Raquel Garcia Belles

Einstein-Podolsky-Rosen correlations between mechanical oscillators revealed through SU(1,1) interferometry

  1. Max-Emanuel Kern,
  2. Stefano Marti,
  3. Raquel Garcia Belles,
  4. Andraz Omahen,
  5. Igor Kladaric,
  6. Arianne Brooks,
  7. Yiwen Chu,
  8. and Matteo Fadel
Quantum correlations are essential for achieving quantum advantage in computing, communication and sensing. Moreover, their observation challenges and constrains our fundamental understanding
of nature. Mechanical oscillators in the quantum regime provide an appealing platform for preparing and investigating quantum correlations at macroscopic scales. Despite substantial progress, however, continuous-variable quantum correlations stronger than entanglement have not yet been observed in this macroscopic regime. Here, we report the experimental observation of continuous-variable Einstein-Podolsky-Rosen correlations between two spatially-separated mechanical oscillators with an effective mass of ∼16μg each. This is achieved by coupling them to a superconducting qubit which allows for engineering a two-mode squeezing interaction when parametrically driven. Crucially, we show that this interaction can be used to witness quantum correlations through the realization of a mechanical SU(1,1) interferometer. Our results expand the toolbox of operations in circuit quantum acoustodynamics and demonstrate that quantum correlations stronger than entanglement can also be observed in macroscopic systems, thereby shedding light on the boundary between quantum and classical regimes.
arxiv pdf

Loss Mechanisms in High-coherence Multimode Mechanical Resonators Coupled to Superconducting Circuits

  1. Raquel Garcia Belles,
  2. Alexander Anferov,
  3. Lukas F. Deeg,
  4. Loris Colicchio,
  5. Arianne Brooks,
  6. Tom Schatteburg,
  7. Maxwell Drimmer,
  8. Ines C. Rodrigues,
  9. Rodrigo Benevides,
  10. Marco Liffredo,
  11. Jyotish Patidar,
  12. Oleksandr Pshyk,
  13. Matteo Fadel,
  14. Luis Guillermo Villanueva,
  15. Sebastian Siol,
  16. Gerhard Kirchmair,
  17. and Yiwen Chu
Circuit quantum acoustodynamics (cQAD) devices have a wide range of applications in quantum science, all of which depend crucially on the quantum coherence of the mechanical subsystem.
In this context, high-overtone bulk acoustic-wave resonators (HBARs) are particularly promising, since they have shown very high quality factors with negligible dephasing. However, the introduction of piezoelectric films, which are necessary for coupling to a superconducting circuit, can lead to additional loss channels, such as surface scattering and two-level systems (TLS). Here, we study the acoustic dissipation of HBAR resonators in cQAD systems and find that the defect density of the piezoelectric material and its interface with the bulk are limiting factors for the coherence. We measure acoustic modes with phonon lifetimes up to 400 μs and lifetime-limited coherence times approaching one millisecond in the quantum regime. When coupled to a superconducting qubit, this leads to a hybrid system with a large quantum coherence cooperativity of CT2=1.1×105. These results represent a new milestone for the performance of cQAD devices and offer concrete paths forward for further improvements.
arxiv pdf