11/10/2023
By Chung Kow

The Kennedy College of Sciences, Department of Physics and Applied Physics, invites you to attend a doctoral dissertation defense by Chung Shong Kow on “Josephson Junction-based Metamaterial for Broadband Amplification.”

Candidate Name: Chung Shong Kow
Degree: Doctoral
Defense Date: Monday, Nov. 20, 2023
Defense Time: 4 – 5 p.m. EDT
Location: Olney 204

Committee:

  • Committee Chair/Advisor: Archana Kamal, Associate Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Viktor Podolskiy, Professor, Assistant Chair, Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Jayant Kumar, Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell

Abstract:
Josephson Traveling Wave Parametric Amplifiers (JTWPAs) are promising platforms for realizing broadband quantum-limited amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching of the signal, idler and pump waves are satisfied – this is rendered particularly challenging in the presence of nonlinear effects, such as self- and cross-phase modulations originating from the Kerr effect, which scale with the intensity of propagating signals. In this thesis, we present a simple JTWPA design based on ‘left-handed’ nonlinear Josephson metamaterial, which realizes autonomous phase matching without the need for any complicated circuit or dispersion engineering. The operation of a left-handed Josephson Transmission Line (JTL) as a broadband amplifier is rooted in the compensation of linear dispersion-induced phase mismatch between signal (idler) and pump waves with nonlinearity-induced phase mismatch; notably, this effect is native to left-handed lines due to opposing directions of phase and group velocities. The resultant efficiency of four-wave mixing process can implement gains in excess of 20 dB over few GHz bandwidths with much shorter lines than required in a right-handed JTWPA. The native phase matching also leads to a considerably simplified design over phase-engineered right-handed JTWPA, and alleviates limitations such as loss of pump tunability and large fabrication footprint. Furthermore, left-handed JTLs effectively double the engineering landscape for Kerr-based JTWPAs, introducing new operational regimes such as the ‘reversed dispersion', which can be leveraged in combination with nondegenerate pumping for achieving flat gain profile over a wide frequency range.

We further study the quantum noise properties of JTWPAs, specifically the effect of distributed loss on quadrature squeezing of the output radiation. To this end, we employ the Nyquist model of dissipation that enables an ab-initio microscopic derivation of field equations in the presence of noise. Using these, we study the effect of frequency-dependent loss asymmetries on squeezing and quantify the reduction in gain and squeezing due to third harmonic generation for a right-handed JTWPA. We find significant suppression of third harmonic generation in the left-handed JTWPA and discuss its implications for robustness of gain and broadband squeezing realizable with these designs.