Universität Hamburg - Ionenfallen:

1.	Individual Addressing of Trapped Ions and Coupling of Motional and Spin States Using rf Radiation M. Johanning, A. Braun, N. Timoney, V. Elman, W. Neuhauser, and Chr. Wunderlich Phys. Rev. Lett. 102, 073004 (2009) – Published February 20, 2009 Cited 6 times Show Abstract Individual electrodynamically trapped and laser cooled ions are addressed in frequency space using radio-frequency radiation in the presence of a static magnetic field gradient. In addition, an interaction between motional and spin states induced by an rf field is demonstrated employing rf optical double resonance spectroscopy. These are two essential experimental steps towards realizing a novel concept for implementing quantum simulations and quantum computing with trapped ions. [View PDF (295 kB)]
2.	Error-resistant single-qubit gates with trapped ions N. Timoney, V. Elman, S. Glaser, C. Weiss, M. Johanning, W. Neuhauser, and Chr. Wunderlich Phys. Rev. A 77, 052334 (2008) – Published May 30, 2008 Cited 6 times Show Abstract Coherent operations with individual trapped Yb⁺ ions are demonstrated that are robust against variations in experimental parameters and intrinsically indeterministic system parameters. In particular, pulses developed using optimal control theory are demonstrated with trapped ions. Their performance as a function of error parameters is systematically investigated and compared to composite pulses. Such pulses are basic building blocks for single and multiqubit quantum gates. [View PDF (274 kB)]
3.	Electrodynamically trapped Yb⁺ ions for quantum information processing Chr. Balzer, A. Braun, T. Hannemann, Chr. Paape, M. Ettler, W. Neuhauser, and Chr. Wunderlich Phys. Rev. A 73, 041407 (2006) – Published April 28, 2006 Cited 14 times Show Abstract Highly efficient, nearly deterministic, and isotope selective generation of Yb⁺ ions by one- and two-color photoionization is demonstrated. State preparation and state selective detection of hyperfine states in ¹⁷¹Yb⁺ is investigated in order to optimize the purity of the prepared state and to time-optimize the detection process. Linear laser-cooled Yb⁺ ion crystals confined in a Paul trap are demonstrated. Advantageous features of different previous ion trap experiments are combined, while at the same time the number of possible error sources is reduced by using a comparatively simple experimental apparatus. This opens a new path toward quantum state manipulation of individual trapped ions, and in particular, to scalable quantum computing. [View PDF (115 kB)]
4.	Self-learning estimation of quantum states Th. Hannemann, D. Reiss, Ch. Balzer, W. Neuhauser, P. E. Toschek, and Ch. Wunderlich Phys. Rev. A 65, 050303 (2002) – Published May 3, 2002 Cited 19 times Show Abstract We report the experimental estimation of arbitrary qubit states using a succession of N measurements on individual qubits, where the measurement basis is changed during the estimation procedure conditioned on the outcome of previous measurements (self-learning estimation). Two hyperfine states of a single trapped ¹⁷¹Yb⁺ ion serve as a qubit. It is demonstrated that the difference in fidelity between this adaptive strategy and passive strategies increases in the presence of decoherence. [View PDF (121 kB)]
5.	Raman cooling and heating of two trapped Ba⁺ ions D. Reiß, K. Abich, W. Neuhauser, Ch. Wunderlich, and P. E. Toschek Phys. Rev. A 65, 053401 (2002) – Published April 12, 2002 Cited 8 times Show Abstract We study cooling of the collective vibrational motion of two ¹³⁸Ba⁺ ions confined in an electrodynamic trap and irradiated by laser light close to the resonances S_1/2-P_1/2 (493 nm) and P_1/2-D_3/2 (650 nm). The motional state of the ions is monitored by a spatially resolving photomultiplier. Depending on detuning and intensity of the cooling lasers, macroscopically different motional states corresponding to different ion temperatures are observed. We also derive the ions’ temperature from detailed analytical calculations of laser cooling taking into account the Zeeman structure of the energy levels involved. The observed motional states perfectly match the calculated temperatures. Significant heating is observed in the vicinity of the dark resonances of the Zeeman-split S_1/2-D_3/2 Raman transitions. Here two-photon processes dominate the interaction between lasers and ions. Parameter regimes of laser light are identified that imply most efficient laser cooling. [View PDF (250 kB)]
6.	Single-Atom Interferometry R. Huesmann, Ch. Balzer, Ph. Courteille, W. Neuhauser, and P. E. Toschek Phys. Rev. Lett. 82, 1611 (1999) – Published February 22, 1999 Cited 9 times Show Abstract The phase shift of the hyperfine Larmor precession of an individual ground-state ¹⁷¹Yb⁺ ion upon pulsed variation of the ambient magnetic field has been measured by microwave-optical double resonance interpreted in terms of Mach-Zehnder interferometry. Averaging over an ensemble of individual measurements, compared with measurements on an ensemble of ions, demonstrates quantum ergodicity. Even a single measurement yields (incomplete) phase information. Outside the peaks and dips of the interferogram, where ion probing is incompatible with ion preparation, the results of measurements are stochastic. This is demonstrated by laser exciting the ion on an E2 line. [View PDF (259 kB)]
