Precision measurement and compensation of optical Stark shifts for an ion-trap quantum processor

Using optical Ramsey interferometry, we precisely measure the laser-induced AC-stark shift on the $S_{1/2}$ -- $D_{5/2}$ "quantum bit" transition near 729 nm in a single trapped $^{40}$Ca$^+$ ion. We cancel this shift using an additional laser field. This technique is of particular importance for the implementation of quantum information processing with cold trapped ions. As a simple application we measure the atomic phase evolution during a $n \times 2\pi$ rotation of the quantum bit.Comment: 4 pages, 4 figure

Comparison of diet quality, physical activity and biochemical values of older adults either reporting or not reporting use of lipid-lowering medication

Objectives: The aim of this study was to compare standard lipid profile, reported dietary intake, and physical activity in older adults who reported taking or not taking a lipid-lowering medication, namely statins. Design: Cross-sectional study utilizing baseline data collected from a subsample of a larger randomized clinical trial, The Study of Exercise and Nutrition in Older Rhode Islanders (SENIOR) Project. Participants and Setting: A total of 115 participants, 33 males and 82 females, over the age of 60, community-dwelling, primarily retired, and from East Providence, Rhode Island and surrounding communities in Rhode Island and Massachusetts. Measurements: Height and weight were measured and used to calculate body mass index. Waist circumference was measured. Medical history and medication use surveys were completed. Dietary assessment was done via three 24 hour recalls using NDS-R. The Yale Physical Activity Survey was used to determine energy expenditure during exercise and a physical activity summary score. Fasting blood samples were obtained to determine lipid profile. Results: 37 participants (32.2%) reported taking lipid-lowering medication, statins exclusively, and 78 (67.8%) reported not taking any lipid-lowering medication. Participants who reported taking statins had better lipid profiles than those participants who reported not taking statins but had significantly lower intakes of vitamin B12, vitamin K, calcium, and potassium. There were no differences between groups on reported physical activity. However, the mean intakes for both groups did not meet the Dietary Reference Intakes for multiple nutrients. Conclusion: Older adults need additional education on the importance of lifestyle changes in reducing CHD risk, whether taking lipid-lowering medications or not

Classical communication and non-classical fidelity of quantum teleportation

In quantum teleportation, the role of entanglement has been much discussed. It is known that entanglement is necessary for achieving non-classical teleportation fidelity. Here we focus on the amount of classical communication that is necessary to obtain non-classical fidelity in teleportation. We quantify the amount of classical communication that is sufficient for achieving non-classical fidelity for two independent 1-bit and single 2-bits noisy classical channels. It is shown that on average 0.208 bits of classical communication is sufficient to get non-classical fidelity. We also find the necessary amount of classical communication in case of isotropic transformation. Finally we study how the amount of sufficient classical communication increases with weakening of entanglement used in the teleportation process.Comment: Accepted in Quantum Info. Proces

Feedback-Optimized Operations with Linear Ion Crystals

We report on transport operations with linear crystals of 40Ca+ ions by applying complex electric time-dependent potentials. For their control we use the information obtained from the ions' fluorescence. We demonstrate that by means of this feedback technique, we can transport a predefined number of ions and also split and unify ion crystals. The feedback control allows for a robust scheme, compensating for experimental errors as it does not rely on a precisely known electrical modeling of the electric potentials in the ion trap beforehand. Our method allows us to generate a self-learning voltage ramp for the required process. With an experimental demonstration of a transport with more than 99.8 % success probability, this technique may facilitate the operation of a future ion based quantum processor

High-fidelity state detection and tomography of a single ion Zeeman qubit

We demonstrate high-fidelity Zeeman qubit state detection in a single trapped 88 Sr+ ion. Qubit readout is performed by shelving one of the qubit states to a metastable level using a narrow linewidth diode laser at 674 nm followed by state-selective fluorescence detection. The average fidelity reached for the readout of the qubit state is 0.9989(1). We then measure the fidelity of state tomography, averaged over all possible single-qubit states, which is 0.9979(2). We also fully characterize the detection process using quantum process tomography. This readout fidelity is compatible with recent estimates of the detection error-threshold required for fault-tolerant computation, whereas high-fidelity state tomography opens the way for high-precision quantum process tomography

Updating ACSM's Recommendations for Exercise Preparticipation Health Screening

The purpose of the American College of Sports Medicine's (ACSM) exercise preparticipation health screening process is to identify individuals who may be at elevated risk for exercise-related sudden cardiac death and/or acute myocardial infarction. Recent studies have suggested that using the current ACSM exercise preparticipation health screening guidelines can result in excessive physician referrals, possibly creating a barrier to exercise participation. In addition, there is considerable evidence that exercise is safe for most people and has many associated health and fitness benefits; exercise-related cardiovascular events are often preceded by warning signs/symptoms; and the cardiovascular risks associated with exercise lessen as individuals become more physically active/fit. Consequently, a scientific roundtable was convened by the ACSM in June 2014 to evaluate the current exercise preparticipation health screening recommendations. The roundtable proposed a new evidence-informed model for exercise preparticipation health screening on the basis of three factors: 1) the individual's current level of physical activity, 2) presence of signs or symptoms and/or known cardiovascular, metabolic, or renal disease, and 3) desired exercise intensity, as these variables have been identified as risk modulators of exercise-related cardiovascular events. Identifying cardiovascular disease risk factors remains an important objective of overall disease prevention and management, but risk factor profiling is no longer included in the exercise preparticipation health screening process. The new ACSM exercise preparticipation health screening recommendations reduce possible unnecessary barriers to adopting and maintaining a regular exercise program, a lifestyle of habitual physical activity, or both, and thereby emphasize the important public health message that regular physical activity is important for all individuals

Coherence of qubits based on single Ca+^+ ions

Two-level ionic systems, where quantum information is encoded in long lived states (qubits), are discussed extensively for quantum information processing. We present a collection of measurements which characterize the stability of a qubit based on the $S_{1/2}$--$D_{5/2}$ transition of single $^{40}$Ca$^+$ ions in a linear Paul trap. We find coherence times of $\simeq$1 ms, discuss the main technical limitations and outline possible improvements.Comment: Proceedings of "Trapped charged particles and fundamental interactions" submitted to Journal of Physics B (IoP

Robust entanglement

It is common belief among physicists that entangled states of quantum systems loose their coherence rather quickly. The reason is that any interaction with the environment which distinguishes between the entangled sub-systems collapses the quantum state. Here we investigate entangled states of two trapped Ca$^+$ ions and observe robust entanglement lasting for more than 20 seconds