Showing papers by "Rainer Blatt published in 2009"
TL;DR: Kirchmair et al. as discussed by the authors performed an experiment with trapped ions that demonstrates a state-independent conflict between non-contextuality and quantum mechanics and showed that the conflict resides in the structure of the theory and is independent of the properties of special states.
Abstract: Quantum mechanics has had notable success in the almost 90 years since it was first introduced, and its predictions have been confirmed in numerous experiments. Nevertheless, many physicists not content with the axioms of the theory have been searching for an explanation of quantum physical predictions in terms of a classical theory. An intuitive feature of classical models is non-contextuality: the property that any measurement has a value independent of other compatible measurements being carried out at the same time. Theory suggests that non-contextuality is in conflict with quantum mechanics, and experiments undertaken with photons and neutrons seem to support this. However, these tests required the generation of special quantum states and left various loopholes open. Here, Kirchmair et al. perform an experiment with trapped ions that overcomes these problems and cannot be explained in non-contextual terms. Contextuality is therefore a property of nature that does not require the generation of special quantum states or quantum entanglement. The question of whether quantum phenomena can be explained by classical models with hidden variables is the subject of a long-lasting debate. One feature of classical models that is thought to be in conflict with quantum mechanics is non-contextuality, with experiments undertaken with photons and neutrons seeming to support this. However, these tests required the generation of special quantum states and left various loopholes open. Here an experiment is performed with trapped ions that overcomes these problems and cannot be explained in non-contextual terms. The question of whether quantum phenomena can be explained by classical models with hidden variables is the subject of a long-lasting debate1,2. In 1964, Bell showed that certain types of classical models cannot explain the quantum mechanical predictions for specific states of distant particles, and some types of hidden variable models3,4,5,6,7,8,9 have been experimentally ruled out. An intuitive feature of classical models is non-contextuality: the property that any measurement has a value independent of other compatible measurements being carried out at the same time. However, a theorem derived by Kochen, Specker and Bell10,11,12 shows that non-contextuality is in conflict with quantum mechanics. The conflict resides in the structure of the theory and is independent of the properties of special states. It has been debated whether the Kochen–Specker theorem could be experimentally tested at all13,14. First tests of quantum contextuality have been proposed only recently, and undertaken with photons15,16 and neutrons17,18. But these tests required the generation of special quantum states and left various loopholes open. Here we perform an experiment with trapped ions that demonstrates a state-independent conflict with non-contextuality. The experiment is not subject to the detection loophole and we show that, despite imperfections and possible measurement disturbances, our results cannot be explained in non-contextual terms.
340 citations
TL;DR: This work presents the first experimental realization of the quantum Toffoli gate in an ion trap quantum computer, achieving a mean gate fidelity of 71(3)%.
Abstract: Gates acting on more than two qubits are appealing as they can substitute complex sequences of two-qubit gates, thus promising faster execution and higher fidelity. One important multiqubit operation is the quantum Toffoli gate that performs a controlled NOT operation on a target qubit depending on the state of two control qubits. Here we present the first experimental realization of the quantum Toffoli gate in an ion trap quantum computer, achieving a mean gate fidelity of 71(3)%. Our implementation is particularly efficient as the relevant logic information is directly encoded in the motion of the ion string.
322 citations
TL;DR: In this article, the first absolute transition frequency measurement at the 10−15−1/15−2 level with a single, laser-cooled ion in a linear Paul trap was reported.
Abstract: We report on the first absolute transition frequency measurement at the ${10}^{\ensuremath{-}15}$ level with a single, laser-cooled $^{40}\mathrm{Ca}^{+}$ ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the $^{40}\mathrm{Ca}^{+}$ $4s\text{ }^{2}S_{1/2}\ensuremath{-}3d\text{ }^{2}D_{5/2}$ electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency ${\ensuremath{
u}}_{{\mathrm{Ca}}^{+}}=411\text{ }042\text{ }129\text{ }776\text{ }393.2(1.0)\text{ }\text{ }\mathrm{Hz}$ is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Land\'e $g$ factor of the $3d^{2}D_{5/2}$ level to be ${g}_{5/2}=1.200\text{ }334\text{ }0(3)$.
