On Measuring Condensate Fraction in Superconductors

An analysis of off-diagonal long-range order in superconductors shows that the spin-spin correlation function is significantly influenced by the order if the order parameter is anisotropic on a microscopic scale. Thus, magnetic neutron scattering can provide a direct measurement of the condensate fraction of a superconductor. It is also argued that recent measurements in high temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped regime is added. Other corrections are mino

Randomized Benchmarking as Convolution: Fourier Analysis of Gate Dependent Errors

We provide an alternative proof of Wallman's [Quantum 2, 47 (2018)] and Proctor's [Phys. Rev. Lett. 119, 130502 (2017)] bounds on the effect of gate-dependent noise on randomized benchmarking (RB). Our primary insight is that a RB sequence is a convolution amenable to Fourier space analysis, and we adopt the mathematical framework of Fourier transforms of matrix-valued functions on groups established in recent work from Gowers and Hatami [Sbornik: Mathematics 208, 1784 (2017)]. We show explicitly that as long as our faulty gate-set is close to some representation of the Clifford group, an RB sequence is described by the exponential decay of a process that has exactly two eigenvalues close to one and the rest close to zero. This framework also allows us to construct a gauge in which the average gate-set error is a depolarizing channel parameterized by the RB decay rates, as well as a gauge which maximizes the fidelity with respect to the ideal gate-set

Unpacking the 'Singapore New Wave'

As the cinema of a small nation, Singapore cinema punches above its weight. The series of international film festival awards won by Singaporean filmmakers alongside the multiple books published on Singapore cinema since the 2010s seem to signal a revival of the industry. This editorial introduction unpacks the term ‘Singapore New Wave’ as a starting point for this special issue to raise questions about the changes that appear to be happening in Singapore’s film industry. By situating the ‘Singapore New Wave’ within global cinema, this essay argues for the importance of considering the issue of survival in the cinema of a small nation, and for an expansion of ways in which film scholars can gain the critical insights traditionally obtained from conventional new wave films. More positively, this more expansive working definition adds to broader new wave literature by exploring unconventional ways in which films can constitute or contribute to a new wave beyond traditional genres, auteurs, styles or themes associated with new wave cinema

Quantum Impurities and the Neutron Resonance Peak in YBa2Cu3O7{\bf YBa_2 Cu_3 O_7}: Ni versus Zn

The influence of magnetic (S=1) and nonmagnetic (S=0) impurities on the spin dynamics of an optimally doped high temperature superconductor is compared in two samples with almost identical superconducting transition temperatures: YBa$_2$(Cu$_{0.97}$Ni$_{0.03}$)$_3$O$_7$ (T$_c$=80 K) and YBa$_2$(Cu$_{0.99}$Zn$_{0.01}$)$_3$O$_7$ (T$_c$=78 K). In the Ni-substituted system, the magnetic resonance peak (which is observed at E$_r \simeq$40 meV in the pure system) shifts to lower energy with a preserved E$_r$/T$_c$ ratio while the shift is much smaller upon Zn substitution. By contrast Zn, but not Ni, restores significant spin fluctuations around 40 meV in the normal state. These observations are discussed in the light of models proposed for the magnetic resonance peak.Comment: 3 figures, submitted to PR

ENHANCING DYNAMICS COURSES WITH MODEL ELICITING ACTIVITIES

Model eliciting activities are assignments which require students to develop models to describe realistic situations. Every MEA follows six principles: model-construction, reality, self-assessment, model documentation, generalizability, and effective prototype. The six principles provide a solid guideline in which instructors can develop more MEAs, which can then be shared and used among several participating universities. Under NSF CCLI Grant #0717595, Cal Poly is currently developing Model Eliciting Activities for the subject of Mechanical Engineering. This report documents the undertakings to implement and enhance two Model Eliciting Activities (MEAs) into the Cal Poly curriculum. Specifically, the development of the Vehicle Accident Reconstruction (VAR) MEA and the Catapult MEA will be covered in detail. The VAR MEA was a project assigned in ME212 “Engineering Dynamics,” which required students to apply momentum principles to a two-vehicle collision. Because of the heavy development time experienced by the MEA research team, a MatLab program which accepted user inputs via a graphical user interface (GUI) was developed. This GUI solved for initial velocities during two-vehicle collisions by applying appropriate momentum and work-energy principles. With this program, instructors can more easily develop crash scenarios, as well as check student work. The Catapult MEA was also a project assigned to ME212 students. It required them to analyze the launch trajectory of an actual scaled catapult using angular motion and work-energy principles. This scaled-catapult was instrumented with one ADXL278 dual-axis accelerometer and four CEA-06-240UZ-120 strain gages. This instrumentation allowed for the experimental data acquisition of the catapult angular velocity, acceleration, and strains. By postprocessing this experimental data using a MatLab program, the experimental results can then be compared to theoretical results. The overall goal for the VAR MEA GUI programming was to reduce instructor workload in order to promote usage the MEA through a broader range of universities. The goal of the Catapult instrumentation was to provide students with actual experimental data, which could then be used to confirm their theoretical model. The system was set up so that they could easily record their own experimental data for each catapult launch

Exchange-Only Dynamical Decoupling in the 3-Qubit Decoherence Free Subsystem

The Uhrig dynamical decoupling sequence achieves high-order decoupling of a single system qubit from its dephasing bath through the use of bang-bang Pauli pulses at appropriately timed intervals. High-order decoupling of single and multiple qubit systems from baths causing both dephasing and relaxation can also be achieved through the nested application of Uhrig sequences, again using single-qubit Pauli pulses. For the 3-qubit decoherence free subsystem (DFS) and related subsystem encodings, Pauli pulses are not naturally available operations; instead, exchange interactions provide all required encoded operations. Here we demonstrate that exchange interactions alone can achieve high-order decoupling against general noise in the 3-qubit DFS. We present decoupling sequences for a 3-qubit DFS coupled to classical and quantum baths and evaluate the performance of the sequences through numerical simulations