PHYS838C Seminar: Ray Mencia, UMD & Calvin He, UMD

Title: Ultrahigh-impedance Josephson circuits for quantum computing, simulations, and metrology

Abstract: Chains of Josephson junctions have probably the largest kinetic per-unit-length inductance, which can exceed the geometric one by about 10^4, primarily limited by quantum phase-slip fluctuations. However, the total inductance is also limited by the stray capacitance, which grows linearly with the chain length. This stray capacitance is unnecessarily large in most circuits because of the high dielectric constant of silicon or sapphire substrates. By releasing Josephson chains off the substrate, we can combine the maximal per-unit-length inductance with the minimal stray capacitance, thereby obtaining the highest impedance electromagnetic structures available today. As a first demonstration, we created a superconducting quasicharge qubit (blochnium), a dual of transmon, made of a weak junction shunted by such a large inductance (hyperinductance) that its impedance reaches over 30 × RQ (200 kOhms). In the second demonstration, we fabricated suspended "telegraph" transmission lines, composed of 5,000+ junctions, whose wave impedance exceeds 5 × RQ (32.5 kOhm). These lines are a unique resource in exploring DC current metrology via Bloch oscillations, as well as in analog quantum simulations of many strongly-correlated 1D systems.

Title:  Relativistic Thomson Scattering as a Potential Intensity Gauge for Petawatt Class Lasers

Abstract:  

As new high peak-power pulsed lasers systems are being built around the world, where the most powerful lasers reach above 1 petawatt (PW), new opportunities to explore physics arise along with challenges to measure the intense beams.  The technology to measure the pulsed beam, however, rely on indirect methods that may not accurately represent the full powered beam at the focus.  In this talk, we explore the possibility of a method to directly characterize the laser’s peak intensity at the focus, name by measuring radiation from electrons scattered at the laser focus, also known as Relativistic Thomson Scattering (RTS).  We present a proof-of-principal study where the onset wavelength of the Doppler-shifted second harmonic of RTS provides a means to estimate intensities between 1018 W/cm2 and 1019 W/cm2.  We also comment on measurements of the angular distribution of RTS and its potential as a laser intensity gauge.