125 citations
TL;DR: In this paper, the authors describe the implementation of a M?lmer?S?rensen gate entangling two 40Ca+ ions using a bichromatic laser beam near-resonant with a quadrupole transition.
Abstract: We give a detailed description of the implementation of a M?lmer?S?rensen gate entangling two 40Ca+ ions using a bichromatic laser beam near-resonant with a quadrupole transition. By amplitude pulse shaping and compensation of ac-Stark shifts we achieve a fast gate operation without compromising the error rate. Subjecting different input states to concatenations of up to 21 individual gate operations reveals Bell state fidelities above 0.80. In principle, the entangling gate does not require ground state cooling of the ions as long as the Lamb?Dicke criterion is fulfilled. We present the first experimental evidence for this claim and create Bell states with a fidelity of 0.974(1) for ions in a thermal state of motion with a mean phonon number of in the mode coupling to the ions' internal states.
124 citations
TL;DR: In this paper, the first absolute transition frequency measurement at the 10−15−1/15−2 level with a single, laser-cooled ion in a linear Paul trap was reported.
Abstract: We report on the first absolute transition frequency measurement at the ${10}^{\ensuremath{-}15}$ level with a single, laser-cooled $^{40}\mathrm{Ca}^{+}$ ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the $^{40}\mathrm{Ca}^{+}$ $4s\text{ }^{2}S_{1/2}\ensuremath{-}3d\text{ }^{2}D_{5/2}$ electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency ${\ensuremath{
u}}_{{\mathrm{Ca}}^{+}}=411\text{ }042\text{ }129\text{ }776\text{ }393.2(1.0)\text{ }\text{ }\mathrm{Hz}$ is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Land\'e $g$ factor of the $3d^{2}D_{5/2}$ level to be ${g}_{5/2}=1.200\text{ }334\text{ }0(3)$.
118 citations
TL;DR: In this paper, a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity was realized, achieving an efficiency of 88±17%.
Abstract: We realize a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity. Photons are created in the cavity with efficiency 88±17%, a tenfold improvement over previous cavity-ion sources. Results of the second-order correlation function are presented, demonstrating a high suppression of two-photon events limited only by background counts. The cavity photon pulse shape is obtained, with good agreement between experiment and simulation. Moreover, theoretical analysis of the temporal evolution of the atomic populations provides relevant information about the dynamics of the process and opens the way to future investigations of a coherent atom–photon interface.
113 citations
TL;DR: This work demonstrates the realization of a universal set of quantum gates acting on decoherence-free ion qubits, and combines these gates to realize the first controlled-NOT gate towards a decoherent-free, scalable quantum computer.
Abstract: Any residual coupling of a quantum computer to the environment results in computational errors. Encoding quantum information in a so-called decoherence-free subspace provides means to avoid these errors. Despite tremendous progress in employing this technique to extend memory storage times by orders of magnitude, computation within such subspaces has been scarce. Here, we demonstrate the realization of a universal set of quantum gates acting on decoherence-free ion qubits. We combine these gates to realize the first controlled-NOT gate towards a decoherence-free, scalable quantum computer.
97 citations
TL;DR: In this paper, the order of ions in a string is deterministically reversed and the reordering can be carried out adiabatically in a planar, linear chip trap.
Abstract: In the endeavour to scale up the number of qubits in an ion-based quantum computer several groups have started to develop miniaturized ion traps for extended spatial control and manipulation of the ions Shuttling and separation of ion strings have been the foremost issues in linear-trap arrangements and some prototypes of junctions have been demonstrated for the extension of ion motion to two dimensions (2D) While junctions require complex trap structures, small extensions to the 1D motion can be accomplished in simple linear trap arrangements Here, control of the extended field in a planar, linear chip trap is used to shuttle ions in 2D With this approach, the order of ions in a string is deterministically reversed Optimized potentials are theoretically derived and simulations show that the reordering can be carried out adiabatically The control over individual ion positions in a linear trap presents a new tool for ion-trap quantum computing The method is also expected to work with mixed crystals of different ion species and as such could have applications for sympathetic cooling of an ion string
61 citations
TL;DR: In this article, the coherence of the individual resonance fluorescence light field is determined from the observed interference of two continuously laser-excited single ions, independently trapped in distinct vacuum vessels.
