Athreya Shankar

Impedance-Engineered Josephson Parametric Amplifier with Single-Step Lithography

  1. Lipi Patel,
  2. Samarth Hawaldar,
  3. Aditya Panikkar,
  4. Athreya Shankar,
  5. and Baladitya Suri
We present the experimental demonstration of an impedance-engineered Josephson parametric amplifier (IEJPA) fabricated in a single-step lithography process. Impedance engineering is
implemented using a lumped-element series LC circuit. We use a simpler lithography process where the entire device — impedance transformer and JPA — are patterned in a single electron beam lithography step, followed by a double-angle Dolan bridge technique for Al-AlOx-Al deposition. We observe nearly quantum-limited amplification with 18 dB gain over a wide 400 MHz bandwidth centered around 5.3 GHz, and a saturation power of -114 dBm. To accurately explain our experimental results, we extend existing theories for impedance-engineered JPAs to incorporate the full sine nonlinearity of both the JPA and the transformer. Our work shows a path to simpler realization of broadband JPAs and provides a theoretical foundation for a novel regime of JPA operation.
arxiv pdf

Characterising Polariton States in Non-Dispersive Regime of Circuit Quantum Electrodynamics

  1. Arvind Mamgain,
  2. Samarth Hawaldar,
  3. Athreya Shankar,
  4. and Baladitya Suri
A superconducting qubit coupled to a read-out resonator is currently the building block of multiple quantum computing as well as quantum optics experiments. A typical qubit-resonator
system is coupled in the dispersive regime, where the detuning between qubit and resonator is much greater than the coupling between them. In this work, we fabricated and measured a superconducting transmon-resonator system in the non-dispersive regime. The dressed states formed by the mixing of the bare qubit and resonator states can be further mixed by applying a drive on the qubit, leading to the formation of polariton states. We report experimental studies of transitions between polariton states at varying driving powers and frequencies and show how the non-dispersive coupling of the higher levels of the qubit-resonator system modifies the polariton eigenstates and the corresponding transition frequencies. We also report close agreement with numerical results obtained from a driven Jaynes-Cummings Model beyond the dispersive regime.
arxiv pdf