wang, Yupeng
2013-10-01
Employing the off-diagonal Bethe ansatz method proposed recently by the present authors, we exactly diagonalize the XXX spin chain with arbitrary boundary fields. By constructing a functional relation between the eigenvalues of the transfer matrix and the quantum determinant, the associated T-Q relation and the Bethe ansatz equations are derived.
Off-diagonal Bethe ansatz solution of the XXX spin-chain with arbitrary boundary conditions
Cao, Junpeng; Shi, Kangjie; Wang, Yupeng
2013-01-01
With the off-diagonal Bethe ansatz method proposed recently by the present authors, we exactly diagonalize the $XXX$ spin chain with arbitrary boundary fields. By constructing a functional relation between the eigenvalues of the transfer matrix and the quantum determinant, the associated $T-Q$ relation and the Bethe ansatz equations are derived.
Algebraic Bethe ansatz for the Temperley–Lieb spin-1 chain
Energy Technology Data Exchange (ETDEWEB)
Nepomechie, Rafael I., E-mail: nepomechie@physics.miami.edu [Physics Department, P.O. Box 248046, University of Miami, Coral Gables, FL 33124 (United States); Pimenta, Rodrigo A., E-mail: pimenta@df.ufscar.br [Physics Department, P.O. Box 248046, University of Miami, Coral Gables, FL 33124 (United States); Departamento de Física, Universidade Federal de São Carlos, Caixa Postal 676, CEP 13565-905, São Carlos (Brazil)
2016-09-15
We use the algebraic Bethe ansatz to obtain the eigenvalues and eigenvectors of the spin-1 Temperley–Lieb open quantum chain with “free” boundary conditions. We exploit the associated reflection algebra in order to prove the off-shell equation satisfied by the Bethe vectors.
Algebraic Bethe ansatz for the Temperley–Lieb spin-1 chain
Directory of Open Access Journals (Sweden)
Rafael I. Nepomechie
2016-09-01
Full Text Available We use the algebraic Bethe ansatz to obtain the eigenvalues and eigenvectors of the spin-1 Temperley–Lieb open quantum chain with “free” boundary conditions. We exploit the associated reflection algebra in order to prove the off-shell equation satisfied by the Bethe vectors.
Algebraic Bethe ansatz for the Temperley-Lieb spin-1 chain
Nepomechie, Rafael I
2016-01-01
We use the algebraic Bethe ansatz to obtain the eigenvalues and eigenvectors of the spin-1 Temperley-Lieb open quantum chain with "free" boundary conditions. We exploit the associated reflection algebra in order to prove the off-shell equation satisfied by the Bethe vectors.
Algebraic Bethe ansatz for the Temperley-Lieb spin-1 chain
Nepomechie, Rafael I.; Pimenta, Rodrigo A.
2016-09-01
We use the algebraic Bethe ansatz to obtain the eigenvalues and eigenvectors of the spin-1 Temperley-Lieb open quantum chain with "free" boundary conditions. We exploit the associated reflection algebra in order to prove the off-shell equation satisfied by the Bethe vectors.
Quantum Monte Carlo with variable spins.
Melton, Cody A; Bennett, M Chandler; Mitas, Lubos
2016-06-28
We investigate the inclusion of variable spins in electronic structure quantum Monte Carlo, with a focus on diffusion Monte Carlo with Hamiltonians that include spin-orbit interactions. Following our previous introduction of fixed-phase spin-orbit diffusion Monte Carlo, we thoroughly discuss the details of the method and elaborate upon its technicalities. We present a proof for an upper-bound property for complex nonlocal operators, which allows for the implementation of T-moves to ensure the variational property. We discuss the time step biases associated with our particular choice of spin representation. Applications of the method are also presented for atomic and molecular systems. We calculate the binding energies and geometry of the PbH and Sn2 molecules, as well as the electron affinities of the 6p row elements in close agreement with experiments.
Quantum Monte Carlo with Variable Spins
Melton, Cody A; Mitas, Lubos
2016-01-01
We investigate the inclusion of variable spins in electronic structure quantum Monte Carlo, with a focus on diffusion Monte Carlo with Hamiltonians that include spin-orbit interactions. Following our previous introduction of fixed-phase spin-orbit diffusion Monte Carlo (FPSODMC), we thoroughly discuss the details of the method and elaborate upon its technicalities. We present a proof for an upper-bound property for complex nonlocal operators, which allows for the implementation of T-moves to ensure the variational property. We discuss the time step biases associated with our particular choice of spin representation. Applications of the method are also presented for atomic and molecular systems. We calculate the binding energies and geometry of the PbH and Sn$_2$ molecules, as well as the electron affinities of the 6$p$ row elements in close agreement with experiments.
Photonic analogue of quantum spin Hall effect
He, Cheng; Liu, Xiao-ping; Lu, Ming-Hui; Chen, Yulin; Feng, Liang; Chen, Yan-Feng
2014-01-01
Symmetry-protected photonic topological insulator exhibiting robust pseudo-spin-dependent transportation, analogous to quantum spin Hall (QSH) phases and topological insulators, are of great importance in fundamental physics. Such transportation robustness is protected by time-reversal symmetry. Since electrons (fermion) and photons (boson) obey different statistics rules and associate with different time-reversal operators (i.e., Tf and Tb, respectively), whether photonic counterpart of Kramers degeneracy is topologically protected by bosonic Tb remains unidentified. Here, we construct the degenerate gapless edge states of two photonic pseudo-spins (left/right circular polarizations) in the band gap of a two-dimensional photonic crystal with strong magneto-electric coupling. We further demonstrated that the topological edge states are in fact protected by Tf rather than commonly believed Tb and their pseudo-spin dependent transportation is robust against Tf invariant impurities, discovering for the first tim...
Spin Waves in a Classical Compressible Heisenberg Chain
Fivez, J.; Raedt, H. De
1980-01-01
The effect of the spin—lattice interaction on the spin dynamics of a classical Heisenberg chain is studied by means of a truncated continued fraction. At low temperature, the spin correlation length and the spin wave frequency show the same simple dependence on the coupling.
Aperiodic quantum XXZ chains: Renormalization-group results
Vieira, André P.
2005-04-01
We report a comprehensive investigation of the low-energy properties of antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain analytical and numerical results for the low-temperature thermodynamics and the ground-state correlations of chains with couplings following several two-letter aperiodic sequences, including the quasiperiodic Fibonacci and other precious-mean sequences, as well as sequences inducing strong geometrical fluctuations. For a given aperiodic sequence, we argue that in the easy-plane anisotropy regime, intermediate between the XX and Heisenberg limits, the general scaling form of the thermodynamic properties is essentially given by the exactly known XX behavior, providing a classification of the effects of aperiodicity on XXZ chains. We also discuss the nature of the ground-state structures and their comparison with the random-singlet phase characteristic of random-bond chains.
Spin chain simulations with a meron cluster algorithm
Energy Technology Data Exchange (ETDEWEB)
Boyer, T. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik]|[Ecole Normale Superieure de Cachan (France); Bietenholz, W. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik]|[Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Wuilloud, J. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik]|[Geneve Univ. (Switzerland). Dept. de Physique Theorique
2007-01-15
We apply a meron cluster algorithm to the XY spin chain, which describes a quantum rotor. This is a multi-cluster simulation supplemented by an improved estimator, which deals with objects of half-integer topological charge. This method is powerful enough to provide precise results for the model with a {theta}-term - it is therefore one of the rare examples, where a system with a complex action can be solved numerically. In particular we measure the correlation length, as well as the topological and magnetic susceptibility. We discuss the algorithmic efficiency in view of the critical slowing down. Due to the excellent performance that we observe, it is strongly motivated to work on new applications of meron cluster algorithms in higher dimensions. (orig.)
Quantum Entanglement of Quantum Dot Spin Using Flying Qubits
2015-05-01
SPDC photon is teleported to a single quantum dot spin by a projective measurement using a Hong Ou Mandel (HOM) interferometer. The SPDC source...photo diode B: Blue CW: Continuous wave DBR: Distributed Bragg reflector EOM: Electro-optics modulator H: Horizontal HOM: Hong-Ou- Mandel InAs
A quantum spin-probe molecular microscope
Perunicic, V. S.; Hill, C. D.; Hall, L. T.; Hollenberg, L.C.L.
2016-01-01
Imaging the atomic structure of a single biomolecule is an important challenge in the physical biosciences. Whilst existing techniques all rely on averaging over large ensembles of molecules, the single-molecule realm remains unsolved. Here we present a protocol for 3D magnetic resonance imaging of a single molecule using a quantum spin probe acting simultaneously as the magnetic resonance sensor and source of magnetic field gradient. Signals corresponding to specific regions of the molecule's nuclear spin density are encoded on the quantum state of the probe, which is used to produce a 3D image of the molecular structure. Quantum simulations of the protocol applied to the rapamycin molecule (C51H79NO13) show that the hydrogen and carbon substructure can be imaged at the angstrom level using current spin-probe technology. With prospects for scaling to large molecules and/or fast dynamic conformation mapping using spin labels, this method provides a realistic pathway for single-molecule microscopy. PMID:27725630
A quantum spin-probe molecular microscope
Perunicic, V. S.; Hill, C. D.; Hall, L. T.; Hollenberg, L. C. L.
2016-10-01
Imaging the atomic structure of a single biomolecule is an important challenge in the physical biosciences. Whilst existing techniques all rely on averaging over large ensembles of molecules, the single-molecule realm remains unsolved. Here we present a protocol for 3D magnetic resonance imaging of a single molecule using a quantum spin probe acting simultaneously as the magnetic resonance sensor and source of magnetic field gradient. Signals corresponding to specific regions of the molecule's nuclear spin density are encoded on the quantum state of the probe, which is used to produce a 3D image of the molecular structure. Quantum simulations of the protocol applied to the rapamycin molecule (C51H79NO13) show that the hydrogen and carbon substructure can be imaged at the angstrom level using current spin-probe technology. With prospects for scaling to large molecules and/or fast dynamic conformation mapping using spin labels, this method provides a realistic pathway for single-molecule microscopy.
Spinning Particles in Quantum Mechanics and Quantum Field Theory
Corradini, Olindo
2015-01-01
The first part of the lectures, given by O. Corradini, covers introductory material on quantum-mechanical Feynman path integrals, which are here derived and applied to several particle models. We start considering the nonrelativistic bosonic particle, for which we compute the exact path integrals for the case of the free particle and for the harmonic oscillator, and then describe perturbation theory for an arbitrary potential. We then move to relativistic particles, both bosonic and fermionic (spinning) particles. We first investigate them from the classical view-point, studying the symmetries of their actions, then consider their canonical quantization and path integrals, and underline the role these models have in the study of space-time quantum field theories (QFT), by introducing the "worldline" path integral representation of propagators and effective actions. We also describe a special class of spinning particles that constitute a first-quantized approach to higher-spin fields. Since the fifties the qua...
The size effect of the quantum coherence in the transverse-field XY chain
Energy Technology Data Exchange (ETDEWEB)
Wang, Lu; Yang, Cui-hong; Wang, Jun-feng [Department of Physics, Nanjing University of Information Science & Technology, Nanjing 210044 (China); Lei, Shu-guo, E-mail: sglei@njtech.edu.cn [College of Science, Nanjing Tech University, Nanjing, 211816 (China)
2016-12-15
Based on the Wigner–Yanase skew information, the size effect of the quantum coherence in the ground state of the finite transverse-field spin-1/2 XY chain is explored. It is found that the first-order derivatives of the single-spin coherence and the two-spin local coherence both have scaling behaviors in the vicinity of the critical point. A simplified version of coherence is also studied and the same characteristics with its counterpart are found.
Law, J M; Benner, H; Kremer, R K
2013-02-13
The temperature dependence of the spin susceptibilities of S = 1, 3/2, 2, 5/2 and 7/2 Heisenberg antiferromagnetic 1D spins chains with nearest-neighbor coupling was simulated via quantum Monte Carlo calculations, within the reduced temperature range of 0.005 ≤ T* ≤ 100, and fitted to a Padé approximation with deviations between the simulated and fitted data of the same order of magnitude as or smaller than the quantum Monte Carlo simulation error. To demonstrate the practicality of our theoretical findings, we compare these results with the susceptibility of the well known 1D chain compound TMMC ([(CH(3))(4)N[MnCl(3)
一维量子自旋链中拓扑有序态的物理描述%Characteristics topological ordered states in one-dimensional quantum spin chains
Institute of Scientific and Technical Information of China (English)
涂鸿浩; 张广铭
2012-01-01
The study of low-dimensional quantum correlated systems is a longstanding important issue in condensed matter physics. In this review article, we will discuss the related problems in one-dimensional quantum spin chains. We briefly introduce the background of one-dimensional quantum spin chains. Then, we present a new class of SO（n） symmetric quantum spin chains and study the topological order in the matrix product ground states of these systems. Moreover, we find a hidden topological symmetry to understand the nonlocal string order parameters and edge states, which provide a unified explanation to the origin of topological order. Based on these results, we introduce a general construction method of the valence bond solid states with a built-in Lie group G and discuss their parent Hamiltonians by For these one-dimensional quantum spin systems, we topological order. using the matrix product representations. also discuss the characterization of their%一维量子多体系统是凝聚态物理学中的重要研究方向之一，其中的新奇量子物态则是重要的研究课题。本文我们首先简要回顾一维量子整数自旋链体系的相关研究背景，然后提出一类SO（n）对称的严格可解量子自旋链模型及其矩阵乘积基态。当奇数n≥3时，体系的基态为Haldane相。利用这类态中隐藏的稀薄反铁磁序，我们找到了刻画这类态的非局域弦序参量，并在隐藏拓扑对称性的统一框架下解释了稀薄反铁磁序以及边缘态等奇特现象的起源。当偶数n≥4时，体系的基态为二聚化态。这些态属于破缺平移对称性的非Haldane相，但同样具有隐藏的反铁磁序。通过这些严格解的研究，我们还得到了一维SO（n）对称的双线性一双二次模型的基态相图，并发现在n≥5时，一维SO（n）对称的反铁磁海森堡模型的基态处于二聚化相中。基于以上这些结果，我们推广构造了一维平移不变且包
Love triangles, quantum fluctuations and spin jam
Lee, Seung-Hun
When magnetic moments are interacting with each other in a situation resembling that of complex love triangles, called frustration, a large set of states that are energetically equivalent emerge. This leads to exotic spin states such as spin liquid and spin ice. Recently, we presented evidence for the existence of a topological glassy state, that we call spin jam, induced by quantum fluctuations. The case in point is SrCr9pGa12-9pO19 (SCGO(p)), a highly frustrated magnet, in which the magnetic Cr ions form a quasi-two-dimensional triangular system of bi-pyramids. This system has been an archetype in search for exotic spin states. Understanding the nature of the state has been a great intellectual challenge. Our new experimental data and theoretical spin jam model provide for the first time a coherent understanding of the phenomenon. Furthermore, the findings strongly support the possible existence of purely topological glassy states. Reference:
Single-electron Spin Resonance in a Quadruple Quantum Dot
Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo
2016-08-01
Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible.
Universal Bethe ansatz solution for the Temperley-Lieb spin chain
Nepomechie, Rafael I.; Pimenta, Rodrigo A.
2016-09-01
We consider the Temperley-Lieb (TL) open quantum spin chain with "free" boundary conditions associated with the spin-s representation of quantum-deformed sl (2). We construct the transfer matrix, and determine its eigenvalues and the corresponding Bethe equations using analytical Bethe ansatz. We show that the transfer matrix has quantum group symmetry, and we propose explicit formulas for the number of solutions of the Bethe equations and the degeneracies of the transfer-matrix eigenvalues. We propose an algebraic Bethe ansatz construction of the off-shell Bethe states, and we conjecture that the on-shell Bethe states are highest-weight states of the quantum group. We also propose a determinant formula for the scalar product between an off-shell Bethe state and its on-shell dual, as well as for the square of the norm. We find that all of these results, except for the degeneracies and a constant factor in the scalar product, are universal in the sense that they do not depend on the value of the spin. In an appendix, we briefly consider the closed TL spin chain with periodic boundary conditions, and show how a previously-proposed solution can be improved so as to obtain the complete (albeit non-universal) spectrum.
Deguchi, Tetsuo; Matsui, Chihiro
2010-06-01
For the integrable higher-spin XXX and XXZ spin chains we present multiple-integral representations for the correlation function of an arbitrary product of Hermitian elementary matrices in the massless ground state. We give a formula expressing it by a single term of multiple integrals. In particular, we explicitly derive the emptiness formation probability (EFP). We assume 2s-strings for the ground-state solution of the Bethe-ansatz equations for the spin-s XXZ chain, and solve the integral equations for the spin-s Gaudin matrix. In terms of the XXZ coupling Δ we define ζ by Δ=cos ζ, and put it in a region 0⩽ζ<π/2s of the gapless regime: -1<Δ⩽1 (0⩽ζ<π), where Δ=1 (ζ=0) corresponds to the antiferromagnetic point. We calculate the zero-temperature correlation functions by the algebraic Bethe-ansatz, introducing the Hermitian elementary matrices in the massless regime, and taking advantage of the fusion construction of the R-matrix of the higher-spin representations of the affine quantum group.
Energy Technology Data Exchange (ETDEWEB)
Kitanine, N
2007-09-15
Spin chains are the basic elements of integrable quantum models. These models have direct applications in condense matter theory, in statistical physics, in quantum optics, in field theory and even in string theory but they are also important because they enable us to solve, in an exact manner, non-perturbative phenomena that otherwise would stay unresolved. The method described in this work is based on the algebraic Bethe Ansatz. It is shown how this method can be used for the computation of null temperature correlation functions of the Heisenberg 1/2 spin chain. The important point of this approach is the solution of the inverse quantum problem given by the XXZ spin chain. This solution as well as a simple formulae for the scalar product of the Bethe states, have enabled us to get the most basic correlation functions under the form of multiple integrals. The formalism of multiple integrals open the way for asymptotic analysis for a few physical quantities like the probability of vacuum formation. It is worth noticing that this formalism can give exact results for two-point functions that are the most important correlation functions for applications. A relationship has been discovered between these multiple integrals and the sum of the form factors. The results have been extended to dynamical correlation functions. (A.C.)
Spin Helicity in Chiral Lanthanide Chains.
Mihalcea, Ionut; Perfetti, Mauro; Pineider, Francesco; Tesi, Lorenzo; Mereacre, Valeriu; Wilhelm, Fabrice; Rogalev, Andrei; Anson, Christopher E; Powell, Annie K; Sessoli, Roberta
2016-10-17
We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and Er) by means of cantilever torque magnetometry. While the Dy and Er derivatives are strongly axial (easy-axis and easy-plane anisotropy, respectively), the Tb derivative is characterized by a remarkable rhombicity. In agreement with these findings, alternating-current susceptibility reveals slow magnetic relaxation only in the Dy derivative. Dilution of Dy(III) ions in the diamagnetic Y-based analogue shows that the weak ferromagnetic intrachain interactions do not contribute significantly to the energy barrier for the reversal of magnetization, which is better described as a single-ion process. Single crystals of the two enantiomers of the Dy derivative have also been investigated using hard X-ray synchrotron radiation at the L-edge of the metal revealing optical activity although with negligible involvement of the 4f electrons of the Dy(III) ion.
Dissipative Quantum Metrology with Spin Cat States
Huang, Jiahao; Zhong, Honghua; Ke, Yongguan; Lee, Chaohong
2014-01-01
We present a robust high-precision phase estimation scheme via spin cat states in the presence of particle losses. The input Greenberger-Horne-Zeilinger (GHZ) state, which may achieve the Heisenberg-limited measurement in the absence of particle losses, becomes fragile against particle losses and its achieved precision becomes even worse than the standard quantum limit (SQL). However, the input spin cat states, a kind of non-Gaussian entangled states in superposition of two spin coherent states, are of excellent robustness against particle losses and the achieved precision may still beat the SQL. For realistic measurements based upon our scheme, comparing with the population measurement, the parity measurement is more suitable for yielding higher precisions. In phase measurement with realistic dissipative systems of bosonic particles, our scheme provides a robust and realizable way to achieve high-precision measurements beyond the SQL.
Classical spin and quantum-mechanical descriptions of geometric spin frustration.
Dai, Dadi; Whangbo, Myung-Hwan
2004-07-08
Geometric spin frustration (GSF) in isolated plaquettes with local spin s, i.e., an equilateral-triangle spin trimer and a regular-tetrahedron spin tetramer, was examined on the basis of classical spin and quantum-mechanical descriptions to clarify their differences and similarities. An analytical proof was given for how the state degeneracy and the total spin S of their ground states depend on the local spin s. The quantum-mechanical conditions for the occurrence of GSF in isolated plaquettes were clarified, and their implications were explored. Corner sharing between plaquettes and how it affects GSF in the resulting spin systems was examined.
Monthus, Cécile
2016-07-01
The iterative methods to diagonalize matrices and many-body Hamiltonians can be reformulated as flows of Hamiltonians towards diagonalization driven by unitary transformations that preserve the spectrum. After a comparative overview of the various types of discrete flows (Jacobi, QR-algorithm) and differential flows (Toda, Wegner, White) that have been introduced in the past, we focus on the random XXZ chain with random fields in order to determine the best closed flow within a given subspace of running Hamiltonians. For the special case of the free-fermion random XX chain with random fields, the flow coincides with the Toda differential flow for tridiagonal matrices which is related to the classical integrable Toda chain and which can be seen as the continuous analog of the discrete QR-algorithm. For the random XXZ chain with random fields that displays a many-body-localization transition, the present differential flow should be an interesting alternative to compare with the discrete flow that has been proposed recently to study the many-body-localization properties in a model of interacting fermions (Rademaker and Ortuno 2016 Phys. Rev. Lett. 116, 010404).
Finite-temperature dynamics and thermal intraband magnon scattering in Haldane spin-one chains
Becker, J.; Köhler, T.; Tiegel, A. C.; Manmana, S. R.; Wessel, S.; Honecker, A.
2017-08-01
The antiferromagnetic spin-one chain is considerably one of the most fundamental quantum many-body systems, with symmetry-protected topological order in the ground state. Here, we present results for its dynamical spin structure factor at finite temperatures, based on a combination of exact numerical diagonalization, matrix-product-state calculations, and quantum Monte Carlo simulations. Open finite chains exhibit a subgap band in the thermal spectral functions, indicative of localized edge states. Moreover, we observe the thermal activation of a distinct low-energy continuum contribution to the spin spectral function with an enhanced spectral weight at low momenta and its upper threshold. This emerging thermal spectral feature of the Haldane spin-one chain is shown to result from intraband magnon scattering due to the thermal population of the single-magnon branch, which features a large bandwidth-to-gap ratio. These findings are discussed with respect to possible future studies on spin-one chain compounds based on inelastic neutron scattering.
Inverse design of disordered stealthy hyperuniform spin chains
Chertkov, Eli; DiStasio, Robert A.; Zhang, Ge; Car, Roberto; Torquato, Salvatore
2016-02-01
Positioned between crystalline solids and liquids, disordered many-particle systems which are stealthy and hyperuniform represent new states of matter that are endowed with novel physical and thermodynamic properties. Such stealthy and hyperuniform states are unique in that they are transparent to radiation for a range of wave numbers around the origin. In this work, we employ recently developed inverse statistical-mechanical methods, which seek to obtain the optimal set of interactions that will spontaneously produce a targeted structure or configuration as a unique ground state, to investigate the spin-spin interaction potentials required to stabilize disordered stealthy hyperuniform one-dimensional (1D) Ising-type spin chains. By performing an exhaustive search over the spin configurations that can be enumerated on periodic 1D integer lattices containing N =2 ,3 ,...,36 sites, we were able to identify and structurally characterize all stealthy hyperuniform spin chains in this range of system sizes. Within this pool of stealthy hyperuniform spin configurations, we then utilized such inverse optimization techniques to demonstrate that stealthy hyperuniform spin chains can be realized as either unique or degenerate disordered ground states of radial long-ranged (relative to the spin-chain length) spin-spin interactions. Such exotic ground states appear to be distinctly different from spin glasses in both their inherent structural properties and the nature of the spin-spin interactions required to stabilize them. As such, the implications and significance of the existence of these disordered stealthy hyperuniform ground-state spin systems warrants further study, including whether their bulk physical properties and excited states, like their many-particle system counterparts, are singularly remarkable, and can be experimentally realized.
Adiabatic quantum computing with spin qubits hosted by molecules.
Yamamoto, Satoru; Nakazawa, Shigeaki; Sugisaki, Kenji; Sato, Kazunobu; Toyota, Kazuo; Shiomi, Daisuke; Takui, Takeji
2015-01-28
A molecular spin quantum computer (MSQC) requires electron spin qubits, which pulse-based electron spin/magnetic resonance (ESR/MR) techniques can afford to manipulate for implementing quantum gate operations in open shell molecular entities. Importantly, nuclear spins, which are topologically connected, particularly in organic molecular spin systems, are client qubits, while electron spins play a role of bus qubits. Here, we introduce the implementation for an adiabatic quantum algorithm, suggesting the possible utilization of molecular spins with optimized spin structures for MSQCs. We exemplify the utilization of an adiabatic factorization problem of 21, compared with the corresponding nuclear magnetic resonance (NMR) case. Two molecular spins are selected: one is a molecular spin composed of three exchange-coupled electrons as electron-only qubits and the other an electron-bus qubit with two client nuclear spin qubits. Their electronic spin structures are well characterized in terms of the quantum mechanical behaviour in the spin Hamiltonian. The implementation of adiabatic quantum computing/computation (AQC) has, for the first time, been achieved by establishing ESR/MR pulse sequences for effective spin Hamiltonians in a fully controlled manner of spin manipulation. The conquered pulse sequences have been compared with the NMR experiments and shown much faster CPU times corresponding to the interaction strength between the spins. Significant differences are shown in rotational operations and pulse intervals for ESR/MR operations. As a result, we suggest the advantages and possible utilization of the time-evolution based AQC approach for molecular spin quantum computers and molecular spin quantum simulators underlain by sophisticated ESR/MR pulsed spin technology.
