Time-dependent Hamiltonian estimation for Doppler velocimetry of trapped ions

The time evolution of a closed quantum system is connected to its Hamiltonian through Schroedinger's equation. The ability to estimate the Hamiltonian is critical to our understanding of quantum systems, and allows optimization of control. Though spectroscopic methods allow time-independent Hamiltonians to be recovered, for time-dependent Hamiltonians this task is more challenging. Here, using a single trapped ion, we experimentally demonstrate a method for estimating a time-dependent Hamiltonian of a single qubit. The method involves measuring the time evolution of the qubit in a fixed basis as a function of a time-independent offset term added to the Hamiltonian. In our system the initially unknown Hamiltonian arises from transporting an ion through a static, near-resonant laser beam. Hamiltonian estimation allows us to estimate the spatial dependence of the laser beam intensity and the ion's velocity as a function of time. This work is of direct value in optimizing transport operations and transport-based gates in scalable trapped ion quantum information processing, while the estimation technique is general enough that it can be applied to other quantum systems, aiding the pursuit of high operational fidelities in quantum control.Comment: 10 pages, 8 figure

An ion trap built with photonic crystal fibre technology

We demonstrate a surface-electrode ion trap fabricated using techniques transferred from the manufacture of photonic-crystal fibres. This provides a relatively straightforward route for realizing traps with an electrode structure on the 100 micron scale with high optical access. We demonstrate the basic functionality of the trap by cooling a single ion to the quantum ground state, allowing us to measure a heating rate from the ground state of 787(24) quanta/s. Variation of the fabrication procedure used here may provide access to traps in this geometry with trap scales between 100 um and 10 um.Comment: 6 pages, 4 figure

Trapping and ground-state cooling of H2+H_2^+

We demonstrate co-trapping and sideband cooling of a $H_2^+ - ^9Be^+$ ion pair in a cryogenic Paul trap. We study the chemical lifetime of $H_2^+$ and its dependence on the apparatus temperature, achieving lifetimes of up to $11^{+6}_{-3} h$ at 10 K. We demonstrate cooling of translational motion to an average phonon number of 0.07(1), corresponding to a temperature of $22(1)\mu K$. Our results provide a basis for quantum logic spectroscopy experiments of $H_2^+$, as well as other light ions such as $HD^+$, $H_3^+$, and $He^+$

An ion trap built with photonic crystal fibre technology

We demonstrate a surface-electrode ion trap fabricated using techniques transferred from the manufacture of photonic-crystal fibres. This provides a relatively straightforward route for realizing traps with an electrode structure on the 100 micron scale with high optical access. We demonstrate the basic functionality of the trap by cooling a single ion to the quantum ground state, allowing us to measure a heating rate from the ground state of 787 ± 24 quanta/s. Variation of the fabrication procedure used here may provide access to traps in this geometry with trap scales between 100 μm and 10 μ