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Research
 
cavity

Ion+Cavity systems

The combination of high-finesse optical cavities and ion traps is attractive for quantum light-matter interfaces. In a 4-rod Paul trap, we have demonstrated cavity cooling of a single Sr ion, and ongoing work seeks to improve the efficiency to approach the doppler cooling limit. A more scalable approach to ion-photon interfaces based on a surface electrode ion trap is being developed with the goal of demonstrating coherent light-matter interactions in the framework of CQED.

 
fibertrap

Hybrid ion trap systems

Scalable QC with ion traps will require interfacing with system components traditionally realized in the bulk, such as light delivery and detection. We have realized a surface-electrode Point Paul trap integrated with a single-mode optical fiber and demonstrated measurement of the fiber mode by the ion. Concurrently we developed precise control techniques for varying the ion height and laterial position in a surface-electrode trap. Further work aims to realize a microfabricated version of the point Paul trap. Ongoing work is also investigating the feasibility of integrating microfabricated, transparent linear ion traps with semiconductor photon detectors.

 
microtrap

Microfabricated ion traps

Surface-electrode ion traps provide one promising system for realizing large-scale quantum computing. However, a significant problem facing ion traps is the "anomalous heating" which grows rapidly with decreasing trap size, due to sensitivity to surface charges. We have demonstrated orders of magnitude reductions in anomalous heating by operating the traps at cryogenic temperatures, and performed a two-ion quantum logic gate in such a system. Current work focuses on characterizing the sensitivity of such traps to laser-induced static surface charges and exploring the effects of various trap electrode materials and processing techniques on trap performance.

 
polar molecules

Polar molecules

Cold, trapped polar molecular ions provide energy scales spanning the RF, microwave, and optical frequencies. The rich, narrow spectra potentially allow the molecules to be coupled simultaneously to both electrical and optical cavities, providing a means to efficiently convert between circuit and cavity QED quantum states. We are constructing an experiment to trap and cool polar molecular ions, using surface-electrode superconducting traps to couple ions to a microwave stripline resonator. This will allow the microwave transitions of the molecules to be explored, and eventually coupled to a high-Q resonator.

 
theory

Theory

Quantum systems with finite coherence times can be used to perform arbitrarily long and difficult quantum computations if the decoherence rate is less than some constant threshold. Understanding the extent to which the accuracy threshold can be increased under physically realistic assumptions is one of the great open problems in the theory of quantum computation. We are interested in (1) the influence of geometry on the accuracy threshold and (2) the behavior of the accuracy threshold for engineered systems, where constant and linear factors matter.