arXiv subjects

Vincent Jouanny

Publications and source records attributed to Vincent Jouanny.

7 recordsLinked to original sources

arXiv2025

Superstrong Dynamics and Directional Emission of a Giant Atom in a Structured Bath

Quantum emitters coupled to waveguides with nonlinear dispersion show rich quantum dynamics with the promise of implementing non-trivial non-Markovian quantum models. Recent advances in engineered photonic environments now allow the realization of discrete-site waveguides with tailored dispersion, yet most implementations of waveguide QED remain limited to a local qubit-waveguide coupling. Here, we study a transmon qubit non-locally coupled to a high-impedance coupled cavity array (CCA), thus implementing a \emph{giant atom} in a structured photonic environment. The non-local coupling produces interference with the CCA modes, selectively enhancing interaction with even and long-wavelength modes, while suppressing coupling to odd and short-wavelength modes. For a subset of symmetric, long-wavelength modes, we reach the superstrong coupling regime. In this regime, measurements of the atomic participation ratio reveal strongly hybridized eigenmodes on a par with a strongly reduced qubit participation at the frequency of maximum hybridization with the qubit, in agreement with theory. Time-domain measurements of the qubit dynamics show clear deviations from the single-mode Jaynes--Cummings model, marked by the emergence of mode--mode interactions. By breaking spatial inversion symmetry of the CCA, the qubit seeds dressed eigenmodes confined to either the right or left of the qubit, which we exploit to implement and characterize a directional photon-emission protocol. These results demonstrate precise control over multimode light--matter interaction in a structured photonic environment.

quant-ph↗

arXiv2025

Emergent cavity-QED dynamics along the edge of a photonic lattice

We investigate qubits coupled to the boundary of a two dimensional photonic lattice that supports dispersionless edge modes, unlike conventional edge modes that sustain propagating photons. As a case study, we consider a honeycomb lattice (photonic graphene) of coupled resonators with a zigzag edge, where the edge modes form a flat band defined only over a restricted region of momentum space. We show that light matter interactions are effectively captured by a dissipative cavity QED model, wherein the emitter coherently couples to a fictitious cavity mode emerging as a superposition of edge modes. This mode has support on only one sublattice and, most notably, displays an unconventional power law localization around the qubit, yet remaining normalizable in the thermodynamic limit, with a spatial range that can be tuned by introducing lattice anisotropy We predict occurrence of vacuum Rabi oscillations and efficient state transfer between distant emitters. An experimental demonstration using superconducting circuits is proposed.

quant-ph↗

arXiv2025

Quantum Acoustics with Tunable Nonlinearity in the Superstrong Coupling Regime

Precise control of mechanical modes in the quantum regime is a key resource for quantum technologies, offering promising pathways for quantum sensing with macroscopic systems and scalable architectures for quantum simulation. In this work, we realise a multimode mechanical cavity coupled to a superconducting Kerr resonator, which induces nonlinearity in the mechanical modes. The Kerr mode is realised by a flux-tunable SQUID array resonator, while the mechanical modes are implemented by a surface acoustic wave (SAW) cavity. Both mechanical and electromagnetic modes are individually addressable via dedicated measurement lines, enabling full spectroscopic characterisation. We introduce a straightforward protocol to measure the SQUID array resonator's participation ratio in the hybrid acoustic modes, quantifying the degree of hybridisation. The participation ratio reveals that our device operates at the onset of the multimode coupling regime, where multiple acoustic modes simultaneously interact with the nonlinear superconducting element. Furthermore, this platform allows controllable Kerr-type nonlinearities in multiple acoustic modes, with the participation ratio serving as the key parameter determining both the dissipation rates and nonlinear strengths of these hybridised modes. Close to the resonant regime, we measure a cross-Kerr interaction between seven pairs of mechanical modes, which is controllable via the SQUID array resonator detuning. These results establish a platform for engineering nonlinear multimode mechanical interactions, offering potential for future integration with superconducting qubits and implementation of multiple mechanical qubits.

quant-ph↗

arXiv2024

Landau-Zener without a Qubit: Unveiling Multiphoton Interference, Synthetic Floquet Dimensions, and Dissipative Quantum Chaos

Landau-Zener-St\"uckelberg-Majorana (LZSM) interference occurs when qubit parameters are periodically modulated across avoided level crossings. We explore this phenomenon in nonlinear multilevel bosonic systems, where interference is influenced by multiple energy levels. We fabricate two superconducting resonators with flux-tunable Josephson junction arrays. The first device, exhibiting weak nonlinearity, behaves like a linear resonator under weak driving but shows LZSM interference akin to two-level systems. With stronger driving, nonlinear effects alter the interference pattern. We theoretically demonstrate that merging LZSM peaks can lead to dissipative quantum chaos. In the second device, where nonlinearity exceeds photon-loss rates, we observe additional LZSM peaks from Kerr multiphoton resonances. Under Floquet theory, these resonances represent synthetic modes of coupled nonlinear cavities, revealing effective coupling as modulation parameters vary. Our findings advance the understanding of LZSM physics and emphasize the control of nonlinear Floquet states and the emergence of chaos in engineered systems, with significant implications for novel applications in quantum dynamics and quantum control.

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arXiv2024

Band engineering and study of disorder using topology in compact high kinetic inductance cavity arrays

Superconducting microwave metamaterials offer enormous potential for quantum optics and information science, enabling the development of advanced quantum technologies for sensing and amplification. In the context of circuit quantum electrodynamics, such metamaterials can be implemented as coupled cavity arrays (CCAs). In the continuous effort to miniaturize quantum devices for increasing scalability, minimizing the footprint of CCAs while preserving low disorder becomes paramount. In this work, we present a compact CCA architecture leveraging superconducting NbN thin films presenting high kinetic inductance, which enables high-impedance CCA ($\sim1.5$ k$\Omega$), while reducing the resonator footprint. We demonstrate its versatility and scalability by engineering one-dimensional CCAs with up to 100 resonators and exhibiting multiple bandgaps. Additionally, we quantitatively investigate disorder in the CCAs using symmetry-protected topological SSH modes, from which we extract a resonator frequency scattering of $0.22^{+0.04}_{-0.03}\%$. Our platform opens up exciting new prospects for analog quantum simulations of many-body physics with ultrastrongly coupled emitters.

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arXiv2023

High-kinetic inductance NbN films for high-quality compact superconducting resonators

Niobium nitride (NbN) is a particularly promising material for quantum technology applications, as entails the degree of reproducibility necessary for large-scale of superconducting circuits. We demonstrate that resonators based on NbN thin films present a one-photon internal quality factor above 10$^5$ maintaining a high impedance (larger than 2k$Ω$), with a footprint of approximately 50x100 $μ$m$^2$ and a self-Kerr nonlinearity of few tenths of Hz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of pH/square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic inductance resonators, opening perspectives towards the fabrication of compact, high-impedance and high-quality multimode circuits, with sizable interactions.

quant-ph↗

arXiv2022

Observation of two-mode squeezing in a traveling wave parametric amplifier

Traveling wave parametric amplifiers (TWPAs) have recently emerged as essential tools for broadband near quantum-limited amplification. However, their use to generate microwave quantum states still misses an experimental demonstration. In this letter, we report operation of a TWPA as a source of two-mode squeezed microwave radiation. We demonstrate broadband entanglement generation between two modes separated by up to 400 MHz by measuring logarithmic negativity between 0.27 and 0.51 and collective quadrature squeezing below the vacuum limit between 1.5 and 2.1 dB. This work opens interesting perspectives for the exploration of novel microwave photonics experiments with possible applications in quantum sensing and continuous variable quantum computing.

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