Tunable ohmic environment using Josephson junction chains

TL;DR

This paper introduces a tunable, wide-band dissipative environment using Josephson junction chains, enabling in-situ control of effective resistance in the microwave domain for quantum circuit applications.

Contribution

It presents a novel design of a double Josephson junction chain with tunable inductance and damping, functioning as a controllable ohmic resistor over a broad frequency range.

Findings

Achieves a tunable resistance up to ~6.5 kΩ in the microwave domain.

Maintains high quality factors for electromagnetic modes.

Demonstrates feasibility with current Josephson junction technology.

Abstract

We propose a scheme to implement a tunable, wide frequency-band dissipative environment using a double chain of Josephson junctions. The two parallel chains consist of identical SQUIDs, with magnetic-flux tunable inductance, coupled to each other at each node via a capacitance much larger than the junction capacitance. Thanks to this capacitive coupling, the system sustains electromagnetic modes with a wide frequency dispersion. The internal quality factor of the modes is maintained as high as possible, and the damping is introduced by a uniform coupling of the modes to a transmission line, itself connected to an amplification and readout circuit. For sufficiently long chains, containing several thousands of junctions, the resulting admittance is a smooth function versus frequency in the microwave domain, and its effective dissipation can be continuously monitored by recording the emitted radiation in the transmission line. We show that by varying in-situ the SQUIDs' inductance, the double chain can operate as tunable ohmic resistor in a frequency band spanning up to one GHz, with a resistance that can be swept through values comparable to the resistance quantum R_q = (h/4e^2) ~ 6.5 k{\Omega}. We argue that the circuit complexity is within reach using current Josephson junction technology.