Low frequency spin dynamics in the quantum magnet copper pyrazine dinitrate
Energy Technology Data Exchange (ETDEWEB)
Kuehne, H.; Klauss, H.H. [Institut fuer Festkoerperphysik, TU Dresden Dresden (Germany); Institut fuer Physik der Kondensierten Materie, TU Braunschweig (Germany); Guenther, M. [Institut fuer Festkoerperphysik, TU Dresden Dresden (Germany); Grossjohann, S.; Brenig, W. [Institut fuer Theoretische Physik, TU Braunschweig (Germany); Litterst, F.J. [Institut fuer Physik der Kondensierten Materie, TU Braunschweig (Germany); Reyes, A.P.; Kuhns, P.L. [National High Magnetic Field Laboratory, Tallahassee, FL (United States); Turnbull, M.M.; Landee, C.P. [Carlson School of Chemistry and Department of Physics, Clark University, Worcester, MA (United States)
2010-03-15
The S = 1/2 antiferromagnetic Heisenberg chain exhibits a magnetic field driven quantum critical point. We study the low frequency spin dynamics in copper pyrazine dinitrate (CuPzN), a realization of this model system of quantum magnetism, by means of {sup 13}C-NMR spectroscopy. Measurements of the nuclear spin-lattice relaxation rate T{sub 1}{sup -} {sup 1} in the vicinity of the saturation field are compared with quantum Monte Carlo calculations of the dynamic structure factor. Both show a strong divergence of low energy excitations at temperatures in the quantum regime. The analysis of the anisotropic T{sub 1}{sup -} {sup 1}-rates and frequency shifts allows one to disentangle the contributions from transverse and longitudinal spin fluctuations for a selective study and to determine the transfer of delocalized spin moments from copper to the neighboring nitrogen atoms. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings
Casa Grande, H. L.; Laflorencie, N.; Alet, F.; Vieira, A. P.
2014-04-01
We investigate the low-temperature properties of the one-dimensional spin-1 Heisenberg model with geometric fluctuations induced by aperiodic but deterministic coupling distributions, involving two parameters. We focus on two aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is to understand how these geometric fluctuations modify the physics of the (gapped) Haldane phase, which corresponds to the ground state of the uniform spin-1 chain. We make use of different adaptations of the strong-disorder renormalization-group (SDRG) scheme of Ma, Dasgupta, and Hu, widely employed in the study of random spin chains, supplemented by quantum Monte Carlo and density-matrix renormalization-group numerical calculations, to study the nature of the ground state as the coupling modulation is increased. We find no phase transition for the Fibonacci chain, while we show that the 6-3 chain exhibits a phase transition to a gapless, aperiodicity-dominated phase similar to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is verified for random spin-1 chains, we show that different adaptations of the SDRG scheme may lead to different qualitative conclusions about the nature of the ground state in the presence of aperiodic coupling modulations.
Spin transport of the frustrated integer spin S antiferromagnetic Heisenberg chain
Energy Technology Data Exchange (ETDEWEB)
Lima, Leonardo S., E-mail: lslima@infis.ufu.br [Instituto de Física, Universidade Federal de Uberlândia, UFU, CEP:38700-128, Patos de Minas, MG (Brazil); Departamento de Física, ICEx, Universidade Federal de Minas Gerais, CEP:31270-901, Belo Horizonte, MG (Brazil)
2014-03-15
We study the effect of the nearest-neighbor (nn) and next-nearest-neighbor (nnn) interactions on spin transport in the quantum integer spin one-dimensional isotropic antiferromagnetic Heisenberg model. The Kubo formalism of the linear response theory is used to calculate the spin conductivity. We obtain the regular part of the spin conductivity, σ{sup reg}(ω), as function of the frequency at T=0 and obtain a strong effect of the (nnn) interaction on magnon transport.
Implementing of Quantum Cloning with Spatially Separated Quantum Dot Spins
Wen, Jing-Ji; Yeon, Kyu-Hwang; Du, Xin; Lv, Jia; Wang, Ming; Wang, Hong-Fu; Zhang, Shou
2016-07-01
We propose some schemes for implementing optimal symmetric (asymmetric) 1 → 2 universal quantum cloning, optimal symmetric (asymmetric) 1 → 2 phase-covariant cloning, optimal symmetric 1 → 3 economical phase-covariant cloning and optimal symmetric 1 → 3 economical real state cloning with spatially separated quantum dot spins by choosing the single-qubit rotation angles appropriately. The decoherences of the spontaneous emission of QDs, cavity decay and fiber loss are suppressed since the effective long-distance off-resonant interaction between two distant QDs is mediated by the vacuum fields of the fiber and cavity, and during the whole process no system is excited.
Adiabatic Theorem for Quantum Spin Systems
Bachmann, S.; De Roeck, W.; Fraas, M.
2017-08-01
The first proof of the quantum adiabatic theorem was given as early as 1928. Today, this theorem is increasingly applied in a many-body context, e.g., in quantum annealing and in studies of topological properties of matter. In this setup, the rate of variation ɛ of local terms is indeed small compared to the gap, but the rate of variation of the total, extensive Hamiltonian, is not. Therefore, applications to many-body systems are not covered by the proofs and arguments in the literature. In this Letter, we prove a version of the adiabatic theorem for gapped ground states of interacting quantum spin systems, under assumptions that remain valid in the thermodynamic limit. As an application, we give a mathematical proof of Kubo's linear response formula for a broad class of gapped interacting systems. We predict that the density of nonadiabatic excitations is exponentially small in the driving rate and the scaling of the exponent depends on the dimension.
Disorder-Induced Order in Quantum XY Chains
Niederberger, Armand; Dziarmaga, Jacek; Cucchietti, Fernando M; Wehr, Jan; Lewenstein, Maciej
2010-01-01
We observe signatures of disorder-induced order in 1D XY spin chains with an external, site-dependent uni-axial random field within the XY plane. We numerically investigate signatures of a quantum phase transition at T=0, in particular an upsurge of the magnetization in the direction orthogonal to the external magnetic field, and the scaling of the block-entropy with the amplitude of this field. Also, we discuss possible realizations of this effect in ultra-cold atom experiments.
DEFF Research Database (Denmark)
Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.
2002-01-01
is in agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted......We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar...
Spin-polarized currents generated by magnetic Fe atomic chains.
Lin, Zheng-Zhe; Chen, Xi
2014-06-13
Fe-based devices are widely used in spintronics because of high spin-polarization and magnetism. In this work, freestanding Fe atomic chains, the thinnest wires, were used to generate spin-polarized currents due to the spin-polarized energy bands. By ab initio calculations, the zigzag structure was found to be more stable than the wide-angle zigzag structure and had a higher ratio of spin-up and spin-down currents. By our theoretical prediction, Fe atomic chains have a sufficiently long thermal lifetime only at T ≦̸ 150 K, while C atomic chains are very stable even at T = 1000 K. This means that the spintronic devices based on Fe chains could work only at low temperatures. A system constructed by a short Fe chain sandwiched between two graphene electrodes could be used as a spin-polarized current generator, while a C chain could not be used in this way. The present work may be instructive and meaningful to further practical applications based on recent technical developments on the preparation of metal atomic chains (Proc. Natl. Acad. Sci. USA 107 9055 (2010)).
Quantum typicality in spin network states of quantum geometry
Anzà, Fabio
2016-01-01
In this letter we extend the so-called typicality approach, originally formulated in statistical mechanics contexts, to SU(2) invariant spin network states. Our results do not depend on the physical interpretation of the spin-network, however they are mainly motivated by the fact that spin-network states can describe states of quantum geometry, providing a gauge-invariant basis for the kinematical Hilbert space of several background independent approaches to quantum gravity. The first result is, by itself, the existence of a regime in which we show the emergence of a typical state. We interpret this as the prove that, in that regime there are certain (local) properties of quantum geometry which are "universal". Such set of properties is heralded by the typical state, of which we give the explicit form. This is our second result. In the end, we study some interesting properties of the typical state, proving that the area-law for the entropy of a surface must be satisfied at the local level, up to logarithmic c...
Quantum Markov Chain Mixing and Dissipative Engineering
DEFF Research Database (Denmark)
Kastoryano, Michael James
2012-01-01
This thesis is the fruit of investigations on the extension of ideas of Markov chain mixing to the quantum setting, and its application to problems of dissipative engineering. A Markov chain describes a statistical process where the probability of future events depends only on the state of the sy......This thesis is the fruit of investigations on the extension of ideas of Markov chain mixing to the quantum setting, and its application to problems of dissipative engineering. A Markov chain describes a statistical process where the probability of future events depends only on the state...... of the system at the present point in time, but not on the history of events. Very many important processes in nature are of this type, therefore a good understanding of their behaviour has turned out to be very fruitful for science. Markov chains always have a non-empty set of limiting distributions....... Finally, we consider three independent tasks of dissipative engineering: dissipatively preparing a maximally entangled state of two atoms trapped in an optical cavity, dissipative preparation of graph states, and dissipative quantum computing construction....
The spin Hall effect in a quantum gas.
Beeler, M C; Williams, R A; Jiménez-García, K; LeBlanc, L J; Perry, A R; Spielman, I B
2013-06-13
Electronic properties such as current flow are generally independent of the electron's spin angular momentum, an internal degree of freedom possessed by quantum particles. The spin Hall effect, first proposed 40 years ago, is an unusual class of phenomena in which flowing particles experience orthogonally directed, spin-dependent forces--analogous to the conventional Lorentz force that gives the Hall effect, but opposite in sign for two spin states. Spin Hall effects have been observed for electrons flowing in spin-orbit-coupled materials such as GaAs and InGaAs (refs 2, 3) and for laser light traversing dielectric junctions. Here we observe the spin Hall effect in a quantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz forces to realize a cold-atom spin transistor. By engineering a spatially inhomogeneous spin-orbit coupling field for our quantum gas, we explicitly introduce and measure the requisite spin-dependent Lorentz forces, finding them to be in excellent agreement with our calculations. This 'atomtronic' transistor behaves as a type of velocity-insensitive adiabatic spin selector, with potential application in devices such as magnetic or inertial sensors. In addition, such techniques for creating and measuring the spin Hall effect are clear prerequisites for engineering topological insulators and detecting their associated quantized spin Hall effects in quantum gases. As implemented, our system realizes a laser-actuated analogue to the archetypal semiconductor spintronic device, the Datta-Das spin transistor.
Quantum Adiabatic Algorithms and Large Spin Tunnelling
Boulatov, A.; Smelyanskiy, V. N.
2003-01-01
We provide a theoretical study of the quantum adiabatic evolution algorithm with different evolution paths proposed in this paper. The algorithm is applied to a random binary optimization problem (a version of the 3-Satisfiability problem) where the n-bit cost function is symmetric with respect to the permutation of individual bits. The evolution paths are produced, using the generic control Hamiltonians H (r) that preserve the bit symmetry of the underlying optimization problem. In the case where the ground state of H(0) coincides with the totally-symmetric state of an n-qubit system the algorithm dynamics is completely described in terms of the motion of a spin-n/2. We show that different control Hamiltonians can be parameterized by a set of independent parameters that are expansion coefficients of H (r) in a certain universal set of operators. Only one of these operators can be responsible for avoiding the tunnelling in the spin-n/2 system during the quantum adiabatic algorithm. We show that it is possible to select a coefficient for this operator that guarantees a polynomial complexity of the algorithm for all problem instances. We show that a successful evolution path of the algorithm always corresponds to the trajectory of a classical spin-n/2 and provide a complete characterization of such paths.
Event-chain Monte Carlo for classical continuous spin models
Michel, Manon; Mayer, Johannes; Krauth, Werner
2015-10-01
We apply the event-chain Monte Carlo algorithm to classical continuum spin models on a lattice and clarify the condition for its validity. In the two-dimensional XY model, it outperforms the local Monte Carlo algorithm by two orders of magnitude, although it remains slower than the Wolff cluster algorithm. In the three-dimensional XY spin glass model at low temperature, the event-chain algorithm is far superior to the other algorithms.
Condensed-matter physics: Quantum mechanics in a spin
Balents, Leon
2016-12-01
Quantum spin liquids are exotic states of matter first predicted more than 40 years ago. An inorganic material has properties consistent with these predictions, revealing details about the nature of quantum matter. See Letter p.559
Spin-dependent quantum transport through an Aharonov-Bohm structure spin splitter
Institute of Scientific and Technical Information of China (English)
Li Yu-Xian
2008-01-01
Using the tight-binding model approximation, this paper investigates theoretically spin-dependent quantum trans-port through an Aharonov-Bohm (AB) interferometer. An external magnetic field is applied to produce the spin-polarization and spin current. The AB interferometer, acting as a spin splitter, separates the opposite spin polarization current. By adjusting the energy and the direction of the magnetic field, large spin-polarized current can be obtained.
Form factors of the finite quantum XY-chain
Energy Technology Data Exchange (ETDEWEB)
Iorgov, Nikolai, E-mail: iorgov@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Kiev 03680 (Ukraine)
2011-08-19
Explicit factorized formulas for the matrix elements (form factors) of the spin operators {sigma}{sup x} and {sigma}{sup y} between the eigenvectors of the Hamiltonian of the finite quantum periodic XY-chain in a transverse field were derived. The derivation is based on the relations between three models: the model of quantum XY-chain, Ising model on 2D lattice and N = 2 Baxter-Bazhanov-Stroganov {tau}{sup (2)}-model. Due to these relations we transfer the formulas for the form factors of the latter model recently obtained by the use of separation of variables method to the model of quantum XY-chain. Hopefully, the formulas for the form factors will help in analysis of multipoint dynamic correlation functions at a finite temperature. As an example, we re-derive the asymptotics of the two-point correlation function in the disordered phase without the use of the Toeplitz determinants and the Wiener-Hopf factorization method.
Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths
Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao
2017-01-01
Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.
Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths.
Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao
2017-01-01
Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.
Spin and polarized current from Coulomb blockaded quantum dots.
Potok, R M; Folk, J A; Marcus, C M; Umansky, V; Hanson, M; Gossard, A C
2003-07-04
We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.
Spin dynamics in a two-dimensional quantum gas
DEFF Research Database (Denmark)
Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank
2014-01-01
We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimp......We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...
Quantum control and coherence of interacting spins in diamond
De Lange, G.
2012-01-01
The field of quantum science and technology has generated many ideas for new revolutionary devices that exploit the quantum mechanical properties of small-scale systems. Isolated solid state spins play a large role in quantum technologies. They can be used as basic building blocks for a quantum comp
Quantum control and coherence of interacting spins in diamond
De Lange, G.
2012-01-01
The field of quantum science and technology has generated many ideas for new revolutionary devices that exploit the quantum mechanical properties of small-scale systems. Isolated solid state spins play a large role in quantum technologies. They can be used as basic building blocks for a quantum comp
Quantum gravitational corrections for spinning particles
Fröb, Markus B
2016-01-01
We calculate the quantum corrections to the gauge-invariant gravitational potentials of spinning particles in flat space, induced by loops of both massive and massless matter fields of various types. While the corrections to the Newtonian potential induced by massless conformal matter for spinless particles are well-known, and the same corrections due to massless minimally coupled scalars [S. Park and R. P. Woodard, Class. Quant. Grav. 27 (2010) 245008], massless non-conformal scalars [A. Marunovic and T. Prokopec, Phys. Rev. D 87 (2013) 104027] and massive scalars, fermions and vector bosons [D. Burns and A. Pilaftsis, Phys. Rev. D 91 (2015) 064047] have been recently derived, spinning particles receive additional corrections which are the subject of the present work. We give both fully analytic results valid for all distances from the particle, and present numerical results as well as asymptotic expansions. At large distances from the particle, the corrections due to massive fields are exponentially suppres...
Quantum discord in spin-cluster materials
Yurischev, M A
2011-01-01
The total quantum correlation (discord) in Heisenberg dimers is expressed via the spin-spin correlation function, internal energy, specific heat or magnetic susceptibility. This allows one to indirectly measure the discord through neutron scattering, as well as calorimetric or magnetometric experiments. Using the available experimental data, we found the discord for a number of binuclear Heisenberg substances with both antiferro- and ferromagnetic interactions. For the dimerized antiferromagnet copper nitrate Cu(NO_3)_2*2.5H_2O, the three independent experimental methods named above lead to a discord of approximately 0.2-0.3 bit/dimer at a temperature of 4 K. We also determined the temperature behavior of discord for hydrated and anhydrous copper acetates, as well as for the ferromagnetic binuclear copper acetate complex [Cu_2L(OAc)]*6H_2O, where L is a ligand.
Bose glass behavior in (Yb1 -xLux)4As3 representing randomly diluted quantum spin-1/2 chains
Kamieniarz, G.; Matysiak, R.; Gegenwart, P.; Ochiai, A.; Steglich, F.
2016-09-01
The site-diluted compound (Yb1-xLux) 4As3 is a scarce realization of the linear Heisenberg antiferromagnet partitioned into finite-size segments and is an ideal model compound for studying field-dependent effects of quenched disorder in the one-dimensional antiferromagnets. It differentiates from the systems studied so far in two aspects—the type of randomness and the nature of the energy gap in the pure sample. We have measured the specific heat of single-crystal (Yb1-xLux) 4As3 in magnetic fields up to 19.5 T. The contribution C⊥ arising from the magnetic subsystem in an applied magnetic field perpendicular to the chains is determined. Compared to pure Yb4As3 , for which C⊥ indicates a gap opening, for diluted systems a nonexponential decay is found at low temperatures which is consistent with the thermodynamic scaling of the specific heat established for a Bose-glass phase.
Optically programmable electron spin memory using semiconductor quantum dots.
Kroutvar, Miro; Ducommun, Yann; Heiss, Dominik; Bichler, Max; Schuh, Dieter; Abstreiter, Gerhard; Finley, Jonathan J
2004-11-04
The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.
Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain
Wang, Weiwei; Gu, Chenjie; Zhou, Yan; Fangohr, Hans
2017-07-01
We theoretically investigate the spin-wave (magnon) excitations in a classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a Dirac-like equation by linearizing the Landau-Lifshitz-Gilbert equation in this antiferromagnetic system, in contrast to the ferromagnetic system in which a Schrödinger-type equation is derived. The Hamiltonian operator in the Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin chain by measuring the expectation values of the wave-packet position.
The Spin Foam Approach to Quantum Gravity
Perez, Alejandro
2012-01-01
This article reviews the present status of the spin foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently introduced new models for four dimensional quantum gravity. The models are motivated by a suitable implementation of the path integral quantization of the Plebanski formulation of gravity on a simplicial regularization. The article also includes a self-contained treatment of the 2+1 gravity. The simple nature of the latter provides the basis and a perspective for the analysis of both conceptual and technical issues that remain open in four dimensions.
Current correlations in quantum spin Hall insulators.
Schmidt, Thomas L
2011-08-26
We consider a four-terminal setup of a two-dimensional topological insulator (quantum spin Hall insulator) with local tunneling between the upper and lower edges. The edge modes are modeled as helical Luttinger liquids and the electron-electron interactions are taken into account exactly. Using perturbation theory in the tunneling, we derive the cumulant generating function for the interedge current. We show that different possible transport channels give rise to different signatures in the current noise and current cross correlations, which could be exploited in experiments to elucidate the interplay between electron-electron interactions and the helical nature of the edge states.
Hypercuboidal renormalization in spin foam quantum gravity
Bahr, Benjamin; Steinhaus, Sebastian
2017-06-01
In this article, we apply background-independent renormalization group methods to spin foam quantum gravity. It is aimed at extending and elucidating the analysis of a companion paper, in which the existence of a fixed point in the truncated renormalization group flow for the model was reported. Here, we repeat the analysis with various modifications and find that both qualitative and quantitative features of the fixed point are robust in this setting. We also go into details about the various approximation schemes employed in the analysis.
Frustrated Ferromagnetic Spin Chain near the Transition Point
Institute of Scientific and Technical Information of China (English)
ZHU Ren-Gui
2011-01-01
@@ The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered.The Hamiltonian is firstly rewritten in a form with rotated spin operators,then bosonized by using the linear spin wave approximation and then treated by using the Green function approach.An integral expression of the quantum correction to the classical ground state energy is derived.The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is-8γ2.%The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered. The Hamiltonian is firstly rewritten in a form with rotated spin operators, then bosonized by using the linear spin wave approximation and then treated by using the Green function approach. An integral expression of the quantum correction to the classical ground state energy is derived. The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is -8r2.
Effect of quantum tunneling on spin Hall magnetoresistance
Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk
2017-02-01
We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.
Spin Wigner molecules in quantum dots
Zutic, Igor; Oszwaldowski, Rafal; Stano, Peter; Petukhov, A. G.
2013-03-01
The interplay of confinement and Coulomb interactions in quantum dots can lead to strongly correlated phases differing qualitatively from the Fermi liquid behavior. While in three dimensions the correlation-induced Wigner crystal is elusive and expected only in the limit of an extremely low carrier density, its nanoscale analog, the Wigner molecule, has been observed in quantum dots at much higher densities [1]. We explore how the presence of magnetic impurities in quantum dots can provide additional opportunities to study correlation effects and the resulting ordering in carrier and impurity spins[2]. By employing exact diagonalization we reveal that seemingly simple two-carrier quantum dots lead to a rich phase diagram [2,3]. We propose experiments to verify our predictions; in particular, we discuss interband optical transitions as a function of temperature and magnetic field. DOE-BES, meta-QUTE 259 ITMS NFP Grant No. 26240120022, CE SAS QUTE, EU 260 Project Q-essence, Grant No. APVV-0646-10, and SCIEX.
Local spin relaxation within the random Heisenberg chain.
Herbrych, J; Kokalj, J; Prelovšek, P
2013-10-04
Finite-temperature local dynamical spin correlations S(nn)(ω) are studied numerically within the random spin-1/2 antiferromagnetic Heisenberg chain. The aim is to explain measured NMR spin-lattice relaxation times in BaCu(2)(Si(0.5)Ge(0.5))(2)O(7), which is the realization of a random spin chain. In agreement with experiments we find that the distribution of relaxation times within the model shows a very large span similar to the stretched-exponential form. The distribution is strongly reduced with increasing T, but stays finite also in the high-T limit. Anomalous dynamical correlations can be associated with the random singlet concept but not directly with static quantities. Our results also reveal the crucial role of the spin anisotropy (interaction), since the behavior is in contrast with the ones for the XX model, where we do not find any significant T dependence of the distribution.
The topological basis realization and the corresponding XXX spin chain
Sun, C. F.; Xue, K.; Wang, G. C.; Zhou, C. C.; Du, G. J.
2011-06-01
In this paper, it is shown that the XXX model can be constructed from the Temperley-Lieb algebra (TLA) generator. We find that the topological basis states are the two eigenstaes of a closed four-qubit Heisenberg XXX spin chain. Specifically, the spin single states and the energy single state of the system all fall on the topological basis states. It is worth mentioning that for the closed 2N-qubit (N=2, 3, 4, ...) Heisenberg XXX spin chain, all the topological basis states for 2N particles are the spin single states of the system. And the number of the topological basis states is equal to the number of the spin single states of the system, which is \\frac{(2N)!}{N!(N+1)!} .
Brachistochrone of entanglement for spin chains
Carlini, Alberto; Koike, Tatsuhiko
2017-03-01
We analytically investigate the role of entanglement in time-optimal state evolution as an application of the quantum brachistochrone, a general method for obtaining the optimal time-dependent Hamiltonian for reaching a target quantum state. As a model, we treat two qubits indirectly coupled through an intermediate qubit that is directly controllable, which represents a typical situation in quantum information processing. We find the time-optimal unitary evolution law and quantify residual entanglement by the two-tangle between the indirectly coupled qubits, for all possible sets of initial pure quantum states of a tripartite system. The integrals of the motion of the brachistochrone are determined by fixing the minimal time at which the residual entanglement is maximized. Entanglement plays a role for W and Greenberger–Horne–Zeilinger (GHz) initial quantum states, and for the bi-separable initial state in which the indirectly coupled qubits have a nonzero value of the 2-tangle.
Entanglement entropy after selective measurements in quantum chains
Najafi, Khadijeh
2016-01-01
We study bipartite post measurement entanglement entropy after selective measurements in quantum chains. We first study the quantity for the critical systems that can be described by conformal field theories. We find a connection between post measurement entanglement entropy and the Casimir energy of floating objects. Then we provide formulas for the post measurement entanglement entropy for open and finite temperature systems. We also comment on the Affleck-Ludwig boundary entropy in the context of the post measurement entanglement entropy. Finally, we also provide some formulas regarding modular hamiltonians and entanglement spectrum in the after measurement systems. After through discussion regarding CFT systems we also provide some predictions regarding massive field theories. We then discuss a generic method to calculate the post measurement entanglement entropy in the free fermion systems. Using the method we study the post measurement entanglement entropy in the XY spin chain. We check numerically the ...
