Prof. R. Blatt.
The group started working in Innsbruck in 1995 and in the meantime it is well established in field of quantum information with trapped ions.
With a linear ion trap and a sophisticated setup of lasers we cool a string of Calcium ions to the ground state and we routinely manipulate the stored quantum information coherently on a narrow quadrupole transition of the ions. The ion spacing in the linear string is large enough to address the ions individually with a laser. Currently, various quantum logical operations are investigated with this setup: We have demonstrated arbitrary single qubit rotations employing the composite pulse technique known from NMR quantum computing. The light (AC-Stark) shift created by driving sideband transitions fundamentally limits the realization of quantum gate operations. We compensate for this light shift with additional laser fields. Combining these techniques, we implemented a two qubit quantum algorithm --the Deutsch-Josza algorithm-- with a single Ca+ ion, encoding the qubits in the electronic state and the vibrational phonon number.
Recently, we also have demonstrated the Cirac-Zoller two-ion controlled-NOT quantum gate with a fidelity of 70-80%. In a second setup we have placed a radially symmetric Paul trap inside a high finesse cavity. Single ions in the trap are laser cooled and their internal state is coherently manipulated. Coherent coupling of the S1/2-D5/2 qubit-transition to the mode of the high-finesse cavity (finesse 35000 at 729 nm) has been demonstrated by spectrally and spatially resolved measurements. With this setup the ion is positioned with nm-precision in the standing wave and thus the ion-cavity coupling is precisely controlled. Measurement of the lifetime of the D5/2 metastable state with the cavity frequency-stabilized to the S1/2-D5/2 qubit-transition reveal a coupling of the ion to the cavity vacuum field. With a further improved scheme and an improved setup interfacing procedures to interconvert static and flying qubits will be investigated.
With single trapped Ba+ ions in a spherically symmetric Paul trap we investigate the spectrum of resonance fluorescence and derive information of the ion's motion which is to be used subsequently for quantum feedback operations. With this setup single-atom-single-photon interferences have been observed which allow the precision determination of the ion's position (and with some improved procedures) the ion's momentum at the quantum level. Coupling the emitted photons of one ion efficiently to another one with a distant mirror allows us to investigate the transport of quantum information at the most fundamental level. Currently we investigate level shifts and dipole forces arising in the standing wave vacuum field in front of the mirror.
A setup for trapping neutral atoms in light potentials is available including a double magneto-optical trap system and the laser for the generating the light potential. As a first step towards trapping atoms in 'designer' potentials, transfer between two traps has been demonstrated, and a light trap formed by a holographically created hollow laser beam is being investigated.
Key expertise is provided by the following senior scientists, all permanently employed by the University of Innsbruck: Prof. Rainer Blatt (R.B.) , Dr. Christoph Becher (C.B.) , Dr. Jürgen Eschner (J.E.), Dr. Hartmut Häffner (H.H.), Dr. Wolfgang Hänsel (W.H.), Dr. Christian Roos (C.R.), and Prof. Ferdinand Schmidt-Kaler (F.S.K.). R.B. has worked with single trapped ions since 1984. He was involved in the first observation of quantum jumps in the fluorescence of a single ion in Hamburg. Collaboration with P. Zoller and I. Cirac resulted in a series of milestone papers about optical cooling and motional manipulation of trapped ions.
C.B., after completion of his doctoral thesis on generation of non-classical light with diode and solid-state lasers at the University of Kaiserslautern (Prof. Wallenstein), worked as postdoctoral researcher in the group of Atac Imamoglu at the University of California, Santa Barbara, USA. At UCSB he did research on quantum optics with semiconductor quantum dots (QD), especially on the deterministic generation of single photons and CQED effects with QDs in microstructures (microcavities, photonic crystals). In Innsbruck he is working on CQED with a single trapped ion in a cavity.
J.E. first worked with single trapped ions from 1993 to 1995, as a postdoc in Hamburg, in the group of Prof. P.E. Toschek. During that time, he investigated in particular the sideband excitation of a single ion and its effect on the ion's motional state. He also developed a novel mechanism for efficient sideband cooling of single trapped particles. From 1995 to 1996, as the holder of an ARC International Fellowship, he joined and later directed an atom optics project at the Australian National University in Canberra, where he built up his expertise in trapping and cooling of neutral atoms. In Innsbruck, since 1996, he has continued his earlier work with ions and has initiated and started an experiment with trapped neutral atoms.
H.H. worked first with ions at the University Mainz with Günther Werth during his PhD. There he measured the magnetic moment of hydrogen-like Carbon and the electron mass with high precision in a Penning trap. As a postdoctoral Feodor-Lynen fellow at NIST Gaithersburg from 2000 to 2001 with William D. Phillips, he build up his expertise with BEC's. In particular, he investigated photoassociation and non-linear dynamics (dynamical tunnelling) with a BEC. In 2002 he joined Rainer Blatt's group in Innsbruck and is pursuing quantum information processing with trapped Calcium ions.
W.H. has gained first experimental experience at the Ecole Normale Superieure in Paris with Dr. Christophe Salomon where he has studied optical trapping and Raman cooling of neutral Cesium atoms (masters thesis). From 1996 to 2001, he continued working with neutral Rubidium atoms at the Ludwig-Maximilian University Munich and the Max-Planck-Institute Garching in the group of Prof. Theodor W. Hänsch. His work was directed towards miniaturized magnetic traps that achieve particularly high field gradients and offer versatile potential shapes (PhD). The development of these traps finally lead to Bose-Einstein condensation on a microchip. In December 2001, he joined the group of Prof. Lene Hau as a postdoctoral fellow at Harvard University, Cambridge, where he participated in the setup of an intense source of cold Rubidium atoms. Since January 2003, he is working in the group of Prof. Rainer Blatt, focussing on quantum information processing with trapped calcium ions and the miniaturization of ion traps.
C. R. first worked with single or few trapped ions from 1995 to 2000, as a PhD student in Innsbruck, in the group of Prof. R. Blatt. During that time, he started investigating how to couple the quadrupole transition of a single trapped calcium ion to the mode of a high-finesse cavity in order to observe cavity QED effects. Later on, he developed techniques for sideband cooling calcium ions to the ground state of the trapping potential. From 2000 to 2002, as the holder of a Marie Curie Fellowship of the EU, he joined the 'ultracold atom group', led by Claude Cohen-Tannoudji and Jean Dalibard at the Ecole Normale Supérieure in Paris, France. There, he worked on creating a truly continuous, coherent beam of cold atoms that might have applications in metrology. Back in Innsbruck, since 2002, he has continued his earlier work with ions, now focussed on the creation of multi-particle entangled states with trapped ions.
F.S.K. first worked on "Precision spectroscopy of atomic hydrogen transitions" at the Max-Planck-Institut fur Quantenoptik in Garching (PhD thesis with Prof. Dr. T. W. Hansch) where he studied and applied advanced techniques of laser spectroscopy and stabilised laser sources for precision spectroscopy and the measurement of fundamental constants. As a postdoctoral fellow he worked on Rydberg atoms (group of Prof. Dr. S. Haroche, ENS Paris), and their interaction with a single quantized field mode inside a superconducting microwave cavity. This experiment is one of the most advanced performing quantum state manipulations and studying entangled states. Currently, at Innsbruck, he is working on experiments investigating ions in linear ion traps and their application for quantum information.
The work at the group is done in close collaboration with the Innsbruck Theory group of Prof. P. Zoller and Prof. Dr. I. Cirac at the Max-Planck-Institut für Quantenoptik in Garching.
The Innsbruck group are currently involved in the EU networks QUBITS, QUEST and QI.
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