Measurements of trapped-ion heating rates with exchangeable surfaces in close proximity
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Measurements of trapped-ion heating rates with exchangeable surfaces in close proximity D. A. Hite, K. S. McKay, S. Kotler, D. Leibfried, D. J. Wineland, and D. P. Pappas National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 U.S.A ABSTRACT Electric-field noise from the surfaces of ion-trap electrodes couples to the ion’s charge causing heating of the ion’s motional modes. This heating limits the fidelity of quantum gates implemented in quantum information processing experiments. The exact mechanism that gives rise to electric-field noise from surfaces is not well-understood and remains an active area of research. In this work, we detail experiments intended to measure ion motional heating rates with exchangeable surfaces positioned in close proximity to the ion, as a sensor to electric-field noise. We have prepared samples with various surface conditions, characterized in situ with scanned probe microscopy and electron spectroscopy, ranging in degrees of cleanliness and structural order. The heating-rate data, however, show no significant differences between the disparate surfaces that were probed. These results suggest that the driving mechanism for electric-field noise from surfaces is due to more than just thermal excitations alone. INTRODUCTION Trapped ions are used to study intriguing physics of quantum mechanics, which has led to useful applications, such as precision spectroscopy [1], ultra-low force sensing [2], highprecision atomic clocks [3, 4], and quantum-logic gate operations for quantum information processing (QIP) [5, 6]. A key aspect of these experiments is the use of the internal states of the ions as quantum bits, coupled to the motional modes of the ions confined in the trap, which are often laser cooled to near the ground state of motion [7]. The internal state lifetimes are long and can be well-protected from outside influences. However, the motional states are readily perturbed by environmental forces, e.g., from electric-field noise at the location and motionalmode frequency of the ions, typically 1 – 10 MHz. This noise couples to the charge of the ions causing motional heating, where the ions uncontrollably acquire additional quanta, or phonons of motion. Since the internal states and the motional states are coupled together to perform quantum logic gate operations, the rate at which the ions heat up can limit the fidelity of the operations. Therefore, motional heating rates have become an important metric in the performance of ion traps used in QIP. Various sources of noise can cause motional heating, however, one source is intrinsic to the trap electrodes themselves. In fact, electric-field noise from the surfaces of the trap electrodes has proven to be a difficult problem to mitigate. For decades, experimental evidence, based on the scaling of the heating rates with ion-electrode distance [8-10], electrode temperature [10-13], and motional-mode frequency [ 8-11, 13-16] has pointed to the surface of the electrodes as the source of the noise [17]. Moreover, th
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