Quantum spin model fitting the Yule distribution of oligonucleotides in DNA
Minichini, C
2004-01-01
A quantum spin chain is identified by the labels of a vector state of a Kashiwara crystal basis. The intensity of the one-spin flip is assumed to depend from the variation of the labels. The rank ordered plot of the numerically computed, averaged in time, transition probabilities is nicely fitted by a Yule distribution, which is the observed distribution of the ranked short oligonucleotides frequency in DNA.
The Master T-Operator for Inhomogeneous XXX Spin Chain and mKP Hierarchy
Zabrodin, Anton
2014-01-01
Following the approach of [Alexandrov A., Kazakov V., Leurent S., Tsuboi Z., Zabrodin A., J. High Energy Phys. 2013 (2013), no. 9, 064, 65 pages, arXiv:1112.3310], we show how to construct the master T-operator for the quantum inhomogeneous GL(N) XXX spin chain with twisted boundary conditions. It satisfies the bilinear identity and Hirota equations for the classical mKP hierarchy. We also characterize the class of solutions to the mKP hierarchy that correspond to eigenvalues of the master T-operator and study dynamics of their zeros as functions of the spectral parameter. This implies a remarkable connection between the quantum spin chain and the classical Ruijsenaars-Schneider system of particles.
Transport of Entanglement Through a Heisenberg-XY Spin Chain
Subramanian, V; Lakshminarayan, Arul
2004-01-01
The entanglement dynamics of spin chains is investigated using Heisenberg-XY spin Hamiltonian dynamics. The various measures of two-qubit entanglement are calculated analytically in the time-evolved state starting from initial states with no entanglement and exactly one pair of maximally-entangled qubits. The localizable entanglement between a pair of qubits at the end of chain captures the essential features of entanglement transport across the chain, and it displays the difference between an initial state with no entanglement and an initial state with one pair of maximally-entangled qubits.
Persistent spin current in a quantum wire with weak Dresselhaus spin-orbit coupling
Institute of Scientific and Technical Information of China (English)
Sheng Wei; Wang Yi; Zhou Guang-Hui
2007-01-01
The spin current in a parabolically confined semiconductor heterojunction quantum wire with Dresselhaus spinorbit coupling is theoretically studied by using the perturbation method. The formulae of the elements for linear and angular spin current densities are derived by using the recent definition for spin current based on spin continuity equation. It is found that the spin current in this Dresselhaus spin-orbit coupling quantum wire is antisymmetrical,which is different from that in R ashba model due to the difference in symmetry between these two models. Some numerical examples for the result are also demonstrated and discussed.
Quantum Zeno effect in atomic spin-exchange collisions
Energy Technology Data Exchange (ETDEWEB)
Kominis, I.K. [Department of Physics, University of Crete, Heraklion 71103 (Greece); Institute of Electronic Structure and Laser, Foundation for Research and Technology, Heraklion 71110 (Greece)], E-mail: ikominis@iesl.forth.gr
2008-07-07
The suppression of spin-exchange relaxation in dense alkali-metal vapors discovered in 1973 and governing modern atomic magnetometers is here reformulated in terms of quantum measurement theory and the quantum Zeno effect. This provides a new perspective of understanding decoherence in spin-polarized atomic vapors.
Quantum Zeno effect in atomic spin-exchange collisions
Kominis, I. K.
2008-01-01
The suppression of spin-exchange relaxation in dense alkali-metal vapors discovered in 1973 and governing modern atomic magnetometers is here reformulated in terms of quantum measurement theory and the quantum Zeno effect. This provides a new perspective of understanding decoherence in spin-polarized atomic vapors.
Geometric measures of multipartite entanglement in finite-size spin chains
Energy Technology Data Exchange (ETDEWEB)
Blasone, M; Dell' Anno, F; De Siena, S; Giampaolo, S M; Illuminati, F, E-mail: illuminati@sa.infn.i [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy)
2010-09-01
We investigate the behaviour of multipartite entanglement in finite-size quantum spin systems, resorting to a hierarchy of geometric measures of multipartite entanglement recently introduced in the literature. In particular, we investigate the ground-state entanglement in the XY model defined on finite chains of N sites with periodic boundary conditions. We analyse the behaviour of the geometric measures of (N- 1)-partite and (N/2)-partite entanglement and compare them with the Wei-Goldbart geometric measure of global entanglement.
Symmetry and Degeneracy in Quantum Mechanics. Self-Duality in Finite Spin Systems
Osacar, C.; Pacheco, A. F.
2009-01-01
The symmetry of self-duality (Savit 1980 "Rev. Mod. Phys. 52" 453) of some models of statistical mechanics and quantum field theory is discussed for finite spin blocks of the Ising chain in a transverse magnetic field. The existence of this symmetry in a specific type of these blocks, and not in others, is manifest by the degeneracy of their…
Symmetry and Degeneracy in Quantum Mechanics. Self-Duality in Finite Spin Systems
Osacar, C.; Pacheco, A. F.
2009-01-01
The symmetry of self-duality (Savit 1980 "Rev. Mod. Phys. 52" 453) of some models of statistical mechanics and quantum field theory is discussed for finite spin blocks of the Ising chain in a transverse magnetic field. The existence of this symmetry in a specific type of these blocks, and not in others, is manifest by the degeneracy of their…
Shen, Ze-Song; Hong, Fang-Yu
2016-11-01
We present a new scheme for quantum interfaces (QIs) to accomplish the interconversion of photonic qubits and spin qubits based on optomechanical resonators and the spin-orbit-induced interactions in suspended carbon nanotube quantum dots (CNTQDs). This interface implements quantum spin transducers and further enables electrical manipulation of local electron spin qubits, which lays the foundation for all-electrical control of state transfer protocols between two distant quantum nodes in a quantum network. We numerically evaluate the state transfer processes and proceed to estimate the effect of each coupling strength on the operation fidelities. The simulation suggests that high operation fidelities are obtainable under realistic experimental conditions.
Building a spin quantum bit register using semiconductor nanowires.
Baugh, J; Fung, J S; Mracek, J; LaPierre, R R
2010-04-02
This paper reviews recent advances in engineering spin quantum bits (qubits) in semiconductor quantum dots and describes an approach based on top-gated semiconductor nanowire devices. Fast electrical single-spin manipulation is achievable, in principle, using the spin-orbit interaction intrinsic to III-V materials, such as InAs, in concert with AC electric fields. Combined with sub-nanosecond gate control of the nearest-neighbor exchange interaction and spin readout by spin-to-charge conversion, a fully electrical solid-state quantum processor is within reach. We outline strategies for spin manipulation, robust readout and mitigation of decoherence due to nuclear fields that, when combined in a single device, should give a viable multi-qubit testbed and a building block for larger scale quantum devices.
The classical and quantum dynamics of molecular spins on graphene
Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Ana; Luis, Fernando; Dressel, Martin; Rauschenbach, Stephan; Kern, Klaus; Burghard, Marko; Bogani, Lapo
2015-01-01
Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic1 and quantum computing2 devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics3,4, and electrical spin-manipulation4-11. However, the influence of the graphene environment on the spin systems has yet to be unraveled12. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets13 on graphene. While the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly-developed model. Coupling to Dirac electrons introduces a dominant quantum-relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully-coherent, resonant spin tunneling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin-manipulation in graphene nanodevices. PMID:26641019
Effects of spin-orbit coupling on quantum transport
Bardarson, Jens Hjorleifur
2008-01-01
The effect of spin-orbit coupling on various quantum transport phenomena is considered. The main topics discussed are: * How spin-orbit coupling can induce shot noise through trajectory splitting. * How spin-orbit coupling can degrade electron-hole entanglement (created by a tunnel barrier) by mo
The quench action approach in finite integrable spin chains
Alba, Vincenzo; Calabrese, Pasquale
2016-04-01
We consider the problem of constructing the stationary state following a quantum quench, using the exact overlaps for finite size integrable models. We focus on the isotropic Heisenberg spin chain with initial state Néel or Majumdar-Ghosh (dimer), although the proposed approach is valid for an arbitrary integrable model. We consider only eigenstates which do not contain zero-momentum strings because the latter are affected by fictitious singularities that are very difficult to take into account. We show that the fraction of eigenstates that do not contain zero-momentum strings is vanishing in the thermodynamic limit. Consequently, restricting to this part of the Hilbert space leads to vanishing expectation values of local observables. However, it is possible to reconstruct the asymptotic values by properly reweighting the expectations in the considered subspace, at the price of introducing finite-size corrections. We also develop a Monte Carlo sampling of the Hilbert space which allows us to study larger systems. We accurately reconstruct the expectation values of the conserved charges and the root distributions in the stationary state, which turn out to match the exact thermodynamic results. The proposed method can be implemented even in cases in which an analytic thermodynamic solution is not obtainable.
Directory of Open Access Journals (Sweden)
Yu.A. Kruglyak
2015-12-01
Full Text Available Spin transport with the NEGF method in the spinor representation, in particular, spin valve, rotating magnetic contacts, spin precession and rotating spins, Zeeman and Rashba spin Hamiltonians, quantum spin Hall effect, calculation the spin potential, and four-component description of transport are discussed in the frame of the «bottom – up» approach of modern nanoelectronics.
How quantum are classical spin ices?
Gingras, Michel J. P.; Rau, Jeffrey G.
The pyrochlore spin ice compounds Dy2TiO7 and Ho2Ti2O7 are well described by classical Ising models down to low temperatures. Given the empirical success of this description, the question of the importance of quantum effects in these materials has been mostly ignored. We argue that the common wisdom that the strictly Ising moments of non-interacting Dy3+ and Ho3+ ions imply Ising interactions is too naive and that a more complex argument is needed to explain the close agreement between the classical Ising model theory and experiments. By considering a microscopic picture of the interactions in rare-earth oxides, we show that the high-rank multipolar interactions needed to induce quantum effects in these two materials are generated only very weakly by superexchange. Using this framework, we formulate an estimate of the scale of quantum effects in Dy2Ti2O7 and Ho2Ti2O7, finding it to be well below experimentally relevant temperatures. Published as: PHYSICAL REVIEW B 92, 144417 (2015).
Dynamics of the classical planar spin chain
Raedt, Bart De; Raedt, Hans De
1978-01-01
In this paper we pay attention to the classical one-dimensional planar spin system and, in particular, to the dynamics of such a model. We use the Monte Carlo method to calculate the static correlation functions, needed to determine the relaxation functions completely. We are then able to give the r
Realization of a holonomic quantum computer in a chain of three-level systems
Energy Technology Data Exchange (ETDEWEB)
Gürkan, Zeynep Nilhan, E-mail: nilhan.gurkan@gediz.edu.tr [Department of Industrial Engineering, Gediz University, Seyrek, 35665 Menemen, Izmir (Turkey); Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore (Singapore); Sjöqvist, Erik, E-mail: erik.sjoqvist@kemi.uu.se [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Department of Quantum Chemistry, Uppsala University, Box 518, SE-751 20 Uppsala (Sweden)
2015-12-18
Holonomic quantum computation is the idea to use non-Abelian geometric phases to implement universal quantum gates that are robust to fluctuations in control parameters. Here, we propose a compact design for a holonomic quantum computer based on coupled three-level systems. The scheme does not require adiabatic evolution and can be implemented in arrays of atoms or ions trapped in tailored standing wave potentials. - Highlights: • We develop a novel scheme for universal holonomic quantum computation. • The scheme involves non-Abelian geometric phases in a spin-chain. • The resources scale linearly with the number of logical qubits. • The scheme does not require adiabatic evolution.
Universal Bethe ansatz solution for the Temperley-Lieb spin chain
Nepomechie, Rafael I
2016-01-01
We consider the Temperley-Lieb (TL) open quantum spin chain with "free" boundary conditions associated with the spin-$s$ representation of quantum-deformed $sl(2)$. We construct the transfer matrix, and determine its eigenvalues and the corresponding Bethe equations using analytical Bethe ansatz. We show that the transfer matrix has quantum group symmetry, and we propose explicit formulas for the number of solutions of the Bethe equations and the degeneracies of the transfer-matrix eigenvalues. We propose an algebraic Bethe ansatz construction of the off-shell Bethe states, and we conjecture that the on-shell Bethe states are highest-weight states of the quantum group. We also propose a determinant formula for the scalar product between an off-shell Bethe state and its on-shell dual, as well as for the square of the norm. We find that all of these results, except for the degeneracies and a constant factor in the scalar product, are universal in the sense that they do not depend on the value of the spin. In an...
Quantum spin liquid ground states of the Heisenberg-Kitaev model on the triangular lattice
Kos, Pavel; Punk, Matthias
2017-01-01
We study quantum disordered ground states of the two-dimensional Heisenberg-Kitaev model on the triangular lattice using a Schwinger boson approach. Our aim is to identify and characterize potential gapped quantum spin liquid phases that are stabilized by anisotropic Kitaev interactions. For antiferromagnetic Heisenberg and Kitaev couplings and sufficiently small spin S , we find three different symmetric Z2 spin liquid phases, separated by two continuous quantum phase transitions. Interestingly, the gap of elementary excitations remains finite throughout the transitions. The first spin liquid phase corresponds to the well-known zero-flux state in the Heisenberg limit, which is stable with respect to small Kitaev couplings and develops 120∘ order in the semiclassical limit at large S . In the opposite Kitaev limit, we find a different spin liquid ground state, which is a quantum disordered version of a magnetically ordered state with antiferromagnetic chains, in accordance with results in the classical limit. Finally, at intermediate couplings, we find a spin liquid state with unusual spin correlations. Upon spinon condensation, this state develops Bragg peaks at incommensurate momenta in close analogy to the magnetically ordered Z2 vortex crystal phase, which has been analyzed in recent theoretical works.
Metastable states of a spin glass chain at 0 temperature
Energy Technology Data Exchange (ETDEWEB)
Derrida, B.; Gardner, E.
1986-06-01
We consider an Ising spin glass chain at 0 temperature. The moments of the total number of metastable states and the typical number of metastable states at a given magnetization are calculated. We find that for all magnetizations less than or equal to msub(max)=0.446042... there is an exponentially large number of metastable states. For magnetizations larger than msub(max), there are no metastable states. The remanent magnetization msub(rem) is known to be 1/3 for single spin flip dynamics when one starts at time t = 0 with all the spins aligned. This shows that the remanent magnetization is not given by the metastable states of maximum magnetization. Our results are valid for a spin glass chain with an arbitrary symmetric and continuous distribution of nearest neighbour interactions.
Exact analytical solution for quantum spins mixing in spin-1 Bose-Einstein condensates
Institute of Scientific and Technical Information of China (English)
Chen Ai-Xi; Qiu Wan-Ying; Wang Zhi-Ping
2008-01-01
This paper solves exactly a set of fully quantized coupled equations describing the quantum dynamics of quantum spins mixing in spin-1 Bose-Einstein condensates by deriving the exact explicit analytical expressions for the evolution of creation and annihilation operators.
Magnon-induced nuclear relaxation in the quantum critical region of a Heisenberg linear chain
Hoch, M. J. R.
2017-07-01
The low-temperature properties of spin-1/2 one-dimensional (1D) Heisenberg antiferromagnetic (HAF) chains which have relatively small exchange couplings between the spins can be tuned using laboratory-scale magnetic fields. Magnetization measurements, made as a function of temperature, provide phase diagrams for these systems and establish the quantum critical point (QCP). The evolution of the spin dynamics behavior with temperature and applied field in the quantum critical (QC) region, near the QCP, is of particular interest and has been experimentally investigated in a number of 1D HAFs using neutron scattering and nuclear magnetic resonance as the preferred techniques. In the QC phase both quantum and thermal spin fluctuations are present. As a result of extended spin correlations in the chains, magnon excitations are important at finite temperatures. An expression for the NMR spin-lattice relaxation rate 1 /T1 of probe nuclei in the QC phase of 1D HAFs is obtained by considering Raman scattering processes which induce nuclear spin flips. The relaxation rate expression, which involves the temperature and the chemical potential, predicts scaling behavior of 1 /T1 consistent with recent experimental findings for quasi-1D HAF systems. A simple relationship between 1 /T1 and the deviation of the magnetization from saturation (MS-M ) is predicted for the QC region.
Dynamical picture of spin Hall effect based on quantum spin vorticity theory
Directory of Open Access Journals (Sweden)
Masahiro Fukuda
2016-02-01
Full Text Available It is proposed that the dynamical picture of the spin Hall effect can be explained as the generation of the spin vorticity by the applied electric field on the basis of the “quantum spin vorticity theory”, which describes the equation of motion of local spin and the vorticity of spin in the framework of quantum field theory. Similarly, it is proposed that the dynamical picture of the inverse spin Hall effect can be explained as the acceleration of the electron by the rotation of the spin torque density as driving force accompanying the generation of the spin vorticity. These explanations may help us to understand spin phenomena in condensed matter and molecular systems from a unified viewpoint.
Non-Markovian Dynamics in Chiral Quantum Networks with Spins and Photons
Ramos, Tomás; Hauke, Philipp; Pichler, Hannes; Zoller, Peter
2016-01-01
We study the dynamics of chiral quantum networks consisting of nodes coupled by unidirectional or asymmetric bidirectional quantum channels. In contrast to the familiar photonic networks consisting of driven two-level atoms exchanging photons via 1D photonic nanostructures, we propose and study a setup where interactions between the atoms are mediated by spin excitations (magnons) in 1D XX-spin chains representing a spin waveguide. While Markovian quantum network theory eliminates quantum channels as structureless reservoirs in a Born-Markov approximation to obtain a master equation for the nodes, we are interested in non-Markovian dynamics. This arises from the nonlinear character of the dispersion with band-edge effects, and from finite spin propagation velocities leading to time delays in interactions. To account for the non-Markovian dynamics we treat the quantum degrees of freedom of the nodes and connecting channel as a composite spin system with the surrounding of the quantum network as a Markovian bat...
Linear and cubic dynamic susceptibilities in quantum spin glass
Busiello, G; Sushkova, V G
2001-01-01
The low temperature behaviour of the dynamic nonlinear (cubic) susceptibility chi sub 3 sup ' (omega, T) in quantum d-dimensional Ising spin glass with short-range interactions between spins is investigated in terms of the quantum droplet model and the quantum-mechanical nonlinear response theory is employed. We have revealed a glassy like behaviour of droplet dynamics. The frequency dependence of chi sub 3 sup ' (omega, T) is very remarkable, the temperature dependence is found at very low temperatures (quantum regime). The nonlinear response depends on the tunneling rate for a droplet which regulates the strength of quantum fluctuations. This response has a strong dependence on the distribution of droplet free energies and on the droplet length scale average. Implications for experiments in quantum spin glasses like disordered dipolar quantum Ising magnet LiHo sub x Y sub 1 sub - sub x F sub 4 and pseudospin are noted.
Implementing causality in the spin foam quantum geometry
Livine, E R; Livine, Etera R.; Oriti, Daniele
2003-01-01
We analyse the classical and quantum geometry of the Barrett-Crane spin foam model for four dimensional quantum gravity, explaining why it has to be considering as a covariant realization of the projector operator onto physical quantum gravity states. We discuss how causality requirements can be consistently implemented in this framework, and construct causal transiton amplitudes between quantum gravity states, i.e. realising in the spin foam context the Feynman propagator between states. The resulting causal spin foam model can be seen as a path integral quantization of Lorentzian first order Regge calculus, and represents a link between several approaches to quantum gravity as canonical loop quantum gravity, sum-over-histories formulations, dynamical triangulations and causal sets. In particular, we show how the resulting model can be rephrased within the framework of quantum causal sets (or histories).
Persistent Spin Current in a Quantum Wire with Weak Rashba Spin-Orbit Coupling
Institute of Scientific and Technical Information of China (English)
WANG Yi; SHENG Wei; ZHOU Guang-Hui
2006-01-01
@@ We theoretically investigate the spin current for a parabolically confined semiconductor heterojunction quantum wire with weak Rashba spin-orbit coupling by means of the perturbation method. By analytical calculation, it is found that only two components off spin current density is non-zero in the equilibrium case. Numerical examples have demonstrated that the spin current of electron transverse motion is 10-3 times that off electron longitudinal motion. However, the former one is much more sensitive to the strength of Rashba spin-orbit coupling. These results may suggest an approach to the spin storage device and to the measurement of spin current through its induced electric field.
Non-Hermitian spin chains with inhomogeneous coupling
Energy Technology Data Exchange (ETDEWEB)
Bytsko, Andrei G. [Rossijskaya Akademiya Nauk, St. Petersburg (Russian Federation). Inst. Matematiki; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany). Gruppe Theorie
2009-11-15
An open U{sub q}(sl{sub 2})-invariant spin chain of spin S and length N with inhomogeneous coupling is investigated as an example of a non-Hermitian (quasi-Hermitian) model. For several particular cases of such a chain, the ranges of the deformation parameter {gamma} are determined for which the spectrum of the model is real. For a certain range of {gamma}, a universal metric operator is constructed and thus the quasi-Hermiticity of the model is established. The constructed metric operator is non-dynamical, its structure is determined only by the symmetry of the model. The results apply, in particular, to all known homogeneous U{sub q}(sl{sub 2})-invariant integrable spin chains with nearest-neighbour interaction. In addition, the most general form of a metric operator for a quasi-Hermitian operator in finite dimensional space is discussed. (orig.)
Heavy hadron spectra from spin chains and strings
Cotrone, A L; Pons, J M; Talavera, P
2007-01-01
We study the spectrum of hadronic states made up of very massive complex scalar fields in a confining gauge theory admitting a supergravity dual background. We show that for a sub-sector of operators dual to certain spinning strings, the mass spectrum exhibits an integrable structure equal to the Heisenberg spin chain, up to an overall factor. This result is compared with the corresponding string prediction.
Spin diffusion in anisotropic Heisenberg chains: S{>=}1/2
Energy Technology Data Exchange (ETDEWEB)
Huber, D.L., E-mail: huber@src.wisc.edu [Physics Department, University of Wisconsin-Madison, 1150 University Avenue, Madison WI 53706 (United States)
2012-11-01
In this paper, we investigate spin diffusion in Heisenberg chains with uniaxial nearest-neighbor interactions. The approach followed is based on an analysis of the infinite-temperature longitudinal spin density and spin current correlation functions. For S=1/2, exact results are presented for the time-dependent correlation functions in the XY limit. Away from this limit, the second and fourth moments of the Fourier transform of the spin density correlation function provide information about spin dynamics for arbitrary values of the spin. The moments are used in an assessment of the accuracy of the Gaussian approximation for the spin diffusion constant for S=1/2. The general behavior of the Gaussian approximation when S>1/2 is discussed, and numerical results for the spin diffusion constant are presented for S=1/2, 1, 3/2, 2 and in the classical limit. A moment-based criterion for the boundary in reciprocal space between diffusive and non-diffusive dynamics that applies to arbitrary values of the spin is presented.
Loop Quantum Cosmology and Spin Foams
Ashtekar, Abhay; Henderson, Adam
2009-01-01
Loop quantum cosmology (LQC) is used to provide concrete evidence in support of the general paradigm underlying spin foam models (SFMs). Specifically, it is shown that: i) the physical inner product in the timeless framework equals the transition amplitude in the deparameterized theory; ii) this quantity admits a %convergent vertex expansion a la SFMs in which the $M$-th term refers just to $M$ volume transitions, without any reference to the time at which the transition takes place; iii) the exact physical inner product is obtained by summing over just the discrete geometries; no `continuum limit' is involved; and, iv) the vertex expansion can be interpreted as a perturbative expansion in the spirit of group field theory. This sum over histories reformulation of LQC also addresses certain other issues which are briefly summarized.
Fractional quantization of charge and spin in topological quantum pumps
Marra, Pasquale; Citro, Roberta
2017-07-01
Topological quantum pumps are topologically equivalent to the quantum Hall state: In these systems, the charge pumped during each pumping cycle is quantized and coincides with the Chern invariant. However, differently from quantum Hall insulators, quantum pumps can exhibit novel phenomena such as the fractional quantization of the charge transport, as a consequence of their distinctive symmetries in parameter space. Here, we report the analogous fractional quantization of the spin transport in a topological spin pump realized in a one-dimensional lattice via a periodically modulated Zeeman field. In the proposed model, which is a spinfull generalization of the Harper-Hofstadter model, the amount of spin current pumped during well-defined fractions of the pumping cycle is quantized as fractions of the spin Chern number. This fractional quantization of spin is topological, and is a direct consequence of the additional symmetries ensuing from the commensuration of the periodic field with the underlying lattice.
Electron spin resonance and spin-valley physics in a silicon double quantum dot.
Hao, Xiaojie; Ruskov, Rusko; Xiao, Ming; Tahan, Charles; Jiang, HongWen
2014-05-14
Silicon quantum dots are a leading approach for solid-state quantum bits. However, developing this technology is complicated by the multi-valley nature of silicon. Here we observe transport of individual electrons in a silicon CMOS-based double quantum dot under electron spin resonance. An anticrossing of the driven dot energy levels is observed when the Zeeman and valley splittings coincide. A detected anticrossing splitting of 60 MHz is interpreted as a direct measure of spin and valley mixing, facilitated by spin-orbit interaction in the presence of non-ideal interfaces. A lower bound of spin dephasing time of 63 ns is extracted. We also describe a possible experimental evidence of an unconventional spin-valley blockade, despite the assumption of non-ideal interfaces. This understanding of silicon spin-valley physics should enable better control and read-out techniques for the spin qubits in an all CMOS silicon approach.
