### Abstract

We experimentally study the ghost critical field (GCF), a magnetic field scale for the suppression of superconducting fluctuations, using Hall effect and magnetoresistance measurements on a disordered superconducting thin film near its transition temperature $$T_c$$. We observe an increase in the Hall effect with a maximum in field that tracks the upper critical field below $$T_c$$, vanishes near $$T_c$$, and returns to higher fields above $$T_c$$. Such a maximum has been observed in studies of the Nernst effect and identified as the GCF. Magnetoresistance measurements near Tc indicate quenching of superconducting fluctuations, agree with established theoretical descriptions, and allow us to extract the GCF and other parameters. Above $$T_c$$, the Hall peak field is quantitatively distinct from the GCF, and we contrast this finding with ongoing studies of the Nernst effect and superconducting fluctuations in unconventional and thin-film superconductors.

### Abstract

We present a microfabricated surface-electrode ion trap with a pair of integrated waveguides that generate a standing microwave field resonant with the 171Yb+ hyperfine qubit. The waveguides are engineered to position the wave antinode near the center of the trap, resulting in maximum field amplitude and uniformity along the trap axis. By calibrating the relative amplitudes and phases of the waveguide currents, we can control the polarization of the microwave field to reduce off-resonant coupling to undesired Zeeman sublevels. We demonstrate single-qubit π-rotations as fast as 1 μs with less than 6% variation in Rabi frequency over an 800 μm microwave interaction region. Fully compensating pulse sequences further improve the uniformity of X-gates across this interaction region.

### Abstract

A definition of quantum singularity for the case of static spacetimes has has recently been extended to conformally static spacetimes. Here the theory behind quantum singularities in conformally static spacetimes is reviewed and then applied to a class of spherically symmetric, conformally static spacetimes, including as special cases those studied by Roberts, by Fonarev, and by Husain et al. We use solutions of the generally coupled, massless Klein-Gordon equation as test fields. In this way we find the ranges of metric parameters and coupling coefficients for which classical timelike singularities in these spacetimes are healed quantum mechanically.

### Abstract

We present a simple cryostat purpose built for use with surface-electrode ion traps, designed around an affordable, large cooling power commercial pulse tube refrigerator. A modular vacuum enclosure with a single vacuum space facilitates interior access and enables rapid turnaround and flexibility for future modifications. Long rectangular windows provide nearly 360 degrees of optical access in the plane of the ion trap, while a circular bottom window near the trap enables NA 0.4 light collection without the need for in-vacuum optics. We evaluate the system's mechanical and thermal characteristics and we quantify ion trapping performance by trapping 40Ca+, finding small stray electric fields, long ion lifetimes, and low ion heating rates.

### Abstract

We report the design, fabrication and characterization of a microfabricated surface-electrode ion trap that supports controlled transport through the two-dimensional intersection of linear trapping zones arranged in a 90° cross. The trap is fabricated with very large scalable integration techniques which are compatible with scaling to a large quantum information processor. The shape of the radio-frequency electrodes is optimized with a genetic algorithm to reduce axial pseudopotential barriers and minimize ion heating during transport. Seventy-eight independent dc control electrodes enable fine control of the trapping potentials. We demonstrate reliable ion transport between junction legs and determine the rate of ion loss due to transport. Doppler-cooled ions survive more than $$10^5$$ round-trip transits between junction legs without loss and more than 65 consecutive round trips without laser cooling.

### Abstract

When matter falls past the horizon of a large black hole, the expectation from string theory is that the configuration thermalizes and the information in the probe is rather quickly scrambled away. The traditional view of a classical unique spacetime near a black hole horizon conflicts with this picture. The question then arises as to what spacetime does the probe actually see as it crosses a horizon, and how does the background geometry imprint its signature onto the thermal properties of the probe. In this work, we explore these questions through an extensive series of numerical simulations of D0 branes. We determine that the D0 branes quickly settle into an incompressible symmetric state—thermalized within a few oscillations through a process driven entirely by internal nonlinear dynamics. Surprisingly, thermal background fluctuations play no role in this mechanism. Signatures of the background fields in this thermal state arise either through fluxes, i.e. black hole hair; or if the probe expands to the size of the horizon—which we see evidence of. We determine simple scaling relations for the D0 branes’ equilibrium size, time to thermalize, lifetime, and temperature in terms of their number, initial energy, and the background fields. Our results are consistent with the conjecture that black holes are the fastest scramblers as seen by matrix theory.

### Abstract

We have studied the Hall effect in superconducting tantalum nitride films. We find a large contribution to the Hall conductivity near the superconducting transition, which we can track to temperatures well above $$T_c$$ and magnetic fields well above the upper critical field, $$\mathrm{H}_{c2}(0)$$. This contribution arises from Aslamazov-Larkin superconducting fluctuations, and we find quantitative agreement between our data and recent theoretical analysis based on time dependent Ginzburg-Landau theory.

#### From the Cover…

.. epigraph:: “Townsend is the best book I know for advanced undergraduate quantum mechanics. It is clear, contemporary, and compact. My students used it as a wonderful springboard to graduate school.” -- Ralph D. Amado, University of Pennsylvania .. epigraph:: “With this second edition, Townsend has succeeded in making a clear and pedagogical textbook on undergraduate quantum mechanics even better.” -- Charles Gale, McGill University

# Recent Publications

Student authorFaculty author

51. Nicholas P. Breznay and Aharon Kapitulnik Observation of the ghost critical field for superconducting fluctuations in a disordered TaN thin film Physical Review B 88 (2013) 223. Yang Bai, Hsin-Chia Cheng, Jason Gallicchio, and Jiayin Gu A toolkit of the stop search via the chargino decay Journal of High Energy Physics 2013 (2013) . C. M. Shappert, J. T. Merrill, K. R. Brown, J. M. Amini, C. Volin, Charlie Doret, H. Hayden, C. -S. Pai, K. R. Brown, and A. W. Harter Spatially uniform single-qubit gate operations with near-field microwaves and composite pulse compensation New Journal of Physics 15 (2013) 083503. Thomas McCaffree Helliwell and D. A. Konkowski Quantum singularities in spherically symmetric, conformally static spacetimes Physical Review D 87 (2013) 104041. G. Vittorini, K. Wright, K. R. Brown, A. W. Harter, and Charlie Doret Modular cryostat for ion trapping with surface-electrode ion traps Review of Scientific Instruments 84 (2013) 043112. Jason Gallicchio and Matthew D Schwartz Quark and gluon jet substructure Journal of High Energy Physics 2013 (2013) . K. Wright, J. M. Amini, D. L. Faircloth, C. Volin, Charlie Doret, H. Hayden, C. -S. Pai, D. W. Landgren, D. Denison, T. Killian, R. E. Slusher, and A. W. Harter Reliable transport through a microfabricated X-junction surface-electrode ion trap New Journal of Physics 15 (2013) 033004. Paul L. Riggins and Vatche Sahakian Black hole thermalization, D0 brane dynamics, and emergent spacetime Physical Review D 86 (2012) 046005. Nicholas P. Breznay, Karen Michaeli, Konstantin S Tikhonov, Alexander M Finkel'stein, Mihir Tendulkar, and Aharon Kapitulnik Hall conductivity dominated by fluctuations near the superconducting transition in disordered thin films Physical Review B 86 (2012) 014514. John S. Townsend A Modern Approach to Quantum Mechanics, Second Edition University Science Books, Sausalito, 2012.