Transformed Dissipation in Superconducting Quantum Circuits

Superconducting quantum circuits must be designed carefully to avoid dissipation from coupling to external control circuitry. Here we introduce the concept of current transformation to quantify coupling to the environment. We test this theory with an experimentally-determined impedance transformation of $\sim 10^5$ and find quantitative agreement better than a factor of 2 between this transformation and the reduced lifetime of a phase qubit coupled to a tunable transformer. Higher-order corrections from quantum fluctuations are also calculated with this theory, but found not to limit the qubit lifetime. We also illustrate how this simple connection between current and impedance transformation can be used to rule out dissipation sources in experimental qubit systems.Comment: 4 pages, 4 figure

The Special Needs of Women on College Campuses

The authors embarked on a journey to understand the special needs of women college students. They discovered two major themes that were explored in greater depth in an attempt to explain why these themes were more specific to college women than other populations. Although these needs may be extrapolated to other populations of college students they were of particular concern to the female college student population. The authors began by selecting a non-scientific restricted pool of female college students than spanned first-year, second-year and junior or third-year students. This student sample was interviewed to discover their concerns or perceptions about violence and sexual discrimination against women on college campuses. The interview questions and responses were abbreviated and included, followed by a discussion of each theme. The interview subjects stated that violence was not a major concern however; they did offer suggestions to improve safety. This led the authors to conclude that although they did not explicitly state violence as a concern it remains an implicit concern. The second theme explored was discrimination based on gender. The interviewed sample had a varied response to having been the victim of gender discrimination. Of greater concern was the perception of what constituted gender harassment, what procedures and processes were in place and available to respond to these occurrences and how to report an incident

State tomography of capacitively shunted phase qubits with high fidelity

We introduce a new design concept for superconducting quantum bits (qubits) in which we explicitly separate the capacitive element from the Josephson tunnel junction for improved qubit performance. The number of two-level systems (TLS) that couple to the qubit is thereby reduced by an order of magnitude and the measurement fidelity improves to 90%. This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single shot measurements.Comment: submitted to PR

Reducing Courts’ Failure-to-Appear Rate by Written Reminders

This article examines the effectiveness of using different kinds of written reminders to reduce misdemeanor defendants’ failure- to-appear (FTA) rates. A subset of defendants was surveyed after their scheduled court date to assess their perceptions of procedural justice and trust and confidence in the courts. Reminders reduced FTA overall, and more substantive reminders (e.g., with information on the negative consequences of FTA) were more effective than a simple reminder. FTA varied depending on several offense and offender characteristics, such as geographic location (urban vs. rural), type of offense, and number of offenses. The reminders were somewhat more effective for Whites and Hispanics than for Blacks. Defendants with higher institutional confidence and those who felt they had been treated more fairly by the criminal justice system were more likely to appear, though the effectiveness of the reminder was greatest among misdemeanants with low levels of trust in the courts. The implications for public policy and pretrial services are discussed

Improving the Coherence Time of Superconducting Coplanar Resonators

The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify surface two-level states (TLS) as an important decay mechanism. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments.Comment: 3 pages, 4 figures for the main paper; total 5 pages, 6 figures including supplementary material. Submitted to Applied Physics Letter

Reduced phase error through optimized control of a superconducting qubit

Minimizing phase and other errors in experimental quantum gates allows higher fidelity quantum processing. To quantify and correct for phase errors in particular, we have developed a new experimental metrology --- amplified phase error (APE) pulses --- that amplifies and helps identify phase errors in general multi-level qubit architectures. In order to correct for both phase and amplitude errors specific to virtual transitions and leakage outside of the qubit manifold, we implement "half derivative" an experimental simplification of derivative reduction by adiabatic gate (DRAG) control theory. The phase errors are lowered by about a factor of five using this method to $\sim 1.6^{\circ}$ per gate, and can be tuned to zero. Leakage outside the qubit manifold, to the qubit $|2\rangle$ state, is also reduced to $\sim 10^{-4}$ for $20\%$ faster gates.Comment: 4 pages, 4 figures with 2 page supplementa

Generation of Three-Qubit Entangled States using Superconducting Phase Qubits

Entanglement is one of the key resources required for quantum computation, so experimentally creating and measuring entangled states is of crucial importance in the various physical implementations of a quantum computer. In superconducting qubits, two-qubit entangled states have been demonstrated and used to show violations of Bell's Inequality and to implement simple quantum algorithms. Unlike the two-qubit case, however, where all maximally-entangled two-qubit states are equivalent up to local changes of basis, three qubits can be entangled in two fundamentally different ways, typified by the states $|\mathrm{GHZ}> = (|000> + |111>)/\sqrt{2}$ and $|\mathrm{W}> = (|001> + |010> + |100>)/\sqrt{3}$. Here we demonstrate the operation of three coupled superconducting phase qubits and use them to create and measure $|\mathrm{GHZ}>$ and $|\mathrm{W}>$ states. The states are fully characterized using quantum state tomography and are shown to satisfy entanglement witnesses, confirming that they are indeed examples of three-qubit entanglement and are not separable into mixtures of two-qubit entanglement.Comment: 9 pages, 5 figures. Version 2: added supplementary information and fixed image distortion in Figure 2