Coherent spin-exchange via a quantum mediator
Baart, Timothy Alexander; Fujita, Takafumi; Reichl, Christian; Wegscheider, Werner; Vandersypen, Lieven Mark Koenraad
2017-01-01
Coherent interactions at a distance provide a powerful tool for quantum simulation and computation. The most common approach to realize an effective long-distance coupling 'on-chip' is to use a quantum mediator, as has been demonstrated for superconducting qubits and trapped ions. For quantum dot arrays, which combine a high degree of tunability with extremely long coherence times, the experimental demonstration of the time evolution of coherent spin-spin coupling via an intermediary system remains an important outstanding goal. Here, we use a linear triple-quantum-dot array to demonstrate a coherent time evolution of two interacting distant spins via a quantum mediator. The two outer dots are occupied with a single electron spin each, and the spins experience a superexchange interaction through the empty middle dot, which acts as mediator. Using single-shot spin readout, we measure the coherent time evolution of the spin states on the outer dots and observe a characteristic dependence of the exchange frequency as a function of the detuning between the middle and outer dots. This approach may provide a new route for scaling up spin qubit circuits using quantum dots, and aid in the simulation of materials and molecules with non-nearest-neighbour couplings such as MnO (ref. 27), high-temperature superconductors and DNA. The same superexchange concept can also be applied in cold atom experiments.
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-06-22
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.
Quantum gravitational corrections for spinning particles
Fröb, Markus B.
2016-10-01
We calculate the quantum corrections to the gauge-invariant gravitational potentials of spinning particles in flat space, induced by loops of both massive and massless matter fields of various types. While the corrections to the Newtonian potential induced by massless conformal matter for spinless particles are well known, and the same corrections due to massless minimally coupled scalars [23], massless non-conformal scalars [25] and massive scalars, fermions and vector bosons [98] have been recently derived, spinning particles receive additional corrections which are the subject of the present work. We give both fully analytic results valid for all distances from the particle, and present numerical results as well as asymptotic expansions. At large distances from the particle, the corrections due to massive fields are exponentially suppressed in comparison to the corrections from massless fields, as one would expect. However, a surprising result of our analysis is that close to the particle itself, on distances comparable to the Compton wavelength of the massive fields running in the loops, these corrections can be enhanced with respect to the massless case.
Entanglement entropy after selective measurements in quantum chains
Najafi, Khadijeh; Rajabpour, M. A.
2016-12-01
We study bipartite post measurement entanglement entropy after selective measurements in quantum chains. We first study the quantity for the critical systems that can be described by conformal field theories. We find a connection between post measurement entanglement entropy and the Casimir energy of floating objects. Then we provide formulas for the post measurement entanglement entropy for open and finite temperature systems. We also comment on the Affleck-Ludwig boundary entropy in the context of the post measurement entanglement entropy. Finally, we also provide some formulas regarding modular hamiltonians and entanglement spectrum in the after measurement systems. After through discussion regarding CFT systems we also provide some predictions regarding massive field theories. We then discuss a generic method to calculate the post measurement entanglement entropy in the free fermion systems. Using the method we study the post measurement entanglement entropy in the XY spin chain. We check numerically the CFT and the massive field theory results in the transverse field Ising chain and the XX model. In particular, we study the post meaurement entanglement entropy in the infinite, periodic and open critical transverse field Ising chain and the critical XX model. The effect of the temperature and the gap is also discussed in these models.
Control and measurement of electron spins in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Kouwenhoven, L.P.; Elzerman, J.M.; Hanson, R.; Willems van Beveren, L.H.; Vandersypen, L.M.K. [ERATO Mesoscopic Correlation Project, Delft University of Technology, Delft (Netherlands); Kavli Institute of Nanoscience Delft (Netherlands)
2006-11-15
We present an overview of experimental steps taken towards using the spin of a single electron trapped in a semiconductor quantum dot as a spin qubit [Loss and DiVincenzo, Phys. Rev. A 57, 120 (1998)]. Fabrication and characterization of a double quantum dot containing two coupled spins has been achieved, as well as initialization and single-shot read-out of the spin state. The relaxation time T {sub 1} of single-spin and two-spin states was found to be on the order of a millisecond, dominated by spin-orbit interactions. The time-averaged dephasing time T{sub 2}{sup *}, due to fluctuations in the ensemble of nuclear spins in the host semiconductor, was determined to be on the order of several tens of nanoseconds. Coherent manipulation of single-spin states can be performed using a microfabricated wire located close to the quantum dot, while two-spin interactions rely on controlling the tunnel barrier connecting the respective quantum dots [Petta et al., Science 309, 2180 (2005)]. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Zero-Temperature Study of a Tetrameric Spin-1/2 Chain in a Transverse Magnetic Field
Vahedi, J.; Arbousara, M. Shabani; Mahdavifar, S.
2017-02-01
We consider an alternating Heisenberg spin-1/2 antiferromagnetic-ferromagnetic chain with the space-modulated dominant antiferromagnetic exchange and anisotropic ferromagnetic coupling (tetrameric spin-1/2 chain). The zero-temperature effect of a symmetry breaking transverse magnetic field on the model is studied numerically. It is found that the anisotropy effect on the ferromagnetic coupling induces two new gapped phases. We identified their orderings as a kind of the stripe antiferromagnetic phase. As a result, the magnetic phase diagram of the tetrameric chain shows five gapped quantum phases, and the system is characterized by four critical fields which mark quantum phase transitions in the ground state of the system with the changing transverse magnetic field. We have also exploited the well-known bipartite entanglement (name as concurrence) and global entanglement tools to verify the occurrence of quantum phase transitions and the corresponding critical points.
The "Proton Spin Crisis" — a Quantum Query
Directory of Open Access Journals (Sweden)
Hansson J.
2010-07-01
Full Text Available The “proton spin crisis” was introduced in the late 1980s, when the EMC-experiment revealed that little or nothing of a proton’s spin seemed to be carried by its quarks. The main objective of this paper is to point out that it is wrong to assume that the proton spin, as measured by completely different experimental setups, should be the same in all circumstances, an assumption explicitly made in all present theoretical treatments of the “crisis”. As spin is a genuine quantum property, without any objective existence outside its measuring apparatus context, proper account of quantum mechanical measurement theory must be taken.
Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit
Bechtold, A.; Li, F.; Müller, K.; Simmet, T.; Ardelt, P.-L.; Finley, J. J.; Sinitsyn, N. A.
2016-07-01
We measure time correlators of a spin qubit in an optically active quantum dot beyond the second order. Such higher-order correlators are shown to be directly sensitive to pure quantum effects that cannot be explained within the classical framework. They allow direct determination of ensemble and quantum dephasing times, T2* and T2, using only repeated projective measurements and without the need for coherent spin control. Our method enables studies of purely quantum behavior in solid state systems, including tests of the Leggett-Garg type of inequalities that rule out local hidden variable interpretation of the quantum-dot spin dynamics.
Topologically protected quantum state transfer in a chiral spin liquid.
Yao, N Y; Laumann, C R; Gorshkov, A V; Weimer, H; Jiang, L; Cirac, J I; Zoller, P; Lukin, M D
2013-01-01
Topology plays a central role in ensuring the robustness of a wide variety of physical phenomena. Notable examples range from the current-carrying edge states associated with the quantum Hall and the quantum spin Hall effects to topologically protected quantum memory and quantum logic operations. Here we propose and analyse a topologically protected channel for the transfer of quantum states between remote quantum nodes. In our approach, state transfer is mediated by the edge mode of a chiral spin liquid. We demonstrate that the proposed method is intrinsically robust to realistic imperfections associated with disorder and decoherence. Possible experimental implementations and applications to the detection and characterization of spin liquid phases are discussed.
Spin chains and channels with memory
Plenio, M. B.; Virmani, S.
2007-01-01
In most studies of the channel capacity of quantum channels, it is assumed that the errors in each use of the channel are independent. However, recent work has begun to investigate the effects of memory or correlations in the error. This work has led to speculation that interesting non-analytic behaviour may occur in the capacity. Motivated by these observations, we connect the study of channel capacities under correlated error to the study of critical behaviour in many-body physics. This con...
Quantum phases of a chain of strongly interacting anyons
Finch, Peter E.; Frahm, Holger; Lewerenz, Marius; Milsted, Ashley; Osborne, Tobias J.
2014-08-01
Quantum gates for the manipulation of topological qubits rely on interactions between non-Abelian anyonic quasiparticles. We study the collective behavior of systems of anyons arising from such interactions. In particular, we study the effect of favoring different fusion channels of the screened Majorana spins appearing in the recently proposed topological Kondo effect. Based on the numerical solution of a chain of SO(5)2 anyons we identify two critical phases whose low-energy behavior is characterized by conformal field theories with central charges c =1 and c =8/7, respectively. Our results are complemented by exact results for special values of the coupling constants which provide additional information about the corresponding phase transitions.
Kosevich, Yuriy A; Gann, Vladimir V
2013-06-19
We study the localization of magnon states in finite defect-free Heisenberg spin-1/2 ferromagnetic chains placed in an inhomogeneous magnetic field with a constant spatial gradient. Continuous transformation from the extended magnon states to the localized Wannier-Zeeman states in a finite spin chain placed in an inhomogeneous field is described both analytically and numerically. We describe for the first time the non-monotonic dependence of the energy levels of magnons, both long and short wavelength, on the magnetic field gradient, which is a consequence of magnon localization in a finite spin chain. We show that, in contrast to the destruction of the magnon band and the establishment of the Wannier-Stark ladder in a vanishingly small field gradient in an infinite chain, the localization of magnon states at the chain ends preserves the memory of the magnon band. Essentially, the localization at the lower- or higher-field chain end resembles the localization of the positive- or negative-effective-mass band quasiparticles. We also show how the beat dynamics of coherent superposition of extended spin waves in a finite chain in a homogeneous or weakly inhomogeneous field transforms into magnon Bloch oscillations of the superposition of localized Wannier-Zeeman states in a strongly inhomogeneous field. We provide a semiclassical description of the magnon Bloch oscillations and show that the correspondence between the quantum and semiclassical descriptions is most accurate for Bloch oscillations of the magnon coherent states, which are built from a coherent superposition of a large number of the nearest-neighbour Wannier-Zeeman states.
Spin chains and Gustafson's integrals
Energy Technology Data Exchange (ETDEWEB)
Derkachov, S.E [Russian Academy of Sciences, St. Petersburg (Russian Federation). Steklov Mathematical Inst.; Manashov, A.N. [Hamburg Univ. (Germany). II. Inst. fuer Theoretische Physik; Regensburg Univ. (Germany). Inst. for Theoretical Physics
2016-12-15
The Gustafson's integrals are the multidimensional generalization of the classical Mellin-Barnes integrals. We show that some of these integrals arise from relations between matrix elements in the Sklyanin's representation of Separated Variables in the spin chain models. We also present several new integrals.
Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction
Directory of Open Access Journals (Sweden)
Yokoyama Tomohiro
2011-01-01
Full Text Available Abstract We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied. PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d
The paramagnetic properties of ferromagnetic mixed-spin chain system
Energy Technology Data Exchange (ETDEWEB)
Hu, Ai-Yuan, E-mail: huaiyuanhuyuanai@126.com; Wu, Zhi-Min; Cui, Yu-Ting; Qin, Guo-Ping
2015-01-15
The double-time Green's function method is used to investigate the paramagnetic properties of ferromagnetic mixed-spin chain system within the random-phase approximation and Anderson–Callen's decoupling approximation. The analytic expressions of the transverse susceptibility, longitudinal susceptibility and correlation length are obtained under transverse and longitudinal magnetic field. Using the analytic expressions of the transverse and longitudinal susceptibility to fit the experimental results, our results well agree with experimental data and the results from the high temperature series expansion within a simple Padé approximation. - Highlights: • We investigate the magnetic properties of a ferromagnetic mixed-spin chain system. • We use the double-time temperature-dependent Green's function technique. • Different single-ion anisotropy values for different spin values are considered. • Our results agree with experimental data and the results from the other theoretical methods.
Anisotropic intrinsic spin Hall effect in quantum wires.
Cummings, A W; Akis, R; Ferry, D K
2011-11-23
We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [N110] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications.
Tuning Electron Spin States in Quantum Dots by Spin-Orbit Interactions
Institute of Scientific and Technical Information of China (English)
LIU Yu; CHENG Fang
2011-01-01
@@ We theoretically investigate the influence of both Rashba spin-orbit interaction (RSOI) and Dresselhaus spin- orbit interaction (DSOI) on electron spin states, electron distribution and the optical absorption of a quantum dot.Our theoretical results show that the interplay between RSOI and DSOI results in an effective periodic potential, which consequently breaks the rotational symmetry and makes the quantum dot behave like two laterally coupled quantum dots.In the presence of RSOI and/or DSOI the spin is no longer a conserved quantity and its magnitude can be tuned by changing the strength of RSOI and/or DSOI.By reversing the direction of the perpendicular electric field, we can rotate the spatial distribution.This property provides us with a new way to control quantum states in a quantum dot by electrical means.
Resonance fluorescence and electron spin in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Zhao, Yong
2009-11-18
The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)
Electron nuclear spin transfer in quantum-dot networks
Prada, M.; Toonen, R. C.; Blick, R. H.; Harrison, P.
2005-05-01
We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of different geometries of a two-dimensional network of quantum dots and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalized to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in the presence of nuclear spin relaxation. We find that the gradual depolarization of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.
The new spin foam models and quantum gravity
Perez, Alejandro
2012-01-01
In this article we give a systematic definition of the recently introduced spin foam models for four dimensional quantum gravity reviewing the main results on their semiclassical limit on fixed discretizations.
Kitanine, N; Niccoli, G
2014-01-01
We solve the longstanding problem to define a functional characterization of the spectrum of the transfer matrix associated to the most general spin-1/2 representations of the 6-vertex reflection algebra for general inhomogeneous chains. The corresponding homogeneous limit reproduces the spectrum of the Hamiltonian of the spin-1/2 open XXZ and XXX quantum chains with the most general integrable boundaries. The spectrum is characterized by a second order finite difference functional equation of Baxter type with an inhomogeneous term which vanishes only for some special but yet interesting non-diagonal boundary conditions. This functional equation is shown to be equivalent to the known separation of variable (SOV) representation hence proving that it defines a complete characterization of the transfer matrix spectrum. The polynomial character of the Q-function allows us then to show that a finite system of equations of generalized Bethe type can be similarly used to describe the complete transfer matrix spectru...
Finite Temperature Properties of Mixed Diamond Chain with Spins 1 and 1/2
Hida, Kazuo; Takano, Ken'ichi; Suzuki, Hidenori
2009-08-01
We formulate statistical mechanics for a mixed diamond chain with spins 1 and 1/2. Owing to a series of conservation laws, any eigenstate of this system is decomposed into eigenstates of finite odd-length spin-1 chains. The ground state undergoes five quantum phase transitions with varying λ, a parameter that controls frustration. We evaluated the residual entropy and Curie constant which characterize each phase and phase boundary at low temperatures. We further find various characteristic finite-temperature properties such as the nonmonotonic temperature dependence of magnetic susceptibility, the multipeak structure in the λ-dependence of entropy, the plateau-like temperature dependence of entropy and the multipeak structure of specific heat.
Flux rectification in the quantum XXZ chain.
Landi, Gabriel T; Novais, E; de Oliveira, Mário J; Karevski, Dragi
2014-10-01
Thermal rectification is the phenomenon by which the flux of heat depends on the direction of the flow. It has attracted much interest in recent years due to the possibility of devising thermal diodes. In this paper, we consider the rectification phenomenon in the quantum XXZ chain subject to an inhomogeneous field. The chain is driven out of equilibrium by the contact at its boundaries with two different reservoirs, leading to a constant flow of magnetization from one bath to the other. The nonunitary dynamics of this system, which is modeled by a Lindblad master equation, is treated exactly for small sizes and numerically for larger ones. The functional dependence of the rectification coefficient on the model parameters (anisotropy, field amplitude, and out of equilibrium driving strength) is investigated in full detail. Close to the XX point and at small inhomogeneity and low driving, we have found an explicit expression for the rectification coefficient that is valid at all system sizes. In particular, it shows that the phenomenon of rectification persists even in the thermodynamic limit. Finally, we prove that in the case of the XX chain, there is no rectification.
Spin-polarized spin-orbit-split quantum-well states in a metal film
Energy Technology Data Exchange (ETDEWEB)
Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)
2008-07-01
Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.
Quantum spin Hall effect and topological insulators for light
Bliokh, Konstantin Y
2015-01-01
We show that free-space light has intrinsic quantum spin-Hall effect (QSHE) properties. These are characterized by a non-zero topological spin Chern number, and manifest themselves as evanescent modes of Maxwell equations. The recently discovered transverse spin of evanescent modes demonstrates spin-momentum locking stemming from the intrinsic spin-orbit coupling in Maxwell equations. As a result, any interface between free space and a medium supporting surface modes exhibits QSHE of light with opposite transverse spins propagating in opposite directions. In particular, we find that usual isotropic metals with surface plasmon-polariton modes represent natural 3D topological insulators for light. Several recent experiments have demonstrated transverse spin-momentum locking and spin-controlled unidirectional propagation of light at various interfaces with evanescent waves. Our results show that all these experiments can be interpreted as observations of the QSHE of light.
Multiple quantum spin counting techniques with quadrupolar nuclei.
Dodd, Andrew J; van Eck, Ernst R H
2004-01-01
Phase incremented and continuous irradiation multiple spin correlation methods are applied to spin [Formula: see text] nuclei with small quadrupole couplings such as (7)Li in LiCl and are shown to successfully produce a coherently coupled dipolar spin network. Application to the analogous Na salt shows successful spin correlation evolving at a slower rate due to the weaker homonuclear dipolar coupling strength between Na nuclei. The results are analysed using a statistical approach. Spin counting is non-trivial as not only multiple quantum coherences between spins are generated but also within the quadrupolar spin levels. Na(2)C(2)O(4) is investigated as a material with non-negligible quadrupole coupling and it is in this limit that the spin correlation techniques are found to break down.
Energy Technology Data Exchange (ETDEWEB)
Ebisawa, T.; Tasaki, S.; Kawai, T.; Akiyoshi, T. [Kyoto Univ., Kumatori, Osaka (Japan). Research Reactor Inst.; Achiwa, N.; Hino, M.; Otake, Y.; Funahashi, H.
1996-08-01
The authors have developed cold neutron optics and interferometry using multilayer mirrors. The advantages of the multilayer mirrors are their applicability to long wavelength neutrons and a great variety of the mirror performance. The idea of the present spin interferometry is based on nonmagnetic neutron spin quantum precession using multilayer spin splitters. The equation for polarized neutrons means that the polarized neutrons are equivalent to the coherent superposition of two parallel spin eigenstates. The structure and principle of a multilayer spin splitter are explained, and the nonmagnetic gap layer of the multilayer spin splitter gives rise to neutron spin quantum precession. The performance test of the multilayer spin splitter were made with a new spin interferometer, which is analogous optically to a spin echo system with vertical precession field. The spin interferometers were installed at Kyoto University research reactor and the JRR-3. The testing method and the results are reported. The performance tests on a new phase-spin echo interferometer are described, and its applications to the development of a high resolution spin echo system and a Jamin type cold neutron interferometer are proposed. (K.I.)
Classical impurities and boundary Majorana zero modes in quantum chains
Müller, Markus; Nersesyan, Alexander A.
2016-09-01
We study the response of classical impurities in quantum Ising chains. The Z2 degeneracy they entail renders the existence of two decoupled Majorana modes at zero energy, an exact property of a finite system at arbitrary values of its bulk parameters. We trace the evolution of these modes across the transition from the disordered phase to the ordered one and analyze the concomitant qualitative changes of local magnetic properties of an isolated impurity. In the disordered phase, the two ground states differ only close to the impurity, and they are related by the action of an explicitly constructed quasi-local operator. In this phase the local transverse spin susceptibility follows a Curie law. The critical response of a boundary impurity is logarithmically divergent and maps to the two-channel Kondo problem, while it saturates for critical bulk impurities, as well as in the ordered phase. The results for the Ising chain translate to the related problem of a resonant level coupled to a 1d p-wave superconductor or a Peierls chain, whereby the magnetic order is mapped to topological order. We find that the topological phase always exhibits a continuous impurity response to local fields as a result of the level repulsion of local levels from the boundary Majorana zero mode. In contrast, the disordered phase generically features a discontinuous magnetization or charging response. This difference constitutes a general thermodynamic fingerprint of topological order in phases with a bulk gap.
Generation of heralded entanglement between distant quantum dot hole spins
Delteil, Aymeric
Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of
Spin and Uncertainty in the Interpretation of Quantum Mechanics.
Hestenes, David
1979-01-01
Points out that quantum mechanics interpretations, using Heisenberg's Uncertainty Relations for the position and momentum of an electron, have their drawbacks. The interpretations are limited to the Schrodinger theory and fail to take into account either spin or relativity. Shows why spin cannot be ignored. (Author/GA)
Exchange cotunneling through quantum dots with spin-orbit coupling
DEFF Research Database (Denmark)
Paaske, Jens; Andersen, Andreas; Flensberg, Karsten
2010-01-01
We investigate the effects of spin-orbit interaction (SOI) on the exchange cotunneling through a spinful Coulomb blockaded quantum dot. In the case of zero magnetic field, Kondo effect is shown to take place via a Kramers doublet and the SOI will merely affect the Kondo temperature. In contrast, we...
Exchange cotunneling through quantum dots with spin-orbit coupling
DEFF Research Database (Denmark)
Paaske, Jens; Andersen, Andreas; Flensberg, Karsten
2010-01-01
We investigate the effects of spin-orbit interaction (SOI) on the exchange cotunneling through a spinful Coulomb blockaded quantum dot. In the case of zero magnetic field, Kondo effect is shown to take place via a Kramers doublet and the SOI will merely affect the Kondo temperature. In contrast, ...
Controlling electron quantum dot qubits by spin-orbit interactions
Energy Technology Data Exchange (ETDEWEB)
Stano, P.
2007-01-15
Single electron confined in a quantum dot is studied. A special emphasis is laid on the spin properties and the influence of spin-orbit interactions on the system. The study is motivated by a perspective exploitation of the spin of the confined electron as a qubit, a basic building block of in a foreseen quantum computer. The electron is described using the single band effective mass approximation, with parameters typical for a lateral electrostatically defined quantum dot in a GaAs/AlGaAs heterostructure. The stemming data for the analysis are obtained by numerical methods of exact diagonalization, however, all important conclusions are explained analytically. The work focuses on three main areas -- electron spectrum, phonon induced relaxation and electrically and magnetically induced Rabi oscillations. It is shown, how spin-orbit interactions influence the energy spectrum, cause finite spin relaxation and allow for all-electrical manipulation of the spin qubit. Among the main results is the discovery of easy passages, where the spin relaxation is unusually slow and the qubit is protected against parasitic electrical fields connected with manipulation by resonant electromagnetic fields. The results provide direct guide for manufacturing quantum dots with much improved properties, suitable for realizing single electron spin qubits. (orig.)
Dynamics of open quantum spin systems : An assessment of the quantum master equation approach
Zhao, P.; De Raedt, H.; Miyashita, S.; Jin, F.; Michielsen, K.
2016-01-01
Data of the numerical solution of the time-dependent Schrodinger equation of a system containing one spin-1/2 particle interacting with a bath of up to 32 spin-1/2 particles is used to construct a Markovian quantum master equation describing the dynamics of the system spin. The procedure of obtainin
Universal temperature dependence of the magnetization of gapped spin chains.
Maeda, Yoshitaka; Hotta, Chisa; Oshikawa, Masaki
2007-08-03
A Haldane chain under applied field is analyzed numerically, and a clear minimum of magnetization is observed as a function of temperature. We elucidate its origin using the effective theory near the critical field and propose a simple method to estimate the gap from the magnetization at finite temperatures. We also demonstrate that there exists a relation between the temperature dependence of the magnetization and the field dependence of the spin-wave velocity. Our arguments are universal for general axially symmetric one-dimensional spin systems.
Q-operators for the open Heisenberg spin chain
Directory of Open Access Journals (Sweden)
Rouven Frassek
2015-12-01
Full Text Available We construct Q-operators for the open spin-12 XXX Heisenberg spin chain with diagonal boundary matrices. The Q-operators are defined as traces over an infinite-dimensional auxiliary space involving novel types of reflection operators derived from the boundary Yang–Baxter equation. We argue that the Q-operators defined in this way are polynomials in the spectral parameter and show that they commute with transfer matrix. Finally, we prove that the Q-operators satisfy Baxter's TQ-equation and derive the explicit form of their eigenvalues in terms of the Bethe roots.
