Quantum router based on ac control of qubit chains

Zueco, David; Galve, Fernando; Kohler, Sigmund; Hänggi, Peter

doi:10.1103/physreva.80.042303

Cited by 90 publications

(108 citation statements)

References 52 publications

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“…In contrast to other recent networking schemes [9] it does not demand control of the intermediate spins or time-varying local fields. Our results hint that a Kondo spin chain satisfying Eq.…”

Section: And (Iii) the Dynamics Is Oscillatory With Period 2tmentioning

confidence: 99%

“…Finally, there is a proposal [8] for distance-independent entanglement through a local quench which, however, lacks the versatility of routing entanglement between multiple sites. A few quantum routers have been recently proposed [9], but harnessing a canonical many-body phenomenon for routing still is an open question.Kondo systems [10][11][12] are very distinctive in the context of entanglement for at least two reasons. Despite being ''gapless,'' they support the emergence of a length scale -the so-called Kondo screening length [10,11]-which can be tuned by varying only one parameter [10] and reflects in the entanglement [8], making it markedly different from other conventional gapless models.…”

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Entanglement Routers Using Macroscopic Singlets

2010

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We propose a mechanism where high entanglement between very distant boundary spins is generated by suddenly connecting two long Kondo spin chains. We show that this procedure provides an efficient way to route entanglement between multiple distant sites. We observe that the key features of the entanglement dynamics of the composite spin chain are well described by a simple model of two singlets, each formed by two spins. The proposed routing mechanism is a footprint of the emergence of a Kondo cloud in a Kondo system and can be engineered and observed in varied physical settings. Introduction.-A high entanglement between two well separated qubits is the central resource for quantum communication tasks. It also facilitates the preparation of multiparticle entangled states [1] for measurement based quantum computation. One could ask whether many-body systems can serve as mediums for entanglement between arbitrary distant qubits in a multisite network. Though this is the most important question from an ''applied'' perspective, the thriving field of entanglement in many-body systems [2] remains focused on the entanglement of blocks and proximal spins. In fact, long-range entanglement between individual spins is notoriously uncommon [3]. There are proposals exploiting weak couplings of distant spins to a spin chain [4,5], but these have limited thermal stability or a very long time scale of entanglement generation. Alternatively, a global quench [6] or specific timedependent couplings [7] may generate entanglement, though this decays with the system size. Finally, there is a proposal [8] for distance-independent entanglement through a local quench which, however, lacks the versatility of routing entanglement between multiple sites. A few quantum routers have been recently proposed [9], but harnessing a canonical many-body phenomenon for routing still is an open question.Kondo systems [10][11][12] are very distinctive in the context of entanglement for at least two reasons. Despite being ''gapless,'' they support the emergence of a length scale -the so-called Kondo screening length [10,11]-which can be tuned by varying only one parameter [10] and reflects in the entanglement [8], making it markedly different from other conventional gapless models. Furthermore, in Kondo systems, the impurity spin is maximally entangled [12] with a block of spins whose spatial extent may be varied at will by tuning .In this Letter, we propose a dynamical mechanism by which long-range distance-independent entanglement may be generated by the switch on of a single coupling suddenly connecting two macroscopic singlets. We show that this mechanism provides an efficient way to route entanglement

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Section: And (Iii) the Dynamics Is Oscillatory With Period 2tmentioning

confidence: 99%

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confidence: 99%

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Entanglement Routers Using Macroscopic Singlets

2010

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“…Moreover, by exploiting just a single bond quench for inducing a nontrivial dynamics, the required control is minimal. This mechanism can demonstrate an entanglement router which unlike previous proposals needs neither ac control of the couplings [17] nor the presence of both ferromagnetic and antiferromagnetic couplings simultaneously [18]. Furthermore, the entanglement amplification mechanism finds a clear physical explanation in the quantum interference between only two eigenvectors of the final Hamiltonian.…”

