Event Details

Quantum noise limited amplifier and non-reciprocal device using Josephson junctions based on van der Waals materials by Dr. Mandar M. Deshmukh (Faculty Member - Tata Institute, Mumbai, India)

2D materials offer the ability to combine contrasting functionalities, and this provides an opportunity to make unique devices. I will talk about two recent examples of experiments from our lab. One uses a proximitized and tunable Josephson junction to create a parametric amplifier, and the other uses a high Tc superconductor to realize a Josephson diode.

The core of quantum information processing involves preparing, manipulating, and efficiently detecting quantum states. In cQED architecture, probing quantum systems in a single-photon regime is challenging as the output signals that carry information about the quantum state of these systems are very feeble. Hence, amplification with the least added noise is crucial before signal processing at room temperature. The Josephson parametric amplifiers (JPA) are the routinely used devices for low-noise amplification of quantum signals, which improves the signal-to-noise ratio significantly. The existing JPAs use Al-AlOx-Al tunnel junctions where magnetic flux is the control knob for biasing the devices. Our recent work demonstrates the implementation of a gate tunable JPA using a graphene Josephson junction (gr-JJ), where we change the device bias using electrostatic gating [1]. Electrostatic control is advantageous over magnetic flux control in cQED devices as it uses a very localized electric field which causes less interference.

Symmetry plays a critical role in determining various properties of a material. Breaking of time-reversal and inversion symmetry in some superconducting systems leads to a non-reciprocal device - the Josephson diode. We demonstrate a Josephson diode working up to 77 K using an artificial Josephson junction (AJJ) of twisted layers of Bi₂Sr₂CaCu₂O_8+δ. The non-reciprocal response manifests as an asymmetry in the magnitude of switching currents and their distributions independent of the twist angle. The asymmetry is tunable with a small magnetic field applied perpendicular to the junction. We report a record asymmetry of 60 % at 20 K. Our results provide a path toward realizing superconducting quantum circuits at liquid nitrogen temperature [2] by engineering the current phase relationship.

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Fig 1, Schematic showing the experimental implementation of a Duffing oscillator. We make a CPW of MoRe, where the central line is terminated to the ground plane through a lumped element parallel LC resonator. We have two parallel plate MoRe–Al2O3–Al capacitors in series. We fabricate a MoRe–graphene–MoRe JJ on an hBN–gr–hBN stack and patch the JJ to the capacitor leads, which results in an LC resonator.