Q-operators for the open Heisenberg spin chain
Frassek, Rouven
2015-01-01
We construct Q-operators for the open spin-1/2 XXX Heisenberg spin chain with diagonal boundary matrices. The Q-operators are defined as traces over an infinite-dimensional auxiliary space involving novel types of reflection operators derived from the boundary Yang-Baxter equation. We argue that the Q-operators defined in this way are polynomials in the spectral parameter and show that they commute with transfer matrix. Finally, we prove that the Q-operators satisfy Baxter's TQ-equation.
Q-operators for the open Heisenberg spin chain
Frassek, Rouven; Szécsényi, István M.
2015-12-01
We construct Q-operators for the open spin-1/2 XXX Heisenberg spin chain with diagonal boundary matrices. The Q-operators are defined as traces over an infinite-dimensional auxiliary space involving novel types of reflection operators derived from the boundary Yang-Baxter equation. We argue that the Q-operators defined in this way are polynomials in the spectral parameter and show that they commute with transfer matrix. Finally, we prove that the Q-operators satisfy Baxter's TQ-equation and derive the explicit form of their eigenvalues in terms of the Bethe roots.
Macroscooic inequivalent entanglement witness in Heisenberg spin Chain
Institute of Scientific and Technical Information of China (English)
Zhang Ting; Chen Ping-Xing; Li Cheng-Zu
2009-01-01
Motivated by the wise idea of entanglement witness(EW),we present an inequivalent entanglement witness(IEEW)that can analogously classify certain eigenstates entangled in inequivalent ways under stochastic local operations and classical communication(SLOCC)in the Heisenberg spin chain.Since the IEEW is the absolute value of magnetization |M| that is a macroscopically measurable quantity,our conclusions provide a macroscopic method to detect incquivalent entanglement between microscopic spins,on the one hand,and clearly show that inequivalent entanglement can yield different macroscopic effects,on the other hand.
Spin-orbit-enhanced Wigner localization in quantum dots
DEFF Research Database (Denmark)
Cavalli, Andrea; Malet, F.; Cremon, J. C.
2011-01-01
We investigate quantum dots with Rashba spin-orbit coupling in the strongly-correlated regime. We show that the presence of the Rashba interaction enhances the Wigner localization in these systems, making it achievable for higher densities than those at which it is observed in Rashba-free quantum...
Electron spin and charge in semiconductor quantum dots
Elzerman, J.M.
2004-01-01
In this thesis, the spin and charge degree of freedom of electrons in semiconductor lateral and vertical quantum dots are experimentally investigated. The lateral quantum dot devices are defined in a two-dimensional electron gas (2DEG) below the surface of a GaAs/AlGaAs heterostructure, by metallic
Spin-orbit interaction induced current dip in a single quantum dot coupled to a spin
Giavaras, G.
2017-03-01
Experiments on semiconductor quantum dot systems have demonstrated the coupling between electron spins in quantum dots and spins localized in the neighboring area of the dots. Here we show that in a magnetic field the electrical current flowing through a single quantum dot tunnel-coupled to a spin displays a dip at the singlet-triplet anticrossing point which appears due to the spin-orbit interaction. We specify the requirements for which the current dip is formed and examine the properties of the dip for various system parameters, such as energy detuning, spin-orbit interaction strength, and coupling to leads. We suggest a parameter range in which the dip could be probed.
A Quantum Spin System with Random Interactions I
Indian Academy of Sciences (India)
Stephen Dias Barreto
2000-11-01
We study a quantum spin glass as a quantum spin system with random interactions and establish the existence of a family of evolution groups $\\{\\mathcal{T}_t()\\}_{\\in}$ of the spin system. The notion of ergodicity of a measure preserving group of automorphisms of the probability space , is used to prove the almost sure independence of the Arveson spectrum $\\mathrm{Sp}(\\mathcal{T}())$ of $\\mathcal{T}_t()$. As a consequence, for any family of $(\\mathcal{T}(), )$-KMS states {ρ()}, the spectrum of the generator of the group of unitaries which implement $\\mathcal{T}()$ in the GNS representation is also almost surely independent of .
Infinite-Range Quantum Dzyaloshinskii-Moriya Spin Glass Model
Institute of Scientific and Technical Information of China (English)
商育民; 姚凯伦
2003-01-01
Based on the replica method and the imaginary time functional-integral technique,we investigate the infiniterange quantum Dzyaloshinskii-Moriya spin glass model.It is found that the quantum Dzyaloshinskii-Moriya spin glass model behaves in a Heisenberg-like manner.The specific heat has the crossover behaviour.The broad Maximum in specific heat is shifted to higher temperature with increasing applied field.These features are in good agreement with the observation of Brodale et al.[J.Magn.Magn.Matter.31-34(1983)1331] The susceptibility of the system has the typical spin glass feature.
Spin-orbit hybrid entanglement of photons and quantum contextuality
Karimi, Ebrahim; Slussarenko, Sergei; Piccirillo, Bruno; Marrucci, Lorenzo; Chen, Lixiang; She, Weilong; Franke-Arnold, Sonja; Padgett, Miles J; Santamato, Enrico; 10.1103/PhysRevA.82.022115
2011-01-01
We demonstrate electromagnetic quantum states of single photons and of correlated photon pairs exhibiting "hybrid" entanglement between spin and orbital angular momentum. These states are obtained from entangled photon pairs emitted by spontaneous parametric down conversion, by employing a $q$-plate for coupling the spin and orbital degrees of freedom of a photon. Entanglement and contextual quantum behavior (that is also non-local, in the case of photon pairs) is demonstrated by the reported violation of the Clauser-Horne-Shimony-Holt inequality. In addition a classical analog of the hybrid spin-orbit photonic entanglement is reported and discussed.
Classical and Quantum features of the spin-curvature coupling
Cianfrani, Francesco; Montani, Giovanni
2007-04-01
We analyze the behavior of a spinning particle in gravity, both from a quantum and a classical perspective point of view. We infer that, since the interaction between the space-time curvature and a spinning test particle is expected, then the main features of such an interaction can get light on which degrees of freedom have physical meaning in a quantum gravity theory with fermions. Finally, the dimensional reduction of Papapetrou equations is performed in a 5-dimensional Kaluza-Klein background and Dixon-Souriau results for the motion of a charged spinning body are obtained.
Coherence and control of quantum registers based on electronic spin in a nuclear spin bath.
Cappellaro, P; Jiang, L; Hodges, J S; Lukin, M D
2009-05-29
We consider a protocol for the control of few-qubit registers comprising one electronic spin embedded in a nuclear spin bath. We show how to isolate a few proximal nuclear spins from the rest of the bath and use them as building blocks for a potentially scalable quantum information processor. We describe how coherent control techniques based on magnetic resonance methods can be adapted to these solid-state spin systems, to provide not only efficient, high fidelity manipulation but also decoupling from the spin bath. As an example, we analyze feasible performances and practical limitations in the realistic setting of nitrogen-vacancy centers in diamond.
Lee, Seungwon; vonAllmen, Paul; Oyafuso, Fabiano; Klimeck, Gerhard; Whale, K. Birgitta
2004-01-01
Electron spin dephasing and decoherence by its interaction with nuclear spins in self-assembled quantum dots are investigated in the framework of the empirical tight-binding model. Electron spin dephasing in an ensemble of dots is induced by the inhomogeneous precession frequencies of the electron among dots, while electron spin decoherence in a single dot arises from the inhomogeneous precession frequencies of nuclear spins in the dot. For In(x)Ga(1-x) As self-assembled dots containing 30000 nuclei, the dephasing and decoherence times are predicted to be on the order of 100 ps and 1 (micro)s.
Pumping of nuclear spins by optical excitation of spin-forbidden transitions in a quantum dot.
Chekhovich, E A; Makhonin, M N; Kavokin, K V; Krysa, A B; Skolnick, M S; Tartakovskii, A I
2010-02-12
We demonstrate that efficient optical pumping of nuclear spins in semiconductor quantum dots (QDs) can be achieved by resonant pumping of optically forbidden transitions. This process corresponds to one-to-one conversion of a photon absorbed by the dot into a polarized nuclear spin, and also has potential for initialization of hole spin in QDs. We find that by employing this spin-forbidden process, nuclear polarization of 65% can be achieved, markedly higher than from pumping the allowed transition, which saturates due to the low probability of electron-nuclear spin flip-flop.
Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots
Institute of Scientific and Technical Information of China (English)
ZHU Fei-Yun; TU Tao; HAO Xiao-Jie; GUO Guang-Can; GUO Guo-Ping
2009-01-01
We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact (QPC) as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.
Rényi entanglement entropy of critical SU (N ) spin chains
D'Emidio, Jonathan; Block, Matthew S.; Kaul, Ribhu K.
2015-08-01
We present a study of the scaling behavior of the Rényi entanglement entropy (REE) in SU (N ) spin chain Hamiltonians, in which all of the spins transform under the fundamental representation. These SU (N ) spin chains are known to be quantum critical and described by a well known Wess-Zumino-Witten (WZW) nonlinear sigma model in the continuum limit. Numerical results from our lattice Hamiltonian are obtained using stochastic series expansion quantum Monte Carlo for both closed and open boundary conditions. As expected for this 1D critical system, the REE shows a logarithmic dependence on the subsystem size with a prefactor given by the central charge of the SU (N ) WZW model. We study in detail the subleading oscillatory terms in the REE under both periodic and open boundaries. Each oscillatory term is associated with a WZW field and decays as a power law with an exponent proportional to the scaling dimension of the corresponding field. We find that the use of periodic boundaries (where oscillations are less prominent) allows for a better estimate of the central charge, while using open boundaries allows for a better estimate of the scaling dimensions. We also present numerical data on the thermal Rényi entropy which equally allows for extraction of the central charge.
Exactly solved mixed spin-(1,1/2) Ising–Heisenberg diamond chain with a single-ion anisotropy
Energy Technology Data Exchange (ETDEWEB)
Lisnyi, Bohdan, E-mail: lisnyj@icmp.lviv.ua [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, 79011 L' viv (Ukraine); Strečka, Jozef, E-mail: jozef.strecka@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)
2015-03-01
The mixed spin-(1,1/2) Ising–Heisenberg diamond chain with a single-ion anisotropy is exactly solved through the generalized decoration–iteration transformation and the transfer-matrix method. The decoration–iteration transformation is first used for establishing a rigorous mapping equivalence with the corresponding spin-1 Blume–Emery–Griffiths chain, which is subsequently exactly treated within the transfer-matrix technique. Apart from three classical ground states the model exhibits three striking quantum ground states in which a singlet-dimer state of the interstitial Heisenberg spins is accompanied either with a frustrated state or a polarized state or a non-magnetic state of the nodal Ising spins. It is evidenced that two magnetization plateaus at zero and/or one-half of the saturation magnetization may appear in low-temperature magnetization curves. The specific heat may display remarkable temperature dependences with up to three and four distinct round maxima in a zero and non-zero magnetic field, respectively. - Highlights: • Mixed spin-(1,1/2) Ising–Heisenberg diamond chain is exactly solved. • Quantum ground states with a singlet-dimer state of the Heisenberg spins are found. • Magnetization curve displays intermediate plateaus at zero and half of full magnetization. • Thermal dependences of specific heat may display up to four distinct peaks.
Computer studies of multiple-quantum spin dynamics
Energy Technology Data Exchange (ETDEWEB)
Murdoch, J.B.
1982-11-01
The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.
Zwick, Analia; Álvarez, Gonzalo A.; Stolze, Joachim; Osenda, Omar
2012-01-01
Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
Ambient nanoscale sensing with single spins using quantum decoherence
McGuinness, L. P.; Hall, L. T.; Stacey, A.; Simpson, D. A.; Hill, C. D.; Cole, J. H.; Ganesan, K.; Gibson, B. C.; Prawer, S.; Mulvaney, P.; Jelezko, F.; Wrachtrup, J.; Scholten, R. E.; Hollenberg, L. C. L.
2013-07-01
Magnetic resonance detection is one of the most important tools used in life-sciences today. However, as the technique detects the magnetization of large ensembles of spins it is fundamentally limited in spatial resolution to mesoscopic scales. Here we detect the natural fluctuations of nanoscale spin ensembles at ambient temperatures by measuring the decoherence rate of a single quantum spin in response to introduced extrinsic target spins. In our experiments 45 nm nanodiamonds with single nitrogen-vacancy (NV) spins were immersed in solution containing spin 5/2 Mn2+ ions and the NV decoherence rate measured though optically detected magnetic resonance. The presence of both freely moving and accreted Mn spins in solution were detected via significant changes in measured NV decoherence rates. Analysis of the data using a quantum cluster expansion treatment of the NV-target system found the measurements to be consistent with the detection of 2500 motionally diffusing Mn spins over an effective volume of (16 nm)3 in 4.2 s, representing a reduction in target ensemble size and acquisition time of several orders of magnitude over conventional, magnetic induction approaches to electron spin resonance detection. These measurements provide the basis for the detection of nanovolume spins in solution, such as in the internal compartments of living cells, and are directly applicable to scanning probe architectures.
The Fock Space of Loopy Spin Networks for Quantum Gravity
Charles, Christoph
2016-01-01
In the context of the coarse-graining of loop quantum gravity, we introduce loopy and tagged spin networks, which generalize the standard spin network states to account explicitly for non-trivial curvature and torsion. Both structures relax the closure constraints imposed at the spin network vertices. While tagged spin networks merely carry an extra spin at every vertex encoding the overall closure defect, loopy spin networks allow for an arbitrary number of loops attached to each vertex. These little loops can be interpreted as local excitations of the quantum gravitational field and we discuss the statistics to endow them with. The resulting Fock space of loopy spin networks realizes new truncation of loop quantum gravity, allowing to formulate its graph-changing dynamics on a fixed background graph plus local degrees of freedom attached to the graph nodes. This provides a framework for re-introducing a non-trivial background quantum geometry around which we would study the effective dynamics of perturbatio...
Designing defect spins for wafer-scale quantum technologies
Energy Technology Data Exchange (ETDEWEB)
Koehl, William F. [Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, IL (United States); Seo, Hosung [Univ. of Chicago, IL (United States); Galli, Giulia [Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, IL (United States); Awschalom, David D. [Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, IL (United States)
2015-11-27
The past decade has seen remarkable progress in the development of the nitrogen-vacancy (NV) defect center in diamond, which is one of the leading candidates for quantum information technologies. The success of the NV center as a solid-state qubit has stimulated an active search for similar defect spins in other technologically important and mature semiconductors, such as silicon carbide. If successfully combined with the advanced microfabrication techniques available to such materials, coherent quantum control of defect spins could potentially lead to semiconductor-based, wafer-scale quantum technologies that make use of exotic quantum mechanical phenomena like entanglement. In this article, we describe the robust spin property of the NV center and the current status of NV center research for quantum information technologies. We then outline first-principles computational modeling techniques based on density functional theory to efficiently search for potential spin defects in nondiamond hosts suitable for quantum information applications. The combination of computational modeling and experimentation has proven invaluable in this area, and we describe the successful interplay between theory and experiment achieved with the divacancy spin qubit in silicon carbide.
Spin Quantum Beats in InP Quantum Dots in a Magnetic Field
2001-06-01
UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP013252 TITLE: Spin Quantum Beats in InP Quantum Dots in a Magnetic Field...Technology" SRPN.05 St Petersburg, Russia, June 18-22, 2001 (0 2001 loffe Institute Spin quantum beats in InP quantum dots in a magnetic field L A... quantum dots . A detailed description of the structure is given in [ ]. The luminescence was excited by 3 ps pulses of a Ti:sapphire laser, 40 meV above
The spin-partitioned total position-spread tensor: An application to Heisenberg spin chains
Energy Technology Data Exchange (ETDEWEB)
Fertitta, Edoardo; Paulus, Beate [Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany); El Khatib, Muammar; Evangelisti, Stefano; Leininger, Thierry [Laboratoire de Chimie et Physique Quantiques–LCPQ/IRSAMC, Université de Toulouse (UPS) et CNRS (UMR-5626), 118 Route de Narbonne, Toulouse Cedex 31062 (France); Bendazzoli, Gian Luigi [Dipartimento di Chimica Industriale “Toso Montanari,” Università di Bologna, Viale Risorgimento 4, I–40136 Bologna (Italy)
2015-12-28
The spin partition of the Total Position-Spread (TPS) tensor has been performed for one-dimensional Heisenberg chains with open boundary conditions. Both the cases of a ferromagnetic (high-spin) and an anti-ferromagnetic (low-spin) ground-state have been considered. In the case of a low-spin ground-state, the use of alternating magnetic couplings allowed to investigate the effect of spin-pairing. The behavior of the spin-partitioned TPS (SP-TPS) tensor as a function of the number of sites turned to be closely related to the presence of an energy gap between the ground-state and the first excited-state at the thermodynamic limit. Indeed, a gapped energy spectrum is associated to a linear growth of the SP-TPS tensor with the number of sites. On the other hand, in gapless situations, the spread presents a faster-than-linear growth, resulting in the divergence of its per-site value. Finally, for the case of a high-spin wave function, an analytical expression of the dependence of the SP-TPS on the number of sites n and the total spin-projection S{sub z} has been derived.
The spin-partitioned total position-spread tensor: An application to Heisenberg spin chains.
Fertitta, Edoardo; El Khatib, Muammar; Bendazzoli, Gian Luigi; Paulus, Beate; Evangelisti, Stefano; Leininger, Thierry
2015-12-28
The spin partition of the Total Position-Spread (TPS) tensor has been performed for one-dimensional Heisenberg chains with open boundary conditions. Both the cases of a ferromagnetic (high-spin) and an anti-ferromagnetic (low-spin) ground-state have been considered. In the case of a low-spin ground-state, the use of alternating magnetic couplings allowed to investigate the effect of spin-pairing. The behavior of the spin-partitioned TPS (SP-TPS) tensor as a function of the number of sites turned to be closely related to the presence of an energy gap between the ground-state and the first excited-state at the thermodynamic limit. Indeed, a gapped energy spectrum is associated to a linear growth of the SP-TPS tensor with the number of sites. On the other hand, in gapless situations, the spread presents a faster-than-linear growth, resulting in the divergence of its per-site value. Finally, for the case of a high-spin wave function, an analytical expression of the dependence of the SP-TPS on the number of sites n and the total spin-projection Sz has been derived.
Quantum evolution from spin-gap to AF state in a low-dimensional spin system
Energy Technology Data Exchange (ETDEWEB)
Gnezdilov, Vladimir [ILTP, Kharkov (Ukraine); Lemmens, Peter; Wulferding, Dirk [IPKM, TU-BS, Braunschweig (Germany); Kremer, Reinhard [MPI-FKF, Stuttgart (Germany); Broholm, Collin [DPA, Johns Hopkins Univ., Baltimore (United States); Berger, Helmuth [EPFL Lausanne (Switzerland)
2010-07-01
The low-dimensional spin systems {alpha}- and {beta}-TeVO{sub 4} share the same monoclinic crystal symmetry while having a different connectivity of VO{sub 4} octahedra and long range order vs. a quantum disordered ground state, respectively. We report a rich magnetic Raman spectrum and phonon anomalies that evidence strong spin-lattice coupling in both systems.
Bonora, Marco; Becker, James; Saxena, Sunil
2004-10-01
We show the use of the observer blind spots effect for the elimination of electron spin-echo envelope modulation (ESEEM) peaks in double quantum coherence (DQC) electron spin resonance (ESR). The suppression of ESEEM facilitates the routine and unambiguous extraction of distances from DQC-ESR spectra. This is also the first demonstration of this challenging methodology on commercial instrumentation.
Entanglement in the XX Spin Chain with Energy Current
Eisler, V
2004-01-01
We consider the ground state of the XX chain which is constrained to carry a current of energy. The von Neumann entropy of a block of $L$ neighboring spins, describing entanglement of the block with the rest of the chain, is computed. Recent calculations have revealed that the entropy in the XX model diverges logarithmically with the size of the subsystem. We show that the presence of the energy current increases the prefactor of the logarithmic growth. This result indicates that the emergence of the energy current gives rise to an increase of entanglement.
Continuous and Discrete (Classical Heisenberg Spin Chain Revised
Directory of Open Access Journals (Sweden)
Orlando Ragnisco
2007-02-01
Full Text Available Most of the work done in the past on the integrability structure of the Classical Heisenberg Spin Chain (CHSC has been devoted to studying the su(2 case, both at the continuous and at the discrete level. In this paper we address the problem of constructing integrable generalized ''Spin Chains'' models, where the relevant field variable is represented by a N × N matrix whose eigenvalues are the Nth roots of unity. To the best of our knowledge, such an extension has never been systematically pursued. In this paper, at first we obtain the continuous N × N generalization of the CHSC through the reduction technique for Poisson-Nijenhuis manifolds, and exhibit some explicit, and hopefully interesting, examples for 3 × 3 and 4 × 4 matrices; then, we discuss the much more difficult discrete case, where a few partial new results are derived and a conjecture is made for the general case.
Quantum spin systems on infinite lattices a concise introduction
Naaijkens, Pieter
2017-01-01
This course-based primer offers readers a concise introduction to the description of quantum mechanical systems with infinitely many degrees of freedom – and quantum spin systems in particular – using the operator algebraic approach. Here, the observables are modeled using elements of some operator algebra, usually a C*-algebra. This text introduces readers to the framework and the necessary mathematical tools without assuming much mathematical background, making it more accessible than advanced monographs. The book also highlights the usefulness of the so-called thermodynamic limit of quantum spin systems, which is the limit of infinite system size. For example, this makes it possible to clearly distinguish between local and global properties, without having to keep track of the system size. Together with Lieb-Robinson bounds, which play a similar role in quantum spin systems to that of the speed of light in relativistic theories, this approach allows ideas from relativistic field theories to be implemen...
Simulating electron spin entanglement in a double quantum dot
Rodriguez-Moreno, M. A.; Hernandez de La Luz, A. D.; Meza-Montes, Lilia
2011-03-01
One of the biggest advantages of having a working quantum-computing device when compared with a classical one, is the exponential speedup of calculations. This exponential increase is based on the ability of a quantum system to create and operate on entangled states. In order to study theoretically the entanglement between two electron spins, we simulate the dynamics of two electron spins in an electrostatically-defined double quantum dot with a finite barrier height between the dots. Electrons are initially confined to separated quantum dots. Barrier height is varied and the spin entanglement as a function of this variation is investigated. The evolution of the system is simulated by using a numerical approach for solving the time-dependent Schrödinger equation for two particles. Partially supported by VIEP-BUAP.
Quantum metrology with spin cat states under dissipation.
Huang, Jiahao; Qin, Xizhou; Zhong, Honghua; Ke, Yongguan; Lee, Chaohong
2015-12-09
Quantum metrology aims to yield higher measurement precisions via quantum techniques such as entanglement. It is of great importance for both fundamental sciences and practical technologies, from testing equivalence principle to designing high-precision atomic clocks. However, due to environment effects, highly entangled states become fragile and the achieved precisions may even be worse than the standard quantum limit (SQL). Here we present a high-precision measurement scheme via spin cat states (a kind of non-Gaussian entangled states in superposition of two quasi-orthogonal spin coherent states) under dissipation. In comparison to maximally entangled states, spin cat states with modest entanglement are more robust against losses and their achievable precisions may still beat the SQL. Even if the detector is imperfect, the achieved precisions of the parity measurement are higher than the ones of the population measurement. Our scheme provides a realizable way to achieve high-precision measurements via dissipative quantum systems of Bose atoms.
Signatures of Majorana zero-modes in nanowires, quantum spin Hall edges, and quantum dots
Mi, Shuo
2015-01-01
This thesis focuses on the investigation of Majorana zero-modes and their quantum transport properties of topological insulators and topological superconductors in several low-dimensional systems, i.e. 1D nanowire system (Chapter 2), 2D quantum spin Hall system (Chapter 3, 4) and 0D quantum dot syst
Driven isotropic Heisenberg spin chain with arbitrary boundary twisting angle: exact results.
Popkov, V; Karevski, D; Schütz, G M
2013-12-01
We consider an open isotropic Heisenberg quantum spin chain, coupled at the ends to boundary reservoirs polarized in different directions, which sets up a twisting gradient across the chain. Using a matrix product ansatz, we calculate the exact magnetization profiles and magnetization currents in the nonequilibrium steady state of a chain with N sites. The magnetization profiles are harmonic functions with a frequency proportional to the twisting angle θ. The currents of the magnetization components lying in the twisting plane and in the orthogonal direction behave qualitatively differently: In-plane steady-state currents scale as 1/N^{2} for fixed and sufficiently large boundary coupling, and vanish as the coupling increases, while the transversal current increases with the coupling and saturates to 2θ/N.
Electron-Nuclear Spin Transfer in Triple Quantum Dot Networks
Prada, Marta; Toonen, Ryan; Harrison, Paul
2005-03-01
We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of delta- and y-junction networks and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalised to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in presence of nuclear spin relaxation. We find that the gradual depolarisation of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.
Spin-dependent thermoelectric transport through double quantum dots
Institute of Scientific and Technical Information of China (English)
Wang Qiang; Xie Hai-Qing; Jiao Hu-Jun; Li Zhi-Jian; Nie Yi-Hang
2012-01-01
We study the thermoelectric transport through a double-quantum-dot system with spin-dependent interdot coupling and ferromagnetic electrodes by means of the non-equilibrium Green's function in the linear response regime.It is found that the thermoelectric coefficients are strongly dependent on the splitting of the interdot coupling,the relative magnetic configurations,and the spin polarization of leads.In particular,the thermoelectric efficiency can reach a considerable value in the parallel configuration when the effective interdot coupling and the tunnel coupling between the quantum dots and the leads for the spin-down electrons are small.Moreover,the thermoelectric efficiency increases with the intradot Coulomb interaction increasing and can reach very high values at appropriate temperatures.In the presence of the magnetic field,the spin accumulation in the leads strongly suppresses the thermoelectric efficiency,and a pure spin thermopower can be obtained.
