Demonstration of an Effective Ultrastrong Coupling between Two Oscillators

Danijela Marković (1) , Sebastien Jezouin (1) , Quentin Ficheux (2, 1) , Sergueï Fedortchenko (3) , Simone Felicetti (3) , Thomas Coudreau (3) , Perola Milman (3) , Zaki Leghtas (1, 4, 5) , Benjamin Huard (1)

1 LPA - Laboratoire Pierre Aigrain
2 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
3 MPQ (UMR_7162) - Laboratoire Matériaux et Phénomènes Quantiques
4 CAS - Centre Automatique et Systèmes
5 QUANTIC - QUANTum Information Circuits

When the coupling rate between two quantum systems becomes as large as their characteristic frequencies, it induces dramatic effects on their dynamics and even on the nature of their ground state. The case of a qubit coupled to a harmonic oscillator in this ultrastrong coupling regime has been investigated theoretically and experimentally. Here, we explore the case of two harmonic oscillators in the ultrastrong coupling regime. Probing the properties of their ground state remains out of reach in natural implementations. Therefore, we have realized an analog quantum simulation of this coupled system by dual frequency pumping a nonlinear superconducting circuit. The pump amplitudes directly tune the effective coupling rate. We observe spectroscopic signature of a mode hybridization that is characteristic of the ultrastrong coupling. We experimentally demonstrate a key property of the ground state of this simulated ultrastrong coupling between modes by observing simultaneous single- and two-mode squeezing of the radiated field below vacuum fluctuations.

Domaines: Automatique / Robotique; Physique Quantique [quant-ph]

Danijela Marković, Sebastien Jezouin, Quentin Ficheux, Sergueï Fedortchenko, Simone Felicetti, et al.. Demonstration of an Effective Ultrastrong Coupling between Two Oscillators. Physical Review Letters, 2018, 121 (4), ⟨10.1103/physrevlett.121.040505⟩. ⟨hal-01944732⟩