Showing papers by "Hartmut Häffner published in 2014"
TL;DR: In this article, a trapped-ion experiment demonstrates that correlations between the system and its environment can be detected without accessing or knowing anything about the environment or its interactions without access or knowledge of the environment.
Abstract: In open quantum systems the correlations between the system and its environment play an important role. A trapped-ion experiment demonstrates that these correlations can be detected without accessing or knowing anything about the environment or its interactions.
99 citations
TL;DR: In this article, the authors used a single ion electric field sensor in combination with in situ surface treatment and analysis tools to investigate the relationship between electric field noise from metal surfaces in vacuum and the composition of the surface.
Abstract: We use a single-ion electric-field noise sensor in combination with in situ surface treatment and analysis tools, to investigate the relationship between electric-field noise from metal surfaces in vacuum and the composition of the surface. These experiments are performed in a setup that integrates ion trapping capabilities with surface analysis tools. We find that treatment of an aluminum-copper surface with energetic argon ions significantly reduces the level of room-temperature electric-field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The noise levels after treatment are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap at room temperature.
65 citations
TL;DR: In this paper, the authors used a pulsed excitation scheme to rapidly add energy to the local motional mode of one of the trapped ions in the chain, and the subsequent energy readout allows them to determine how the excitation has propagated throughout the chain.
Abstract: We experimentally study energy transport in chains of trapped ions. We use a pulsed excitation scheme to rapidly add energy to the local motional mode of one of the ions in the chain. Subsequent energy readout allows us to determine how the excitation has propagated throughout the chain. We observe energy revivals that persist for many cycles. We study the behavior with an increasing number of ions of up to 37 in the chain, including a zig-zag configuration. The experimental results agree with the theory of normal mode evolution. The described system provides an experimental toolbox for the study of thermodynamics of closed systems and energy transport in both classical and quantum regimes.
64 citations
TL;DR: Detailed derivations of the composite cavity system mediated by a silica waveguide as well as the control scheme are given, which allows for universal quantum operations on the spin coherent state quantum memories.
Abstract: We propose a hybrid architecture for quantum information processing based on magnetically trapped ultracold atoms coupled via optical fields. The ultracold atoms, which can be either Bose-Einstein condensates or ensembles, are trapped in permanent magnetic traps and are placed in microcavities, connected by silica based waveguides on an atom chip structure. At each trapping center, the ultracold atoms form spin coherent states, serving as a quantum memory. An all-optical scheme is used to initialize, measure and perform a universal set of quantum gates on the single and two spin-coherent states where entanglement can be generated addressably between spatially separated trapped ultracold atoms. This allows for universal quantum operations on the spin coherent state quantum memories. We give detailed derivations of the composite cavity system mediated by a silica waveguide as well as the control scheme. Estimates for the necessary experimental conditions for a working hybrid device are given.
28 citations
TL;DR: In this paper, a spatially resolved multitime correlation function of interacting many-body systems with scalable experimental overheads is proposed. But this approach is limited to single-site addressability.
Abstract: We establish a novel approach to probing spatially resolved multitime correlation functions of interacting many-body systems, with scalable experimental overheads. Specifically, designing nonlinear measurement protocols for multidimensional spectra in a chain of trapped ions with single-site addressability enables us, for example, to distinguish coherent from incoherent transport processes, to quantify potential anharmonicities, and to identify decoherence-free subspaces.
25 citations
TL;DR: In this paper, the ground-state quantum correlations of an Ising model can be detected by monitoring the time evolution of a single spin alone, and the critical point of a quantum phase transition is detected through a maximum of a suitably defined observable.
Abstract: We show that the ground-state quantum correlations of an Ising model can be detected by monitoring the time evolution of a single spin alone, and that the critical point of a quantum phase transition is detected through a maximum of a suitably defined observable. A proposed implementation with trapped ions realizes an experimental probe of quantum phase transitions which is based on quantum correlations and scalable for large system sizes.
19 citations
TL;DR: In this paper, the authors present measurements of resistive and sympathetic cooling of ion clouds confined in a Penning trap and observe a significant deviation from exponential cooling behavior which is explained by an energy transfer model.
Abstract: We present measurements of resistive and sympathetic cooling of ion clouds confined in a Penning trap. For resistive cooling of a cloud consisting of one ion species, we observe a significant deviation from exponential cooling behavior which is explained by an energy-transfer model. The observed sympathetic cooling of simultaneously confined ion species shows a quadratic dependence on the ion charge state and is hence in agreement with expectations from the physics of dilute non-neutral plasmas.
18 citations
TL;DR: In this paper, the authors demonstrate a method to couple two motional modes of a single trapped ion, where the coupling mechanism is based on applying electric fields rather than coupling the ion's motion to a light field.
Abstract: Atomic ions, confined in radio-frequency Paul ion traps, are a promising candidate to host a future quantum information processor. In this article, we demonstrate a method to couple two motional modes of a single trapped ion, where the coupling mechanism is based on applying electric fields rather than coupling the ion's motion to a light field. This reduces the design constraints on the experimental apparatus considerably. As an application of this mechanism, we cool a motional mode close to its ground state without accessing it optically. As a next step, we apply this technique to measure the mode's heating rate, a crucial parameter determining the trap quality.
13 citations
TL;DR: In this article, an experimental scheme to perform spectroscopy on ions and atoms with a lambda-level structure is presented. But the scheme is limited to 2S 1/2 − 2P1/2 and 2D 3/2− 2P 1/3/2 transitions in 40Ca+ and requires a measurement time of 10 min.
Abstract: We present an experimental scheme to perform spectroscopy on ions and atoms with a lambda-level structure. By rapidly switching lasers between both transitions, we circumvent the complications of both dark resonances and the ac-Stark effect. We demonstrate the scheme on the 2S1/2 − 2P1/2 and 2D3/2 − 2P1/2 transitions in 40Ca+ and, within a measurement time of 10 min, extract the centre frequencies of both dipole transitions with a statistical uncertainty on the order of 200 kHz. We also apply this method to directly observe the micromotion modulated fluorescence spectra of both transitions and for the first time measure the dependence of the micromotion modulation index on the trap frequency for both transitions.
9 citations