Abstract: We observe quantum interference of photons emitted by two continuously laser-excited single ions, independently trapped in distinct vacuum vessels. High contrast two-photon interference is observed in two experiments with different ion species, Ca+ and Ba+. Our experimental findings are quantitatively reproduced by Bloch equation calculations. In particular, we show that the coherence of the individual resonance fluorescence light field is determined from the observed interference.
60 citations
TL;DR: In this paper, an ion-based cavity-QED system is described in which the internal dynamics of an atom is coupled to the modes of an optical cavity by vacuum-stimulated Raman transitions.
Abstract: We describe an ion-based cavity-QED system in which the internal dynamics of an atom is coupled to the modes of an optical cavity by vacuum-stimulated Raman transitions. We observe Raman spectra for different excitation polarizations and find quantitative agreement with theoretical simulations. Residual motion of the ion introduces motional sidebands in the Raman spectrum and leads to ion delocalization. The system offers prospects for cavity-assisted resolved-sideband ground-state cooling and coherent manipulation of ions and photons.
49 citations
TL;DR: Measurements of an intensity-field correlation function of the resonance fluorescence of a single trapped 138Ba+ ion provide a direct measurement of the field of the radiating dipole of asingle atom and exhibits its strong nonclassical behavior.
Abstract: We report measurements of an intensity-field correlation function of the resonance fluorescence of a single trapped $^{138}\mathrm{Ba}^{+}$ ion. Detection of a photon prepares the atom in its ground state, and we observe its subsequent evolution under interaction with a laser field of well-defined phase. We record the regression of the resonance fluorescence source field. This provides a direct measurement of the field of the radiating dipole of a single atom and exhibits its strong nonclassical behavior. In the setup, an interference measurement is conditioned on the detection of a fluorescence photon.
01 May 2009
TL;DR: The first absolute transition frequency measurement at the 10;-15 level with a single, laser-cooled 40Ca+ ion in a linear Paul trap is reported on, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard.
Abstract: We report on the first absolute transition frequency measurement at the 10;{-15} level with a single, laser-cooled 40Ca+ ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the 40Ca+ 4s ;{2}S_{1/2}-3d ;{2}D_{5/2} electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency nu_{Ca;{+}}=411 042 129 776 393.2(1.0) Hz is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Landé g factor of the 3d;{2}D_{5/2} level to be g_{5/2}=1.200 334 0(3).
TL;DR: In this paper, the authors combine the merits of a high-fidelity entangling operation on an optical transition (optical qubit) with the long coherence times of two clock states in the hyperfine ground state (hyperfine qubit), by mapping between these two qubits for state initialization, state detection, global qubit rotations, and mapping operations.
Abstract: In an experiment using the odd calcium isotope $^{43}\mathrm{Ca}^{+}$, we combine the merits of a high-fidelity entangling operation on an optical transition (optical qubit) with the long coherence times of two ``clock'' states in the hyperfine ground state (hyperfine qubit) by mapping between these two qubits For state initialization, state detection, global qubit rotations, and mapping operations, errors smaller than 1% are achieved, whereas the entangling gate adds errors of 23% Based on these operations, we create Bell states with a fidelity of 969(3)% in the optical qubit and a fidelity of 967(3)% when mapped to the hyperfine states In the latter case, the entanglement is preserved for $96(3)\phantom{\rule{03em}{0ex}}\mathrm{ms}$, exceeding the duration of a single gate operation by three orders of magnitude
TL;DR: In this article, the authors present an overview on qubit encoding with Ca+ and several state-of-the-art operations involving two and three qubits, using decoherence-free subspaces and encoding logical qubits using two physical qubits.