Quantum dot spin coherence governed by a strained nuclear environment
Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.
2016-01-01
The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin–photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity. PMID:27615704
Quantum computing by optical control of electron spins
Liu, Ren-Bao; Sham, L J
2010-01-01
We review the progress and main challenges in implementing large-scale quantum computing by optical control of electron spins in quantum dots (QDs). Relevant systems include self-assembled QDs of III-V or II-VI compound semiconductors (such as InGaAs and CdSe), monolayer fluctuation QDs in compound semiconductor quantum wells, and impurity centers in solids such as P-donors in silicon and nitrogen-vacancy centers in diamond. The decoherence of the electron spin qubits is discussed and various schemes for countering the decoherence problem are reviewed. We put forward designs of local nodes consisting of a few qubits which can be individually addressed and controlled. Remotely separated local nodes are connected by photonic structures (microcavities and waveguides) to form a large-scale distributed quantum system or a quantum network. The operation of the quantum network consists of optical control of a single electron spin, coupling of two spins in a local nodes, optically controlled quantum interfacing betwe...
Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap.
Murmann, S; Deuretzbacher, F; Zürn, G; Bjerlin, J; Reimann, S M; Santos, L; Lompe, T; Jochim, S
2015-11-20
We report on the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These chains are stabilized by strong repulsive interactions between the two spin components without the need for an external periodic potential. We independently characterize the spin configuration of the chains by measuring the spin orientation of the outermost particle in the trap and by projecting the spatial wave function of one spin component on single-particle trap levels. Our results are in good agreement with a spin-chain model for fermionized particles and with numerically exact diagonalizations of the full few-fermion system.
Spin structure factors of Heisenberg spin chain in the presence of anisotropy and magnetic field
Rezania, H.
2017-02-01
We have theoretically studied the spin structure factors of spin chain in the presence of longitudinal field and transverse anisotropy. The possible effects of easy axis magnetization are investigated in terms of anisotropy in the Heisenberg interactions. This anisotropy is considered for exchange coupling constants perpendicular to magnetic field direction. The original spin model hamiltonian is mapped to a bosonic model via a hard core bosonic transformation where an infinite hard core repulsion is imposed to constrain one boson occupation per site. Using Green's function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the position of peak in the longitudinal structure factor at fixed value for anisotropy moves to higher frequency with magnetic field. Also the intensity of dynamical structure factor decreases with magnetic field. A small dependence of longitudinal dynamical spin structure factor on the anisotropy is observed for fixed value of magnetic field. Our results show longitudinal static structure factor is found to be monotonically increasing with magnetic field due to increase of spins aligning along magnetic field. Furthermore the dispersion behaviors of static longitudinal and transverse structure factors for different magnetic fields and anisotropy parameters are addressed.
Novotny, M.A.; Guerra, M.; Raedt, H. De; Michielsen, K.; Jin, F.
2012-01-01
An efficient algorithm for the computation of the real-time dependence of a single quantum spin-1/2 coupled to a specific set of quantum spin-1/2 baths is presented. The specific spin baths have couplings only with the spin operators Sx between bath spins and the central spin. We calculate spin expe
Thermodynamics of Inozemtsev's elliptic spin chain
Energy Technology Data Exchange (ETDEWEB)
Klabbers, Rob, E-mail: rob.klabbers@desy.de
2016-06-15
We study the thermodynamic behaviour of Inozemtsev's long-range elliptic spin chain using the Bethe ansatz equations describing the spectrum of the model in the infinite-length limit. We classify all solutions of these equations in that limit and argue which of these solutions determine the spectrum in the thermodynamic limit. Interestingly, some of the solutions are not selfconjugate, which puts the model in sharp contrast to one of the model's limiting cases, the Heisenberg XXX spin chain. Invoking the string hypothesis we derive the thermodynamic Bethe ansatz equations (TBA-equations) from which we determine the Helmholtz free energy in thermodynamic equilibrium and derive the associated Y-system. We corroborate our results by comparing numerical solutions of the TBA-equations to a direct computation of the free energy for the finite-length hamiltonian. In addition we confirm numerically the interesting conjecture put forward by Finkel and González-López that the original and supersymmetric versions of Inozemtsev's elliptic spin chain are equivalent in the thermodynamic limit.
Exact solution of the trigonometric SU(3) spin chain with generic off-diagonal boundary reflections
Li, Guang-Liang; Cao, Junpeng; Hao, Kun; Wen, Fakai; Yang, Wen-Li; Shi, Kangjie
2016-09-01
The nested off-diagonal Bethe ansatz is generalized to study the quantum spin chain associated with the SUq (3)R-matrix and generic integrable non-diagonal boundary conditions. By using the fusion technique, certain closed operator identities among the fused transfer matrices at the inhomogeneous points are derived. The corresponding asymptotic behaviors of the transfer matrices and their values at some special points are given in detail. Based on the functional analysis, a nested inhomogeneous T-Q relations and Bethe ansatz equations of the system are obtained. These results can be naturally generalized to cases related to the SUq (n) algebra.
Exact solution of the trigonometric SU(3) spin chain with generic off-diagonal boundary reflections
Li, Guang-Liang; Hao, Kun; Yang, Wen-Li; Shi, Kangjie
2016-01-01
The nested off-diagonal Bethe Ansatz is generalized to study the quantum spin chain associated with the $SU_q(3)$ R-matrix and generic integrable non-diagonal boundary conditions. By using the fusion technique, certain closed operator identities among the fused transfer matrices at the inhomogeneous points are derived. The corresponding asymptotic behaviors of the transfer matrices and their values at some special points are given in detail. Based on the functional analysis, a nested inhomogeneous T-Q relations and Bethe Ansatz equations of the system are obtained. These results can be naturally generalized to cases related to the $SU_q(n)$ algebra.
Exact solution of the trigonometric SU(3 spin chain with generic off-diagonal boundary reflections
Directory of Open Access Journals (Sweden)
Guang-Liang Li
2016-09-01
Full Text Available The nested off-diagonal Bethe ansatz is generalized to study the quantum spin chain associated with the SUq(3 R-matrix and generic integrable non-diagonal boundary conditions. By using the fusion technique, certain closed operator identities among the fused transfer matrices at the inhomogeneous points are derived. The corresponding asymptotic behaviors of the transfer matrices and their values at some special points are given in detail. Based on the functional analysis, a nested inhomogeneous T–Q relations and Bethe ansatz equations of the system are obtained. These results can be naturally generalized to cases related to the SUq(n algebra.
Spectral dualities in XXZ spin chains and five dimensional gauge theories
Mironov, A; Runov, B; Zenkevich, Y; Zotov, A
2013-01-01
Motivated by recent progress in the study of supersymmetric gauge theories we propose a very compact formulation of spectral duality between XXZ spin chains. The action of the quantum duality is given by the Fourier transform in the spectral parameter. We investigate the duality in various limits and, in particular, prove it for q-->1, i.e. when it reduces to the XXX/Gaudin duality. We also show that the universal difference operators are given by the normal ordering of the classical spectral curves.
Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain
Tiegel, A. C.; Dargel, P. E.; Hallberg, K. A.; Frahm, H.; Pruschke, T.
2013-02-01
In order to study the interplay between Kondo and Ruderman-Kittel-Kasuya-Yosida interaction, we calculate the spin-spin correlation functions between two Kondo impurities coupled to different sites of a half-filled open Hubbard chain. Using the density-matrix renormalization group (DMRG), we reexamine the exponents for the power-law decay of the correlation function between the two impurity spins as a function of the antiferromagnetic coupling J, the Hubbard interaction U, and the distance R between the impurities. The exponents for finite systems obtained in this work deviate from previously published DMRG calculations. We furthermore show that the long-distance behavior of the exponents is the same for impurities coupled to the bulk or to both ends of the chain. We note that a universal exponent for the asymptotic behavior can not be extracted from these finite-size systems with open boundary conditions.
Energy Technology Data Exchange (ETDEWEB)
Rojas, Onofre, E-mail: ors@dex.ufla.br [Departamento de Ciencias Exatas, Universidade Federal de Lavras, 37200-000, Lavras-MG (Brazil); Strečka, Jozef [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Lyra, Marcelo L. [Instituto de Física, Universidade Federal de Alagoas, 57072-970, Maceio-AL (Brazil)
2013-05-03
The spin-1/2 Ising–Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin–spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations. -- Highlights: ► Using local gauge symmetry we solved the spin-1/2 Ising–Heisenberg tetrahedral chain. ► The frustration temperature was calculated using the correlation functions. ► Thermal entanglement, concurrence and threshold temperature were analyzed. ► The zero-field specific heat was exactly calculated and discussed.
Correlations and diagonal entropy after quantum quenches in XXZ chains
Piroli, Lorenzo; Vernier, Eric; Calabrese, Pasquale; Rigol, Marcos
2017-02-01
We study quantum quenches in the XXZ spin-1 /2 Heisenberg chain from families of ferromagnetic and antiferromagnetic initial states. Using Bethe ansatz techniques, we compute short-range correlators in the complete generalized Gibbs ensemble (GGE), which takes into account all local and quasilocal conservation laws. We compare our results to exact diagonalization and numerical linked cluster expansion calculations for the diagonal ensemble, finding excellent agreement and thus providing a very accurate test for the validity of the complete GGE. Furthermore, we use exact diagonalization to compute the diagonal entropy in the postquench steady state. We show that the Yang-Yang entropy for the complete GGE is consistent with twice the value of the diagonal entropy in the largest chains or the extrapolated result in the thermodynamic limit. Finally, the complete GGE is quantitatively contrasted with the GGE built using only the local conserved charges (local GGE). The predictions of the two ensembles are found to differ significantly in the case of ferromagnetic initial states. Such initial states are better suited than others considered in the literature to experimentally test the validity of the complete GGE and contrast it to the failure of the local GGE.
Institute of Scientific and Technical Information of China (English)
LI Yu-Xian
2008-01-01
Spin-dependent Andreev reflection and spin polarization through a diluted magnetic semiconductor quantum wire coupled to normal metallic and superconductor electrodes are investigated using scattering theory. When the spin-orbit coupling is considered, more Andreev conductance steps appear at the same Fermi energy. Magnetic semiconductor quantum wire separates the spin-up and spin-down electrons. The Fermi energy, at which different-spin-state electrons begin to separate, becomes lower due to the effect of the spin-orbit interaction. The spin filter effect can be measured more easily by investigating the Andreev conductance than by investigating the normal conductance.
Nonreciprocal spin wave elementary excitation in dislocated dimerized Heisenberg chains.
Liu, Wanguo; Shen, Yang; Fang, Guisheng; Jin, Chongjun
2016-05-18
A mechanism for realizing nonreciprocal elementary excitation of spin wave (SW) is proposed. We study a reference model which describes a magnonic crystal (MC) formed by two Heisenberg chains with a lateral displacement (dislocation) and a longitudinal spacer, and derive a criterion to judge whether the elementary excitation spectra are reciprocal in this ferromagnetic lattice. An analytical method based on the spin precession equation is used to solve the elementary excitation spectra. The solution is related to a key factor, the spatio-temporal structure factor [Formula: see text], which can be directly calculated through the structural parameters. When it keeps invariant under the reversions of the external magnetic field [Formula: see text] and the dislocation [Formula: see text], or one of them, the spectra are reciprocal. Otherwise, the SW possesses nonreciprocal spectra with direction-dependent band edges and exhibits a directional magnetoresistance effect. This criterion can be regarded as a necessary and sufficient condition for the (non)reciprocity in the spin lattice. Besides, this novel lattice provides a prototype for spin diodes and spin logic gates.
Energy Technology Data Exchange (ETDEWEB)
Brunel, V
1999-06-29
This thesis presents three studies that are respectively the spin-1 disordered chain, the non magnetic impurities in the spin-1/2 chain and the reaction-diffusion process. The spin-1 chain of weak disorder is performed by the Abelian bosonization and the renormalization group. This allows to take into account the competition between the disorder and the interactions and predicts the effects of various spin-1 anisotropy chain phases under many different disorders. A second work uses the non magnetic impurities as local probes of the correlations in the spin-1/2 chain. When the impurities are connected to the chain boundary, the author predicts a temperature dependence of the relaxation rate (1/T) of the nuclear spin impurities, different from the case of these impurities connected to the whole chain. The last work deals with one dimensional reaction-diffusion problem. The Jordan-Wigner transformation allows to consider a fermionic field theory that critical exponents follow from the renormalization group. (A.L.B.)
Doped Heisenberg chains: Spin-S generalizations of the supersymmetric t-J model
Energy Technology Data Exchange (ETDEWEB)
Frahm, Holger E-mail: frahm@itp.uni-hannover.de
1999-10-25
A family of exactly solvable models describing a spin S Heisenberg chain doped with mobile spin-(S - ((1)/(2))) carriers is constructed from gl(2|1)-invariant solutions of the Yang-Baxter equation. The models are generalizations of the supersymmetric t-J model which is obtained for S ((1)/(2)). We solve the model by means of the algebraic Bethe Ansatz and present results for the zero temperature and thermodynamic properties. At low temperatures the models show spin charge separation, i.e. contain contributions of a free bosonic theory in the charge sector and an SU(2)-invariant theory describing the magnetic excitations. For small carrier concentration the latter can be decomposed further into an SU(2) level-2S Wess-Zumino-Novikov-Witten model and the minimal unitary model M{sub p} with p 2S + 1.
The two-body random spin ensemble and a new type of quantum phase transition
Energy Technology Data Exchange (ETDEWEB)
Pizorn, Iztok; Prosen, Tomaz [Department of Physics, FMF, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana (Slovenia); Mossmann, Stefan; Seligman, Thomas H [Instituto de Ciencias FIsicas, Universidad Nacional Autonoma de Mexico, CP 62132 Cuernavaca, Morelos (Mexico)], E-mail: tomaz.prosen@fmf.uni-lj.si
2008-02-15
We study in this paper the properties of a two-body random matrix ensemble for distinguishable spins. We require the ensemble to be invariant under the group of local transformations and analyze a parametrization in terms of the group parameters and the remaining parameters associated with the 'entangling' part of the interaction. We then specialize to a spin chain with nearest-neighbour interactions and numerically find a new type of quantum-phase transition related to the strength of a random external field, i.e. the time-reversal-breaking one-body interaction term.
The two-body random spin ensemble and a new type of quantum phase transition
Pižorn, Iztok; Prosen, Tomaž; Mossmann, Stefan; Seligman, Thomas H.
2008-02-01
We study in this paper the properties of a two-body random matrix ensemble for distinguishable spins. We require the ensemble to be invariant under the group of local transformations and analyze a parametrization in terms of the group parameters and the remaining parameters associated with the 'entangling' part of the interaction. We then specialize to a spin chain with nearest-neighbour interactions and numerically find a new type of quantum-phase transition related to the strength of a random external field, i.e. the time-reversal-breaking one-body interaction term.
Spin Glass a Bridge Between Quantum Computation and Statistical Mechanics
Ohzeki, Masayuki
2013-09-01
In this chapter, we show two fascinating topics lying between quantum information processing and statistical mechanics. First, we introduce an elaborated technique, the surface code, to prepare the particular quantum state with robustness against decoherence. Interestingly, the theoretical limitation of the surface code, accuracy threshold, to restore the quantum state has a close connection with the problem on the phase transition in a special model known as spin glasses, which is one of the most active researches in statistical mechanics. The phase transition in spin glasses is an intractable problem, since we must strive many-body system with complicated interactions with change of their signs depending on the distance between spins. Fortunately, recent progress in spin-glass theory enables us to predict the precise location of the critical point, at which the phase transition occurs. It means that statistical mechanics is available for revealing one of the most interesting parts in quantum information processing. We show how to import the special tool in statistical mechanics into the problem on the accuracy threshold in quantum computation. Second, we show another interesting technique to employ quantum nature, quantum annealing. The purpose of quantum annealing is to search for the most favored solution of a multivariable function, namely optimization problem. The most typical instance is the traveling salesman problem to find the minimum tour while visiting all the cities. In quantum annealing, we introduce quantum fluctuation to drive a particular system with the artificial Hamiltonian, in which the ground state represents the optimal solution of the specific problem we desire to solve. Induction of the quantum fluctuation gives rise to the quantum tunneling effect, which allows nontrivial hopping from state to state. We then sketch a strategy to control the quantum fluctuation efficiently reaching the ground state. Such a generic framework is called
Quantum measurement and entanglement of spin quantum bits in diamond
Pfaff, W.
2013-01-01
This thesis presents a set of experiments that explore the possible realisation of a macroscopic quantum network based on solid-state quantum bits. Such a quantum network would allow for studying quantum mechanics on large scales (meters, or even kilometers), and can open new possibilities for
Quantum measurement and entanglement of spin quantum bits in diamond
Pfaff, W.
2013-01-01
This thesis presents a set of experiments that explore the possible realisation of a macroscopic quantum network based on solid-state quantum bits. Such a quantum network would allow for studying quantum mechanics on large scales (meters, or even kilometers), and can open new possibilities for appli
Quantum Control nd Measurement of Spins in Cold Atomic Gases
Deutsch, Ivan
2014-03-01
Spins are natural carriers of quantum information given their long coherence time and our ability to precisely control and measure them with magneto-optical fields. Spins in cold atomic gases provide a pristine environment for such quantum control and measurement, and thus this system can act as a test-bed for the development of quantum simulators. I will discuss the progress my group has made in collaboration with Prof. Jessen, University of Arizona, to develop the toolbox for this test-bed. Through its interactions with rf and microwave magnetic fields, whose waveforms are designed through optimal control techniques, we can implement arbitrary unitary control on the internal hyperfine spins of cesium atoms, a 16 dimensional Hilbert space (isomorphic to 4 qubits). Control of the collective spin of the ensemble of many atoms is performed via the mutual coupling of the atomic ensemble to a mode of the electromagnetic field that acts as a quantum data bus for entangling atoms with one another. Internal spin control can be used to enhance the entangling power of the atom-photon interface. Finally, both projective and weak-continuous measurements can be performed to tomograhically reconstruct quantum states and processes.
Quantum dust magnetosonic waves with spin and exchange correlation effects
Energy Technology Data Exchange (ETDEWEB)
Maroof, R.; Qamar, A. [Department of Physics, University of Peshawar, Peshawar 25000 (Pakistan); Mushtaq, A. [Department of Physics, Abdul Wali Khan University, Mardan 23200 (Pakistan); National Center for Physics, Shahdra Valley Road, Islamabad 44000 (Pakistan)
2016-01-15
Dust magnetosonic waves are studied in degenerate dusty plasmas with spin and exchange correlation effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, spin magnetization energy, and exchange correlation, a generalized dispersion relation is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The exchange-correlation potentials are used, based on the adiabatic local-density approximation, and can be described as a function of the electron density. For three different values of angle, the dispersion relation is reduced to three different modes under the low frequency magnetohydrodynamic assumptions. It is found that the effects of quantum corrections in the presence of dust concentration significantly modify the dispersive properties of these modes. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects (e.g., the cores of white dwarf stars and giant planets) and in plasma-assisted nanotechnology (e.g., quantum diodes, quantum free-electron lasers, etc.)
Wang, Hong-Fu; Zhu, Ai-Dong; Zhang, Shou
2013-05-20
We propose an efficient protocol for optimizing the physical implementation of three-qubit quantum error correction with spatially separated quantum dot spins via virtual-photon-induced process. In the protocol, each quantum dot is trapped in an individual cavity and each two cavities are connected by an optical fiber. We propose the optimal quantum circuits and describe the physical implementation for correcting both the bit flip and phase flip errors by applying a series of one-bit unitary rotation gates and two-bit quantum iSWAP gates that are produced by the long-range interaction between two distributed quantum dot spins mediated by the vacuum fields of the fiber and cavity. The protocol opens promising perspectives for long distance quantum communication and distributed quantum computation networks.
Roy, Soumya Singha
2012-01-01
Nuclear Magnetic Resonance (NMR) forms a natural test-bed to perform quantum information processing (QIP) and has so far proven to be one of the most successful quantum information processors. The nuclear spins in a molecule treated as quantum bits or qubits which are the basic building blocks of a quantum computer. The development of NMR over half a century puts it in a platform where we can utilize its excellent control techniques over an ensemble of spin systems and perform quantum computation in a highly controlled way. Apart from a successful quantum information processor, NMR is also a highly powerful quantum platform where many of the potentially challenging quantum mechanical experiments can be performed.
Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells
Energy Technology Data Exchange (ETDEWEB)
Yang, Wen; Chang, Kai; /Beijing, Inst. Semiconductors; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-19
Spin Hall effect can be induced both by the extrinsic impurity scattering and by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. This difference gives a direct mechanism to experimentally distinguish the intrinsic spin Hall effect from the extrinsic one.
Spin-dependent quantum transport in nanoscaled geometries
Heremans, Jean J.
2011-10-01
We discuss experiments where the spin degree of freedom leads to quantum interference phenomena in the solid-state. Under spin-orbit interactions (SOI), spin rotation modifies weak-localization to weak anti-localization (WAL). WAL's sensitivity to spin- and phase coherence leads to its use in determining the spin coherence lengths Ls in materials, of importance moreover in spintronics. Using WAL we measure the dependence of Ls on the wire width w in narrow nanolithographic ballistic InSb wires, ballistic InAs wires, and diffusive Bi wires with surface states with Rashba-like SOI. In all three systems we find that Ls increases with decreasing w. While theory predicts the increase for diffusive wires with linear (Rashba) SOI, we experimentally conclude that the increase in Ls under dimensional confinement may be more universal, with consequences for various applications. Further, in mesoscopic ring geometries on an InAs/AlGaSb 2D electron system (2DES) we observe both Aharonov-Bohm oscillations due to spatial quantum interference, and Altshuler-Aronov-Spivak oscillations due to time-reversed paths. A transport formalism describing quantum coherent networks including ballistic transport and SOI allows a comparison of spin- and phase coherence lengths extracted for such spatial- and temporal-loop quantum interference phenomena. We further applied WAL to study the magnetic interactions between a 2DES at the surface of InAs and local magnetic moments on the surface from rare earth (RE) ions (Gd3+, Ho3+, and Sm3+). The magnetic spin-flip rate carries information about magnetic interactions. Results indicate that the heavy RE ions increase the SOI scattering rate and the spin-flip rate, the latter indicating magnetic interactions. Moreover Ho3+ on InAs yields a spin-flip rate with an unusual power 1/2 temperature dependence, possibly characteristic of a Kondo system. We acknowledge funding from DOE (DE-FG02-08ER46532).
Spin effects in perturbative quantum chromodynamics
Energy Technology Data Exchange (ETDEWEB)
Brodsky, S.J.; Lepage, G.P.
1980-12-01
The spin dependence of large momentum transfer exclusive and inclusive reactions can be used to test the gluon spin and other basic elements of QCD. In particular, exclusive processes including hadronic decays of heavy quark resonances have the potential of isolating QCD hard scattering subprocesses in situations where the helicities of all the interacting constituents are controlled. The predictions can be summarized in terms of QCD spin selection rules. The calculation of magnetic moment and other hadronic properties in QCD are mentioned.
Spin-free quantum computational simulations and symmetry adapted states
Whitfield, James Daniel
2013-01-01
The ideas of digital simulation of quantum systems using a quantum computer parallel the original ideas of numerical simulation using a classical computer. In order for quantum computational simulations to advance to a competitive point, many techniques from classical simulations must be imported into the quantum domain. In this article, we consider the applications of symmetry in the context of quantum simulation. Building upon well established machinery, we propose a form of first quantized simulation that only requires the spatial part of the wave function, thereby allowing spin-free quantum computational simulations. We go further and discuss the preparation of N-body states with specified symmetries based on projection techniques. We consider two simple examples, molecular hydrogen and cyclopropenyl cation, to illustrate the ideas. While the methods here represent adaptations of known quantum algorithms, they are the first to explicitly deal with preparing N-body symmetry-adapted states.
Chaos And Quantum-classical Correspondence For Two- Coupled Spins
Emerson, J V
2001-01-01
Two approaches to quantum-classical correspondence are distinguished according to the classical dynamical theory with which quantum theory is compared. The first of these, Ehrenfest correspondence, defines a dynamical regime in which the quantum expectation values follow approximately a classical trajectory. The second of these, Liouville correspondence, applies when the quantum probability distributions remain well approximated by a density in the classical phase space. The former applies only for narrow states, whereas the latter may remain valid even for quantum states that have spread to the system size. A spin model is adopted for this correspondence study because the quantum state is discrete and finite- dimensional, and thus no artificial truncation of the Hilbert space is required. The quantum time-evolution is given by a discrete unitary mapping. The corresponding classical model is volume-preserving (non-dissipative) and the time-evolution is given by a symplectic map. In classically chaotic regimes...
Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi
2016-10-01
Experimental identification of quantum spin liquids remains a challenge, as the pristine nature is to be seen in asymptotically low temperatures. We here theoretically show that the precursor of quantum spin liquids appears in the spin dynamics in the paramagnetic state over a wide temperature range. Using the cluster dynamical mean-field theory and the continuous-time quantum Monte Carlo method, which are newly developed in the Majorana fermion representation, we calculate the dynamical spin structure factor, relaxation rate in nuclear magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model whose ground state is a canonical example of the quantum spin liquid. We find that dynamical spin correlations show peculiar temperature and frequency dependence even below the temperature where static correlations saturate. The results provide the experimentally accessible symptoms of the fluctuating fractionalized spins evincing the quantum spin liquids.
Farberovich, Oleg V.; Bazhanov, Dmitry I.
2017-10-01
A general study of [Tb2] molecular magnet is presented using the general spin Hamiltonian formalism. A spin-spin correlators determined for a spin wave functions in [Tb2] are analyzed numerically and compared in details with the results obtained by means of conventional quantum mechanics. It is shown that the various expectation values of the spin operators and a study of their corresponding probability distributions allow to have a novel understanding in spin dynamics of entangled qubits in quantum [Tb2] system. The obtained results reveal that the properties of spin-spin correlators are responsible for the entanglement of the spin qubit under a pulse magnetic field. It allows us to present some quantum circuits determined for quantum computing within SSNQ based on [Tb2] molecule, including the CNOT and SWAP gates.
Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions
Peng, Yang; Vinkler-Aviv, Yuval; Brouwer, Piet W.; Glazman, Leonid I.; von Oppen, Felix
2016-12-01
We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2 π . This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8 π -periodic (or Z4) fractional Josephson effect in the context of recent experiments.
Pure dephasing of single Mn spin in semiconductor quantum dots
Liu, Dingyang; Lai, Wenxi; Yang, Wen
2017-08-01
We present comprehensive analytical and numerical studies on the pure dephasing of a single Mn spin in a semiconductor quantum dot due to (i) its sp-d exchange interaction with an electronic environment, and (ii) its hyperfine interaction with the nuclear spin environment. For (i), by modeling the electronic environment by an open two-level system, we provide exact analytical expressions and present detailed analysis for the Mn spin pure dephasing in both the Markovian and non-Markovian regimes. This provides a clear physical picture and a general theoretical framework based on which we estimate the Mn spin pure dephasing due to various fluctuations (such as thermal excitation, optical pumping, tunneling, or electron/hole spin relaxation) of the electronic environment and reveals a series of interesting behaviors, such as thermal, optical, and electrical control of the crossover between the Markov and non-Markov regimes. In particular, we find rapid Mn spin pure dephasing on a nanosecond time scale by the thermal fluctuation and optical pumping, but these mechanisms can be strongly suppressed by shifting the electron envelope function relative to the Mn atom with an external electric field through the quantum-confined Stark effect. The thermal fluctuation mechanism is also exponentially suppressed at low temperature. For (ii), we find that the Mn spin dephasing time is limited by the thermal fluctuation of the nuclear spins to a few microseconds even at low temperature and its value varies from sample to sample, depending on the distribution of spinful isotopes on the nearest-neighbor sites surrounding the substitutional Mn atom. Our findings may be useful to understand and suppress the Mn spin pure dephasing for its applications in quantum information processing.
A note on symmetry reductions of the Lindblad equation: transport in constrained open spin chains
Buca, Berislav
2012-01-01
We describe a simple prescription by which distinct (non-equilibrium) steady states, namely fixed points of dynamical semi-groups, can be classified in terms of eigenvalues of a globally conserved quantity, i.e. a unitary operator which simultaneously commutes with the Hamiltonian and the set of all Lindblad (jump) operators. As an example, we study quantum transport properties of an open Heisenberg XXZ spin 1/2 chain driven by a pair of Lindblad jump operators satisfying a global `microcanonical' constraint, i.e. conserving the total magnetization. Interestingly, numerical simulations suggest that a pair of distinct non-equilibrium steady states becomes indistinguishable in the thermodynamic limit, and exhibit diffusive spin transport in the easy-axis regime.
Quantum vs Classical Magnetization Plateaus of S=1/2 Frustrated Heisenberg Chains
Hida, Kazuo; Affleck, Ian
2005-06-01
The competition between quantum and classical magnetization plateaus of S=1/2 frustrated Heisenberg chains with modified exchange couplings is investigated. The conventional S=1/2 frustrated Heisenberg chain is known to exhibit a 3-fold degenerate \\uparrow\\downarrow\\uparrow-type classical plateau at 1/3 of the saturation magnetization accompanied by the spontaneous Z3 translational symmetry breakdown. The stability of this plateau phase against period 3 exchange modulation which favors the \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state (\\bullet\\hskip -1pt-\\hskip -1pt\\bullet = singlet dimer) is studied by bosonization, renormalization group and numerical diagonalization methods. The ground state phase diagram and the spin configuration in each phase are numerically determined. The translationally invariant Valence Bond Solid-type model with 4-spin and third neighbor interactions, which has the exact \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state, is also presented. The phase transition to the classical \\uparrow\\downarrow\\uparrow-type ground state is also observed by varying the strength of 4-spin and third neighbor interactions. The relation between these two types of models with quantum plateau states is discussed.
Casting Loop Quantum Cosmology in the Spin Foam Paradigm
Ashtekar, Abhay; Henderson, Adam
2010-01-01
The goal of spin foam models is to provide a viable path integral formulation of quantum gravity. Because of background independence, their underlying framework has certain novel features that are not shared by path integral formulations of familiar field theories in Minkowski space. As a simple viability test, these features were recently examined through the lens of loop quantum cosmology (LQC). Results of that analysis, reported in a brief communication [1], turned out to provide concrete arguments in support of the spin foam paradigm. We now present detailed proofs of those results. Since the quantum theory of LQC models is well understood, this analysis also serves to shed new light on some long standing issues in the spin foam and group field theory literature. In particular, it suggests an intriguing possibility for addressing the question of why the cosmological constant is positive and small.
Tunable Few-Electron Quantum Dots as Spin Qubits
Elzerman, Jeroen; Hanson, Ronald; Greidanus, Jacob; Willems van Beveren, Laurens; de Franceschi, Silvano; Vandersypen, Lieven; Tarucha, Seigo; Kouwenhoven, Leo
2003-03-01
Recently it was proposed to make a quantum bit using the spin of an electron in a quantum dot. We present the first experimental steps towards realizing a system of two coupled qubits. The Zeeman splitting between the two spin states defining the qubit is measured for a one-electron dot in a parallel magnetic field. For a two-electron dot, we control the spin singlet-triplet energy difference with a perpendicular magnetic field, and we induce a transition from singlet to triplet ground state. We find relaxation from triplet to singlet to be extremely slow (> 1 mus), which is promising for quantum computing. We couple two few-electron dots, creating the first fully tunable few-electron double dot. Its charge configuration can be read out with a nearby QPC acting as an integrated charge detector.
Linear spin-wave study of a quantum kagome ice
Owerre, S. A.; Burkov, A. A.; Melko, Roger G.
2016-04-01
We present a large-S study of a quantum spin ice Hamiltonian, introduced by Huang et al. [Phys. Rev. Lett. 112, 167203 (2014), 10.1103/PhysRevLett.112.167203], on the kagome lattice. This model involves a competition between the frustrating Ising term of classical kagome ice, a Zeeman magnetic field h , and a nearest-neighbor transverse spin-flip term SixSjx-SiySjy . Recent quantum Monte Carlo (QMC) simulations by Carrasquilla et al. [Nat. Commun. 6, 7421 (2015), 10.1038/ncomms8421], uncovered lobes of a disordered phase for large Ising interaction and h ≠0 —a putative quantum spin liquid phase. Here, we examine the nature of this model using large-S expansion. We show that the ground state properties generally have the same trends with those observed in QMC simulations. In particular, the large-S ground state phase diagram captures the existence of the disordered lobes.
Spin-helix states in the XXZ spin chain with strong boundary dissipation
Popkov, Vladislav; Schmidt, Johannes; Presilla, Carlo
2017-10-01
We investigate the non-equilibrium steady state (NESS) in an open quantum XXZ chain attached at the ends to polarization baths with unequal polarizations. Using the general theory developed in Popkov (2017 Phys. Rev. A 95 052131), we show that in the critical XXZ \
Bartucci, R; Gambacorta, A; Gliozzi, A; Marsh, D; Sportelli, L
2005-11-15
Membranes of thermophilic Archaea are composed of unique tetraether lipids in which C40, saturated, methyl-branched biphytanyl chains are linked at both ends to polar groups. In this paper, membranes composed of bipolar lipids P2 extracted from the acidothermophile archaeon Sulfolobus solfataricus are studied. The biophysical basis for the membrane formation and thermal stability is investigated by using electron spin resonance (ESR) of spin-labeled lipids. Spectral anisotropy and isotropic hyperfine couplings are used to determine the chain flexibility and polarity gradients, respectively. For comparison, similar measurements have been carried out on aqueous dispersions of diacyl reference lipid dipalmitoyl phosphatidylcholine and also of diphytanoyl phosphatidylcholine, which has methyl-branched chains. At a given temperature, the bolaform lipid chains are more ordered and less flexible than in normal bilayer membranes. Only at elevated temperatures (80 degrees C) does the flexibility of the chain environment in tetraether lipid assemblies approach that of fluid bilayer membranes. The height of the hydrophobic barrier formed by a monolayer of archaebacterial lipids is similar to that in conventional fluid bilayer membranes, and the permeability barrier width is comparable to that formed by a bilayer of C16 lipid chains. At a mole ratio of 1:2, the tetraether P2 lipids mix well with dipalmitoyl phosphatidylcholine lipids and stabilize conventional bilayer membranes. The biological as well as the biotechnological relevance of the results is discussed.
Spin structure of electron subbands in (110)-grown quantum wells
Energy Technology Data Exchange (ETDEWEB)
Nestoklon, M. O.; Tarasenko, S. A. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Jancu, J.-M. [FOTON-INSA Laboratory, UMR 6082 au CNRS, INSA de Rennes, 35043 Rennes Cedex (France); Voisin, P. [CNRS-Laboratoire de Photonique et de Nanostructures, 91460 Marcoussis (France)
2013-12-04
We present the theory of fine structure of electron states in symmetric and asymmetric zinc-blende-type quantum wells with the (110) crystallographic orientation. By combining the symmetry analysis, sp{sup 3}d{sup 5}s* tight-binding method, and envelope-function approach we obtain quantitative description of in-plane wave vector, well width and applied electric field dependencies of the zero-magnetic-field spin splitting of electron subbands and extract spin-orbit-coupling parameters.
Spin and Rotations in Galois Field Quantum Mechanics
Chang, Lay Nam; Minic, Djordje; Takeuchi, Tatsu
2012-01-01
We discuss the properties of Galois Field Quantum Mechanics constructed on a vector space over the finite Galois field GF(q). In particular, we look at 2-level systems analogous to spin, and discuss how SO(3) rotations could be embodied in such a system. We also consider two-particle `spin' correlations and show that the Clauser-Horne-Shimony-Holt (CHSH) inequality is nonetheless not violated in this model.
Comparison of quantum and classical relaxation in spin dynamics.
Wieser, R
2013-04-01
The classical Landau-Lifshitz equation with a damping term has been derived from the time evolution of a quantum mechanical wave function under the assumption of a non-Hermitian Hamilton operator. Further, the trajectory of a classical spin (S) has been compared with the expectation value of the spin operator (Ŝ). A good agreement between classical and quantum mechanical trajectories can be found for Hamiltonians linear in Ŝ or S, respectively. Quadratic or higher order terms in the Hamiltonian result in a disagreement.
Quantum spins and quasiperiodicity: a real space renormalization group approach.
Jagannathan, A
2004-01-30
We study the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional bipartite quasiperiodic structure, the octagonal tiling, the aperiodic equivalent of the square lattice for periodic systems. An approximate block spin renormalization scheme is described for this problem. The ground state energy and local staggered magnetizations for this system are calculated and compared with the results of a recent quantum Monte Carlo calculation for the tiling. It is conjectured that the ground state energy is exactly equal to that of the quantum antiferromagnet on the square lattice.
Quantum codes from linear codes over finite chain rings
Liu, Xiusheng; Liu, Hualu
2017-10-01
In this paper, we provide two methods of constructing quantum codes from linear codes over finite chain rings. The first one is derived from the Calderbank-Shor-Steane (CSS) construction applied to self-dual codes over finite chain rings. The second construction is derived from the CSS construction applied to Gray images of the linear codes over finite chain ring {\\mathbb {F}}_{p^{2m}}+u{\\mathbb {F}}_{p^{2m}}. The good parameters of quantum codes from cyclic codes over finite chain rings are obtained.
Mixed-state quantum transport in correlated spin networks
Ajoy, Ashok; 10.1103/PhysRevA.85.042305
2012-01-01
Quantum spin networks can be used to transport information between separated registers in a quantum information processor. To find a practical implementation, the strict requirements of ideal models for perfect state transfer need to be relaxed, allowing for complex coupling topologies and general initial states. Here we analyze transport in complex quantum spin networks in the maximally mixed state and derive explicit conditions that should be satisfied by propagators for perfect state transport. Using a description of the transport process as a quantum walk over the network, we show that it is necessary to phase correlate the transport processes occurring along all the possible paths in the network. We provide a Hamiltonian that achieves this correlation, and use it in a constructive method to derive engineered couplings for perfect transport in complicated network topologies.
Magnetic field sensing subject to correlated noise with a ring spin chain
Guo, Li-Sha; Xu, Bao-Ming; Zou, Jian; Shao, Bin
2016-01-01
In this paper, we focus on the magnetic field sensing subject to a correlated noise. We use a ring spin chain with only the nearest neighbor interactions as our probe to estimate both the intensity B and the direction θ of the magnetic field when the probe reaches its steady state. We numerically calculate the quantum Fisher information (QFI) to characterize the estimation precision. On the one hand, for estimating B, we find that the coupling between spins in the probe plays an important role in the precision, and the largest value of the QFI can be achieved when θ = π/2 together with an optimal coupling. Moreover, for any direction, the precision scaling can be better than the Heisenberg-limit (HL) with a proper coupling. On the other hand, for estimating θ, we find that our probe can perform a high precision detection for θ ~ π/2, with the QFI much larger than that for any other directions, especially when the coupling is tuned to the optimal value. And we find that the precision scaling for θ ~ π/2 can be better than the HL, but for other directions, the precision scaling is only limited to the standard quantum limit (SQL). Due to the computational complexity we restrict the number of spins in the probe to 60. PMID:27623048
Many-body localization phase in a spin-driven chiral multiferroic chain
Stagraczyński, S.; Chotorlishvili, L.; Schüler, M.; Mierzejewski, M.; Berakdar, J.
2017-08-01
Many-body localization (MBL) is an emergent phase in correlated quantum systems with promising applications, particularly in quantum information. Here, we unveil the existence and analyze this phase in a chiral multiferroic model system. Conventionally, MBL occurrence is traced via level statistics by implementing a standard finite-size scaling procedure. Here, we present an approach based on the full distribution of the ratio of adjacent energy spacings. We find a strong broadening of the histograms of counts of these level spacings directly at the transition point from MBL to the ergodic phase. The broadening signals reliably the transition point without relying on an averaging procedure. The fast convergence of the histograms even for relatively small systems allows monitoring the MBL dynamics with much less computational effort. Numerical results are presented for a chiral spin chain with a dynamical Dzyaloshinskii-Moriya interaction, an established model to describe the spin excitations in a single-phase spin-driven multiferroic system. The multiferroic MBL phase is uncovered and it is shown how to steer it via electric fields.
Magnetic field sensing subject to correlated noise with a ring spin chain
Guo, Li-Sha; Xu, Bao-Ming; Zou, Jian; Shao, Bin
2016-09-01
In this paper, we focus on the magnetic field sensing subject to a correlated noise. We use a ring spin chain with only the nearest neighbor interactions as our probe to estimate both the intensity B and the direction θ of the magnetic field when the probe reaches its steady state. We numerically calculate the quantum Fisher information (QFI) to characterize the estimation precision. On the one hand, for estimating B, we find that the coupling between spins in the probe plays an important role in the precision, and the largest value of the QFI can be achieved when θ = π/2 together with an optimal coupling. Moreover, for any direction, the precision scaling can be better than the Heisenberg-limit (HL) with a proper coupling. On the other hand, for estimating θ, we find that our probe can perform a high precision detection for θ ~ π/2, with the QFI much larger than that for any other directions, especially when the coupling is tuned to the optimal value. And we find that the precision scaling for θ ~ π/2 can be better than the HL, but for other directions, the precision scaling is only limited to the standard quantum limit (SQL). Due to the computational complexity we restrict the number of spins in the probe to 60.
Quantum Computing via Singlet-Triplet Spin Qubits in Nanowire Double Quantum Dots
Institute of Scientific and Technical Information of China (English)
XUE Peng
2011-01-01
We propose a new structure for quantum computing via spin qubits with high fidelity.Each spin qubit corresponds to two electrons in a nanowire double quantum dot,with the singlet and one of the triplets as the logical qubit states.The entangling gate is effected by virtual charge dipole transitions.We include noise to show the feasibility of this scheme under current experimental conditions.
Hybrid quantum systems with ultracold spins and optomechanics
Shaffer, Airlia; Patil, Yogesh Sharad; Cheung, Hil F. H.; Wang, Ke; Date, Aditya; Schwab, Keith; Meystre, Pierre; Vengalattore, Mukund
2016-05-01
Linear cavity optomechanics has enabled radiation pressure cooling and sensing of mechanical resonators at the quantum limits. However, exciting and unrealized avenues such as generating massive macroscopic nonclassical states, quantum signal transduction, and phonon-based manybody physics each require strong, nonlinear interactions. In our group, we are exploring three approaches to realizing strong optomechanical nonlinearities - i. using atomically thin graphene membranes, ii. coupling optomechanical systems with ultracold atomic spins, and iii. using microtoroidal optomechanical resonators strongly coupled to atoms trapped in their evanescent fields. We describe our progress in each of these efforts and discuss ongoing studies on various aspects of quantum enhanced metrology, nonequilibrium dynamics of open quantum systems and quantum transduction using these novel hybrid quantum systems. This work is supported by the DARPA QuASAR program through a Grant from the ARO.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-05-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Low-Energy Effective Theories of Quantum Link and Quantum Spin Models
Schlittgen, B
2001-01-01
Quantum spin and quantum link models provide an unconventional regularization of field theory in which classical fields arise via dimensional reduction of discrete variables. This D-theory regularization leads to the same continuum theories as the conventional approach. We show this by deriving the low-energy effective Lagrangians of D-theory models using coherent state path integral techniques. We illustrate our method for the $(2+1)$-d Heisenberg quantum spin model which is the D-theory regularization of the 2-d O(3) model. Similarly, we prove that in the continuum limit a $(2+1)$-d quantum spin model with $SU(N)_L\\times SU(N)_R\\times U(1)_{L=R}$ symmetry is equivalent to the 2-d principal chiral model. Finally, we show that $(4+1)$-d SU(N) quantum link models reduce to ordinary 4-d Yang-Mills theory.
Guterding, Daniel; Jeschke, Harald O; Valentí, Roser
2016-05-17
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-01-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions. PMID:27185665
Performance of an irreversible quantum Carnot engine with spin 12.
Wu, Feng; Chen, Lingen; Wu, Shuang; Sun, Fengrui; Wu, Chih
2006-06-01
The purpose of this paper is to investigate the effect of quantum properties of the working medium on the performance of an irreversible Carnot cycle with spin 12. The optimal relationship between the dimensionless power output P* versus the efficiency eta for the irreversible quantum Carnot engine with heat leakage and other irreversible losses is derived. Especially, the performances of the engine at low temperature limit and at high temperature limit are discussed.
Entanglement Observables and Witnesses for Interacting Quantum Spin Systems
Wu, L A; Sarandy, M S; Lidar, D A
2004-01-01
We discuss the detection of entanglement in interacting quantum spin systems. First, thermodynamic Hamiltonian-based witnesses are computed for a general class of one-dimensional spin-1/2 models. Second, we introduce optimal bipartite entanglement observables. We show that a bipartite entanglement measure can generally be associated to a set of independent two-body spin observables whose expectation values can be used to witness entanglement. The number of necessary observables is ruled by the symmetries of the model. Illustrative examples are presented.
Pulse and quench induced dynamical phase transition in a chiral multiferroic spin chain
Azimi, M.; Sekania, M.; Mishra, S. K.; Chotorlishvili, L.; Toklikishvili, Z.; Berakdar, J.
2016-08-01
Quantum dynamics of magnetic order in a chiral multiferroic chain is studied. We consider two different scenarios: ultrashort terahertz excitations or a sudden electric field quench. Performing analytical and numerical exact diagonalization calculations, we trace the pulse induced spin dynamics and extract quantities that are relevant to quantum information processing. In particular, we analyze the dynamics of the system chirality, the von Neumann entropy, and the pairwise and many-body entanglement. If the characteristic frequencies of the generated states are noncommensurate, then a partial loss of pair concurrence occurs. Increasing the system size, this effect becomes even more pronounced. Many-particle entanglement and chirality are robust and persist in the incommensurate phase. To analyze the dynamical quantum transitions for the quenched and pulsed dynamics we combined the Weierstrass factorization technique for entire functions and the Lanczos exact diagonalization method. For a small system we obtained analytical results including the rate function of the Loschmidt echo. Exact numerical calculations for a system up to 40 spins confirm phase transition. Quench-induced dynamical transitions have been extensively studied recently. Here we show that related dynamical transitions can be achieved and controlled by appropriate electric field pulses.
Higher spin de Sitter quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Basu, Rudranil [Physique Théorique et Mathématique,Université Libre de Bruxelles and International Solvay Institutes,Campus Plaine C.P. 231, B-1050 Bruxelles (Belgium); Indian Institute of Science Education and Research,Dr. Homi Bhabha Road, Pashan, Pune 411008 (India)
2015-10-23
We consider Einstein gravity with positive cosmological constant coupled with higher spin interactions and calculate Euclidean path integral perturbatively. We confine ourselves to the static patch of the 3 dimensional de Sitter space. This geometry, when Euclideanlized is equivalent to 3-sphere. However, infinite number of topological quotients of this space by discrete subgroups of the isometry group are valid Euclidean saddles as well. The case of pure Einstein gravity is known to give a diverging answer, when all saddles are included as contribution to the thermal partition functions (also interpreted as the Hartle Hawking state in the cosmological scenario). We show how higher spins, described by metric-Fronsdal fields help making the partition function finite. We find a curious fact that this convergence is not achieved by mere inclusion of spin-3, but requires spin-4 interactions.
Higher Spin de Sitter Quantum Gravity
Basu, Rudranil
2015-01-01
We consider Einstein gravity with positive cosmological constant coupled with higher spin interactions and calculate Euclidean path integral perturbatively. We confine ourselves to the static patch of the 3 dimensional de Sitter space. This geometry, when Euclideanlized is equivalent to 3-sphere. However, infinite number of topological quotients of this space by discrete subgroups of the isometry group are valid Euclidean saddles as well. Pure Einstein gravity is known to diverge, when all saddles are included as contribution to the thermal partition functions (also interpreted as the Hartle Hawking state of in the cosmological scenario). We show how higher spins, described by metric-Fronsdal fields help making the partition function finite. Counter-intuitively, this convergence is not achieved by mere inclusion of spin-3, but requires spin-4 interactions.
Institute of Scientific and Technical Information of China (English)
ZHU Zhi-Cheng; TU Tao; GUO Guo-Ping
2011-01-01
We propose an efficient method to create multipartite spin entangled states in quantum dots coupled to a nano electro-mechanical resonator array. Our method, based on the interaction between electron spins confined in quantum dots and the motion of magnetized nano electro-mechanical resonators, can enable a coherent spin-spin coupling over long distances and in principle be applied to an arbitrarily large number of electronic spins.%@@ We propose an efficient method to create multipartite spin entangled states in quantum dots coupled to a nano electro-mechanical resonator array.Our method, based on the interaction between electron spins confined in quantum dots and the motion of magnetized nano electro-mechanical resonators, can enable a coherent spin-spin coupling over long distances and in principle be applied to an arbitrarily large number of electronic spins.
One-dimensional spinon spin currents
Hirobe, Daichi; Sato, Masahiro; Kawamata, Takayuki; Shiomi, Yuki; Uchida, Ken-Ichi; Iguchi, Ryo; Koike, Yoji; Maekawa, Sadamichi; Saitoh, Eiji
2017-01-01
Quantum spin fluctuation in a low-dimensional or frustrated magnet breaks magnetic ordering while keeping spin correlation. Such fluctuation has been a central topic in magnetism because of its relevance to high-Tc superconductivity and topological states. However, utilizing such spin states has been quite difficult. In a one-dimensional spin-1/2 chain, a particle-like excitation called a spinon is known to be responsible for spin fluctuation in a paramagnetic state. Spinons behave as a Tomonaga-Luttinger liquid at low energy, and the spin system is often called a quantum spin chain. Here we show that a quantum spin chain generates and carries spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr2CuO3. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.
