arXiv subjects

I. C. Rodrigues

Publications and source records attributed to I. C. Rodrigues.

4 recordsLinked to original sources

arXiv2021

Cooling photon-pressure circuits into the quantum regime

Quantum control of electromagnetic fields was initially established in the optical domain and has been advanced to lower frequencies in the gigahertz range during the past decades extending quantum photonics to broader frequency regimes. In standard cryogenic systems, however, thermal decoherence prevents access to the quantum regime for photon frequencies below the gigahertz domain. Here, we engineer two superconducting LC circuits coupled by a photon-pressure interaction and demonstrate sideband cooling of a hot radio frequency (RF) circuit using a microwave cavity. Because of a substantially increased coupling strength, we obtain a large single-photon quantum cooperativity $\mathcal{C}_{\mathrm{q}0} \sim 1$ and reduce the thermal RF occupancy by 75% with less than one pump photon. For larger pump powers, the coupling rate exceeds the RF thermal decoherence rate by a factor of 3, and the RF circuit is cooled into the quantum ground state. Our results lay the foundation for RF quantum photonics.

quant-ph↗

arXiv2021

Level attraction and idler resonance in a strongly driven Josephson cavity

Nonlinear Josephson circuits play a crucial role in the growing landscape of quantum information and technologies. The typical circuits studied in this field consist of qubits, whose anharmonicity is much larger than their linewidth, and also of parametric amplifiers, which are engineered with linewidths of tens of MHz or more. The regime of small anharmonicity but also narrow linewidth, corresponding to the dynamics of a high-$Q$ Duffing oscillator, has not been extensively explored using Josephson cavities. Here, we use two-tone spectroscopy to study the susceptibility of a strongly driven high-$Q$ Josephson microwave cavity. Under blue-detuned driving, we observe a shift of the cavity susceptibility, analogous to the AC Stark effect in atomic physics. When applying a strong red-detuned drive, we observe the appearance of an additional idler mode above the bifurcation threshold with net external gain. Strong driving of the circuit leads to the appearance of two exceptional points and a level attraction between the quasi-modes of the driven cavity. Our results provide insights on the physics of driven nonlinear Josephson resonators and form a starting point for exploring topological physics in strongly-driven Kerr oscillators.

cond-mat.mes-hall↗

arXiv2019

Photon-Pressure Strong-Coupling between two Superconducting Circuits

The nonlinear, parametric coupling between two harmonic oscillators has been used in the field of optomechanics for breakthrough experiments regarding the control and detection of mechanical resonators. Although this type of interaction is an extremely versatile resource and not limited to coupling light fields to mechanical resonators, there have only been, very few reports of implementing it within other systems so far. Here, we present a device consisting of two superconducting LC circuits, parametrically coupled to each other by a magnetic flux-tunable photon-pressure interaction. We observe dynamical backaction between the two circuits, photon-pressure-induced transparency and absorption, and enter the parametric strong-coupling regime, enabling switchable and controllable coherent state transfer between the two modes. As result of the parametric interaction, we are also able to amplify and observe thermal current fluctuations in a radio-frequency LC circuit close to its quantum ground-state. Due to the high design flexibility and precision of superconducting circuits and the large single-photon coupling rate, our approach will enable new ways to control and detect radio-frequency photons and allow for experiments in parameter regimes not accessible to other platforms with photon-pressure interaction.

quant-ph↗

arXiv2019

Coupling microwave photons to a mechanical resonator using quantum interference

In recent years, the field of microwave optomechanics has emerged as leading platform for achieving quantum control of macroscopic mechanical objects. Implementations of microwave optomechanics to date have coupled microwave photons to mechanical resonators using a moving capacitance. While simple and effective, the capacitive scheme suffers from inherent and practical limitations on the maximum achievable coupling strength. Here, we experimentally implement a fundamentally different approach: flux-mediated optomechanical coupling. In this scheme, mechanical displacements modulate the flux in a superconducting quantum interference device (SQUID) that forms the inductor of a microwave resonant circuit. We demonstrate that this flux-mediated coupling can be tuned in-situ by the magnetic flux in the SQUID, enabling nanosecond flux tuning of the optomechanical coupling. Tuning the external in-plane magnetic transduction field, we observe a linear scaling of the single-photon coupling strength, reaching rates comparable to the current state-of-the-art. Finally, this linear scaling is predicted to overcome the limits of single-photon coupling rates in capacitive optomechanics, opening the door for a new generation of groundbreaking optomechanical experiments in the single-photon strong coupling regime.

quant-ph↗