Configuration interaction calculations of the controlled phase gate in double quantum dot qubits

We consider qubit coupling resulting from the capacitive coupling between two double quantum dot (DQD) single-triplet qubits. Calculations of the coupling when the two DQDs are detuned symmetrically or asymmetrically are performed using a full configuration interaction (CI). The full CI reveals behavior that is not observed by more commonly used approximations such as Heitler London or Hund Mulliken, particularly related to the operation of both DQDs in the (0,2) charge sector. We find that there are multiple points in detuning-space where a two-qubit entangling gate can be realized, and that trade-offs between coupling magnitude and sensitivity to fluctuations in detuning make a case for operating the gate in the (0,2) regime not commonly considered.Comment: 4 pages, 5 figure

The Effect of On-Line Videos on Learner Outcomes in a Mechanics of Materials Course

The Mechanics of Materials course is one of the core engineering courses included in the curriculum of mechanical, civil, mining, petroleum, marine, aeronautical, and several other engineering disciplines. As a core course, the Mechanics of Materials course typically has large enrollment. Initiatives aimed at improving the effectiveness of the engineering core courses can have a major impact on engineering education by virtue of the large number of students affected. Computers afford opportunities for creative instructional activities that are not possible in the traditional lecture-and-textbook class format. The study described in this paper examines the effectiveness of asynchronous online video that has been used in various ways in a Mechanics of Materials course over the past four years. The content delivered via the Internet included concept videos, problem-solving videos, and videos of demonstrations and laboratory activities. In this study, four differing approaches to present the Mechanics of Materials course to approximately 1000 students in 17 course sections over a four-year period were compared. The first approach involved traditional, face-to-face lectures. The second approach completely replaced the face-to-face lectures with videos recorded by the instructor outside of the classroom, but covering the same topics as the classroom lectures, and then posted to a class web site. The instructor was available in his office during class time to answer questions. The third approach combined face-to-face lectures with videos. The fourth approach was an inverted format where students watched videos at home and worked on homework during class. Using common final exam scores as a quantitative measure of effectiveness, results showed that overall student performance was maintained as class sizes and instructor workloads increased. Additionally, there was some indication that the inverted approach was better suited for higher-ability students

Empirical entropic contributions in computational docking: Evaluation in APS reductase complexes

The results from reiterated docking experiments may be used to evaluate an empirical vibrational entropy of binding in ligand–protein complexes. We have tested several methods for evaluating the vibrational contribution to binding of 22 nucleotide analogues to the enzyme APS reductase. These include two cluster size methods that measure the probability of finding a particular conformation, a method that estimates the extent of the local energetic well by looking at the scatter of conformations within clustered results, and an RMSD-based method that uses the overall scatter and clustering of all conformations. We have also directly characterized the local energy landscape by randomly sampling around docked conformations. The simple cluster size method shows the best performance, improving the identification of correct conformations in multiple docking experiments. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60220/1/20936_ftp.pd

Coherent Electron Transport by Adiabatic Passage in an Imperfect Donor Chain

Coherent Tunneling Adiabatic Passage (CTAP) has been proposed as a long-range physical qubit transport mechanism in solid-state quantum computing architectures. Although the mechanism can be implemented in either a chain of quantum dots or donors, a 1D chain of donors in Si is of particular interest due to the natural confining potential of donors that can in principle help reduce the gate densities in solid-state quantum computing architectures. Using detailed atomistic modeling, we investigate CTAP in a more realistic triple donor system in the presence of inevitable fabrication imperfections. In particular, we investigate how an adiabatic pathway for CTAP is affected by donor misplacements, and propose schemes to correct for such errors. We also investigate the sensitivity of the adiabatic path to gate voltage fluctuations. The tight-binding based atomistic treatment of straggle used here may benefit understanding of other donor nanostructures, such as donor-based charge and spin qubits. Finally, we derive an effective 3 × 3 model of CTAP that accurately resembles the voltage tuned lowest energy states of the multi-million atom tight-binding simulations, and provides a translation between intensive atomistic Hamiltonians and simplified effective Hamiltonians while retaining the relevant atomic-scale information. This method can help characterize multi-donor experimental structures quickly and accurately even in the presence of imperfections, overcoming some of the numeric intractabilities of finding optimal eigenstates for non-ideal donor placements