Active impedance matching of a cryogenic radio frequency resonator for ion traps.

A combination of direct current (DC) fields and high amplitude radio frequency (RF) fields is necessary to trap ions in a Paul trap. Such high electric RF fields are usually reached with the help of a resonator in close proximity to the ion trap. Ion trap based quantum computers profit from good vacuum conditions and low heating rates that cryogenic environments provide. However, an impedance matching network between the resonator and its RF source is necessary, as an unmatched resonator would require higher input power due to power reflection. The reflected power would not contribute to the RF trapping potential, and the losses in the cable induce additional heat into the system. The electrical properties of the matching network components change during cooling, and a cryogenic setup usually prohibits physical access to integrated components while the experiment is running. This circumstance leads to either several cooling cycles to improve the matching at cryogenic temperatures or the operation of poorly matched resonators. In this work, we demonstrate an RF resonator that is actively matched to the wave impedance of coaxial cables and the signal source. The active part of the matching circuit consists of a varactor diode array. Its capacitance depends on the DC voltage applied from outside the cryostat. We present measurements of the power reflection, the Q-factor, and higher harmonic signals resulting from the nonlinearity of the varactor diodes. The RF resonator is tested in a cryostat at room temperature and cryogenic temperatures, down to 4.3 K. A superior impedance matching for different ion traps can be achieved with this type of resonator.

A cryogenic radio-frequency ion trap for quantum logic spectroscopy of highly charged ions.

A cryogenic radio-frequency ion trap system designed for quantum logic spectroscopy of highly charged ions (HCI) is presented. It includes a segmented linear Paul trap, an in-vacuum imaging lens, and a helical resonator. We demonstrate ground state cooling of all three modes of motion of a single 9Be+ ion and determine their heating rates as well as excess axial micromotion. The trap shows one of the lowest levels of electric field noise published to date. We investigate the magnetic-field noise suppression in cryogenic shields made from segmented copper, the resulting magnetic field stability at the ion position and the resulting coherence time. Using this trap in conjunction with an electron beam ion trap and a deceleration beamline, we have been able to trap single highly charged Ar13+ (Ar XIV) ions concurrently with single Be+ ions, a key prerequisite for the first quantum logic spectroscopy of a HCI. This major stepping stone allows us to push highly-charged-ion spectroscopic precision from the gigahertz to the hertz level and below.

Interaction-driven dynamics of 40K- 87Rb Fermion-Boson gas mixtures in the large-particle-number limit.

We have studied effects of interspecies attraction in a Fermi-Bose mixture over a large regime of particle numbers in the 40K-87Rb system. We report on the observation of a mean-field driven collapse at critical particle numbers of 1.2 x 10(6) 87Rb atoms in the condensate and 7.5 x 10(5) 40K atoms consistent with mean-field theory for a scattering length of aFB = -284a(0). For large overcritical particle numbers, we see evidence for revivals of the collapse. Part of our detailed study of the decay dynamics and mechanisms is a measurement of the (87Rb- 87Rb- 40K) three-body loss coefficient K3 = (2.8 +/- 1.1) x 10(-28) cm6/s, which is an important parameter for dynamical studies of the system.