Publications (11)91.39 Total impact

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ABSTRACT: The hyperfine structure of the S1/2D5/2 quadrupole transition at 729 nm in 43Ca+ has been investigated by laser spectroscopy using a single trapped 43Ca+ ion. We determine the hyperfine structure constants of the metastable level as A=3.8931(2) MHz and B=4.241(4) MHz. The isotope shift of the transition with respect to 40Ca+ was measured to be 4134.713(5) MHz. We demonstrate the existence of transitions that become independent of the firstorder Zeeman shift at nonzero low magnetic fields. These transitions might be better suited for building a frequency standard than the wellknown 'clock transitions' between m=0 levels at zero magnetic field. 

Article: Long Lived Entangled States
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ABSTRACT: We investigate entangled states of two trapped 40Ca+ ions. By encoding the quantum information in the Zeemanmanifold of the ground state, we observe entangled states lasting for more than 20 seconds. 
Article: Controlling Three Atomic Qubits
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ABSTRACT: We present a series of experiments where up to three ions held in a Paul trap are entangled, a given number of ions is selectively read out while conditional singlequantumbit (qubit) operations are performed coherently on the remaining ion(s). Using these techniques, we demonstrate also a state transfer of a quantum bit from one ion to another one using two measurements and entanglement between an auxiliary ion and the target ion  also known as teleportation.  [Show abstract] [Hide abstract]
ABSTRACT: The generation, manipulation and fundamental understanding of entanglement lies at the very heart of quantum mechanics. Entangled particles are noninteracting but are described by a common wavefunction; consequently, individual particles are not independent of each other and their quantum properties are inextricably interwoven. The intriguing features of entanglement become particularly evident if the particles can be individually controlled and physically separated. However, both the experimental realization and characterization of entanglement become exceedingly difficult for systems with many particles. The main difficulty is to manipulate and detect the quantum state of individual particles as well as to control the interaction between them. So far, entanglement of four ions or five photons has been demonstrated experimentally. The creation of scalable multiparticle entanglement demands a nonexponential scaling of resources with particle number. Among the various kinds of entangled states, the 'W state' plays an important role as its entanglement is maximally persistent and robust even under particle loss. Such states are central as a resource in quantum information processing and multiparty quantum communication. Here we report the scalable and deterministic generation of four, five, six, seven and eightparticle entangled states of the W type with trapped ions. We obtain the maximum possible information on these states by performing full characterization via state tomography, using individual control and detection of the ions. A detailed analysis proves that the entanglement is genuine. The availability of such multiparticle entangled states, together with full information in the form of their density matrices, creates a testbed for theoretical studies of multiparticle entanglement. Independently, 'GreenbergerHorneZeilinger' entangled states with up to six ions have been created and analysed in Boulder.  [Show abstract] [Hide abstract]
ABSTRACT: We report adiabatic passage experiments with a single trapped $^{40}$Ca$^+$ ion. By applying a frequency chirped laser pulse with a Gaussian amplitude envelope we reach a transfer efficiency of 0.990(10) on an optical transition from the electronic ground state S$_{1/2}$ to the metastable state D$_{5/2}$. This transfer method is shown to be insensitive to the accurate setting of laser parameters, and therefore is suitable as a robust tool for ion based quantum computing. 
Article: Teleportation with atoms
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ABSTRACT: The teleportation of an atomic state accomplishes the complete transfer of information from one particle to another, employing the nonlocal properties of quantum mechanics. Recently, two groups have achieved the deterministic teleportation of a quantum state between a pair of trapped ions. Following closely the original proposal of Bennett et al., a highly entangled pair of ions is created, a complete Bellstate projective measurement involving the source ion and one of the entangled pair is carried out, and state reconstruction conditioned on this measurement is performed on the other half of the entangled pair. 
Article: Robust entanglement
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ABSTRACT: It is common belief among physicists that entangled states of quantum systems lose their coherence rather quickly. The reason is that any interaction with the environment which distinguishes between the entangled subsystems collapses the quantum state. Here we investigate entangled states of two trapped Ca+ ions and observe robust entanglement lasting for more than 20 s.  [Show abstract] [Hide abstract]
ABSTRACT: Teleportation of a quantum state encompasses the complete transfer of information from one particle to another. The complete specification of the quantum state of a system generally requires an infinite amount of information, even for simple twolevel systems (qubits). Moreover, the principles of quantum mechanics dictate that any measurement on a system immediately alters its state, while yielding at most one bit of information. The transfer of a state from one system to another (by performing measurements on the first and operations on the second) might therefore appear impossible. However, it has been shown that the entangling properties of quantum mechanics, in combination with classical communication, allow quantumstate teleportation to be performed. Teleportation using pairs of entangled photons has been demonstrated, but such techniques are probabilistic, requiring postselection of measured photons. Here, we report deterministic quantumstate teleportation between a pair of trapped calcium ions. Following closely the original proposal, we create a highly entangled pair of ions and perform a complete Bellstate measurement involving one ion from this pair and a third source ion. State reconstruction conditioned on this measurement is then performed on the other half of the entangled pair. The measured fidelity is 75%, demonstrating unequivocally the quantum nature of the process.  [Show abstract] [Hide abstract]
ABSTRACT: Trapped ions can be prepared, manipulated and analyzed with high fidelities. In addition, scalable ion trap architectures have been proposed (Kielpinski et al., Nature 417, 709 (2001).). Therefore trapped ions represent a promising approach to large scale quantum computing. Here we concentrate on the recent advancements of generating entangled states with small ion trap quantum computers. In particular, the creation of Wstates with up to eight qubits and their characterization via state tomography is discussed.
Publication Stats
1k  Citations  
91.39  Total Impact Points  
Top Journals
 Physical Review A (2)
 Nature (2)
 Applied Physics B (1)
 Journal of Modern Optics (1)
Institutions

20012007

University of Innsbruck
 Institut für Experimentalphysik
Innsbruck, Tyrol, Austria