Abstract: With trapped ions quantum information can be encoded in various two-level systems or quantum bits (qubits). Here, we present an overview on qubit encoding with Ca+ and several state-of-the-art operations involving two and three qubits. The use of decoherence-free subspaces and encoding logical qubits using two physical qubits may offer an advantageous route towards implementing scalable quantum information processing.
TL;DR: In this article, the order of the ions in a string is deterministically reversed and the reordering can be carried out adiabatically with the use of a linear chip trap.
Abstract: In the endeavour to scale up the number of qubits in an ion-based quantum computer several groups have started to develop miniaturized ion traps for extended spatial control and manipulation of the ions. Shuttling and separation of ion strings have been the foremost issues in linear-trap arrangements and some prototypes of junctions have been demonstrated for the extension of ion motion to two dimensions (2D). While junctions require complex trap structures, small extensions to the 1D motion can be accomplished in simple linear trap arrangements. Here, control of the extended field in a planar, linear chip trap is used to shuttle ions in 2D. With this approach, the order of ions in a string is deterministically reversed. Optimized potentials are theoretically derived and simulations show that the reordering can be carried out adiabatically. The control over individual ion positions in a linear trap presents a new tool for ion-trap quantum computing. The method is also expected to work with mixed crystals of different ion species and as such could have applications for sympathetic cooling of an ion string.
TL;DR: Jost et al. demonstrate entanglement between separated mechanical oscillator, consisting of the vibrational states of two pairs of atomic ions held in different locations, which may open the way to the generation of entangled states of larger-scale mechanical oscillators and the scaling-up of quantum information processing based on trapped ions.
Abstract: A neat experiment shows that the mechanical vibration of two ion pairs separated by a few hundred micrometres is entangled — their motions are intrinsically and inseparably connected in a quantum way. Superposition and entanglement are hallmarks of quantum mechanics, and are usually demonstrated for properties such as electron spin and photon polarization. Now with the demonstration of entanglement between distinct mechanical oscillators — familiar at a larger scale as springs or pendula — these esoteric phenomena take a tentative step nearer the world of our everyday existence. Jost et al. demonstrate entanglement between separated mechanical oscillators, consisting of the vibrational states of two pairs of atomic ions held in different locations. Such experiments may open the way to the generation of entangled states of larger-scale mechanical oscillators and the scaling-up of quantum information processing based on trapped ions.
02 Jun 2009
TL;DR: In this paper, the authors discuss the implementation of high fidelity entangling operations based on a global interaction of a single laser beam with a string of trapped ions, which is called global entangling.
Abstract: We will discuss the implementation of high fidelity entangling operations based on a global interaction of a single laser beam with a string of trapped ions.
TL;DR: In this article, a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity was realized, achieving state-of-the-art performance.
Abstract: We realize a deterministic single-photon source from one and the same calcium ion interacting with a high-finesse optical cavity. Photons are created in the cavity with efficiency (88 +- 17)%, a tenfold improvement over previous cavity-ion sources. Results of the second-order correlation function are presented, demonstrating a high suppression of two-photon events limited only by background counts. The cavity photon pulse shape is obtained, with good agreement between experiment and simulation. Moreover, theoretical analysis of the temporal evolution of the atomic populations provides relevant information about the dynamics of the process and opens the way to future investigations of a coherent atom-photon interface.
14 Jun 2009
TL;DR: In this article, an entangling gate was used to entangle a pair of 40Ca+ ions without having recourse to ground state cooling, which opens the way to performing an operation which does not preserve the ions' motional state like for example state detection.
Abstract: Laser-ion interactions that collectively couple the pseudo-spins of a string of trapped ions to one of the string's vibrational modes [1] have been used by us to entangle a pair of 40Ca+ ions with very high fidelity [2–4]. In addition, we experimentally confirmed that this gate mechanism allows for entangling ions without having recourse to ground state cooling [3]. This opens the way to performing an entangling gate after having applied an operation which does not preserve the ions' motional state like for example state detection.