Section: Introductionmentioning

confidence: 83%

Entanglement amplification in the nonperturbative dynamics of modular quantum systems

et al. 2013

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We analyze the conditions for entanglement amplification between distant and not directly interacting quantum objects by their common coupling to media with static modular structure and subject to a local (single-bond) quenched dynamics. We show that in the nonperturbative regime of the dynamics the initial end-to-end entanglement is strongly amplified and, moreover, can be distributed efficiently between distant objects. Due to its intrinsic local and nonperturbative nature the dynamics is fast and robust against thermal fluctuations, and its control is undemanding. We show that the origin of entanglement amplification lies in the interference of the ground state and at most one of the low-lying energy eigenstates. The scheme can be generalized to provide a fast and efficient router for generating entanglement between simultaneous multiple users.

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“…However, one can also suddenly change a local coupling, as may be easier in gate controlled systems such as quantum dots coupled to leads, and for a spin chain version of such systems, called Kondo systems, the mechanism to generate entanglement has also been worked out [19]. Other mechanisms to generate entanglement between distant spins may involve kicked systems [20,21] or long distance state swap induced quantum gates [22,23], which also seems feasible in optical lattices and solid state spin chains in diamonds (see also alternative mechanism for entanglement distribution through the latter in Ref. [24]).…”

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Quench-induced growth of distant entanglement from product and locally entangled states in spin chains

2013

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We study the problem of entangling two spins at the distant ends of a spin chain by exploiting the nonequilibrium dynamics of the system after a sudden global quench. As initial states we consider a canted/spiral order product state of the spins, and singlets of neighboring pairs of spins. We find that within the class of canted order initial states, no entanglement is generated at any time except for the special case of the Néel state. While an earlier work had shown that the Néel state is indeed an excellent starting resource for the dynamical generation of long distance entanglement, the curious fact that this is the sole point within a large class of initial product states of the spins was not noted. On the other hand, we find that an initial state which is a series of nearest neighbor Bell states, and well motivated by some physical realizations, is also a good starting resource for end to end entanglement in a similar way to the Néel state. The scheme is shown to be robust to random single spin flip in the initial Néel state as well as randomness of the couplings.PACS numbers: 03.67. Bg, 03.67.Hk, 75.10.Pq Entanglement induced between distinct parts of a many-body system due to the nonequilibrium dynamics following quenches have attracted much attention recently. This has been largely motivated by experimental developments which allow for the realization of long time nonequilibrium dynamics -notably with ultracold atoms in optical lattices [1][2][3][4]. The potential for realizing such dynamics in ion traps has been also pointed out in both theoretical studies [5][6][7], as well as the realization of spin chains [8,9]. Some studies have examined the time development of entanglement between complementary blocks of a one dimensional spin system [6, 10-13] as well as between proximal spins [14,15]. However, in the field of quantum information, it is most desirable to achieve long range entanglement, i.e., the entanglement between two individual spins separated by a significant distance. For example, it is essential for teleportation of a quantum state over a distance [16] and thereby to link well separated quantum registers. Motivated by this point, studies have also been made of the creation of long-range entanglement between the end spins of a spin chain through the nonequilibrium dynamics that follows a quench. The first study in this context considered a chain of harmonic oscillators which were suddenly coupled [17]. For spin chains, the first study in this context considered a sudden quench in the Ising anisotropy parameter of a XXZ model [18]. This was a global quench in the sense that all couplings of the Hamiltonian of a system were changed in the same way by the quench. Such quenches may be easier to realize in systems with limited local addressability such as for ultracold atoms in optical lattices. However, one can also suddenly change a local coupling, as may be easier in gate controlled systems such as quantum dots coupled to leads, and for a spin chain version of such systems, called Kondo sy...

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Quantum router based on ac control of qubit chains

Cited by 90 publications

References 52 publications

Entanglement Routers Using Macroscopic Singlets

Entanglement Routers Using Macroscopic Singlets

Entanglement amplification in the nonperturbative dynamics of modular quantum systems

Quench-induced growth of distant entanglement from product and locally entangled states in spin chains

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