Leibfried, Dietrich

Friday Sept 6, 2013
Time: 14:00
Place: ETH Science City, HPF G6
Host: Jonathan Home

Towards scalable quantum information processing and quantum simulation with trapped ions

Dietrich Leibfried
National Institute of Standards and Technology, Boulder, CO USA

Quantum information processing (QIP) and Quantum Simulation (QS) can potentially provide an exponential speedup for certain problems over the corresponding (known) algorithms on conventional computers. At NIST we are mainly working on establishing quantum technologies with trapped ions for scalable quantum information processing and quantum logic clocks. Most requirements for QIP and QS have been demonstrated in this system, with two big challenges remaining: Improving operation fidelity and scaling up to larger numbers of qubits. The architecture pursued at the Ion Storage Group at NIST is based on quantum information stored in long lived internal (hyperfine) states of the ions. We investigate the use of laser beams and microwave fields to induce both single-qubit rotations and multi-qubit gates mediated by the Coulomb interaction between ions. Moving ions through a multi-zone trap architecture allows for keeping the number of ions per zone small, while sympathetic cooling with a second ion species can remove energy and entropy from the system. After a brief introduction to these elements, I will present the current status of experiments and some future perspectives for QIP and QS. In particular, we have prepared mixed strings of Mg+ and Be+ ions close to the ground states of all axial normal modes by applying two laser fields that were near-resonant with the Mg+ ions only. The resulting electromagnetically induced transparency actively cooled the Mg+ ions while the Be+ ions were sympathetically cooled. We also combine unitary processes on the Be+ ions with engineered dissipation into a zero-temperature bath, realized by optical pumping on a certain transition of the Be+ and sympathetic cooling on the Mg+ ions, to deterministically produce and stabilize an approximate Bell state of two trapped-ion qubits, independent of their initial state.  In another experiment, we have Coulomb coupled two Be+ ions held at 30 mm distance in a double-well potential to exchange a single quantum of motional excitation and also entangled their internal states based on this “remote” interaction. This can be viewed as the basic building block for simulating spin-spin interactions in arbitrary 2D-lattices of ions. I will also discuss characterization and cleaning of ion-trap surfaces to combat “anomalous” motional heating. Finally, I will report on results for using photonic band-gap (holey) fibers for efficient single mode delivery of 10s of mW of UV light (313 nm and 280 nm).

This work has been supported by IARPA, ONR, and the NIST Quantum Information Program