7.	Transient internal dynamics of a multilevel ion M. Schubert, I. Siemers, R. Blatt, W. Neuhauser, and P. E. Toschek Phys. Rev. A 52, 2994 (1995) – Published October 1, 1995 Cited 19 times Show Abstract The autocorrelation g⁽²⁾(τ) of the photon-counting signal from laser-induced light scattering off a single trapped and laser-cooled Ba⁺ ion shows dramatic nonclassical effects: g⁽²⁾(τ) increasing upon delay τ close to zero (‘‘antibunching’’) is accompanied (i) by its extreme peak values, (ii) by long transients and long appearance of subunity values (‘‘sub-Poissonian light’’), both extending much beyond the lifetime of the ion’s resonance level, and (iii) by modulation from magnetic precession, as is common with quantum beats. These phenomena highlight the internal multilevel structure of the ion, hint at optical pumping, and prove the coherent evolution of the ion’s internal state. The preparation of the ion in a coherent superposition by spontaneous decay is demonstrated. The counting variance of the scattered light, measured in terms of Mandel’s Q parameter, deviates from that of classical light by up to ΔQ=-7×10^-4. [View Page Images or PDF (2,506 kB)]
8.	Ion storage in the rf octupole trap J. Walz, I. Siemers, M. Schubert, W. Neuhauser, R. Blatt, and E. Teloy Phys. Rev. A 50, 4122 (1994) – Published November 1, 1994 Cited 7 times Show Abstract Confinement of ion clouds in an rf octupole ion trap is investigated with particular emphasis on the trapping stability, which is position dependent. Excitation spectra of trapped clouds of Ba⁺ ions are observed, and the kinetic energy of ion clouds is derived. The spatial extension of ion clouds is measured, providing the basis for an experimental study of the trapping stability. For ion clouds in an rf octupole trap the mean kinetic energy is smaller and the spatial extension is larger than in comparable Paul traps. [View Page Images or PDF (2,032 kB)]
9.	Photon antibunching and non-Poissonian fluorescence of a single three-level ion M. Schubert, I. Siemers, R. Blatt, W. Neuhauser, and P. E. Toschek Phys. Rev. Lett. 68, 3016 (1992) – Published May 18, 1992 Cited 43 times Show Abstract The photon pair correlation in the laser-excited fluorescence of a single trapped and cooled Ba⁺ ion shows antibunching and, in addition, novel nonclassical phenomena absent in the fluorescence of two-level atoms. They include excessive transient values of the correlation caused by optical pumping, and temporally extended sub-Poissonian photon emission probability which arises from the transient excitation of nonabsorbing Raman coherence. The fluorescence also displays sub-Poissonian photon statistics. [View Page Images or PDF (600 kB)]
10.	Dynamics of ion clouds in Paul traps I. Siemers, R. Blatt, Th. Sauter, and W. Neuhauser Phys. Rev. A 38, 5121 (1988) – Published November 15, 1988 Cited 15 times Show Abstract Velocity distribution and spatial distribution of ion clouds in Paul traps have been investigated both theoretically and experimentally. The kinetic energy and the width of the spatial distribution have been measured as function of the trap parameters. This is compared with theoretical results obtained from model calculations based on Brownian motion of trapped particles. [View Page Images or PDF (1,274 kB)]
11.	Observation of Quantum Jumps Th. Sauter, W. Neuhauser, R. Blatt, and P. E. Toschek Phys. Rev. Lett. 57, 1696 (1986) – Published October 6, 1986 Cited 198 times Show Abstract We have recorded the laser-excited resonance fluorescence of one to three Ba⁺ ions and observed Bohr's "quantum jumps" when an ion decayed to the metastable ²D_5/2 state, suddenly quenching its fluorescence. Most of the jumps mark Raman-Stokes scattering from the ²S_1/2 and ²D_3/2 levels. [View Page Images or PDF (657 kB)]
12.	Localized visible Ba⁺ mono-ion oscillator W. Neuhauser, M. Hohenstatt, P. E. Toschek, and H. Dehmelt Phys. Rev. A 22, 1137 (1980) – Published September 1, 1980 Cited 136 times Show Abstract An individual barium ion, continuously observed by laser fluorescence, has been isolated in a Paul rf quadrupole trap at room temperature. By optical sideband cooling its microscopically measured image has been reduced in thickness to ∼ 2 μm in the object plane, the diffraction limit. Estimated ion temperatures reached are T_i≃10 to <36 mK. With cooling, the ion could be held indefinitely, without cooling ∼ 30 s. In the future the technique seems capable of attaining kinetic temperatures ∼ 10^-8 K, much lower than realized so far by other means, with corresponding far-reaching implications. [View Page Images or PDF (619 kB)]
13.	Optical-Sideband Cooling of Visible Atom Cloud Confined in Parabolic Well W. Neuhauser, M. Hohenstatt, P. Toschek, and H. Dehmelt Phys. Rev. Lett. 41, 233 (1978) – Published July 24, 1978 Cited 170 times Show Abstract An assemblage of < 50 Ba⁺ ions, contained in a parabolic well, has been visually observed and cooled by means of near-resonant laser irradiation. [View Page Images or PDF (843 kB)]