Active protection of a superconducting qubit with an interferometric Josephson isolator

Abstract

Nonreciprocal microwave devices play critical roles in high-fidelity, quantum-nondemolition (QND) measurement schemes. They impose unidirectional routing of readout signals and protect the quantum systems from unwanted noise originated by the output chain. However, cryogenic circulators and isolators are disadvantageous in scalable superconducting architectures because they use magnetic materials and strong magnetic fields. Here, we realize an active isolator formed by coupling two nondegenerate Josephson mixers in an interferometric scheme and driving them with phase-shifted, same-frequency pumps. By incorporating our Josephson-based isolator into a superconducting qubit setup, we demonstrate fast, high-fidelity, QND measurements of the qubit while providing 20 dB of protection within a bandwidth of 10 MHz against amplified noise reflected off the Josephson amplifier in the output chain. A moderate reduction of 35% is observed in T 2E when the Josephson-based isolator is turned on. Such a moderate degradation can be mitigated by minimizing heat dissipation in the pump lines.

Charge-Noise Insensitive Chiral Photonic Interface for Waveguide Circuit QED

“…The lateral dimension of the entire circulator can be a few millimeters [39]. These properties make our chiral interface highly attractive for, e.g., on-chip routing of microwave signals [10,[14][15][16][17][18][19][20][21][22][23]36,37] as well as fundamental studies of chiral waveguide QED [3,4,7,46].…”

“…However, such components are off-chip, requiring additional space inside the experimental apparatus. Most of the existing proposals for on-chip circulators break TRS by tailored active control [10,[14][15][16][17][18][19][20][21][22][23], e.g., via a synthetic magnetic field [22], or by dynamically modulating switches and delays [23]. On-chip circulators that can be operated in a passive form, thereby simplifying its experimental implementations, however remain elusive.…”

Multiparametric amplification and qubit measurement with a Kerr-free Josephson ring modulator

“…limit the saturation power of the device [14][15][16][17], while the lack of directionality and fixed gain-bandwidth product are inherent to the choice of parametric coupling used in the amplifier. However, there are numerous theoretical [18][19][20] and experimental works [21][22][23][24][25] showing that applying multiple, simultaneous couplings in an amplifier containing two or more modes/ports can result in devices which potentially circumvent some or all of these limitations.…”

Synthesis of parametrically-coupled networks

“…The success of Josephson parametric amplifiers in enabling high-fidelity readout of superconducting qubits has led to a flurry of research into parametrically-coupled networks, including amplifiers, frequency converters, and parametric non-reciprocal networks [1][2][3]. While much of the recent parametric amplifier activity is aimed at increasing amplifier saturation power and bandwidth [4][5][6][7][8], a parallel research path has focused on generating nonreciprocal frequency conversion and amplification-an effort motivated by the need to improve qubit isolation from noise in the measurement chain, with the ultimate goal of minimizing the reliance on bulky ferrite circulators [9][10][11][12][13]. Recent work on parametric conversion has additionally expanded into electro-optomechanical systems [14][15][16], specifically facilitating the use of mechanical modes to mediate electrical to optical transduction.…”