Quantum Optics Seminar by Eva M. Weig – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Eva M. Weig

Nanomechanical resonators, freely suspended, vibrating nanostructures, are receiving an increasing amount of attention both in fundamental experiments and in sensing applications, and show great promise as linking elements in future hybrid nanosystems. A realization of this potential relies on the development of versatile platforms to integrate and control high quality nanomechanical devices.

One example of such a platform is based on dielectrically controlled pre-stressed silicon nitride string resonators. Nanomechanical resonators fabricated from tensile-stressed silicon nitride have been known for their unusually high room temperature quality factors of several 100,000 in the 10 MHz eigenfrequency range for several years. Dielectric transduction by means of electrically induced gradient fields has been developed to complement this class of resonators by providing a toolbox for frequency tuning, actuation and detection [1]. Taking advantage of the gradient field, strong coupling of vertically and horizontally polarized vibration modes can also be achieved.

We have investigated the dynamics of these strongly coupled nanomechanical modes, which can be described as a classical two-mode system, and demonstrated coherent control of the resulting normal modes [2]. Furthermore, Rabi-, Ramsey- and Hahn-echo-type experiments reveal that all relaxation times T1, T2 and T2* are equal. This not only indicates that energy relaxation is the dominating source of decoherence, but also demonstrates that reversible dephasing processes are negligible in such collective mechanical modes. Hence not only T1 but also T2 can be increased by engineering larger mechanical quality factors.

Here I will explore the origin of the large mechanical quality factor as well as the underlying dissipation mechanisms limiting the performance of the devices, and will point out a strategy to increase the mechanical quality factor by about one order of magnitude [3,4]. 

References

[1]    Q. P. Unterreithmeier et al., Nature 458, 1001 (2009).
[2]    T. Faust et al., Nature Physics 9, 485 (2013).
[3]    T. Faust et al., Phys. Rev. B 89, 100102(R) (2014).
[4]    J. Rieger et al., Nature Comm. 5, 3345 (2014).