Towards the generation of nonclassical phononic states using quantum electromechanics

Superconducting quantum circuits have enabled the generation and the manipulation of highly non-classical states of microwave radiation. This has been achieved with the exquisite control offered by superconducting qubits: an... [ view full abstract ]

Superconducting quantum circuits have enabled the generation and the manipulation of highly non-classical states of microwave radiation. This has been achieved with the exquisite control offered by superconducting qubits: an artificial two-level system in a cryogenic environment whose state can be controlled and detected with exceptionally high fidelity. This has far-reaching applications both in the domain of quantum information as well as for the fundamental study of quantum mechanics. Recently, several groups have extended this control to the motional degree of freedom of a mechanical resonator [1, 2]. This new field of quantum accousto-dynamics opens up attractive prospects for the transduction of quantum information [3], in particular by enabling a bidirectional transfer of quantum states between microwave and optical photons.

We continue recent work done in the development of ultra-high quality membranes [4] in order to apply it to the domain of electromechanics. These extremely high aspect ratio membranes, made from high-stress silicon nitride, provide an excellent platform for the study of both quantum information technologies and fundamental research: firstly, their so-called "soft-clamping" localizes, through a phononic shield, the motion of the mode to a central defect inside the phononic crystal, decoupling the mechanical state from the substrate and thus greatly improving its protection from decoherence; secondly, they can be dispersively coupled to a microwave resonator [3], which allows us to generate a parametric interaction between a microwave and a mechanical mode of very distinct frequencies. An example of such a softly clamped membrane realized in the lab is represented in Figure 1a. Owing to the presence of the phononic crystal, a bandgap is opened in the engineered range of frequencies. This bandgap is measured in Figure 1b, and simulated in Figure 1c.

Finally, in collaboration with the group HQC at Laboratoire Pierre Aigrain, we are developing a microwave detector able to perform single photon detection in order to project the microwave field onto a Fock state basis. This device based on a superconducting qubit will enable us to prepare non-classical states of motion of the membrane by phonon subtraction, in close analogy with quantum optics experiments performed on propagating light fields [5].

[1] Y. Chu et al. (2018) arXiv:1804.07426

[2] K. Satzinger et al. (2018) arXiv:1804.07308

[3] A. Reed et al. (2017) Nat. Phys. 13, 11631167

[4] Y. Tsaturyan et al. (2017) Nat. Nano. 12, 776

[5] A. Ourjoumtsev et al. (2006) Science 312 5770