Thermal stability in exchange-spring chains of spins
Pellicelli, Raffaele; Solzi, Massimo
2016-02-01
Thermal stability and switching behaviour have been compared in pure-hard and soft-hard Heisenberg linear spin chains of the same total length and equal magnetic parameters (except for magnetic anisotropy) with the anisotropy axis and external magnetic field parallel to the chain direction. The zero-temperature energy barriers and finite-temperature transition rates between remanent equilibrium states have been calculated by utilizing the string method and the forward flux sampling (FFS) method, respectively. Depending on the assumed interfaces, the FFS method could in fact fail to correctly sample the characteristic transition paths at interfaces at which these paths have probabilities much lower than those associated with other non-characteristic transition paths. This can especially occur in the case of the asymmetric energy landscapes and multiple asymmetric minimum energy paths (MEPs) of soft-hard systems. Therefore, a proper interface definition is needed in order to deduce the correct transition rates. In particular, we show that the thermal switching of soft-hard chains starting in the soft or in the hard part turns out to occur with an equal rate provided that the interfaces of the FFS method are defined on the basis of the corresponding zero-temperature MEPs. The thermal stability of a soft-hard chain in the remanent equilibrium state could be to some extent lower with respect to that of a pure-hard chain, due to the shorter hard-part length crossed by the domain wall formed in the chain and also to the related slightly smaller energy barrier. However, its switching field at zero temperature is verified to be widely lower than that of the pure-hard chain. Analytical expressions of switching fields and energy barriers have been deduced in various cases.
Skyrmions and edge-spin excitations in quantum Hall droplets
Energy Technology Data Exchange (ETDEWEB)
Oaknin, J.H. [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, 28049, Madrid (Spain); Martin-Moreno, L. [Departamento de Fisica de la Materia Condensada, Instituto de Ciencia de Materiales de Aragon, Consejo Superior de Investigaciones Cientificas, Universidad de Zaragoza, Zaragoza 50015 (Spain); Tejedor, C. [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, 28049, Madrid (Spain)
1996-12-01
We present a microscopic analysis of spin textures in quantum Hall droplets for filling factors {nu}{approx_equal}1. We obtain analytical many-body wave functions of spin excitations which describe all of the necessary quantum numbers. An adequate linear combination of these eigenstates leads to wave functions in which the spatially dependent spinor can be factorized. This displays the topological structure of several spin textures, some of which are located at the bulk, and others at the edge. For the former, we obtain bulk charged skyrmions that can be expressed as a condensate of spin excitons interacting via a two-body repulsive interaction. The size of the skyrmion is given by the number of excitons present in the condensate. We also obtain the skyrmion energy as a function of its size for both zero and finite Zeeman energy. For the edge excitations we find that a branch of these spin textures starts with lower energy than the branch of polarized charge edge excitations. When the number of electrons is of the order of a few tenths, there are no crossings of the spin and charge branches so that edge-spin textures can be responsible for the edge reconstruction of the droplet. On the contrary, edge reconstruction is always found to be due to polarized charge excitations when the number of electrons is larger than one hundred. {copyright} {ital 1996 The American Physical Society.}
Spin-S kagome quantum antiferromagnets in a field with tensor networks
Picot, Thibaut; Ziegler, Marc; Orús, Román; Poilblanc, Didier
2016-02-01
Spin-S Heisenberg quantum antiferromagnets on the kagome lattice offer, when placed in a magnetic field, a fantastic playground to observe exotic phases of matter with (magnetic analogs of) superfluid, charge, bond, or nematic orders, or a coexistence of several of the latter. In this context, we have obtained the (zero-temperature) phase diagrams up to S =2 directly in the thermodynamic limit owing to infinite projected entangled pair states, a tensor network numerical tool. We find incompressible phases characterized by a magnetization plateau versus field and stabilized by spontaneous breaking of point group or lattice translation symmetry(ies). The nature of such phases may be semiclassical, as the plateaus at the 1/3th ,(1-2/9S)th, and (1-1/9S)th of the saturated magnetization (the latter followed by a macroscopic magnetization jump), or fully quantum as the spin-1/2 1/9 plateau exhibiting a coexistence of charge and bond orders. Upon restoration of the spin rotation U (1 ) symmetry, a finite compressibility appears, although lattice symmetry breaking persists. For integer spin values we also identify spin gapped phases at low enough fields, such as the S =2 (topologically trivial) spin liquid with no symmetry breaking, neither spin nor lattice.
All-electrical generation of spin-polarized currents in quantum spin Hall insulators
Tao, L. L.; Cheung, K. T.; Zhang, L.; Wang, J.
2017-03-01
The control and generation of spin-polarized current (SPC) without magnetic materials and an external magnetic field is a big challenge in spintronics and normally requires a spin-flip mechanism. In this Rapid Communication, we show the theoretical discovery of all-electrical generation of SPC without relying on spin-flip spin-orbit coupling (SOC). We find that the SPC can be produced as long as an energy-dependent phase difference between the spin up and down electrons can be established. We verify this through quantum transport calculations on a gated stanene zigzag nanoribbon, which is a quantum spin Hall (QSH) insulator. Our calculations indicate that the transient current as well as ac conductance are significantly spin polarized, which results from the genetic phase difference between spin up and down electrons after traversing the system. Our results are robust against edge imperfections and generally valid for other QSH insulators, such as silicene and germanene, etc. These findings establish a different route for generating SPCs by purely electrical means and open the door for interesting applications of semiconductor spintronics.
Quantum kinetics of spinning neutral particles: General theory and Spin wave dispersion
Andreev, P A
2013-01-01
Plasma physics give an example of physical system of particles with the long range interaction. At small velocity of particles we can consider the plasma approximately as a system of particles with the Coulomb interaction. The Coulomb interaction is isotropic. Systems of spinning neutral particles have long-range anisotropic interparticle interaction. So, they can reveal more reach properties than plasma. Furthermore for studying of systems of spinning particles we can develop kinetic and hydrodynamic methods analogous to used for the plasma. We derive kinetic equations by a new method, which is the generalization of the many-particle quantum hydrodynamics. Obtained set of kinetic equations is truncated, so we have closed set of two equations. One of them is the kinetic equation for quantum distribution function. The second equation is the equation for the spin-distribution. Which describes the spin kinetic evolution and gives contribution in time evolution of the distribution function. Our method allows to o...
Wang, Dong; Ming, Fei; Huang, Ai-Jun; Sun, Wen-Yang; Ye, Liu
2017-09-01
The uncertainty principle configures a low bound to the measuring precision for a pair of non-commuting observables, and hence is considerably nontrivial to quantum precision measurement in the field of quantum information theory. In this letter, we consider the entropic uncertainty relation (EUR) in the context of quantum memory in a two-qubit isotropic Heisenberg spin chain. Specifically, we explore the dynamics of EUR in a practical scenario, where two associated nodes of a one-dimensional XXX-spin chain, under an inhomogeneous magnetic field, are connected to a thermal entanglement. We show that the temperature and magnetic field effect can lead to the inflation of the measuring uncertainty, stemming from the reduction of systematic quantum correlation. Notably, we reveal that, firstly, the uncertainty is not fully dependent on the observed quantum correlation of the system; secondly, the dynamical behaviors of the measuring uncertainty are relatively distinct with respect to ferromagnetism and antiferromagnetism chains. Meanwhile, we deduce that the measuring uncertainty is dramatically correlated with the mixedness of the system, implying that smaller mixedness tends to reduce the uncertainty. Furthermore, we propose an effective strategy to control the uncertainty of interest by means of quantum weak measurement reversal. Therefore, our work may shed light on the dynamics of the measuring uncertainty in the Heisenberg spin chain, and thus be important to quantum precision measurement in various solid-state systems.
Hamerly, Ryan; Inagaki, Takahiro; Takesue, Hiroki; Yamamoto, Yoshihisa; Mabuchi, Hideo
2016-01-01
A network of optical parametric oscillators is used to simulate classical Ising and XY spin chains. The collective nonlinear dynamics of this network, driven by quantum noise rather than thermal fluctuations, seeks out the Ising / XY ground state as the system transitions from below to above the lasing threshold. We study the behavior of this "Ising machine" for three canonical problems: a 1D ferromagnetic spin chain, a 2D square lattice, and problems where next-nearest-neighbor couplings give rise to frustration. If the pump turn-on time is finite, topological defects form (domain walls for the Ising model, winding number and vortices for XY) and their density can be predicted from a numerical model involving a linear "growth stage" and a nonlinear "saturation stage". These predictions are compared against recent data for a 10,000-spin 1D Ising machine.
Hamerly, Ryan; Inaba, Kensuke; Inagaki, Takahiro; Takesue, Hiroki; Yamamoto, Yoshihisa; Mabuchi, Hideo
2016-09-01
A network of optical parametric oscillators (OPOs) is used to simulate classical Ising and XY spin chains. The collective nonlinear dynamics of this network, driven by quantum noise rather than thermal fluctuations, seeks out the Ising/XY ground state as the system transitions from below to above the lasing threshold. We study the behavior of this “Ising machine” for three canonical problems: a 1D ferromagnetic spin chain, a 2D square lattice and problems where next-nearest-neighbor couplings give rise to frustration. If the pump turn-on time is finite, topological defects form (domain walls for the Ising model, winding number and vortices for XY) and their density can be predicted from a numerical model involving a linear “growth stage” and a nonlinear “saturation stage”. These predictions are compared against recent data for a 10,000-spin 1D Ising machine.
Emergence of the Persistent Spin Helix in Semiconductor Quantum Wells
Energy Technology Data Exchange (ETDEWEB)
Koralek, Jake; Weber, Chris; Orenstein, Joe; Bernevig, Andrei; Zhang, Shoucheng; Mack, Shawn; Awschalom, David
2011-08-24
According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit (SO) coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be recovered in a two-dimensional electron gas (2DEG), despite the presence of SO coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix' (PSH). SU(2) is restored, in principle, when the strength of two dominant SO interactions, the Rashba ({alpha}) and linear Dresselhaus ({beta}{sub 1}), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term ({beta}{sub 3}) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as {alpha} {yields} {beta}{sub 1}. Here we observe experimentally the emergence of the PSH in GaAs quantum wells (QW's) by independently tuning {alpha} and {beta}{sub 1}. Using transient spin-grating spectroscopy (TSG), we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant SO terms, identifying {beta}{sub 3} as the main SU(2) violating term in our samples. The tunable suppression of spin-relaxation demonstrated in this work is well-suited for application to spintronics.
Singular eigenstates in the even(odd) length Heisenberg spin chain
Giri, Pulak Ranjan
2014-01-01
Introducing a regularization scheme, we derive a set of equations for the rapidities of the singular solutions, whose distinct and self-conjugate solutions produce Bethe eigenstates. We obtain singular eigenstates and their corresponding eigenvalues of the transfer matrix of the spin-1/2 XXX chain. For an even length spin-1/2 XXX chain, we show that the singular solutions \\{\\lambda_\\alpha\\} are invariant under the sign changes of their rapidities, \\{\\lambda_\\alpha\\}=\\{-\\lambda_\\alpha\\}. For odd N length spin-1/2 chain in the three down-spin sector, it has been analytically shown that there exist singular solutions in any finite length of the spin chain of the form N= 3\\left(2k+1\\right) with k=1, 2, 3, \\cdots. It is also shown that there exist no singular solutions in the four down-spin sector for some odd length spin-1/2 XXX chains.
Quantum dynamics and entanglement of spins on a square lattice
DEFF Research Database (Denmark)
Christensen, Niels Bech; Rønnow, Henrik Moodysson; McMorrow, Desmond Francis;
2007-01-01
Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas...... this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made...
NMR evidence for peculiar spin gaps in a doped S=1/2 Heisenberg spin chain
Energy Technology Data Exchange (ETDEWEB)
Utz, Yannic; Rudisch, Christian; Hammerath, Franziska; Grafe, Hans-Joachim; Mohan, Ashwin; Ribeiro, Patrick; Hess, Christian; Wolter, Anja; Kataev, Vladislav; Nishimoto, Satoshi; Drechsler, Stefan-Ludwig; Buechner, Bernd [IFW Dresden (Germany); Singh, Surjeet [Indian Institute of Science Education and Research, Pune (India); Saint-Martin, Romuald; Revcolevschi, Alexandre [Laboratoire de Physico-Chimie de l' Etat Solide, Universite Paris-Sud, Orsay (France)
2012-07-01
We present {sup 63}Cu Nuclear Magnetic Resonance (NMR) measurements on undoped, Ca-doped and Ni-doped SrCuO{sub 2} single crystals. SrCuO{sub 2} is a good realization of a one-dimensional S=1/2 Heisenberg spin chain. This is manifested by the theoretically-expected temperature-independent NMR spin-lattice relaxation rate T{sub 1}{sup -1}. In Sr{sub 0.9}Ca{sub 0.1}CuO{sub 2} an exponential decrease of T{sub 1}{sup -1} below 90 K evidences the opening of a gap in the spin excitation spectrum, which amounts to {Delta}=50 K. DMRG calculations are presented to discuss the origin of this spin gap. New results on SrCu{sub 0.99}Ni{sub 0.01}O{sub 2} also indicate the presence of a spin gap, which is twice as large as in Sr{sub 0.9}Ca{sub 0.1}CuO{sub 2}, despite the minor doping level of Ni compared to Ca. We discuss different possible impacts of Ca (S=0) and Ni (S=1) doping on structural and magnetic properties of the parent compound.
Magnetic properties of manganese based one-dimensional spin chains.
Asha, K S; Ranjith, K M; Yogi, Arvind; Nath, R; Mandal, Sukhendu
2015-12-14
We have correlated the structure-property relationship of three manganese-based inorganic-organic hybrid structures. Compound 1, [Mn2(OH-BDC)2(DMF)3] (where BDC = 1,4-benzene dicarboxylic acid and DMF = N,N'-dimethylformamide), contains Mn2O11 dimers as secondary building units (SBUs), which are connected by carboxylate anions forming Mn-O-C-O-Mn chains. Compound 2, [Mn2(BDC)2(DMF)2], contains Mn4O20 clusters as SBUs, which also form Mn-O-C-O-Mn chains. In compound 3, [Mn3(BDC)3(DEF)2] (where DEF = N,N'-diethylformamide), the distorted MnO6 octahedra are linked to form a one-dimensional chain with Mn-O-Mn connectivity. The magnetic properties were investigated by means of magnetization and heat capacity measurements. The temperature dependent magnetic susceptibility of all the three compounds could be nicely fitted using a one-dimensional S = 5/2 Heisenberg antiferromagnetic chain model and the value of intra-chain exchange coupling (J/k(B)) between Mn(2+) ions was estimated to be ∼1.1 K, ∼0.7 K, and ∼0.46 K for compounds 1, 2, and 3, respectively. Compound 1 does not undergo any magnetic long-range-order down to 2 K while compounds 2 and 3 undergo long-range magnetic order at T(N) ≈ 4.2 K and ≈4.3 K, respectively, which are of spin-glass type. From the values of J/k(B) and T(N) the inter-chain coupling (J(⊥)/k(B)) was calculated to be about 0.1J/k(B) for both compounds 2 and 3, respectively.
Nonequilibrium Transport through a Spinful Quantum Dot with Superconducting Leads
DEFF Research Database (Denmark)
Andersen, Brian Møller; Flensberg, Karsten; Koerting, Verena
2011-01-01
We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel...
Energy Technology Data Exchange (ETDEWEB)
Deng, Xian-Yan, E-mail: 58845736@qq.com [Graduate School, Tianjin Polytechnic University, Tianjin 300387 (China); Kong, Long-Juan [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China)
2014-07-01
The ground-state properties and quantum phase transitions (QPTs) in spin-1/2 Heisenberg-Ising alternating chain has been investigated by the iTEBD algorithm. Four different ground-state phases, i.e., a ferromagnetic phase (FM), an antiferromagnetic phase (AF), a stripe phase (SP), and a disordered phase were distinguished. The disordered phase, which has nonzero string orders and the doubly degenerate entanglement spectrum, was observed as Heisenberg coupling J{sub H}>0.5. The disordered phase in such a model is found to belong to the same topological phase as the Haldane state. In the disordered phase, every two nearest-neighbor spin-1/2 spins connected by the Ising coupling behave like an integer (S=1) spin. Furthermore, the QPTs from the disordered phase to the AF and SP phases belong to the Ising universality class with central charges c=c{sup ¯}=1/2.
Far-from-equilibrium spin transport in Heisenberg quantum magnets.
Hild, Sebastian; Fukuhara, Takeshi; Schauß, Peter; Zeiher, Johannes; Knap, Michael; Demler, Eugene; Bloch, Immanuel; Gross, Christian
2014-10-03
We study experimentally the far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice. After controlled imprinting of a spin spiral pattern with an adjustable wave vector, we measure the decay of the initial spin correlations through single-site resolved detection. On the experimentally accessible time scale of several exchange times, we find a profound dependence of the decay rate on the wave vector. In one-dimensional systems, we observe diffusionlike spin transport with a dimensionless diffusion coefficient of 0.22(1). We show how this behavior emerges from the microscopic properties of the closed quantum system. In contrast to the one-dimensional case, our transport measurements for two-dimensional Heisenberg systems indicate anomalous superdiffusion.
Quantum logical operations for spin 3/2 quadrupolar nuclei monitored by quantum state tomography.
Bonk, F A; deAzevedo, E R; Sarthour, R S; Bulnes, J D; Freitas, J C C; Guimarães, A P; Oliveira, I S; Bonagamba, T J
2005-08-01
This article presents the realization of many self-reversible quantum logic gates using two-qubit quadrupolar spin 3/2 systems. Such operations are theoretically described using propagation matrices for the RF pulses that include the effect of the quadrupolar evolution during the pulses. Experimental demonstrations are performed using a generalized form of the recently developed method for quantum state tomography in spin 3/2 systems. By doing so, the possibility of controlling relative phases of superimposed pseudo-pure states is demonstrated. In addition, many aspects of the effect of the quadrupolar evolution, occurring during the RF pulses, on the quantum operations performance are discussed. Most of the procedures presented can be easily adapted to describe selective pulses of higher spin systems (>3/2) and for spin 1/2 under J couplings.
Versatile microwave-driven trapped ion spin system for quantum information processing.
Piltz, Christian; Sriarunothai, Theeraphot; Ivanov, Svetoslav S; Wölk, Sabine; Wunderlich, Christof
2016-07-01
Using trapped atomic ions, we demonstrate a tailored and versatile effective spin system suitable for quantum simulations and universal quantum computation. By simply applying microwave pulses, selected spins can be decoupled from the remaining system and, thus, can serve as a quantum memory, while simultaneously, other coupled spins perform conditional quantum dynamics. Also, microwave pulses can change the sign of spin-spin couplings, as well as their effective strength, even during the course of a quantum algorithm. Taking advantage of the simultaneous long-range coupling between three spins, a coherent quantum Fourier transform-an essential building block for many quantum algorithms-is efficiently realized. This approach, which is based on microwave-driven trapped ions and is complementary to laser-based methods, opens a new route to overcoming technical and physical challenges in the quest for a quantum simulator and a quantum computer.
Edge physics of the quantum spin Hall insulator from a quantum dot excited by optical absorption.
Vasseur, Romain; Moore, Joel E
2014-04-11
The gapless edge modes of the quantum spin Hall insulator form a helical liquid in which the direction of motion along the edge is determined by the spin orientation of the electrons. In order to probe the Luttinger liquid physics of these edge states and their interaction with a magnetic (Kondo) impurity, we consider a setup where the helical liquid is tunnel coupled to a semiconductor quantum dot that is excited by optical absorption, thereby inducing an effective quantum quench of the tunneling. At low energy, the absorption spectrum is dominated by a power-law singularity. The corresponding exponent is directly related to the interaction strength (Luttinger parameter) and can be computed exactly using boundary conformal field theory thanks to the unique nature of the quantum spin Hall edge.
Numerical evidence of quantum melting of spin ice: quantum-classical crossover
Kato, Yasuyuki; Onoda, Shigeki
2015-03-01
Unbiased quantum Monte-Carlo simulations are performed on the simplest case of the quantum spin ice model, namely, the nearest-neighbor spin-1/2 XXZ model on the pyrochlore lattice with an antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange couplings, J and J⊥. On cooling across TCSI ~ 0 . 2 J , the specific heat shows a broad peak associated with a crossover to a classical Coulomb liquid regime characterized by a remnant of the pinch-point singularity in longitudinal spin correlations as well as the Pauling ice entropy for | J⊥ | J⊥ c ~ - 0 . 104 J , as expected for bosonic quantum Coulomb liquids. With negatively increasing J⊥ across J⊥ c, a first-order transition occurs at a nonzero temperature from the quantum Coulomb liquid to an XY ferromagnet. Relevance to magnetic rare-earth pyrochlore oxides is discussed.
Dissipation-driven quantum phase transitions in collective spin systems
Energy Technology Data Exchange (ETDEWEB)
Morrison, S [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Parkins, A S [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)], E-mail: smor161@aucklanduni.ac.nz
2008-10-14
We consider two different collective spin systems subjected to strong dissipation-on the same scale as interaction strengths and external fields-and show that either continuous or discontinuous dissipative quantum phase transitions can occur as the dissipation strength is varied. First, we consider a well-known model of cooperative resonance fluorescence that can exhibit a second-order quantum phase transition, and analyse the entanglement properties near the critical point. Next, we examine a dissipative version of the Lipkin-Meshkov-Glick interacting collective spin model, where we find that either first- or second-order quantum phase transitions can occur, depending only on the ratio of the interaction and external field parameters. We give detailed results and interpretation for the steady-state entanglement in the vicinity of the critical point, where it reaches a maximum. For the first-order transition we find that the semiclassical steady states exhibit a region of bistability. (fast track communication)
Global phase diagram and quantum spin liquids in a spin-1/2 triangular antiferromagnet
Gong, Shou-Shu; Zhu, W.; Zhu, J.-X.; Sheng, D. N.; Yang, Kun
2017-08-01
We study the spin-1 /2 Heisenberg model on the triangular lattice with the nearest-neighbor J1>0 , the next-nearest-neighobr J2>0 Heisenberg interactions, and the additional scalar chiral interaction Jχ(S⃗i×S⃗j) .S⃗k for the three spins in all the triangles using large-scale density matrix renormalization group calculation on cylinder geometry. With increasing J2 (J2/J1≤0.3 ) and Jχ (Jχ/J1≤1.0 ) interactions, we establish a quantum phase diagram with the magnetically ordered 120∘, stripe, and noncoplanar tetrahedral phase. In between these magnetic order phases, we find a chiral spin liquid (CSL) phase, which is identified as a ν =1 /2 bosonic fractional quantum Hall state with possible spontaneous rotational symmetry breaking. By switching on the chiral interaction, we find that the previously identified spin liquid in the J1-J2 triangular model (0.08 ≲J2/J1≲0.15 ) shows a phase transition to the CSL phase at very small Jχ. We also compute the spin triplet gap in both spin liquid phases, and our finite-size results suggest a large gap in the odd topological sector but a small or vanishing gap in the even sector. We discuss the implications of our results on the nature of the spin liquid phases.
Institute of Scientific and Technical Information of China (English)
FU Xi; ZHOU Guang-Hui
2009-01-01
We investigate theoretically the spin current in a quantum wire with weak Dresselhaus spin-orbit coupling connected to two normal conductors.Both the quantum wire and conductors are described by a hard-wall confining potential.Using the electron wave-functions in the quantum wire and a new definition of spin current, we have calculated the elements of linear spin current density jTs,xi and jTs,yi(I = x, y, z).We lind that the elements jTs,xx and jTs,yy have a antisymmetrical relation and the element jTs,yz has the same amount level jTs,xx and jTs,yy.We also find a net linear spin current density, which has peaks at the center of quantum wire.The net linear spin current can induce a linear electric field, which may imply a way of spin current detection.
Exact solution of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chain
Directory of Open Access Journals (Sweden)
L. Čanová
2009-01-01
Full Text Available The geometric frustration in a class of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chains is investigated by combining three exact analytical techniques: Kambe projection method, decoration-iteration transformation and transfer-matrix method. The ground state, the magnetization process and the specific heat as a function of the external magnetic field are particularly examined for different strengths of the geometric frustration. It is shown that the increase of the Heisenberg spin value S raises the number of intermediate magnetization plateaux, which emerge in magnetization curves provided that the ground state is highly degenerate on behalf of a sufficiently strong geometric frustration. On the other hand, all intermediate magnetization plateaux merge into a linear magnetization versus magnetic field dependence in the limit of classical Heisenberg spin S → ∞. The enhanced magnetocaloric effect with cooling rate exceeding the one of paramagnetic salts is also detected when the disordered frustrated phase constitutes the ground state and the external magnetic field is small enough.
Energy Technology Data Exchange (ETDEWEB)
Viennot, David, E-mail: david.viennot@utinam.cnrs.fr; Aubourg, Lucile
2016-02-15
We study a theoretical model of closed quasi-hermitian chain of spins which exhibits quantum analogues of chimera states, i.e. long life classical states for which a part of an oscillator chain presents an ordered dynamics whereas another part presents a disordered dynamics. For the quantum analogue, the chimera behaviour deals with the entanglement between the spins of the chain. We discuss the entanglement properties, quantum chaos, quantum disorder and semi-classical similarity of our quantum chimera system. The quantum chimera concept is novel and induces new perspectives concerning the entanglement of multipartite systems. - Highlights: • We propose a spin chain model with long range couplings having purely quantum states similar to the classical chimera states. • The quantum chimera states are characterized by the coexistence of strongly entangled and non-entangled spins in the same chain. • The quantum chimera states present some characteristics of quantum chaos.